S~£:^>^;^*:^: 
 
 
 
HUMAN   PHYSIOLOGY:
'**'
DESIGNED FOR
COLLEGES AND THE HIGHER CLASSES IN SCHOOLS,
FOR GENERAL READING.
1/
     BY WORTH1NGTON HOOKER, M. D.,
PROFESSOR OF THI THEORY AND PRATTIC*. "K >1LDICINE IN TALE COLLEGE;
      AUTHOR OF " PHYSICIAN AND PATIENT."
3
^EON
Illustrated by nearly 200 Engravings.  /-n~->>___
         NEW YORK
PUBLISHED BY FARMER, BRACE, & CO.
      NO. 4, COURTLANDT-STREET.
            1854. 

2  5-
Entered, according to Act of Congress, in the year of our Lord,
          One thousand eight hundred and fifty-four,
            BY WORTHINGTON HOOKER, H. D.,
   In the Clerk's OfRce of the District Court of Connecticut.
    R. H. HOBBS,                                       pt j^ At-VORn
Stereotypy, Hartford, Ct.                               Printer,'New York. 
- -  123
CONTENTS.

    PART  I.
   CHAPTER I.
Pack
Organized and Unorganized Substances,   ...  13
                  CHAPTER  II.
The Distinction between Animals and Plants, .   .  21
                  CHAPTER III.
Man in his relations to the Three Kingdoms of Na-
    ture,  ..............27

                   PART II.
                  CHAPTER  IV.
General views of Physiology, with  a Brief Account
    of some of the Structures  of the Body,  .  .  35
                  CHAPTER  V.
Digestion,..............42
                  CHAPTER  VI.
Circulation of the Blood,.........64
                  CHAPTER VII.
Respiration,.............86
                  CHAPTER VIII.
Formation and Repair,.........109
                  CHAPTER  IX.
Cell-Life,    .............123 
IV
CONTENTS.
                  PART III.
                  CHAPTER X.
The Nervous System,.........139
                  CHAPTER  XL
The Bones,.............1™
                 CHAPTER  XII.
The Muscles,............196
                 CHAPTER XIII.
The Language of the Muscles,......222
                 CHAPTER XIV.
The Voice,  ......'.......243
                  CHAPTER XV.
The Ear,..............271
                 CHAPTER  XVI.
The Eye,..............287
                 CHAPTER XVII.
Connection of the Mind with the Body,   .   .  .  318
                 CHAPTER XVIII.
Differences between Man and the Inferior Animals, 347
                 CHAPTER  XIX.
Varieties of the Human Race,......367
                  CHAPTER XX.
Life and Death,...........381 
PREFACE.
  I have aimed so to write this book, that it shall be fitted both for gen-
eral reading, and for instruction.   It is designed for the family as well as
for the school.  It seemed desirable that these two objects should be ac-
complished at the same time,  and I have  not found them to be at all in-
compatible.  The instruction needed by the family on this subject, differs
not from that  which is required in  the school-room, either in  regard to
the facts to be communicated, or the manner in which  it should be done.
No one will question the truth of this, so far as  the facts are concerned.
But it is true even as to the mode of communicating them.  In both cases
there needio be clearness in statement, arid fullness of illustration.  Actual
instruction is to be given in both cases, and to minds that  are very nearly
in the same attitude.  I could not, therefore, see the necessity of writing a
book on this subject for the people which should differ from one written
for the school.  Besides, it has seemed to me desirable that there should
be a greater community of interest between the school and the family than
as yet exists;  and this object  books equally interesting to both will tend
to promote.
  It may be proper for me to say a word in relation to the  style of the
work.  I have adopted the style of the lecture-room, because, that while
it is not inconsistent with conciseness, it is the more natural mode of in-
struction, especially when so much reference is made to illustrative figures.
It has enabled me also to keep  in view more effectually the attitude of the
minds I address.   I have had my readers before me  continually as  an
imaginary audience.  I have  avoided technical terms as far  as possible.
Whenever they are used they are sufficiently explained at the time, so
that no glossary is  needed.   Some points commonly considered hard to
be understood are treated of, but I have endeavored to simplify them, by 
vi
PREFACE.
full illustration,  and by a  presentation  of the truth uncomplicated with
speculations and hypotheses.   And these  points are so introduced, that
the mind is prepared by the previous investigation to understand them.
I have aimed so to arrange the topics, as to have a preparation constantly
going on in the mind of the  student, fitting him for the proper under-
standing of what is to come after.   By this natural  gradation in the  de-
velopment of the whole subject  some of the deep things in Physiology
can be made clear, which it would otherwise be impossible for the student
to understand.  It is proper to state here, that I intend to prepare a work
for younger  scholars, in which some of the simple points in Physiology
will be illustrated.  This,  by  familiarizing their minds with the subject,
will fit them for a more thorough understanding of the present work.
   Although Physiology is  becoming a prominent study in the schools and
colleges in some parts of our  country, its importance is no where as  yet
appreciated as it should be.  It should be made a regular branch  in our
Educational System.  This has been already done in France.   " A com-
petent knowledge," says Carpenter, " of Animal Physiology and Zoology
is there required from every candidate for  University honors ; and men
of the highest scientific reputation do not think it beneath them to write
elementary books, for the instruction of the beginner."
  The importance of Physiology as a study, will appear from various con-
siderations.
  Many  of the subjects comprised in Physiology have, in the case of
most students, been already studied in a different phase, or mode, in other
branches.  Thus, if the student has attended to the  Mechanical Powers
in his Natural Philosophy, he finds in the human body the principles of
the pulley and the lever illustrated in great variety and  perfection.  The
principles in relation to strength in  the form and arrangement of struc-
ture he sees exemplified in the frame-work of the body in the most ad-
mirable manner.  If he has studied Hydraulics, he sees in the body the
most perfect, and at the same time the most complicated hydraulic ma-
chinery,  working  incessantly  throughout  life in  the circulation  of  the
blood.  The principles of Pneumatics he finds applied in the respiration—
those of  Optics in the eye—those of Acoustics in the ear—and those of
Musical  Sounds in the apparatus of the voice.   And then, his chemical 
PREFACE.
Vll
knowledge meets with new applications in his observation of the changes
and the processes going on in the body.
  The relations,  then, of Physiology to some of the common  branches
taught in the higher classes in schools, are of the most intimate charac-
ter.   Physiology, in part, merely extends these branches into a new and
interesting field 5  and the student who has once  entered this field recurs
to these same branches with a renewed interest.  Hydraulics, Pneuma-
tics, Optics, &c, have now a  new attraction for him, from this, to  him
novel, application of their principles.  The interest  thus  awakened in
his mind  is worth much in itself, aside from the mere addition- made to
his knowledge.   And the interest is enhanced by the consideration, that
in the human body he sees the applications of these principles to mechan-
ism that exhibits the skill of perfect wisdom and almighty power.
   But there are relations of Physiology to still other studies which should
be noticed.
   The analogies  that exist between the human body and all other living
things, in  relation  to structure and  growth, are numerous and striking.
Though life is so diverse in its processes and in the  forms which  we see
it evolve in the whole range of animated nature, it in some important re-
spects displays a great similarity, which it is interesting to trace through-
out its diversified manifestations.  Growth, or  nutrition, as you will see   |
in the following pages, is essentially the same in the Plant as it is in the
 Animal.   Botany, therefore, taught as it should be, has quite an intimate
relation to Animal Physiology.  The Science of Life is, in many respects,
 one  Science;  and if,  in  studying any of  its subdivisions, we fail to take
 this broad view of it, and to trace out the analogies referred, to, we lose a
 large part of the interest of the study.  Human Physiology, the subject
 of study in this book, is but a part of a science which offers to the student
 wide fields  of observation exceedingly diversified  and full  of interest.
 This being so, I  could not avoid in the following pages making occasional
 reference to the analogies existing between the  phenomena of life as ex-
 hibited in the human system, and those which we see in the living world
 around us.  So that as the student proceeds with the study, he will find
 himself interested in the phenomena of life in whatever  form they are
 presented. 
           ■•,/■'
                ''      '['■
 VU1                       PREFACE.
   This leads me to say that this study of nature, in its broad common re-
 lations and its beautiful and  extensive  analogies, should  be made very
 prominent in our systems of education.  It is the application of the prin-
 ciples of abstract science to the forms, and especially the living forms of
 nature all about us, that gives Interest to these  principles, and makes us
 to understand and appreciate them.  It is here that we find a very seri-
 ous defect in the prevalent mode  of education, even at the present time,
 notwithstanding all our improvements.   Let us look at it a moment.  We
 live in the midst of a material world, animate and  inanimate, and have
 daily converse, so to speak, with material forms of every variety, present-
 ing phenomena of the highest interest  and of endless diversity.   And
 yet, through almost all the  period of childhood, and perhaps we may say
 youth also, this book of nature is in the school-room very nearly a sealed
 book.  The very process of education shuts in the pupil from this broad
 contemplation of the world in which  he lives.  He is drilled through
spelling, reading, grammar, &c, but he is left in total ignorance of the
 beautiful flowers, and the majestic trees outside of the school-room.  How
very few even of  thoroughly educated  adults, know  the processes  by
which  a  plant or  a tree grows!   And the same  can be said of other
phenomena of nature.
  The defect which I have  pointed out runs through the whole of educa-
tion.  We can see  it even in the prevalent  mode of teaching the natural
sciences themselves.   One would suppose  that here the facts, the phe-
nomena, would command the chief attention of the  teacher  and the stu-
 dent.  But it is very commonly not so.  The mere technicalities and the
 classification are made much too  prominent.   Botany, really one of the
 most interesting of all  branches of natural  science, is thus  ordinarily
 made one of the driest of studies.  To teach this aright, the phenomena
 of vegetation, so varied and so beautiful, should constitute the chief ma-
 terial of instruction, and  the mere classification should  be  considered al-
 though necessary, as wholly a secondary thing.
  The great facts of the  world, both  of  mind and matter,  should furnish
 really the material for education, and those branches that are  ordinarily
 pursued with such  assiduity should be considered as merely subsidiary to
 the teaching  of these  facts.  The whole order of education must be re- 
PREFACE.
IX
versed.   Instead of beginning the child's education with learning to spell
and read, the object should be to make -him an  observer of nature, and
the spelling and reading should  be done in connection with this, and as
subsidiary to it.  Things and not words, or mere signs, should from  the
first, constitute the substantial part of instruction.  The child should be
made, at home, in the school, and everywhere, a naturalist in the largest
sense of that word.  We should aim to impart to  him a spirit in con-
sonance with  the  following  precept  of Hugh  Miller, the  famous self-
taught geologist.   " Learn to make a right use  of your eyes; the com-
monest things are worth looking at—even stones  and weeds, and  the
most familiar animals."
   As it is now, no one becomes  a naturalist early in life, except in spite   \
of the tendencies of his education.  The study of nature is not only  not   i
encouraged, but is absolutely discouraged in our educational system.   If
any one, like Hugh Miller, by the force of a taste that can not be repress-
ed by the training of the school-room, undertakes to make a " right use
of his eyes," and  curiously examines '^ stones and weeds," he is regard-
ed by the world of spellers and readers and  grammarians and cipherers,
as a strange genius.  But he is pursuing  from an irresistible  internal
force, the very course  that I would  have every student, even  from his
childhood,  encouraged  to pursue, in a measure  at least, by the external
circumstances of his education.   The tendencies of his  training should be
decidedly in this direction.
   If the general mode of education were changed in the manner indicated,
education would have much less of the character of mere drudgery than
it now has.  Not that  there would be any the  less labor; but the labor
would be made lighter by the interest imparted to it—the interest, which
always results from the study of facts and phenomena, and never from the
learning of mere words and technicalities and  classifications.   I would
gladly dwell on this subject, and show by varied illustrations how the
mode of instruction referred to, should be pursued, and especially with
younger  scholars;  but  the limits of  a preface will not allow me to enter
so large a field.
  The change which I have pointed out can not be effected at once.  It
will require time.   Confirmed traditional customs are to be done  away, 
X
PREFACE.
the habits  of teachers are to be altered, and-the proper books are to a
great extent to be yet written, especially such as are fitted for the first
years of education.
  If the  study of nature should be thus made prominent in  education,
human physiology would be considered altogether its most interesting and
important branch, and for several reasons.  First: there is no where to
be found so curious a collection  of mechanisms, or so interesting and
wonderful a series  of processes, as in  the human body.  In nothing else
in the wide world  are the principles of so many departments of science
so extensively and perfectly exemplified.  Life works here  its most com-
plicated set of  machinery.  Secondly:  the singular and mysterious con-
nection of the immaterial and immortal soul with the material and perish-
able  body,  gives intense interest to this study.  In Physiology we  do
not study matter alone, or spirit alone, but both matter and spirit united,
and often acting together.  This circumstance distinguishes this from all
other studies.   Thirdly: it is our own frames, moved by the spirit within
us, that we study.   The subject has a personal interest for us, that is not
presented by most  studies, and  by none in so large a degree  as in this.
And Fourthly: the study is of great importance, because a judicious and
efficient Hygiene must be  based upon a knowledge of the laws of physi-
ology. We cannot know how to keep our functions in the condition of
health, without understanding the laws that regulate them.  I have said
but little  in this book in regard to hygiene, and that only incidentally, be-
cause that subject would require  of itself a whole volume to elucidate it
properly.
  I have not thought it proper to indulge to any great extent in those re-
flections, which the  contemplation of so perfect and diversified a congeries
of mechanisms as are presented in man would naturally suggest, in regard
to the skill  of the great builder of the universe.  Such reflections would
extend the  book to  too great length.   Besides, they are so readily sug-
gested to the mind of both teacher and scholar, that it is entirely un-
necessary for the author to dwell on them.
  I have treated of some subjects, on which, from the difficulty of un-
derstanding them, there has been a disposition  in many minds to go be-
yond what we know, and  indulge in unwarranted speculation.   On  these 
PREFACE.
XI
   points I have taken pains to draw the line very distinctly between what is
   known, and what is  supposed.   I deem it to be important to prevent the
   minds of the  young from  being led  away from the simple truths of
   science by ingenious speculations and plausible reasonings.   Let me not
   be understood to decry all hypothesis.   I only object  to the  mingling of
#  facts  and suppositions together in  one indiscriminate mass, as is often
   done.  The disposition to do this, which is more common than is generally
   supposed, exerts so  injurious an influence upon  the habits  of the mind,
   and so confuses its views of  truth, that we ought to look upon it as one of
   the most serious evils to be guarded  against  in education.   It  is really
   one of the most prominent obstacles to the  progress of truth on all sub-
   jects, both in  individual minds, and in the minds of the community at
   large.  This disposition, so apt to be fostered in the enthusiastic mind* of
   youth, by ingenious but dreamy speculations,  should  be  corrected at the
   outset, and the mind should in its forming stage, be habituated to the dis-
   crimination  between the proved, the  true, and that  which  rests on pre-
   sumptive, perhaps  merely plausible evidence.  This discrimination should
   therefore be exemplified in books designed for  instruction, and this I have
   attempted in the present volume.
      I have divided the book into Three Parts.  The  First, which I have
   made as short as  possible, is merely preliminary to the consideration of
   the particular subject of the book.   In the Second  Part, I present the
   human  structure,  simply as a structure, and  show how it is constructed
   and kept in repair.  In the Third Part, I treat of all those subjects which
   relate to the  uses  for which  the  structure is designed.   This natural
   division  of  the whole subject, not  only presents it to the  mind  of the
   student  in  an  interesting point of  view, but secures  that natural grada-
   tion in its development, which  I have  spoken  of as being necessary to a
   clear understanding of its deeper and  more intricate portions.
 
 
PHYSIOLOGY.
                     PART FIRST,
                        CONTAINING,
CHAPTER I.—Organized and Unorganized Substances. CHAPTER II.—The Distinction
  between Animals and Plants. CHAPTER III.—Man in his Relations to the Three
  Kingdoms of Nature.
                    CHAPTER  I.

          ORGANIZED AND UNORGANIZED SUBSTANCES.

  1. The crystal and the plant are  both wonderful growths.
As you look at them, you think of the crystal as having been
formed, and  of the plant as having grown.   But in one sense
they have both grown to be what they are.  The  crystal was
once a minute nucleus, and the plant was once a little germ.
  2. -In one respect they are alike in their growth—both have
increased from particles taken from things around them.  But
the processes by which this  is done  are different  in the two
cases.  The  crystal has increased or grown by layer after layer
of particles.   There are  no spaces or passages by which parti-
cles of matter can be introduced inside of it.  Any part of it,
when once  formed, is not  altered.   It can  receive additions
upon the outside alone.  But it is not so with the plant.  This
enlarges by particles which  are introduced  into passages and
interstices.   It grows, as it is expressed, by absorption or by in-
tussusception.
  3. How, now, is this absorption effected ?   It is done by cer-
tain vessels or organs, constructed in the root of the  plant for
this purpose.  These take up or absorb  fluid matter from  the
earth.  There are other organs which circulate this fluid through
all the plant; and others still which  use it for the purpose of
growth or formation.  There are no such organs in the crystal,
for it has no inner growth.  The plant is therefore said to be
an organized substance or being, and the  crystal is an unor-
ganized substance.  And so we speak of the organic structure,
or the organization of plants.
                              2 
14                HUMAN  PHYSIOLOGY.
         Organized beings.  Mechanical, chemical, and vital principles.___________

  4. These organs, which thus absorb, and circulate, and con-
struct, do not act simply on mechanical  principles.   Ihe plant
is not merely soaked with fluid, which the heat of the sun may
expel, as it does water from a porous mineral substance.  Inese
organs are active agents, and  they perform their duty with a
force, and after a manner, for which no  mechanical principles
can  account.   No mechanical powers  could alone supply the
leaves of the  mighty tree of the forest with sap from its deep
roots; much less could they form these leaves.
  5. Neither  do these organs act simply on chemical princi-
ples.  While man, through the agency  of  chemistry, can form
some of  the crystals which are found in nature, he can not by
any arrangement of constituents make  a  plant, a flower, or a
leaf.  And the plant, left alone to the action of chemical prin-
ciples, wilts; and at  length ceases to be a plant, and becomes
common unorganized matter.
   6. Mechanical and  chemical principles, it is true, are both
employed to some extent in the growth of plants ; but they are
under the control of other principles, which we term vital.  And
so we speak of the plant not  only as an  organized  substance,
but as a living being.
   7. What I  have said of plants, in distinction from minerals,
may also be said of animals.   They are also organized living
beings,  and they have  generally a  more complex organization
than plants, as you will see as I proceed.
   8. The whole  material world,  then, that we see around us,
we divide into two parts—the unorganized and lifeless, and the
organized  and living.  The distinctions thus  pointed out be-
tween organized  and  unorganized matter are essential and
fundamental.   But let us look  at some other distinctions, which
either arise from these  or accompany them.
   9. One distinction is this.  All the parts of the mineral are
independent of each other, while it is otherwise  with the plant
or  the animal.  Accordingly, we examine the properties of min-
erals in a different way from those  of plants and animals.  The
chemist can ascertain all the properties of a crystal or a rock,
if you give him but a small piece of it.  But the botanist  can
not ascertain all the  properties of a plant by looking at some
one part of it.  If  he examine the flower, this gives him no
knowledge of  the root.   In order to know all about the plant,
he must examine every part by itself, and then  look at it in its
 relations to  the other parts.  The  same  can  be said of the
 physiologist, in his investigation of the properties of animals. 
      ORGANIZED  AND  UNORGANIZED  SUBSTANCES.   15
                  Assimilation in organized substances.

   10. As the crystal is forming by layer after layer of particles,
no change is effected  in  these  particles as they are  becoming
arranged in the  layers.  But in the case of the living organ-
ized  being,  a  change is produced in  the particles which are
taken up by the absorbents.   And the change, ordinarily,  is
both  a gradual and a complex  one.  In the plant, a change is
produced in the particles in  the very act  of  absorption;  but
this change  is  only the beginning of a process which is after-
wards perfected.  The sap is not thoroughly fitted for nutrition
when it  first begins to circulate.   It is carried up through the
vessels of the trunk or stalk to the leaves.   There the last step
of the process is  taken, and the sap is now ready to be used  in
the growth of the  plant  or  tree.   So, also, in  the animal, the
nutritious part  of the food,  taken up  by the absorbents in the
digestive organs, is first acted  upon  by  certain  little  glands,
through which it passes,  is then poured into the circulation,  to
be mingled with the blood, and is carried with  the Wood to the
lungs, to be exposed to the air; and thus  it is fitted for the nu-
trition or growth of the body.  This process, which is thus car-
ried on in the  plant and  in  the animal, is very properly called
assimilation.   For  the particles that are  taken up by  the ab-
sorbents in the root of the plant are, by this process, made like
to the plant; and the particles  taken up by the absorbents  in
the stomach *  are made like to the "animal.   So obvious is this,
in the case of the animal, that some French physiologist speaks
of the blood as chair coulante, or  running flesh.
   11. Another prominent distinction  between organized  and
unorganized substances is in relation to permanency.   Constant
change appears in  all organized  bodies;  while permanency is
written upon all  substances  which are unorganized.  In organ-
ized beings, continual change is going on  at every point.  It is
a condition  of their  being.   This is  true, not only of  the de-
cline of  a plant or  animal, but even  of its growth.   For, in its
growth,  as the parts  enlarge internally as well as externally,
they  change not  only the arrangement of the  particles, but, to
a  great  extent, they  change  the particles  themselves.  It is

  * The word stomach requires some little explanation, as  it is used in physiology in two
senses—in a limited sense,  and also in an extended one.  It is used in its limited sense, as
referrin" to the cavity at the beginning of the alimentary canal, as it is termed; this lat-
ter term bein" applied to the series of cavities, the stomach and the small and large intes-
tines  which are found  in  the digestive apparatus in the  higher orders of animals.  In
comparisons, however, between these animals and those whicli have a more simple digest-
ive apparatus, the word stomach is used in a more extended sense, as being synonymous
with the term alimentary canal.  It is used in this  sense, also, when, as in the present
case it is referred to in a comparison between animals and vegetables. 
16
HUMAN PHYSIOLOGY.
          Organized substances changing. Unorganized permanent.____________^

true,  as  well  of the towering tree as of the tiny plant, that
these changes have  been going on  during all  its growth; so
that, at its maturity, it is, both in relation to the  arrangement
of its particles, and  in relation  to  the particles themselves, a
very different  thing from what it was when it pushed its germ
up through the ground, or even when it was but a small tree.
Not only has  it received  into its interstices  and passages new
particles, but  it has thrown off from the  pores of its leaves,
those outlets for the refuse of plants, vast quantities of parti-
cles which are no longer  of use in  its structure.  So, in  all
animals,  the  same internal changes  are going on, and to a
much greater extent;  because,  from the activity of their na-
ture, there is  more  of wear and tear, and, therefore, more  of
refuse matter  to be disposed of.   As  you will see in  another
part of this bools,  the human body, that most complicated of
organized beings, undergoes these changes very largely.
  12. It is not thus with  unorganized substances.  The crys-
tal, so fast as  it is formed, becomes  permanent.  No  changes
occur within  it.   In itself, it  is  unchangeable.   It can  not
change its own particles, as the plant or the  animal does.  It
can be changed only by external addition, or by external dimi-
nution, through the influence of agents acting upon its surface.
  13. With the constant changes going on in organic nature,
there  is constant succession. Plants and animals produce other
plants and animals, and themselves die, making  room for their
successors.   But the crystal does not form other  crystals, and
then crumble into  dust.  In itself, it is both  unchangeable and
unproductive.
  14. This distinction between organized and unorganized sub-
stances, in relation  to change  and succession,  meets  the  eye
everywhere.    The  mountains,  the rocks, and even the  stones
under our feet, remain the same  year after year,  while all vege-
table and animal life is ever changing its forms and manifesta-
tions.  There  are  the changes of growth, and the changes of
decay and death,  all  around and within us;  and they  are
strangely mingled together.   There is death  even  in  the
changes of life, as  the waste particles  are taken away, and are
replaced  by the new; and life springs  out of the very bosom
of death, as  from decayed nature new forms  of vigor and
beauty arise.   The mountains stand as they have  stood, as the
passing generations have looked upon them, while the continual
changes of vegetation have been going on upon  and  around
them.  The seasons crown their  battlements with the emblems 
     ORGANIZED AND UNORGANIZED SUBSTANCES.    17
           Different forms of organized and unorganized substances.

of their  ever-returning mutations  of  life, decay, and death;
and  even the mighty trees, that have  shed  their leaves from
year to year, in obedience to the great law of change, but have
themselves stood, at  length bow their  heads  to the same law,
and give place to other lords of the forest.  From the " ever-
lasting hills," which  thus remain the  same, though change is
ever about  and upon them, man gets the unchangeable and
imperishable rock to  construct his habitation, while he himself
is changeable and perishable—the creature of a day,  whose
life is  as a vapor.   He wears the precious stones, and traffics
in the  golden ores, which have existed from the creation of the
world, through all the changing  and  dying generations, and
passes  away, leaving  them to others as changeable and perish-
able as himself.
   15.  Another distinction between organized and unorganized
substances relates to the forms which they  assume.   There is
regularity in both, but it is different  in  each.  Unorganized
matter is disposed to arrange its particles in  straight lines, and
with angles mathematically exact.   You see this in the  beautiful
crystal;  and you also  see it, less definitely,  but magnificently,
displayed in the regular battlements and columns of rocks and
mountains.   The tendency is to regularity;  and irregularity is
the result of interfering circumstances.  A similar disposition
to regularity is  manifest  in organized substances, but in  a
different manner.  It is disposed to curved, rather than straight
lines, and seldom makes lines or angles with mathematical ex-
actness.   We see this  law  of  regularity  exemplified both in
animal and vegetable life.  The leaf, for example, has  the same
general shape, that is,  the same general arrangement of par-
ticles,  when it attains its full  size, that it  had when  it  was
small; and the same can be said of the arm of the man, com-
pared with  his arm when a child.   Illustrations might be cited
to any extent, but these are sufficient.
   16.  While the law of regularity is  not commonly as exact
in organized substances as it is in  the unorganized, it is quite
as authoritative.   While it does not ordinarily observe the per-
fectly straight lines and the unvarying angles which we  always
find in the crystal, the general plan and contour are very strictly
preserved amid all the changes of animal  and vegetable  life.
And, in some cases, the same  mathematical exactness that we
find in the mineral  world  is found  in organized  beings.   I
know  not that this  is ever  true of straight lines and angles;
but  it is often true  of curved lines.  There are many very
                             2* 
 18               HUMAN PHYSIOLOGY.
               Regularity in form—in some cases wonderful.

 beautiful examples in  the vegetable world.  I will  give but a
 single one.  If you look at the common white daisy, before the
hundreds  of little buds  in its bosom have opened  into  tiny
flowers, you  will see them arranged with  great  exactness in
crossing curved lines,  such as you  often see on  the back of
a watch case.   A similar  arrangement you will find in many
flowers.
   11. This  regularity is  more wonderful  in  organized  sub-
stances than in the unorganized, because it rules in them in the
midst of constant change.   In  the case of  the crystal, as there
are no internal  changes  in it, and  as each layer of it, when
formed, is permanent, regularity is comparatively, so to speak,
easily secured.   But in the case of the leaf, as it is growing to
its full size, and of the arm,  as  it grows  from infancy to be
the stalwart arm of manhood, continual  change is going on at
every point;  and regularity here is  obviously a more difficult
achievement.
   18. This  regularity  appears  still more wonderful, when we
look at the infinite  variety of forms in organized  matter, in
both the vegetable and the animal world.   In all  these forms,
each part of  every  animal and  of  every  plant maintains its
own peculiar plan  and contour.  Take, for example,  the leaf in
its endless varieties.  How definitely does each variety preserve
its individual character, and how easily is it distinguished from
every other variety!   The same can be said of every part of
every organized being.
   19. Another circumstance still must be mentioned, as adding
to the  wonderfulness  of  this regularity.  It has  been scrupu-
lously maintained, through all  the  changes  of the world from
its creation,  when  God pronounced the works of  his  hands to
be " very good."   The leaf of  every tree, for example, is  like
the leaf of its ancestral trees back to that time; and so it will
be in all its successors  to the end of the world.   " The trees of
the garden," which delighted the eyes of our first parents, and
refreshed them with  their shade in their innocence, and amid
which they hid  themselves after their sin from the presence of
their Maker, undoubtedly had the same characteristic shapes,
and the same leaves and flowers which their successors present
to our eyes.
   20. Again, it is interesting  to notice that, in  the  midst of
this regularity, so strictly maintained in each specific form from
age to  age, there is a measure of irregularity allowed.  While
each kind of tree, for example, has specific characteristics in 
      ORGANIZED AND UNORGANIZED SUBSTANCES.   19
              Variety of form; yet regularity preserved. Size.

 the arrangements of branches  and other parts,  and  in  the
 shapes of its leaves, no two trees of the same  kind are exactly
 alike,  and there is  always much variety in the leaves  of  the
 same kind.   The wonder is, that so much  latitude is allowed
 in this respect, and yet the specific characteristics of each kind
 are  so thoroughly preserved.  We can  readily see that if a
 pattern, definite in all its details, were to be copied exactly in
 each kind of vegetable and animal form, the distinctions between
 them  could be more easily preserved.   But  Omnipotence is
 able to combine  a  wide latitude and  variety of form in each
 kind, with a strict and uniform preservation of  its characteristic
 contour and arrangement.  We have a striking exemplification
 of the above remarks in the variety  of the human countenance.
 While the face of man is so entirely different  from the face of
 every other animal,  at  the  same time, among  the hundreds of
 millions of the human family, how uncommon it is to find two
 faces that are very nearly alike.
   21.  In  the animal world, we see remarkable  examples  of  the
 preservation of regularity of form in the exact correspondence
 which exists so commonly between the two  halves of the  body.
 For example, the brain has two halves, which are precisely alike,
 and the same is true  of the nerves which are distributed from
 it.   And so of  other parts.  But, mingled with this symmetri-
 cal arrangement of parts, there are other parts  which are  irreg-
 ular in their shape.   This is the  case with the stomach,  the
 heart, the liver, etc.   There are  some animals which  are alto-
 gether destitute of this arrrangement of two similar halves^ of
 the body.   The oyster is a familiar example.   The shell  of this
 animal is strikingly in contrast, in this respect, with the  shells
 of some other of the bivalve tribe, as, for instance, the common
 clam.
  22.  There is  a distinction between organized and unorganized
 substances, in regard to size, which must not pass unnoticed in
 this connection.  The size of  unorganized bodies has no fixed
 limit.   A crystal or a  rock may grow to any  imaginable size,-
 if the particles  forming it are sufficiently abundant.  But  or-
 ganized bodies have  limits fixed  to their  growth.   There is, it
 is true,  more or less latitude  to  these limits;  but  they  are so
well defined in  the case of most vegetables and animals, that
when growth reaches  much beyond or below the limit, it is
recognized as a remarkable  fact.   Gigantic  and dwarfish vari-
ties are rare exceptions to the general rule.
  23.  The last  distinction, between organized and unorganized 
20                HUMAN  PHYSIOLOGY.
      Difference between organized and unorganized in structure and elements.

substances, which I shall mention relates to their structure.
While unorganized substances are made of one form of matter,
either solid or liquid, or gaseous, organized bodies are made of
a mixture of fluids and solids.  They are therefore more or less
soft  and flexible; while the  solid, unorganized substances are
hard and brittle.   There is  a still further difference in struc-
ture.  Organized substances  are  much  more  compound  than
the  unorganized.  Most of  the  unorganized  substances are
composed of only two or three  elements.  Thus, air is com-
posed of oxygen and  nitrogen, water of oxygen and hydro-
gen; and most of the mineral salts are  composed of three
elements—as, for example, carbonate  of lime, or  chalk, which
is composed of oxygen, carbon, and calcium, the  mineral base
of lime.  But organized  substances are  composed  of at  least
three or four elements,  and sometimes more.   The four princi-
pal elements in the composition of organized bodies are, oxygen,
nitrogen, hydrogen, and carbon.  But there are other elements
introduced  for  special  purposes.  Thus,  carbonate  of lime (a
combination  of calcium  with two of the common elements,
carbon and oxygen,) is diffused very generally throughout the
textures of  plants, giving them firmness and strength.  In the
grass tribe, silex is deposited under the surface, producing the
necessary combination  of strength and  lightness, a very small
quantity of the silex answering the  purpose.   In animals  of
the higher orders, phosphate and carbonate of lime compose in
part  the framework  of the  body.  We find  iron,  too, in the
blood.  Of the fifty-four elementary substances discovered  in
mineral bodies, only eighteen or nineteen have been found in
plants and animals, and some of  these in very small amounts.
The  essen tial components of living substances are  the four non-
metallic elements mentioned above—oxygen,  hydrogen, nitro-
gen,  and carbon; while  the bulk of the  inorganic world is
composed of the metals and their compounds, viz., the alkalies
and  the earths.  And it  is interesting to observe that, of the
four  elements which compose the  bulk of the animal and vege-
table world, both the fluids and the  solids, three are gaseous,
while but one, carbon, is a solid substance. 
DISTINCTIONS BETWEEN ANIMALS  AND PLANTS.   21

          Locomotion.  Stomach and other central organs.
                   CHAPTER  II.

       THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS.

  24.  Having pointed out in the first chapter the distinctions
between organized and unorganized substances, I now proceed
to consider the distinctions between the two classes of organ-
ized beings—animals and vegetables.  I shall first notice those
differences which are obvious when we look at the great major-
ity  of  animals  and vegetables; and shall  then point out those
which  are essential, in order that we may have a clearer view of
those  exceptional cases,  in  regard to which it  is somewhat
difficult to decide to which of the two kingdoms they belong.
  25.  One of the  most  obvious distinctions  is in  relation to
locomotion.   The plant remains in one place ;  while the animal
moves  about, in the air, or in the water, or upon the surface of
the earth.  And the  structures of the animal and the plant of
course  differ, so as to accommodate these two very  different
modes  of existence.  I will particularize.   As  the animal moves
from place to  place, it must, for this reason, if for no other,
have an apparatus of  nourishment and growth different from
that of the plant.   The plant, by means  of its absorbents in
the roots,  takes up from the earth, in the form of sap, its nutri-
tion, or food, as it may very properly be  called.  The moving
about  of the animal would in itself forbid its deriving its food
directly from the earth, even if the earth contained the proper
materials  for  its  nourishment.    Another  contrivance  must
therefore be resorted to, in order  to effect nutrition in its case.
So  a  cavity is provided in its  body,  called a stomach, into
which  nutritious substances  can be introduced.  And this cav-
ity  is  lined with  absorbents, which there do for  the animal
just what the  absorbents in the roots  of the plant do for the
plant.
  26.  Besides  the stomach, there  are other  great central  or-
gans which are peculiar to  most  animals, in distinction from
vegetables—as the  heart, the liver, the lungs, &c.   In the
plant,  there are no such central  organs upon which the whole
plant depends.  Branches and roots may be cut off extensively,
and even a  large  portion of the stem or trunk may be des-
troyed ; and  yet what remains of the plant may still live.  And 
22                HUMAN PHYSIOLOGY.____________
             Feeling.  Motion.  Sensitive plant and catch-fly.________________

even more than this.   A small portion of it may be made to
take root and live by itself.  It is not so with most animals.
Mutilation can not be carried  far without injuring some large
organ which is essential to  the life of the whole; and no part
taken from its extremities can be made in any way  to live by
itself.
  27. Another obvious distinction is this.   Animals are sen-
tient and spontaneously-moving beings, while vegetables are not.
The animal feels the action of agents upon it, and this it can
not do without consciousness and thought.  The evidences of the
existence of consciousness and thought, and the consequent spon-
taneous motion, are very slight in some animals.  Still, there is no
doubt of their existence in these cases.  We see these evidences
plainly in the great majority of animals; and we infer, very
properly, the existence of sensation and thought in those excep-
tional cases, where the evidences are doubtful or absent,  as we
find in them other marks of animal in distinction from vege-
table life.
  28. The distinctions which I have mentioned are those which
we  see generally existing.   Let us see how far they are essential
and universal.
  29. The distinction in  regard to locomotion, if we look  at
the animal  as a whole, has  its exceptions.   There are some
animals that are entirely confined  to one spot during all their
existence, as  the  coral animal  and  the  sponge.  But,  while
some animals are thus confined, they have  the power of spon-
taneous motion in some of their parts, which is  exercised for
the purpose  of obtaining  food, and, in some cases, for  the
avoidance of danger.  This power is not possessed  by any plant.
Some few plants, as the sensitive plant and the venus catch-fly,
(dionaea muscipula,) exhibit a property which  resembles it, but
it is essentially a different  thing.   In these cases,  the influence
of the stimulus that excites the  motion is communicated from
particle to particle, from the  point where the  stimulus  is  ap-
plied ; and  the motion is  only  in one direction, and  not in
various directions, as is the case with spontaneous animal mo-
tions.  This can be very readily seen, if we compare the motion
of the sensitive plant or the catch-fly with those of the little fresh-
water polype,  called the Hydra.  This animal, of which  I give
you here an enlarged representation, and also a representation
of  its natural size, is found in ponds.   It attaches itself to any
floating object—a stick or  straw, as seen in the Figure—by a
kind of sucker.  Thus supporting itself, it stretches out its long 
   DISTINCTIONS BETWEEN  ANIMALS AND  PLANTS. ~  23
            Digestive cavity.  Nervous system.  None in plants.

arms, to take for its  food any
minute  worm  or insect  which
may  float within  their  reach.
When it  catches  one, it directs
it to the mouth, a, which opens
into the stomach or general cav-
ity.   Now,  in  doing  all  this,
there is a variety, a compound
character  in the motion, which
is  in plain  contrast  with  the
simple motion of the leaves of
the  catch-fly and the  sensitive
plant.
  30. The  distinction, in  rela-
tion to  a digestive  cavity,  can
not be made  out  in the case of
some of the lower animals.  And,
if it could be, it is not an essen-
tial   distinction.    For it  only
relates  to  a mere difference of
arrangement in the  absorbents
that take  up the nutritious  substance in the two cases.  The
absorbents in the  stomach  of  the animal, as before remarked,
perform the same  office that the  absorbents do in the root of
the  plant.   They only do  it in a different place, and after  a
different manner.  The same remarks,  substantially, can be
made in regard to the other  large central organs which are
found in most animals.
  31. The last of the distinctions, which I  mentioned as being
commonly observed, is  really the essential distinction between
plants and  animals.   I mean the capacity for sensation and
spontaneous motion, which exists only in the  animal.  There
is nothing truly analogous to  this in the plant.   And we, ac-
cordingly, find a peculiar structure in animals, devoted to these
functions, and  others connected with  them.  This structure is
the  nervous system.   No trace of  such a structure  has ever
been discovered in any plant.  If there were any true analogy
between animal motion and the motions of the sensitive plant
and the catch-fly, we should be able to find in them traces of ner-
vous structure; for the structure of these  plants  is so plainly
developed, that its constituent parts  are easily distinguished.
   32. The nervous system is  evidently not essential  to nutri-
tion, for this is as well effected in the plant as in the animal.
 
24
HUMAN PHYSIOLOGY.
           Thought and will. Instinctive and automatic motions.  __________

This is accomplished  in both in substantially the  same way.
The means by which it is done, and its arrangements are modi-
fied, as you have seen, in the two cases, to suit the  differing
circumstances.  The nervous system, observe,  then, is, for par-
ticular purposes, superadded in the animal  to what  is common
both to the animal and the plant, and so constitutes the essen-
tial difference between them.  And so, all the functions relating
to nutrition, which are of course common to plants and animals,
are called functions of organic life.   But the functions which
are performed by the system superadded  in  the animal, the
chief  of which  are sensation  and  spontaneous motion, are
termed functions of animal life.  These are  sometimes also
called functions of relation, from the  especial connection which
they form between the animal and all that is around him.
  33.  These  animal functions, sensation  and spontaneous mo-
tion, imply thought and will.   The  order  of action  is this:
sensation—thought  in regard  to it—action of the will in con-
sequence of thought—then,  from this  action, an  impression
carried through nerves to organs  termed muscles—motion  in
them  from their contraction.   This order, • however, is not
always  observed.    The first link, sensation,  may  be absent.
Thought, without any preceding  sensation, may prompt the
will, and spontaneous  motion results.  The action of the will,
too, may be left out, or may be in opposition.  Thus, emotions
may produce action of the  muscles, the will  not concurring,
and perhaps opposing; as when we laugh at what is ridiculous,
or weep at what is  sad, in  spite of restraining efforts  dictated
by the will.
  34. There  are  also instinctive motions, and motions which
are termed automatic, with which the will has no  direct con-
nection.  And the  connection of sensation with them  is,  in
some  cases at least, doubtful.   The action  of the  muscles,  in
swallowing, breathing, &c, and  the  action  of that compound
muscle, the heart, are  examples  of motions more or  less dis-
connected from the  will, and  also from sensation.   The action
of the heart is wholly removed from  the direct influence  of the
will, and it is at least not obvious that it is  influenced directly
by sensation.   It  is influenced indirectly by both, through the
agency of emotions awakened by them.  The muscles of breath-
ing, on the other  hand, though ordinarily involuntary, may  be
directly influenced  both  by the will  and by  sensation.   You
can at will breathe  faster and more  deeply, and sensations  of
uneasiness in the  chest modify the breathing. 
   DISTINCTIONS BETWEEN ANIMALS  AND PLANTS.   25
          Central organs of nervous system. Most developed in man.

  35. For all these different actions, thus produced in different
ways, there are central parts of the nervous system upon which
the causes of these actions produce the impressions or impulses
from which the actions  result.  Thus, when a sensation is fol-
lowed by a  spontaneous  action of muscles,  an impression is
conveyed by nerves  to  the  central  organ; the will  there  acts,
and  the  impulse  there  given  by this action of the will is car-
ried by other nerves to the muscles, which execute the intended
movement.
  36. These  central  parts or organs, which are the media, the
instruments  of impressions,  are in different parts of the body
of the animal; but  the most important  of them is what we
call the brain.  This  part is developed most in those animals
that give the greatest evidences of intelligence; and, therefore,
it is more prominent in man than in any other animal.
  37. It may be  remarked,  as a general truth, that the nervous
system, and its associate or subordinate system, the muscular,
are developed in different degrees or forms, to suit the different
characters and wants of animals.  In man, they are more  com-
plex and perfect than in any other animal.  The brain, in him, is
a large organ, occupying  the  skull.   The  spinal marrow, and
other central  parts, and the  nerves, are largely developed.  And
the muscles which are  moved by this nervous system form  a
large portion  of the bulk of the body.   The organs of nutrition,
analogous to those which make up  nearly the  whole of the
plant, occupy the two cavities of the  trunk of the body, the
thoracic  and  the abdominal.  But, as we descend  in the animal
kingdom, the nervous system becomes continually  less promi-
nent, and the system of mere nutrition more so.  We at length
come to  animals,  in which the nervous system is a  mere small
appendage to the system of  nutrition, and  only serves to direct
the muscles  in securing the food of the  animal.   In some of
these, we not only do not find a brain, but we fail  to discover
any traces of a nervous system.  This is true of the Hydra,
noticed in § 29.
  38. The nervous system, which so clearly distinguishes  most
animals from all  plants, is  fairly presumed to exist, though in
an exceedingly slight degree, in those beings in  which it can
not be found, but in  which we find other characteristics of the
animal kingdom.  And it  is presumed, also,  that the exercise
of thought and the  action  of the will, which  most animals so
plainly exhibit, while they become  less and less obvious as we
descend  in  the scale, are not wholly obliterated in the  very
                             3 
26                HUMAN  PHYSIOLOGY.
         No nervous system in some animals; yet feeling and thought.___________

lowest animals.   It  may, perhaps,  be said, that as muscular
■action, as mentioned in  §  34, is sometimes produced even in
man without the intervention of thought or the will, it may be
produced in animals of the lowest order altogether in this way.
But we may more rationally infer  that, as  the  chief object of
motion in  them is the securing of food, it is guided by the
action of a will  in  obedience  to their sensations.   In other
words, it is truly a spontaneous, and not a mere automatic mo-
tion.   And  it is  probable  that there is in the very lowest of
animals some degree, though it may indeed be slight,  of enjoy-
ment in the  sensations received from the moving water about
it, and from the satisfying of its wants  in the process  of nutri-
tion.   We will take the Hydra, a  representation of  which is
given in Fig. 1, page 23,  as an illustration of the above remarks.
It is a minute gelatinous  animal, in which  no nervous or mus-
cular fibres can be found.   And yet it has  an  extraordinary
power of extending and contracting itself.  When it is alarmed,
it draws in its arms, and  shrinks into the form of a little glob-
ule ; and if you should see it in this condition, you would not
suspect that  it had any arms  or  tentacula.   But  when it is
searching for food, it often  extends  its  body and its arms to a
great length; and when  it  grasps  its  prey, it puts it into its
stomach, which constitutes, so  far  as  we can see, its  whole
body.   We can not conceive  of all these motions, thus exe-
cuted to effect certain definite objects, without the agency of a
will, and without sensations to  prompt  the will and guide the
motions.  The animal must have a power of choice, or it would
put a bit of stick or  straw into its stomach as readily as a
worm or an insect.  But the tentacula never grasp, among the
various bits of things which float against them,  any thing be-
side the appropriate food of the animal.  And it undoubtedly
enjoys its food as really, though perhaps not as vividly, as any
human epicure; and has in some  measure the  same pleasur-
able sensations which  locomotion produces in us, as  it floats
along so quietly, with  its arms  hanging down from  its body.
Though there be no nervous fibres to be seen in the loose gela-
tinous structure of this  little  creature, yet, as the phenomena
which it exhibits  are known  to be produced by the nervous
system  in those animals whose structure is more plainly  and
thoroughly  developed,  we justly  infer that  there  must  be
nervous matter, in some form, in this  and other similar  ani-
mals.
   39. One  more  important distinction between  animals  and 
          MAN  IN HIS RELATIONS TO NATURE.       27
        Peculiar endowments of man.  Abstract reasoning. Conscience.

plants remains to be noticed.  It relates to their chemical com-
position.  I stated, in § 23, that organized substances are com-
posed mostly of four elements—oxygen, hydrogen, nitrogen, and
carbon.  Plants differ from animals, in having but little nitro-
gen in their composition.  It was formerly supposed that they
contained none of this element.  It is found only in particular
parts of plants,  as  the seeds.  We may regard carbon  as the
most characteristic constituent of vegetables, and nitrogen of
animals.  And  in  this connection it is interesting to observe
that, while carbon is  largely thrown off from the lungs of ani-
mals, in the shape of carbonic-acid gas, it is as largely absorbed
by the leaves of plants.   Of this fact  I  shall take more par-
ticular notice when I come to the subject of respiration.
                   CHAPTER  III.

  MAN IN HIS RELATIONS TO THE THREE KINGDOMS OF NATURE.

  40. Man is commonly spoken of as being at the head of the
animal kingdom, and in the book  of the naturalist is made an
order of the class  termed Mammalia.   As the basis  of the
whole classification  is mere  material organization, and has no
reference at all to mental or spiritual endowments, the classifica-
tion, in regard to man, is in its principle correct.  At the same
time, it must be admitted, that it  fails to recognize altogether
the  essential distinctions between man  and other animals.
These distinctions, making, as  they do, a  wide gap—" an im-
passable chasm," as Professor Guyot expresses it—between man
and  the inferior animals, are  to be found in certain peculiar
spiritual endowments which  man  possesses.   These I will no-
tice now in the  briefest manner, leaving it for another part of
this book to treat more fully of this and other kindred subjects.
One of these endowments is the  power of abstract reasoning.
Other animals in a  certain sense reason, that is, they make in-
ferences; but they  never arrive  at  any  general  or abstract
truths.   Another endowment is a moral one, linking man in his
spiritual nature  to the Deity.  It is conscience, or the knowledge
and  sense of what  is right, in distinction from what is wrong.
Other animals, in  obedience to the passions  of  fear and love, 
28
HUMAN PHYSIOLOGY.
             Immortality. Real relation to the animal kingdom.

 sometimes appear to the superficial  observer to have an idea of
 what is right, as such; but there is not the slightest evidencer
 that they really have any such knowledge.
   41. In view  of these endowments of  man, it is  wrong to
 consider him merely as being  at the head of the animal king-
 dom.  He  is something more than this.  He is so much and
 so  distinctly more, that the accepted classification of him, on
 the ground of mere  difference  of  organization,  gives a most
 inadequate  idea of his true position in the scale of being.  It
 leaves entirely out of view the essential distinctions;  and it
 separates man from other animals, as you will see, by a distinc-
 tion of organization which is  of rather a trivial, perhaps ques-
 tionable, character.
   42. The  force of this view of the subject is enhanced, if we
 take into consideration that great fact, revealed  to us by God
 in his Word, that man is destined to immortality.  It may be
 objected that, as this fact is learned only by revelation, and  not
 by observation,  it  is  not  to be regarded as a scientific fact.
 But, granting that  there is truth in the  objection, it certainly
 is allowable to  allude to the  revelations of Scripture, as con-
 firming or enforcing views  developed by scientific observation.
 This is all that I have done in this case.   The view which I
 have presented is based upon  endowments that are recognized
 by the scientific observer, without the aid of revelation; and I
 appeal to the  revealed fact of  man's immortality, as adding
 force  to  this view,  and not as  being at all  necessary  to  the
 establishment of its truth.
   43. Let  us look  at this subject  in another point of view.
 The grand essential distinction between animals and plants lies,
 as you have seen  in the last chapter, in  the  fact that animals
 have  a nervous  system.  Now, with this  system,  as  you have
 also seen, appear  certain mental manifestations.   These  differ
 widely in different animals, and are  most prominent in those in
 which this system is most prominent and complicated.   As  we
 trace upward these  complications, when we come to  man,  we
 find certain mental manifestations, which separate him by "an
 impassable  chasm"  from all other  animals.   Till we arrive at
 him, the difference is one of degree,  for the most part.  But in
 his case  it  is a difference of kind,  and a very wide  one.   Of
 such a difference  the naturalist should certainly take very dis-
 tinct cognizance; and, if it be not consistent for him to do so
in his classification, great force and prominence should be given
to these views in his instructions  on  this subject.   As the super- 
MAN  IN HIS RELATIONS TO  NATURE.       29
         The hand of man. No other animal really has such a member.

^adding of the nervous system  separates the animal from the
 plant, so, also,  as  Professor Guyot  very justly maintains, the
 superadding of such  endowments  as we find in man separates
 him, by a chasm quite as " impassable," from other animals.
   44. The distinction commonly  received  as the ground of
 classification for man, I have said, is a trivial, perhaps a ques-
 tionable one.  He is said to have two hands, and so makes the
 order Bimana; while apes and monkeys are said to have four
 hands,  and are, therefore,  considered  as  making the order
 Quadrumana.  Now, if we observe carefully and fully the won-
 derful  endowments of the human hand, we  shall hardly be
 willing to allow that  monkeys  and apes have four such mem-
 bers.   With a full view of the  capabilities of the human hand,
 those members can not be considered as hands, but as members
 possessing some of the  properties  of both  hands and feet.
 They are given to these  animals to enable them to climb with
 facility, and to  grasp their food;  and they have none of that
 infinite variety of motion, which is so striking a peculiarity of
 the hand of intelligent  man.  The  ground upon which they
 are said to have  four hands is that which is thus stated by
 Cuvier. "That which constitutes  the hand, properly so called,
 is the faculty of opposing the thumb to the other fingers, so as
 to  seize upon the most minute objects."   No animal besides
 man has this  arrangement, except the Quadrumana.   It  is
 claimed, therefore, that they have hands,  although they are
 very imperfect when  compared with the hand of man.  The
 imperfection is  indeed  so great, as  to  make us at least reluc-
 tant to admit the claim set up by the naturalist.  " While,"
 says Carpenter, " the  thumb in  the human hand can be brought
 into exact opposition  to the extremities of  all  the fingers, whe-
 ther singly or in combination, in those Quadrumana which most
 nearly  approach man, the thumb is so short, and the fingers so
 much  elongated, that their tips can scarcely  be brought  into
 opposition, and the thumb  and fingers are so weak, that they
 can  never be opposed to each other with  any degree of force.
 Hence, although admirably adapted for clinging round bodies
 of a certain size, such as the small branches of trees, &c, the ex-
 tremities of the  Quadrumana can never seize any minute object
 with such precision, nor support large ones with such firmness,
 as  are essential to the dexterous performance of operations for
 which  the hand is admirably adapted."   Indeed, what is called
 the thumb of the Quadrumana  is so short and slender, that Eus-
 tachius, the  anatomist, very properly said  that, regarded as an 
30                HUMAN  PHYSIOLOGY.
       Other peculiarities.  Chin.  Erect posture. Weeping and laughing.

imitation of the thumb of man, it is a ridiculous affair.   If,
then, we take into view the extensive and varied capabilities ot
the human hand, we  must agree with  Sir Charles Bell, when
he says that "we ought to define the hand as belonging exclu-
sively to man."  This  view of the subject has always impressed
itself upon the minds of acute observers in all ages.   Aristotle
said, that man alone  possesses hands deserving of the name.
Anaxagoras said, that " man is the wisest of animals, because
he possesses hands."  And the  opinion, thus uttered by these
philosophers some centuries before the  Christian era,  is fully
echoed at the present  time.
  45. It would  seem, then, that, if mere organization  be  ad-
hered to, as the basis  of classification, it is desirable that some
ground of distinction  in relation to man be fixed upon, which
is more definite  than  the  commonly received one.   It is to be
remembered, however, that, in classification, some one very ob-
vious peculiarity that presents itself to  the eye is  ordinarily
made use  of as  a mark of distinction,  while accurate and full
discriminations are followed  out entirely separately  from  the
mere  classification.  This is  done  in the  case of man.   His
structure differs in many respects from that of the inferior  ani-
mals.  It would make this chapter too long  to point out all
the differences.  Some of  them are important, while others are
not.  As an example  of the latter, I will mention the fact, that
no  animal  but man has  a chin.   Every other animal  has its
lower jaw retreating from  the teeth, instead of projecting for-
ward below, as in man.   One of the most important and strik-
ing peculiarities of man's structure is that general arrangement
which enables him to be in the erect posture.  No other animal
naturally assumes this posture, or is able to maintain it for any
length  of time; and most animals assume one which is en-
tirely the opposite of  this.  Even the monkey,  when taught by
man to stand and walk, is by no means erect; but his lower
limbs are crooked, and the moment that he escapes the neces-
sity of being an  imitator, he is on all fours.  There is a distinc-
tion of an interesting character, which  concerns both the  ner-
vous and muscular systems.  I refer to the fact, that no animal
but man  can  shed tears, or  perform those muscular motions
which are necessary to the acts of weeping and laughing.   In
view of this marked distinction, man has sometimes been desig-
nated as " a laughing and crying animal."
   46.  But the great essential distinctions, to which all  the rest
are really tributary, are, as I have before stated, of a mental or 
MAN IN  HIS RELATIONS TO  NATURE.       31
              Tendency to skepticism.  Robinet's doctrines.

spiritual character.   And these should always be made peculi-
arly prominent,  whenever the distinctions  between  man and
the inferior animals  are  treated of  by the naturalist.   This
should be  done, not  only because  they  are essential, but also
because, as I have just  hinted, all other distinctions are  subor-
dinate and tributary to  them.  It is the mental peculiarities of
man, for the  most part at least, that  render necessary those
peculiarities which distinguish his organization  from that of
other animals.   I will not dwell  on this point, as I shall speak
of it in another  part  of this book.
   47.  In view of this whole subject, it  may be said, that the
classification upon which  I have  commented is not of itself of
very great importance,  provided  that the definite distinctions,
which have  been pointed  out  as  existing between man and
other  animals, be clearly recognized by the naturalist.  The
tendency, however, evidently is, to  lose  sight of these distinc-
tions in the exclusive regard which  is paid to mere material
organization.  This  tendency, it  is true, is  effectually counter-
acted  in the  case of the great  majority of scientific men, by
the comprehensive and  Christian views which they take of the
whole subject; but, still, it manifestly exists, and gives  rise to
many sceptical  notions, especially in  superficial and theorizing
observers.   Great care, then, should be taken to  oppose this
tendency in all  public  teaching  on this subject, whether it be
done by books or lectures.
   48. There is  a disposition, on the part of some writers,  to
obliterate the grand  distinction  between man  and the inferior
animals, and other distinctions which are stamped by the Cre-
ator upon his works. Some go so far as to maintain, that there
is not only no line to  be drawn between the animal and the
vegetable kingdoms,  but none even between organized and un-
organized  substances.   Robinet, and  many  other European
authors, teach that  all matter has living properties, and _ that
every object that we  see, whether mineral, vegetable, or animal,
is the result of repeated and progressive efforts of nature.  The
ultimate aim  of these  efforts is considered  to be the formation
of man, who is  looked  upon  as  the  perfection of organization
evolved by these efforts.  In advocating this theory, they make
great  use of  resemblances  and  analogies, and even represent
the  fantastic  shapes .which minerals sometimes assume, from
their slight resemblance to parts of the human body,  " as  so
many proofs," in the language of Carpenter, " of this long and
bungling apprenticeship of nature to  man-making."   Although 
 32                HUMAN  PHYSIOLOGY.
              Gradations in nature. Wrong ideas of perfection._______________

 such ridiculous doctrines are  seldom formally advanced, there is
 a disposition in many scientific men to indulge in speculations
 which have more or less resemblance to them.   They seem dis-
 posed  to confuse with the veil of mystic scepticism the clear
 characters which God has imprinted upon the manifestations
 of his power.  It  is well, therefore, to fix  these  characters
 definitely in the mind, in order to guard against the  fascinating
 and  bewildering speculations of a false science.   A true science,
 forsaking the  mazes of speculation, and  inquiring only for the
 facts, reads with admiration  and reverence the clear lines of
 God's handiwork, and attributes to no imaginary agency, termed
 Nature, what bears  the marks of exquisite design and Almighty
 power.
   49.  An idea, somewhat akin to that of Robinet, is sometimes
 entertained, viz., that the varieties  in the mineral,  vegetable,
 and  animal kingdoms are mere gradations in nature.  There
 would  be some plausibility in this notion if it were  difficult to
 distinguish the minerals of the most perfect kind from the lowest
 plant, and then the plants of the highest order from  the lowest
 animal.  But the difficulty lies in other quarters.  The most per-
 fect in  the  three kingdoms are distinguished from each other in
 the most marked manner; and  it is only when the character-
 istic  qualities are the least developed-that there is any difficulty.
 One  kingdom is a no  more perfect formation than  another.
 The  crystal, with its  exact lines and angles—the plant, with
 its curvilinear and  less  definite  shapes—and the symmetrical
 animal, are equally perfect in their kind.  Each  is made for
 a  definite purpose,  and is perfectly adapted to that  purpose.
 In none is there any imperfection which could  be remedied by
 endowments taken  from another kingdom  of nature.  In the
 vast  variety of forms which nature presents, there is  to be seen
 no vain struggling after a higher and better  state.  There is no
 progressiveness, aiming at an ideal perfection.  Neither are there
 gradations leading to it.  All the works of the Creator are per-
 fectly adapted to the spheres which they fill.  They were all
 from "  man, made in His image," down  to  the humblest ani-
 mal  or plant,  pronounced to be "very good,"  as  they came
from His hand.
   50. Let me  not be understood to say that there are no (ni-
dations in nature.  There are some of a very interesting char-
acter ;  but they do not obey  any such laws as those  which are
indicated by Robinet and  other fanciful theorizers.   There are
gradations in both  the animal and vegetable world.    You ob- 
          MAN IN HIS RELATIONS  TO NATURE.       33
               Man inferior to other animals in some respects.

serve them as you go  from the simplest plant up to the most
complicated.  And so of animals.   But these two  kingdoms
of nature are separate  in their gradations,  and are not in one
series together, as is represented by Robinet.   And the grada-
tion in each kingdom is by no means an unbroken and regular
one, going  up, step by step, from  the lowest  to the highest.
For example, in the animal kingdom, there are not constant
and regular  additions made, as you  trace the gradations up-
ward.   And though man stands at the top of the series, it is
not  as  a compound, made up of all the  excellencies found
below him,  with additional excellencies peculiar to himself.
Superior as he is, as a whole, to all other animals, yet in some
respects he is inferior to many of them. He is inferior to them
in the wonderful capabilities of instinct.  Some animals  can do
some things  better than he  can.   The monkey is a better
climber.  Some  animals can do what he can not.   Birds and
winged insects  fly, but he  can not.   These points  could be
illustrated to any extent, but this will suffice.
   51. Man is often spoken of as being the most perfect of ani-
mals.  This, as you will see from what was said in a previous
paragraph, is  not true in the  strict  sense of the word.  His
organization  is more complicated, and  he has more and  higher
endowments than any other animal; but the perfection of struc-
ture, and  of adaptation in contrivance to the  purposes aimed
at,  is as  manifest in all  the varieties of animals  as it is in
man.
   52. In  one respect, there is a gradation existing through the
three kingdoms of nature.   It is in regard to formation or nu-
trition.   All the elements which are found in the composition
of animals exist in  the mineral world.  But  these  elements,
with very few exceptions,  can not be transmitted directly to
animals,  but they are transmitted  indirectly through vegeta-
bles.  No animal, therefore,  can live  on mineral substances,
although these substances contain all  the elements found in its
composition.   But  vegetables draw their nutriment  from the
mineral world, and then furnish nutriment to animals.  There
is, therefore,  in  relation  to formation, a gradation running
through the three kingdoms, from the mineral up  to the ani-
mal.
  53. At  the  summit of the last step in this gradation stands
man.  To him, not only is the animal kingdom tributary, but
so, also, are the mineral and vegetable kingdoms.  They  are all
made for him, to beautify and gladden this his temporary home, 
34                HUMAN  PHYSIOLOGY.

              All nature tributary to man. Imperfectly so.
and to sustain him in it.   The subjec tion $*™£^?
undoubtedly perfect in his primeval condit<® *J™^™
the garden of Eden.  But now, we see this tribute 7 subjecbon
manifested only as a general fact, with many exceptions  These
mark this  life as  thl  imperfect state, and  this  world as the
Smporary  home of  manfin  which he can prepare  himself
for the perfect and everduring state and home  of another life
beyond. 
PART  SECOND.
                         CONTAINING,
CHAPTER IV.—General Vlyws or Physiology, with a Brief Account of some of the
  Structures in the Body.  CHAPTER V.-Digestion.  CHAPTER VI.—Circulation.
  CHAPTER VII.—Respiration. CHAPTER VIII.—Formation and Repair. CHAPTER
  IX.—Cell Life.
                    CHAPTER  IV.

GENERAL VIEWS OP PHYSIOLOGY, WITH A BRIEF ACCOUNT OP SOME
              OF THE STRUCTURES IN THE BODY.

   54.  The  contents of the previous chapters are  preliminary
to the  consideration of the real subject of this work, the Physi-
ology of Man.  But they were necessary, in order to accomplish
a very  prominent object which I have in view.  It is my wish
that the student, as he examines the functions of the  human
system, should at the same time  observe  the analogies existing
between man and other living beings, in the processes of life.
He will, in this way, get an enlarged view of  man in his rela-
tions to the world around  him, and will be prompted to observe
the phenomena of life, in  whatever department of  nature they
may be presented to his  view.   And, in  order to promote this
object  effectually, I shall, as I proceed with the development of
the physiology of man, refer occasionally to the analogous phe-
nomena in other animals, and also in plants.   This will serve
to fix more definitely in the mind of the student the main facts
that are to be communicated, at the same time that the bound-
aries of his knowledge will be extended  over  fields full of in-
terest.
   55.  This  is a  work on Physiology, and  not on Anatomy.
Physiology  treats of the  offices or functions  of the different
parts of the structure, while Anatomy has regard to the struc-
ture itself.   In the following pages, I shall introduce the anat-
omy of the system only so far as it is necessary to elucidate its
physiology.
   Before proceeding to an examination  of the individual sub-
jects which  will claim our attention, it will be proper to present
some general views of  them in their relations as a whole. 
36               HUMAN PHYSIOLOGY.________
           Natural division of the subject.  Interest of the study.  _____________

   56. You have seen, in  the preliminary chapters, that organ-
ized living beings have much that is common to them all.  This is
true so far as nutrition  is concerned.  You have seen that the
animal grows very  much  as  the  plant  does, and that  the
arrangements for its  growth vary from those of the plant only
so far as  the difference of the source of its  nourishment,  and of
the circumstances  under  which it  is obtained, require.  The
grand  distinction,  as  you  have seen,  between animals and
vegetables  is to be  found  in  the  functions belonging  to  the
nervous system.   These functions are wholly separate from the
nutritive 'functions, which animals  perform in common with
plants.
   57. This view of the subject suggests a natural  division of
the physiology of man  into two parts, viz., the nutritive func-
tions,  and  the  animal  functions, or those  connected with  the
nervous system.  In  other  words,  the first division will com-
prise all those subjects which relate  to the  building and  repair-
ing of the human structure ; and the second will comprise those
which relate to  the uses for  which the structure is made.  The
first class of subjects includes digestion, circulation,  respiration,
formation, and excretion.  The second class includes locomotion,
sensation, the five senses, the voice,  instinct, thought, &c.
   58. The student will see at one glance, that a wide range of
exceedingly interesting subjects opens  before  him.  Contem-
plated as a mere mechanism, the human system is full of won-
ders.  The principles of common Mechanics, of Hydraulics, of
Pneumatics, of  Optics, of Acoustics, are abundantly illustrated
in the human body, by contrivances of  the most exact and ex-
quisite adaptation.  But this congeries of beautiful mechanisms
is all regulated  by a nervous system, making it, by its  minute
fibrils,  to be alive with feeling in  every part.  Sensation and
sympathy govern, through the nerves, in a wonderful  manner,
the ever-varying adjustments of all  the parts of the complicated
system.  It is not only mechanism, but living mechanism, that
develops  to us its wonders, so numerous and diversified.   And
then,  when we look at  the soul—"that side of  our  nature
which is  in relation with  the Infinite"—connected  as it is by
the nerves with every part  of  this  mechanism, the  interest of
the study before us  appears exceedingly great, and its  variety
never ending.   The study is a peculiar one.  It is not the body
merely that you are to study in these pages;  but it is the body
and spirit  united.  The  study differs from  all others  in  this
respect.  In other studies, you  look at  either  matter alone, or 
GENEEAL VIEWS.
37
  ______________Bones. Two parts, animal and mineral.  Cartilages.

 spirit alone;  but here you look at them  both, as brought to-
 gether in mysterious union.
   59.  It will  be proper, here, to say something in general of
 the structure of the human  frame, before  proceeding to a  par-
 ticular view of individual subjects.  I do this in order to avoid
 a frequent turning aside for  explanation, which would not only
 be inconvenient, but would  mar the  interest  of the study.  It
 will not be necessary to go into a full description of the nume-
 rous and diverse textures, or  tissues, (as they are commonly
 called,) of the body.   I will  notice only some of the principal
 of them.                             J              *    F
   60.  From  the osseous or bony tissue, the solid part of the
 framework  of the body is made.  Bone is composed in part
 of animal  matter,  and  in  part  of mineral.   The  mineral
 part  is mostly phosphate of lime.  These  two parts of bone
 are  in different  proportions  to  each  other  in the  different
 periods of life.  The mineral part in the child is about one-
 half  of the  bone;  in  the adult,  four-fifths;  and  in  the  old,
 seven-eighths.  The bones are therefore  very brittle in old age,
 while they are  somewhat yielding  in childhood.  The mineral
 and the animal  portions of bone  can be separated from each
 other.  If a bone be put into diluted muriatic acid, the mineral
 part  will after a time become  united with the acid, and  the
 animal part will be  left, having the perfect  shape of the bone.
 Thus separated from the mineral  part,  it is so flexible, that it
 can  be tied  into a  knot without affecting its shape.   On  the
 other hand, by subjecting a bone for some time to the action of
 heat, the  animal part can be  removed, and the mineral part be
 left by  itself.
   61. The  animal part of bone is cartilage,  or gristle.  This
 part is  formed first,  constituting a  sort of mould, in which  the
 bone is to be formed.   The mineral matter is gradually depos-
 ited in  the cells of the  cartilage.  In the very  young child, you
 can see that this process is not completed, especially if you  ob-
 serve the bones of  the head.  The bones are  not united  to-
 gether, as they are in the adult; and there is so little of mineral
 matter  near  their edges, that  they can be bent with a very
 slight  pressure.  The proportion of mineral  matter  which is
 deposited in the  cartilaginous  bones  varies much  in  different
 animals.  In many fishes, there is  almost none of this deposit,
the skeleton retaining  its  cartilaginous  character  throughout
life.
  62.  Besides  the cartilaginous portion of bones, there are car-
                             4 
38
HUMAN PHYSIOLOGY.
             Ligaments.  Muscles.  Tendons. Cellular tissue.________________

tilages which are destined to remain  so,  instead  of having
mineral deposits made in their cells.   The ends  of the bones
are tipped with them.  They are placed between all the twenty-
four bones of the spinal column.   They form the  connecting
links  between the breastbone and  the  ribs.  Cartilage consti-
tutes  the body  of the  outer  ear,  of the eyelids,  and of  the
lower part of the nose.  The transparent  part of  the  eye is
formed of cartilage.   This  substance is  placed wherever firm-
ness and tenacity are required without hardness.
   63. The bones are  united together by ligaments of various
degrees of strength, according  to  the necessity  of the case.
They  are moved by muscles, which, in man,  are bundles of
reddish fibres.  Muscular substance  is what  is commonly called
the meat in animals.   It is of various colors  in  different ani-
mals,  or  in the same  animal  at different periods  of life.   All
motion in animals is produced by muscles.   I will not go into
an  explanation of their  action now, any further  than to say,
that they act by contracting or shortening their fibres.  Com-
monly there are tendons united with the muscles.   These ten-
dons are  composed  of strong  white fibres, and have no power
of contraction themselves.    They  serve  merely as  the  cords
by which the contracting muscles  move the bones and  other
parts.
   64. The most common tissue in  the body is what is called
by the names,  cellular membrane,  cellular  tissue, and areolar
tissue. This  last name is most commonly used by physiologists
at the present time.   The word areolar comes from the Latin
word  areola,  meaning a small open space.   The term is appro-
priate, because  this tissue is filled with minute spaces or cells.
The word cellular is quite as  appropriate; and, as this will be
more  familiar to you, I  shall make use  of it whenever I shall
have occasion to speak of this  tissue.   That you may under-
stand what this  tissue  is, I will  refer you to its appearance as
you see it in  different meats.  It is  the delicate white substance
that you see  between the different  layers of muscle in a piece
of meat.   If you notice  particularly, you  will see  that  it is
also between all the  different fibres of the muscles.  As the
spaces or cells communicate together, butchers sometimes " blow
up" this tissue in veal, in  order to make the meat look more
plump.   This tissue is the universal packing material  of the
body.   It is to be found  almost  everywhere.   It surrounds
every thing,—vessels,  nerves, muscles,  organs,  &c.   It enters
into their  composition, uniting together different tissues,  and 
GENERAL VIEWS.
39
FIG. 2.
        Communication between cells of cellular tissue. Shown in dropsy.

also the fibres of the same tissue.   It varies much in its com-
pactness in different parts.   It is very fine and compact where
it is necessary that it  should be so ;  while  in  other  cases it is
loose and delicate, allowing a free motion  of the  parts which it
envelops  and connects  together.   It is  abundant  and loose
among the muscles, and between them and the  skin.   Fig. 2
represents a portion of cellu-
lar  tissue, inflated and dried,
exhibiting the  arrangement
of  its larger  meshes.   This
 is  magnified  twenty diame-
ters.   The free communica-
tion  which  exists  between
the interstices or cells in this
tissue is  exemplified in drop-
sy.   These cells are bathed,
in the healthy state,  with  a
small  amount of  a  watery
fluid;   and  when  this  in-
creases largely, forming the
disease  termed  dropsy,  it
obeys the force of gravity in
the  cells,  and  accumulates
most in  the lowest parts of
the lower  extremities.   This
tissue is very elastic in health,
so that if you press on the
skin, there is  no indentation left when the pressure is  taken
away, for the  elastic cellular tissue  at once rises from its state
of compression, pushing the skin before  it.  But  in dropsy it
loses its elasticity by over distension;  therefore there  is pitting,
as  it is  termed, after removing the pressure.  We sometimes
have an opportunity of seeing the communication between the
cells manifested by the introduction of air  into them.   This has
occurred in some cases in which  an opening has been made, by
disease or accident, from the air  tubes in the lungs into the cel-
lular  tissue in the  walls of the chest.   The  whole  body  has
been  seen largely swollen,  from the  air  which has  from this
cause  accumulated  in  this tissue  directly  under  the skin.
Among the many tricks of impostors, the inflation of the cel-
lular tissue of the head  has been practised ; and as it produces
a frightful appearance, and  therefore excites pity, the trick is a
very successful one.
CELLULAR TISSUE. 
40                HUMAN PHYSIOLOGY.
        Deposits of fat. Its uses. How kept in its cells.  Mucous tissue.__________

  65.  There are here  and there in  the cellular tissue deposits
of fat.  Various purposes are answered by these deposits.  They
are  sometimes of use  in  promoting a free motion of  the adja-
cent parts.  The eye has, intervening between it  and  the bony
socket, a cushion of fat, on which it rests, and against which
it is pressed when  any violence is offered to it.  Fat, as  a non-
conductor, is a protection against the cold, and it is therefore
deposited largely in the cellular tissue  under the skin, in ani-
mals that inhabit cold climates.   Fat, also, sometimes serves as
nourishment to the system when  its necessities require it.   In
diseases  in  which food  cannot  be taken in  any amount, the
fat  is  absorbed  into  the system.   The heat of the body is
maintained  also, in part, by this process.  This occurs  in the
torpid  condition  of hybernating animals.   They commonly be- •
come very fat in autumn, as a preparation  for  the winter, and
in the  spring they come forth very lean,  their store of fat having
been used up for the  purposes of nutrition  and  heat  during
their confinement.   The fat thus deposited in the cellular mem-
brane or tissue is not diffused merely in the interstices, but it is
confined in cells  of its own, which lie in these interstices.   Mi-
nute blood-vessels, pass from the fibres  of the cellular tissue to
these fat cells.  The fat, which is an  oily fluid,  is kept  from
oozing through the pores of the cells that hold  it by the blood,
which  is very nearly four-fifths  water, and by the watery fluid
which  I have spoken  of as bathing all the  interstices of the
cellular tissue; for oil, you know, will not pass  through any
porous substance that is wet with any watery fluid.   If a por-
tion of cellular membrane containing fat be dried, the fat, which
in  the  moist state is wholly  confined  to its cells, now oozes
through  their pores.   This is  the  reason that a lump of fat, as
it is called, feels so oily after it has been exposed  for a while to
the  air.
  66.  The mucous tissue  is that which lines all the cavities of
the  body that have  outlets. It  lines the mouth  and the cavities
of the  nose, and descends into the lungs, the stomach, &c.  It
takes its name from the fluid called mucus, which is constantly
secreted by innumerable minute glands, that are situated in the
substance of this membrane.   The  chief object of this  viscid
fluid is  to protect  the membrane from the substances which
come in contact with  it, which would otherwise produce some
irritation.  This membrane is continuous with the skin, shading
off  into it insensibly, as you may observe on the lips.
  67.  The serous tissue or membrane  forms the outer coat or 
                     GENERAL VIEWS.                  41
  __________  Serous membranes.  Compound character of the organs.

 lining of nearly all those organs the inner coat of which is mu-
 cous membrane.   This is the case with the lungs, the stomach,
 and the intestines.  The serous  membranes are white, smooth,
 and  shining, and are lubricated with  a  watery fluid,  called
 serum.  Every serous membrane forms a cavity or sac without
 an  outlet, differing in this respect entirely from the mucous
 membranes.  Thus, in the  case of the  lungs, the serous mem-
 brane lining the  outside of each of these organs passes from
 the lungs to the  walls of the chest, lining  the inside of them,
 and  thus makes a sac without an  outlet for each lung.   This
 sac could be dissected  off, and taken out whole.  When the
 fluid which  lubricates the  inside of this  sac  increases to  any
 extent, the disease called dropsy in the chest is produced.  The
 membrane which thus lines the outside of the  lungs  and the
 inside of the walls of the chest is called the pleura, and it is the
 seat of the disease termed pleurisy.
   68. I have thus described  some  of the  principal  of the tis-
 sues  which  make up the human structure.   The  other tissues
 will be spoken of in the  proper connection as we proceed.   Be-
 fore dismissing this subject, I will call your attention to  the fact,
 that  the organs of the body are generally composed  of several
 tissues united together.  Thus, the stomach has three coats, as
 they are termed,—the mucous as the inner coat, the serous as
 the outer, and the muscular between them.   And then we have
 the cellular tissue uniting these together.   Besides these, there
 are arteries, and veins, and  nerves, so that the stomach, which
 looks like a simple pouch, is really quite  a composite thing.
 And the same can be said of the other organs.
   69. Before entering upon the  particular consideration of the
 functions by which the system is built up  and kept in repair,
 it will be well to take a general view of  them, that you may
 see  them in their connection  and mutual dependence.  Each
 of  these functions has its  special and appropriate part to play,
 in  effecting  the  formation  and  repair of the structure.   The
 material from  which  all parts of  the  body  are formed and
 repaired is the blood.  There are organs whose  special duty it
 is to  make  this material; organs which distribute it;  and or-
 gans  which use it after it is distributed.  There are also organs
 whose duty  it is to receive the blood after it has been used, and
fit it to be used again.  This common building material  of the
body is made out of the food; and  the succession of processes
by  which it is done I will describe in the next chapter.   After
it is made, it is distributed by the complicated apparatus of the 
42
HUMAN PHYSIOLOGY.
           Summary of nutritive functions.  Processes of digestion._____________

circulation. This apparatus is therefore the common carrier of the
building material of the system.  It is the numberless little form-
ative vessels, so small as to be  invisible to the naked eye, that
use the blood thus  brought to them, and  make and  keep in
repair all the various structures  that we see in the body.   When
the blood  has been used  by these  formative vessels, it is not fit
to be used again until it is submitted to a purifying process by
exposure to air;  and to this particular object the lungs are de-
voted.   And besides all this, as there are continually some par-
ticles which, in the wear and  tear  of the  machinery, become
useless, and even  injurious, they must be got rid of in some
way;  and so there are  organs for this purpose—organs  of
waste,  as they are  termed.  It  is also to be remembered, that
the processes to which I  have now alluded are  so carried on,
that the heat of the body, as  will be fully explained hereafter,
is steadily maintained.  In  the following chapters of this  part,
I proceed  to a particular examination of the functions of which
I have now given a brief summary.
                    CHAPTER V.

                         DIGESTION

  70. I shall include, under the term  digestion, all those pro-
cesses which are necessary to  effect the separation  from  the
food of its nutritious portion, and the introduction of it into the
circulation.  A summary of these processes may be thus given.
The food is broken  up  and  ground  in  the  mouth, and  it is at
the same time mixed with the saliva.  It is then taken into the
stomach, where it is kept in  constant motion, and  is under the
solvent  action of a  fluid of a  peculiar character.   When it is
brought into the right  condition, it is passed from  the stomach
into the  intestines.   Here it is acted  upon by two fluids, the
bile, the secretion  of the  liver, and the  secretion of another
gland, the pancreas or  sweet-bread.   These  secretions have
some agency in separating from the mass its nutritious portion,
and this is taken up or absorbed, in  the form of a milky fluid,
by little vessels lying on the surface of the inner membrane of the
intestine.   These vessels unite together to form  a large tube,
and through this the milky fluid is poured into the circulation,
to replenish the blood. 
DIGESTION.                      43
        Mastication.  Teeth various, according to different kinds of food.

  Having given this summary of the processes which make up
digestion, I proceed to speak of them more particularly in the
order of their succession.   In  doing  so, I shall notice some of
the points in which other animals differ from man, in  regard to
these processes and the arrangements of the apparatus of diges-
tion.
  71. Mastication is an important part in the process of diges-
tion.  The teeth, which perform this act, are very hard bodies.
The body of a tooth is  composed  of two substances.   The in-
ner part is called the ivory, and  the outer is called the enamel,
which is exceedingly hard.  The teeth are of different shapes
for  different  modes  of action.  There are  long and pointed
teeth, for tearing; others, for cutting, which have a sharp edge;
and others, for grinding,  having for  this purpose  a broad  and
irregular surface.  The teeth are differently shaped in animals,
according to  the kinds of food which they eat.   Thus, the  her-
bivorous, or  vegetable-eating  animals, have grinding teeth to
bruise their food; while the carnivorous, or flesh-eating animals,
have sharp-edged teeth and long-pointed teeth, by which their
food is torn and cut  in pieces.   And it is to be  observed,  that
the movement of the  jaws always corresponds with  the char-
acter of the  teeth.  In the carnivorous animals, the motion of
the lower jaw upon the upper is a mere up-and-down, or hinge-
like motion.    As they  have  no grinding  teeth, there is no
need of any  lateral  or grinding motion.   But in  the animals
that have grinding  teeth, there  is a lateral  motion, to enable
them to grind.  You see  this  difference very plainly, if you ob-
serve the dog and the horse while they are eating.  In Fig. 3,
you see represented the  teeth of  a  carnivorous animal.   The
front teeth are long and pointed,  for rending, while  the back

              FtG. 3.
TEETH OF CARNIVOROUS ANIMAL. 
44
HUMAN PHYSIOLOGY.
                    Man an omnivorous animal._________________

teeth  have a sharp edge for cutting.  In Fig 4, you see repre-
sented the broad and irregular grinding surfaces of the teeth ot
herbivorous animals.  In animals that live on insects, the teeth
present conical  points, which press into  corresponding depres-
sions in the opposite jaw, as  represented in Fig. 5.  In those
that live  on soft  fruits, the teeth are rounded, as  in Fig. 6.
These are quite in contrast with the  tearing teeth of the carniv-
orous, and the grinding teeth of the herbivorous.

                fig 5.                         FIG- 6-
                                    TEETH OF FRUGIVOROUS
                                           ANIMAL.
  TEETH OF INSECTIVOROUS ANIMAL.

  72. There is an arrangement of the enamel and the ivory in
the teeth of the herbivorous which ought not to pass  unnoticed.
Instead of having the enamel cover the ivory, as  in the teeth
of the carnivorous, the two substances are arranged  in upright
layers, as  seen in Fig.  4.   The  object  of this is  plain.  The
ivory wears away faster than the harder enamel, and, therefore,
the surface of the tooth always presents projecting hard ridges,
fitting them for grinding thoroughly.  A miller would say, that
these are stones that never need picking.
   73. So perfect  is the correspondence of the teeth with the
kind of food on which the animal lives, that the skillful natural-
ist can infer very correctly, from  the examination  of the teeth
of an animal alone, the character of the food on which it lives,
and even the general  arrangement of  its structure.  As man
has the three kinds of teeth which I have noticed, he is said to
be omnivorous, or an eater of all  kinds of food.  In him, the
front teeth are the cutting ones; what are  called  the stomach
and eye teeth are the tearing ones; and the large  back teeth
are shaped for grinding.  It will be observed  that the tearing
teeth, as they have not  a very sharp point, and are  no  longer
than the other teeth, have but little power when compared with
the  long  and  sharp  tearing  teeth  of a carnivorous animal, as
seen in Fig. 3.  As man can make use of instruments  to cut
 
DIGESTION.
45
            Whales have no teeth.  Substitute for teeth in birds.

his food in pieces, he does not need  such power in his teeth as
carnivorous animals have.  Allowance should be made for this
in estimating the amount of  carnivorous adaptation in man.
   7-4.  There are a  few of the  Mammalia that have no teeth.
This is the case with  the common whale.  In his case, instead
of teeth, there hang down from the upper jaw, as represented
in Fig. 7, plates of a  fibrous substance, called whalebone, which
have  their fibres separated  at  their free  extremities, so as to
make a sort of sieve.  This is intended to catch the  little gela-
tinous animals,  which the  whale devours in great numbers.
FIG. 8.                FIG. 7.
WHALEBONE.      SKULL OF WHALE.
For  this purpose, he draws in the water, making it  to  pass
through this sieve, and then expels it from the nostrils or blow-
holes.   Birds, too,  have  no teeth.   Their  place is supplied
by a contrivance in the stomach itself, for the breaking up of
the food.   This will be  described  in  another  part  of this
chapter.
  75.  While  the food is  cut  and ground by the teeth, it is at
the same time thoroughly moistened by the saliva, which is
poured forth from certain glands in the neighborhood.  There
are three pairs of these glands.  Fig. 9 shows the glands  on
one side.  The parotid gland, 1, is the largest.  This is  situated
in front  of  the  lower part of the ear.   It is the seat of the
swelling in the disease called mumps.   Its duct, 2, passes over
one large muscle and between the fibres of another, and pours
its contents  into the mouth opposite the second small grinder of
the upper jaw.  If you press on this part of the cheek,  you can 
46                HUMAN PHYSIOLOGY.

          Formation of the saliva.  Three pairs of salivary glands.
FIG. 9.
SALIVARY GLANDS.
feel in the mouth an  increased flow of the saliva.   The sub-
maxillary gland, 3,  is situated  inside of the lower  jaw at its
lower part;  and its  duct, 4, opens  into the mouth  at the side
of the frsenum of the  tongue.   The sublingual gland,  5, lies
under the tongue, and  discharges its secretion by a duct at the
side  of that  organ.   These saliva  factories, as we  may term
them, are in much  more  active operation  at some  times than
at others.  They are especially active when we are eating ;  and
it is commonly estimated  that,  during  an ordinary meal, about
eight ounces of saliva are poured into  the mouth.   This large
amount is wanted to moisten the food thoroughly  before it is
swallowed; and it is supposed, also, that it has some chemical
influence in preparing the food for the action of the gastric
juice in the stomach.  More  saliva than usual is needed, also,
when we are speaking,  in order  to keep the parts properly lubri-
cated, for the passage of the air in and  out  during speaking
dries up the saliva by evaporation.   And, accordingly, the  mo-
tion of the parts at such times  stimulates  a larger flow, just as
pressure  on the cheek  will do  it,  as  before  remarked.  This
result is favored by the arrangement of the duct of the parotid
gland, which, as you have seen, passes over one large muscle, and
then through the body of another.   Chewing any thing excites 
DIGESTION.
47
             Flow of saliva affected by sympathy.  Swallowing.

an increased flow of the saliva; and the tobacco chewer does a
real  injury to the salivary glands, by keeping them constantly
in excessive operation, in addition to the ruinous effects of this
drug on the system at large.  When he eats, these over-worked
factories can not turn out as good an article  as they should, nor
will  it  be in sufficient quantity.
   76.  It is supposed that, besides the mere  mechanical stimu-
lus of  the motion of  the parts, the stimulus of sympathy is also
concerned in  exciting these  glands  to increased action.   The
glands are supposed to be affected in  this way by the stimula-
tion  of the food on the surface of the mouth,  about the orifices of
their ducts.    That sympathy does have an  influence  on their
secretion is evident from the very  familiar fact, that the thought
of food will  often, as it is expressed, cause the mouth to water.
   77.  The fact, that these  glands do not all secrete the same
kind of fluid,  has led to an interesting discovery in relation to
them.   The  submaxillary glands  secrete  rather a viscid  fluid,
while that which is poured  forth  by the parotid and sublingual
glands is perfectly limpid.   Now, it has been found, by various
observations  and experiments on animals, that while the teeth
are  cutting  and  grinding  the food, and the parotid and  sub-
lingual glands are pouring out the saliva to moisten it, no secre-
tion  comes  from  the submaxillary glands.   But these glands
pour out their viscid  fluid the moment  that  the tongue thrusts
the food back towards the  throat, in  the beginning of the act
of swallowing.  The special object of this viscid fluid is then to
cover the food, so that it may, to  use a common expression, slip
down easily into the  stomach ;  and it has  nothing  to do with
the moistening of the food, this  being the  particular  office  of
the other two pairs of glands.
   78.  When the  food  has  been ground  by the teeth,  and
moistened by the saliva, it is carried  by the act of swallowing
into  the stomach.   This act,  simple  as it appears  to  you, is a
very complicated one, and  is performed by the conjoined and
agreeing action of many different muscles.  The food is first
thrust back  over the surface of the tongue into the large cavity
in the  back  of the throat, called the pharynx.  In the pharynx
are the openings  of two tubes—the oesophagus or gullet, which
is the passage into the stomach, and the trachea* or windpipe,
the passage to the  lungs.   As the oesophagus lies behind the

  * This term is sometimes used,  as here, to mean the whole of the tube conducting to
the lungs, including the larynx, which is at the top of this  tube, and sometimes it is
restricted to that part of the tube which is below the larynx. 
48                HUMAN PHYSIOLOGY.
            Parts employed in swallowing.  Office of the epiglottis.

 trachea, the food, in passing to it, must  go directly over the
 opening into  the  trachea.  To prevent  the food from entering
 the  trachea, therefore, there is a  little tongue-shaped body,
 called the epiglottis, extending back from the root of the tongue,
 and acting as  a lid to the glottis, the opening into the trachea.
 When we are swallowing, this lid is shut down; but it is always
 raised up when we are breathing or speaking.  When we swal-
 low, not only does  the lid shut  down, but the  larynx  rises to
 meet the lid, as you  may readily perceive, if you  place your
 fingers upon what is called Adam's apple while you  are swal-
 lowing.   With the  aid  of Figures 10  and 11,  all  this will be
 very clear to you.   In  Fig.  10, you have a  side view of the
parts engaged in swallowing, as  if the  head were divided into
two halves by a vertical section.   At i,  is the cavity of the nos-
tril ; at  h, are the lips; a is  the divided bone of the chin;
b is the  tongue, between which and the spinal column, /, is the
large cavity of the pharynx.   In front of this cavity hangs the

                           FIG. 10.
VERTICAL SECTION OF THE THROAT.
palate, g, as a door or valve, to direct the  air coming from the
trachea, d, either through  the  mouth or throuo-h the nostrils
according to its position.   The oesophagus, e, is behind the tra-
chea, and the epiglottis, c, shuts down when  we swallow to let 
DIGESTION.
49
Mode of action of the oesophagus in swallowing.
the food  pass over it into the
oesophagus.   In  Fig. 11, you
have  a view of the same parts
from  the  rear.  At 1, is a sec-
tion of the bones  at  the base of
the skull; 3, 3, are the  cavities
of the nostrils; 2, 2, the walls
of the pharynx spread apart; 5,
the pendulous  palate;  6, 6, the
arch  of the palate; 8, the root
of the tongue; 9, the epiglottis,
and 10, the glottis, or  opening
into the  larynx;   13,  the  oeso-
phagus; 14, the trachea.  The
pharynx,  you  see, is  a  funnel-
shaped cavity, tapering down to
the  oesophagus,  the  opening of
which is  considerably below the
opening of the trachea.
   79. When the food enters the
oesophagus, it  is  carried through
that tube into  the stomach by  the ac-
tion of muscular  fibres.  These fibres
are represented in Fig. 12.  The cir-
cular fibres are seen at a and b.  These
are removed  at c, so  as to show the
longitudinal fibres.  It is by the con-
sent of action  between  these different
sets of fibres that the  food is propelled
through the oesophagus.   As the food
descends, a dilatation of the  circular
fibres must  everywhere take place
where the  food is, and  a  contraction
of  them  immediately  behind  it—the
dilatation  making  the way for  it,  and
the contraction forcing it along.  And
in  animals that chew the cud, these
actions must be reversed when the ball
of food is forced up through the  oesoph-
agus into the mouth.
   80. The food being introduced  into
the  stomach,  is here  subjected  to the
action of the  gastric  juice.   This  is a
                               5
FIG. 11.
VIEW OF THE THROAT FROM
         BEHIND.

           FIG. 12.
CESOPHAGUS LAID OPEN. 
            50                HUMAN PHYSIOLOGY.________
                             Gastric juice. Chemical in its action.

            peculiar fluid, somewhat acid in its character, which is secreted
            by very minute follicles, or bag-like cavities, situated in the sub-
            stance of the mucous  membrane.   Ordinarily there is none of
            this fluid  in  the  stomach when there is no food there. _ Dr.
            Beaumont made some very interesting observations on this, as
            well as  many other points, in the remarkable  case which fell
            under his  care.   The individual, Alexis  St. Martin, received a
            wound in his left side  by the bursting of a gun.   The wound,
            which opened into the  stomach, never entirely closed, but an
            orifice remained, after  the healing  process had done all that it
            could.   Through this  orifice, Dr. Beaumont could look into the
            stomach, and observe  Avhat was going  on there.  He describes
            the mucous membrane, in its healthy state, as having a velvet-
            like appearance, with  a  pale  pink  color, and as  being covered
            with a very thin,  transparent, viscid  mucus.   On introducing
            some food, or irritating the mucous  membrane  mechanically,
            he saw, by the  aid of a  magnifying glass, "innumerable lucid
            points " projecting on  the surface, and from these there exuded
            a pure, limpid, colorless  fluid.  These points were the  follicles
            which  secrete the gastric  juice, now rendered turgescent  by
►            being stimulated to action.
              81.  The amount of gastric juice secreted is  generally about
            in proportion to the amount of food which the necessities of the
            system require.   When  the quantity of  food taken  is very
            much  more  than  is  required,  there  can  not  be a  sufficient
            amount of gastric juice secreted to digest all of the food ;  and
            some of the food must therefore remain undigested, and will prove
            a source of irritation  to  the stomach.  If the amount of food
            taken from day to day is  not very excessive, but is only a little
            above  the proper quantity, there will  be  enough  of the gastric
            juice made to digest it;  but  the daily overtaxing of  the pow-
            ers of  the secreting follicles will, after  a while, produce derange-
            ment in the stomach, and perhaps permanent disease.
              82.  The action  of  the gastric juice upon the  food  is of a
            chemical nature.   In  order that it may act effectually on  all
            portions of the  contents of the stomach,  this organ is" kept in
            constant motion by the fibres of its  muscular coat.  These fibres
            are so  arranged that, as they contract and relax,  they keep up
            a sort  of churning  of  the contents, and thus effect a  thorough
            mixture of them with the  gastric  juice.   In Fig. 13, you see
            these fibres represented.   At 1, is  the opening  of the oesopha-
            gus into the stomach ;  and  at  4, is  the part which opens into
            the  intestine.   The fibres are in different  layers, running in 
            DIGESTION.                     51

Churning of the food in the stomach.  The chyme.
FIG. 13.
MUSCULAR FIBRES OF THE STOMACH.
different directions.  The outer peritoneal coat, 5, 5, is dissected
off and turned back, showing some of the fibres that run length-
wise of the organ, 6 ;  and some of them transverse, 7 ;  and
others, 8, that run obliquely.   You can readily see what effect
the contraction of these  different  fibres will have on the shape
of the stomach.   The  contraction of the longitudinal fibres, 6,
brings the large, bulging end of the stomach, 2, and the small
end, 3, nearer together.   The transverse fibres,  when they con-
tract, diminish the capacity of the stomach transversely.   And
the oblique fibres modify these  two motions by their oblique
action.
   83.  By the combined chemical and mechanical action of the
stomach, its contents are, after  a little time—in three or four
hours—reduced to an uniform, greyish, semi-fluid mass, called
chyme.   While this process has  been going on, the communi-
cation  between the stomach and the intestines has been entirely
closed  by a valve, called the pylorus.   This is represented at 5,
in Fig. 14, which presents a view of the inside of the stomach.
This valve is made of a fold of both the mucous and  muscular
coats of  the stomach.   It is a very faithful sentinel, as is indi-
cated by its name, which is derived from two Greek words, sig-
nifying to guard  the gate.   It will not ordinarily permit any
undigested food to pass it.   While the process of  digestion is 
52
HUMAN PHYSIOLOGY.
The pylorus.  A sentinel.  On duty only during digestion.
FIG. 14.
      INTERIOR OF THE STOMACH AND SMALL INTESTINE.


going on, the  motions produced by the muscular fibres cause
the contents to move about,  and of course they are thrown
against the pylorus, as well as any other part of the stomach.
But the valve remains closed, until some portion comes against
it that is thoroughly changed to chyme, and is  therefore fit to
pass on into the intestine.  It then opens to let this pass, and
it  does so for any other  portions that have become chyme.
Toward the conclusion of the digestion  of  a meal, small quan-
tities pass  at first, and  after a while,  the  contents  pass  quite
rapidly through the valve.
   84. Although this  sentinel-valve thus performs its duty so
faithfully in relation to nutritive substances,  it seems to let other
substances  pass very readily.  Solid substances, swallowed by
mistake, as buttons, pieces of money, the pits and skins of vari-
ous fruits, often pass the valve without any trouble.  The valve
seems to be on duty as  a sentinel only during  the process of
digestion;  and, if the attempt to go through with this process
prove  unavailing, the pylorus, though  it  let such  hard  sub-
stances as I have  mentioned  pass without  difficulty, resists the
passage  of the undigested food, sometimes causing much  un-
easiness, and  even perhaps  pain, by so  doing.   In such  a case,
either the valve after a time gives over its resistance, or, hold- 
DIGESTION.
53
          Theories of digestion.  Eating between meals. Eating fast.

ing out, the action of the stomach is reversed, and the offending
matter is thrown off by vomiting.
   85.  It is not a little amusing  to  read  the  different theories
which  were formerly broached to explain  the process of diges-
tion.   Some supposed it to be a concoction, heat  being, in their
view, the  chief agent; some, a kind of putrefaction ;  some, a
chemical solution; some,  a  trituration;  and  some, a process
dependent upon  the action  of the nerves.   Of these various
theories, the celebrated  Hunter playfully remarked:  " To ac-
count for  digestion, some have made the stomach a mill; some
would  have it to be a stewing-pot, and some, a brewing-trough ;
yet, all the while, one would  have  thought that it must have
been very evident that the stomach was  neither a mill, nor a
stewing-pot, nor a brewing-trough, nor any  thing but a  sto-
mach.^  All these theories are now done  with; and it is pretty
well ascertained,  that digestion is a chemical process—in part a
solution,  and in  part  a  fermentation—and  that  mechanical
agency is  employed only for the purpose of thoroughly exposing
the food to the action of the gastric juice.
   86.  The  process of digestion, as  it has been described, is a
regular process, requiring  a certain average  period  of time for
its completion.   If, during the  progress of it, fresh food be in-
troduced,  its regularity is  broken in upon, and the process  fails
to be well done.  Then, too, if, immediately after the completion
of  the process, a new supply of food be taken, harm  is done,
because the organ  has  not  its needed interval of rest.   For
these reasons, the practice of eating  between meals  is a very
injurious one.  Eating fast does harm, because,—1st, the food is
not sufficiently ground ;  2d, it is not mixed thoroughly with the
saliva; and, 3d,  more food is taken than  would  be  sufficient to
satisfy the hunger if the  individual ate  slowly, and,  therefore,
more than can be easily digested.  Great variety in food stimu-
lates the  appetite unduly, and too much is consequently eaten.
Exercise' facilitates  digestion, if  it  be not violent.  An experi-
ment  was  once  tried upon  two dogs, which was  thought to
prove  that exercise  hindered digestion.   Two  dogs  were  fed
freely, and while one was  left to lie still, the other was made to
run about violently.  Both  dogs were killed after  an hour or
two, and  it was found that, while  digestion had gone on thor-
oughly in  the dog that was allowed to  remain quiet, in  the
other  the food was  undigested.  This only proved that violent
exercise, taken immediately after eating, impedes digestion.  It
has been found, on the  other  hand, that light exercise  pro- 
54
HUMAN PHYSIOLOGY.
         Cause of hunger, state of the system. Its seat in the stomach.___________

motes the process; and daily experience, among laborers, shows,
that very strong exercise does not  interfere with  it,  if a little
interval of rest be  allowed, so that the  process may be fairly
begun.
  87. The sensation of hunger has been attributed  to various
causes,—as the empty state of the stomach, the presence of the
gastric juice irritating the  mucous membrane, &c.   It  cannot
arise from emptiness;  for, if it were so, it should  occur sooner
than it does after eating, and  it  should  not be absent  in dis-
ease, as it often is for a long time, when the stomach is, almost
entirely empty.  It can not arise from the irritation of the gas-
tric juice ; for it was found by Dr. Beaumont, in  his observa-
tions of the stomach of Alexis St. Martin, that this fluid is not
secreted  till  after food is  introduced into  the  stomach.  The
cause of  hunger is evidently in the state of the system.  It is
a state of want.   Nutriment is needed by the formative vessels,
the builders and repairers of the  system, of  which I shall speak
particularly in the  chapter on  Formation  and Repair.   And
they make  their wants known as  distinctly as the  bricklayer
does, when he calls  for more brick and  mortar.   Through the
nerves, an impression is  communicated from  these to the sto-
mach, and the sensation of hunger is  the result.  That the sen-
sation is  seated there  is  evident  from the  fact, that  it  can be
temporarily relieved by putting indigestible substances into the
stomach.  These produce the effect by causing other  sensations
there, which take the place, for the time being, of  the sensation
of hunger.  After, however, the  momentary effect is over, the
sensation of hunger returns again in its  full force.  The cause,
then, of the sensation is  in the  system at large, but its seat is
in the stomach.   Its  degree  of  urgency  depends  upon this
general state that causes  it.  If eating be delayed much beyond
its usual  time, or  if the system has been exhausted by the wear
and tear  of severe labor, the sensation of hunger is very urgent.
So, too, if disease has impoverished the system, as soon as the
stomach  is in a condition to respond to  the call of the forma-
tive vessels  that set themselves to work to repair the  waste, the
hunger is often excessive.   Observe, here, that in order to have
the sensation of  hunger, not only must there be  a want in
the system at large,  but  the stomach must be in a state fitted
to receive the notice of this want.  And fortunately it is  seldom
in this state except when in a condition to do its work.  If it
were otherwise, food would often be  introduced into it when it
could not be digested.  The stomach is sometimes incapacitated 
DIGESTION.
55
             Sensation of hunger affected by the mind. Thirst.

for receiving the notice  of the want  of the  system by mental
impressions.   In this case, an impression is communicated from
the brain to the stomach, through the nerves, which counteracts
the impression conveyed from the system to this organ, and so
neutralizes the sensation of hunger.   Grief thus often  destroys
the appetite for food.  One thing more  is to be  observed in
relation to hunger.   Although this sensation is caused by  the
want of the  system, it is removed long  before the nutriment
reaches its  final destination, and supplies the want.  How is
this ?  It is either because the new sensations produced in  the
stomach,  by the commencing process  of digestion, take  the
place of the sensation of hunger, or  an  impression is sent all
over the system from the filled stomach, which, so to speak, stills
the clamor of want with the immediate prospect of a supply.
  88.  Nearly the  same  remarks can be made in relation to
thirst, that have been made in  regard to  hunger.   The seat of
this sensation is  in the fauces  or  throat.   Its cause is evidently
not there;  for the mouth and throat  may be very dry, and  yet
there may  be little or no thirst; while, on the other band, there
may be much thirst, although the mouth and throat are moist.
The cause of the sensation is like the cause of hunger, in  the
system, at  large; and, therefore, no  local cause,  producing a
dryness of the throat, can cause thirst independent  of a general
condition.
  89.  Before describing the remainder of the process of diges-
tion, I  will call your  attention to the arrangement of the sto-
mach,  and the other organs of the  abdomen  engaged in this
process.  Fig. 15 exhibits them  as they present themselves in
a front view, except that they are somewhat separated  from
each other, instead of being as closely packed, as they are in  the
abdomen.  The large end of the stomach, you see, lies to  the
left side,* and at this end  is  the spleen.   The pancreas is  be-
hind the right end of the stomach.  Above the stomach, and
mostly to the right  side, is the largest organ in the abdomen,
the liver.   It is represented as turned upward in the Figure.
The stomach is  directly connected with the small intestines at
the pylorus.   At the end of this long and winding tract begin
the large intestines.   The duct of the gall bladder, and that of
the pancreas, empty their contents into the small intestine at its
beginning.   The office  of the spleen has not  yet  been ascer-
tained.   Neither has that of the worm-like appendage at  the
* As this is a front view, the right side of the Figure is the left side of the body. 
56               HUMAN  PHYSIOLOGY.
Arrangement of the digestive organs.
FIG. 15.
GALL BLADDER
 LARGE INTES
    TINES,


 BEGINNING OF
  LARGE IN-
   TESTINES.

WORM-LIKE AP-
  PENDAGE.
LARGE INTES-
   TINES.
SMALL INTES-
   TINES.
SMALL INTESTINES.

       DIGESTIVE ORGANS.
beginning  of the large intestines.   The omentum,  or caul,
which  hangs  like a  curtain from the  front  part  of  the sto-
mach down in front of the intestines, is  not represented in  the
Figure.
   90.  There is one arrangement in  the abdomen  which must
not pass unnoticed.   If the intestines were  left to lie  loose in
this cavity, they would  constantly be subject  to displacement
and injury.   They are therefore  fastened to  the backbone by
an arrangement, which secures them from  any such  accident,
and at the same time allows of a sufficiently free motion of differ- 
DIGESTION.
57
              The arrangement of the mesentery. Its offices.

ent parts of this  tube.   It  is this.   The intestinal tube makes
the margin of a broad  sheet of membrane, the other  edge of
which is gathered up and fastened to the spinal column.  The
arrangement is  like a ruffle with a puffed  edging.  The mem-
branous sheet is called  the mesentery.  As  the intestinal tube,
the puffed  edging, is much longer  than  the ruffle  itself,  the
mesentery, it is gathered on to the ruffle, as a seamstress would
express it.  Now, the mesentery is  composed of two folds  of
the peritoneum, the smooth, shining, outer covering  of the in-
testines.  The  arrangement will be  easily understood by  the
diagram in Fig. 16, which represents a section of the intestine
with  the mesentery.   The cav-
ity of the  intestine, a,  is  lined              fig. 16.
by the  mucous  membrane  re-
presented  by the  inner  circle.
Next comes the muscular coat,
and next  the  peritoneal, the
outer, which, instead of making
a circular tube, as the other two
coats  do, passes  backward  on
both  sides  of the intestine, to
make  the  mesentery, b.  After
being  attached to the spine by     PLAN 0F THE mesentery.
means of cellular tissue, it is re-
flected off to pass over other portions of the intestine, as seen at
c, c.  Between the two layers of the peritoneal membrane, in the
mesentery, is considerable space, as  seen at b.  This space is
filled up with blood-vessels, nerves,  lacteals with their small
glands, soon to  be described, all bound together by the com-
mon  packing  material  of the  body, the cellular tissue. You
see, therefore, that the mesentery subserves more than one use.
Besides fastening the  whole tract of  the intestinal canal to the
spine,  so as to guard  it against accident, it acts as a secure
medium for the communication  of the blood-vessels and nerves
with the intestines.  And, besides, as you will soon see, it con-
tains the little tubes which convey all  the nutriment into  the
blood for the growth and repair of the body.
   91.  I now go on to describe the remainder of the process of
digestion.  The chyme, (§ 83,) as it  passes into the small intes-
tine from the stomach, has  mingled with  it the  bile and  the
secretion of the pancreas.  These are poured into the intestine
at  the point represented at 6, in Fig.  14.   These secretions un-
doubtedly have some  agency in  separating the nutritious part
 
58                HUMAN PHYSIOLOGY.
Chyme. Chyle. Luteals.  Thoracic duct.
of the chyme from that which is not so.   When thus separat-
ed, it is absorbed by the  innumerable small vessels, called lac-
teals, which are situated in the mucous membrane.  This nutri-
tious part of the chyme is a milky fluid, called the chyle.   The
lacteals which absorb it are  little tubes or ducts.  These enter
certain glands, called  the  mesenteric glands, for the purpose of
having some effect, we know not what, produced upon it.   They
then pass on, as seen in Fig. 17, to pour their contents into the
FIG. 17.
.'- ORIGINS
     OF
  LACTEALS.
SECTION OF INTESTINE SHOWING THE LACTEALS.
thoracic duct.   This duct, which is about the size of a common
quill, running up on the left side  of the aorta, the  great artery
of the heart, pours its  contents into the junction  of two  veins
at the  top of the chest.  As the circulation of the chyle in the 
DIGESTION.
59
Mechanical continuance of the thoracic duct. Chyle makes blood.
thoracic duct needs all the mechanical help that it can have, the
mode of the joining of this duct with these veins is calculated
to facilitate the freeness of the discharge of the  chyle.   As
the two large  currents in the  veins, v  and v, v,  in Fig. 18,
FIG. 18.
      JUNCTION OF THE THORACIC DUCT WITH THE VEINS.


unite, there is created,  by the forward motion  of these  cur-
rents, a tendency  to  a  vacuum at the angle  at which they
meet, the  point  where the  thoracic duct, t, d, opens.   There
is, therefore, a suction power, as  it  is  termed,  exerted  upon
the fluid in this  duct.    The  chyle,  thus mingled with the
blood, becomes a part of it.   Or rather, I should  say, that the
blood is made from the chyle, and, as it is constantly used for
formation and repair in  all  parts of the  system, it is thus as
constantly replenished.  The material by which all the textures
of the body are made and  are kept in repair, is furnished to
the system through this  small duct, in the form of a milky
fluid.   You observe in Fig. 17, certain lymphatic vessels.  These
are trunks of absorbents, hereafter to be spoken of particularly,
which bring a fluid called  lymph, to be mingled with the chyle,
and to be poured with it into the circulation.
   92. The extent  of surface  on which the absorbent lacteals
open can not be appreciated, if you look merely at the outside
of the small intestines.  It can be done only by looking at the
inner mucous coat.   This  coat is really much  more extensive
than the outer coat, or the middle one, the muscular, and it is
full of folds, as represented  in  Fig. 14, on page  52.  The ob- 
60
HUMAN PHYSIOLOGY.
   Extent of absorbing surface in intestines.  Alimentary canal in different animals.

ject  of  this is  to  offer a very large  absorbing  surface to  the
chyme  as it passes, and  also to prevent its passing along as
rapidly as it would if the mucous surface were perfectly smooth,
instead  of having  folds.   Before leaving this subject, I would
again call your attention  to the analogy which  exists between
absorption in animals and in  plants.   The  lacteals  do for  the
animal in its stomach, what the absorbents do for the plant in
the extremities  of its roots.   Both absorb and assimilate nutri-
ment.   The function is  the  same.   It differs in the two cases
only in  the circumstances  under  which it is performed.
   93. The digestive apparatus varies much in different animals,
according to the kinds of  food on which they live.   As a gene-
ral rule, the more the food differs in character from  the animal
itself, the more complicated  and extensive is  the  apparatus.
Thus, the  herbivorous animals have  a very long  alimentary
canal, and  the  beginning of it, the  stomach, is a complicated
organ.  While, on the other hand, in the carnivorous, the flesh
which they eat  being very, much like their own flesh, and, there-
fore, not requiring very much of a process  of assimilation,  the
stomach is  a  simple organ, and the  alimentary canal is very
short.   In the sheep, for example, the alimentary canal is about
twenty-eight times the length  of the body, but in the lion it is
only three  times its length.   In man, who lives on a  mixed
diet, the alimentary canal is about six times the length of  the
body.
   94. The stomach is more complicated in  animals that chew
the cud than in any other animals.  It has four distinct cavities,
and, as  you will see, a singular mechanism is called  into opera-
tion  in managing the .food as it  passes through them.  In Fig.
19, you have a representation  of the stomachs  of the sheep, as
they appear exteriorly.   The course which  the  food pursues is
this.  As the animal crops the food, it passes into the first sto-
mach, which is little else  than a great reservoir to hold it and
to soak  it.   Then it passes into the second stomach, from which
it is returned  into the mouth.  On being swallowed again, it
passes from the oesophagus into the third, and thence into the
fourth stomach.  In Fig.  20, you see the interior of these four
stomachs;  and by the aid of this  I will describe the process of
digestion  in the  sheep more  particularly.  You  see the very
large first  stomach, or paunch,  in which the food  is accumu-
lated.   It is not yet masticated  thoroughly, for the  animal  has
swallowed  it as fast  as he could, and  packed it away in this
reservoir.   From this it is passed,  in small quantities at a time, 
DIGESTION.
61
Digestion in the sheep.
(ESOPHAGUS.  _____
ORIFICE OF
 STOMACH.
3d STOMACH.
STOMACHS OF THE SHEEP.
FIG. 20.
INTERIOR OF THE STOMACHS OF THE SHEEP.
into the second stomach, the  honey-comb, so  called  from the
peculiar network of folds in it.   Here the food is rolled up into
balls  by the  action  of the  muscular  fibres  in this network.
                              6 
62               HUMAN  PHYSIOLOGY.
    Digestive apparatus in birds.  Different in the grain-eating and the flesh-eating.

Each ball of food is passed up through the oesophagus into the
mouth, where it is chewed and thoroughly mixed with the saliva,
in doing  which the  animal seems to have  great enjoyment.
Then it is swallowed,  and, as it passes from the oesophagus,  in-
stead of going  into the  paunch, as it did when swallowed the
first time, it is directed through the groove  seen in the Figure
into the third  stomach, the manyplies.  This has many folds,
like the leaves of a book, so that the  food is  exposed to a large
surface in  this cavity.   It passes  from this to the fourth sto-
mach, the reed.  Here, and here  only, it  is  acted  upon by the
gastric juice.  This, therefore, is the true stomach, all the other
cavities furnishing only preparatory steps to the true process of
digestion.   It is from this  fourth stomach  that what is called
the rennet  is taken.  When fluid matter is swallowed, it goes
directly into the second stomach, and not  into the  first, the
paunch; so that, in the case of the  sheep, the drink goes one
way, and the solid food another.  And, what  is still more singu-
lar, while  the animal  is a suckling, the milk passes  directly into
the fourth  stomach through the  third, which has its  folds so
closed together as to form a mere  tube to conduct it to its des-
tination.    And the  great  paunch and the honey-comb are
wholly useless  until  the animal  begins to  crop  its  food  for
itself.
   95.  In  birds, the  digestive  apparatus is necessarily  very
peculiar, from the fact that they do not  masticate their food.
They have,  on  this account, an arrangement in the  stomach
itself for grinding the  food.  In  the cavity called  the gizzard
are two  opposing surfaces, made  very hard, so that  by rub-
bing  together  they  bruise  the grains;  and  while they are
thus  ground, as between  two  millstones,  the gastric juice
is poured down upon them from  above.  This arrangement is
seen in Fig. 21, which represents the  digestive apparatus in the
turkey laid open.  At b is the  gizzard, showing the two  hard
surfaces, which are  rubbed  together  by the  stout muscles that
make  the  great bulk of the  organ.   Above, at  a,  are  the
glands which pour forth the  gastric juice.   And above this
part of the stomach there is, in all grain-eating birds, a large
sac bulging out from  the oesophagus, called  the  crop, 'which is
a reservoir for the food, just as the paunch is in the ruminating
animals.   In those  birds that live on  flesh or fish there is  no
such  grinding  apparatus;  and  the walls  of the stomach are
quite thin, and  it presents no hard surfaces.
   96.  It would be  interesting, were it consistent with the plan 
DIGESTION.
63
Digestion in the turkey.  Digestive apparatus in different animals.
FIG. 21.
STOMACH OF THE TURKEY.
of this book, to go  into  a further examination  of the varieties
in the digestive  apparatus in different animals.  They have a
very wide range, being according to the wants of the animal in
each case.   The  kind  of food, the  mode of life, and the pur-
pose which the animal is designed to fulfill, are the circumstances
which govern  these variations.  The proportion which the di-
gestive  apparatus bears*to^pther parts varies very much; and
in some of the lower orders of animals, the body seems to  be
all stomach.  In such cases, the only appendages  are those which
seize the food and direct  it into the orifice of this organ.   This 
64
HUMAN PHYSIOLOGY.
         Apparatus of the circulation. Heart, arteries, veins, capillaries.

is the case with the  hydra, represented in Fig.  1.  And, what
is very singular, the  outside of the body of this animal is just
as capable of acting  as a stomach  as  its inside.   For you may
turn it inside out, as you  can a stocking, and yet it will go on
to catch and digest its food as usual.   But, wide as the varia-
tions are in  the digestive  apparatus of animals,  the same com-
mon object  is aimed at in  all—the assimilation (§ 10) of nu-
trient substances  to  the  animal, to produce  a  material from
which its structure can be built and  kept in repair.  There is,
therefore, much that  is common to them all in the modes in
which  this  object is accomplished.   And even  the  analogy
which exists between the animal and plant, in regard to assimi-
lation, does not relate to the fact alone, but in some measure to
the modes in which the process is effected.
                    CHAPTER  VI.

                  CIRCULATION OF THE BLOOD.

   97. In the last chapter I described the manner in which the
 blood is made from  the food.  The blood, thus prepared, is
 circulated in every part of the body, that it  may be used for
 the  purposes of  construction and  repair.   The  apparatus by
 which this is done acts, as I have before said, as the common
 carrier of the material which is used  everywhere in the body
 by the laborers, the builders, to whom it is thus brought.
   98. This apparatus consists of several parts—a great central
 organ, the heart,  situated in the chest;  the arteries, the tubes
 by which the blood is conducted to all parts of the body •  the
 veins, other tubes, which bring the blood  back to the  heart-
 and capillaries, a network of exceedingly minute vessels, throuo-h
 which the blood passes as it goes from the extreme arteries into
 the beginnings  of the veins.  The  blood goes from  the heart
 through  a large  artery, called the aorta, which sends forth
 branches; and  these divide and subdivide, so that the extreme
 arteries, through which  the blood  flows into the capillary net
work, are very minute.  And the  veins which receive the blood
from  this network to carry it back to the heart, are equallv
minute;  but  joining together more and more, as they proceed 
THE CIRCULATION.                 65
         Heart a forcing and suction pump.  Arteries firm tubes.  Why.

toward the heart, they are at length all united into two great
venous trunks, one from above and the other from below, which
pour  their  contents  into  this organ.   The capillaries,  taking
their name  from  the Latin word, capilla, a hair, are so  small
that they can  not be  seen by the naked eye.  In  any small
cut, the blood which oozes out conies from multitudes of these
vessels.  They serve to hold the blood, while the formative ves-
sels, that construct and repair the body, may select from it such
materials as they need for their purposes.
   99.  The heart is a great central forcing and suction pump, in
the midst of this  circulating  apparatus.   When it contracts, it
forces  the  blood out through the aorta and its branching ar-
teries  into all parts of the system.   And when it enlarges  or
dilates itself, it, by suction, as  it is termed, receives the  blood
returning from the system through the veins.   The blood never
ceases  to go  these rounds.  The necessity for this continual
motion you will perceive as I  proceed with the development of
the subject.
   100. The arteries differ from the veins in their structure and
arrangement.   The arteries are  firm  tubes, while the veins are
lax in  their structure.   The object of the difference is obvious.
As the blood is forced into the  arteries by the powerful action
of the heart, it is  necessary that they should be  strong and
firm, else, they would be liable, to dilatation and  rupture, and
death would frequently result.   As  it is, it is not  a common
event to have an artery dilate and burst,  though it does occa-
sionally happen.   When dilatation does  occur in an artery, it
is  called an aneurism.  But the arteries  need to  be firm, not
only for the sake of security against  rupture, but also that the
force of the heart may  propel  the blood  to the extremities  of
the arterial system.   If  the  arteries were  lax tubes, like the
veins, the impulse would soon be lost in the yielding tubes, and >
the blood would move very sluggishly in the small arteries at a
distance from the  heart.   What we call the pulse, is caused by
this impulse.   If the arteries were lax  tubes, the  pulse would
not be felt at any great distance from  the  heart.    Instead  of
being distinct, as it now is, with  every beat of the  heart almost
to the  very extremities  of the arterial system, it would  be ren-
dered  confused by the yielding  of the  tubes, even  quite near
the heart, and  at  a  distance  from that organ  it would  be en-
tirely lost.
   101. Besides the  firmness  of the arteries, there  is another
circumstance which favors the  freeness  of the flow of  blood
                           6* 
66                HUMAN PHYSIOLOGY.
               Different arrangement of arteries and veins.

through them.  It is their mode of division.  The branch of
an artery leaves the main trunk at a sharp angle, making thus
only a slight deviation from the direction of the current;  while,
on the other hand, in the veins where  the current  flows in an
opposite direction, the branch unites with the trunk at nearly a
right angle.  This difference is represented in Fig. 22 ; 1 being
the artery,  and 2  the  vein.
FIG. 22.
ARTERY AND VEIN.
  102.  The venous system  has a much  greater capacity than
the arterial.  That is, all the veins of the body are together ca-
pable of holding more blood than all the arteries are.  And the
blood moves very rapidly and directly from  the heart through
the arteries, but it comes back to the heart quite slowly through
the veins.  Every thing is arranged  to  promote this rapid cir-
culation through the arteries, while the venous system is calcu-
lated  for a slow  but sure progress of the  blood  back  to the
heart.   To secure this, valves, made of folds  of the inner lining
of the veins are so arranged  as to prevent the blood from flow-
ing in the wrong  direction.   Fig. 23 represents  a vein cut open
so as to show these valves.  A shows the valves as they appear
when the vein is laid open and spread  out;  B, as they appear
when the vein  is  simply laid  open; and  C  represents the ap-
pearance of the  outside of  the vein where  there  are  valves. 
          THE CIRCULATION.                  67

in veins.  Dangerous to wound an artery.  Therefore well guarded.
FIG. 23.
VALVES IN THE VEINS.
 The need which there is of this  help to the circulation through
 the veins is obvious.   The  suction power of the heart is not
 competent, unaided, to move the blood throughout all  the lax
 venous system.   These pocket-like valves, therefore, are made
 in the veins to assist the  circulation there.  They do so in this
 way.  Every  motion of the muscles or  other parts about the
 veins tends to keep the blood in motion, and the valves serve to
 prevent  this motion from being  in the wrong direction.  The
 difference in force  and velocity with which the blood  moves in
 the arteries and in the veins, is  made manifest when they are
 wounded.   The  blood  flows from a wounded vein in  a slow
 and steady stream.  From  an artery it flows  rapidly, showing
 the impulse of the heart in its  jets, which correspond exactly
 with the pulse.   Hence comes the  danger in wounding an ar-
 tery, while  the wound of  a  vein  is ordinarily attended with no
 danger.  Accordingly, we find that the "Maker of our bodies"
 has so placed  the arteries that they cannot easily be wounded,
 while many of the veins are quite freely exposed.   The arteries
 are deeply  seated, except  in  some few  cases where this is im-
 possible ; but  the veins are often superficially situated.   You
 can see this, for example,  in the bend of the arm.   Some large
 veins appear there  just under the skin, while the artery which
supplies the arm is imbedded among the muscles and tendons.
In eveiy part of  the body, the most secure spot  is chosen for
an artery.   Thus, at the knee joint,  the artery, instead  of run-
ning over the  surface of bone, where it would be liable to be 
68
HUMAN PHYSIOLOGY.
       Few arteries superficial.  Mode of stopping the bleeding of an artery._______

wounded, lies deep in the ham at the rear  of the  joint.   The
same is  true of the elbow joint, just  alluded  to, and of other
parts of the body.  Although there  are arteries  everywhere,
they are so uniformly deeply seated, that it is only in a few lo-
calities that you can readily find one.  You can feel one pul-
sating at the wrist, and also on the  temple.   Here the arteries
are superficial, only because it  is impossible that it should be
otherwise.
   103.  When  the physician bleeds a  patient, he commonly
does it at the bend  of  the  arm, as  being the most convenient
place for the operation.   A ligature of some sort, as a ribbon, is
tied around the arm above the elbow, with sufficient tightness
to interrupt  the flow of  blood  toward the  heart in the super-
ficial veins, but not so  tightly as  to  prevent the  free supply of
blood to  the arm by the artery.   It is commonly tied as tightly
as it can be without stopping the pulse at the wrist.  An open-
ing is then made in one  of the veins; and, as  the  blood flows
freely into the arm from the heart through  the artery,  on its
return, so much of it as passes  through  the opened vein is dis-
charged at that point.
   104.  It will  be  proper here to give  some practical instruc-
tion, in regard  to  stopping the flow of blood  from a wounded
artery, as many lives have  been lost from the ignorance  of  by-
standers  when such accidents have  happened.  Enveloping the
part in cloths,  which is so  commonly done at such times, does
no good, but only serves to catch and conceal the blood as it
flows.  Pressure upon the artery,  on that side  of the wound
which is  toxoard the heart, will of course interrupt the supply of
blood from this organ  to the wound.  Firm pressure with  the
thumb will do it.  But the pressure must be made at the right
point, that is, directly upon the  artery.   You may not, in all
cases, press upon the  right spot at  once.   If you do not, the
blood will continue  to flow.   In this case, press  at different
points, until you find the point at which you see that pressure
stops the flow of blood from  the  wound.  But you may not be
able to find the right  spot.   If you can not, you can tie a  slip
of strong cloth or a handkerchief around the limb, above the
wound, and twist a stick  in it until  the bleeding stops.   In  one
or the other of these ways, you can prevent the loss  of blood
until the surgeon arrives  to take charge of the case.
   105.  Although there is no such free communication between
arteries as exists between the capillaries, there is some amount
of communication, and particularly in certain parts of the body. 
THE CIRCULATION.
69
               Aneurism. Communication between arteries.

 And it is well that it  is so, for it sometimes helps the surgeon
 to save a limb, when he could not do it if  there were no com-
 munication.  I have already alluded  to a disease of the arteries
 called aneurism.   An artery has three coats, one of which is a
 strong  fibrous one.  When  this is  thinned or ruptured, the
 other two coats bulge  out, forming a pulsating tumour.  And,
 as the blood is constantly pumped  into this by the force of the
 heart, it enlarges, and at length it may burst, and the life  of
 the patient will be destroyed  by the  loss of blood.   When an
 aneurism formed in a limb, as for example in the ham, the sur-
 geon, in former times, used to  save  the life of the patient by
 amputating the limb above the aneurism.   Putting a ligature
 round the artery above the aneurism would of course stop the
 flow of blood into it;  but it was supposed that the limb would
 die,  in that case, from  the want of a  proper  supply of blood.
 But it was found, at length, that this  was not so; and surgeons
 now, in such cases, cure the disease, and save the limb too, by
 tying the artery.  Immediately  after  the operation the limb is
 cold, and there is plainly very little circulation  in it.   But in a
 few hours the circulation becomes free, and  in a little time it is
 as well established as ever.   This is  effected by the communi-
 cations which exist between the branches which go off from the
 artery above the  aneurism, and those which go off below  it.
 It is obvious,  however, that this would  not  be  thoroughly
 effected if no change took place in the size of the communicat-
 ing arteries.  But this change does occur.   Some of them be-
 come  enlarged  to meet the  necessity of the  case.  This is  a
 most interesting fact; and  so  is  also the fact, that these commu-
 nications between branches  of arteries are very common in the
 neighborhood of  those places  in the  body, where  aneurism,
 from strains produced  by violent and sudden motion, is peculi-
 arly apt to appear.  This same  provision avails, of course, when
 aneurism  is cured by pressure made  upon  the artery above it,
 a measure which modern  surgery has found in many cases to
 be as effectual as tying the artery.
   106. There  have been  great differences  of opinion among
 physiologists, in regard to the proportionate amounts of agency
 that the different  parts of the  apparatus have in  carrying on
 the circulation.   The heart manifestly exerts the chief agency,
 both by its forcing and its suction power.  You can get a clear
idea of the manner in which  it  exerts these two forces in this
way.   Fill a ball of India  rubber, to which  a tube  is attached,
 with water, and immerse the tube in water in a vessel.  If you 
70                HUMAN PHYSIOLOGY.___________
    Action of the heart illustrated.  Agency of the capillaries in the circulation.

press the sides of the ball together, some of the water is forced
out into  the vessel.  This  represents the  contraction  of the
heart.  If, now, you allow the ball by its  elasticity to  resume
its round shape, the water rushes into it from  the  vessel.   This
represents the dilatation of the heart.   The  dilatation of the
ball results from  its elasticity; and so it is supposed by some
that the dilatation of the heart results from the same cause, its
contraction alone being produced by muscular  action.  Whether
this be  so or not, the dilatation is  an active one, and the blood
rushes into the heart from the veins by suction, as it is termed.
The dilatation  is so active that, as has been  shown by  experi-
ments on animals, even a great amount of pressure is not able
to prevent its taking place.
   107.  But, great as the agency of the  heart is, it is not true
that it is the only moving power, and that the  arteries and veins
are mere passive conducting tubes.  There are various phenomena
which show that the arteries, the  capillaries,  and even the lax
veins, exert a considerable  agency in circulating  the  blood.   I
will merely allude  to some  of these  phenomena.  Determina-
tions  of blood  to particular parts  show that  the blood-vessels
have an active  agency in the circulation.  In inflammation of
any part, there is an increased activity of the  particular portion
of the circulating apparatus supplying that part.   In the act of
blushing, there is a local  activity  of the circulation somewhat
independent  of the heart.  This is also true of the circumscribed
flush of hectic.
   108.  There  is one  portion of the circulation  in which the
active  agency  of the  capillaries is  especially manifest.   The
veins, as I have told you, receiving  the blood  from all parts of
the body, at length are all  united  into two veins, which empty
their contents into the heart.  But there is a very remarkable
exception to  this.  The veins which collect the blood from the
viscera in the abdomen unite in one large trunk, called the  vena
portae;  and this,  instead of pouring its  contents into the large
vein  that  goes up to the heart,  divides, like an  artery, into
branches, which take all  this Wood  to the liver for the manufac-
ture  of bile.   Fig. 24  represents  this circulation of the  vena
portae.  1,  1, are  the veins coming  from the intestines ; 2 is the
trunk of the vena portae ;  and 3, 3, are  the branches of it dis-
tributed in the liver.  Now, it can  not  be pretended  that the
suction  power of the heart extends its influence through the veins
that bring the blood from the liver, then through the capillaries
of this organ, and then  through all the veins that bring the 
                  THE  CIRCULATION.                 71

Circulation in the liver.  Why the veins are full and the arteries empty after death.
FIG. 24.
         CIRCULATION OF VENOUS BLOOD IN THE LIVER.


blood to the liver, even to the capillaries of the abdominal vis-
cera.   There  must  be, in this case, some propelling  power in
the capillaries, and some, too, also in the veins.  If there were
not, another subordinate heart would  obviously be needed in
the vena portae, to pump up the blood from all the veins of the
abdominal viscera, and then to send it  through all its branches
into the capillaries of the liver.
   109. The veins have a less active  agency in the circulation
than  any of the  other  parts of  the apparatus.   It is  for this
reason  that commonly after death  the veins  are  found  quite
full of blood, while  the arteries are nearly empty.  The appa-
ratus  of the circulation may  be regarded as forming a circle of
organs in this order—the heart, the arteries, the capillaries, and
the veins.  The blood  is constantly going the rounds  of this
circle.   It is plain that, as the apparatus  is about to stop, there
must  be an accumulation in the weakest, least  active,  and most
relaxed of this circle of organs. The arteries and capillaries force
the blood into the veins to  the last moment of life.  This effect 
72                HUMAN PHYSIOLOGY.
            The blood changed in the capillaries from red to dark._______________

probably extends no further than the smaller veins; but the heart,
by its active dilatation, draws the blood from them into the larger
veins.  And as these two forces, at the two  ends of the venous
system, are at work up to  the last moment, the whole  of this
system is filled with blood.
  110. The fact,  that the  larger arteries are commonly found
nearly empty of blood  after death, gave  the  ancients the idea
that air circulated  in arteries, while  blood  circulated in veins.
Hence, the name, artery, is derived from  two Greek words, sig-
nifying to hold air.    And hence, also, by long established cus-
tom, in common language, the blood is spoken of as running in
our veins;  and it would sound  strangely, if, in common, and
especially in poetical language, we should  speak of it as running
in our arteries also.  Although  there were  from time to time
some glimpses of the true idea of the  circulation, it was not
really  developed  and demonstrated   till about two hundred
and  thirty years  ago.  Harvey spent eight years in maturing
his ideas on the subject.  When  he  published them, they en-
countered much opposition; but he  lived long enough to see
them almost universally received by the medical world, although
the profession  was in a much less enlightened state than it is at
the present day.
  111. I will  now take you a step farther  in the development
of the plan of the  circulation.  I have said that the office of
the arteries is  to  conduct the blood  to the network of capil-
laries,  and that  in  the capillaries the blood  has reached its
place of destination where it is to be used.  The formative ves-
sels, appended to  the capillaries, take  from the  blood what they
need for their  various purposes, and  at the same time there is
added to the blood  refuse matter from the waste of  the  tissues.
The blood, then, is  changed while  it  is in the capillaries.  You
see  the change in  its  color.   In the arteries it was red; but,
after passing through the  capillaries, it appears in  the veins of
a purple  color.  It  is also as much changed in  other properties.
It is no longer fitted to  nourish the body.  It would even prove
a poison  to any organ if it  should flow into its capillaries.  If it
should, for example, be  sent to the brain, instead of bright ar-
teriaj blood, that organ would  cease to do its office ;  insensibility
would ensue, and life would soon be destroyed, if the  flow of
red blood could not be established.
  112. This purple blood, which comes back to the heart from
the capillaries  by the veins,  must, therefore, be in  some way
changed  to red blood, before it is again sent all over the system 
THE CIRCULATION.
73
          Change in the blood in the lungs.  Course of the circulation.

through the arteries.  This change is effected in the lungs.  As
the purple blood returns to the heart, it is  sent by the heart to
the lungs, in order  to  be exposed  to  the  air before it is sent
again over the system.   For this purpose there are two circula-
tions, and the heart is  a double organ;  or rather, there are in
effect two hearts for the two  circulations, for the two sides of
the heart have no communication with each other.   The appa-
ratus for all this is very complicated, but  I think it can be made
clear to you.
   113. I present, first,  a diagram,  which is intended to repre-
sent merely the  course of the  circulation, without regard to
proportionate size, or to minutiae in the arrangement of the ap-
paratus.   Let a represent the right side  of the heart, c the left
side, b the lungs, and d the general  system of the  body.  The
arrows show the  direction in which the blood flows.   In all the
shaded part the blood is venous  or purple, and  in the part not
shaded it is arterial  or  red.   We will  now take  some point of
beginning, and trace on the Figure the course of the circulation.

                            FIG. 25.
     DIAGRAM SHOWING THE COURSE OF THE CIRCULATION.

We will start at or, the right side of the heart.   The blood re-
ceived here, of a  purple  color, from  the whole body by  the
veins, is sent by the heart to b, the lungs.  Here it changes to
red blood, and passes by veins back to the heart—but, observe,
it is to the left side of the heart, c.  It is now sent by this  left
half of the heart to all parts of the system, represented  by d.
Here, in the capillaries, it ischanged to purple blood, and goes
back by veins to the right side of the heart, a, the place where
we  started. 
74
HUMAN PHYSIOLOGY.
           Two circulations and two hearts.  Arrangement of valves.

    114. You see, then, that there are two separate circulations,
 one through the general system, and the other through the lungs
 alone.   In both circulations the  blood is sent from the heart
 by arteries, and is brought back to it by veins.  But notice that,
 while in the  general circulation the red blood is in the arteries,
 and the purple in the veins, in the circulation through the lungs
 it is reversed—the red blood is in  the veins, and the purple is
 in the arteries.  So, also,  while the change of  the blood in the
 capillaries of the general  system is from red  to purple, in the
 capillaries of the lungs it is  from purple to red.
   115.  There are not only two sides or  halves  of  the heart,
 separated entirely from each other, but each of these sides has
 two apartments,  with valves or folding doors between them, so
 arranged that the blood can pass  one way through  them, but
 not the other.  There  are also valves at  the beginning of the
 great artery of the heart, the  aorta.   These  are  so arranged
 that the blood can  go freely out of the  heart  into the artery,
 but  not a drop can get back from the  artery into the heart.
 There are similar valves, also, at the beginning  of the great ar-
 tery, by which the purple  blood is  sent  from  the heart to the
 lungs.
   116. In Fig. 26, is represented a  section of the  right side of
 the heart, for the purpose of giving you an idea of the arrange-
 ment and the relative size of the two apartments.   The auricle,
 a, so called  because  a part of it  has some  resemblance  to
 an  ear, receives  the blood  from   the  whole  system  by two
 large veins, b, b,  called the  venae cavce.
 From the auricle it  passes into the ven-
 tricle, v, which by its contractions sends
 it to the lungs through  the  pulmonary
 artery, /.  The valve between  the  au-
 ricle and ventricle is composed  of three
 membraneous sheets, which  are held at
 their edges by small tendinous cords, d,
 just as a sail is held by the  ropes at its
 corners.  This valve permits  the blood
 to pass from the auricle into  the ventri-
 cle ;  but when it attempts to pass back
from  the ventricle  to the   auricle,  it section of the right
pushes back the sheets of the valve, they  si°e of the heart.
beyig prevented from going too  far back
by the tendinous cords.  There are also valves at  e, the bee-inning
of the pulmonary artery, which allow the blood  to pass through
 
THE CIRCULATION.                  75
Relation between the auricles and the ventricles.
them into the artery, but no blood can pass through them from
the artery back into the ventricle.   I shall soon call your atten-
tion again to these different valves,  that you may see more par-
ticularly their structure and arrangement.
   117. The auricle and ventricle act in this way in propelling
the blood.   When the auricle  contracts, the ventricle dilates *
to receive the blood from the auricle.  The valves between them
are open while this is taking  place.  But the next moment the
ventricle contracts and the  auricle dilates.   You  at once see,
that if now the valves between them should be open, the blood
would be forced back into the  auricle.   But  the membranous
sheets of these valves shut  upon  each  other as the ventricle
contracts, and  thus  prevent the  blood from going back.   It
therefore is discharged through the  pulmonary artery, /, the
valves there being open.   And when  the ventricle  dilates, you
can see that the blood would,  from suction, enter it from the
artery as well as from the auricle, if the valves at the orifice of
the artery  should remain open.   They are  accordingly shut
when the  ventricle  dilates.    You see, then, that when the
auricle dilates  and the  ventricle contracts, the valves  between
the auricle  and ventricle are closed, and the valves at the mouth
of the  pulmonary artery  are open;  and, on  the other hand,
when the ventricle dilates  and the auricle contracts, the valves
between them are open, and  the valves of the pulmonary artery
are closed.
    118.  Dr. Carpenter has a very good illustration of the rela-
tion of the actions of the auricle and ventricle, in a representa-
tion given in  Fig. 27.   The  apparatus  which is represented
consists of  two pumps, a and  b, the  pistons of which  move up
and down alternately.  These  are connected with  a pipe, c, /,
in which there are two valves,  d and e, opening in the direction
of the arrows.   The  portion c  of the pipe represents the venous
trunk discharging its blood into  the heart,  and the portion /,
the artery  which  is  the  outlet  for the blood.   The  pump, a,
represents the  auricle, and the pump, b,  the ventricle.   When
the piston  in a is raised, the fluid  enters through c to fill it by
suction, as  it is termed.   When, now, its piston is  lowered, the
fluid is'forced through the valve d into the pump b, (which re-
presents the ventricle,) whose piston is  at the same time raised
to receive it.   And when the piston in b is lowered in its turn,

   • Thi« HilntHtion is an active one, as was stated in § 106, when  speaking of the heart
 as aTJholt  TheventrlckJ does not dilate because the blood is forced into .t, but the
 blood rushes into it because it dilates. 
76
HUMAN PHYSIOLOGY.
Ventricles larger and stronger than the auricles. Valves of the aorta.
FIG. 27.
the fluid being prevented from  returning into a, by the closure
of the valve d, is forced through the valve e into /, representing
the discharging tube, the  artery.  At the same time, a fresh
supply of fluid is received  into a by the raising of its piston.
   119.  I have  described  the auricle  and ventricle of one side
of the heart, the right side.   The left side  is constructed very
much in the same way.  You will observe, in Fig. 26, that the
ventricle is much more capacious than the auricle.   The auricle
is  indeed the  antechamber to the ventricle.   The ventricle,
too,  you  see,  is much thicker in its walls.   It is  made very
strong, because  it  does by far  the principal  part of the  work.
I remark  here, in  passing, that the size of the whole heart is
about that of the closed hand of the individual.
   120.  I will now call your attention to a more particular view
of the valves of the  heart.   We will take, first,  the valves
which are at the beginning of the aorta, the great artery of the
body, going out from the  left ventricle.   These are very  much
like the valves of the veins seen in  Fig. 23.  There are three
of them.  They are like little pockets arranged around the ori-
fice of the artery,  and looking  toward  the  tube of the artery.
Of course, when the ventricle  contracts, and forces  the  blood
into the  artery, these  pockets are pressed  by the  blood flat
against the sides of the artery.  But when the ventricle dilates,
and  the blood  attempts to go back  from the artery into the
ventricle, it gets into these pockets, and bulges them out toward
the heart, and thus the mouth of the artery is closed.  But you
can see that if  these  pocket-like valves had plain curved edges
they  would not effect a  perfect closure.  There would  be  a 
THE CIRCULATION.
77
  _________________Peculiar provision in the valves of the aorta.

 little space in the very middle of the orifice of the artery which
 would be left open.  This is made plain by Fig. 28, which pre-
 sents the  orifice of  the  artery  with
 its closed  valves, as  it would  appear
 seen  from  the  interior of the heart,           FIG- w-
 if the three valves  had  plain  curved
 edges.   There would  be  a space left
 between them.   But this difficulty is
 remedied by  a very simple contriv-
 ance.   A  little fleshy projection is
 placed upon the middle point of the
 edge  of each  valve, of such  a size
 that  the  three projections  together
 just fill the space A.   When, there-
 fore, the valves are closed, no blood
 can go back from the artery into the
 ventricle.   This arrangement is shown in Fig. 29, in which the
aorta, a, is laid open  and spread out, so as to show the three
valves with  their projections on the edges.   At b and c, are the
openings of the two arteries  that supply the walls of the heart

                          FIG. 29.
VALVES OF THE AORTA.
with blood for their growth and  repair, for the heart is con-
structed  and repaired from its own blood.   The valves at the
orifice of the pulmonary artery are arranged in the same man-
ner as those which are at the orifice of the aorta.
   121.  The  valves which  are between the auricles and  the
                             7*
 
78               HUMAN PHYSIOLOGY._____________
         Arrangement of the valves between the auricles and ventricles.__________

ventricles I have already partially described.   They are folds
of strong white membrane, their edges being held by numerous
small tendinous cords.  And these cords are manned, as we may
express it, by muscles attached to the walls  of the heart.   The
office of these muscles  is to hold  on to the cords that are fast-
ened  to  the edges of the  valves,  and prevent these sheets  of
membrane from flapping back  too far when the powerful ven-
tricle contracts.  It is by a nice adjustment  of forces  that these
valves act  with  such exactness.   They are of greater  extent
than the valves which  are  at  the  mouth of the aorta and the
pulmonary artery, and, therefore, it would not do to leave them
to act alone, as those valves do, upon simple mechanical princi-
ples.   The living muscular  fibre must be  introduced as the
agent to control  and  regulate  these  principles in their applica-
tion here.  If it were not done, the consequence would be, that
when the ventricle contracts with  prodigious force, as it some-
times does  when the circulation is in a great state of excitement,
the light tendinous fastenings would be ruptured by the pres-
sure of the blood upon the valves.   As it  is now,  the  strong
but yielding muscular  bundles, to which   these tendons are
attached, regulate with great exactness the closing of the valves.
Even if there were  no need   of any  regulation, by muscular
action, of the movement of these valves—if the  tendons would,
in all cases, let the valves go  back to just the right point—as
they are not extensible,  and have no elasticity, it is manifest
that there would be more danger of rupture than there is with
the present arrangement.  The  tendons cannot be stretched, and,
therefore, under great pressure they might  break.   In Fig.  30
is a representation of a portion  of this valvular apparatus.  The
engraving was made  from a drawing of the part  taken from
the heart, and pinned  upon a board for the purpose.  At  m,
you see the sheet  of membrane;  o, o, are two  of the muscles
attached to the inside of the ventricle, to hold  on to the ten-
dons, h, that are fastened to the edge of the membrane.  This
membrane is now in the  position that it is when the valves are
open, that is, lying in  a  line with the little tendons and their
muscles.  But when the ventricle  contracts,  the blood, pushing
against the membrane m, carries up the free edge to which the
tendons are fastened, which, meeting the free edges of the other
valves, closes with them the communication  between the auricle
and ventricle.
   122. In looking at Fig. 26, you observe that, while there are
valves between the auricle and ventricle, and at the mouth of 
_______THE CIRCULATION.                 79
No valves at the openings of the venae cavse.  Why this.
FIG. 30.
   PART OF THE VAVULAR APPARATUS BETWEEN THE AURICLE
                     AND THE VENTRICLE.

 the artery going out from  the ventricle, there  are none at the
 openings of the two venae cavce, the veins that pour their con-
 tents into the auricle.   Why is this ?   Why is there no need
 of valves here to prevent a  regurgitation into these veins when
 the auricle contracts ?   It  is because that, as  the auricle con-
 tracts, there is at the same time the dilatation  of the strong
 ventricle,  making, of course, a suction in that  direction  so
 powerful as to counteract most fully any tendency  to regurgita-
 tion into the veins.   You readily see, that  if the  arrangement
 were reversed, and the auricle were  stronger than the ventricle,
 then, when the auricle contracted, there  would be regurgitation
 into the venae cavae, if there were no valves there to prevent it.
 The same remarks could be made in regard to the pulmonary
 veins, that pour their contents into the left  auricle.
   123. Having thus examined the heart in detail,  you  are now
 prepared to look at it as a  whole.   For this purpose, I present
 to you, in  Fig. 31, a front view of the heart, in which a is the
 right auricle, receiving  the  purple blood from the whole body
 by the two large veins,  h and i, called the vence cava ;  b is the
 right ventricle, that receives the blood  from the right auricle,
 and sends it to the lungs by the pulmonary artery, f;  c is the
 left auricle, which receives  the  red blood  from the lungs, by
 the pulmonary veins, g, g,  g; d is  the  left ventricle that re-
ceives the blood from the left auricle, and sends it all over the
body through the aorta, e.   You observe, that  you see but a
part of the left auricle  and ventricle, they lying partly behind
the right ventricle.  You do not see the very beginning of the 
80                HUMAN PHYSIOLOGY.

                General view of all the parts of the heart.
FIG. 31.
FRONT VIEW OF THE HEART.
aorta, for, as  it rises from the left ventricle it is at first con-
cealed behind the top of the right ventricle and the beginning
of the pulmonary artery.   It  then  forms an arch, from which
it sends forth branches to the head and upper extremities; and
it afterwards  passes down behind the heart, to supply with its
branches the trunk of the body and the lower extremities.  In
the line of division between the two ventricles, b and  d, you
see one of the  coronary arteries,  as they are  called,  which,
coming from the beginning of the aorta, as described in § 120,
supply the walls of the heart with blood.
   124.  To make  you  quite familiar with the relations of the
different parts of this  complicated  organ, and with the course
of the blood through  its different apartments, I give you, in 
THE CIRCULATION.                 81
  _________ Course of the blood through the different cavities of the heart.

Fig. 32, a map of the heart, with the names placed upon the
parts.   I will describe the circulation with this map before you.
The dark blood is received from all parts of the body by the
vence cavce—from the parts  above by the descending cava, and
FIG. 32.
MAP OF THE CIRCULATION.
from the parts below by the ascending cava.  These veins pour
the blood into the right auricle.   From this  it passes into the
right ventricle, which sends it by the pulmonary artery to the
lungs.   From the lungs it  returns by the pulmonary veins  to
the left  auricle.   It then passes into the left  ventricle, from
which it is sent by the  aorta to all parts of the body.
   125.  In Fig. 33  is represented the heart,  situated between
the two lungs, with the arteries which carry blood from it, and 
82                HUMAN PHYSIOLOGY.
         Situation and connections of the heart.  Its harmonious action.__________

the veins which pour their blood into it.  The lungs are repre-
sented as being drawn apart to the right and left m front, so
as to expose fully the heart and its vessels. The sac containing
the heart, and the packing cellular tissue  are removed, so as to
lay the heart and its vessels bare. At a is the trachea or wind-
pipe ; on  either side of it are  the two  arteries, the  carotids,
which  go to the head; c is the artery which goes to the arm;
6, b, are the jugular veins coming from the head, d, d, the veins

                           FIG. 33.
        LUNGS, HEART, AND PRINCIPAL BLOOD-VESSELS.

from the arms, all empting their contents, as you see, into the
descending cava; e  is the right auricle, receiving the blood
from the two cavae; / the  ascending cava; g the right ventri-
cle, i the left ventricle, and h the descending aorta.
   126.  I have been thus particular, and have led you through
some repetitions  in the description of some of the figures, in
order that you may get a clear idea of the complicated mecha-
nism of the circulation.   And now, perhaps, you will  inquire,
in what way all  these four apartments of the heart contract
and dilate, so as to  have the organ act as one  harmonious
whole.  You  have seen how the auricle and ventricle of one 
THE CIRCULATION.                 83
        The causes of the two sounds of the heart. Its forward impulse.

side act in relation to each other—the auricle contracts when
the ventricle dilates, and the ventricle contracts when the auri-
cle dilates. Now, the harmony of action between the two sides
is  preserved  by having  the two  auricles  act together,  and
the two ventricles act together.   And  this action produces
two sounds, which may be heard by applying the  ear to the
chest of any one  on the left  side.   The first sound is  rather
a  prolonged  and  heavy one,  the second is  light and  quick.
They are very well represented by the syllables lub-tup.   The
first sound occurs when the strong  action of the  heart is per-
formed, that is, when the ventricles contract.   It is  owing
to several  causes.  One of these is  the  impulse  of the heart
against the walls  of the  chest;  the cause  of which  I  shall
speak  of  soon.   Another is the  flapping together  of the
valves between  the auricles and the ventricles, to prevent the
blood from regurgitating into the auricles, when the ventricles
contract to force out  their contents.   The  light  and quick
second sound is caused principally by the flapping together of
the valves at the mouths of the  aorta and the  pulmonary
artery when  the ventricles dilate.   The  pulse (which  I have
already remarked upon in  § 100) is produced by the impulse
given to the blood by the contraction of the ventricles.   There
is, therefore, a pulse in the arteries  of the circulation through
the lungs, as well as in those of the circulation through the
general system.  Wherever there is an artery there is pulsation.
   127. The impulse of the heart against the front wall of the
chest on the  left side is easily explained.  The heart is so en-
veloped  by the  lungs,  that only a  small portion of it  comes
near to the front wall of the chest, and such is the situation of
the heart, that this portion comes to  the left of the middle line
of the chest.  The position of the heart is an oblique one, its
upper part being both farther back and more to the right than
its lower part.   Keeping in view this position of the heart, you
will readily see  how the impulse is  produced against the front
of the chest at its lower  part.  The aorta, in going from the
heart  makes an  arch  upward and  backward, to go down in
front'of the  spine; and it is the tendency to straighten  out,
produced in this arch by the force of the blood thrown into it
by the ventricle, that causes the throwing of  the heart forward
by a spring.   This is easily seen  as illustrated by Fig. 34, in
which a is the spinal column ; b, the front wall  of  the chest;
d the heart • and c, the arch of the aorta.   When the heart
throws the blood into this  arched tube it  tends to straighten it; 
84
HUMAN PHYSIOLOGY.
Arrangement of the sac of the heart.  Its lubrication.
FIG. 34.
 but, as the aorta  is fastened to  the
 fixed spine behind, there  can be no
 impression  made  in  that  direction.
 The straightening  of the  arch  must
 therefore occur in  the other direction,
 to the front; and  therefore the heart
 is thrown a little forward, as represent-
 ed by the dotted lines.   The change
 of position  thus produced is indeed
 but slight, but it is sufficient to  cause
 the  impulse.   The  entrance of  the
 blood into the pulmonary artery per-
 haps aids in  the result, but not very
 materially.
   128.  The heart, as I  have  already
 hinted,  is inclosed  in a sac, called  the
 pericardium, which, at its upper part,
 is fastened all around the vessels that proceed from the heart.
 This sac is lined on the inside by a serous membrane, which also
 lines the outside of the heart, being reflected over upon it from
 the pericardium.  This membrane forms, therefore, a sac without
 any outlet.  This is made plain  by Fig. 35.  In this diagram,
 showing the plan of the serous membrane of the pericardium'
a, a are the auricles; v, v, the ventricles;  b, c, the vessels pro-
ceeding from the heart; p the serous membrane lining the out-
side of the heart; pf, the same  membrane reflected from the
FIG. 35.
PLAN OF THE PERICARDIUM. 
CIRCULATION.
85
  ^^^^^  Action of the heart involuntary. Number of its beats.

upper part of the heart on to the inside  of the pericardium.
The arrangement of this membrane, as it fits on to the heart,
is much  like the  common  double nightcap,  as it fits on to
the head;  and if it were dissected off  whole from the outside
of the heart  and the inside  of  the  pericardium, it would be
like such a nightcap when taken off  from  the head—that is, a
sac without an outlet.   Now, this  sac  is kept moistened by a
fluid exuding  from its whole  surface, so that, as that part of it
which  lines the  outside of the heart, in the motions  of that
organ, rubs against that part which lines the pericardium, the
lubrication prevents any injury from  the friction.  This lubri-
cating fluid is continually renewed, the exhalents and the absorb-
ents balancing each other in their action.  When the  exhalents
secrete more fluid than the absorbents can take up, it accumu-
lates, making what is called dropsy of the heart.
   129. The heart, as you have seen, is a complex arrangement
of muscles.  And these muscles are  wholly involuntary; that
is, they are not at all under the direct control of the will.  No
one can by an exercise  of the will  make his heart beat slower
or faster.   As I shall  show you in another chapter, this organ
is kept at work by its nervous connection with the spinal mar-
row.  It has no  repose, as the voluntary muscles  have, unless
you call the intervals between the  contractions and dilatations
of its several parts intervals  of repose.  The amount of work
which  it  does is enormous,  if we calculate it for a lifetime.
The heart of an adult beats, that is, each one of the four cham-
bers of this  organ dilates and contracts,  about 70  times in
a  minute.   This  would  make  100,800 times in  24 hours,
36,792,000 times in a year, and  2,575,440,000 times in a life
of 70 years.  In children, the  action of the heart is much more
rapid, and in disease it sometimes reaches in  them to 160 or
even 200  beats in a minute.   It  is thus that this organ, situ-
ated in the centre of the complicated apparatus of the circula-
tion, labors continually, by night and by day, in keeping the
blood in motion.   The two circulations of the general system
and of the lungs  are ever going on.   The blood is ever moving
in all the  cavities of the  heart, in every artery, and  vein, and
capillary.   It never stops till it is arrested by death.
8 
86                HUMAN  PHYSIOLOGY.

         Apparatus of respiration.  Air-cells in the lungs. Their si:
                  CHAPTER  VII.

                       RESPIRATION.

  130. You saw, in  the last chapter, that the purple venous
blood is sent to the  lungs to be changed into arterial blood.
The great object of the apparatus of respiration is to introduce
the air to  the blood,  so that it may act upon it, and produce
this change.  Another object is effected at the same time, viz.,
the production of the voice, by the  striking of the air upon
the vocal  chords in  the larynx, as it is forced out from  the
lungs.  This will be made the subject of a future chapter, and
I propose now to show how the  chief object of respiration,
which is so immediately essential to the continuance of life, is
secured.
  131. The lungs are spongy bodies, filling up a large part of
the chest, and surrounding the heart.  They are  in common
language,  the lights ; and  you can see what they are in man
by observing the lights of other animals.   They are composed
chiefly of  air-tubes, air-cells, blood-vessels,  and  nerves, packed
together with the common packing material of the body, cellu-
lar membrane.   The spongy lightness of the lungs is owing to
the air-cells or vesicles.  You can get some idea of the propor-
tion  of these  cells  to  the solid  part  of  the organs if you
inflate the lungs of some animal, as the sheep or calf, by blow-
ing into  the  windpipe.  These  cells  are  exceedingly  minute.
It is in them that the change is effected in the blood.  The
capillaries holding the  blood branch out  on the walls of the
cells, and  the blood is acted upon by the air through the pores
of the  vessels.   The object, therefore, of respiration is to in-
troduce the air freely into these cells.   The air enters through
the windpipe, and this branches out into tubes called bronchi,
which divide and subdivide, till they become very minute,  and
then end in the air-cells.  These cells are estimated to be about
the -rioth of an inch in diameter.  Some calculations have
been made in regard to the extent  of surface which they would
all make if they could be spread out in one sheet.  There is of
course no great accuracy in such calculations; but we can readily
see that the aggregate surface must be immense, and, therefore,
the blood is thus very extensively exposed  to the action of the 
RESPIRATION.                    87
Air-tubes. Relative situation of the lungs and the heart.
air.   In Fig. 36 is represented the lung  of one'side, d;  the
branches of the bronchi of the other lung, c, at the lower part
ot which, e, they are represented as they branch out minutely
to open into  the  air-cells; b is the trachea or windpipe, and a
                    LUNGS AND AIR-TUBES.


is the larynx at the top of it.  It is through a chink called the
glottis, in the larynx, that all the air passes as it goes into and
out from the lungs.  This will be particularly described here-
after.
  132.  In Fig. 33, in the last chapter, you see represented the
relative situation of the heart and lungs, the lungs being some-
what separated, however, from the  heart, to the right and left,
in order to show that  organ fully.  In their natural position
they are close to the  heart, and cover  up  all of it, except a
small portion  in front and to the left side, where its beating is
so plainly felt.   Both the heart and the lungs are suspended  in
the chest to the upper  part of the walls of this cavity, and are
fastened also to the spinal column in the rear. The large vessels
of the heart, and the bronchi of the lungs, serve as the princi- 
88
HUMAN PHYSIOLOGY.
     Pleura. Mechanism of breathing.  Provision for expansion of the chest.

pal means of suspending these organs, as you  can readily see
by the Figure.  The lungs are  covered by a  white, shining
membrane, which also lines the inside of the walls of the chest
(§ 67.)  called the  pleura.  This is always kept lubricated by
a watery  fluid, so that, as the lungs expand  and the chest
moves, the friction will  be  attended with no inconvenience or
injury.  You  may perhaps ask why, as the lungs follow the
walls of the chest in its expansion, they could not have been
fastened to  these walls  throughout  their whole surface.   The
principal reason probably is that, if this  were the arrangement,
the  intimate  vascular  connection, which would in  this  case
exist between the walls of the chest and the lungs, would ex-
pose the delicate  texture  of these organs more frequently to
injury from  external violence.   As it is now, the effusion, or the
inflammation, consequent  upon a  blow  on the chest,  is not
apt  to  affect the lung in the neighborhood,  because  it has
no direct connection with it by nerves and blood-vessels.
   133.  You are now prepared to see by what mechanism the
air is alternately introduced to and expelled from the lungs.  The
chest incloses a large space, which can be made much greater by
certain movements of its walls. It is this expansion of the cav-
ity of the chest, effected by certain muscles, which, by creating a
vacuum, causes the air to  rush into the  chest through the tra-
chea, just as air rushes into the bellows  when the space within
is expanded by the separation of  its walls.  That you may un-
derstand how the expansion  of  the chest is  effected, I  now
proceed to describe the chest.   In Fig.  37 you see the frame-
work of the chest.  At b, b, is the spinal column, the  grand
pillar supporting  the walls of this  cavity.  The ribs, c, c, go
from this with a  large curve round to the breastbone, a, in
front.  The ribs, however,  do not join directly with the breast-
bone, but there are  cartilages intervening, as you observe in
the Figure.   The  collar-bone  goes from  this breastbone across
to  the  top of the  shoulder.   The ribs  are  twelve on each
side. The lowest  two are  attached only to the spine, and are
called floating ribs.  The whole is so constructed as to allow a
very considerable expansion of the cavity.  As, in effecting this
expansion, the ribs are carried upward and forward with the
breastbone,  the ends of the  ribs at  the spine  move but very
slightly.  As  the chest  is kept in constant motion, lightness in
its walls is  an object of some importance; and, at  the same
time, it is necessary that the  structure should be a strong one,
in order to guard  effectually the lungs from injury.   Both of 
            RESPIRATION.                    89

Framework of the chest.  Bones. Cartilages.  Muscles.
FIG. 37.
these objects are secured, by having the walls  in front and at
the side composed  of so  many bones, well bound  together by
the muscles which move them.   If these bones were all in one,
it would be necessary that it should be quite thick, to answer
as a defence, and then it would be a heavy and unwieldy thing
to move.   The cartilages which  connect the ribs to the breast-
bone are a great safeguard.   They give elasticity to the struc-
ture as a whole, and  the  ribs are not very liable to be broken,
because of the yielding of the cartilages with which  they are
connected.
   134. This framework is filled out with connecting material,
chiefly muscles, which  effect  the expansion of the  chest in in-
spiration.   First, there is  a large expanse of muscle  and tendon
stretching across the lower part of the chest, separating its con-
tents from the contents of the abdomen below.  The  edge of this
muscle, which is called the diaphragm, is fastened to the spine
behind, to the end of the breastbone before, and all around the
lower ribs.  It is arched upward ; and against its concave sur-
face press upward the liver and stomach, while  the lungs and 
90
HUMAN PHYSIOLOGY.
Diaphragm. Its action in inspiration and expiration.
the heart press downward against its convex surface.  The dia-
phragm is  represented in Fig. 38.   The ribs are cut away in
front, so  as to give a front view of the cavity of the chest, U, c,
the lungs  and heart being  entirely removed.   D  D  is the
diaphragm, very high in the  central portion, which  is tendin-
ous, but  descending very low at its edges  at  the sides and in
the rear.
FIG. 38.
DIAPHRAGM.
  Front View.
   135.  You can see that, if all  the  muscular fibres in the dia-
phragm contract, the arch will be flattened, and thus the room
in the chest will be  enlarged.  To occupy this new room thus
made, the air rushes in through the windpipe.  This is inspira-
tion   In  expiration, the  reverse movement takes place—the
arch of  the diaphragm rises, and, compressing the lungs, forces
the air  out of them through the trachea.   In inspiration, as
the  diaphragm  is  flattened,  it  pushes down  before  it the
stomach, liver, &c  and hence the pressing out of the abdomen,
which is so sensibly felt if the hand be placed upon it during
the act of inspiration.  In  expiration, on the other hand the 
RESPIRATION.
91
         In expiration little muscular action.  Elasticity the chief agent.

abdomen retreats inward.  These  two opposite states of the
arch of the diaphragm, and of the walls  of the abdomen, are
represented in Fig. 39.   It is a  side view, the  ribs being cut
away.   C c is the cavity of the  chest, and C a, the cavity of
the abdomen.  The diaphragm and the abdomen are represented

                           FIG. 39.
                           Side View.

as they are in expiration.  The dotted line marks the flattening
of the arch of the diaphragm, and the projection  of the ab-
domen, as they occur in inspiration.   It  is supposed that in
ordinary expiration, there is little, if any, muscular action—
that as the diaphragm, which in  inspiration pushed down the
stomach and  liver, and  thus thrust out the walls  of the ab-
domen  ceases to contract and  relaxes, the mere elasticity of
the parts below, and especially of the abdominal walls, restores
the former condition of things, and so the diaphragm is car-
ried upward, and expiration results.   When, however, the ex- 
92
HUMAN PHYSIOLOGY.
           Other muscles, besides the diaphragm, act in inspiration._____________

piration is at all forcible, it  is produced in part by the action
of the muscles of the abdomen and some of the muscles about
the chest.
   136. While this dome-shaped muscle, the diaphragm, is the
principal agent by which the chest is enlarged, there are other
muscles which do the same  thing in another way.  In Fig. 40,
a is the spine; c, c, c, the ribs ;  6, the breastbone ; d, the col-
lar-bone ; g, the diaphragm.  You observe, on the  right side

                           FIG. 40.
of the chest,  certain  muscles,  i, extending from  the spinal
column in the neck to the first rib.  When these contract, the
effect will be  to  raise this  first rib, and all the  others, being
attached  to it, of course  follow.   And, as the  ribs,  as  you see
in Fig. 37, slant downwards from the spine toward the front,
the result will be, that all the ribs will be carried together for-
ward and upward.  This result  is the more effectually secured
by muscles which pass from rib to  rib, as seen at e, e, e, e.   In
this Figure, the ribs, c, c, c, are left bare on the left side, to show 
RESPIRATION.
93
' Arrangement of muscles between the ribs.
the arch of the  diaphragm, g, the  dotted  line indicating it on
the right side.
   137.  There are two layers of muscles  connecting  the  ribs,
the fibres of which  cross each  other, as represented  at M, in
Fig. 41.  RR are parts of two ribs.   The spaces between the


                           FIG. 41.
ribs are filled with  muscular fibres, arranged as represented in
in the Figure.  If the fibres were straight, as at L, they could
not bring the  ribs  as  near together  as the oblique fibres do.
For, as muscles can not shorten themselves, at the farthest, more
than one-third of their length, the straight fibres  could bring
the ribs only one-third nearer together, while it is obvious that
the oblique fibres, with the  same contraction, can do  much
more  than that.    These muscles between the ribs not only,
then, help to raise all the ribs as a body, as mentioned in § 136,
but they bring each rib nearer to the one above it.  This in-
creases the expansion  of the chest, especially as the ribs are so
joined to the  spine, that if a rib be  moved upward, it must be
carried outward as well as forward.   You can see, then, that
by the operation of these muscles in  the neck and  between the
ribs, the diameter of the chest will  be increased from front to
rear, and also from side to side.
   138.  The chest is  expanded, then, in two ways—by flatten-
ing the  arch  of  the  diaphragm, and by raising the  ribs.   In
ordinary quiet respiration,  this expansion is effected chiefly by
the diaphragm.    But when there is a call  for  more active
respiration as in violent exercise, the  muscles which raise the
ribs act strongly, and  hence the heaving of the chest,  as it is
called.   Their action is violent when  from disease, as in asthma
for example, it is difficult  to introduce sufficient  air into the
lungs.
   139. The lungs, heart, &c, accurately fill the chest in all the
variations of size to which its cavity  is subjected in respiration.
V 
94
HUMAN PHYSIOLOGY.
               Change in the blood effected in the air-cells._____________________

For, when the chest is expanded, the spongy lungs swell out to
follow its walls, and  the  air rushes in  through the trachea to
fill  the  expanding air-cells.  If, now, there were an  opening
through the walls of the chest, communicating with the out-
side of the lung, when the  chest expanded, the air would rush
in at this opening as well as through the trachea, and the lung
would be compressed in proportion to the freeness of the open-
ing.  This has sometimes occurred  from  disease  and  from
wounds.   If a free  opening  were made  at the  same time in
both sides, both lungs would be compressed, and death would
be produced by suffocation, as  really as if some  obstruction in
the windpipe prevented the air from entering the lungs.
  140.  I have said  that the change  in the blood, from purple
to red, is effected in the air-cells.   The blood and  the air are
brought very near together for this purpose;  and yet they are
kept entirely separate,  except  when, from disease, the blood
escapes into the air-cells and air-passages, and is then expecto-
rated mingled with air.   It is supposed that the air in the cells
acts upon the blood  through  the pores of the vessels containing
it,  which branch  out  on  the  walls  of the  cells; for if dark
venous blood be inclosed in a bladder, the air will  act through
the pores of the bladder, and  gradually change  the outer por-
tion of the blood to  a red color.
   141.  These  air-vesicles,  then, do an important work.   The
change which is effected in them is immediately essential to the
continuance of health, and  even of life.  If the air be in any way
shut out from them  death  occurs  at once.  And so important
is it that  they should  do  their work well, that extraordinary
provisions are made to secure  an  abundance  of room for them
under all circumstances.   For the cavity of  the chest, as you
have seen in this chapter, can be expanded to a very  great ex-
tent.   It would indeed be difficult to  conceive how  a greater
range of expansion  could be  secured.   As the  air-cells  are
called upon  to do more work at some times than at others,
there are special provisions for a larger dilatation  of  the chest
than is  required  in ordinary quiet  respiration.   Thus  when,
from violent exercise, the blood is  coursing rapidly through the
lungs, and more  air is therefore  needed to  change  it to  red
 arterial blood, the  chest is  largely expanded by calling into
 action muscles, which do  but  little,  if any thing, in ordinary
 breathing.
    142. As  the apparatus of respiration is  so especially ar-
 ranged to secure room for the lungs  under  all circumstances, 
                       RESPIRATION.                   95
           Injury done to the air-cells by compression of the chest.

it must be very deleterious to the  health  of the body to inter-
fere with this  arrangement.  If the expansion of the chest in
breathing be limited by any  pressure, every  air-cell must  be
embarrassed in doing its part in  changing the blood.   Either
all of them must be unduly contracted, or some of them must
become obliterated, so  that there will  not  be  as many vesicles
as there should  be.  In either case, the organ  is disabled  in
proportion  to  the amount of  the  compression.   The blood is
not as good as it would be if there were enough vesicles, and
they could perform their work without constraint.   The vigor
of the system is therefore lessened.   And, besides,  the lungs
themselves are  especially liable to disease from this unnatural
confinement.
  143.  Much injury is undoubtedly done to the lungs that are
thus confined,  when any strong exercise is taken.   If the chest
be left free to expand to  its fullest extent when occasion re-
quires, this injury is  avoided.  For when the  strongly and
rapidly contracting heart pumps the  blood in such quantities
into the lungs, the widely expanding  chest draws  in the due
amount of air to change the extra amount of blood.  All the
air-vesicles are ready to do their duty, and, therefore, no violence
is done to the  delicate  texture  of  the  lungs.   But if these or-
gans be compressed, the dilatation of those vesicles that are not
obliterated, in  the midst of the commotion of the difficult res-
piration, is very unequally effected,  and some  of them  are
stretched beyond their proper dimensions.  At the same time,
the blood  must be  here  and there obstructed  in its  passage
through the lungs, producing what is termed congestion. And
if this violence be repeated from  time to time, permanent dis-
ease will after a while  be the result.
  144. From  the considerations  in the  two last paragraphs it
is manifest, that the interference with the due  expansion of the
lungs, which so commonly results  from  the modes of  dress in
the female sex, must be one of the prominent causes  of con-
sumption, to say  nothing  of  other diseases arising from this
cause.  This interference is effected in two ways—chiefly  by
compression  of- the chest  directly, but also  by the pressure
which the load  of clothing hanging from the girt waist must
make upon the upper part of the  abdomen.  This latter cause
interferes with that forward movement of the abdomen which,
as you saw in § 135, is necessary to the flattening of the arch
of the diaphragm in  the  act of inspiration.  The extent  to
which compression of  the chest is sometimes carried is seen  by 
96                HUMAN PHYSIOLOGY.
         Change of the form and capacity of the chest by compression.___________

comparing the two outlines in Fig. 42.  One is an outline,
the Venus de Medicis, the  universally recognized beau ideal
of beauty of form in the female, and the other is an outline


                           FIG. 43.
of the form of a lady with an artificially small waist.   In Fig.
43  is represented the framework of the chest of its  natural
size, and as it is sometimes contracted by fashion.  The  Figures
FIG. 43.
representing the  contraction of the chest may appear at the
present time as caricatures, for a very small waist is not con-
sidered now to be as essential to  beauty in the female form, as
it was  twenty-five years ago.  The truth, as uttered by medical
men, has had some effect.  But  the  evil is remedied only in 
RESPIRATION.
97
         Cause of death in drowning. Singular provision in the whale.

part.   The chest of the female is still too much begirt, in obe-
dience to  the tyranny of fashion, to allow of the free expan-
sion, to secure which such special  pains are taken by nature.
The  evil begins  in childhood.  The chest  is moulded during
its growth to the shape which fashion prescribes.  It could not
be done after the chest has  attained its full size.  The torture
of the compression necessary to do it  could not be  endured.
In childhood, therefore,  while the boy's chest is  left  to  grow
in its natural shape and dimensions, the girl is begirt so tightly
as to  embarrass her respiration, because nature is too ungen-
teelly large  in  her patterns  to  suit her case.  The subject is
an important one ;  but as this book is  not designed to treat of
hygiene, I can not go into it further.
   145. It is the  interruption of the change which  is effected
by the air upon the blood  in the lungs, that produces death in
drowning.   The  very common supposition,  that considerable
water  gets into  the lungs in  drowning, is erroneous.   Very
little water ordinarily gets in—not  enough to occasion any em-
barrassment.  The difficulty is, that the air is kept  out, and
not that the water  gets in.  The  drowning person makes at-
tempts to inspire, but  the moment that the water reaches the
epiglottis, the door of the windpipe, it causes at once, by its
irritation,  a spasmodic closure of the epiglottis, so that almost
no water is  introduced.   In the mean  time, the  purple blood
continues  to be thrown by the  right ventricle of the heart into
the lungs.   But  the  little air contained there soon parts  with
its oxygen ;  and  then the change in the blood ceases  to occur,
and dark blood is sent from  the lungs to the heart, and thence
to all the  organs.   These can not go on to  do their duty with-
out the stimulus  of arterial  blood.   The brain, therefore, gives
out, and there is insensibility.   The muscles cease to act, and
all motion is gone.  If a good  supply of arterial blood could
be furnished to all  the organs until breathing could  be again
commenced, life would be preserved.   And there is provision
for such a  supply in  certain animals  that  can remain under
water  for some  time.  For  example,  in the whale there are
larov reservoirs for containing arterial blood, which can be  used
for°the supply of the organs while he remains  under water.
When the supply begins to be exhausted, the animal of course
has those uncomfortable sensations which  a predominance of
purple blood is so apt to produce.   He manifests his uneasiness
by his puffing and blowing,  as he  rises  to the surface, to get a
fresh  supply of air, and with it a fresh supply of arterial blood
in tl)'' reservoirs.               9 
98
HUMAN PHYSIOLOGY.
              Respiration in fishes.  Arrangement of the gills. ^_____________

  146.  The apparatus of respiration varies in different animals.
It appears in three forms—lungs,  gills, and trachea  or  air-
tubes.   The gills of the fish are arranged in fringed laminae, m
order to present by all its minute divisions a large surface ;  and
these delicate organs are covered with a lid to protect them
from injury.   The  blood-vessels which contain the blood to be
changed branch out on the surface of the fringes of the lami-
na, just as the blood-vessels in lungs branch out on the surface
of the air-vesicles.  The  air which  is to change it is mingled
with the water.   It acts upon the blood, as the
water containing it, after being taken  into  the
mouth  of the fish, passes out through these la-
minae, as through a sieve.  That the air in the
water is the  cause  of the change can be proved
by experiment.   If a fish be  placed  in  a  vessel
with its orifice closed, so that  no air can  enter, it
will soon  die from suffocation, because the air in
so small a  portion of  water is soon used up.
Although the fish can not with  his  gills use air
that is  not mingled  with  water, it is supposed
that it  is merely because the gills soon  become
dry when exposed to the air, and that the air
would act  on the blood  in the gills if they were
only kept moist.   Indeed, in  the land crab, that
has the power of living for  some time out of the
water, it has been found that  there is a gland in
the gill-chamber which furnishes  a secretion to
keep the gills moist.   Gills differ much  in their
shape  and  arrangement in the various aquatic
animals.  In Fig. 44  is represented the arenicola
or lob-worm.  Here,  the  gills  are in the form of
tufts arranged along the outside  of the  body.
They take a somewhat similar form in the larvae
of many aquatic insects, as seen in  Fig. 45.  A
large surface is presented to  the air  contained in
the water by the delicate and beautifully arbor-
escent gills of these animals.   Tn insects, we find
the respiration effected  by  tracheal  or air-tubes.
These go  into all parts  of the body, and the air
contained in them acts upon the blood in the ves-
sels which branch out upon their walls.   The in-
sect, therefore, has  no distinct respiratory organs
situated in any  one  part  of the  body, but the   lob-worm.
 
RESPIRATION.                     99
Respiration in insects. Tracheae. Stigmata.
air is carried into every part.  This seems to
be necessary on account  of the feeble circula-
tion  in the  insect.   The  trachea which,  as
Cuvier says, conduct the air in search of the
blood, as the blood has no  means of travelling
in search  of air, open on the surface by stig-
mata, as they are called, which are of various
shapes and number in different insects.   In
the  grasshopper  there are  twenty-four,  ar-
ranged in four  rows.   You can kill an insect
by suffocation by simply covering the stigmata
with varnish.   In Fig.  46 are represented the
trachea in an  insect, the nepa or water-scor-
pion.  The tracheae, as you see, send branches
out in every direction, so that air is introduced
                            FIG 46.
LARVA OF THE
   MAY-FLY
WING CUT OFF.

   2d PAIR OF
RESPTRATOKV  APrARA'ITK OF THE  WA 1 FR-?(OKTMON. 
100              ITrMAN  PHYSIOLOGY.___________
             Respiration in birds.  Apparatus for it extensive.__________________

into every part  of the body.   There  are lungs, so to speak,
everywhere in the insect.
   147.  The  apparatus  of respiration  is  largely  developed in
birds for two objects—to provide for the extensive change in
the blood which is required by their great activity,  and to give
lightness to  the  body.  To  secure  these objects there are air-
sacs connected with the lungs, and located in different parts of
the body;  and in birds that  fly rapidly and are long upon the
wing, these  sacs  are  very  extensive,  and  even  many of the
bones are made  hollow,  and  are connected  with the  air sacs.
By this arrangement, the air is introduced  extensively to the
blood in the capillaries on the walls  of  these sacs, and at the
same time the body is made very light.   And the heat gener-
ated by the effort of flying must expand  the air in the air-sacs
and swell them out, and thus make the body lighter.  In Fig. 47
is seen this arrangement  of air-sacs in the ostrich.  The lungs,
I, I, are quite small, but the  air-sacs, c, c, c,  are  very large.
The orifices by which they communicate with the lungs you see

                            FIG. 47.
                               *
U'NGS OF TUl: OS'IT.U H. 
                      RESPIRATION.                   101
                Changes produced in the air in the lungs.

in the Figure.  In birds  of great powers of flight, the air-sacs
are much  more  extensive.   This arrangement of air-sacs  in
different parts of the body of the bird bears  some analogy to the
trachea distributed in the bodies of insects.
   148.  You have seen that the  object of the apparatus of re-
spiration is to change venous blood into arterial, and you have
also seen how the air is  introduced  to the blood in  order  to
effect this  change.  And now the interesting inquiry arises,
what  are  the actual changes which occur, both in the blood
and in  the air, in the lungs.   If you take a tumbler filled
with lime-water,  and breathe into it through a tube, the lime-
water will become turbid, and will  soon deposit a sediment.
This is  chalk, or carbonate of lime, formed by the union  of
the carbonic  acid gas exhaled from  the  lungs with  the  lime
in  the  lime-water.   Whence comes this carbonic acid gas,
and how is it formed ?  In order to answer this question satis-
factorily, we must look at the chemical constitution of the air
which we breathe.   It is composed of two  gases, oxygen and
nitrogen.   In every 100  parts  of common  air,  there are  79
parts  of nitrogen  and 21 of oxygen.   It is found  that the
oxygen is that constituent of the  air which  is necessary  to
life.  If an animal be placed in a closed jar filled with com-
mon air, he will soon die, and the oxygen will be found to  have
disappeared, while  the nitrogen remains very nearly the same
in amount.   If, now, you place an animal in a jar of  nitrogen,
and another in a  jar of oxygen, the one in the nitrogen will die
immediately, while the other will be  very  lively until the oxy-
gen is mostly used up by his lungs.  The animal in the pure
oxygen will breathe  at first more rapidly than  the animal in
thenar of common air;  and it  is thought that oxygen is too
stimulating for the lungs, and  therefore needs  to be diluted
with the nitrogen, as it is in the air that we breathe.
   149. In the case  of both  the animal  in the jar of air, and
that in  the jar of oxygen, carbonic acid is  found to have taken
the place of the oxygen which has disappeared.  This  gas is
made by a union of oxygen with carbon  or charcoal.  It was
formerly supposed that  this union is effected in the lungs—
that carbon is thrown off from  the venous blood in the lungs,
and that the oxygen of the air there unites with it, and so car-
bonic acid appears in the air expired from the chest. But it has
been discovered that the exchange is made in a different man-
ner.  It is not made in the lungs.  The oxygen is absorbed  by
the blood, and goes with it to the heart to be sent all over the 
102               HUMAN  PHYSIOLOGY.
                Changes produced in the blood by the air.________________

system.  And it is in the capillaries  that the oxygen unites
with carbon  to  form carbonic acid.   The union  takes  place
while the blood is changing from arterial to venous, and is an
essential  part of the change.   The carbonic acid  thus formed
in the capillaries, is brought back to the heart in the venous
blood, and is discharged "from the system in the lungs.  That
the change takes place  as stated has been abundantly proved
in various ways. • It has been found by experiments which I
will not detail, that carbonic acid exists in considerable amount
in venous blood; while, on the other hand, there is much oxy-
gen in arterial blood.  The plain  inference from  this is, that
oxygen unites with  the  blood  as  it passes  through the lungs,
goes with it to the capillaries, and there unites with the carbon,
giving us the carbonic acid which we find  in the blood in the
veins, after it has passed into them from the capillaries.  It has
been found, also, that if frogs or  other  cold-blooded animals
be placed in hydrogen or nitrogen, (gases which produce no in-
jurious effect on them,) they will give off for some time nearly
as much carbonic acid  as  they would have done in common
air.  In this case, as no oxygen is introduced into the lungs,
the carbonic acid can  not come  from any union effected  in
these organs  between carbon  and oxygen, but it must be dis-
charged by exhalation from the blood as it is  passing through
the lungs.  Of course the discharge of the carbonic acid ceases
after a little time; for, there being no new supply of oxygen by
way of the lungs, as there is when the animal is breathing com-
mon air, there can be no new formation of carbonic acid.  But
even cold-blooded animals  can not live in these gases for any
great length of time, although they are not positively deleterious
to them, for oxygen is needed for the continuance  of their func-
tions.  And in  the warm-blooded animals, a  constant supply
of it  is  necessary—they will  die  if cut off from this supply
even for  a short time.
   150. The change which  takes place in the blood, as it passes
through  the lungs, occurs to some extent when the blood is ex-
posed to the air in any way.   Thus,  if blood be drawn from a
vein into a bowl, the  surface of it becomes red by the action
of the air upon it.  Carbonic  acid is discharged from it, and
the oxygen of the air takes its place, uniting with the blood,
just as the process occurs  in the lungs.  A larger part of the
blood  will  be thus changed, if it be shaken  so  as  to expose
more of  it to the air.  The change  takes place to some extent
even if a membrane be interposed between, as when  the blood 
RESPIRATION.
103
      Quantity of carbonic acid given out by the lungs.  Necessity of ventilation.

 is  inclosed  in a  bladder.    The oxygen of the air, in this
 case, is introduced  through the minute pores of the bladder,
 and the carbonic acid gas escapes through them.   Precisely in
 this way is the change effected in the lungs,  as already stated
 in § 140.  The blood is separated from  the air by being con-
 fined in blood-vessels, and the air in  the vesicles acts upon it
 through the minute pores of these vessels.  And, as the blood is
 divided into innumerable little streams, every part of it is acted
 upon by the air  in the  vesicles.   Though the texture of the
 lungs is exceedingly delicate, and  the separation between the
 air and the blood is almost as nothing, yet the  blood is confined
 to its limits, even though  it courses through these organs with
 great, rapidity, and  it never mingles with  the air except as a
 consequence of actual disease.
    151.  The quantity  of carbonic acid gas discharged from the
 lungs in the course  of twenty-four  hours is very great.  Many
 experiments have been tried and calculations made to ascertain
 its amount, and I am  within bounds when I state, that there is
 at least three-quarters of a pound of charcoal in the carbonic
 acid thrown off from  the lungs of a common-sized adult in the
 course  of twenty-four hours.   This  gas is  a deadly poison.
 When accumulated in a considerable amount, as when char-
 coal is burned in an open furnace in a  close room,  it may prove
 immediately destructive to life.  And  in the very prevalent
 neglect  of ventilation, the frequent accumulation of this gas
 from the respiration must  prove more or less injurious to the
 health.   Whenever the proper amount of  oxygen gas is with-
 held from  the  lungs, and  carbonic acid takes  its place, the
 quality of the blood is impaired  from incompleteness  in the
 change effected in the lungs, and  the vigor of the body must
 in this  way be lessened, to say nothing of the deleterious influ-
 ence of this gas upon  the nervous system.  Though the results
 are  not immediate  and palpable, great  injury is continually
 done to the health  of  multitudes by the  accumulation of this
 gas, in small close apartments, and in  crowded assemblies.  A
 congregation of twelve hundred people in two  hours throw off
 from their lungs an amount  of carbonic  acid that  contains
 seventy-five pounds of charcoal.  And yet little pains is com-
 monly taken to carry off this vast quantity of poisonous  gas,
 and replace it with pure air.
   152.  As so much oxygen is absorbed in the  lungs of all  ani-
 mals, and so much carbonic acid is thrown out from them, the
inquiry  arises how the air is replenished with  oxygen, and is 
104
HUMAN PHYSIOLOGY.
      Carbonic acid exhaled from the lungs of animals absorbed by plants.________

cleared of the carbonic acid which is thus so largely mixed with
it.  It is found that this is done, to a great extent at least, by the
leaves of plants.   The process which goes on in these lungs, as
they may be called, of  the plants, is quite the  reverse of that
which is going on in the  lungs of animals. The carbon of the car-
bonic acid which is thrown off from the lungs of animals is ab-
sorbed by the leaves of  plants, and the leaves replenish the air
with the oxygen, which is so  constantly and  abundantly ab-
sorbed in the lungs of the  animal creation.  Thus, the animal
and vegetable kingdoms are sources  of supply to each other.
But it may be thought that there would be apt to be a surplus
of oxygen in the atmosphere in warm climates, where the vege-
tation is so luxuriant;  while, on the other hand, there would
be an accumulation of  carbonic acid  gas in the colder regions.
This would be so, if the air were not so movable that the equi-
librium  is readily secured in either case.
   153.  It is an interesting fact, that the presence  of  light is
necessary to the process which I have described as going on in
the leaves of plants.  Each leaf may be considered as a labor-
atory, and the light as the chief agent in effecting the chemical
changes  that  occur in it.  And  it is  found  that no artificial
light can do the work.   It is  only the light of the sun that is
competent to this chemistry. And as these innumerable labor-
atories are  everywhere  at work,  absorbing the  carbon and ex-
haling the oxygen, to purify the air rendered  noxious by the
laboratories of the  animal creation, we must confess it to be a
mystery as to how the chemistry of the lungs of animals, and that
of the leaves of plants should be kept so nicely balanced. The
balance is so strictly maintained, that the chemical composition
of the air is always found to be  almost exactly  the same.
   154.   The  heat of the body is maintained by  the union
which takes place in the capillaries between  the  carbon and
hydrogen of the system, and the  oxygen which  is  introduced
into the blood through  the lungs.   It is a process analogous to
combustion.   When  carbon or charcoal  is burned in  a  ves-
sel containing air, the oxygen disappears, for it  unites with
the  carbon, and carbonic acid gas, therefore, appears in its
place.  The same union occurs in this case between carbon and
oxygen, as we find occuring in the capillaries.   A sort of com-
bustion, then, is going on in every part of our bodies.  And, as
heat is  evolved in the one case, so it is in  the other. The same
can be said of the  burning of hydrogen and oxygen together.
Heat is caused by the union thus produced between them, and 
RESPIRATION.
105
     Animal heat. Produced by a sort of combustion. Three sources of fuel.

so it is when they unite  in the body.  The water  which is ex-
haled from the lungs comes from this union of  oxygen and
hydrogen.   It was formerly supposed that the union between
the oxygen and  the  carbon  and hydrogen takes place in the
lungs, and  that the heat is made there, and then is distributed
over the whole system.  But it was objected to this supposi-
tion, that it made the lungs a sort of furnace for the rest of the
body, and that, if the supposition were correct, there ought to
be a much higher degree  of heat in these  organs than  any-
where  else, which is not the  case.  Ingenious theories  were
broached to get over  this difficulty; but it was at length dis-
covered that the union between the oxygen and the carbon and
hydrogen occurs  in the capillaries  of the body, instead of the
lungs, and  that the combustion, therefore, that produces the
heat is everywhere, instead of being in one locality.
   155.  The fuel for this combustion comes from three sources.
One of  these is the waste of  the tissues.  This furnishes a con-
siderable amount  of the carbon  and hydrogen for the union
with the oxygen, in all animals that are  subjected, from their
activity, to much wear  and  tear of the system.  I barely al-
lude to this now, and  shall enlarge upon it soon.  Another
source of the fuel for combustion is food.  The  oily, sugary,
and starchy kinds of food are  devoted in a great measure to
this particular  purpose.  These furnish a  sort of  floating fuel,
as  we may express it, which  is carried about in the blood.
Hence,  we see, that our diet must necessarily be varied accord-
ing to the  weather and the climate. In cold weather, the heat
of the body is more rapidly  abstracted than in warm weather,
and, therefore, we need then  more of that food which affords a
supply of carbon  and hydrogen.   And so as to climate.  The
enormous quantity of oily food often consumed by inhabitants
of  very cold climates is used  up by being burned, as we may
say, in the capillaries to keep up the animal heat.  Of course,
keeping the body warm by fire and clothing relieves from the
necessity of  taking any large  quantities  of fuel-making  food.
Still under the most favorable circumstances in  this respect,
there is a need of variation in  diet to suit  the weather and the
climate and we make this variation for the  most part instinct-
ively.   Indeed there is a marked  provision in nature for it.  I
will mention but a single example of this  provision.  While
there is a laro-e amount of fat in the bears and seals and whales
which afford food for the Esquimaux and Greenlander, there is
very little  in the  animals which furnish  a part of the diet of the 
106
HUMAN PHYSIOLOGY.
        Animal heat differs in cold and wurin-bloocled animals.  Why.

inhabitants of tropical climates.   Another source, still, of ani-
mal heat is the store of fat which is laid up in the body.   One
design of this  accumulation  of fat  in  different parts of the
body seems to be to provide  for the heat when other sources
fail.   Thus, when disease destroys the appetite, and thus cuts
off the supply of food, the fat wastes away, or rather is burned
up, to keep up  the  temperature of the  body.   The fat  is the
great  means of maintaining the requisite temperature when hi-
bernating animals become torpid for the winter.  They  become
very fat in the autumn, before crawling into their winter quar-
ters, and in the spring they come out very lean, their fat having
been consumed in keeping up the low degree of temperature re-
quired during this time.
  156.  As the  amount  of heat  produced, when charcoal is
burned  in air, or  when  oxygen  and  hydrogen are burned
together, depends upon the quantities of carbon and hydrogen
that unite with the  oxygen, so, also, the degree of animal heat
depends upon the quantities of carbon and hydrogen that unite
with the oxygen in  the capillaries.   This may be illustrated by
referring to the effects of exercise on  the heat of the  body.
When the circulation is quickened  by exercise, the blood passes
more  rapidly than usual  through the lungs, the respiration is
consequently quickened, more air is introduced  into the lungs,
and therefore oxygen is  more rapidly absorbed by  the blood.
At the same time, the action of the muscles effects  a waste in
their structure  by the wear and tear, so that more carbon and
hydrogen are ready to be released to  be united with the in-
creased  oxygen.  Hence  comes the heat produced by exercise.
So,  too, those animals which are  the  most  active,  ordinarily
have the most animal heat, and have the most extensive respi-
ratory apparatus, so that there may be a free supply of absorbed
oxygen  to unite with the carbon and hydrogen of the changing
tissues.   It is in birds and insects that this  union takes place
most largely, and in them, therefore, the respiratory apparatus
is very largely developed.  This is to be attributed to their mus-
cular  activity, which produces so much waste matter that must
be removed from the system.  Cold-blooded animals, on the
other  hand, are very inactive.  There is not, therefore,  much
wear  and tear of the tissues.   There is  comparatively  little
waste, therefore, to  be thrown  off.   And so but little oxygen
needs to be introduced into  the lungs, and consequently little
heat is  generated.   To realize  fully the  contrast between the
warm and the cold-blooded animals in these respects,  observe, as 
RESPIRATION.
107
     Uniformity of animal heat in the warm-blooded. Interesting experiments.

the representative of the one class, a canary bird, and a frog as
the representative of the other.   The frog is generally quiet,
and  only now and  then  takes  a  leap or croaks; but the bird
is ever in restless motion, and sings much  of the  time with
all his might.   The bird  is warm with the heat generated by
the constant union of oxygen with carbon and hydrogen in its
capillaries ; but the frog is nearly as cold as the water in which
he is immersed.  The bird breathes  rapidly, to let the oxygen
of the air  largely into his lungs ; but the frog scarcely seems
to breathe at all, so scanty is the supply of  oxygen which he
needs.
   157. Cold-blooded animals are very nearly of the same tem-
perature with the substances that  are around them; but warm-
blooded animals have a certain degree of temperature, which
they maintain with  considerable uniformity under all variations
of temperature in the atmosphere.  This in man is about ninety-
eight degrees of  Fahrenheit.  This, you  observe, is  above the
temperature of the surrounding air, except in exceedingly hot
weather.  The human body is therefore always giving off heat.
Indeed it  is essential to comfort that it should part with con-
siderable  heat, f<5r  any near approach of the atmosphere to
ninety-eight degrees produces  an uncomfortable sensation of
heat.   But the  amount of heat  which  the  human body can
bear for a short time is much greater  than the facts above
alluded to would lead us to suppose.  It was long taken for
granted, that it  could  not safely bear, even for  a short time,
a heat  much higher than that which is endured in hot climates.
The truth on this subject was at length discovered by accident.
Two Frenchmen were  employed  by government, in  1760, to
devise  some method of destroying an insect which infested the
grain at that time.   The  result of their experiments was the
discovery, that by subjecting the grain to a  certain degree of
heat in an oven the insect was  destroyed, and  the grain not
injured.   While  they  were  trying their experiments, a girl
offered to go into the oven and mark the height of the mer-
cury in the thermometer.  It stood at 260° ; and, after remain-
ing there  for ten minutes, which  she  found that  she could do
without any great inconvenience, she marked it  at 288°, that
is 76° above the boiling point of water.  These facts led to the
famous experiments of Dr. Fordyce  and Sir Charles Blagden,
in England.  With wooden shoes, tied on with list, they went
into a  room in which  the thermometer showed  the air to be
at 260°.  Their watch chains were so hot that they could scarcely 
 108              HUMAN PHYSIOLOGY.
             Different degrees of torpor in hybernating animals.

touch them, and eggs were roasted hard in twenty minutes, and
beefsteak  was cooked in thirty-three  minutes.   And yet the
same air that produced these results was breathed by them with
impunity, and  it raised  the  heat of the body but  very little.
The air which was breathed  out from the lungs was so much
cooler than the air of the room, that it was refreshingly cool to
the nostrils, and to the fingers as they blowed upon them.  In
such cases, the evil effects of the heat  are prevented chiefly by
the great amount of perspiration that occurs, the vaporization of
this abstracting the heat, which would otherwise accumulate in
the body and produce disastrous  results.   The exhalation from
the lungs, also, has some influence.
   158.  In the  state  of  hibernation, to which I have several
times referred, the  torpidity varies in degree in different ani-
mals.  In cold-blooded animals, respiration and circulation may
cease altogether in this  state.  In them the movements of life
are often, perhaps we may say generally, as fully suspended as
they are in the seed that  is kept from heat and moisture.   They
may be preserved in  this state for a long time and yet revive.
Serpents and frogs  have been kept in an ice-house  for three
years, and then have been revived on being brought out into a
warm atmosphere.  In the warm-blooded animals that  hiber-
nate the torpidity is  less deep than in those which are cold
blooded.  In them the respiration and the circulation become
very slow, but never  entirely cease.   Indeed some species take
food with them into their winter quarters, and occasionally wake
up sufficiently to eat.   But most of them are in a quiet, deep
sleep, from which they do not arouse at all till the winter  is
past.   In  this state, as life is nearly, sometimes quite at a stand,
there is no wear and tear, and therefore no change in the tissues,
and so there is  no need  of the introduction  of oxygen by the
respiration.  Dr. M.  Hall, in  his  experiments and observations,
found that the bat, when completely torpid, consumed no oxy-
gen, and discharged no carbonic  acid from the lungs, although
its circulation was not entirely suspended.
   159.  The more active  is the respiration of animals, the less
able are they to bear a deprivation of air.  A warm-blooded
animal will die  if it be  under the water  only a  few minutes;
but a  cold-blooded  animal  can live under the water for some
time, because it is not in so urgent need of oxygen.   And, for
the same reason, a warm-blooded animal, in a state of hiberna-
tion, may be kept under  water for a long time without destroy-
ing life, although when in its active state it would die on being 
                FORMATION  AND REPAIR.            109
              Formative vessels appended to the capillaries.

kept under water for only a few minutes.   And this suggests a
probable explanation of those  cases, in which individuals have
been restored, after  having  been under the water longer than
the usual time that suffices to destroy life in drowning.  In such
cases, the condition  is not  simply that of a  drowned person.
A blow, or the shock of body or  mind, or both, may have in-
duced a suspension of  active vitality, like  that which we see in
the animal in a state of hybernation.   The bare fact of immer-
sion in the water  may have but little or even nothing to do
with the actual condition.   Such a state of things is especially
to be suspected  in those cases in  which the countenance does
not exhibit the usual dark and full appearance of drowned per-
sons.
   160.  I have thus  shown the extensive play which the respi-
ration has in the vital operations of the system.   I have shown
what the chemical changes  are, which  it effects directly  in the
lungs, and indirectly in  the  system.   And you  have seen how
the animal heat  is produced by these  changes,  and how unac-
countably it is so regulated, that  it seldom varies  to any ex-
tent from its fixed standard.   But it is to be remembered that,
while the lungs, and even the capillaries, everywhere are thus
chemical  laboratories,  the nervous  system exerts  a constant
influence upon this  chemistry of the body.  This is especially
seen in regard to the production  of heat,  but  it  is true  of
the whole range of  the chemical operations.  The laboratories
would  all cease their  work if their nervous  connections were
destroyed.
                    CHAPTER  VIII.

                     FORMATION AND REPAIR.

    161. The building and the repairing of  the  various struc-
  tures of the body are done  by vessels appended  to  the capil-
  laries.  The capillaries  having received from  the arteries  the
  blood, the building material, the formative vessels select from
  it while it is in these capillaries, whatever they need for their
  purposes.   The selection  is made  according to the tissue  or
  structure to be formed.  Those vessels which, for example, form
r bone, select from the blood very different constituents from those
  which make nerve or muscle.
                              10 
110              HUMAN  PHYSIOLOGY.
        Selecting power of the formative vessels.  Their concert of action.

   162.  It is wonderful that the blood can be formed from such
a variety of food as is often taken into the stomach.   But it is
far more wonderful that from the blood can be made so many
and such different structures.  How different are the teeth from
the gums which surround them ; and yet both are made from
the blood.  Observe, in some particular part of the body, how
many different structures there are which are all made  from the
same  common material.  Take,  for example, those which are
in and around the eye.  There  are, the skin of the eyelids ; the
eyelashes;  the vascular lining on  the  inside of the lids; the
cartilages of the lids; the firm,  white coat of the eye, giving
to the  eyeball  its firmness; the thin, transparent window in
front, setting into the  firm, white coat, like a watch-glass into
the case ; the beautiful iris, a round moving curtain with a cen-
tral opening;  the lens  behind this opening;  the optic nerve ex-
panded on the  inside of the cavity of the  eye; the muscles
that move the  eye, with their tendons; the tear-gland;  the
cushion of  fat on which the eye reposes; the bone which forms
the socket, &c.  All these various textures are formed from the
blood ;  and the different workmen are  as unerring in their se-
lections from this common material, as if they were intelligent
beings.   Indeed, no ordinary intelligence could accomplish such
a selection.   It is effected, inscrutably to us, under the  direction
of an all-wise Intelligence, and by Almighty power.
   163.  But these builders of the  body not only have the power
of selecting their  building materials  from the blood,  but they
work in concert.   Each company of builders work  together in
harmony, as  if  they  were  under intelligent leaders.   And
though  different companies may be in close  proximity, there is
no disagreement nor interference.  For example, the builders
of a tooth and the builders of the gum around it, do not en-
croach on each other;  but each do their appropriate work with-
in their assigned limits.   Even  when different structures are
intermingled, as  when  tendon and muscle mingle  together at
their place of union, there is no  confusion in the work of the
two sets of laborers.  In Fig. 48 you see the difference in struc-
ture between the transparent cornea  in the  front  part of the
eye and the white coat, the sclerotic coat, into which the cornea
is  set like  the crystal of a watch.  It is  represented as seen
magnified  320  times.   The  dotted lines mark  the  place of
union.   The cornea, a, is a much  more open structure, you ob-
serve, than the  sclerotic coat,  b.  The builders of these  two
structures, though some of them are in such near neighborhood 
    FORMATION  AND  REPAIR.             Ill

Concert of action shown in producing different shapes.

               FIG. 48.
 never encroach on each  other, but each set adheres strictly to
 its own kind of work.  The sclerotica-makers never go to mak-
 ing the open work which you see in the cornea.   If they should
 do so at any point there would be a little transparent window
 at that point in the white of the eye ; and if the cornea-makers
 should at any point make close work like that in the sclerotica,
 there would be a white spot in the cornea.
    164.  The concert of action which we observe in  the different
 sets of formative vessels  is to be looked at in another point of
 view.   It is such that they give a definite and peculiar shape to
 the structure which  they make.   Each bone differs in  shape
 from every other bone, each muscle from every other muscle;
 and so of other parts.  There  is very great variety of shape in
 the structures of the body ;  and each shape can be determined
 only by a certain concert among the builders.  That you may
 realize  in some measure the  extent of  this variety,. observe
 again the numerous  different textures which I have mentioned
 as making  up the eye.   Each  of these  has  its  own peculiar
 shape, and  its definite limits.   Its  builders work after a  fixed
 plan, and within fixed bounds.
   165.  This concert of action may be looked at in still another
 point of view.   If the different structures in the body  were
 made, as a  crystal is, by layer  after layer  of particles deposited
 upon the outside, wonderful as the  concert among  the  little
 builders would be  in that case,  it would not be any thing like
 as wonderful as it is now.  In  the growth, that is the construc-
 tion of any part, the addition is made by the formative vessels at
 every point  of the part, and not upon the outside merely.   As
these builders are at work  enlarging the  part in the growth
from infancy to childhood,  they must so act in concert, as  to 
 112               HUMAN PHYSIOLOGY.
             Change of action. The teeth.  Tadpole and frog.

 preserve the same general form in the part during all the suc-
 cessive  stages of growth.  And, as all the different structures
 of the body enlarge together, there must be agreement between
 different sets ; else there would be encroachment and confusion.
 Thus in the  growth of  the  tiny arm of infancy to the sturdy
 arm of manhood, each  set of builders must during all this time
 keep within its proper limits, so that there may be just the right
 proportion, and the right position  of  bone,  and  muscle, and
 tendon, and  ligament, and  cellular  membrane,  and  skin, and
 nail, &c., that make up the arm.
   166.  But this  concert of action appears the most wonderful
 when a  new action, or change of action is called for.  In the
 transition from  childhood to youth, for example,  the builders
 of the apparatus of the voice, the  larynx, all at once become
 unusually active in their work, and  a great enlargement of this
 musical instrument, for such it is, takes place, so  that it may
 now utter the grave notes of manhood.  Soon, too, the beard-
 builders begin their new work  upon the face.  And during the
 period of childhood new operations have been continually insti-
 tuted among the  builders   of  the  teeth, as one  tooth  after
 another has made its appearance, and  as the  new set have re-
 placed the old.   To produce in the  enlarging jaw a new set of
 teeth to take the place of the smaller  and less  numerous first
 set, and to bring them out  in a symmetrical  arrangement, re-
 quire a  very complicated series of operations.  To effect each
 one of these, there must be concert of action among the forma-
 tive  vessels;  and  there  must be  a most wonderful concert
 among the different sets  and succession of builders, to  make
 all these series  of  operations work out  at length  the general
 result.
   167.  This  change  of  action  in  the  formative  vessels is
 strikingly exemplified  in some animals.  I refer to  those that
 so entirely change their forms during the period of their exist-
 ence.  I will give  two examples.  The first is the common
 frog.  He is at first what is termed a tadpole, and goes through
 many successive  changes to become a complete frog.  These
 changes are represented in the following figures.   The relative
 sizes are not preserved, the tadpole state being represented re-
 latively  much too  large, for the purpose  of showing   more
 clearly the development  of the  legs.   The young  tadpole is
represented in Fig.  49.   It has  a large head  and  body, and  a
long flat tail  by which it swims  easily.  There are no promi-
nences to indicate the putting forth of any thing like limbs.  It 
          FORMATION AND REPAIR.             113

Change of action in the silk-worm.  Concert preserved in these cases.
FIG. 50.
has gills, which  are  loose  fringes on each side of the  head.
These  gills  after a time disappear,  and  it has another set of
gills arranged under a fold  of skin very much  like the  gills of a
fish.  The form  is  then-as in  Fig. 50.  The next change is
this.  The hind  legs  begin to grow out as  seen  in  Fig.  51.
Next, the fore legs appear  as seen in Fig. 52.   The tail is still
very large.   This now gradually disappears while the legs grow
as represented in Fig. 53.  In Fig. 54, representing the perfect
frog, the tail has entirely  disappeared.   With these  exterior
changes interior  ones  have been going  on also.   The animal,
which   was  at the  first  a  real fish,  breathing  with  gills
and swimming in water, has lost its gills, and has now a pair
of lun<rs ;  and it is no  longer able to remain long under water,
without coming to the surface to breathe the air.
   168. The other example is the silk-worm.   It is represented
in Fig.  55.   When it has attained its full growth, it passes into
what is termed its chrysalis state, Fig. 56, it having previously
woven  for  itself from  its silken   thread  a  case or cocoon.
While  it is in this  state of inactivity great changes are going
on in its structure, and it  at length becomes  a perfect winged
insect, as represented in Fig. 57.
   In the two cases which I have described, in each successive
change, the  concert of  action  in the formative vessels is  pre- 
114               HUMAN  PHYSIOLOGY.____________

                Change of action to meet new exigencies.____________

served, but it is after a new plan.  This change of plan makes
the concert of action exceedingly wonderful.
FIG. 57.
  169.  The change of action in the formative vessels, which is
sometimes  called for by accident and disease, exhibits in an in-
teresting manner  the concert  between  these  vessels  as  in-
fluenced by  circumstances.  When a  bone is broken,  these
formative vessels  set themselves to work to repair the  injury,
by forming new bone between  and  around the two ends of
bone, which new  bone we call callus.   In this case,  the bone-
builders  extend their  range of operations to meet the  new
necessity ;  and in doing so they  maintain the  same  concert
which marked their usual operations  before the  bone was
broken.   I stated in § 105, that  when  an artery is tied,  to
cure an aneurism, the circulation in the limb is kept  up by the
small arteries that go off from it above  the  ligature,  communi-
cating with those that branch off below;  and that, in order to
make the  circulation  perfect,  some of  these communicating
arteries  gradually enlarge,  to meet the  necessities  of the case.
Now, this  enlargement is  not  a mere  dilatation produced by
the distending blood.   The arteries grow in  thickness  as well
as in  capacity.  The artery-builders are awakened to  a  new ac-
tivity, and  make the arteries in this quarter after a larger pat-
tern than the one originally designed for them.
  170.  Concert of action under successive changes is  strikingly
exhibited in the processes of inflammation.   The following ac-
count of these processes  is from  a work published  by  the
author, entitled " Physician and Patient."   " You see a swelling. 
                 FORMATION AND  REPAIR.            115
               Illustration from processes of inflammation.

It after a while begins  to soften.  There is matter  in it, but it
is not yet very near the  surface.  But soon,  at  some point, it
comes nearer and nearer to the surface, the wall of the  abscess
thus becoming constantly more thin,  till, at length, it opens
and  discharges.  The  discharge continues  till  the swelling is
nearly all gone, and the  remainder  is  absorbed, and the part
is restored to its natural state.   Just look  for  a moment at
the  complicated  character of this apparently simple operation.
Here is quite a large deposition of substance which  is to be re-
moved ; and this is the object to  be effected.   Observe  how it
is done.   The softening  of  the swelling is not a mere  change
of solid substance into  a  fluid, as  if by decay, but it is  the re-
sult  of an active process, which  we call suppuration.  When
this  process is  properly performed  good pus  is made, or as
the old writers in  medicine rather quaintly expressed it, laud-
able  pus.   This  process  of suppuration, when it is well done,
does not go on here and  there in the swelling, making it like a
honeycomb with  a multitude  of little abscesses;  but there is a
consent, an  agreement  of action by  the vessels of the part, as
really  as  if  they worked   intelligently.   It is this  consent
of action  which not  only  makes   the line  of  movement
in the abscess, but points it towards  the  surface, instead  of
giving it some other direction,  laterally or inward, upon some
of the internal organs.   But it is further to  be observed, that
in this agreement of action, the vessels  of the  part do not all do
one  thing.  Three  different  offices are  performed by them in
the  different quarters  of the abscess.   While  some of these
little workmen are forming the pus, there  are others thinning
the  wall  of the abscess in  the  direction  of the surface,  by
absorbing  or taking  up the  substance there; while there are
others still, in the rear, and at the sides of the abscess, deposit-
ing  substance, in order to make  a  barrier to prevent the  pus
from being diffused in the surrounding  parts.   Each class  of
these workmen  perform  their particular work with even more
exactness and  harmony,  than would be  expected of  any com-
pany of intelligent laborers  under the  direction  of a  leader.
The absorbents absorb together, the wall-builders  build together,
and  the  makers  of pus make pus together, and deposit it in a
common reservoir.
   171. But observe  farther,  and you  will  soon see an entire
change come  over the whole scene of operations.   When the
absorbents have  completed their  passage for the pus through
the skin, the pus is gradually discharged from its reservoir, and 
116               HUMAN  PHYSIOLOGY.
              Formative vessels and absorbents act in concert.

the " occupation " of the pus-makers is soon " gone."   The, wall
builders also cease  their work,  and while the vacancy becomes
filled up  by contraction  and  deposition, the wall of defense, so
carefully  maintained so long as was  needed, is  now taken  up
by the absorbents, workmen which  seem to know just when, as
well as how, to do their duty."
   172. Here  you  have  concert  of action exemplified in  a
complicated set of associated actions, to accomplish a tempo-
rary purpose.    These  actions,  as you see,  change  in  the
different stages of the process, each one being performed just at
the time, and  during the period that it is wanted.   And when
the temporary purpose  aimed at is  accomplished, the vessels of
the part resume  at once their ordinary duties.   It is to be ob-
served  also, that the concert of action is  not confined  to  the
formative vessels; but it appears  also  in  those vessels  called
absorbents,  of which I shall  speak  soon  more  particularly.
And these two sets of vessels do  not interfere with each other,
but  have a sort of agreement together in  accomplishing  the
general result.   This concert of action is  plainly seen  among
the absorbents, not only in this case, but in all the cases that I
have cited  as  exhibiting it among  the formative vessels.  For
example, in the  case of the frog  (§ 167) while the formative
vessels are  constructing the legs, the absorbents are  removing
the  tail.  So  in the  case   of the teeth  (§  166) while  the
formative vessels are constructing the second set, the absorbents
remove the  ends of the fangs of the teeth in  the first set, so
that they are loosened in their sockets, and are thus taken  out
of the way  of the  coming teeth.   And indeed, wherever there
is  formation, there  is  absorption ; and the same  concert  of
action  always appears.
   173. I have spoken of the great variety of structures, which
are made out of the same  material, the blood.  Besides this,
all  the different secretions   are  also  formed  from the same
material.  This appears wonderful when we look at the differ-
ence between  such secretions  as  the tears, the  ear-wax,  the
gastric juice, the bile, &c.  And it appears  more wonderful still,
when we  consider that  these various  glands, or factories, as we
may call them, are built from the  same material  out  of which
they make  their products.   There is one  curious  exception to
this.   It is  in  the case of that large  gland,  the  liver.  This
gland is  built and kept in repair, like  all the other glands,  by
arterial blood.   But while they make their secretions  out  of
this arterial blood, the liver makes its  secretion out of venous 
                FORMATION AND  REPAIR.             117
         Formation of all parts from the blood. Waste. Lymphatics

blood, which is  brought to  it for that purpose as described  in
§ 108.
   174. Thus, all the solids and fluids in the body are made
from the blood.   Even the  heart itself is made from the blood
which it pumps  out into the aorta;  for from this  aorta go out
some small arteries, to carry blood to the walls of the heart for
its  growth  and repair.    These  arteries are represented  in
Fig. 31.
   175. There is not only construction  going on in  every  part
of  the system, but there is  waste also.  The wear and tear of
the ever-moving machinery  continually makes some of the  par-
ticles useless, and these must in some way be removed.   I  pro-
pose now to show how this  is done.
   176. There are two kinds of waste particles; and for the dis-
posal of them two different plans are  pursued.   Some of the
waste particles,  though wholly useless where  they are, can be
rendered fit to be used again by being subjected to certain  pro-
cesses.  These, therefore, are not thrown out of the system, but
are taken up by absorbents, and are  carried where the neces-
sary processes can be applied to them;  and then they are in-
troduced into the  blood, to  make again a part of the  building
material.  But there  are some  waste particles that can not be
used again ; and these  are  so managed as to  be got rid of  at
various outlets of the system.  These two kinds of particles are
taken up by two  different  sets of absorbents.   The selecting
power which they thus exert is as unerring as if they were  pos-
sessed of intelligence ;  and it is  wholly unaccountable, although
some physiologists have attempted to explain it.
   177. The particles which  can be used again are taken up by
absorbents, which are termed lymphatics.   These vessels are
much like the lacteals, the  absorbents in the intestines.  They
unite together, as they come from  all parts of the  body,  into
two trunks.   One of these   is the thoracic duct (described in
8 91),  which is the common  duct,  both of the lymphatics
and the lacteals,  (Fig. 17,) and in  which the chyle  and  the
lymph, as the fluid in the lymphatics is called, are mingled to-
gether.  The other trunk, which receives the lymph from but a
small part of the body empties  its contents into a large vein at
the right side of the top of  the  chest.   The largest part of the
lymph, therefore, unites with the chyle, and is poured with  it
into the circulation, and the rest reaches the same destination
by another way.   It all  becomes with  the chyle a part of the
blood.  But before this is done it passes, like the chyle, through 
 118               HUMAN  PHYSIOLOGY.      _________
            Two kinds of waste particles.  Excretion and secretion.

 glands, in order to fit it to become again a part of the building-
 material of the  body.  These glands are every where in the
 track of the lymphatics.   They are often enlarged from disease,
 and then they can be readily felt.  This is often the case with
 these glands in the neck.  In  relation to this appropriation of
 waste particles, which I  have  thus described, it may be  truly
 said that man  lives in part upon  his own flesh.
   178. Those  waste  particles  which are  entirely useless are
 taken up by the  veins  directly into the circulation.  They then
 travel the  rounds with the blood, and are  thrown off from the
 system  by organs appropriated for that purpose.  These organs
 are the  lungs, the skin, the liver, the  kidneys,  &c.   Each of
 these excretory organs is fitted to throw off  its particular part
 of the  waste.   Thus the lungs, excrete  a kind  different  from
 that which the skin  does; and so of the rest.   The  lungs, as
 you saw in the chapter on respiration, throw  off in the form of
 carbonic acid gas, large quantities of the carbon evolved in the
 wear and  tear of the  system.    The liver, the  skin, &c. throw
 off parts of the waste  which differ from that which  is thrown
 off by the lungs.  Why it is that the waste matter is thus in-
 troduced into  the  circulation to be carried to the excretory or-
 gans, instead  of having special channels  appropriated to the
 particular office of carrying it to its outlets, we know not.   And
 how it can thus be mixed with the blood, and be carried about
 the system  without proving noxious, is a mystery.  That it can-
 not be long retained  in the blood without doing injury, is shown
 by the  evil results, which  come  from a suspension of excretion
from any of the organs that I have mentioned.
   179.  It is interesting to observe that some of the excretory
 organs perform other functions besides that of mere excretion.*
Thus the  lungs,  while they excrete carbon,  absorb  oxygen,
 without which life  could not go on.   At the same time,  too,
they act as the bellows for the organ of the voice, the larynx,
as you will  see in  the  chapter on that  subject.   So  also, the
liver, while  it excretes what would be noxious if it remained in
the blood, puts its  excretion into  such a form, that it  proves, as
you  saw in the chapter on digestion, an auxiliary in some of
the processes of the digestive organs.

   The words excretion and secretion, are often applied to the same thing.  Excretion,
strictly speaking, should be applied only to something to be thrown off, and not to some-
thing formed to be used.  But sometimes an excretion is so formed, that it can be used,
and then the word secretion  is  also applicable to it. Thus the bile, while it is  an ex-
cretion containing noxious particles to be thrown off from the  system, is put to use,
and so it is as often called a secretion as an  excretion. 
FORMATION AND REPAIR.
119
The skin.  Cuticle.  True skin. Papilla
FIG. 58.
   180. The skin, while it is an extensive excreting organ, per-
forms  other important offices.   It  serves  as  a firm yet  very
flexible and soft covering to  the body, protecting its  internal
parts from injury.  It is highly endowed with nerves for two pur-
poses—the one, that it may act as a sentinel to warn of danger;
and the other, that it may be  the seat of the sense of touch.
That you may see how well it is fitted
to  perform these various functions,
I  will  describe  here its structure.
What is very commonly spoken of as
the skin,  is not  really the skin, but
only a covering  for  it.   When the
skin is rubbed off* as  it is expressed,
it  is only this covering of the skin, or
cuticle, which is removed.   The skin
which is raised by a blister is this cu-
ticle.   The great object of the cuticle
is  to  protect the true skin, which is
very highly endowed with nerves for
the purposes  mentioned  above, and
which therefore,  if uncovered, would
prove a source of severe suffering. As
it is, the cuticle protects the skin  effec-
tually, and yet does not interfere with
its functions as the organ of the sense
of touch.  It is  of so slight and so
soft a texture, that the nerves of touch
may   readily  receive  impressions
through it.   It is composed, as you
will see in the next chapter, of many
layers of  minute  round  cells,  the
outermost  layers being  made up of
these cells broken, and emptied of the
fluid  which  they contained.  The
true skin, which  the cuticle covers, is
of a fibrous  texture, with a  good
supply of both nerves and blood ves-
sels.  On the surface of this true skin
next to the cuticle are eminences called
papillae.   In these are seated the ex-
tremities  of the nerves  of  touch.
Fig. 58 represents a highly magni-
fied section  of a bit of the skin from
  Vertical section of the
SOLE  OF THE FOOT. 
120               HUMAN PHYSIOLOGY.
        Tubing in the skin.  Insensible perspiration.  Sebaceous glands.

the sole of the foot; a is the cuticle ; c is the true skin ; b re-
presents the papillae.   You observe that the deepest layers of
the cuticle,  next to these  papillae,  are  more colored -than the
outer ones.  The coloring  matter of  the  skin is situated here.
You observe  also a tube which runs up  through the  cutis or
true skin  and the cuticle,  and in the latter part of its course
has a sort of cork-screw arrangement.  This is  the discharging
tube of the sweat-gland, d, lying within the true skin, and sur-
rounded with globules of fat.   These glands are more numer-
ous in some parts of  the skin than in  others.  They are par-
ticularly numerous on  the palms of the hands, and on the soles
of the feet.   Mr. E. Wilson  counted, with  the  aid  of  the mi-
croscope, 3528 of^ them in  a square  inch on the  palm of the
hand.  Reckoning the length of one  of these at one quarter of
an inch it gives 882 inches or 73£ feet of  tubing in this small
space.  He calculated the  amount of this tubing in  the skin of
the whole body  as  being  48,600 yards, or nearly 28  miles.
The amount of excretion from the seven millions of these tubes,
which open on the  surface of  the skin,  is  very great.   Many
experiments have been tried to determine what the  amount
is in 24 hours, but approximations  only to the truth, of course,
could be  obtained,  and the  results  of the experiments  have
differed much.  While the excretion is  great in amount, it is
very  important.  It is, as  you  have  seen  in  the  chapter on
Respiration, a great  means of  regulating the  temperature of
the bodj'.  It is also the means of discharging from the body
a portion of its waste.  This waste is  dissolved in  or mingled
with  the  water or vapor  of the  perspiration.   The perspira-
tion is ordinarily insensible, as it is  termed ;   that is, it is in the
form  of vapor.  But  sometimes, as in  vigorous exercise, when
the sweat glands are rendered very active, chiefly to prevent too
great an accumulation of heat, the perspiration becomes sensible.
   181. There  is  another  set  of  glands  in the skin  called
sebaceous glands,  which  secrete  an  oily  fluid.  They  have
also  thin tubes  like  the sweat  glands.   They  are   most
abundant where  the  skin specially  needs  an  oily  lubrica-
tion,  as  where  there are  folds  in  the  skin  or hairs,  or
where the skin is exposed  to friction,  or to the drying  atmos-
phere.  They are very abundant on the face and head.  The
amount of the oily secretion  of these  glands is very great in
the skin of races fitted to inhabit  warm  climates.  Every hair
has sebaceous glands connected  with  it,  as  represented  in
Fig. 59 ;  in  which b  is  the hair emerging  from  the skin; 
FORMATION AND REPAIR.
121
Influence of labor on wear and tear, and on absorption.
FIG. 59.
       •C
     HAIR
and sebaceous glands.
a a are the sebaceous glands pouring their
secretion by thin  tubes  into  the tube  or
canal in which the hair grows;  c the root
of the hair surrounded with fat globules.
From all this you see that the skin, with
its two sets of glands and tubes, its nerv-
ous  papillae, and its layers of  constantly
renewed cells, making  the  cuticle, is  a
complicated  organ, and  is  thus fitted  to
perform its functions as  an organ of  sen-
sation, and at the same time of excretion,
while it is  also a  pliable but firm  cover-
ing for the body.
   182.  You have seen in the facts  de-
veloped in  this chapter,  that there is con-
stant change going on in all parts of the
body.   Particles which have become use-
less are taken up by the absorbents, while
the formative vessels deposit others to take
their places.  The rapidity with  which
this change  occurs, depends mostly upon
the activity of the individual.   The busy
laborer, whether the labor be bodily or  mental, requires more
nourishment than the indolent man,  because  there  is more
waste in his case, from the wear and tear occasioned by motion
or thought, and there  is therefore a necessity for a larger sup-
ply of repairing material.  The difference,  it is true, is not as
great in regard to mental labor,  as in regard to  that of the
body ; but  still it is very apparent.   This dependence of the
amount of change in the system upon the  degree of activity is
very manifest, if  we compare different  animals  together in this
respect.  I  have  already contrasted  the frog  and  the canary
bird, in regard  to respiration  (§ 156,) and they can  be  con-
trasted  in  this  respect also.   As  the frog  makes but  little
exertion either of body or mind, there is but little change in his
body, and  but little nutriment  is  required  to supply the small
waste that occurs.   But  in  the   ever  active  canary  there  is
much waste from  this action, and therefore  there must be much
eating to supply  the material of repair.  As he sings and hops
from perch to perch, his mind as well as his body is vastly
more active than that of the frog; and so  the  particles in his
brain and nerves,  as well as in his muscles,  are oftener changed.
You see the same thing still more strikingly, if you  contrast
                            11 
122              HUMAN PHYSIOLOGY.
  Change varies in different parts of the body, and in the same body at different times.

the torpid state  of  the  hibernating animal in winter, with his
active  state in the  warm weather.   In his torpid  state life is
dormant, almost at a stand still, sometimes entirely so.  And
the more perfect the quiescence, the less  is the change, and the
less, therefore, the need  of nutrition.   The fat which he  lays
up  in the autumn  (§65)  answers  all  his necessities both for
nutrition and for heat.
  183. The proportion, thus seen to exist between the amount
of change and the  degree of activity,  is exemplified in a com-
parison between  different parts of the body.  In those which
are most actively used the change .of decay and repair is going
on  most constantly.  The  active  muscles and nerves are con-
tinually changing ;  while the bones, which are only passive in-
struments of  motion are changed very  slowly.  And it is a sig-
nificant fact,  that in the  case  of the  muscles and  nerves,  the
waste particles are to a large extent of the entirely useless kind
(§  176), for they  are  mostly  absorbed by  the veins, there
being  in them  but few lymphatics.  That is,  whenever  we
think,  or feel, or move, we  render entirely useless quantities of
the particles which  make up the structure of the muscular and
nervous systems, and these are got rid  of at the proper  out-
lets, while other particles immediately take their places.
  184. It is a very  prevalent notion in the community, that the
human body changes throughout  once  in every seven years.
But you have seen  that the change is very unequal in different
parts  of the  body,  and is dependent to  a great  extent on  cir-
cumstances.  Sometimes  very  rapid  changes occur.  Thus,
when one has been  much reduced by sickness, and then on re-
covery quickly regains his usual bulk, the  body is very exten-
sively changed in a short period of time.  Ordinarily the  cir-
cumstance which most  influences the  change is, as  you have
seen,  the  degree of activity which exists, whether we  look at
an animal as a whole, or at  the tissues separately.
  185. In  this  constant change going on in the  body, life and
death may be said to be brought into very near companionship.
Every  act of the mind, and every movement of the body breaks
down  some of  the  structure; and the particles,  which are no
longer fitted to  maintain the  living functions, must be taken
away as refuse dead matter, and  new particles endowed  with
vital  affinities  must take   their place.    Action,  destruction,
repair,  are the  successive  events  which  are ever occurring in
in every part of our frame.  Action is followed by destruction,
and in  proportion to its intensity; and  repair is necessary to 
CELL-LIFE.
123
          The formative vessels shown by the microscope to be cells.

fit for further action.   And so through life the nutritive func-
tions  are  thus  struggling against  the  tendency to  decay and
death, till at length at the appointed limit the struggle is given
over, the vital affinities release  their hold, the common laws of
dead matter take possession of the body, and the soul passes to
a world where decay  and change are unknown.
                     CHAPTER  V.

                         CELL-LIPE.

   186. In previous chapters, in treating of the construction of
the body, I have spoken of the formative vessels  in  accordance
with  the  common language  of  physiologists.   The  common
idea has  been hitherto, that the work  of  construction is  per-
formed by vessels appended to the capillaries.  The capillaries
were considered as the repositories of the blood,  they receiving
it from the  arteries,  and holding  it in readiness for the  use  to
which it is to be put by the formative vessels.  These formative
vessels, it was supposed, exercised in some way a power of se-
lection in  regard to the constituents  of the blood, and  also a
power of  uniting the  constituents thus  chosen into particular
forms.  In  this way physiologists accouuted for  the formation
of all the different structures in the body.   What shape these
formative  vessels had, or how they were arranged no  one pre-
tended to know.  But of their existence no one  had  a  doubt,
for there seemed to be an absolute necessity for supposing some
apparatus of vessels  appended  to the  capillaries for the  per-
formance  of this function.
   187. But the microscope has  of late years  revealed pheno-
mena  which have changed  our ideas on this subject,  and
which must to  some extent change our  modes of expression in
relation to  it  also.   It has  showed  us agencies which differ
from those which we had supposed to exist.   The subject is an
interesting one, and I  propose in this chapter to give you some
glimpses of this interior life, as it may be termed, of the body.
   188. It is found by the aid of the microscope, that  all the
minute operations of  the system  are performed by the agency
of cells.  They are  not such cells as I described in  § 64 as
existing in the cellular tissue, which are mere  interstices, com-
municating  together.   But they  are bladders or sacs,  and are 
124               HUMAN PHYSIOLOGY.
    Cells when first formed globular.  Seen in the blood and in most other parts.

filled either with a fluid  alone, or with a fluid containing some
grains of solid substance, termed molecules.  The usual form of
the cell when  it first appears is globular or spheroidal.   It is
seldom, however, seen in this form;  for, besides the change of
form from  the pressure  of neighboring  cells, the  cells  them-
selves often  change  into  various shapes, as  you  will see  in
another part  of this chapter.'
   189.  Cells can be seen in the blood.  If the web of the foot
of a live frog be placed  under  the  microscope, you can see
them  sweeping along in the blood vessels, like  so many little
bladders, varying their shape, according as they press on each
other, or on the sides of the vessel.  This is very well  repre-
sented in Fig. 60, in which a portion of the web of a frog's foot
is seen as magnified 110 diameters.   The dark  irregular spots
which you see, as  at 3,3,  are  pigment cells, which give  the
color to the part.
                           FIG. 60.
CAPILLARIES IN THE WEB OF A FROg's FOOT.
   190.  Cells  may be seen in most of  the fluids  besides  the
blood, and also in the solids.   The solid parts  of animal bodies, 
CELL-LIFE.                   125
FIG. 61.
        Character and color of tissues dependent on the contents of cells.

are composed either of cells, or of structures produced by cells,
or of a mixture of these  structures with  cells.   The same can
be said also of plants.   Cells, therefore, are the real formative
vessels in both classes of organized beings.
   191. We have very striking exhibitions of the
cells in the lower orders of animals.   The Hydra,
a  representation  of which is given  in  Fig.  1,
seems to be made up  of little else than  cells.
If you observe under the microscope one  of its
arms, as it moves about, the  motion appears to
be a  motion  of the  cells  upon each  other.
There are no fibres to be seen, to which the mo-
tion can be attributed.   Fig. 61 represents one of
these arms highly magnified.   The cells, as you
see, have somewhat  of a spiral arrangement.
   192. The  character  of many of the  tissues
in the  body  depends  on  the contents of  the
cells.  The cell  itself,  or the cell-wall, as it is
termed,  is considered  to  be  always the  same.
But the contents vary,  and this variation makes
generally the  variation in the  character, and in
the color also, of the various  textures.   For ex-
ample, all the glands are constructed essentially
on the same plan; and  their difference depends
upon the  contents of the cells in them.   Thus
the liver differs from the  tear-gland, chiefly be-
cause the former has cells which fill  themselves
from the blood with the components of bile, while
the  other has  cells which  fill themselves with the  components
of the tears.   The color of various parts, as the  iris of the eye,
the  skin  of the  dark-colored,  the  hair, &c, depends upon  a
coloring matter, which constitutes either a part or the whole of
the contents of particular cells.  So in plants the various colors
displayed  result  from  the various coloring matters which cer-
tain cells contain.  Some contain yellow coloring matter, others
red  &c.   When various colors appear  together in any flower,
there  are, where the colors bound upon  each other, cells lying
side by side which contain different coloring  matters.   And in
the shading off of the  colors, the effect is produced wholly by
the variation in the quantities of the coloring matter in  the cells.
   193. It is  clear from the facts  which have been  stated,  that
the cells  have a  selecting power.  In the body  they take from
the common pabulum  or material, the blood, such  constituents
                               11*
00 o\
In the arm of the
   Hydra. 
126 •             HUMAN PHYSIOLOGY.
              Cells absorb and select.  Cells real laboratories.

or substances as  they need  for  their particular purposes.  I
have  already  given illustrations  of  this, in  speaking  of the
difference in the glands.  This  selecting power is seen in the
cells everywhere.  Every cell  contains  its own peculiar consti-
tuents, which it  has taken from the blood.  For example, there
are fat-cells which receive fatty matter from the blood, rejecting
every thing else; pigmentary cells receiving nothing  but color-
ing matter from the blood, &c.   The same thing appears too
in plants.  There are cells which receive from  the sap volatile
oil;  others, fixed  oil; others, starch;  others, coloring matter,
<fec.
   194. Fluids, and sometimes gases  enter the cells continually.
The  pores  through which  they enter  are  not visible  even
through the  microscope, but of course such  pores  must exist.
Their entrance is controlled by the selecting  power to which I
have alluded.
   195. This selecting  absorption thus performed by cells, as
revealed by the microscope,  is one of the most wonderful  and
mysterious  phenomena in the material world.   There is here
a power in these  cells  which is unaccountable.   The selection
is made by the  little cell as unerringly, as if its pores were con-
trolled by an intelligence residing there.  It has been said  that
this selection is  a mere result of  affinity ; that a certain affinity
exists between the contents of the cell, or the cell itself, for the
constituents which are absorbed.  But if it be so, the mystery
comes no  nearer  to being solved than  before.  For how are
these affinities, so numerous  and various, established, and what
are  the principles by  which they  are governed ?  In  either
case the wisdom and power of the Creator may  be  considered
as  making, in this  minute  interior  life  of all organized  sub-
stances,  some of their most wonderful manifestations.
   196.  There is not only a selecting  power in the cell, but there
is often a  converting  power, by which new compounds are
formed from the  constituents introduced into  it. The cell  in
this case, though  so small as to be seen only by a microscope
of considerable power, is a  real  laboratory,  effecting chemical
changes in its contents.  There  can  often be seen quite a brisk
movement in the molecules in the cell while  these changes are
going on.
   197.  Some cells produce  other cells.  This is  the sole office
of some of  them.  In some cases  new cells  are  made by  a
separation of a cell  into two or more.   A sort of hourglass
contraction takes  place at the middle, by an inflection or  fold- 
CELL-LIFE.                      127
           Different offices of cells. Office of red cells in the blood.

ing in of the inner cell-wall, for the cell has two walls.   At the
same time the cell becomes elongated.   An entire  separation
into two cells is thus, after a little time, effected;  and then each
of these cells  becomes two more, and so  on.   In other cases
cells  are  formed within  cells.   When this takes place, the
nucleus, that is an aggregation or mass* of solid matter in the
cell, separates into two different parts, each of which has a cell
formed around it.
   198. Cells, as you have already seen, do not all perform the
same office, but there are  cells for a great variety of purposes.
A consideration of these will develope to you still  greater won-
ders in the cell-life, and show you in the most interesting man-
ner how great the Creator is in the minute operations of nature,
as well as in those which are large and  obvious to the naked
eye.
   199. There are  different kinds  of  cells in the blood.  There
are colored and colorless ones.   The office  of the colorless ones
has not yet been satisfactorily determined.   But we know more
about the colored ones.  These give  the red color  to the blood.
They are  not  red  when looked at singly,  but are of a yellow
cast;  and the red  color appears only when several are together.
One office of these colored cells  is to carry oxygen to  all parts
of the system, and return the carbonic  acid to the lungs to be
thrown off.  By carrying these cargoes back  and forth in  the
circulation, these  little cells  perform a very important  office.
A very valuable part of the cargo of these cells is iron.   In low
states of the system, when the red  cells  are deficient, the  ad-
ministration of iron in some form  is often found to  be very
effectual,  in connection with a good  diet, in remedying the defi-
ciency.  The  proportion  of  these   red  cells  varies   much  in
different animals.   It  is largest  in  those which  are  the most
active, and  which, therefore, as  you saw in the chapter  on
Respiration, consume the  largest  quantity of oxygen.  The
proportion is greater generally in birds than in the mammalia,
and it is  much greater in the latter than  in reptiles or fishes.
In  man it varies  much  in  different individuals.   These cells
are abundant in the ruddy, strong, and active; while it is other-
wise in the inactive, pale, and feeble.
   200. There are  cells for absorption, and cells for  secretion
  * To the common ear the word mass, which is ordinarily used in relation to aggregates
of some size, seems out of piace when applied to a collection of molecules which is so
imall, that it can only be seen by a microscope of high power ;  but though so small, it is
to the little cell containing it a moss. 
128              HUMAN PHYSIOLOGY.
             Manner in which absorption is performed by cells.

and excretion.  Of these I will give  some examples.   I  have
said in the chapter on Digestion, that the vessels called lacteals
absorb chyle from the contents of the intestine.  It was formerly
supposed that they did  this through their open  mouths on the
surface  of the mucous  membrane.  But  the microscope has
shown that this is not so.  The absorption is accomplished by
cells, which are  developed for this  purpose at the  extremities
of the lacteals.  They take up the  chyle and discharge it into
the lacteals,  and  they are dissolved away in the  very act of
emptying themselves.   A new crop  therefore of cells appears
every time the process of absorption is to be  performed.   And,
what is still more  curious, every time that absorption is to  take
place, there is cast off, as a preparatory step, a sort of pavement
of cells from over every point in the  mucous membrane where
there is an extremity  of  a  lacteal.  The absorbing cells  are
thus uncovered, so that they can perform their duty.  All this
can be  made clear by the following  diagram.  I must premise
that the surface of the mucous membrane of the intestine is not
a perfectly smooth surface, but  examined by a microscope it is
seen to be covered with eminences  and depressions.   Absorp-
tion takes place  on the eminences, while  the depressions are
the seats of secretion.   In the diagram, Fig. 62, you  have  a
                           FIG. 62.
   DIAGRAM SHOWING ABSORPTION IN A MUCOUS MEMBRANE.

representation of the  arrangement  of one of  the  eminences
highly magnified.  A,  represents it as it  is in the  intervals
of digestion when absorption is  not going on, and B as it is
during absorption ;  a a are the absorbent vessels or  lacteals ;
b b basement membrane, as it is termed,  an exceedingly thin
membrane acting as a basement to the pavement cells c c ;  d d, 
CELL-LIFE.
129
              Manner in which secretion is effected by them.

the absorbing  cells.   When  absorption  is not  going on, the
prominence is  somewhat  shrunken, and the pavement  cells
cover it.   There  are  some granules  or small grains, d,  in A,
which are, it is  supposed, the germs of the absorbing cells,
which you see developed in B.  When absorption is taking
place, the  prominence is swelled out as represented, the lacteal
vessels are full, and  the absorbing  cells appear at their ex-
tremities, while the pavement cells  have been thrown off, so
that the chyle may have free access to the absorbing  cells
through  the pores or interstices of the basement membrane.
   201.  While  absorption thus  goes  on  in the  eminences,
secretion takes place in the depressions.   The diagram, Fig. 63,
                           FIG. 63.
    DIAGRAM SHOWING SECRETION IN A MUCOUS MEMBRANE.
represents  one  of  these  depressions,  or follicles,  as  they are
termed,  in two opposite states, when secreting, and when not
secreting.  In A, secretion is  not going on, and the  cells e, in
the follicle remain  quiet.  In B, on the other hand, secretion
is  taking place, and it is done by the casting off of cells, as
represented.   These cells discharge  their fluid  contents into
the cavity of the intestine, and disappear, while other  cells take
their places.   These follicles  are really little glands.  And the
various glands, the salivary glands, the liver, the pancreas, &c,
are made  up essentially of such follicles arranged in different
ways.  You  see,  therefore,   in this diagram,  the manner in
which  secretion is  effected everywhere.  The secreted matter
is received by the absorbing cells, through the interstices of the
basement membrane, from the blood in the capillaries  which lie
under this  membrane.
   202. The  pavement cells,  of which  I have  spoken, cover
every part of the mucous coat or membrane, and  answer as  a
protection  to it.   There is  a  similar arrangement  over  the
whole  outer surface of the body.  Next  to the  true  skin is  a 
130
HUMAN PHYSIOLOGY.
         Muscles made up of cells.  Their contraction and relaxation.

basement membrane, and  upon  these, as in  the  case  of  the
mucous coat of the alimentary canal, lie pavement cells.  These
cells,  constituting the  cuticle or scarf-skin,  are much  more
numerous than  in  the  alimentary canal.  There are many
layers  of them.   The outer  cells dry by exposure to the  air,
and become scales.   As these are rubbed off, the  cells below
take their places ; and there is a constant supply of fresh cells
from the basement membrane.
  203. There are some cells which are devoted entirely to  the
production  of motion, for  an ordinary muscle is composed of
great numbers of chains of cells  included in sheaths bound to-
gether.  A muscle appears to the naked eye to be  made up of
fibres.   Each one of these  fibres is found by the miscroscope to
be composed  of from 500 to 800 fbrillce, or  minute fibres.
And each of these fibrillae is  a series or chain of cells.   In Fig.
64, a, is represented  a  fibre  as seen under  the  microscope,
                          FIG. 64.
FIBRE OF A MUSCLE.         * ltx- Da-
                                 a
showing  the fibrillar  of which it is com-
posed.  They are separated at the broken
end  by the violence  in tearing  the fibre.
In b, you see one of the fibrillar very highly
magnified,  showing  that it is a chain of
cells.  In the diagram, Fig, 65, is repre-
sented the  condition  of a fibrilla in  the
two  states of contraction and relaxation.
In a it is relaxed.   In b it is contracted,
the cells  being shortened, and at the same
time widened.  And as all the cells in the
muscle are thus widened when the muscle
contracts, we  see the  cause  of the well
known swelling out of muscles when  they
are in action.  That you may form some
idea of the size of these cells in muscles, I
will  state that in the space of the square
of a tenth part of an inch, thus,      there  muscular fibril ;
are over  100,000 of these cells. Q When   a relaxed; t contracted. 
CELL-LIFE.                     131
                Hoofs, horns, nails, and teeth made by cells.

a  large  muscle  contracts what an innumerable multitude of
these cells are set in  action !
   204. There are cells whose  office it is to make certain solid
deposits.   Hoofs, horns, nails,  and teeth are made in this way.
Even the  hard  enamel of the teeth  is constructed by cells.
They deposit it in the form of prisms of hexagonal shape as
seen in Fig. 66, which represents a vertical section  of enamel
as seen under the microscope.  Their shape is more plainly seen
in A, Fig. 67, which represents a transverse section of enamel.
The line of these prisms is generally wavy,  but they  are for the
most part parallel to each other.  At B are some of these prisms
separated.  They are more magnified here than in Fig. 66.
                           FIG. 66.
A, Transverse section. B, Separated priams of it.
   205. Perhaps the most wonderful exhibitions of the functions
of the cell  are presented to  us in the nervous system.  The
nerves are bundles of tubes of  exceeding  fineness.  They vary
from TeVoth to i u,oo uth of an inch in diameter.  Now, each
of these little tubes,  or  tubuli,  as they are called, was once a
chain of cells.   The  cells in each chain or row,  as the micros- 
132
HUMAN PHYSIOLOGY.
   Nerves composed of tubes made from cells.  Cells in the gray substance of the brain.

 cope has shown, gradually became incorporated together to be-
 come a tube, and in this tube is  contained  the true nervous
 matter.  And it is supposed that each of these tubuli  preserves
 itself separate and distinct, from its origin in the  brain, or some
 other of  the central organs of the nervous system, to its ter-
 mination in some fibre, or on  some surface.  For no communi-
 cations between the tubuli have ever been found by any micros-
 copist.  The manner in which these tubuli are made from cells
 may be illustrated by the diagram
 in Fig. 68,  in which the  steps by          fig.  68.
 which the row of cells A  becomes     A                 B
 the tube B are represented.           Q
   206. It  is  these tubuli,  thus     Q
 formed from cells, that constitute     O
 the means of nervous communica-     Q
 tion  between all parts  of  the  sys-     O
 tem.  Thus,  when a  muscle con-     O
 tracts in obedience  to the  will,
 an impression is conveyed through those tubuli that connect the
 brain with the fibres of the muscle, or rather with the cells of
 which these fibres are composed.  These tubuli  exist in all the
 nerves, and in the white parts of the brain and spinal  marrow.
 They transmit, but they have  nothing to do with originating
 what is transmitted.  This is done by another part  of the nervous
 system, the reddish gray substance, which is seen in the brain
 and spinal marrow, as entirely distinct from the white  portion.
 This gray substance, in which all nerve force, as it is  termed, is
 produced, is made up chiefly of cells.   These cells, which  have
 a nucleus or central particle, are originally globular, but many
 of them assume various shapes, and often  shoot out branches.
 Some of the shapes are very fantastic as represented in  Fig. 69.
 These are magnified 200 diameters.
   207. In the views which I have given of cell-life, I have not
 attempted to describe all the phenomena which have been dis-
 covered, but only enough of them to give the student a general
 view of this  interior  unseen life, that is  at work so busily at
 every point of every living substance.  The cell, you have seen,
 performs a great variety of functions.   It is the agent by which
all vital operations are  carried on.  The very beginning of  life,
so far as we can see, is in the cell which the microscope reveals
to us.   Its first manifestation is here.   We can suppose a germ
as the origin of a cell, but we do not see it if it exist.
   208.  All  animated  nature  is built up  by cells.  The first 
CELL-LIFE.
133
All organized substances built up by cells.
NERVE CELLS IN THE GRAY SUBSTANCE.
thing which  comes  from the supposed germ is  a cell.   And
this single cell is the parent of  all the cells which build up the
whole structure, whatever it be.   It is by these cells thus pro-
duced, that all plants and animals are constructed.   "A globu-
lar mass,"  says Carpenter,  " containing a large number of cells
is  formed  before any diversity of parts shows itself; and it is
by the subsequent development,  from this  mass, of different
sets of cells, of which some are  changed into cartilage, others
into nerve, others into muscle, others into vessels, and so on,
that the several parts of the body are ultimately formed.  Of
the cause of  these transformations, and of the regularity with
which  they take place  in the different parts, according to  the
type or plan  upon which the animal is constructed, we are en-
tirely in  the  dark;  and we may probably never know  much
more than  we do at present."
   209.  A beautiful exemplification of what has just been stated
is  seen in the development of the animal in the interior  of an
egg, and particularly in the  egg of the bird tribe.  By an ex-
                             12 
134              HUMAN PHYSIOLOGY.
                  Arrangement of the parts of the egg.         __________

amination of different eggs at different stages of the process of
hatching, the various  steps in the  development of the animal
have been observed and noted.  It is a series of most wonderful
processes,  that go on  concealed from our  view  by that sym-
metrical inclosure of lime.   Of  these I will present the general
outlines.   In the middle of  the egg is  the yellow  yolk, com-
posed of albumen and oil globules.  It is surrounded by an ex-
ceedingly thin sac, which keeps it separate from the albumen,
the white of the egg that envelopes it.  The yolk, b, Fig. 70, is

                           FIG. 70.
SECTION OF A BIRDS' EGG.
lighter than the white, and it therefore always seeks the highest
point in  the egg.   But there is a particular contrivance which
prevents it from actually touching  the  shell.   It is held down
by two very delicate ligaments e,e, connecting it with the white
lining of the shell.  And you will observe,  too, that the  cica-
tricula, or germ-spot, a, which is a collection of cells beginning
the process which is to  form the animal, being lighter than the
yolk is always at the top of it, in order  to receive  the warmth
from the body of the bird as it sets upon its eggs.   Besides all
this, there  is at the blunt end of  the egg, f, a bubble of air
which is intended as  an invigorating  draught  for the  lungs
of the young bird, preparatory to its bursting its  shell.
  210.  When the processes preparatory to the formation of the
animal commence,  the yolk itself is composed in part of cells,
as represented  in Fig.  71,  A.  In the midst of it there  is a
germinal spot, a, with  a vesicle in it, b.  This vesicle produces 
CELL-LIFE.
135
Succession of cells in the yolk before the animal is formed.
   DEVELOPMENT OF CELLS IN THE YOLK DURING INCUBATION.

a  cluster of cells.   But these cells, and  those which in part
compose  the yolk  are  temporary, and  all disappear.  Before,
however, the cluster of cells in  the  germinal spot disappear,
there are seen  in  the  midst of them  two twin  cells.   These
multiply ; and what is  singular, they do it by doubling, so that
there are successively  4, 8,  16, 32, &c.   At length  there is a
mass of  them, like a mulberry, as at e, in B.  This  mass then
sends off cells at its edges which  makes  a layer,/, all  round
the  yolk as represented  in  C.   A second layer, g,  is formed
inside of the first  as seen in D.  In  the case  of the higher
animals a third layer is added.
   211. There  is no formation of the animal yet.   But  now a
single large cell appears  in  the  centre of the mulberry-shaped
mass of cells, and from  this begins the formation of the animal.
All the other parts of the egg—the cells, the yolk, the white—
are  tributary to the   action which proceeds from  this cell.
Within its wall is a ring-like nucleus.   This takes  the shape of
a  pear,  and  then   it is  afterward very  much like  a violin.
From  this  nucleus are  produced  cells which  form  all  the
various parts of the animal, the heart,  lungs,  stomach,  brain,
limbs, <fec.   And these  are made out of  the yolk and the  white
of the egg. 
136              HUMAN PHYSIOLOGY. ____________
      Office of the allantois.  All animals and plants come from simple cells.________

  212.  There is one contrivance made use of during this  de-
velopment of the  animal, which  must not pass  unnoticed.   A
very delicate bag, called the allantois, is formed, which is attach-
ed to the embryo, and at length almost envelopes it.   The office
of this is to  expose the blood of the embryo to the air.  This is
accomplished through the pores of the shell, against which the
allantois with its  minute blood-vessels presses.   This organ is
in fact  the  temporary breathing apparatus of  the  developing
animal.   The development  can be arrested  by smearing  over
the egg with some substance that will prevent the entrance of
air  through  the shell.   When the  animal is fully developed,
and is  ready to  come forth  from his prison, he  inhales the air
provided  for him, as before described, and with  the strength
given to him by the stimulus of  the air in his lungs, he bursts
the crust of lime that incloses him.
   213.  I have  described these processes which take place in
the egg, in  order that  you  may see the  mysterious  connection
between the simple cells that form  in the beginning, and the
full development of the  complete and diversified  organization.
In  the formation  of all  animals, and we may say plants  also,
there is a similar  connection, varied  of course according to the
circumstances of each case.   As  we  observe the various steps
of the process, the mind  is filled with wonder.   As we look at
the egg, containing nothing but a yolk surrounded by albumen,
with its little cell  of air at the end, and see it wholly separated
from every  living  organization, shut up entirely by itself in  a
wall of lime, we can hardly believe that the mere  application
of beat will  cause in the contents a series of processes, which
will result in an animal  so  complete, that it can burst its own
prison walls, and,  as is the  case with some of the  tribe, at once
walk forth into the open air.   The processes by which all  this
is effected have been  narrowly watched by the eager eye of
scientific inquiry;  but the mystery remains unsolved, and pro-
bably to man it  will always remain so.
   214.  From the  views which I have presented in this chapter
it is manifest, that the grand distinction between organized and
unorganized substances  is to be found  in this  cell-life  of the
organized.  In unorganized substances  particles  or  molecules
are  the  only things which  we know of as being  concerned in
their formation.   But in the construction of  organized  sub-
stances  or beings, every thing is done by the  agency of cells.
And in this cell-life of the living  world we have another beauti-
ful example of the divers and almost numberless results, which 
CELL-LIFE.
137
       The power of the Deity shown in the minute operations of Nature.

the Creator works out by simple  and single means.   As gravi-
tation holds  atoms together in masses of every size from  the
minutest to the largest, and keeps  the  mighty orbs in their
appointed circuits, so the cell-organization constructs and moves
all  living things, however small, however large, and however
diversified.
   215. As we examine the various workings of this cell-life, we
can not  but  perceive the truth of the old  adage, Natura in
minimis  maxima est—nature is greatest in its smallest things.
The power of mere bulk or  mere force we can comprehend by
mental addition, however great  that power may be.   We  can
imagine  a power which we  see, to  be indefinitely multiplied,
and thus can form the idea  of immense power.  But  when
with the microscope we  see  minute  cells  working out such
results as we have contemplated in this  chapter,  and inquire
how it is done,  we  see that there is a hidden  power here that
utterly defies our conception.   The mechanics and the chemis-
try of the cell, who can understand them ?  From the inscruta-
ble movements  of this hidden power, at work wherever  life is,
in the  cells, its  laboratories, we get  a  higher  idea of Omnipo-
tence than we can  get from the grandest  and most terrific ex-
hibitions  of mere force.   We get from them the idea of an all-
pervading, as well as an all-wise power, working not merely in
every locality, but at  every point of the universe.   And  the
revelations which the microscope makes to us seem to draw us
very near to the Infinite.  As we gaze with wonder and delight
at the secret operations of his power thus opened  to us, we seem
almost to be admitted to his presence; and even our awakened
curiosity, amid the wonders now brought into our field of vision,
does not  suffice to remove the awe which almost oppresses us.
   216. How great  is  the  inner beauty  of the living  world
around us !   We admire the symmetrical  forms,  and the beau-
tiful colors  which  nature presents to  us  in such variety;  but
there is an inner world of beauties throughout nature, still more
perfect and resplendent, which is hidden  from the naked  eye
of man, though it is all open to the Omniscient.   If you would
get some idea of the beauty of  this inner world, take the most
delicately beautiful of all the specimens of man's workmanship,
and examine it with a microscope; and then  compare it with
some living  texture or coloring.  Compare  in  this  way,  for
example, the most perfect painting of a flower with the flower
itself.  The painting loses all its beauty as it is magnified;  but
in the  bosom of the flower the microscope  developes to you
                            12* 
138
HUMAN PHYSIOLOGY.
              The inner beauty developed by the microscope.

beauties far transcending those which are seen by the unassisted
eye.   Even such  living structures  as  are  unattractive to  the
naked  eye,  present under  the microscope wonderful  beauty in
the delicate lines of their textures.   It is true of every one  who
has used this instrument in his observation of nature,  that he is
impressed with the fact, that great as is the  beauty of nature,
as we  look out upon it, it is  vastly inferior both in kind and in
amount to  that  inner  beauty seen so completely by  the  all-
seeing  Eye, and now developed to  us in part by the skill and
ingenuity of man.   And it  suggests to us the  hope, that in a
new state of being, and with higher faculties, we shall  be  able
to look farther into these  inner beauties of the universe, than
we now can with all the aids which our ingenuity can devise. 
PART THIRD,
                          CONTAINING)

CHAPTER X.—The Nervous System. CHAPTER XI.—The Bones.  CHAPTER XII.—The
  Mosclb. CHAPTER XIII.—The Language of the Muscles. CHAPTER XIV.—The
  Voice.  CHAPTER XV.—The Ear. CHAPTER XVI.—The Eve. CHAPTER XVII.—The
  Connection of the Mind with the Body.  CHAPTER XVIII__Differences between
  Man and the inferior Animals.  CHAPTER XIX.—Varieties of the Human Race.
  CHAPTER XX.—Life and Death.
                     CHAPTER  X.

                    THE NERVOUS SYSTEM.

   21*7. Thus far we have contemplated man merely as a struc-
ture.   We have observed the  means  by which the body is
built and is kept  in  repair.   We have seen  that in  regard  to
these functions of nutrition, man and  all animals have much in
common with plants.   So far as these functions are  concerned,
they vary from plants only in the modes by which the nutrition
is  effected.   The  difference  in this respect is not an essential
one.  The absorbents in the root of the plant do for the plant
what the lacteals in the digestive  organs do  for the animal,
the  difference between  them  being  only  according to  the
differing circumstances.   So also, circulation  and formation are
in  all essential points the same  in these two  different depart-
ments of animated nature.  The microscope has in the most
striking manner shown this to be true of formation, for vegeta-
bles and animals are alike  constructed, as you  have seen, by
cells.
   218. The functions of which I have treated in the previous
chapters, as being common to plants and animals, are  called the
functions of organic life, because they  concern merely  the struc-
ture,  the organization.   But  there are other  functions.   The
body, with all its  complicated  parts, is  constructed and kept in
repair for certain uses.   These uses are secured by the nervous
system,—a system, which I have spoken  of in § 32, as being
superadded to what the animal has in common with  the plant,
and which, therefore, constitutes the essential difference between
the animal and  the  plant.  This system  furnishes the  means
of the relations of the animal  to the world  around him.   He
receives  his  impressions from  external things  through  this 
 140               HUMAN  PHYSIOLOGY.
             The nervous system and its subordinate instruments.

 system ; and  through it he acts upon external things.   He
 feels  through  the  nerves,  and  by the nerves  excites  those
 motions  by which  he acts  on both material  and  immaterial
 existences.   The  functions,  therefore, which   are  performed
 through this system,  are  called functions of animal  life, in dis-
 tinction from the functions of organic life,  which  are common
 to vegetables and  animals.  They  are sometimes  also called
 functions of relation, in  view of the relations  which it estab-
 lishes  between sentient  and moving  beings,  and all external
 things.
   219. But there are intermediate instruments, through which
 the nervous system exercises its functions.   The  nerves do not
 themselves move, but they excite motion in muscles, and these
 move bones and other parts.  Neither is  sensation  performed
 by the nerves  alone.  The different senses, for example, have
 different organs, with arrangements differing  according to the
 kind of  sensation.   Mere nerves do not alone  see, or hear, or
 taste, or  smell, or touch.   There are special organs constructed
 for these purposes ; and  through these the nerves receive im-
 pressions.   Thus the nerve of sight cannot of itself see; but
 the eye being there, so formed  as  to have  pictured on a mem-
 brane  the images of objects, the  nerve receives an  impression
 from these images,  and this impression  is  transmitted through
 the trunk of the nerve to the brain,  where  the  mind takes cog-
 nizance of it;  and this constitutes seeing.
   220. While then  the  nervous  system is the great essential
 means of connection between  the  mind and   external  things,
 there are other subordinate means,  as we  may consider them.
 They are organs of various kinds, through which the nerves  act
 and are acted upon.  The nervous  system, therefore,  may be
 viewed as presiding over  the sentient and moving machinery, in
 the complex structure of the human  system,  which we have
 been examining in the previous chapters.
   221. The nervous system in the lower  orders of animals is
very simple, and forms an exceedingly  small part of the  animal.
But, as we rise in the scale, we find that, as the limits of rela-
tion  to  external things  enlarge,  this system becomes  more
prominent;  till, in man,  in whom these relations, both  mental
and  physical, are much  more extensive  than in  any other
animal, it is very prominent and greatly complicated.
   222. The interest of the class of subjects, now to  be  opened
to you, much transcends  that of the  subjects  which we have
already gone over.  If you  look at a child as  it first opens its 
                  THE NERVOUS  SYSTEM.             141
            All knowledge acquired and communicated by nerves.

eyes upon this world, you see a  being, whose  senses are com-
mencing their work as  inlets of knowledge to  the soul within.
Nothing is  known at the outset, of shapes, or colors, or dis-
tances,  or any other relations of things.   This  is  all to be
learned, through the nerves and their subordinate organs.  And
as all knowledge is acquired through the nerves, so it is com-
municated through nerves to  others.  It  is communicated by
the motions that are excited  in the muscles by  the nerves—the
motions of the countenance varying its expression ; the motions
of the limbs, or gestures ;  but especially by the motions which
produce and articulate the voice.   Thought and feeling can be
communicated in no other way than by muscular motion.
   223.  From what has now been said, you readily see, what
will be the subjects of  the third part of this book.   They are
those which relate to the nervous system and its connections or
dependencies.  They are, the nervous system itself; the organs
of locomotion, the muscles, and the bones; the voice ;  the ex-
pression of the countenance, and  the language of the muscles
generally ; the senses,  with  their organs;  instinct;  thought;
reason.
   224.  As preparatory to  a particular view of  these subjects, I
will give you  a general view of  the nervous system, with the
functions performed by  the various parts of it.   I  shall reserve
for another  chapter a  particular view  of  some of the higher
functions of this system, and a consideration of some subjects,
which we can better  examine after we have  considered the
organs of locomotion and the senses.
   225.  The  nervous  system may  be considered as  having
three parts ; 1, certain central parts,  as the brain and  spinal
marrow;  2, nervous trunks,  which  going  from these  central
parts  divide and subdivide, as the arteries do, till  they become
exceedingly minute; and 3,  the  nervous expansion  in the
organs, having a relation to the nervous trunks similar to that
which the capillaries bear to the arteries.  In what we call sen-
sation we  suppose that  an  impression is produced  in the  nerv-
ous expansion, that the trunk serves  to transmit it, and that
through the  nervous centre,  the  brain, it is communicated to
the mind.
   226.  Let us see now what is necessary to this compound act,
termed  sensation.  First, it is  necessary that the  organ where
the nerve  is expanded be in a condition to let the nerve  receive
the impression.   If the eye be so injured  in its textures, that
the impression  can not be  made on the nerve,  there can be no 
142               HUMAN  PHYSIOLOGY.
         Necessary conditions of nervous action in sensation nnd motion.

vision.  So, too, of the other senses.  Taste and smell are often
impaired, sometimes even destroyed for a time, by an inflam-
mation of the mucous membrane, on which the nerves devoted
to these senses are expanded.  This is sometimes the case in a
common cold.   It  is  necessary  also,  that  the  trunk of the
nerve be in  a  proper condition.   If the nerve  of vision  be
pressed  upon by  a  tumor, there will be no  impression trans-
mitted from the images formed in the eye.  So, too, if a nerve
going to any part of the body be cut off, there can be no trans-
mission  of  impressions to the brain from that part.   Again, it
is necessary to sensation, that the brain should be in a state to
communicate the impression to  the mind.   If  the  brain  be
pressed   upon strongly  by a  depression of the  skull  from
violence, or by effusion of blood by the rupture of an artery, as
sometimes  occurs in  apoplexy, there  can   be no sensation.
Excitement of mind, too, sometimes prevents the occurrence of
sensation, by its action upon the connection between the mind
and the brain.  The pain of a wound received in  battle is often
unfelt, until the excitement of the battle is over.   The aching
of a tooth is often stopped by the excitement consequent upon
going to the dentist to have  it extracted.  I once burned my
hand in the beginning of  a chemical lecture, but felt no  pain
till I had  finished  it, and then  the pain  was  at once  very
severe.   In these  cases the cause of the pain is acting all the
while upon the nervous  extremity, and the trunk of the nerve
is capable of transmitting the impression, but the state of the
mind is  such, and  such is the consequent  condition of  the
brain, that  the sensation  does not occur—one link in the neces-
sary chain  is defective.
   227.  The same can be said, in  regard to the  necessity of
each of these links  of the chain, in relation to voluntary mo-
tion, as  well  as sensation.  The brain  must be in a condition
to be acted  upon by the  mind;  the nervous trunk must  be
capable   of transmitting the impression ; and the muscle must
be in such a state,  and in such connection with  the  extreme
nervous fibres, that it  can respond to the call of the brain.
   228.  Before  going further, I will give you some idea of the
proportions and  arrangement of  the  central  organs  of  the
nervous  system.  In  Fig. 72  you  have presented a  general
view of this system,—the central organs with the nerves going
out from them.   At a is the cerebrum, the  upper large brain,
filling up  a  considerable  portion  of  the skull;  at 6 is the
cerebellum, the lesser brain, lying beneath the cerebrum at its 
THE  NERVOUS SYSTEM.
143
General plan of the nervous system.
FIG. 72.
NERVOUS TRUNKS IN  MAN. 
144
HUMAN PHYSIOLOGY.
                  Hemispheres and lobes of the brain.

back part: at c is the great facial nerve, the chief nerve of the
face;  the spinal marrow, d, sends off  branches on either side
in its whole  length ;  at e is  the brachial plexus,  a bundle of
nerves coming from the  spinal marrow,  which  here  unite
together, and are then distributed to all parts of the arm ; at i
is a  similar  plexus from which  are distributed nerves to the
lower extremity; /, g, and h point to different nerves  in the
arm,  and I, m, n, and o  to different nerves in the leg.  You
observe that the whole  of this nervous system is  divided into
exactly similar halves.  The  cerebrum and  the cerebellum are
both  double  organs, and the nerves of  one side  are just like
those of the other.
   229. Having thus  observed the  general arrangement of the
nervous system, I call  your attention next to the  arrangement
and  structure of the brain which are seen in Fig. 73.  This
                            FIG. 73.
          h i k  m   e
BRAIN AND NERVES.
Figure presents to view a perpendicular section of the brain, as
made from front to rear, dividing  it into two  halves.  You
have here a view of the inner surface of one hemisphere, as it is 
THE NERVOUS SYSTEM.
145
             Cerebrum. Cerebellum.  Convolutions.  Membranes.

 termed, of the cerebrum, the large upper brain, which is com-
 monly described  as having three  lobes  or divisions,  a, the
 anterior; 6, the middle;  and c  the  posterior.   At /  is the
 broad  band of white  fibrous  matter, which  unites  the two
 halves or  hemispheres together, of course  divided  in the
 section ;  at d  is the cerebellum showing a peculiarly beautiful
 arrangement, called the arbor vita,  or tree of  life; at g is the
 beginning of the optic nerve which goes  to the  eye;  I is the
 nerve of smell; e is the commencement of the spinal marrow.
 The  many nerves  which  you see,  are  distributed to  various
 parts of the face; the nerve at h  goes to  the  tongue;  at i to
 the throat, and at m to one of the muscles of the eye.  From
 the beginning  of the spinal marrow go forth many nerves, one
 of which, k, is  a very important one, as it sends off branches to
 the lungs, the  heart, and  the stomach.  It is  this part of the
 nervous system, the top of the spinal cord, that it is most im-
 mediately essential  to the continuance  of life.  For  it is  by
 their nervous connections  with  the  top  of the spinal  marrow,
 that the heart  and lungs continue to perform their duty.  It
 has been ascertained, by experiments upon  animals,  that the
 cerebrum, and  even the cerebellum,  can  be destroyed, and yet
 the animal will continue to breathe,  and  the circulation will go
 on for some time.   But  the  moment  that this  part of the
 spinal cord, from which the heart  and lungs  are supplied with
 nerves, is destroyed, the  breathing and the  circulation stop
 and the animal dies.  So, too, in  apoplexy, if the effusion  of
 blood  take  place at the top of the  spinal marrow, death will
 occur  more certainly, and in much shorter  time, than if the
 effusion take place in the cerebrum or cerebellum.
   230. You observe that the cerebrum  has deep  irregular
 furrows on its surface, and  that it presents  undulating tortuous
 projections.   These  are  called the convolutions of the brain.
 Into the furrows between  them dips down the membrane,  in
 which branch out the arteries that supply the brain with blood,
 and the veins that return it from this organ.    This membrane
 is from its soft  and delicate texture, called the pia mater (pious
 mother), while  the stout fibrous membrane, which  lies outside
 of this next to  the  bony covering  is called the dura mater, or
hard mother.   The  names are  entirely inappropriate, for the
latter serves  as a  protection to the brain, and the former is
 merely  a vehicle or medium for  the entrance of the  blood
vessels  into the  brain.  There is another  membrane  lying
between these  which is called the arachnoid  membrane,  be-
                           13 
146               HUMAN PHYSIOLOGY.
          Gray and white substance. Proportions and arrangement.

cause  in  its tenuity and delicacy -it resembles  the spider's
web.   It is  one of the  serous  membranes, and it serves as a
protecting envelope to the brain, and  at the same time by its
serum, keeps this organ bedewed with moisture over its whole
surface.
  231. The substance of which the brain is composed  is very
soft, something like blanc-mange.  It is the softest organ in
the body.   It is not uniform  throughout  in color.   All  around
the white inner part of the brain there is a thick layer of gray
substance.   In Fig. 74 you have  a  horizontal section of the

                            FIG. 74.
SECTION OF THE BRAIN.
brain, showing the proportions  and arrangement of the  gray
and the white substances.  As the gray substance dips down,
as you  see  in the figure,  into  all the furrows,  its extent is
greater  than you  would suppose at the  first view.  In the
middle  is  represented  the  broad  connection  which  exists
between the  two hemispheres of the  brain.  You observe in 
THE NERVOUS SYSTEM.
147
The gray substance made of cells, the white of tubes.
 Fig. 73, and Fig. 74, that there is no apparent arrangement of
 the external parts of the brain, which would give countenance
 to the idea of the phrenologist, in relation to a division into
 particular organs.  The convolutions, so far  from presenting
 any well defined arrangement, are exceedingly irregular.
   232.  The gray substance, which  is sometimes called  the
 cortical (bark-like) substance, because it surrounds the white
 central part of the brain, is made up, as I said in the Chapter
 on Cell-Life, § 208, of cells, while the white part is composed of
 exceedingly minute tubes.   These tubes are continued  into the
 nerves, and as they hold the nervous matter, they constitute the
 medium of communication between the  brain and all parts of
 the body.  This function of communication is the sole function
 of the white nervous matter.  In the brain this white matter is
 a mere collection of tubes, and these branching out in bundles
 form the nerves.  These  tubes are supposed  to  be entirely
 separate from  each other, from their  beginning in the brain to
.their termination in  the various  parts  of  the  body, for the
 microscope, as stated in § 205, has never discovered any union
 between them at any point.  The brain then is a great central
 organ of communication,  where innumerable  minute tubes are
 brought together, each of which is  connected with some one
 moving fibre, or  some one sensitive point in the  body.   Those
 which are connected with mus-
 cular  fibres transmit  impres-
 sions  from  the  brain,  and              FIG- 75-
 those  which   are connected
 with sensitive points  transmit
 impressions  to   it.    Of  the
 size  of these tubes you  can
 judge   by   Fig.  75,  which
 shows  some  of  them  as  they
 appear  magnified 350 diam-
 eters.   They vary much  in
 size, but  the  cause  of  this
 variation  has  not been  dis-
 covered.
    233. The office of  the gray
 substance,  it  is  quite  well         nervous  tubuli,
 ascertained,  is  very  different          Magnified 350 diameters.
 from  that of the white  sub-
 stance,  as  the  difference  in
 its  structure  would lead  us  to suppose.  It is more  nearly
 
148               HUMAN  PHYSIOLOGY.
      Office of the gray substance.  Proportioned to the amount of intelligence.

connected  with  the mind than the white substance.   When,
for example, motion is produced  in obedience to the will, the
impression producing  the motion  is  transmitted  through the
white  matter, but  the  cause of this impression  does  not act
directly  on this matter.  The impression  is  caused  by the
action of the mind on the gray matter, and the  white substance
only serves to transmit it.  The gray matter,  therefore, has a
more active  agency than the white in the phenomena  of the
mind and the nervous  system.   It  is the first link in the chain
of connection between the  spiritual and  the physical  in our
nature.  Hence, in examining the brains  of animals, we find
that the higher is the intelligence, the more  abundant is the
gray  substance; and  it is  especially abundant in man, by the
large development of the convolutions.
   234. The  question  arises  here,  whether,  as  in motion the
active agency is on the part of the gray matter in the brain,
there is  also gray  matter at the extremities of the nerves  of
sensation, exerting an active  agency there.   It would seem that
it  should  be  so.   When  voluntary motion is produced, the
action of the mind is on the gray substance, and the white sub-
stance of the  brain and the nerves transmits the impression of
this action.  But in sensation the first step in the process is not
in the brain, but in the nervous extremities.  Now in this first
step, in the  actual production of the impression  to be trans-
mitted to  the brain,  we should suppose  the  gray matter as
necessary as in  the production of the impression to be trans-
mitted from the brain  in effecting  voluntary motion.  Else we
must conclude,  that, while  the white substance  can have no
active agency in the  brain, but serves only for transmission, at
its other extremity, expanded in the organs, it  serves for  both
transmission  and  production.  Dr.  Carpenter supposes, there-
fore, that there is a sort of gray matter in the expanded extrem-
ities of all  nerves of sensation.   But the microscope has never
discovered  the existence of  this matter in any nervous  expan-
sion, except in the nerve of  the eye, in the retina,  and in some
parts  of  the internal ear.   And some facts  seem  to militate
against Dr. Carpenter's view of the subject.   If, for instance,
you hit the trunk of a nerve, as the little  nerve so often hit at
the elbow, a sensation  is produced, which is in some measure
referred  to the  part to which the  nerve is distributed.   From
such facts it would appear, that in  sensation the white nervous
matter does  not  merely  transmit impressions,  but  has an
agency also  in   originating  them.  There  is  then probably 
THE NERVOUS  SYSTEM.
149
   The gray substance well supplied with arterial blood.  Ganglions and plexuses.

no gray matter  ordinarily in the  expanded  extremities of  a
nerve, but they  are merely  terminations  of  the tubes which
make up its trunk.
  235. The cells which form the peculiarity of the structure of
the  gray substance are often, as you saw in Fig. 69, of very
singular appearance from their prolongations.  They lie in  the
interstices  of  a  vascular network.   A due supply  of arterial
blood is absolutely essential to the vigorous performance of  the
functions of the gray  substance.   If the supply be cut off in
any  way, as by  the failure of the  heart's action in  fainting,
insensibility and  the loss of the power of motion  are the conse-
quence.   While  the gray substance is on the outside of  the
brain, it is on the  inside of the  spinal marrow.  It is also on
the inside of the little bodies called ganglions, scattered here
and  there, as depositories of nervous  force, or as little brains, as
we may term  them.  These ganglions are not merely a part of
the  apparatus of  communication.   They are different  from
plexuses, which  are mere combinations  of nervous trunks, as
seen in Fig. 77,  t  t being the trunks, which, after uniting with

                           FIG.  76.
each  other in various ways, again  separate  to go to their
different destinations.  At g, in  Fig. 76, is a  ganglion into
which the  fibres / of the  nerve n run.   It then divides  again
into branches b.   These ganglions produce nervous force, and
therefore are composed like the brain in part of gray substance.
The spinal marrow, too, produces as well as transmits, and so
                            13* 
150
HUMAN PHYSIOLOGY.
Changes in the nerve-cells.  Termination of the nervous fibres.
this substance forms a part of it.   This gray substance, as it is
in constant operation, is subject to much wear and tear, as  we
may express it,  and therefore the changes  of repair are con-
stantly  going on  in its  structure.  Hence, the .necessity for so
large  a  supply of blood, as is secured by the network of vessels,
among  which the cells peculiar to this substance are scattered.
The microscope  has  fully  demonstrated the  reality of these
continual changes, for it shows us, whenever a portion  of this
substance is  examined by it, the  cells in all the various stages
of development mingled together.  The freshly made simple
cells are seen among those which  have  been formed for some
time,  and which have put forth their long off-shoots, as seen in
Fig. 69.
   236.  The  extremities  of  the fibres, or rather  of the tubuli
(Fig. 75) of the nerves terminate variously.   The most common
termination is in loops, as seen in  Fig. 78, which represents the
FIG. 78.
; lM?
MB
NERVES OF  TOUCH
OF THE THUMB.
termination of the  nerves  as seen through the microscope in
a thin perpendicular section of the  skin  in the thumb.  The
three eminences in this figure are those of the papillae, as they
are termed, which you can see are arranged in curvilinear rows,
if you look at the ball of the thumb.   In Fig. 79 you see this
same loop-like  arrangement in  the nervous tubuli, as  seen
through  the microscope, on the  sensitive sac that lines the
cavity of a tooth, the  entrance for the nerves and bloodvessels
©f this sac  being at the end of the root.
  237. One very singular termination  of  the  nervous tubuli, is
in what  are called Pacinian corpuscles,  after Pacini, the first
microscopist that discovered them.   They are found attached
to the nerves in the hand and foot more  often than any where 
THE NERVOUS SYSTEM.
151
Pacinian corpuscles.  Their office not known.
NERVES IN A TOOTH.         PACINIAN CORPUSCLES.
else.   Their structure, which is  seen  in  Fig. 80,  A, highly   ,
magnified, is very curious.   They  are attached to the branches
of the  nerves  on which  they  cluster  by  little peduncles or  '
stalks.  At a  is  the peduncle;  b  is  the nervous  fibre or
tubulus;  / is  its termination in the corpuscle.   The corpuscle
itself is composed of layers of a very delicate fibrous membrane
inclosing  each  other like the coats of an onion, to the number
of sometimes sixty, the inner ones, d, being closer together than
the  outer ones, c,  are.   In B  is represented a  portion of a
nerve of a finger, with clusters of  these  corpuscles of about the
natural size.  Of what use  these singular bodies are we know
not.   But the fact  that  they are always found  in  certain
regions of the  body shows that they are placed there for some
definite purpose.   It has been supposed  by some that they are
minute electrical  batteries, because they bear some resemblance
to the electrical organs found in some fishes.
   238. There is a wonderful fact  in regard to the  healing of
wounded  nerves which must not  pass  unnoticed.   You know 
152
HUMAN PHYSIOLOGY.
               Healing of nerves. Nice fitting of the tubuli.

that if a nerve be divided, all communication  between the part
that it supplies with  branches  and the  brain is  cut  off.   No
impressions can  be transmitted through  it to and from  the
brain.   But the two cut ends of the nerves can grow together,
and the communication  can thus be  more  or less  restored.
Sometimes it is as perfect as before.  Now,  if you call  to
mind the structure of a nervous trunk, you will see that this is
passing wonderful.   It is made up, you will recollect, of tubuli
which are  entirely separate from each other, and each one
of  these goes from  its  origin in the  nervous centre to its
destination by itself.  It is difficult to conceive, therefore, how
the nerve can be  healed without  creating confusion.  For to
avoid this  it would seem  to be necessary, that each little tube
at its cut  end must unite with its corresponding end, and not
with the end of some tube with which it has  no relation.  For
■example, if the  nerve  distributed to the hand  were cut, it
would not  do, as it seems to us, to have tubuli which go to the
thumb unite with those which go  to a finger.   And besides, as
I shall  soon  show  you  that  the tubuli,  through  which  the
impression that  produces  motion is  transmitted, are  separate
from  those which  transmit the  impression  that  causes  sen-
sation, it would not do  for a  tubulus  of one kind  to  unite
in  the  healing  with one of  the other  kind.   We can not
conceive how a  confusion in sensations and  motions  can be
avoided, unless the end  of each fibre or tubulus is  united
with  its corresponding  end;   and  such   an accurate union
of  the  multitude of tubuli in a nerve seems an  impossibil-
ity.  That there is, however, a very accurate  union effected, is
manifest from the observations of  M.  Brown Sequard.   He
examined in animals  nerves which were  divided twelve months
before, and could not discover the point of division even  with
the aid of  the microscope.  If the tubuli were not all made as
perfectly continuous  as  before the  nerve was  divided,  the
microscope would have revealed the defect.   But it takes  time
to effect this adjustment of the tubuli, for  it was found by Dr.
Haighton in   his experiments nearly fifty years ago, that  after
dividing  nerves,  their functions were not restored  till  some
time after  they  were apparently healed.   This  shows  most
deafly, that the arrangement of the  tubuli, which is  required
for the communication of impressions through them, is gradu-
ally effected after the  union takes place.
  239.  Taking this view of this interesting point,  the difficulty
is greatly enhanced, when we look at the union of parts  that 
THE NERVOUS SYSTEM.             153
Nerves of the spinal marrow compound.
did  not originally belong  together, as,  for  example, when  a
piece of skin is dissected  from the forehead, and  is twisted
down  so as to be made to grow  on to the  nose  to supply
a deficiency there.  Here new relations entirely are established
between the  nerves  of the  divided  parts, and, as we should
expect, there is confusion  in the sensations.  The  patient, at
first, whenever the new part of  his nose  is touched  refers the
sensation to the forehead.   But this confusion of the  sensations
is after a while  removed.  And it is curious to  observe, that
while  the  old nervous connections  are  breaking  up,  and the
new ones  are becoming  established, there is  an interval of
partial, sometimes entire,  insensibility in the part.  How these
new relations can be established consistently with the known
arrangement of the tubuli in the nerves is a mystery.
   240. As I  have already hinted, there are different nerves for
different purposes.  The  nerves through  which the mind sends
its  messages  to  the   muscles,  are  not  the  same with  those
through which  it receives  impressions in sensation.  In and
about the face, the nerves of  motion and  sensation are, for the
most part, entirely separate  from each other.   But in  other
parts of the body, the fibres or tubuli for motion and sensation
are mingled  together in  the same  nervous trunk, inclosed in
one sheath.  It is found that each of  the nerves, coming out
from  each side of the spinal  marrow, has  two  roots, which
unite together and are inclosed in one sheath.
This arrangement is  represented in  Fig. 81,       fig. 81.
in which a is a portion of the spinal  cord;
d  the  anterior root;  b the  posterior root; e
the trunk  formed by the union of these  two
roots;  and f a branch of  the  nerve.  At c,
on the posterior root is one of the ganglions, or
little  brains,  of  which I spoke  in  §  235.
Why they  are placed  on these posterior roots,
and  not on  the anterior, or why they  are          \  J
placed  here   at all,  we  know  not.  It  has
been  ascertained  by  many experiments  on    spinal cord.
animals, that  the posterior roots  are composed              m
of tubuli, which bring impressions to the spinal marrow; while
the  anterior  are composed  of  tubuli which  carry impressions
from the spinal marrow.   For,  if the spinal cord of an animal
be laid  bare, and a posterior root be irritated, pain is produced;
but if  an  anterior root be irritated, violent motions are caused
in the  parts to which the  nerve is  distributed.   That is, the
 
154              HUMAN PHYSIOLOGY.
                  Different nerves for different offices.

posterior root is a nerve of sensation, and  the  anterior a nerve
of motion.   It is a mere  matter  of convenience that they unite,
and  are  mingled together in the same sheath, for they are to
be distributed  in the  same parts.   In and  about the face the
nerves of motion  and sensation are kept for  the most  part
separate, as  before stated, merely because it would be no  con-
venience in any case to put them together  in one sheath.
  241.  But not only are there  different  nerves for sensation
and for  motion, but there are also different nerves for different
kinds of sensation.   Thus, in  the eye,  the optic  nerve which
transmits the  impressions from the images  formed  on   the
retina, as will  be shown in the Chapter on  the Eye, is wholly
separate from  the  nerve  by which  any pain or irritation is felt
in this  organ.  The latter is called  a  nerve of common  sen-
sation—the  former  a  nerve  of special  sensation.  So in  the
nose, the nerve that takes cognizance  of  odors  is a different
one from that by which irritation on  the same membrane is
felt.   The snuff-taker smells the snuff with one nerve, and  feels
its tingling with another.
  242.  The nerves devoted to one kind of sensation can not in
any  case perform the function  of those  of any  other kind.
Each nerve is fitted for its own  peculiar office,  and has for this
its own  peculiar susceptibility.   Thus, the nerve  of touch is
insensible to light, and,  on the  other hand, the nerve of vision
is insensible to touch.  If, therefore, the nerve  of  vision be
paralyzed, but  the  nerve of common sensation  in the eye be
unimpaired, although there is no seeing, the eye is as sensible
to irritation  as ever.  On the other  hand, if the nerve of vision
be unimpaired, and the nerve  of  common  sensation be  par-
alyzed, as sometimes happens, the  individual  can see, but he
has lost the sentinel that stands guard over the eye, and by its
warning of pain keeps  it from injury.   What, therefore, is
flying in the  atmosphere may lodge in the eye, and though it
produce  no  pain, it  will  excite  inflammation by irritating  the
capillaries.  The eye  in some of these  cases is destroyed,
by the inflammation which thus arises  from  the  loss of sensi-
bility to the touch.   When the  nerve of common sensation is
in a healthy state, the moment any thing gets into the  eye
great pain is  produced, and the tears flow and the eyelids are
in constant  motion; and if by these instinctive means, as we
may term them, the irritating substance is not removed, other
means are at  once resorted  to. But when this nerve is  par-
alyzed, although the irritating substance  produces no pain, it 
                  THE NERVOUfe SYSTEM.              155
         Different degrees of sensibility in the various parts of the body.

gradually causes inflammation  in  the delicate vascular texture
of the eye.  Pain, then, in this case, as well as in every  other,
is  a safeguard against danger.  The part is endowed with an
acute sensibility to touch, because it is needed as a sentinel in a
part so delicate and yet so exposed.
   243,  This leads me to remark, that the different parts  of the
body are endowed with different degrees of sensibility, accord-
ing  to their necessities, in relation to the warning of danger.
Accordingly, the skin is the most sensitive part or organ  of the
body, that it may warn at  once of the  approach of  danger;
while the  internal  parts have much less sensibility, some of
them none. . In  the performance  of operations,  therefore, the
great suffering  is in  the  cutting  of the skin.   There is very
little sensibility  in the muscles,  and there is none in  the  bones.
The following fact illustrates the use of the sensibility of the
skin  in  the prevention  of injury.  A man who  had lost  all
sensibility in his right hand, but retained the power of motion,
lifted the cover of a pan when it was burning hot.  Although
he was  not aware of any effect at the moment, the consequence
was the  loss of  the skin of the fingers and of the palm  of the
hand, laying bare the muscles and tendons. If the  sensibility
had not  been lost, that is, if the nervous tubuli which transmit
sensation had not been paralyzed, the warning of pain  would
have been instantly given to the brain, and  orders would have
been sent to the  muscles to relax their grasp of the cover;  and
so  rapid are these transmissions, that  the cover would have
been dropped soon enough to prevent  any great amount of
injury from being done.
   244. Although there is so  little  sensibility in the internal
parts in their healthy condition, yet when they  become inflamed
they become sensible of pain, sometimes acutely so.   Thus, an
inflamed  bone  is the seat of severe pain; and  the  tendons,
although  nearly  insensible  ordinarily,  become  very painful
when inflamed,  as  any one that has a  deep-seated felon can
testify.   The question as  to the cause of this change of sen-
sibility I will not stop to discuss, but that there is a benevolent
object in it is very manifest.  If inflammation caused no pain
in such parts, it  might go on  to  a  destructive extent without
the  person's  being aware of  the danger, and therefore without
his applying for medical means,
   245. It was formerly supposed that a nerve must  of  course
have an  exquisite sensibility.  But  there is  no  sensibility in
nerves devoted  to motion.   Neither is there any in  the brain 
 156               HUMAN  PHYSIOLOGY.
       Insensibility of the heurt to the touch.  Respiratory nerve of the face.

 itself.   Portions  of it can be cut off without producing  any
 pain.   The  heart, too, is  insensible  to  the  touch.   A case
 proving this fell under the  observation of Harvey, the  dis-
 coverer of the circulation of the  blood.  A young nobleman,
 from an injury received in a fall, had a large abscess on the
 chest, which  occasioned such a destruction of  the  parts, as to
 leave the lungs  and heart exposed,  Charles I., on hearing of
 the  case, desired  to  have   Harvey  see  it.   "When,"  says
 Harvey, "I had paid my respects to this young nobleman,  and
 conveyed to him the  king's request, he  made  no concealment,
 but  exposed  the left  side of his  breast, when I saw a  cavity,
 into which I could introduce my fingers and thumb; aston-
 ished with the novelty, again and again I explored  the wound,
 and first marveling at the extraordinary  nature of the case, I
 set about  the  examination  of the heart.   Taking it in  one
 hand, and  placing  the finger on  the wrist,  I  satisfied myself
 that it was indeed the heart which I grasped.   I then brought
 him to  the king, that  he might behold and touch so extraordi-
 nary a thing, and that he might perceive, as I did,  that unless
 when we  touched  the  outer  skin, or when  he saw our fingers
 in the cavity, this young nobleman knew  not  that we touched
 his heart!"  This absence of sensibility  in the heart  is  not
 because  it is  not well  endowed  with  nerves.   It is  well
 endowed, but it  is with  nerves which are devoted  to another
 purpose.   They  are  nerves of sympathy,  which establish  a
 connection with every part of the  body, making  this  organ to
 be so easily affected by motion, by disease, and by every pass-
ing emotion in the  mind.
   246.  In the  face we have an example of different sets  of
nerves for different  classes of motions.   All  those motions that
are used in  the expression  of the countenance are associated
together by  a  certain nerve.  This nerve has nothing to do
with other motions, as mastication.  Other nerves are  provided
for them.   Sometimes this nerve of expression is paralyzed on
one  side.   The result is, that while the individual  can  masti-
 cate equally well  on  both sides,  he can  laugh, and  cry, and
frown, only on one side, and  he can not close the eye on the side
 affected.  In Fig, 82  is  a representation of this condition of
 things.   The left eye can not be closed by any effort, and  the
 left side of the face is  wholly devoid of expression.   This nerve
 of expression is often paralyzed by itself, the other nerves in  the
 neighborhood, both nerves of sensation and of  motion, being
 entirely unaffected.  This nerve has been called the respiratory 
   THE NERVOUS SYSTEM.              157

Paralysis of the respiratory nerve of the face.

            FIG. 82.
PARALYSIS OF  THE  NERVE  OF EXPRESSION
              on one side of the face.
nerve of  the face, because it  controls motions which are con-
nected with the movements of respiration.  If you observe how
the various  passions and emotions are expressed,  you will see
that there is a natural association  between the muscles of the
face and  those of the  chest  in this expression.  This is very
obvious in laughing and in weeping.  But this association can
be effected only through nervous connections.   And these con-
nections in this case are very  extensive and  intimate.  When
the nerve of expression, or  facial  respiratory perve, is  par-
alyzed,  all the motions  of the face  connected  with the respi-
ration  are absent.   Though the individual may sob in weep-
ing, or send forth the rapid and  successive expirations of
laughter,  yet the  face  on  the side where  the  nerve is  par-
alyzed  will  be perfectly quiescent.  So,  too, those movements
of  the  nostrils  which are sometimes used in expression,  can
not be  performed.   Sneezing  and sniffing up can not be done
                             14 
158              HUMAN  PHYSIOLOGY.
            Nerves of the eye.  Paralysis affecting different nerves.

on  the affected  side.  Neither  can  the  individual  whistle,
because a  branch of  this  nerve goes  to the  muscles at the
corner  of  the  mouth,  which  are  therefore  disabled,   Sir
Charles  Bell, in cutting a tumor from  before  the  ear  of  a
coachman,  divided this branch of the nerve.   Shortly after, the
man  thanked  him  for  curing  him of a formidable disease,
but complained that he could no longer whistle to his  horses.
  247. The  eye  has  six  different  nerves, each for a different
service.  1. The  optic nerve.   This has nothing to do with the
motions or the common sensations of the eye.   Its sole office  is
to transmit impressions from the  images formed in the  eye to
the brain.   2. A nerve of common sensation, by which any irri-
tation in the eye is felt.  3.  A nerve which is distributed to the
muscles of the eye generally, and  to no other  parts of this organ.
4. A nerve  which  goes to one particular muscle, one of the oblique
muscles of the eye.   It is an involuntary muscle which performs
the insensible rolling  motions of the eyeball, and is associated
with the muscles of expression in the countenance by means of
nervous connections.   5. A nerve which goes to another single
muscle, which  turns  the eye outward,  6, A branch  of the
respiratory nerve, which regulates the  motion  of  the  eyelids,
and has much to do, therefore, with the  expression of the coun-
tenance.  To this small organ, then, are distributed six different
nerves, each having  its distinct office, and its separate origin in
the brain.   How various  are the transmissions through these
nerves, and  how nicely adjusted must all  the  parts of this
complicated  apparatus be, that each  may perform  its office
without interference with the rest!
  248. I have already alluded incidentally to the  fact, that one
nerve  may be paralyzed, and others  distributed to the same
parts may be entirely unaffected.   Thus the nerve of expression
in the  face may be paralyzed alone, the face retaining its usual
sensibility and its power of performing other motions than those
of expression, as  mastication, because the nerves of common
sensation and of common motion are untouched by the disease.
So, too, in  the nerves which  go  out from the  spinal marrow,
composed of tubuli of motion and sensation mingled together,
one set of the tubuli may  be affected while the other  is not;
for in paralysis it is often the case that  the sensibility remains
while the power of motion is gone, and vice versa.   Sir Charles
Bell relates  an interesting case, in which  the paralysis was
different on the two sides  of the body.   A mother was seized
with a paralysis, in which there  was a  loss of muscular power 
                 THE  NERVOUS  SYSTEM.              159
          Nerves, though having different offices, all alike in structure.

on one side, and  a  loss of sensibility on the other.  She could
hold  her child with the arm of the  side  which retained its
power of motion but had  lost its sensibility.  But she could do
it only when she  was looking  at it.   She could  not feel her
child on the arm, and  therefore when  her attention  was drawn
to any thing else, and she ceased to have her eyes fixed on the
child, the muscles having no overseer, as we may say,  to keep
them at work, were relaxed at once, and  the child  would fall
from her arm.  In this case, bound  up in the same sheaths were
two sets of tubuli, one set of which were useless in the nerves
on one side  of the  body, and the  other set were useless in the
nerves of the other side.
   249.  We should suppose that there would be a difference in
the construction of the nerves, corresponding with the different
uses to  which they are devoted.  But  it is not so.  The micro-
scope shows us that  the nerves of motion and  of common and
special  sensation  are all alike in their  structure, and chemistry
shows us that they are  alike also in their composition.  The
question arises, then, why the impression producing motion can
not  be  transmitted  by  the  same  nerve with  the  impression
causing sensation.  The reason is evidently not to be found in
the  nervous  trunk itself, as  this is  the same in all cases.   It is
in the circumstances of the two ends of the nerve—that which
is in the nervous centre from whence it arises, and  that which
is expanded in some part of the  body.   You can  see at once
that the nervous tubuli  which end in the  fibres of a muscle
can not transmit  sensation to the brain from the  skin over the
muscle, because they do not go to  the  skin  at  all.  There are
other tubuli that  are distributed there  for that purpose, mingled
indeed  in most cases with the tubuli  for motion, but yet  kept
entirely distinct from them.   And  besides,  there is probably
something in the mode of arrangement of the extremities of a
nerve of sensation, which differs from  that which exists in the
distribution of  a  nerve of motion,  so  as to make  it impossible
for a nerve of motion to receive the impression  producing sen-
sation, even where the  impression  is  made  directly upon the
muscle  itself.   There is also probably a different ending of the
nerves of sensation and motion in the nervous centre, the brain,
or spinal  marrow,  that makes the  one  kind  incapable of
performing the duties of the other  kind.
   250.  There  have  been  many hypotheses in regard  to the
action of the  nerves.  The most  common  theory, even up to
modern times,  was this—that the  brain is not only the great 
 160               HUMAN PHYSIOLOGY.
          Nerve-force not electricity. Proved by facts and experiments.

 centre of the nervous system, but its central workshop, as we
 may express it, and that in it is secreted a nervous fluid, which
 is distributed through all the  body by the nerves, they being,
 as it was  supposed,  bundles of conduit-pipes.  This fluid was
 supposed to move back and forth in the nerves, going outwards
 towards the extremities  of  the nerves to excite  motion, and
 going  inward to  the brain  to convey the sensation of external
 impressions.   This theory has been exploded by the researches
 of Sir Charles Bell and others, and during the last half century
 important  and numerous discoveries  have been made, in rela-
 tion to the functions of different parts of the nervous apparatus.
 And though there are many things in this system, which links
 the spiritual  with  the physical, that we shall  never understand,
 the bounds  of our knowledge  in regard to it are undoubtedly
 to be largely widened by future researches.
   251. It  is a favorite idea with some physiologists that nerve-
 force, as it is termed, is identical with electricity, and that the
 nervous system is  therefore a system  of electrical batteries, with
 an apparatus  for a sort of telegraphic communications.  They
 ground their opinion upon the fact, that a current of electricity
 passed along nerves  may produce motion or sensation, accord-
 ing to the character of the nerve through which  it is passed,
 and  also upon the  analogy which  exists between nerve-force
 and  electricity in  the instantaneousness  of their transmission.
 But  facts  and experiments  have wholly disproved this alleged
 identity.  Some of these I will  briefly relate.   Mechanical and
 chemical stimuli  produce  the  same  nervous action that elec-
 tricity does.   This shows that  the electricity acts merely as a
 stimulus to wake up the nerve-force, instead of  being that force
 itself.  Experiments have been tried, to  detect, if possible, the
 existence of an electrical current in  a nervous trunk while the
 parts  to which it is  distributed were in action, but  in  vain.
 Thus, Prof. Matteucci  laid bare the large nerve of the leg of a
 horse, and  although by irritating its roots he excited powerful
 action  of the muscles of the leg, the instrument in connection
with the nerve  was  entirely unaffected, though it was so ex-
tremely delicate that it would indicate an infinitesimally small
 disturbance of the  electrical equilibrium.  Again, a ligature put
around a nerve will  by its compression prevent nervous trans-
mission through it, but will not hinder the passage of  an  elec-
trical current.  Still again, if a piece  of a nerve be cut  out, and
some  good conducting  substance  be introduced in its place,
electricity will pass, but there can be no transmission of nerve- 
THE NERVOUS SYSTEM.
161
     Products of nervous action—sensation, motion voluntary and involuntary.

force to  the parts below the division.  Besides all this, nerve-
force  differs  from  electricity in the fact that it can be confined
to the nervous trunk, or even to a small portion of the trunk, as
when a motion is very limited in extent; while electricity not
only passes through the whole trunk, to all the  parts to which
the nerve is distributed, but is diffused  in the parts around it.
Thus, if  an electrical current be passed through the main nerve
of the limb of an  animal, it will  go through  every branch
of that nerve, and cause all the muscles of the limb to contract;
but nerve-force may be so insulated  in a  small  portion  of the
nerve, that a single toe may be moved alone.  And some of the
electricity will  be diffused  at once in the muscles and  other
parts around the trunk of the nerve before it reaches any of the
branches that  go  off from it.   Indeed, the muscles are much
better  conductors of electricity  than  the nerves, which should
not be if the nerves were particularly  designed for its transmis-
sion, as the hypothesis would claim.   And both muscles and
nerves are nothing like as good conductors as  a common copper
wire.
   252. We have  thus  far  contemplated nervous  action, for
the  most  part,  only in  two  forms—as  producing  sensation
and voluntary motion.   In sensation the action  is  from the
extremity of the nerve to  the nervous centre; but in  motion it
is from the centre to the extremities of the nerves, as they are
expanded  among the fibres  of  the muscles.   This voluntary
motion,  you see, may arise  in consequence of sensation, as
when  you withdraw the  hand  from  the fire,  if the heat  be
painful; or  it may  occur  without a  preceding sensation,  as
when  the thinking mind  wills  to perform certain motions for
effecting  some purpose.   In either case it is supposed that the
gray vesicular or cellular substance of  the brain is in immediate
connection with  the mind, and  that  the  white  tubular matter
of the brain and the nerves serve only for transmission.   That
is, both in sensation and motion the effective physical  agency is
in the vesicular gray substance.  This  is the working part of
the telegraphic apparatus of the mind, while the innumerable
tubuli  of the white  matter  of  the brain and  nerves are the
communicating wires.
   253. Much of the muscular motion of the body is produced
without  the agency of the will, and  sometimes even in oppo-
sition to it.  This is true of the motions caused by emotions in
the mind.   For example, the  muscular motions in sobbing and
in laughing often occur in  opposition to the strong action of the
                               14* 
HUMAN PHYSIOLOGY.
              Involuntary motion. Excitor and motor nerves.

will.  In this case, the emotion produces its effect upon the gray
vesicular substance, and from this the impression is transmitted
through the nerves to the muscles.
  254.  There are some common motions which are  performed
to a greater or less extent without the agency of the will.  The
muscles which perform  them are  called involuntary muscles.
The muscles of respiration, for example, ordinarily act without
our willing them to do so.  If they did not, respiration would
stop when we sleep, or become stopped from disease.  But the
will can quicken these muscles in  their action.   They are
therefore not wholly involuntary.   But there are  some  purely
involuntary muscles.  The muscular coat of the stomach, which
I spoke of in the Chapter on Digestion, as being constantly in
motion when the stomach is filled with food, is  of  this  char-
acter.   No effort of the  will can quicken or retard the action of
this muscle.  That exceedingly  compound  muscular  engine,
the heart, is a collection or arrangement of purely involuntary
muscles.   No effort of the will  can  directly  influence  its
motions, though  it may do  it indirectly, by so  directing the
thoughts as to awaken emotions  calculated to  produce this
effect.   That  beautiful  circular curtain in the eye, the iris, has
the size of its circular  opening, the pupil, controlled, as you will
see  in the Chapter on the Eye, by an involuntary muscle.
  By  what  agency,  you  will inquire,  are  these involuntary
motions produced?  The answer  to this question will open to
you a new view of the nervous system.
  255.  I have already alluded to the two roots which unite to
make up each nerve that conies from the spine.   One of these
roots is  composed of tubuli through  which  impressions are
transmitted  to. the spinal  marrow;  and the  other contains
tubuli, through  which an  impression  is transmitted from the
spinal marrow to the muscles, causing them to contract. ■  Each
nerve, then, coming from the spine, is made up of two distinct
nerves, or two distinct sets of tubuli.   One of these is called an
excitor  nerve, the other a motor nerve.   In the case  of the
muscles of respiration, every time that they act, the  process  is
this—an impression is transmitted from  the  lungs through an
excitor nerve to the spinal marrow, the gray vesicular substance
there responds to this impression, and  sends in consequence an
impression by a motor nerve to  the muscles.   So in the case
of the iris, which 'contracts to prevent too  much light from
entering the eye, the  light as it strikes  the retina produces an
impression, which is transmitted  through an excitor  nerve, and 
THE NERVOUS SYSTEM.              163
     Reflex action of nerves. Sometimes sensation with it, and sometimes not.

in consequence  another  impression  is transmitted through  a
motor nerve to the iris.   So also, the presence of food in the
stomach  produces an impression which is transmitted  through
the excitor nerve, and another  impression is returned  through
the motor nerve, exciting the muscular coat  to action.   And in
the act of swallowing an impression is  transmitted from the
food thrust  back into   the throat,  and then impressions are
returned to the many muscles engaged in  this compound act,
(§ 78).   The action of the nerves illustrated by these examples
is termed their reflex  action, because  the impression transmitted
by  one nerve to the spinal marrow  is  reflected from it by
another.
  256.  You see that  I use the rather indefinite word, impres-
sion, in relation  to the transmissions through the nerves.  It is
the best word that can  be  employed, because although some-
thing is  transmitted, we know not what  that  something is.
The result of the transmission is different in the excitor nerve
from what it  is in the motor nerve.   The  result differs also in
the excitor nerves according to circumstances.  In some cases
it is accompanied with  actual  sensation, while  in  others it is
not.  That is, the brain sometimes  participates in the result,
and sometimes  it is  confined to the spinal  marrow.   Thus, in
the act of respiration, the impression carried from the lungs by
the excitor nerves comes from the presence of dark blood in the
lungs.   Ordinarily,  a mere impression, and nothing like sen-
sation, is transmitted.  The  respiratory  muscles, most of the
time, go  on  to  do  their work, in obedience to the  impres-
sions communicated from the lungs,  without the  process being
recognized by the mind.  But when there is embarrassment
in the  lungs, the quiet  process, carried on through the agency
of the spinal marrow alone, is  not adequate to meet  the exi-
gency.  In some way, the brain becomes a party in the ope-
ration.  The  act of breathing  is now accompanied with pos-
itive sensations, and  there  is a  mixture  of voluntary  and
involuntary muscular  action.  So, also, the ordinary movements
of the stomach  are attended  with no positive sensations.  That
is, there  is no  transmission to  the brain  of any impression of
which the mind  takes cognizance.  But if there be disturbance
there, and  extraordinary movements are produced, then cogni-
zance is taken of them, and sensations of various kinds result.
  257. The  spinal marrow,  in relation to  the  involuntary
muscles, seems ordinarily to be in a  great measure independent
of the brain ;  while on the other hand, in relation to voluntary 
164              HUMAN PHYSIOLOGY.
            The spinal marrow performs two separate functions.

motion and sensation, it forms the chain of communication be-
tween  the  brain  and  the  moving and  sentient parts.   In this
respect the dependence is perfect.   In injuries of  the spine,
therefore, the extent of the loss of  the power of motion and of
sensibility depends on the  nearness of the injury to  the brain.
The higher up the injury is, the larger is the number of nerves
whose  connection with the brain is cut off, and  therefore the
greater is the extent of body rendered  insensible and motionless.
  258. The spinal marrow then performs two separate functions
—one, in producing involuntary motion, as an organ by itself;
and another,  as  an organ in connection with the brain, in the
production of voluntary motion  and  sensation.  The arrange-
ment, by which it does two  things which are so different from
each other, will be clear to you, if you bear  in mind the fact
that the  spinal marrow, like  the brain,  is  composed of the two
nervous substances, the white tubular, and the gray vesicular sub-
stance.  When the spinal marrow acts as a  mere medium of
communication for the brain, the transmission is made directly
through the tubes of the white substance to and from the  brain
—to the brain in sensation, and from it in voluntary motion.
Thus, when a sensation is  felt in the foot, the impression made
there  is transmitted through the  nerve to the spinal  marrow,
and up through the white  part of this  organ  to the brain.   It
touches none of the  gray  substance of the spinal  marrow, but
goes to the gray  substance of the brain.   And when the foot is
moved, an impression  is returned  from the brain through the
white part of the spinal marrow, and then  through  the nerve
which goes from  it to  the muscles that move the foot.   But, on
the other hand,  when the spinal marrow acts by itself, inde-
pendently of the brain, producing what is called reflex  action,
(§ 255,) the  impressions  that are transmitted, some of them
begin, and  some end in the gray  substance  of the  spinal
marrow.   The impression on an  excitor  nerve ends there, and
the impression on a motor nerve  begins there, the latter result-
ing from the former, except when motion is produced by dis-
ease in the  spinal marrow itself.  Thus, in breathing, as de-
scribed in § 255, an  impression  goes  from the lungs through
excitor nerves to  the  gray substance,  and that is the end of it;
but  another  impression begins there  as a  result of  it, and  is
transmitted to the involuntary muscles moving the chest.
   259. One  marked distinction  between  the  brain and spinal
marrow  is, that  the  brain has its intervals  of rest; but the
functions of  the  spinal marrow  never cease for a moment  as 
THE NERVOUS SYSTEM.              165
         The brain rests. The spinal marrow does not. Convulsions.

long as life  continues.   In sleep the  brain is more or less at
rest, and it is in a state of  entire torpor when the sleep is pro-
found.    But  during sleep the  heart  beats, the  respiratory
muscles work the chest, and the muscular  coat of the  stomach
churns the food if there be  any there.   For these motions, with
many others, are dependent upon the spinal  marrow, and not
upon the brain;  and  so,  while the brain sleeps, the spinal
marrow keeps up the operations of the system that are essential
to the continuance of life, in  the manner  described in  §  255.
So,  also,  in  apoplexy, when  the  brain  is  torpid  from the
pressure of blood, the spinal marrow, being unaffected, keeps up
the  functions of those  organs which  are dependent upon it.
But besides the motions that I have mentioned, as being  kept
up by the spinal marrow,  when  the brain is torpid  from  any
cause, there are  other motions which can  be excited  by stimu-
lating nerves that are connected with the spine.   For example,
the act of swallowing can be produced  by  pouring a liquid into
the  mouth,  and motion can  be produced in the muscles  of a
limb by irritating the limb at different points.   If you  cut off
the  head  of a frog, and thus destroy all sensibility,  you can
produce movements in his  limbs  by irritating them.   You
can, indeed,  make   the whole  body  to  move  together, by
producing irritation at many points  at the  same time.   So, too,
if a man be paralyzed in his lower limbs  by  a blow upon
the spinal column, these parts, which he  cannot move  by his
will, can be excited  to motion  by irritation  with electricity
or other agents.
   260.  The  motions of the  muscles in convulsions are  pro-
duced  by the agency  of the spinal marrow.   The irritation
causing them sometimes  exists  in the spinal  marrow itself,
being the result of disease there.  But commonly the irritation
is in some other part of the  system, and  it produces the  con-
vulsive  movements  by  sending an impression through  excitor
nerves to the spinal marrow, to be reflected back through the
motor  nerves, as described in § 255.  The  brain during the
convulsion is in a  torpid state, the  individual being  uncon-
scious.  That the brain is  involved to some extent in the con-
vulsion  is very clear, and sometimes the  cause of the  convul-
sion is in this organ.   But it is probable that the convulsive
movements are directly dependent on the  spinal marrow,  and
that even  when the  cause is in the  brain,  it is by the action of
the  spinal marrow, sympathizing  with and  affected   by the
diseased brain, that the convulsion is  produced.  And when 
166              HUMAN  PHYSIOLOGY.
          Involuntary action of voluntary muscles. How produced.

the cause is in some other part, as in the irritation of teething
or indigestion,  the impression is  sent directly  to  the  spinal
marrow, and is reflected from it to the muscles, the brain being
only secondarily affected.
   261. It is worthy of remark, that in convulsions there is a
purely involuntary action of muscles, that are ordinarily under
the control of the will.  How is this ?  How  are  they taken
away from the  usual  control  of the will  so suddenly and so
entirely ?   It is not possible that  any temporary new connec-
tions can be established all at once by the disease,—that there
is, to use illustrations of a familiar character, a sort of unship-
ping of the usual connection, and a hitching on  of  another for
the time  being, or a  switching  off  from  one  track  on to
another.   These voluntary  muscles must  have all the time a
connection with the gray substance of the spinal marrow, just
as the involuntary muscles have, only it is not'as intimate and
extensive.  If it were not so, they could not act occasionally as
involuntary muscles.   Being  thus  connected with  the gray
substance, both  in the brain  and  spinal marrow,  when they
act in obedience to the will, the impression  exciting their ac-
tion comes to  them  from  the gray  substance  in  the  brain
through the white part of the spinal marrow ; but when they
act involuntarily, the  impression  comes  from the gray  sub-
stance in the spinal marrow, and not from the brain.
   262. I  may remark farther,  that  the voluntary muscles  act
involuntarily more often than is  commonly  supposed.   As
already stated,  (§259) in  animals, from which the head has
been removed, the voluntary muscles can be excited to involun-
tary  action,  resembling voluntary  movements, although of
course with the  removal of the head were destroyed all sensa-
tion and  all exercisejof the will.  And in the case of the man
paralyzed by injury in the back, alluded  to  also in § 259, in-
voluntary movements can be excited in the voluntary muscles.
A pigeon, whose cerebrum had been removed, would fly when
thrown into the  air, would run when it was pushed, and would
drink when its  beak was put into water.  There was  no sensi-
bility and no will in this case, for they can not be without the
cerebrum.  The  movements  were involuntary,  though  per-
formed by voluntary muscles.   Now as these facts prove that
voluntary muscles are,  through their connection with the spinal
marrow,  capable of acting as  involuntary muscles also, the
question  arises,  whether they do not much of the time act in
part as involuntary muscles, and sometimes  wholly so.   That 
                  THE NERVOUS SYSTEM.              167
            Walking. Reverie.  Brain not directly essential to life.

 this is the case, a little  reflection will  show.  When we are
 walking we use voluntary muscles.   But manifestly  a distinct
 act  of the will is not put forth  for every motion performed
 in walking.   The mind may be at the same time fixed  upon
 something else ;  and there seems ordinarily to be only an oc-
 casional action  of the will, as when we change our course, or
 when some obstacle is in  the  way, requiring a variation  from
 the  regular consecutive series of movements.  There is a dis-
 tinct action of the will when the movements begin ; but after
 this the motions seem for  the most part almost automatic, and
 are  probably produced by the reflex action of the spinal mar-
 row, the will interfering only when occasion requires.  This is
 more manifestly the case when one is walking in a reverie, and
 perhaps finds himself on awaking from it, in a different place
 from that  to which he had willed to go.  It is as if the brain
 set the machinery of the limbs to work, and  then  delivered it
 over to the care of the spinal marrow, interfering only when it
 needs to do so to  meet some  difficulty, or when it  wishes to
 give a new direction to the movement,  or to  stop it.   And in
 a reverie, the brain occupied with other things, neglects  even
 to  exercise this  superintendence, and   leaves the machinery
 wholly to  the guidance of the spinal marrow.  The same re-
 marks can  be made in regard to other motions, as in  speaking,
 singing, playing on an instrument, <fec.  In all these cases the
 voluntary  muscles act in  some measure involuntarily,  being
 governed by an  association in their action which is far from
 being wholly dependent upon the brain, and the  direction of
 the will.   I shall recur to this point again,  when I come to
 treat of the connection between the mind and the body.
   263. Many experiments have been  tried upon animals in
 reference to the functions of the brain, and of the spinal  mar-
 row.   I have  already alluded to  some  of  them.   It  was
 formerly supposed, that the brain was the only centre of nerv-
 ous power,  and that it was  immediately essential to  the  pre-
 servation of life.  But these  experiments have shown that this
 is far from  being the truth.  The brain, it has been found, has
 nothing to  do directly with the  maintenance of life.  Animals
 live for some time after the brain is destroyed.  A pigeon was
 kept alive  for  some months after its cerebrum was removed.
 Its condition was very much like that of a man, the functions
 of whose cerebrum are suspended by the  pressure of a  frac-
tured portion of the  skull.  Although,  like  him, the animal
had  lost all sensation  and voluntary motion, yet, like him, it 
168              HUMAN PHYSIOLOGY.
            Upper part of the spinal cord directly essential to life.

continued to breathe, and  its heart continued  to  beat.  Of
course so extensive an injury of so important an  organ will at
length cause death;  but life  continues  long  enough in such
cases to show, that this organ is  not immediately essential to
its  continuance.   The functions  most  essential to life,  the
respiration and  circulation, are, as you  have seen, kept  up by
the spinal marrow. The very upper part of this organ is espe-
cially devoted to this  purpose.  You may take out the brain
of an animal, and destroy all  its spinal marrow,  except this
upper portion of it, and the animal will still  breathe, and its
heart will beat.  But  if you destroy just this small portion of
the  spinal marrow, though you  leave  the rest  of it and the
brain untouched, the  animal will  die at once from the  cessa-
tion of the  respiration and the  circulation.  In the Spanish
bull-fight, when the matadore at length kills  the  animal, by
adroitly piercing the spine in the  back  of  the neck, he inflicts
his  wound upon this upper part of the spinal marrow.
  264.  If after cutting off the head of  a frog, you divide the
spinal marrow in the  back, you can produce  involuntary mo-
tions in bo'th the upper and lower extremities.  But you can not
produce them at the  same time in both together, for the divi-
sion of the  spinal marrow in the back separates  it into  two
independent  parts. When, therefore,  you irritate  the  upper
extremities, the motion is confined to them, and  the lower ex-
tremities are  quiescent.   And  if you  irritate the lower extrem-
ities, the motion produced there does not extend  to the upper.
The division  can be carried much farther with similar results.
If the spinal marrow be divided above and  below  where  a pair
of nerves is given off,  so  as to  separate  this point wholly from
the rest of the nervous system, the reflex action can be excited
in the nerves connected with this  point.   That is, an irritation
of the parts supplied by the excitor nerve of this  little segment
of the spinal marrow will produce an impression in  that seg-
ment,  which will be  reflected by  the motor nerve  to  the
muscles.  The gray substance  of the spinal marrow may, there-
fore, be regarded as a chain of little brains, in some measure
separate from each  other.  But  while  there  are thus  many
centres of reflex action, there  is  only one  centre of  sensation
and voluntary motion, and that centre,  the brain, is connected
with the mind.  Some  physiologists  have  maintained that
there is  sensation independent of the  brain;  but  it may be
considered as most abundantly proved,  that it is through the
brain alone  that  the mind feels  and  acts, or rather that we 
                 THE NERVOUS SYSTEM.              169
           Two systems of nerves, cerebro-spinal and sympathetic.

know nothing  in this world of  a sentient  and acting mind
existing without a brain.
  265.  The system of nerves which we  have been examining
is termed the cerebro-spinal, from its two great central organs,
the brain and  spinal marrow.   But there is  another  nervous
system, the functions of which are involved in much mystery.
It is called the  system of the great sympathetic, or the sympa-
thetic system.  Sometimes it is called the nervous system of
organic life, because it is so intimately and  extensively con-
nected with the nutritive processes ; while the system that we
have been considering is  called the nervous  system of animal
life, because  it regulates  the functions peculiar to animals in
distinction from  plants,  sensation, and  spontaneous  motion.
While  the sympathetic  system is  thus connected with  the
nutritive processes, it is also supposed to be the means of effect-
ing the sympathetic connection between different parts of the
body, and to act as the  medium by which  the passions  and
emotions of the mind produce their effects upon the functions
of the different organs.   In this  system  there are many gang-
lions or little brains, which communicate with  each other by
nerves.   There is  a chain of them along in front of the spinal
column, and there are two quite large ones  in the abdomen.
This system has connections everywhere with the cerebro-spinal.
The purposes aimed  at in the  particular arrangements of this
system  are as yet but little understood, and we probably never
shall know as  much  about it  as we shall about  the  cerebro-
spinal system.   The arrangement of the sympathetic  system
differs very materially from the cerebro-spinal.  It is a single
system,  and has no symmetrical  arrangement,  while  the
cerebro-spinal has throughout two halves which are precisely
alike.
   I have thus  described the arrangements and functions of the
nervous system to such an extent, as will prepare you for the
consideration of  those subordinate organs, by which the  pur-
poses of this system  are  accomplished.   After  treating of the
organs of locomotion, the voice, and the senses, I shall call your
attention again to this  system,  presenting some  views of its
uses and connections, which you will  then be better prepared
to understand.
                            15 
170
HUMAN PHYSIOLOGY.
Bones the framework of the body.  Composition of bone.
                    CHAPTER  XI.

                         THE BONES.

   266.  The bones  furnish the points of support and  attach-
ment for  the muscles  which  move the different parts of the
body.   They are, therefore, the passive  instruments of  loco-
motion.   I treat of the bones before the  muscles, because you
will then  better understand the  action and the arrangement
of the muscles.
   267.  The bones, forming the  framework  of  the  body, not
only furnish points of  support and  attachment to the muscles,
but in many cases  serve to defend important organs from in-
jury.  Thus, the soft brain is thoroughly secured from harm
by being  inclosed in the skull; and the lungs are surrounded
by walls of  bone so arranged, as you saw in the  chapter on
Respiration, that, while they defend  the  lungs from external
violence, they secure a wide range of motion for the necessary
expansion of these organs.
   268.  The bones  are composed of two  parts, the earthy or
hard portion, and the animal  portion which is soft.   Each of
these portions, as was stated in § 60, can  be obtained separate
from the other.   These two portions of bone exist in different
relative proportions in the different periods of life.   In the
child the animal  portion predominates,   while the mineral
does in old age.  It  is  a wise provision in  regard  to the
child, for if his  bones were  as  brittle as those of old  age,
or  even as those of middle life,  they would be often  broken
in the falls to which the child in its feebleness and carelessness
is subjected.
   269.  There are some points of  interest in relation  to the
structure of bone and its growth.   I stated in § 61 that  bone is
generally formed in  cartilage, the cartilage being formed first as
a mould for the bone.  Bone is deposited in two forms, solid and
cellular.   In  the flat bones, as in the skull, the  cellular struc-
ture lies between two plates of solid bone.  In the long bones
the  cellular  part  is at  the two ends, and is covered  with a
thin plate of solid bone, while the  shaft is a hollow  tube
with the  bone  very  much  condensed.   This arrangement 
                         THE BONES.                   171
             Structure of bone. Long bones hollow.  Marrow.

is  seen  in  Fig.  83,   representing
the  thigh-bone and the  bone of the          fig. 83.
arm.  Certain well known mechanical
principles are observed in this arrange-
ment.  The bone would be  unneces-
sarily heavy if it  were solid through-
out.  Lightness in a moving limb is
of  considerable importance.   At the
same time strength is to be  carefully
provided for  in  a bone  which is to
sustain  the weight of the body,  and
to  which  the large muscles of the
thigh are  attached.  By  having the
bone hollow, both of  these  objects,
lightness and firmness,  are  secured.
The principles involved are recognized
by the  architect  in the  construction
of pillars, and we see them exemplified
in the  hollow stalks of plants.   The
hollow  pillar  has  more strength than
the  same  quantity of matter would
have if in one  compact mass;  and
the stalk which supports the full clus-
ters of grain, would break  under its
load  as  it  moves  back  anj^ forth in
the  wind,  if it were solid instead of
being hollow.  But the  round cavity
of  the shaft  of  the bone  does  not
extend  to the ends.  These are ne-
cessarily large, in order to  present broad  surfaces for  articu-
lation with the neighboring bones; and strength and  light-
ness are secured in this case by a cellular arrangement of the
bony matter, the  outer plate of solid  bone being comparatively
thin.  There  is obviously more firmness  in the  resistance  to
shocks or pressure, secured in this way, than there would be if
the bony matter were all  consolidated into a shell containing a
cavity.
   270.  The round canal in the shaft and the cellular structure
at the ends  are filled with  an oily substance called  marrow.
This, like all other fatty substances, is contained in fat cells,  as
described in the  chapter on Cell-Life.   The marrow  is  also
present in the cellular structure between the plates of the flat
bones.  The cavities  and  the cells  in bones have branching
 
172
HUMAN PHYSIOLOGY.
        Mode of nutrition in bones.  No bloodvessels in their solid parts.

about in them bloodvessels, which are branches of arteries and
veins that enter the body of the bone at some particular points,
in the long ones near the middle of the shaft.   It is from these
bloodvessels, together  with those that  come from the mem-
brane investing the  bone, called periosteum, that the bone is
nourished.   But,  although an artery runs through the body of
the bone, to branch out upon the walls of its cavity, none of its
branches enter the very substance of the bone.  How then is
the bone nourished, that  is,  constructed and  kept in repair?
The manner in which  the  material for this purpose is carried
to every point of  the solid bone has been developed by the aid
of the microscope, and I will describe  it to you.  If we  cut
across  the  solid  portion  of  a bone, and examine  it with a
microscope, we see here and there  orifices  of certain minute
canals  that run  lengthwise  of the  bone.   These  canals  are
found to communicate  with the cavity of the bone and receive
therefore blood, or some of the constituents of the blood, from
the bloodvessels which are situated there.   These orifices, as
seen under the microscope, are  represented in Fig. 84.   Around
these orifices a a, you  see little dark spots  arranged  in rings,
with lines  running to them from the orifices.  By magnifying
the section of bone still more, we see what these spots and lines
are.  The  dark   spots  are small  cavities,  and the lines  are
minute tubes running to them.  In Fig.  85  is a representation
of this arrangement as  seen in a little portion of the section of
bone, more highly  magnified  than it  is  in Fig.  84.   The

              FIG. 84.
•  SECTION OF BONE. 
THE BONES.
173
               No sensibility in bones.  Variety of shape.

tubes pass  out from the canals to the rows of cavities which
are around the  canals, and  thus a circulation is  kept up at
every point of the solid bone.  It is  supposed  that the blood
itself does  not circulate in these little channels and cavities
in the solid bone,  but a fluid containing the  constituents  of
bone.  For these  channels are too  small even to   admit the
cells which the microscope shows us as swimming in the blood.
The fluid that circulates in them is  selected from  the blood,
which is contained in the bloodvessels in the cavity of the
bone, and in the periosteum that  envelopes it.
   271.  It is a very common popular notion, that the bones are
endowed with great sensibility, and especially the central  part,
the marrow.   The surgeon is very often asked if the sawing of
the bone in amputation is not very painful, and if when the saw
reaches  the  marrow  it does not  produce agony.  But the
bones have in their healthy state no perceptible sensibility, as
I have before stated, and the sawing of the bone in  amputation
occasions no suffering.  Wheh,  however, a bone becomes in-
flamed, severe pain is one of the symptoms.   And it is well
that it is so ; for if it were not,  disease might go.on to  pro-
duce disastrous results in  a part so covered up by others, with-
out any warning of the danger of the case.
   272.  The bones are of every  variety of  shape,  to  suit the
various offices which they are to fulfill.  You will see this to be
true,  as you cast your eye over the skeleton as represented in
Fig. 86.   You first observe the somewhat round box of bones,
which contains  the  brain, and  at  the same time furnishes
sockets for the eyes, extended  irregular surfaces for the appara-
tus of smelling, and for that of the taste, a place for the organs
of hearing, and at its lower part, in connection with the lower
jaw, a mill for grinding the food.   Then you observe the many
bones of the thorax  or  chest, containing and protecting the
heart and the  lungs.  The spinal  column, k, composed  of
twenty-four bones, you see as a firm but  movable pillar, ex-
tending the whole  length of  the body, and  having its  base
firmly planted  upon that stout thick bone, the sacrum, which
is wedged in so tightly like the key-stone of an arch, between
the broad spreading bones on either side.   To this pillar are
strongly fastened the walls of the  chest; and from the chest
thus  supported by the spine  hang  the lax front  and  lateral
walls of the abdomen.  Then  below you see the pelvis, as it is
called,—a set of large bones so arranged in  a bowl-form, as to
offer a broad surface of support to the contents of the abdomen.
                            15* 
174
HUMAN  PHYSIOLOGY.



  The bones of the skeleton.



         FIG. 86.
SKELETON. 
THE BONES.
175
                  Bones of the cranium and the face.

The bone called the  ilium, m and I, on either  side, with its
flaring  upper surface,  is especially  serviceable  in this  way.
The pelvis  also furnishes a  socket for the  round head of the
thigh bone  s, and points of attachment for the large muscles
that move the lower  extremity.   You observe the  large bones
of the thigh and  leg,  intended to give firmness to the lower
extremity, and the lighter bones of the arm and forearm, fitted
for extent and quickness of  motion.   And finally, you notice
the  numerous bones of which the hand and foot are made up,
giving them with the intervening cartilaginous coatings, great
elasticity, and vast variety of motion, especially in the hand.
   273. I will notice  with  some  particularity  some  of the
bones, of which  I have  given a general description, as they are
united together  to form the whole  skeleton.   I  can not notice
them all, nor dwell upon every point  of interest, for this would
require much more space than I can devote to the subject.  I
shall, therefore,  select those  points which can be  made  most
clear and interesting.
   274.  I first call your attention to the bones of the head, as
you see  them in Fig.  87.  There are twenty-two bones in the
whole head.   Fourteen of these belong to the face,  while eight
belong to the cranium, that is that part of the skull which in-
closes the brain.  Of these, notice  particularly the large  bone
in front  called the frontal bone, a, making the forehead, and
below  forming the upper portion  of the orbits  of the  eyes;
the parietal  bone, 6, the upper lateral part of  the dome of the
FIG. 87.
BONES OF THE HEAD. 
176
HUMAN PHYSIOLOGY.
       Why so many bones in the skull. The two tables, and the sutures.

skull;  and c the temporal bone  on which  the parietal bone
rests.   There is a  large bone  in the rear forming the  back of
the cranium as the frontal bone does the front.  There  are
also two bones in the base  of the cranium which  are out of
sight in this view of the skull.  You may, perhaps, be disposed
to inquire why this box for holding the brain, should be made
of so many bones.   One reason is, that the enlargement  of the
skull  from infancy to  adult  age is  effected  more easily and
better than it would be if the cranium were one bone.  Another
reason is, that even in the adult,  in whom these bones are at
length so tightly united, violence is less apt to produce injury,
from the giving, as it is  expressed, of the bones  upon each
other, than it would be  if one bone made the whole structure.
And this is especially true of the child, in whom the bones are
very imperfectly united.   Hence it is that the frequent falls of
children upon their heads so seldom  do any injury.
   275. The principal bones of the head are composed of two
solid plates, while  the bony matter between these plates is ar-
ranged in a cellular or sponge-like form.  The outer table or
plate (for both  of these  terms are used  in  relation to it) is
rather rough, and in some parts has ridges  for the attachment
of muscles.  But the inner plate  is very smooth on account of
the soft delicate organ that is  contained in the cranium.  It is
so brittle that it has been called the vitreous table, from its re-
semblance  to glass in this respect.  The  modes of the joining
of the  bones differ in the two tables.  In the outer table  the
joining is by a minute dovetailing, called a suture.  Numerous
little projections from one bone  fit accurately into correspond-
ing spaces in the edge of the other.   This is very well repre-
sented in Fig. 88,  in which you  see the sutures on the top of
the skull; b being the suture which is  formed between  the
two parietal bones; a a, that between  the parietal  and  the
frontal bone  in front;  and c c, that between the parietal  and
the bone which forms the back of the cranium.  A  better
joining for bones of such  a shape as these have can not be con-
ceived of.  But the inner table is joined differently.   It is so
brittle that the small projections of the dovetailing mode  of
joining would  not answer  here,  for they  would  break very
easily.  The joining  accordingly is  in this  case  by smooth
accurately  fitted edges, somewhat beveled, so  that one slightly
overlaps the other.
   276. The  upper part of the cranium is  in the  shape of a
dome,  and is  constructed upon the  same principles that such 
             THE BONES.                    177

The cranium a dome.  Contrivances for giving it strength.
FIG. 88.
SUTURES-IN THE  SKULL.
 structures are in regard to resistance  to  pressure or violence.
 Just  as in the domes that are built by man, so in this dome
 of  the cranium, great strength is  secured around  the lower
 part,  so as to resist outward lateral pressure.  In  the dome
 of  St. Paul's there is a double  iron  chain   around its base
 for this purpose, of course  concealed from view.  In the head
 of  man  the  dome may be  considered  as composed  of the
 frontal bone in front, the parietal bones  at the side, and the
 occipital  bone in  the rear.  In  front you see the  base  of
 the dome strongly fortified, in the heavy  arches that form the
 upper part of the sockets of the eyes, and on the jutting edges
 of which  are the eyebrows.   In the rear  the base of  the occi-
 pital  bone  is very thick, and is fortified with ridges which
 furnish attachment to the large muscles in  the back  of the
 neck.  But the most marked and interesting contrivance for the
 strengthening of the base of this dome is at  the side.   It is where
 the parietal bone b, as seen in Fig. 87, is joined by the temporal,
 c.   The joining here is not by suture, for that  would  afford no
 resistance to lateral pressure,  either outward  or inward.  To
 secure this object, the lower bone, the  temporal, laps over the
upper, the parietal, with a  beveled edge.  It abuts  upon  or
against it.  It has  the relation to the  parietal of a buttress to 
178
HUMAN PHYSIOLOGY.
                Defenses of the brain. Many and efficient.

 an arch.   You can  readily see that  when great pressure  is
 made on the top of the head, as when  a heavy load is  carried
 there, there must be a tendency to outward lateral pressure at
 the base of the dome  of the cranium, and that this is effectually
 resisted by the temporal bones acting as buttresses.  The same
 thing is true, also, when a blow is inflicted on the top of the
 head. And if a blow be  received at the side  of the head, on
 the temporal bone, it  is evident that the bones will not be so
 apt to be fractured and pressed inward upon the brain, as they
 would be, if they were united by suture.
   277.  You are now  prepared to see, to what extent the brain
 is guarded  against the effects of violence  inflicted upon the
 head.  These  effects  come  either  from fracture of the bones,
 or from concussion without fracture.   In either case the vibra-
 tion of the parts concerned  is the cause of these effects.  The
 guards of the brain defend it from  injury by lessening or dif-
 fusing this  vibration.  And it is  to be observed, that when
 vibration passes from one texture to  another, it loses  some of
 its force in the change.  No two substances vibrate just alike ;
 and when a vibration  in one is communicated to  another, it is
 modified, and  is therefore lessened.  Some  substances modify
 and lessen vibrations  communicated to them more than others
 do.   If you apply  these principles  to the effects of violence on
 the head, you at once see that the brain would be much more
 apt to receive a dangerous shock from the vibration occasioned
 by a  blow, if its coverings  were condensed  into one firm and
 thick layer of substance, than it is now.   So also, if the bones of
 the head were in one solid layer, instead of having two layers, or
 plates, with the spongy structure between, and the integuments
 were  all consolidated into one thick  substance, there wrould be
much more  liability to fracture than there is with the present
 arrangement.   Observe now how many, and how various  are
the textures, through which the vibration of a blow must pass,
before it reaches the brain.   Outside of the bone there  is first
the hair; next comes  the skin; then there is the cellular mem-
brane containing some fat;  then a muscular coat;  and lastly,
the lining  membrane over  the surface of the bone.  These
 various textures must deaden very much the force  of a blow,
 and  especially the outer cushion of  hair,  and those  inner
 cushions, as we may call them, of fatty cellular membrane and
 of muscle.   Then,  when the vibration  reaches the bone, it is
 lessened  by the two  plates with the  intervening cells, and
 there is diffused largely among the many bones that unite with 
THE BONES.
179
                Skull especially guarded at some poiuts.

the one  on which the force comes.   Then as the  shock goes
into the brain,  it is still  farther lessened by the  membranes
which cover that organ.  These greatly diminish the vibration,
precisely as a coating of leather on the inside of a bell would
deaden its  vibration when  produced by a blow  upon the out-
side.   With  all  these provisions the result is, that comparative-
ly few of the blows received by the head do harm.  The skull
may be considered as  a sort of helmet for the brain, its effect-
iveness as  a defense being very much  increased by its  cover-
ings and linings.
   278. There are some especial guards at particular points in
the  cranium, where there  is  much liability to  exposure  to
violence.   Thus, as  the lower part of the  frontal bone, where
the eyebrows are, is especially exposed, the distance from the
suBface to  the brain is made  considerable by an  intervening
chamber in  the bone, called  the frontal sinus.   This sinus,
which varies much in size in different individuals, is lined with
a membrane, and  communicates with the  nose.  You can see
that this arrangement is  a great protection to the bone at that
point.  The outer plate could be broken, while the inner is not
injured.  But the protection which  this  arrangement  affords,
is not confined  to that single point; it serves  also to  deaden
the vibration  of a blow  received by  any part of the forehead,
or by the forehead as  a whole.   The side of the head,  too, is
peculiarly  exposed  to blows.    And,  therefore, the  skull  is
peculiarly guarded at this point. Beside  the overlapping of
the temporal bone upon the parietal, to which I have  before
alluded, the  parietal bone is  made thicker, at  its  lower part,
where it is most liable to be struck, than  it is  in most of the
other  parts  of  it.  Then,  too,  the  place of joining   of the
temporal and parietal bones is covered over by a thick muscle,
the  contractions of which you can feel if  you  press your
fingers upon the temple while moving the lower jaw as  in eat-
ing.  This cushion  of muscle is of great use in breaking the
force of a blow  received in that  quarter.   Other points  might
be  specified where there is arrangement for special protection,
but those to  which I have alluded will suffice.
   279. The cranium not only contains  and protects the brain,
but it at the  same time serves various other purposes, and pro-
tects  other important organs.   The tender and delicate eye has
there a bony socket with jutting prominences all around it, to
guard it against violence.  The  exceedingly minute and com-
plicated apparatus of the hearing is also carefully protected by 
 180              HUMAN PHYSIOLOGY.
              Complicated and extensive cavities in the nose.

 the skull, and the most  important part of it is furnished with
 winding and intricate apartments, halls of audience, in that part
 of the temporal  bone which  is  so hard, that it is called the
petrous or rock-like  bone.  To the bones  of the cranium are
 attached in  various ways, the fourteen bones of the face.   All
 these,  with  the  exception of the lower jaw, are immovable.
 The two principal of them are the upper jaw bone, and the
 cheek  bone.   The former makes with its mate of  the other
 side the forward  portion of the roof  of the mouth, the palate
 bones  making its rear portion; and it furnishes the sockets for
 the teeth.   It also at its upper part makes  nearly the whole of
 the floor  of the orbit of the eye.  The  cheek-bone forms the
 outer lateral part of  the socket of the eye,  and sending back  a
 process or projection to unite  with one from the temporal bone,
 c, Fig.  87, forms the zygoma or arch, inside of which the tempo-
 ral muscle passes down to be fastened to the lower jaw.  The
 bones of the nose make quite a complicated series of  cavities,
 for the purpose of presenting, in the mucous membrane, which
 lines them,  a  large  surface, over which the nerve of smell is
 expanded.   A representation of these cavities  is given in Fig.
 89 ; in which a is the mouth ;
 b, the  opening into  the nos-              FIG- 89-
 tril; d, a part of the base of         m   g   I        i
 the skull; c, the communica-
 tion  of the nostril  with  the
 back of the throat; e, the cur-
 tain of the palate; I, the front-
 al sinus ; m, another large si-
 nus ; g, i, h, spongy bones pro-
jecting into  the  cavity of the
 nostril.  There is a large sinus,
 that is not seen  in this figure,
 which  lies over the teeth in         e           a
 the jaw-bone.  The different    inner bones of the nose.
 sinuses are lined with the mu-
 cous membrane extending into them from the nose.  These, with
 the spongy  bones make  a very large  extent of surface in the
 cavities devoted to the sense of smell.  The branches of the
 nerves of smell  enter these  cavities, to  be  distributed over
 thin walls,  through  many small openings in a bone in the
 roof of the nose, giving it a sieve-like  appearance.
   280. The lower jaw is a bone shaped something like ahorse
 shoe, with its ends  turned considerably upward.  It has two
 
THE BONES.
181
Structure of teeth. Three different kinds of texture.
smooth projecting  surfaces which articulate with two corres-
ponding shallow cavities in the temporal bone.  Its prominence
at the  lower part in front, the chin, is peculiar to man, there
being no  such prominence in any other animal.  The  lower
jaw has sockets for the teeth, and it is  so constructed, and is
so arranged with muscles, that these  teeth  can be  brought to
bear against the teeth of the upper jaw  in  cutting and grind-
ing motions.
   281. The  teeth  are very  nearly  like the  bones  in their
structure, but they  differ from them in some particulars which
it will be  interesting to notice.  Every tooth has in it three  dis-
tinct structures, which differ in hardness, for reasons which  will
appear clear to you as I proceed.  The dentine or ivory consti
tutes the body both of the tooth and of its fangs.   In the body
of the tooth there is a coating of that very hard substance, the
enamel, over the whole surface of the ivory.   This is thickest
over the top of the tooth, and grows thinner on the  sides till
it is entirely gone  where the gum begins.   The ivory in  the
fangs has a coating of a very different character, called  the
cementum.  It is not hard like the enamel.   This arrangement
is represented  in Fig. 90.   This is a tooth with  two fangs or
roots;  1,  is the enamel; 3, the  den-             VJfl Qn
tine or  ivory:  2, and 7, the cement-
um ; 4, an unnatural enlargement of
the  cementum, making  an  excres-
cence ;  5, the  cavity of  the tooth
supplied with bloodvessels and nerves
which  come  through the  channels
that you  see running up the  middle
of each fang.   This cavity is analo-
gous to that which is found in the
shafts  of  the long  bones  as seen in
Fig. 83.  The ivory and the cement-
um are seen by the microscope to be
very  different textures.   The ivory
is traversed by innumerable branch-
ing tubes running  from within  out-
ward  towards  the  cementum,  as
represented in Fig. 91.  This  is a
section of a  small  portion  of  the
dentine and cementum in the fang of a tooth, very much mag-
nified, a, a, being the dentine,  and c, c, the cementum, evidently
a different structure.   The structure of the enamel as exhibited
                           16
        Vertical
SECTION OF A TOOTH. 
182               HUMAN  PHYSIOLOGY.

              How teeth are different from bones, and why.
FIG. 91.
by the  microscope is  represented  in Fig. 66  and 67,  in  the
chapter on Cell-Life.   I have  been  thus particular in  the
description of the  parts of a  tooth, that you may see how
compound even so apparently simple a part  of the body is.
The three different structures in it are built by cells, and  the
cells of each part select from the blood such constituents as
are needed for their purpose.
   282.  A tooth differs from a  common bone  in one import-
ant particular—when  once formed it is  never altered  in  its
size.   A bone  grows with  the  growth of other parts of the
body ;  but a  tooth, when it first protrudes  through the gum is
as large as it ever will  be. The reason  of this  is,  that  so
hard a  substance  as enamel can not be made changeable as
bone is.   Its hardness is inconsistent with any thing like cir-
culation in it, and without circulation there can be no change.
If the enamel were not needed, and  the teeth could be com-
posed only of  dentine, they could  grow  as  other  bones do.
And if they could grow, one  set of  teeth might  be made to
answer  the purpose.  As it is,  the second  set are  needed, be-
cause as the jaws grow, the first set are ueither  large enough in
proportion to the  size of the jaws,  nor numerous enough to
fill up  the whole  space.   If the first set were  to be the only
set, when the jaws became  of their full size, the teeth would be
altogether too  small, and would be quite separated from each
other.   Twenty small teeth (the number of the first set)  in the
jaws of an adult, in place of the thirty-two large teeth  of the
second  set, would present a very odd  appearance, besides being
incapable of doing the service required of them. 
                       THE BONES.                    183
       Hyoid bone.  Patella.  Spinal column. Its firmness and flexibility.

  Under the lower jaw is a little bone, called from its resem-
blance to the Greek letter  v,  the hyoid or u-like  bone.   Its
round end is towards the root of the tongue,  and its two ends
reach backward towards the spine.   The larynx is suspended
from  it as from  a frame, and  the muscles  that  draw up  this
bone, draw up the larynx with it.  It is one  of  the few bones
in the body that are not  directly connected  with any other
bone.  The patella, or kneepan, is one-of  these bones.  The
four little bones in the ear, of which  I shall speak particularly
when I come to treat of the sense of hearing, are  not connected
with any other bone.
   283. I  pass now to the bones of the  trunk of the body.  I
shall  speak first of the spinal column, or the backbone, as it is
called  in  common language, as  if it were  all one bone.   In
some respects it does act as one  bone, although  it is made up
of twenty-four distinct bones.  It is the  great  pillar of   the
body.  As such, it has the  head resting  on  its top, and  it fur-
nishes support for the walls  of the chest, and for the muscles
which make up the most of the walls of the  abdomen.  To it
also are fastened, as you have seen in the chapter on Digestion,
the mass of intestines in the abdomen, and  indeed to some  ex-
tent all the viscera both of the  abdomen  and the  thorax.  Sus-
taining, therefore, as it does so much  weight in so many ways,
it stands firmly planted on its great pedestal,  the strong broad
bone of the pelvis, the sacrum.   And  this pedestal is supported,
as I have before said, after the manner of a keystone, between
the lighter spreading bones of the pelvis on  either side.  But
while the  spinal column acts as a strong and firmly supported
pillar, it is necessary that it should he flexible for the  different
motions of the body.  It is  therefore  composed of twenty-four
bones called the vertebra, so that, as in any considerable motion
of the column  as a whole,  there  is but little  motion between
any two of them, the motion does not interfere with its office as
a firm pillar.  It is most free in its uppermost part, the neck ;
it is considerable in its lower part, the small  of the back;  and it
is least of all in that part to which the ribs are  joined.  You
readily see the  reasons for  this difference in motion in different
parts of the column.  For the varied  motions of the head there
is need of a free movement between the vertebrae.   Then for  the
twisting and turning motions  of the body, you  have the  free
movement between  them  at  the  lower part of the column,
which is easily provided for  there, because there are attached to
that portion of it nothing but parts that are pliable.   It is  not 
184               HUMAN  PHYSIOLOGY.
             Vertebrae.  Processes for locking strongly together.

so with that portion of it that forms the supporting pillar of the
framework of the chest.   There is  little motion here between
the vertebrae, because the joining  of the ribs to the column
forbids it.
   But besides serving as a firm pillar,  and as a flexible chain,
the spinal column also  forms a canal or tube in which  the
spinal marrow, one of the most delicate and  important organs
in the body, is securely lodged.  This canal extends through its
whole length, and from the spinal marrow included in it there
pass out the nerves to go to all parts of the body.
   284.  Having  thus presented a  general view of the  spinal
column, I will now give a particular description  of the form
and arrangements of the bones of which it is composed, so that
you may  understand how the various  objects of this wonderful
structure are  secured.  In Fig. 92 you  see a  representation of

           FIG. 92.
               c
A VERTEBRA.
one of the vertebra?;  a, being the body of the bone ; b, the hole
which forms this  vertebra's  part  of the canal for the spinal
marrow ; and c, the spinous process.  It is these spinous pro-
cesses that make the  row of projecting points seen  down  the
length of the back.  There are six other processes, only four of
which you can see in  the figure.  Four of these processes serve
to lock  the vertebra with its two  adjoining ones  above and
below, which they  do so strongly,  that'there can be no disloca-
tion of them without  a fracture.  Fig. 93 gives  a side view of
a vertebra.  Strong ligaments bind these bones together, and
there are very numerous muscles attached to the  processes, so 
THE BONES.
185
Spinal column. Canal through it. Cartilages.
that this jagged column of bones is very thoroughly enveloped
in softer substances.
   285. In Fig. 94. you  see the  whole
spinal column with the sacrum  on which
it stands.   It  is  laid  open by a verti-
cal section dividing it into two  halves, so
as to show the manner in which  the bones
form the tube  that  contains the  spinal
marrow.  The darkly shaded strip through
the  length  of  the figure represents  this
tube.  It extends, you  see, down  beyond
the limits of the column itself through the
sacrum.   It  is  bounded in  front  by the
bodies of the vertebrae represented as sawn
through from front to rear, and  by the
spinous processes behind also sawn in the
same way.   In this  canal you  see  there
is a  row of little openings,  arranged just
behind  the  bodies  of  the   vertebrae.
Through these  openings,  each  of which
is between two of the vertebrae, the nerves
go out from the spinal marrow.   The ar-
rangement is such, that the nerves are
very securely guarded against the hazard
of pressure in the movements of the verte-
bra?  upon each other.   You  see also that
there are spaces between the bodies of all
the vertebrae.   These are filled  with  car-
tilages, which vary in  thickness  in differ-
ent parts of the  column, from one quarter
even  to three quarters  of an inch, being
thickest  in  the  lower part of the back,
where the backward and forward motion
of the vertebrae upon each  other is the     spinal column.
greatest.  Each  cartilage  is firmly  fas-
tened to the two vertebrae, between which
they are situated, by the rough surface of the body of the bone
which you, see represented in Fig. 92.   This arrangement of
cartilages is an important provision for the motion of the spinal
column.   It  contributes greatly to its flexibility.   When  you
stoop forward, all of the cartilages are  compressed, and when
you rise  up  they return to  their usual size  by their elasticity.
And  besides this, they serve to  diminish any shock  which
                             16* 
186
HUMAN PHYSIOLOGY.
             Spinal column shaped so as to guard against shocks.

might otherwise be transmitted through  the  column of bones
to  the  head with too  great  force.   There is another guard
against the injurious transmission  of shocks to  the brain, in the
shape of the spinal column, the twenty-four  bones being ar-
ranged, not  in a straight line, but in  a double curve.  The
vibration, communicated upward through the spinal columnr is
thus not only lessened by  the elasticity of the  cartilages, but is
also distributed in different directions by the  curved arrange-
ment of the  bones.  If the column  had  been made straight,
the  head  would  have  been  subject to frequent jars  in  the
movements  of the body,  which  would  be disagreeable  and
often injurious.
   286.  You have thus seen  how three different objects,  ap-
parently incompatible with each other, are accomplished in  the
arrangement of the spinal  column.  To put twenty-four bones
together in such a way,  that they shall form a strong firm
pillar for the whole frame, and yet they shall  make a column
or chain flexible enough for the various  motions of the trunk
of the body,  and  at the same time provide in this column a se-
cure canal for the rod of nervous matter which moves all  the
muscles of the body, is to produce  a piece of mechanism which
far transcends any thing that has ever been  contrived by  the
ingenuity of man.
   287. There remains to be  noticed one especial  contrivance
in the spinal column.   It is  at its summit, and it is for  the
purpose of providing for the free motions of the head in various
directions, and at the  same time securing the spinal marrow at
that part from  all hazard of pressure  from  these  motions.
These two objects are accomplished in this way.  The head in
moving backward and forward rocks on two smooth surfaces on
the first vertebra.   But when the  head moves to the right and
left, this first vertebra moves along with the head on the second
vertebra.  And there is a tooth-like process that projects up
from the second vertebra inside of the first, around which this
rotary motion is performed.  In Fig. 95 is represented the first
vertebra.  J. J. are the two surfaces on which the  head rests,
and  rocks  backward and  forward.  A is the  opening for  the
spinal marrow.  L is the  strong ligament which  confines  the
tooth-like process that projects upward from the  second verte-
bra.   In Fig. 96 is the second vertebra.  P is the tooth-like
process, around which the first vertebra rotates,  carrying  the
skull with it.  You see it is smaller at its root than at its top.
This smaller part is bound firmly by the  ligament in the first 
                       THE BONES.                     187
                Arrangement of first and second vertebrae.

vertebra.  It is shaped thus to prevent its slipping out from the
ligament.  J, J, are the two surfaces on which the first verte-
bra moves as it rotates around the tooth-like  process.   Fig. 97
shows the two bones together, the tooth-like process being con-
fined in the ring of the upper bone.  Special pains are taken to
make this arrangement secure,  that the process  may not be
in danger of pressing upon the spinal marrow at this important
point.   It is thus that the lateral rotary motion of the head and
the forward and backward motion are secured by two joints,
just  as  is done in the mounting  of a telescope.  The difference
between the two cases is, that in the mounting of the telescope
there are no difficulties to overcome,  while  in arranging the

                           FIG.  95.
(SECOND VERTEBRA. 
188              HUMAN PHYSIOLOGY.
Special defense of spinal cord in neck of birds.
mounting of the head, as we may term it, a peculiar contrivance
and a nice  adjustment are needed to prevent injury of a very
important organ.   It  is a wonderful  contrivance,  by which  so
much and so varied motion can be effected in the very walls that
contain the soft and delicate  spinal marrow, without injuring
it.  You will fully appreciate this, if you observe the extent and
variety of the motions of the head and neck, executed chiefly
with the two bones that I have described.
   288. In the neck of birds there is a contrivance of a different
character, for the arrangement which  answers for the motions
required by man, obviously could not secure the very free mo-
tions which the bird executes with its neck.   As the bird bends
its neck  at such abrupt angles in all directions, a peculiar ar-
rangement of the vertebrae is necessary, to  prevent the spinal
marrow from being pressed upon.   The arrangement is a sim-
ple, but  effectual one.  I can make this plain
to you by the rough diagram in Fig. 98.   A, A,       F1G- 9a
are two of the vertebrae of the neck laid open.
B is the  spinal canal, and C is the spinal mar-
row.   You observe that each vertebra is larger
at its  ends than in the middle, allowing at the
joinings of the bones, where  the  motion is,  a
considerable space between the bone  and the
spinal cord.   Now if each of these bones were
of equal size throughout, and the spinal mar-
row filled up the canal, you  can readily see
that when  any  two of  these were much bent  spinal column
upon each other, there would be pressure upon       in Birds-
the spinal  cord; and  pressure would produce palsy, and often
destroy life.   But with the simple arrangement above described,
free motion, almost to  a right-angle in some directions, can be
executed without pressing on the cord.  And besides this, you
can see that the cord by this  arrangement will not be  bent at
an angle, as the  vertebra?  are, but in a curve, for the spaces in
the spinal canal at the joinings allow of a lateral movement of
the spinal marrow at these points.
  289. It would be interesting to consider in full the variations
in the spinal column in different classes of animals.   But I will
only allude to  a few of them.  In  quadrupeds,  as they have
their heads  suspended, instead of being supported, as in man,
upon a column of bones, the spinous processes in the neck are
very large,  and project  much, for the  attachment  of strong
muscles which hold up the head and move it.   There is also
 
THE BONES.
189
FIG. 99.
VERTEBRA
  of a Fish.
FIG. 100.
           Spinal column in fishes, reptiles, and in neck of giraffe.

attached to these processes, a very stout fibrous ligament, com-
monly called  the paxy-waxy, to assist in sustaining the head.
In fishes the  spinal column is so arranged as to
give it a great flexibility.   In Fig. 99 is repre-
sented one of the vertebrae of a  fish.  If you
compare it with a human vertebra, as seen  in
Fig. 92,  you will see  that it differs very widely
from it.   It has no transverse or side processes.
While the human vertebra has one spinous pro-
cess that projects  behind, this has two ff one
in front and one in the rear, or rather, according
to the usual  position of the fish, one  above and
one below.   The body of the vertebra has a cup-
like cavity on each side towards its neighboring
vertebra.  When, therefore, two of these vertebrae
are joined together, their two cup-like cavities make
one cavity of  the shape of a double cone, as  seen  in Fig. 100.
This is a representation of a section
of a portion of the  spine of a fish.
The division  is made  so as to  cut
the vertebrae  into two halves, and
thus  show  these   cavities.   Each
one of these  contains a sac which
is filled  with  a gelatinous  fluid.
This arrangement,  which  secures
very great flexibility of the spinal
column,  you  can  examine  at any
time when you have  fish  on  the
table.   The long spinous processes
make the broad frame-work of the  spinal column of a fish.
animal, to which  its  muscles  are
attached.  In  reptiles there  is still  greater  flexibility  of  the
spine  than  in fishes.   This is secured in  two ways, by the
great  number of the  vertebrae, and by a peculiar arrangement
of them.  There are three  hundred  and four vertebrae in the
boa constrictor,  over three hundred  in the  common ringed
snake, and over two hundred  in the rattle-snake.   The articu-
lations of the vertebrae in reptiles are with  a ball  and socket
arrangement.   The forward  part of each vertebra has a  deep
cup-like  depression, in which plays a round  smooth ball from
the  back part of the  next vertebra.   And  as these joints are
firmly  bound  together by ligaments, the spinal column is very
strong as well as flexible.   In the gracefully flexible neck of the
 
190
HUMAN PHYSIOLOGY^
          Arrangement of collar-bone, shoulder-blade, and breastbone.

giraffe we  have the same  ball and socket articulations of the
vertebrae.
   290. The  framework of the chest I have already described
sufficiently in  the chapter on Respiration.  The breastbone,
which is flat and  of simple form in  man, is  much larger and
less simple in its form in some animals.  In birds it is not only
broader, but  it  has a  keel-shaped projection for  the attachment
of the large muscles used in flight. . The clavicle, g, Fig. 86 (so
called from  its resemblance to a key,) and  commonly called
the collar-bone, is  attached at one end to the top of the breast-
bone, and at  the other unites with a process of the scapula, or
shoulder-blade  at the  top of the shoulder joint.   It is a  prop  to
the shoulder,  pressing it outward ; and accordingly it i* large in
those  animals,  the movements  of whose  superior extremities
tend to bring the shoulders towards each other, while it is very
slender, or absent even,  in  those  the  tendency of whose move-
ments is to  keep the  shoulders apart.   Thus in birds the
drawing down of the  wings by the strong muscles would  bring
the shoulders towards each other, were this not prevented by
stout clavicles.   Sometimes a  second  bone is  added  for the
same purpose.  But in the horse  and  other similar animals, the
pressure of the body  downwards  between the shoulders  tends
to separate them, and here we find the clavicle deficient because
it is not needed.  The scapula, or shoulder blade is a thin bone
with a stout raised spine or ridge running across it, and ending
in forming the  top  of the  shoulder joint.  It is  situated differ-
ently from any other bone in the body.   It is  imbedded  in
muscles and has a very  free motion.   Its design is to give free-
dom of motion to the arm.  It is directly connected with the
skeleton only by its union with the clavicle.  In Fig. 101 you
see the arrangement  of the clavicle, scapula, and breastbone.
C, C, are the scapulae or shoulder-blades.  A, is the upper part
of the breastbone.   B, B, are the  clavicles fastened  to the
breastbone at one  end,  and to the  shoulder-blade at the  other
end at E, which is a process of the shoulder-blade, making the
projecting top of the  shoulder-joint.  D, is  another process of
the shoulder which serves for the attachment of muscles and
ligaments.  It  is called the coracoid  process, from its resem-
blance to the beak of  a  crow.
   291. The  upper extremity  is  divided into  three parts, the
arm, the forearm, and the  hand.   The arm has but one long
bone, the humerus, i, Fig.  86.  This has a  round  head which
moves in  a shallow oup formed  by the shoulder-blade.   The 
THE  BONES.
191
Collar-bones. Shoulder-blades.  Bones of the forearm.
FIG. 101.
THE  COLLAR-BONES  AND  THE SHOULDER-BLADES.
                                         FIG. 102.
 
192              HUMAN  PHYSIOLOGY.
   Arrangement of the bones of the forearm for rotary motion.  Bones of the hand.

shallowness of the socket is  the cause of the frequent disloca-
tion of the shoulder.  But if there were a deep socket like that
in which the head of the thigh-bone is, the arm could not have
any thing like the freeness of motion that it now has.  Such an
arrangement would involve too much of a sacrifice of necessary
uses for the  sake  of security.   At its lower part the  humerus
makes a  hinge  joint with  the forearm.   The  forearm  has
two bones, the radius, b, Fig. 102, and the ulna, a.  The par-
ticular arrangement of  these two bones is worthy of notice.
The hinge-like motion  of the forearm upon the arm is per-
formed by the ulna alone.   This bone has a beak-like process,
which works  over a smooth round surface  at the  end of the
humerus.  It is the outside of  this  process which  you feel at
the point of the elbow.  The other  bone, the  radius,  has
nothing to do with this motion.  This only rolls  on the  ulna
in the rotary motions of the forearm.   But at the other end of
these  bones, at the wrist, the arrangement is reversed.   Here, it
is the radius on which the hand moves in a hinge-like manner,
while the ulna at c rolls on the  radius, as the radius does on the
ulna at the elbow.  You can readily  see that as the radius rolls
on the ulna at the elbow, and the ulna on the radius at the wrist,
a very free rotary motion of the forearm is provided for.  The
combination of this motion with the motions at the wrist, the el-
bow, and the shoulder, secure that almost endless variety of move-
ment, which is so striking a peculiarity of the upper extremity,
as  compared with the lower.   The hand is divided into three
parts, the carpus, p, Fig. 86,  composed of eight small bones,
the metacarpus, q, composed of bones which are like  the bones
of  the fingers, r.   The  eight bones  of the carpus are firmly
packed  together,  but they have  a  slight motion  upon  each
other, and this, together with the motion  of the  metarcarpal
bones, makes the hand a more easy, light,  and springy instru-
ment  than it would be, if these  bones were all consolidated into
one.  The metacarpal bones  are the framework of  the flat part
of  the hand,  and to them are joined  the first row of  the bones
of  the fingers.  The  metacarpal bone of the thumb has a very
free motion upon the carpus, differing in this respect altogether
from  the metacarpal bones in  the  body of the  hand.   The
bones in the  wrist and hand are bound together by very strong
ligaments.  Those which are seen in the palm of the hand are
represented  in  Fig.  103.  Those which you see at a, b, and c
bind  the  small bones of the wrist together, and  also tie them
strongly to the bones of the forearm, the ends of which you see 
THE BONES.
193
Ligaments of the wrist and the hand.
FIG. 103.
in the Figure.   The bone at b, to which so many of these liga-
ments are attached, is the prominent bone which you feel at the
beginning of the palm of the hand on the side towards the
body.  The ligament g connects this bone with the metacarpal
bone of the little finger.   At d, d, are ligaments which running
across the hand bind  the metacarpal bones together at their
beginning.  At e, e, are  similar ligaments where the  bones  of
the fingers join  them.   The bones of the fingers and thumb are
strongly  held together  by lateral ligaments,  as seen  at /,/.
The various ligaments of the wrist and hand  permit a slight
motion between the bones; and  thus  the hand has freedom
and ease  in  its  motions while it is  also a very  strong and firm
instrument.
   292. The lower  extremities have  some resemblance to the
upper in  their structure and arrangement, but  they differ from
them in  some important respects.   Here firmness is the chief
object, while freedom of motion is  the great thing to be secured
in the structure of the upper  extremities.  The lower extremi-
                            17 
194              HUMAN PHYSIOLOGY.
Bones of the leg and the foot.  Arranged for firmness.
FIG. 104.
ties  are chiefly  for locomotion, but the upper are fitted for a
variety of purposes.  The  body  is supported upon the lower
extremities,  and, therefore, the thigh-
bones have  sockets in the  broad flar-
ing bones of the pelvis m and I, Fig. 86.
In Fig. 104 is represented a rear view of
the thigh-bone.   Its head, a, is round,
and fits into  a  deep  socket in  the
pelvis.  At  6 is  a depression in which
one end of  a stout short ligament is
fastened, its other end being attached
to the bottom of the socket.  At c is
the neck of the bone; at d and e are
two projections to which are attached
large muscles  to  move  the  limb.
Along the shaft of the bone,  g, there
is a rough ridge, h, to which  muscles
are fastened;  i and k are two smooth
surfaces for articulation  with  the leg
below.  At  t, Fig. 86  is  the  bone
called the patella  or  kneepan, which
answers  as a defense to  the joint,
and  at  the  same time   affords  a
mechanical  advantage to the  muscles
which throw the leg forward.  These
muscles  are  fastened to  the upper
part of the patella, and then a  con-
nection is formed by a strong tendon
between  its lower  part and the  large
bone of  the  leg.  You see  at  once
that the leg  can be thrown  forward
with more force by this  arrangement,
than it could be if the tendon of the
muscles passed  over the front of the
joint without any  patella.   I  shall
refer to this again in the Chapter on  the Muscles.   The leg,
like the forearm, has two  bones, v and u, Fig. 86 ; but unlike
them they are constructed and arranged for strength, and not
for freedom of motion.   The foot, like  the  hand, is divided into
three parts.  The tarsus, a, Fig. 105,  is that part of the foot
which extends from the  heel  to  the middle of the foot.   It is
composed of seven  bones, the  largest of which makes the body
of the heel. •  The metatarsus, b, has five long bones reaching
 
THE BONES.
195
Elasticity of the foot.  Arrangement for oiling the joints.
FIG. 105.
from the tarsus to the toes.  The toes, c, have fourteen bones.
The object of having so many bones in the body of the foot is
to give a certain springiness to it, which guards against shocks,
and facilitates motion.   Its arched form also tends to secure the
same  object.  In every movement of the foot there is  a slight
motion between all these bones.  Thus in walking, when the foot
first touches the ground, it does so at the heel,  as represented in
Fig. 105.   Then as the body moves forward, the fore-part of the
foot is brought down, the weight of the body  at length press-
ing upon  the ground at the ball of the foot, b.   In  executing
this  movement, elasticity  is given to the tread of the foot by
the very  slight motion  which  occurs  between  these many
bones.  If the body of the foot were  all one bone  it would
manifestly be a very stiff and  awkward affair, and ease and
grace in walking would be an impossibility.  With such a foot
we should not walk  much better than one does with  a wooden
  &"                                              FTP  106
   293.  Before leaving the  subject of the
bones, I  will call your  attention  to the
provision  which  is  made  for  the  easy
movement of their  joints.   The  ends  of
the bones are tipped with cartilage, so as
to afford a firm but smooth surface for the
motion  of the one bone  upon the other.
Besides this  provision, the  ends of every
two bones that move upon each other are
lined with a membrane, so arranged  as to
make a blind sac.   This  is illustrated  in
Fig. 106, in which a  and b are the  ends
of two  bones, the  sac, c, lying between
them represented here as detached  from
the bone, in order  that the arrangement        diagram
may be  clear to you.   It is as if a small   showing the lining of a joint.
 
196
HUMAN PHYSIOLOGY.
           Each fibril of a muscle supplied by a nervous tubulus.

bladder were introduced between  the  two ends of the bones,
and were  fastened  all over the surfaces that press  together.
The  inside of this sac is kept lubricated with a bland fluid re-
sembling the white of egg,  so that the joint may work easily.
This fluid is secreted by the membrane  itself, and the moving
machinery of the human system  may therefore be said to oil
its own joints.  In the knee-joint, the  broad surfaces of which
are subjected to so much pressure, there are two flat  pieces  of
cartilage loose in the joint, which operate like friction wheels in
lessening  the friction.  There  is  a similar  provision  in  the
articulation  of  the lower jaw.  This  member  does  so much
work in talking, and such heavy work in mastication,  that each
of its  joints has  a  movable cartilage  for the  diminution of
friction.   Sometimes when the lubricating fluid is deficient,  or
becomes too  thick, a disagreeable  crackling noise  is  produced
by these cartilages in the motions of the jaw.
                  CHAPTEK  XII.

                       THE MUSCLES.

  294.  Having described the bones, I now proceed to  speak
of the muscles, which move them and other parts of the frame.
I have  already described the structure of muscles in  § 203 in
the chapter on Cell-Life.   Each fibril, you there saw, is a chain
of cells, and it is the shortening of all these chains of cells in a
muscle that produces its contraction.  The action of  a  muscle
is dependent upon the nerves.  Each fibril  has a  nervous fibril
or tubulus, (§  232.) by which its connection with  the brain or
spinal marrow is established.  And each fibril is in this respect
probably wholly separate from every other fibril.  When,  there-
fore, the mind wills that a certain motion  shall be performed,
an impression  (§ 232) is sent to each fibril of every muscle en-
gaged  in  that motion,  through  the  tubulus devoted to that
fibril.  When the  action is a very compound one, calling into
operation  many muscles, a multitude of these impressions are
communicated through  a  multitude  of  distinct channels or
tubuli.  The individual is not at all conscious of the compound
nature of muscular action, and he knows nothing of the muscles 
THE MUSCLES.
197
            Relation of muscles and tendons.  Their relative size.

which produce  any particular movement, unless he has studied
anatomy and  physiology.   He  wills the  movement to take
place, and  at once the requisite impressions are sent along the
appropriate channels or tubuli to their destination.  These im-
pressions must differ in  degree or intensity  in producing differ-
ent amounts of motion ;  and they must  differ in  some cases  in
different parts  of the same muscle,  as  some fibres  are put  in
motion  while others are not, or as some act with more force
than others.   I will not dwell  here  on this  point, as I shall
recur to it in  another part of this  chapter,  when  I  come  to
speak of the compound character, and the varieties of motion.
   295.  Muscles commonly end in tendons, which, as they are
white and  shining, are quite in contrast with the  red muscular
fibres.   The tendons have in themselves no power of contrac-
tion, but are mere  passive cords.  They have the  same relation
to the  muscles, that ropes have  to  the men  that pull them.
They are of various shapes, according to circumstances.  Long
and slender tendons may be seen on the back of the hand  in
thin persons, the  muscles that pull them being in the full arm
above.   The tendons are not bounded by a distinct line where
they join the muscles, but tendinous  and muscular fibres inter-
twine,  so that they appear to  run insensibly into each other.
Tendinous fibres also mingle in the same way with the fibres  of
bone, making so strong  an union, that a great force exerted  in
pulling  on the tendon will sooner effect a rupture of  the tendon
or the bone, than a separation of the connection between them.
The tendons  are  very strong,  being  made of very condensed
fibrous substance.  The tendon of a muscle is, therefore, much
smaller  than the muscle itself.   This  is a circumstance of much
importance in the arrangement of the moving apparatus of our
frames.   The  bulky muscles and the slender tendons,  are  so
arranged, for example, in the limbs, as to give them both free-
dom of motion and beauty of form.   The muscles that move
the fingers  help to  make up the  full part of the arm, while
their slender tendons occupy but  little space as they play over
the bones  of the wrist.  If there were no tendons,  and the
muscles were extended to the parts which they move, the hand
would be a large cumbrous mass, instead of the light and agile
thing that it is now.   For the  muscles would of necessity  be
continued of their full size, and, therefore, the bones would  of
course  be  very large  in order to  afford an attachment to the
muscles.
   296.  In  the  action of the muscles upon the bones, we have
                           17* 
198               HUMAN PHYSIOLOGY.
         The three kinds of lever exemplified in the action of muscles.

examples of the three kinds  of levers treated of  in natural phi-
losophy.  Some of these I will  now notice.  The first kind of
lever has the fulcrum between  the  weight and  the power, as
represented in Fig. 107.   F  is the fulcrum, W the weight, and

                         FIG. 107.
FIRST KIND OF LEVER.
P the power.  You have examples of this lever in the common
pump handle, the beam of a pair of scales, the crowbar, as
commonly used, scissors, &c.   You have an example of this form
of lever in the  human body, in the action  of the muscles in
moving  the head back  and forth  on the  top  of  the spinal
column.  In this case, when the head is  moved forward, the
top of the spine is the fulcrum, the weight to be moved is the
back of the head, and the power is the contraction of the  muscles
that bow the head forward.  When the head is bent backward,
the power  is the contraction  of the muscles behind, and the
weight is the front part of the head.  The muscles  that move
the head backward are stronger  than  those that move it for-
ward.  It is necessary that it should be so, for there is more of
the head in front of the point of support or fulcrum  than there
is behind it.  Hence, when sleep relaxes the muscles, if we are
sitting up the head falls forward.
  297. In the second kind of lever the weight is between the
fulcrum and the power, as  represented in Fig.  108.   The com-
mon wheelbarrow is  an example of this  form of lever.  You
have an example of it in the body in the raising of the heel

                            FIG. 108.
SECOND KIND OF LEVER. 
THE MUSCLES.                  199
                   Motion of the foot in walking.

from the ground in walking.  In  doing this the weight to be
raised  is the whole body, the foot being  the lever, and  the
forward part of the foot being the fulcrum.   This will be made
clear by Fig. 109.  W is  the large bone of the leg sustaining
FIG. 109.
the weight of the body; F, is the fulcrum, the forward part of the
foot that presses on the ground as the heel is  raised; and P, is
the large muscle in the calf of  the  leg, the  power that raises
the heel, the end of the lever.
   298.  In  the third form of lever the power is between the
weight  and the fulcrum.  A common example of this is  seeu
in the raising  of a ladder.   The fixed foot of the ladder is the
fulcrum, the ladder itself  is the weight, and the  power is ap-
plied as far from the fulcrum as it can be.   Fig. 110, represents

                          fig. no.
THIRD KIND OF LEVER.
a lever of this kind.  This form of lever is  more frequently
used than the other  forms in the human body.  We have an
example of it in bending the forearm upon the arm as seen in
Fig.  Ill, in which 1 is the  bone of the arm;  2, the bones of
the forearm ; 4, the  muscle which bends the forearm  upon the
arm; 5, its double headed attachment above; and 6,  its at- 
200
HUMAN PHYSIOLOGY.
Two objects aimed at in muscular action ; quickness and power.
tachment to the ulna, the chief bone of the forearm.  In this
case the fulcrum is  at 8, the joint of the elbow, the weight is
the hand with whatever it holds, and the power is applied  at
the point where the tendon is fastened to the ulna, that is, as in
the case of the ladder, between the fulcrum and the weight.
The muscle which straightens the forearm upon the arm is
represented  at 7.  I shall  remark  upon this in another  con-
nection.
   299.  In the management of the three kinds  of levers there
are two different objects aimed at under different circumstances.
One object  is  to  move  a  great weight with a  small power.
Here quickness is not aimed at, but the weight is moved slowly.
The other object is to move the weight quickly, an  object in-
consistent with the moving of any very heavy weight.   When
the object is to move a heavy weight slowly, the lever is  so
managed as to get a good purchase, as it is expressed.  Thus
in the case  of the lever of the second kind, Fig. 108, if the
weight be a heavy one, the power is commonly applied at some
distance  from  the weight.   The nearer the power  is to the
weight, the greater must it be to move the weight.  The smaller
the power,  the further must it be from  the  weight in order to
raise  it.  But though a small power  if at a  distance from
the weight answers to raise it, yet in this case the power must
move through  a considerable space to move the weight but
little; while to raise the weight to the  same height, a power
nearer to it passes  through but little space.   This will be made
clear to  you by Fig. 112.  F is the fulcrum,  and  W the weight.
If the lever, A, be raised to the line, B, the dotted  lines will
show the different spaces which the power passes  through, ac-
cording  to its distance from the weight.   If the power be at P, 
THE MUSCLES.                  201
Quickness more often important thun power.
FIG. 112.
 it passes  through the space indicated by the dotted line a in
 moving the weight W to c.   But if it be at p, it passes through
 a  much shorter  space, b, in raising the  weight to the same
 height.   The  more important, therefore, in this form of lever
 quickness of movement is,  the  nearer to  the  weight is  the
 power applied.   Let us look at the application  of these prin-
 ciples to the example of this kind of lever, which I cited from
 the human  body, represented  in Fig. 109, the  raising  of  the
 weight of the body on the foot in walking.   The power is here
 applied  quite near to the weight, for quickness  in  raising  the
 heel in walking and running is of great importance.  By hav-
 ing the  heel project farther  behind, the muscle could be  at-
 tached farther from the weight, and  thus  act with more power.
 But there  would in this case  be a sacrifice of quickness of move-
 ment,  and besides this, the lengthened heel would present a
 very awkward and ugly appearance.
   300. But it is in examples  of  levers of the third kind that
 we find these principles best illustrated.   This form of lever is
 much  more often  used in the  mechanism  of the muscles than
 the other forms.   I refer you to the  example given of this lever
 in the action of the biceps muscle  in bending the forearm, as
 shown in Fig. 111.  In this case it is of much more importance
 to move small weights quickly, than to move heavy ones slowly.
 Therefore the power is applied  quite  near to the fulcrum.  The
 tendon of  the biceps, as you  see, is fastened to the main  bone
 of the forearm  near the fulcrum, the elbow.   You can readily
 see  that the  point where the power is applied would  pass
 through but a little  space^ in moving a weight through a con-
 siderable one.   The lower jaw, in its upward motion, is a lever
of the same kind.  In this case, force rather than quickness is
required  in breaking and grinding the food.   Here, therefore,
the power,  the action  of the muscle, is applied farther from
the fulcrum than in the case  of the biceps  muscle of the  arm, 
202              HUMAN PHYSIOLOGY.

             Force most important in the case of the lower jaw.

and nearer to the weight to be  moved, or the point where the
resistance  is which is  to be overcome.  It is  applied also in a
different direction, a point which I  shall  however speak  of  in
another connection.   The muscles which move the lower jaw
upward can be seen in Fig. 113.   One is the large spreading
FIG. 113.
MUSCLES OF FACE AND NECK.
muscle b, the swelling of which, in its contraction, we can feel,
if we place the fingers on the temple while moving the lower
jaw upward.   The other is the short  strong muscle c, the front
edge of which is so far forward, that one-third at least of the
lower jaw-bone is embraced by this muscle.   Now, if you com-
pare this bone as a lever with  the  forearm as acted upon  by
the biceps, you will at once see that the power is applied much
nearer to  the weight, or the resistance to be overcome, in the
case of the jaw, than in  the case of the arm.   It is so even when
the  resistance to be overcome is at the front teeth;  and it  is
much more  so when the resistance is at the back part of the
mouth, as when  we are grinding our food.   Here, indeed, a por-
tion of the muscular force is brought to bear upon the resistance
in a direct line.   It is  not merely because the  back teeth are 
THE MUSCLES.
203
Mechanical disadvantage in muscular action.
stronger than the front ones, but also because the power is nearer
the resistance, that we can  crack a nut more  easily with  the
back, than we can with the  front teeth.
   301.  It is clear that the biceps muscle acts, as it is expressed,
at a mechanical  disadvantage, if we regard mere power or force,
and leave out of view quickness of motion.  If it were inserted
further  down on the forearm, nearer  the  hand,  it could raise
much greater weights than it now can.  And the same  can be
said of most of the other muscles of the body.  But force is
sacrificed for the sake  of quickness in most cases, because  the
latter is more important.  In the few cases in which force is
more important, as  in the case of the lower jaw  just cited,  the
reverse  arrangement is provided.  The gain in quickness in the
arrangement of the biceps muscle can be illustrated on Fig. 114.

                           FIG. 114.
F being the fulcrum, the power in raising the weight, W, to c,
if acting at P, passes through the space indicated by the dotted
fine a.  But if it act at p, it will pass through  all the space 6,
and of course raise the weight more slowly than when acting at P.
  302.  Most of the muscles work at a mechanical disadvantage
in another way.  I refer to the direction in which the muscle
acts on the bone to be moved.   This is seldom  at right angles,
and therefore a considerable part of the force  exerted is lost.
This can be made clear to you by Fig. 115.  Let b represent
the bone  of the arm, and  r  its fulcrum, or point of support in
the shoulder.   You readily see that if the bone be acted on by
a muscle, m, at right-angles to it, it will require less force to
move it to a given point than would be  required if the same
muscle were placed in the  position represented  by n.  For the 
204
HUMAN PHYSIOLOGY.
When loss in power, gain in quickness.
muscle n, acting obliquely on the bone would expend a part of
its force  in  pressing the end of the bone  upward against the
socket of the joint at r.
   303.  But in this  case also, what is lost in power is gained in
quickness of movement.  This  can be shown on  the figure.
We will suppose that the muscle contracts or shortens itself the
half of the length of the tendon.   If the muscle were placed as
at m, the bone would be carried to the line a, c.   But if the
muscle be placed as at n, the same degree of contraction would
raise the bone to  the line a,  d, the point of the bone  where the
tendon of the muscle is attached moving in the curved line as
marked.  The  resistance  to be overcome, of  course, requires
much more power  for the obliquely placed muscle,  n, to raise
the bone to the line a, d, than for the muscle  m to  raise it to
a, c ;  and therefore a much larger muscle is needed  than there
would be if it acted at right-angles to the bone  as at m.  And
the muscle  which raises the arm at the shoulder, acting as it
does  at so  great disadvantage,  is a very  large muscle.   The
muscle, n, in the figure represents  only the line of its action,
and not at all its  shape.  If you observe the various motions of
the arm in  which this muscle has a part, you will appreciate
the necessity of so  arranging it as to secure quickness of move-
ment.   This was  the chief object to be aimed at in its arrange-
ment; and  the second and less  important object,  power,  is
secured, so far as it is needed, by simply making the muscle a
large one.
   304.  The mechanical disadvantage, which I have  noticed as
resulting from the oblique action of the muscles, is in part ob-
viated by a very simple contrivance.  It is  done by making the 
THE MUSCLES.                  205
Contrivance to change the direction of force.
tendon of the muscle work over an enlargement of the bones at
the joints.   The operation of this contrivance can
be made clear by Figs. 116 and  117.   Let r and      FIG- 116>
o (Fig. 116) be the two bones of a joint, and let
the muscle m bo attached  to the  bone o at i.  As
it contracts, almost all its force  will  be spent in
drawing the bone o  upward against the bone r,
because  it acts almost entirely in a line with the      ,
bones.   But let  the  ends of the bones  be en-
larged as in Fig. 117, and  you can see that the
direction of the  tendon  of the  muscle m  is so
changed where it is attached to the bone, that the      FIG-117,
muscle can now very  easily make the  lower bone
turn upon the  upper.  The  enlargement  then of
the bones at the joints, which is needed  to  give
the requisite extent of surface for working them,
answers  also another  good purpose in thus alter-
ing the direction of force in the  muscles.  In the
case of  the knee-joint  there is an  additional contrivance for
making this change of direction still greater.  A movable bone,
the patella or kneepan, besides  acting as a protection to the
joint, effects also the purpose referred to.   The manner in which
it does this can be made plain by Fig. 118, in which a represents
the end  of the thigh-bone ;  b, the end
of the large bone of the leg articulat-         fig. n?
ing with it; c, the patella ; d, the large             .
tendon which comes from the muscle           * \Y
above, and is fixed into  the patella;     i       \ y
and e, the tendon which goes from     \      \ \
the patella to the large  bone of  the      i       \
leg below.  The dotted  line shows     J        *
how much the direction of the force     (
of the  muscle is changed by this ar-    a\      y I  Jc
rangement. The movement performed       ^^mt^   Wf
by this muscle is throwing the leg and    -7 f ™ "N  If/
foot forward, which it is by the above      I         xlt
arrangement of the patella enabled to      V          w/
do  with great ease  in  walking, and      \        u
with great force in the act of kicking.        \       *
  305.  The pulley is used in the ar-        \
rangement of the muscles, though by         '
no  means  as  often as the  lever.   It
serves, whenever, it is  used, to give the force a different direction
                            18 
206              HUMAN PHYSIOLOGY.
                 The pulley-arrangement in muscles.

from what it  would otherwise have.  I  will cite  but a few
examples.  At the wrist  and the ankle there are broad liga-
ments, which bind down the tendons of  the muscles, and sus-
tain to them the  relation of pullies.   If it were not for these
ligaments the tendons at these joints would  fly out continually
when the muscles are in  action, making projecting cords under
the skin.  And if the  skin were  removed, the tendons would
be in a position  similar to  that represented at A, in Fig. 119.
fig. 119.
In this Figure, C is the tendon of the great toe in its position as
bound down by ligaments.   Now if the muscle were  in  the
position represented by A, it is plain that  it would  act at  a
greater  mechanical  advantage than in the position C; but the
toe would not be moved as quickly;  and besides, if the tendons
projected in this way, the foot would be a very cumbrous piece
of machinery, compared with what it is  now, with the tendons
bound down around the slender ankle.  So that both  beauty
and use are secured by the arrangement.
   306.  There is a  beautiful application of the pulley in  the
case of the  muscle that draws down, the lower jaw, called
the digastric muscle.   It is represented in Fig. 120,  in which
a is one end of the muscle attached behind the ear, and b is the
other end  attached to the inside of the lower part of  the chin. 
THE MUSCLES.
207
Manner in which the lower jaw is drawn down.
FIG. 120.
DIGASTRIC  MUSCLE.
It is  muscular at the two  ends, and tendino^ in its middle
part.   This middle part runs through a loop or ring in a small
muscle as represented  in the Figure.  This little muscle  is
fastened above to a small process of bone under the  ear, and
below to the hyoid, or U-shaped bone, c, which is  situated just
above the  larynx.  Now when the jaw is  to  be drawn down,
the two fleshy ends  of  the  digastric  muscle  contract,  and the
middle tendinous  part works in the ring provided in the  little
muscle.  This muscle is so slender, that its loop is of itself alone
hardly strong enough, as we should suppose, for the tendon of
so large a muscle as  the digastric to work in.  And we accord-
ingly find that there is  an additional security in a strong liga-
ment, which fastens the tendon of the digastric muscle to the
hyoid bone.  This ligament (which I have not represented in
the figure,  because it would  confuse your  view of the pulley-
action of the parts) is sufficiently  long  to  allow of all the
freedom of motion  necessary to  drawing  the jaw downward.
You see at once that one object of this arrangement of the di-
gastric muscle is  to secure  beauty of form  in the neck.  A
muscle extending from the  top of the  chest to  the chin  in  a
straight direction would very effectually draw down the lower jaw,
but it would be a great deformity.   This is avoided by the pulley-
arrangement of the digastric muscle.  But this muscle answers
another purpose besides drawing down the jaw.   If while the jaw
be held fast  by muscles which  draw  it upward, the  digastric
contracts, it will draw up,  as you can readily see by the Figure,
the hyoid bone, c,  and with it, of course, the larynx which is at- 
208              HUMAN PHYSIOLOGY.
                Straight and oblique muscles of the eye.

tached to it.  Now precisely this set of motions occurs when we
swallow.   The mouth  is  shut by the drawing up of the jaw,
and then the contraction of the digastric muscle  draws up the
larynx, as you can perceive if you place your fingers  on the
larynx, or Adam's apple, as  it is called, when you perform the
act of swallowing.  The  little muscle  in which  the  loop is,
renders some assistance to the digastric in thus drawing up the
hyoid bone and the larynx, as you can see by the Figure.
   307. I will  notice  one  more  example  of the  pulley-ar-
rangement.   It  is in  the eye.   There  are six  muscles that
move the eye-ball.  Five of them are  represented in Fig. 121.
There  are  four straight muscles,  three  of  which are marked
FIG. 121.
a,  b, c; the fourth  is behind  b,  the  upper edge  of it  only
being seen in the Figure.  These muscles are at their origin in
the back part of the socket of the eye arranged round the  optic
nerve,  and passing forward  are attached  to the  sclerotic coat,
the firm white coat of the eye.  The two lateral muscles, b, and
its opposite, move the  eye to the one  side  and the  other, and
the two muscles, a and c, perform the up and down motions.
But  there are  certain oblique  rolling  motions of the  eyeball
which can not be executed by these straight muscles.   For these
motions two muscles  are  provided, one of which has a  pulley-
arrangement, as represented in  the Figure.   This  muscle, s, has
a long tendon which passes  through a ring in cartilage in the
roof of the socket, and then turning back is  fastened as you see
to the  upper part of the eyeball.  This muscle, as stated in the
chapter on the Nervous System, is under the direction  of one
nerve alone.   It is an involuntary muscle which  performs the
insensible rolling motions of the eyeball, and like the other in-
voluntary muscles of the body,  is at work while we  are asleep,
as well as when we  are  awake.  It is the  muscle which rolls
about  the eye tremulously when it is open in the insensible
state sometimes produced  by disease. 
THE MUSCLES.
209
             Opposing muscles.  Compound muscular action.

  308. Every muscle  performing a motion has its  opposing
muscle or muscles, which perform the opposite motion.  In the
case of any two  opposing muscles the one  must be in some
measure  relaxed while the  other is in action.   Thus in alter-
nately bending the elbow, and straightening it, there is alternate
action and relaxation in the two opposite  muscles 4 and 7, as
represented in Fig. 111.  So in moving the head  back  and
forth the muscles in front and rear are  alternately contracted
and relaxed.   Paley very aptly compares this to the action of
two sawyers in  a pit, as they move the saw back and forth.
The comparison,  however, is not strictly true,  because the  re-
laxing muscle is never wholly relaxed.  There is indeed in every
muscle  some  amount  of contraction which is  independent of
action through the nerves, whether it be reflex, or produced by
the will.  For this  reason the muscles cut off in amputation
of a limb retract.   So also if the muscles on  one  side of the
face be  palsied, the muscles on the other side draw the  mouth
to that side.  The mouth is held in the middle of the face by
the equal action of pairs of muscles.  The  head, too, is held in
equilibrium in the same way.  In what is called wry-neck, this
tonic contraction, as it is sometimes termed,  is greater in the
muscles on one side than it is on the  other.  In some  cases a
cure can be effected only by dividing  the contracted muscles.
In strabismus, or squinting,  one of  the straight muscles of the
eyeball  contracts too strongly for its opposing muscle,  and as
in wry-neck,  dividing the contracting muscle is often  necessary
to remedy the difficulty.
   309.  Most motions are not performed  by single muscles, but
by the joint and agreeing  action  of  several,  and sometimes
many muscles.   And as  these muscles  may  vary  to a great
extent in their degree of contraction, the  motions produced by
them are not only compound, but are  exceedingly varied.   To
illustrate this compound  and varied character of motion, I will
refer to a single  example in which only two  muscles are con-
cerned in the motion.   In Fig. 113 you  see a pair of muscles,
one  of which is marked h, which extend from the large protu-
berances behind the ears to the top of the breast-bone.  In the
neck of a thin muscular person  these muscles are very promi-
nent.  AVhen they contract equally, the head is bent straight
forward in the middle line  between the  muscles, and a  line
drawn from the middle  of  the forehead down  to the  breast-
bone would strike exactly at the point where these two muscles
unite.  But if one muscle  contracts more strongly  than the
                           18* 
210              HUMAN PHYSIOLOGY.
           Variety in muscular action. Exemplified in the tongue.

other, the head as it bows forward bows  towards the side on
which  is  the  strongest contraction.   And as the  degrees of
contraction in  these two muscles  may be endlessly varied, so
there may be an endless variation in the  degree  of  inclination
of the head to one side or the other, as it is bent forward.  If
then so great a variety in the  direction of motion may be pro-
duced by variation in the degrees of action in two muscles, you can
readily see that an almost infinite  variety of motion must result
from this variation, where many muscles  are called into action.
   310.  I know not any part of the body, which  exemplifies in
so palpable a manner the compound and diversified character
of muscular motion as the tongue.   It is mostly a bundle of
muscular fibres, apparently mingled  together in confusion, but
really arranged  in perfect order, so that it can be moved with
great definiteness in  all  directions, forward,  backward, upward,
downward, to either  side, and in all intermediate directions.  If
you  stand before a glass, and opening your mouth, move the
tongue rapidly  about in all these directions, you think of a har-
lequin performing his antics.   But all this wonderful variety of
movement is produced  in  obedience  to the  definite  action of
nerves, whose fibres are  mingled with the muscular fibres of the
tongue.  And in order to produce each motion there is an agree-
ment of action  not between merely many of these  fibres, but
between multitudes of them.
   311.  With the view which I have given you of the compound
and  varied character of  muscular motion,  you are prepared to
take a general  survey of the muscular system.   For this pur-
pose I call your attention to  a side view of the muscles of the
body as presented in Fig. 122.   I must premise, that you can
get no idea from this Figure of the number of the muscles in
the body,  for you see here only the outer layer of muscles, and
there are many muscles concealed by them.  You observe that
they are of various shapes and sizes, according to the motions
which  they are designed to produce, and  the  circumstances
in which they are placed.  They  are  round, long,  short, flat,
fan-shaped,  circular,  serrated,  &c.   I will  point  out  some
of them.   At  a is  the very large  muscle  that  makes the
fleshy prominence at the upper  part of the arm, and the
office of which  is to raise  the arm, carrying  it out  from the
body.  You observe that its fibres are not all arranged  alike
but lie  in  different  directions.   The  result is, that while the
arm  is raised by the muscle as a  whole, it may be  carried at
the same  time  forward  or backward by the  varying action of 
THE  MUSCLES.
211
External layer of the muscles of the body.
FIG. 122.
MUSCLES OF THE BODY. 
212               HUMAN  PHYSIOLOGY.
            General description of the muscles in various parts.

these  different fibres.  There are  many of  the  muscles of  the
body  which  are made  thus  to  produce various  results by
variation of the action of different parts of the same  muscle.
And the regulation of this  variation by the nerves is  one of
the most  wonderful and  mysterious things which we  find in
our study of the nervous system.   For  each fibre in the cases
referred to is told, as we may express it, just how much it must
do  in  order to produce  the  requisite  general  motion of the
muscle.  It is  manifestly much more wonderful thus  to  pro-
duce  various but accurately graduated  contraction in different
parts  of the muscle, than  to produce an uniform contraction in
all its fibres.
   312. I go on with my notice of the particular muscles.  At
b is the biceps  muscle, which bends the forearm upon the arm,
and at c is another  muscle that assists  the biceps.   At e is the
large  muscle in the back of the arm, which acts in opposition
to the biceps, and straightens  the forearm upon the arm.  At
d is a muscle which rolls the radius outwards,  and thus turns
the palm of the hand upward as seen in the Figure.  At g is a
very large broad muscle  coming from the whole length of the
back,  and at  the  axilla  or  arm-pit,  its  fibres  are collected,
twisted, and folded upon each other.   The muscle is  fastened
by a  stout tendon to the  upper and back  part of the  bone of
the arm, and its office is to pull the arm backwards and down-
wards.  At h  is a serrated  muscle, which  rising from the ribs,
goes  to the shoulder-blade, and  serves to  draw the shoulder-
blade forwards. At i is one  of the broad muscles of  the ab-
domen.  At I  and k are two large  muscles  that move the
thigh.  At o and p, as seen  on the right  thigh, and  at n, as
seen on the left, are three large muscles, which  are fastened to
the kneepan, and  serve to throw  the leg forward  as described
in § 304.  At  q is  the tendon that forms  the  outer hamstring,
and at r are the two  tendons which form  the  inner one.   The
muscles to which these tendons belong, serve to bend  the leg
upon   the  thigh, drawing it upward and  backward.   At s is
the muscle which  makes the  bulk of the  calf  of  the leg.   It
lifts the heel upward  and  backward, and it is seen in action in
the right leg  of the Figure.   Its  strong  tendon, which is at-
tached to the  top of  the  heel bone is  called, on account of its
strength, the tendon  of Achilles.   This muscle  is  in Fig.  109,
the power P which raises the weight of the body, W,  on the
fulcrum, F, as the heel is raised from the ground in walking.
   313. In Fig. 123 you have a rear view of the muscles.   At 
THE  MUSCLES.
213
Rear view of the external layer of the muscles.
FIG. 123.
REAR VIEW OF THE MUSCLES. 
214              HUMAN  PHYSIOLOGY.
     Some muscles are very small.  Symmetrical arrangement of the muscles.

a is a very broad muscle, which rising from the back is attached
to different parts of the shoulder-blade.  You  can see that
this irregularly shaped  muscle, will  move  the shoulder-blade
variously, according to the various action of the different fibres
of the muscle, which run in  so  different directions.  At c you
see the rear part of  the muscle that raises  the arm.  At b is
the extensive muscle that you  saw  in Fig. 122  at g, which
draws  the  arm backward. .  At e is a large muscle that draws
the thigh backward.   At g,  h,  and / are  the muscles whose
tendons  form  the two  hamstrings.   At i  is  the muscle that
forms the calf of the  leg, and raises the heel.
   314. I have thus  described to  you  a few of  the principal
muscles in the body, that you may have some idea of the modes
in which they act, and the manner in which they are arranged.
Those  which I have  described are all muscles of considerable
size.   But  there  are some  exceedingly small  muscles  in  the
body, producing some very delicate motions.  For example, all
the variations in the  note of the  voice result, as you will see in
the Chapter on  the  Voice,  from  the variation of  tension of
the vocal ligaments, which is regulated by certain  very small
muscles.  As the laborer sings over his work, great is the con-
trast between the delicate action  of these little muscles, and the
strong action of the muscles of  his stalwart arm.   A variation
of less than a hair's  breadth in  the  contraction of the muscles
of the  vocal ligaments suffices to produce an appreciable differ-
ence in the note of the voice.
   I  have thus  far spoken  of the  bones  especially as  being
moved by the  muscles.  But other  parts are  moved by them
also.   In the- case of the voice, just alluded  to, the little muscles
move  cartilages  to  which the  vocal ligaments  are attached.
The tongue  and the palate are moved by muscles.  Muscles
move the skin.   In  man this is generally  very much coefined
to the face.   The mouth, the eyelids,  the  eyebrows, &c, are
moved by muscles.   In many animals the skin is moved ex-
tensively by muscles, as for example  when  the horse shakes his
skin to get rid of the biting flies.
   315. In the arrangement  of the  muscles great regard has
been paid by the maker of our bodies to convenience and sym-
metry, and not merely to mechanical  advantages.   Thus, the
muscles moving the  fingers  are mostly placed in the forearm,
while  the slender tendons pass over the surface of the bones  in
the wrist.  The flowing outline of the arm is thus secured, and
the hand is made a light, and at the same time, a strong ap- 
                       THE MUSCLES.                   215
          Contrivances in muscles and tendons of the hand and foot.

paratus.   The  same can be said  substantially of the arrange-
ment of the  muscles and tendons in the leg  and foot.  There
is  one arrangement in the foot which is worthy of especial no-
tice.  There  is a muscle in the fleshy part of the leg, which by
a long tendon, divided in  the foot into four tendons, bends the
last joints of the toes.   There is  also a short thick muscle  in
the  bottom  of  the foot which  joins the tendons of the first
named muscle, and assists it in bending the  toes.  It is as  if
two different sets of men were placed in two different positions,
with ropes arranged so  as to pull in the same direction.  The
question arises, why the toes are not bent by a single muscle,
lodged conveniently in the fleshy part of the leg.  The reason
probably is,  that the muscle placed in the  sole  of  the foot is
needed there  as a filling up  in the arch of  the foot, and so the
force necessary to  bend  the  toes is  divided between the two
positions.
   316. There is another contrivance in this muscle that bends the
toes  which I will notice here.  Its four tendons pass to the last
bones in the toes, and in doing so they go through the tendons
of the muscle that  bends the second joints.   These latter divide
at their  ends where they join the bones for this purpose.  A
similar arrangement also is made in the fingers for the tendons
of the second and third joints.  This is represented in Fig. 124,

                             FIG. 124.
in which e is the tendon which goes to the last bone c through
the division in/, which goes to the second bone b.   It is mani-
fest that this is the best way of packing the tendons, as we may
express it.   Any other  conceivable arrangement would add  to
the bulk of  the finger.  As they are represented in the figure
they are raised up, instead of being closely packed down upon
the bone, as  they are in reality.
   317. I have already alluded to  the fact that many muscles
unite in producing most of  the movements of the  body, and
that,  as they  vary in the  degrees  of their  contraction, the
variety of  motion resulting from  both these causes,  is exceed- 
 216               HUMAN  PHYSIOLOGY.
                Complicated action of associated muscles.

 ingly great.  I will now call your  attention more particularly
 to these points, as you can more readily appreciate them after
 the general view which you have taken of the muscular system.
 Even when only a part of the body is put in  motion, there are
 often many muscles engaged in the  act.  Take, for example,
 the act of swallowing, which I have  described in § 78  in the
 Chapter on Digestion.  In this compound act the muscles of the
 jaw  close  the  mouth, the tongue thrusts the food back  into
 the throat, the digastric muscle (§ 306),  pulls up the larynx,
 and the epiglottis is  at the  same time shut down by muscles
 upon the  opening into the larynx, to let the food slide over it.
 In speaking and singing the action of the muscles is much more
 complicated than in the act of swallowing.  The muscles of the
 chest work the bellows of the organ (for such is the relation of
 the chest to the musical instrument, the larynx,) the muscles of
 the vocal ligaments put them in the  state of tension  required
 to produce the note intended, the muscles of the epiglottis raise
 it to  let the sound out, and  the muscles  of the throat, palate,
 tongue, and lips, give articulation to the sound as it comes from
 the larynx.  And observe, that  some of the same parts are en-
•gaged in the act  of speaking that are  engaged in that of swal-
 lowing, but are  put in  different positions for the two acts.
 Thus, the  epiglottis is raised up  when we speak, and is  shut
 down when we swallow, and the larynx is raised up when we
 swallow, and is drawn down  again when we speak.   And how
 quickly we pass from the  one  act to  the other, as we mingle
 our  talking and  eating together!  And we do  it with such
 facility and precision, that it is a very rare accident that a crumb
 or a drop slips into the larynx.   Observe farther, that when we
 take  a breath, as well as when we speak, the epiglottis must be
 raised,  the air passing in, instead of passing out as in speaking.
 The parts, therefore, are often engaged in these different acts,
 not  only  distinct from  each  other, but inconsistent with each
 other also, and they change from  one of these acts to another
 so readily, that as we  eat, and  breathe, and talk, we  are con-
 scious of no disturbance, and scarcely ever of any effort in the
 change.  No change of  action in any machinery of man's in-
 vention can be at all compared with  this in  the precision and
 facility  of the change, much less in its complicated character.
   318. But if there be complication and variety of action when
 but one part of the body is put in motion by the muscles, there
 will be  vastly more when the muscles of  the  body as a whole
 are brought into  action.   If  you look at  Fig. 122, you see the 
THE MUSCLES.
217
             Constant change in complicated muscular movements.

 muscles generally in more or less action, and the action of each
 one has its particular relation to the attitude assumed.   If now
 the attitude be varied, this particular relation of each muscle
 must be  varied also.   If, for example, the right foot be carried
 forward so as to  bring the weight of the body on to that foot,
 instead of the left, on which it now rests, as represented in the
 Figure, all the  muscles of the frame will have a different rela-
 tion in their action.   And not only this,  but while the body is
 changing from  the one attitude to the  other, there will be a
 continual change of this relation.   At no one moment durino-
 the act or motion, which changes the attitude, will the state of
 contraction in  each muscle  be precisely the same, that it is at
 any other moment.   Thus, the state of the muscles in the be-
 ginning of the change  of attitude  is altogether  different from
 what  it is when the movement is half accomplished.  And the
 same  can be said of any other two points in the progress of the
 movement.   The  same  is  true of any  other general  action
 of the muscles.   Thus, if one is pulling with his feet braced, the
 muscles do  not remain  in the same relative  condition all the
 time,  but as the body  which  is pulled yields, the relative tension
 of the muscles  is changed every  moment.  But  there is no
 movement which exemplifies this change of relative  condition
 of the muscles  so well as that of balancing.  If with the views
 which I have presented  in your mind, you observe some  one
 who is skillful in balancing, you will be impressed with the  ever
 changing but precisely regulated degree of tension in the differ-
 ent muscles, and with  the variety of combination in  their
 action.
   319. I will not comment to any extent upon the general
 movements and  attitudes of the body.  But I
 will here simply  call your  attention to one      FIG- 125'
 mode  of action, in which a large  number  of        |——__,
 the muscles are called into play, on account of        I      |
 its analogy to an expedient  often used in me-        //
 chanics.  I refer  to what is  called the toggle-       //
joint.   This I will  explain.  Let c, a, and c, b,      JU
 represent  two bars connected  together, like a    c ^\......"^
 carpenter's folding rule, by a hinge  or joint at      \\
 c.   Suppose the two ends, a  and b, to be  fitted       \\
 into the two  blocks represented in  the Figure.        Vj   ,
 If now the block at b is fixed, and the block  at       I_____J
 a is movable,  and force be applied to the joint         &
c carrying it towards d,  the  block at a will be  toggle-joint,
                               19 
218
HUMAN PHYSIOLOGY.
            Examples of the toggle-joint in muscular movements.

pressed upward  with  considerable  power.   If  on the  other
hand, the block at b is movable, and that at a is fixed, the block
at b will be pressed downward.  We see this latter form of the
contrivance  applied in printing presses.   In the human body
this toggle-joint is used  in  both ways.  When one  stoops  to
take a heavy weight upon his back or shoulder,  he puts both
the knee and the hip-joints  into the condition that the toggle-
joint  is when  it is  bent; and then  as he  straightens up, the
weight is  raised by an action of the joints precisely similar  to
that of the toggle-joint in machinery.  In the case  of the knee,
the straightening of the joint is done by the muscles  on the
front part of the thigh, that draw up the kneepan with the
tendon attached to it.  This is using the principle of the toggle-
joint in pressing upward.   It is also sometimes used in pressing
downward.  In crushing any thing with the heel, we give great
force to the blow on the  principle of the toggle-joint, by flexing
the knee and straightening the limb as we bring down the heel
upon the thing to be crushed.  In pushing any thing before us,
we bend the elbow as preparatory to  the act, and then thrust
the arm out straight, thus  exemplifying the toggle-joint.  The
horse gives great force to his kick in the same way.  The great
power exerted by beasts of draught and burden is to be referred
very much to the principle of the toggle-joint.   When a horse
is to  draw a heavy load, he bends all his  limbs, especially the
hinder  ones, and then  as he  straightens them, he starts the
load.  In this  case the ground is the fixed block of the me-
chanism, the body of the horse to which the load is attached is
the movable one, and his limbs are so many toggle-joints.  By
this application of the  principle we see  draught horses  move
very heavy loads.   " So, (admitting fable to be fact,") says Dr.
Griscom, " when the farmer, in answer to his petition for assist-
ance, was commanded by Hercules to exert himself to raise his
wagon from the  pit, he placed his shoulder against the wheel,
and drawing his body up into a crouching attitude, whereby  all
his joints were  flexed, and making  his feet the fixed points,  by
a powerful muscular effort,  he straightened the toggle-joints  of
his limbs, and  the wheel was raised from its bed of miry clay.
His  horses at the same moment extending their joints, the
heavily laden wagon was carried beyond the reach of  farther
detention."
   320. The hand is the most wonderful of all parts  of the
body, in  regard to  variety and  complication  of movement.
There are over fifty muscles, which are engaged  in the various 
                       THE  MUSCLES.                  219
             Great variety of action in the muscles of the hand.

 motions of the upper extremity, all of which, of course, have
 more  or  less reference to  the hand.  Indeed the hand is  the
 part of the  upper  extremity to which all its other parts  are
 tributary, and  therefore we may properly  consider all these
 muscles as in a great measure belonging to the hand.  If now
 you call to mind the fact, that each one of these muscles can
 vary the  amount of its  contraction in all degrees, from the most
 powerful  action down  to the slightest movement, you  can
 readily see  that fifty muscles with this power of variation  can
 produce an almost  endless number of combinations of  motion.
 The variety  would  be exceedingly great, even if every muscle,
 whenever it  acted,  had  always the same amount of contraction.
 But the power of varying the amount of contraction multiplies
 the variety to an inconceivable extent.
   321. If you watch the movements of the hand with its fingers,
 as you exercise  it  in a great  variety of motions, you can  get
 some idea of its capabilities  in this respect.   If,  too, you  ob-
 serve its movements in different individuals in all kinds of labor
 and handiwork, you will be  still more impressed  with  the  ex-
 treme variety of its  movements.   It is capable of performing the
 heaviest and rudest work, and at  the same time the most deli-
 cate.   How  wide the difference  between wielding the ax or the
 sledge-hammer, and moving the engraver's tool in some of  the
 finest  productions  of his art!  How firm is  its grasp of  the
 hammer, and yet how gentle is its pressure upon  the graver, as it
 moves it in almost invisible lines!  The shape  of the  hand, with
 its fingers of unequal length,  and its thumb opposite to them,
 capable of touching the tip of each of the fingers, or all of them
 together, enables it to accommodate itself to a  vast variety of
 shapes and sizes of  objects; and its delicate papillae,  filled with
 nerves, and arranged in rows,  as you can see, on the  tips of the
 fingers under the skin, endow this wonderful instrument with a
 sensibility  which guides its  muscular  movements.   When,
 therefore,  we consider the almost endless variety of its motions,
 the delicacy  and accuracy of its sense of touch,  and besides
 these, the force and grace with which it acts in  the  expression
 of thought and feeling, we hardly wonder that some  have fixed
 upon the  hand as man's  distinguishing  characteristic, and  we
 are impressed with the thought, that it is a fitting instrument
of work and  expression for that mind, which is the image of
God in man.
  322. Having thus taken a survey of the muscular system, let
us look for a moment at the whole  machinery, as it works when 
220              HUMAN PHYSIOLOGY.
         Nice adjustment of the muscular movements. How effected.

it is engaged at the same time in some general movement, and
in some special movements of  some departments  of it.   Look,
for example, at some one who is busied in conversation while he
is walking, and is perhaps at the same time twirling something
in different directions in his fingers.   Here you have a general
action of the muscles as described in § 318, and with it a par-
ticular action of two sets of muscles in two different parts  of the
body;  and yet so well do  the  nerves regulate  these various
movements, that  there is no  disturbance or  confusion  in the
complicated machinery.   While the  muscles  of the  arm and
fingers are  at work executing their diversified motions, the little
muscles of the larynx  are ever varying the notes of the  voice,
and the muscles of articulation are putting that voice into every
variety of shape.   And while these movements are going on in
these particular parts of the system,  the  machinery as a  whole
is executing one of its grand general  movements.  And besides
all this, the muscles of  respiration are at  work  all the while, in-
troducing air into the lungs to change the blood, and forcing it
out through the trachea to  make the vocal  ligaments vibrate;
and that compound muscle the heart is pumping at the rate of
seventy times  a minute sending the  blood  through  its  tubes
every where ;  and if there be any food in the stomach, the mus-
cular fibres of that organ are at work churning the food  to
make more blood.   How complicated is the machinery that per-
forms all these operations, and yet with what precision every mus-
cle, nay, every individual fibre works in obedience  to the nerves !
  323.  The question arises,  how in  all the diversified action of
the muscles their nice adjustment is effected.   How do  the
muscles know, as  we may express it,  just how much to  do in
each movement?   When, for example,  you reach your  hand
up to touch some object, how does each muscle know just what
degree of contraction is necessary to make the  hand go with
precision to the particular  point arrived at ?  And so when one
is playing on an instrument with the fingers, as the piano, vary-
ing their pressure continually in accordance with the desired loud-
ness of the sound, how does each muscle know just what amount
of contraction  is required of it in each movement ?  Though the
senses of vision and touch  afford some assistance in the guidance
of muscular action in such cases, something else is manifestly
necessary.   Sir Charles Bell, therefore, supposes that there is
what he  calls  a muscular sense, which acts  as a guide  to the
muscles,  in  connection  with the senses of sight and touch.   In
some  cases  it is the sole  guide.  On  this subject, Sir Charles 
                      THE MUSCLES.                   221
             Sir Charles Bell's description of the muscular sense.

says, " When a blind man, or a man with his eyes shut, stands
upright,  neither  leaning  upon or  touching aught;  by what
means is it that he  maintains  the  erect position ?  The sym-
metry of his body is  not the cause ;  the statue of the finest pro-
portion must be soldered to its pedestal, or the wind will cast it
down.   How is it, then, that a man sustains the perpendicular
posture, or inclines in due degree towards the winds that blow
upon him ?  It is obvious  that ,he has  a sense by which  he
knows the  inclination of  his body, and that he has a ready ap-
titude to adjust it, and to correct any deviation from the per-
pendicular.  What sense then is  this ? for he touches nothing,
and sees nothing ; there is no organ of sense hitherto observed
which can serve him, or in any degree aid him.   Is it not that
sense which is  exhibited  so early in the  infant, in the fear of
falling ?   Is it not the full development of that property which
was early shown in the struggle of the infant while it yet lay in
the nurse's arms ?  It can only be by the adjustment of muscles
that the limbs are stiffened, the body  firmly balanced, and kept
erect.   There is no  other source of knowledge, but a sense of
the degree of exertion in his muscular frame, by which a man
can know the position of his body  and limbs, while he has no
point of vision to direct his efforts,  or the contact  of any exter-
nal body.   In truth, we stand by so fine  an exercise of  this
power, and the muscles are, from habit, directed with so much
precision,  and with  an effort so slight,  that we do  not know
how we  stand.   But if we attempt  to walk  on a narrow ledge,
or stand in a situation where we are in danger of falling, or rest
on one foot, we become then subject to apprehension ; the actions
of the muscles are, as it were, magnified  and demonstrative of
the degree in which  they are excited."
   324.  It  is obvious then that this muscular sense informs the
mind of the changing postures  of the  body,  and guides the
muscles in  effecting these postures.  And it has  a particular set
of nervous  fibres devoted to it, separate from those fibres which
excite the  muscles  to action, though they are ordinarily  in-
closed in the same sheath.   This sense, it may also be remarked,
is a source of  pleasure,  as well as  the other senses.  The  mo-
tions of the body are attended with  a sense of enjoyment, which
lightens  labor, and adds  zest to  our active sports.  The enjoy-
ment of the muscular sense we see constantly exemplified in the
gambols of animals.   It may be still further remarked, that this
sense is capable of being educated like the  other s'enses.   But
of this I  shall speak  in another place.
                              19* 
222              HUMAN  PHYSIOLOGY.

            All thought and feeling communicated by muscles.
                  CHAPTER   XIII.

                 LANGUAGE OP  THE MUSCLES.

   325. As the nerves of sensation are the inlets of all know-
ledge  to  the  mind, the nerves  of motion are the outlets by
which all knowledge is communicated.   Thought  and feeling
are expressed  only by muscular motion.  It is true that there
are some  accompanying and subordinate  modes of expression,
as the flowing of tears, the action of the  capillaries producing
blushing,  and  the  paleness occasioned  by fear.  But these
could  not of themselves alone communicate thought and feel-
ing, and can do so  only by being associated with other signs.
They only add  force  to  the expression  already produced by
muscular  action.   Indeed they are signs which can not be un-
derstood, unless muscular action interpret  them.   Thus if tears
flow, we know not whether they are  tears of joy or sorrow, ex-
cept as the expression of the countenance  informs us ; and ex-
pression, as I shall  show you  in  this chapter, is  wholly the
result of the action of muscles.  So too, the muscles of the face
tell  us, whether  the blush  that mantles there is the blush of
shame, or of modesty.   And when we see paleness caused by
fear, we know that this is the cause, only from the expression
of the countenance and the attitude of the body, which may
very properly be called the expression of the body, though it is
much less marked than the expression of the countenance.
  326. It is by the voice chiefly that thought and feeling are
communicated.   And every variation of note, or of articulation,
is caused, as I shall show you in the next chapter, by the action
of muscles.  When  the muscles of the hand communicate to
others  thought  and  feeling  by  writing,  they merely  translate
the  language of the muscles of  the  vocal organs into conven-
tional signs.   Leaving the language of these vocal muscles for
another chapter, I shall in this notice the language of the other
muscles of the body and especially of those of the face.
  327. As we watch an animated speaker, we see that it is not
the face alone, that adds force to his  utterances by its  corres-
ponding expressions.  Various parts of the body in a measure
do the same thing.   The head is nodded or shaken, the shoulder
is shrugged, the  foot is stamped, and above all, the hand exe- 
THE .LANGUAGE OF THE MUSCLES.        223
                Extent of range of the language of the muscles.

 cutes  a great variety of motions,  in correspondence with the
 thoughts and feelings which the mouth utters.  Sometimes too,
 the whole frame,  is brought into action.   The gestures and the
 attitudes, which  are  but gestures  of the whole body, are im-
 portant aids to the orator in conveying his thoughts and feelings
 into the minds of his auditors.
   328.  This language  of the  muscles is  used  to  a greater ex-
 tent than we are  conscious  of in our ordinary intercourse.   We
 are not aware  how  much we  communicate in  this way.  This
 language is by no means confined to those palpable acts which
 this subject  suggests at  once  to the  mind,—the  broad laugh
 of merriment; the sighing, and sobbing, and weeping of grief;
 the stamping of the foot in anger ;  the pointing of the finger in
 calling attention  to any particular subject; the gesture  used in
 beckoning one to come to  you, &c.   But it includes numerous
 little and  scarcely observed motions,  which  in   great  variety
 add to the  significance of  the  words which we utter.   And in
 the case of  the countenance, far more is  communicated in the
 aggregate by the constant  gentle play of the muscles, than by
 the broader and more palpable expressions, which  are  occasion-
 ally produced  by their stronger  action.   The deaf mute can
 gather from the language of the muscles,  as it  accompanies the
 voice that he  can not  hear, much more  information as to the
 passing conversation than  one would suppose that he could.
 And the full capabilities of this language we can only learn, by
 observing  to what wonderful  extent the  deaf and dumb can
 communicate with each other by the use of natural signs,  with-
 out any aid from those which  are  artificial.*
   329.  While in man the   muscles of the face are  the  chief
 agents of expression, in other  animals  the very limited  expres-
 sion of which they are capable, is chiefly  effected by other parts
 of the body.   For example, the dog wags his tail, the cat puts
 up her back, the  game-cock spreads out his ruff of feathers on
 his head, &c.   Rage is  almost the only passion which  can be
 expressed by animals in the countenance.  They can snarl, but
  * I was much struck  with an illustration of the great range of the language of  natural
 signs, in an exhibition made many years ago by the lamented Gallaudet before the legisla-
 ture of Massachusetts.  Previous to exhibiting the attainments of his pupils, he requested,
 that if any deaf and dumb person who had  not been educated in an asylum were present,
 his friends would bring  him forward,  that he might show how much could be  communi-
 cated by natural signs.  A man came forward, and Mr. Gallaudet learned from  him by
 natural signs alone such facts as these,—the pluce of his residence, the fact that his  parents
 were living, the number of his brothers and of his sisters, the fact that he had seen Mr.
 G. before in a certain place, &c.  Any one, it may be remarked in this connection, who
 has been engaged  in teaching the deaf and  dumb, and who has, therefore, become skilled
 in the use of sign-language, can converse quite readily by signs with foreigners from any
part of the world. 
224
HUMAN PHYSIOLOGY.
              Principal muscles used in smiling and laughter.

they can not laugh or cry.   Hence it has been said, that man
can  be very  properly distinguished  from  other  animals  by
calling him " a laughing and crying animal."
   330.  Though the variety of expression in the  human coun-
tenance is very great, it is ordinarily produced  by the  action
of very few muscles.  The principal muscles are these—the
muscle  that wrinkles the  eyebrow,  causing frowning;  the
muscles which draw down the  corners of the mouth;  and
those which draw them up.  When  a smile occurs, it is pro-
duced by  the  muscles which raise the corners of  the  mouth.
When sadness is expressed, it is done by the muscles by which
the corners of the mouth are drawn  down.   Hence the origin
of the common expression, " down in the mouth."   In laughter,
the muscles which raise the corners of the mouth act strongly,
wrinkling the cheek, simply because the corner of the mouth is
carried up so far as to push up the cheek before it.   One other
muscle is brought into some action—the circular  muscle which
closes the eyelids—for the eyelids are brought nearer together
in laughter, though in mere smiling  they are  not.   In Fig.
126,  representing broad  laughter, you  see the  two  effects
spoken of above, the wrinkling of the upper part of the  cheek,

                          FIG. 126.
 
          THE  LANGUAGE OF THE MUSCLES.        225

                Muscles used in the expression of grief.

and  the partial  closure  of  the  eyelids.   In  weeping, the
muscles  that draw down  the corners of the mouth, which in
the mere expression  of sadness  act slightly, now act strongly.
At the  same time the frowning  muscle wrinkles the eyebrow.
In ordinary weeping it does so but slightly, but in weeping
from pain this muscle  is strongly contracted.  So it is also
when there is crossness  mingled with the grief.  Fig.  127,

                          FIG. 127.
which is the face of a faun weeping from pain, illustrates these
points.   Sir Charles Bell, from  whose work on the Anatomy
of Expression  most  of the figures in this chapter  are  taken,
says that he represents  the expression of weeping  in the face
of a faun,  because it is mean and  ludicrous as seen  in  the
countenance of man.
   331.  It is very commonly supposed  that the  eye has much 
226              HUMAN PHYSIOLOGY.
              Prominent agency of the mouth in expression.

to do with the expression of  the countenance, and hence  such
phrases as these are  in universal use—a  speaking eye; a wild
eye;  the witchery of the eye; the eye flashed, <fec.  But the eye
of itself has no active  agency  in  expression.   The muscles
which move it have, but not to any  great extent ordinarily.
Of them I shall speak in another part of this  chapter.  The
apparent expression which the eye has is merely apparent, and
not real.  It results # altogether from  the position of the parts
about the  eye.  This  can  be proved  to you by any portrait
painter.   It is related of an  artist that, when a royal visitor
was admiring a sketch of the face of a weeping child, he said
to him, " has your majesty a mind to  see how easy it is  to
make this very child laugh ?"   As the king said that he should
like to see it, the artist rubbed out a little at the corners of the
mouth and on the eyebrows, and added a few strokes to represent
the corners of the mouth as raised, and the eyebrows as with-
out wrinkles, and the face, which was  the moment before  the
very picture of grief, now exhibited a merry laugh.  Afterward
he as readily restored the original  expression.   Now in this
case there were the same eyes in the two expressions.  The al-
terations were made  only  in the neighboring parts, and the
same  eyes were  apparently  weeping  eyes at one  time and
laughing ones at another.
   332.  In Fig.  128 and 129  'you  can see  how much the
mouth alone affects the expression of  the whole countenance.
The apparent expression of the  eye is wholly altered  by the
FIG. 128.                     FrG. 129.
 
226              HUMAN PHYSIOLOGY.
              Prominent agency of the mouth in expression.

to do with the expression of  the countenance, and hence such
phrases as these  are in universal use—a speaking  eye;  a wild
eye ; the witchery of the eye; the eye flashed, &c.  But the eye
of itself has no active  agency  in  expression.   The muscles
which move it have,  but not to any great extent ordinarily.
Of them I shall speak in another part of this  chapter.  The
apparent expression which the eye has is merely apparent, and
not real.  It results m altogether from  the position of the parts
about the eye.   This can be proved to  you by  any portrait
painter.  It is related of an artist that, when a royal  visitor
was admiring a sketch of the face of a weeping child, he said
to him,  " has your majesty a mind to see how easy it is  to
make this very child laugh ?"  As the king said that he  should
like to see it, the artist rubbed out a little at the corners of the
mouth and on the eyebrows, and added a few strokes to represent
the corners of the mouth as  raised, and the eyebrows as with-
out wrinkles, and the face, which was the moment before  the
very picture of grief, now exhibited a merry laugh.  Afterward
he as  readily restored the original  expression.   Now in this
case there were the same eyes in the two expressions.  The al-
terations were made  only in the neighboring parts, and  the
same eyes were apparently weeping  eyes at one  time and
laughing ones at another.
   332.  In Fig.  128 and 129  'you  can  see how much  the
mouth alone affects the  expression of the whole countenance.
The  apparent expression of  the  eye is wholly altered  by the
FIG. 128.                     FIG. 129.
 
THE LANGUAGE OF  THE MUSCLES.       227
               The eye has little active agency in expression.

change about the mouth.   If we could add at the same  time
a  change at the eyebrows, the expression of the eye would be
much more affected.
   333. The language which is ordinarily used, in relation to
the  agency of  the eye in the  expression  of the countenance,
implies that the eye itself,  apart from  any motion, changes in
the  changing expression.   How this is done is not inquired;
but  there seems to be an ill defined  notion  that  the  animal
spirits, as it is  expressed, flow into the  eye  more or less freely
writh the  changing feelings,  or  that  a  nervous  influence is
exerted in  some way upon the  eye,  altering its appearance.
These notions are so universal, and  are so inwrought into our
language, and especially the language of poetry, that scientific
men even are apt to use the  expressions to  which they give rise,
in their descriptions of the language of the passions.  Even Sir
C. Bell, in his  celebrated book on the Anatomy of Expression,
in describing the expression of the emotion  of joy,  uses the
phrase, the  eye is lively  and sparkling.  Let me not be under-
stood to mean, that I would have the expressions, in such uni-
versal use in common language and  in  poetry, given up.   I
would as soon  claim that the expression, the sun rises,  should
be  abandoned in  common  language.   But as the  astronoriier
would have it understood, that the apparent fact, that the sun
rises, is only apparent, not  real, so as a physiologist, I would
have it understood, that  the apparent active agency of the eye
in the expression  of the countenance  is  not  real.  And as it
would be objectionable to speak of the sun as rising, in  a book
on astronomy,  so in a professional  book on  the Anatomy of
Expression  it is objectionable, in a description of  the physical
signs of an emotion, to use  the common phrases in regard to
the agency  of the eye in expression.
   334. Having thus noticed the principal  muscular motions
that are concerned in the expression of the countenance, I pro-
pose now to go more extensively into  the  subject, and show
you how other  muscles, besides those to which I have alluded,
act in  producing certain expressions.   I  shall also show how
the expressions are varied by combinations of  muscular  action,
for it is as  true  of the muscles of expression  in the face, as it
is of the muscles generally, as stated in § 309, that almost every
movement is produced, not by the action  of one muscle alone,
but by the  action of several, sometimes many muscles.  The
various  expressions of  the countenance are  all of them com-
pound results, some of them more so than others. 
228              HUMAN PHYSIOLOGY.
            Description of the muscles of expression in the face.

  335.  I will first call your attention to the particular muscles
of expression  in the face, and indicate  their mode  of  action.
They are represented iu Fig. 130.   There is a thin flat  muscle
FIG. 130.
MUSCLES OF THE FACE.
covering the whole top of the head, represented at 1, 2, and 3 ;
3 being its thin  tendinous  part.  It is fastened  to the large
bones behind, and in front its fibres end in the skin of the fore-
head and the eyebrows, and in the circular muscle of  the eye-
lids, 4.  When it contracts, therefore, it raises the  skin of the
forehead and  the  eyebrows;  and if it contract strongly,  it
wrinkles the forehead.  The circular muscle of the eyelids, 4,
when  it contracts closes the eye.  This and the  large frontal
muscle just described, you can see, must have much to do with
the expression of the countenance.  There is a very important
though small muscle which is not seen on  this figure.   You
see  it on Fig. 113,' at a.   It  is attached to the bone at the side
of the  top of the nose, and is inserted into the skin of  the eye-
brow.   It is called the corrugator supercilii,  or wrinkler of the
eyebrow.  From the agency which this muscle  has in the ex-
pression of  certain passions  and emotions, comes the word in
so  common use, supercilious.  Though a  little  muscle, it  is 
            THE LANGUAGE  OF THE MUSCLES.       229
                    Muscles of the face continued.

 truly a  supercilious one.   It has, as you will  see as we go on,
 a  large play  in  many varieties  of  expression,  produced by
 combinations of action in the muscles of  the face.  There are
 two muscles  on the nose, 5 and 6, which compress the nose,
 and wrinkle its skin.   They have some agency in certain ex-
 pressions of the countenance.  At 7 is the  circular muscle of
 the mouth.  When this  contracts it closes the lips, and if it
 act strongly it pushes them out.  This is the muscle with which
 in part pouting is done.   At 8 is a muscle which is fastened
 above to the bone of the  nose,  and runs down, its fibres ending
 in the wing of the nose, and in the upper lip.  When  it con-
 tracts,  therefore, it moves the  wing of the  nose outward, and
 draws  up the lip.  You see  this  muscle in action  in some
 emotions, the nostrils appearing spread out.   At 9 is a muscle
 which  raises the lip, and at 10 and 11 are two muscles, that
 raise the corner of the mouth, carrying it a  little to one side.
 At 13 is the muscle which acts in opposition to  the two last.
 It pulls  the corner of the mouth down.   At 12 is the  muscle
 which pulls down the lower lip.   At  18  is the muscle in the
 side of  the  mouth, which draws the corner of  the  mouth
 backward, and also serves to press the cheek inward, and thus
 prevent the food from getting outside of the teeth when  we are
 chewing it.  This muscle  also, by its compressing power, forces
 out the air from the mouth when the cheeks are distended, as
 in blowing a horn or a trumpet.  Hence it is called buccinator,
 from buccinare, to blow a trumpet.  At 15  is a  large muscle
 which closes the lower jaw against the upper, and although its
 chief use  is to  masticate the food,  it has  some agency in
 the expression  of  the countenance, in fixing the teeth firmly
 together, as in the expression of rage.   There are three muscles
 which  move the  ear;  19, moving it upward;  17, forward;
 and 21, backward.  These have  but little power in man, but
 in some animals  they  move  the  ear  considerably, and are
 prominent agents of expression.
   336.  In Fig. 131  the muscles about the mouth, which have
 so much to do with the expression of the countenance, are very
 distinctly shown.  At a is the muscle which draws up the wing
 of the nose and the lip ; b raises the lip; c raises the corner of
 the mouth; d and e raise the corner of the mouth,  and  at the
 same time  carry it outward ; n  draws it outward ;  m draws it
 downward and  outward in which it is assisted by a  broad thin
muscle, o, which situated  just under  the  skin comes up from
the neck; I draws  the  lower lip  downward; and i is the cir-
                           20 
230
HUMAN PHYSIOLOGY.
Muscles of expression about the mouth.
FIG. 131.
MUSCLES ABOUT THE  MOUTH.
cular muscle which  closes the lips, and  thrusts  them  out in
pouting.  At h is a short muscle which is fastened  to the  sockets
of the teeth, and has its fibres ending in the skin of the chin.  It
therefore draws the chin up when it contracts.   It has so much
agency in the expression of scorn and contempt that it has been
called the superbus.   It is by the action of this muscle, together
with the circular muscle i, that the expression termed pouting
is produced.   The muscles which I  have thus described are all
in pairs;  and  in  every pair both muscles  contract  always
exactly  alike, unless  affected by disease.  We laugh and frown
and  weep  on both  sides  alike.  All  of these muscles of ex-
pression in the face  are governed in  their  action by the
branches  of one  nerve, the  respiratory nerve  of the  face.
When this nerve, therefore, is paralyzed on one  side, and not
on the other, as is no uncommon occurrence, these  muscles on
the  paralyzed  side are motionless, and  the individual can laugh
and  frown and  weep on only  one side of the face.  In Fig. 82
you  have illustrated the result  of  this  partial paralysis, the
face  being perfectly quiescent  on the  left side.  The contrast
would have been  still  greater  if  the face *had been   repre-
sented as in more decided action, as laughing, for  example. 
           THE  LANGUAGE  OF THE  MUSCLES.        231
            Action of particular muscles in passions and emotions.

   337. Having thus described  the  muscles of the face which
 are the agents of expression, I will now show their action in the
 expression of different passions and emotions.   And I remark,
 that you will see, as I proceed, that so far from there being any
 one muscle devoted to the expression of one emotion or passion,
 expression is commonly the result of the combined  action of
 many muscles.   And you will  also  see  that, by virtue of this
 combination, the same muscle  often takes a part in  the ex-
 pression of various emotions.
   338. When the frontal  muscle (1, 2, 3, Fig. 130) contracts
 it raises the eyebrows.  This motion expresses either doubt or
 surprise, and  the observer determines which it is, by the ex-
 pression of other parts of the countenance accompanying  it, or
 in  other  words,  by  the action of other muscles in the face.
 When this muscle contracts very strongly, it draws up the eye-
 brows so  much,  as  to push  up the  skin of the forehead, and
 wrinkle it.  This, as you will  soon see, is one of the many na-
 tions of the face  which make  up the expression of great bodily
 fear.   In joy this muscle acts moderately, raising the eyebrow,
 therefore, but a little.  This  muscle often acts  in connection
 with  the  corrugator  supercilii, the wrinkler of the  eyebrow.
 This  may be  seen  in Fig. 132, respresenting a  testy, peevish,
jealous melancholy.   Here   the  corrugator  and  the frontal
 muscles are both in  strong action.   You see  also in this face
 certain muscles about the  mouth acting forcibly.  The muscle
 which draws the  corner of the  mouth down is in action  while
 the  superbus {h, Fig. 131,)  is  drawing  up  the  chin which
 pushes up the lip  before  it.   At the same time the muscle
 which draws up the wing of the nose and the lip, (a, Fig.  131,)
 contracts to some extent, producing  an  arching of the mouth,
 and a peculiar shape of the wings of the nose.   The upper lip
 is arched by the action of this muscle in such a way, as  to fit
the arching upward of the lower lip, produced  by the superbus
and the muscle which draws  down the corner of the mouth.
   339. In the expression just described, and illustrated by the
figure, you see that the  muscle which draws down the corner
of the mouth  has a considerable agency.   Now, this  muscle is
the chief agent in the expression of sorrow, as you saw in the
first part of this chapter.   The  difference in  the  two cases lies
in the combination  of action  of  the  muscles.  Thus, in sorrow
the muscle which draws down  the  corner of the mouth, does
not have  the superbus to act with it, as in the case of the
passion, or rather compound  feeling, represented in Fig. 132. 
232
HUMAN PHYSIOLOGY.
Action of the muscles in fretful melancholy.
FIG. 132.
So  also, in some forms  of grief the corrugator supercilii acts
quite strongly, as seen  in Fig. 127, where the grief is repre-
sented as caused by bodily pain.   It performs a different office
in this case from what it does  in the case of the expression re-
presented by Fig. 132, simply through the accompanying action
of other muscles, thus illustrating  the effect of combination in
muscular action in  varying the character  of the expression.   I
have  already alluded to the different degrees of  action in this
muscle  in  different  forms of grief in § 330.   In  quiet sorrow
this muscle is not in action, but there is a general languor re-
laxing the muscles of the face, while the corners  of the mouth 
           THE  LANGUAGE OF THE  MUSCLES.        233
          Action of the muscles in calm pleasure, and in admiration.

are slightly depressed.  It is a state of the muscles directly op-
posite to that which exists when there is a calm quiet pleasure.
Then most of  the muscles  are in a  state of gentle action, and
the corners of the mouth  are a little raised, giving the radiance
of  a light   smile  to the  whole  countenance.    The  frontal
muscle, slightly raising the  eyebrows, adds to the effect.
   340.  The  attitude, for so we may call it, of the countenance
in admiration,  is quite nearly allied to that which I  have just
described.  The  brow is expanded by the action of the frontal
muscle, and  there  is a slight smile produced by the  raising of
the corners of  the mouth.  But  the expression differs in some
respects from  that of mere pleasure.  The frontal muscle acts
rather more  strongly in the former than in the latter, the  eye
is more wide open, and is fixed upon the  object of the admira-
tion, and the mouth is apt to be open, the jaw falling a little,
so that we can see the edge of the lower  teeth and the tip of the
tongue.  In  both pleasure and admiration the  expression varies
much in different individuals, according to their temperaments,
being characterized  by activity in some, and in others more by
relaxation or even languor.
   341.  Let me now call your attention to an expression of the
countenance,  in which many of  the muscles are in a state  of
strong action.  I refer to  the expression of rage represented in
Fig. 133.  The combination of  muscular  action  here  is quite
extensive.  The  corrugator supercilii  acts forcibly,  but  un-
steadily, as is the case with the action of all  the muscles in the
expression of this passion.   The frontal muscle acts at the same
time, raising  the  eyebrows.   The  eyes  are  opened  widely,
showing the  rolling eyeballs.  The muscle that raises the upper
lip, b,  Fig. 131,  and  the  muscle that raises  the wing of the
nose and the lip, are in strong action.   The nostrils  are there-
fore spread out to  the utmost, and the  upper lip is  drawn up-
ward.   But  as the  circular  muscle  of the  mouth  also acts
strongly,  there is  only that part  of the upper  lip to which
the muscles,  a  and b, Fig. 131, are attached, that  can be drawn
up.  This point  is just where the  sharp  eye-teeth, or canine
teeth, as they are sometimes  called, are  situated.  They are
therefore  seen  laid  bare.   This allies  man to the  snarling
brute, that shows his sharp teeth in his rage.   Cooke, the tra-
gedian,  is said to have had  great  power in the  use of these
muscles.  " In him," says Sir Charles Bell, "the ringentes (the
snarling muscles)  prevailed; and what determined hate could
he  express, when, combined with the oblique cast of his eyes, 
234               HUMAN PHYSIOLOGY.
Complicated muscular action in expressing rage.



             FIG. 133.
he drew up the  outer part of the upper lip,  and  disclosed a
sharp angular tooth !"  In  rage the teeth are firmly closed by
the muscles which  move the lower jaw, and when  utterance is
given to it by the voice, these  muscles but slightly relax to let
the words out through the almost closed teeth, and  are rigid
again as soon as the words are finished.
   342. The expression of mere bodily fear, represented in Fig.
134, is very different from that of rage,  although some  of  the
muscles  act in the  same way in both.  The frontal muscle acts
very forcibly, raising the  eyebrows to their  utmost extent, and
the eyeballs are largely uncovered, giving to the eyes a  broad
stare.   The corrugator supercilii  is perfectly relaxed,  while in
rage it is strongly  contracted.   The  lip is raised and the nos-
trils are spread  out  by the same muscles, a and  b, Fig. 131,
which act so forcibly in rage.  But the  circular muscle  of  the
mouth, i, is relaxed,  so that the whole hp is raised, instead of 
THE LANGUAGE OF THE  MUSCLES.        235
Movements of the eye in expression.
FIG. 134.
a part of it, as is the case when rage  is expressed.  The lower
jaw is fallen, while in rage it is in the opposite condition.  The
hair  is  raised up by  a general action of the whole frontal
muscle, 1, 2, 3, in Fig.  130.
   343. The muscles of the eye, that  is, those which move the
eyeball have some agency in  certain expressions of the counte-
nance.   Thus, in admiration, the fixing of the eye upon the ad-
mired object makes a part of the expression.  In the expression
of devotion the eye turns instinctively upward.   There are cer-
tain  involuntary motions of the eyeball, which have  much to
do with expression in certain states of the body, and in certain
emotions.  These motions are performed by the oblique mus-
cles (8 307.)    When the straight muscles which ordinarily con-
trol the motions  of the eye lose their power from a state  of
general  insensibility, the eye is given  over to the action  of
these oblique  muscles, which  are involuntary,  and therefore is 
236
HUMAN PHYSIOLOGY.
                 Muscles of expression peculiar to man.

rolled about in its socket, being turned upward all the time, so
that the white of the eye only is seen.   This occurs in sleep, in
fainting, in the stupor of disease, and in the approach of death.
  344. The loss of power in the voluntary muscles of the eyeball
and eyelid is often seen ludicrously exhibited in the intoxicated
man.   He squints and sees double from deficiency of action in
the straight muscles  of the eyeball.   The  oblique involuntary
muscles of course roll the eye in proportion to the  deficiency of
these straight muscles.  The voluntary muscle too, which holds
up  the upper lid, fails to do its duty, and  the lid is constantly
disposed to fall over  the eye.  The frontal muscle is therefore
called upon to aid it.   Hence, in the effort of  the drunkard to
keep his eyes open, you see  him raise  up  the  eyebrows, the
eyelids being of course dragged up after them to a little extent.
"It is," says Sir Charles Bell, "the struggle of the drunkard to
resist, with his half-conscious efforts, the rapid turning up of the
eye, and  to  preserve  it under  the  control  of the  voluntary
muscles, that makes him see objects distorted, and  strive, by
arching his eyebrows, to  keep the upper  lid from descending.
The puzzled appearance which this gives rise to, along with the
relaxation of the  lower part of the face, and the slight paralytic
obliquity of the mouth, complete the degrading expression."
   345. I  have thus pointed out the agency of the several mus-
cles that  are engaged  in  the expression  of the  countenance.
Most  of  them are peculiar to man, being found in no other
animal.   The inferior  animals are variously endowed in regard
to muscles of expression.   But even  those that have the most
expression, have  but few of those muscles which we find in the
face of man  devoted to  this purpose.  They have the muscles
that move the eyes, those which raise the upper lip and thus
expose the  teeth, and to some extent those which distend the
nostrils.   The horse  is especially endowed  in regard to this
latter motion.  In that glowing and beautiful description of the
horse in Job it  is said, "the glory of his nostrils is terrible."
But most animals, even of the higher orders, have  but a limited
motion of the nostrils  compared  with man.  In him  they have
much more to do with the expression of the countenance than
is commonly supposed.   Their chief agency is in the expression
of the nobler passions, and Sir Charles Bell remarks, that  the
great tragedians, Mrs. Siddons and Mr. John Kemble, exhibited
their power in this respect in a remarkable manner.
   346.  None of the inferior animals have the corrugator super-
cilii.  Indeed they have no eyebrows to move.   The eyebrow 
            THE LANGUAGE OF THE MUSCLES.        237
                   Muscles of expression in animals.

is a strong peculiarity of man, and in view of its agency in the
expression of the countenance, varied as it is by the frontal mus-
cle and the corrugator, it has been said  by some one, that it is
" the rainbow of peace, or the bended bow of discord."  So also,
the muscles that raise and depress the  corners of the mouth
are wholly peculiar to man.   It is sometimes said that the dog
smiles.   But if you observe him closely, you will see that as he
separates his lips or opens  his mouth, at the same time that he
wags his tail, there is no raising of the  corners of the mouth,
and therefore no true smiling.  The idea  that he  smiles has
come from mere association with other motions by which he indi-
cates pleasure.   The same can be said of the expression of sorrow
in the  dog and  other animals.   There is little of it in the face
itself, amounting to nothing more than a  mere downcast look,
if  even that; and we connect the idea of sorrow with the face,
by the force of association, from hearing the cries and witness-
ing the movements which distress produces.  The grand peculi-
arities  of human expression are in  the muscles whose action I
have noticed in this paragraph, viz., the muscle that wrinkles the
eyebrow, the muscle  that  raises it, and those muscles which
move the corners of the  mouth up and down.   No animal but
man can frown, or weep, or laugh, for it has not the muscles by
which  these acts are  done.
   347. Fear and  rage  are almost the only passions  that are
expressed in the faces of animals.   And  in some of them there
are special provisions  in muscular endowment, for the expression
of these mere brutal passions, particularly for rage.   Thus, in
beasts  of prey  the ringentes, or snarling  muscles have  great
power.   They raise the lip strongly, and display the sharp long
teeth which are to rend their prey in  pieces.  The eye  too is
made terrible  by certain muscles which  are  not found in man.
They are muscles which draw the eyelids backward upon the
prominent eyeball, thus  producing a fixed staring of  the eye,
and  exposing  its  brilliant  white coat, which by reflecting the
light gives the eye a  sparkling appearance.   These muscles Sir
Charles Bell calls scintillantes, from the apparent  scintillating
effect which they produce.   In  the cat  tribe  light is reflected
from the bottom of the eye,  when  the pupil is dilated so as to
admit the light over a large portion of the  retina.   This occurs
in  an  obscure light  simply  because the pupil is then so  much
dilated.  The  light is not  created in the eye, and it is no indi-
cation of passion, as has  been supposed.
  348. You  have seen  the  fact  most fully illustrated in this 
238              HUMAN PHYSIOLOGY.
           Variety of combination in muscular action in expression.

chapter, that it is from combinations of action among the mus-
cles, that the  various expressions  of the countenance, result.
To  produce each one of these  combinations, there must be a
consent of action between the muscles.  Some are relaxed, while
others  are contracted; and those which  are contracted are in
different  deo-rees  of  contraction.  Sometimes this harmony of
action is sportively destroyed by one who has great command
over the muscles  of the face, and the most incongruous expres-
sions result, mingled together  in the same countenance, giving
it a very  ludicrous appearance.  And I may remark, that the
portrait painter is not always true to nature, but sometimes fails
to depict the full  harmony of muscular action in the expression
of the  countenance.   I have noticed some of the combinations
of muscular action in expression; but the view which you thus
get of  them  gives you but a faint  idea of the  infinite variety
of expression of which the human countenance is capable, as the
result of these combinations.  In order to obtain some adequate
idea of this variety, keeping the  views presented in this chapter
in your mind, watch  some one engaged in speaking or in conver-
sation,  in whom the play of the muscles of expression is peculi-
arly free.   By  so doing you will acquire new views of the capa-
bilities of the countenance in communicating thought and feeling,
and you will learn a lesson in  this respect which the deaf mute
from necessity learns every day.
  349. But we do not get a full view of the combination of
muscular action in expression,  if we confine our observations to
the countenance.   As I remarked in the first part of this chap-
ter, the muscles of other parts of the body,  and  sometimes of
the whole frame, are brought into action in connection  with the
muscles of the face, in expressing  thought  and  feeling. The
attitudes  and motions of  other parts of the body correspond
with the  attitudes and motions of the countenance, so as to
produce  an harmonious effect.'  The band  is  more used than
any other part  in aid of the countenance in expression;  but  the
whole  body is  often  brought  more or  less  into action. The
character of a passion can  sometimes be inferred  from the atti-
tude merely, or from the mode of walking, as you see one at a
distance.

                    " You may sometimes trace,
          A feeling in each footstep, as disclosed,
          By Sallust in his Cataline, who, chased
          By all the demons of all passions, showed
          Their work  even by the way  in which he trode." 
THE LANGUAGE OF THE MUSCLES.        239
         Action of the respiratory muscles and the circulation in expression.

    350. But  it is the muscles of  the respiratory organs which
 sympathize most with the  muscles of the face  in  expression.
 This sympathy is  the result of a nervous connection, and the
 nerve  of expression in the face is  therefore, as before  stated,
 sometimes called the respiratory nerve of the face.   Observe the
 prominent agency which the muscles of the chest bave in the
 decided, expression of the passions and feelings.   In laughing
 the individual draws  in a full breath, and then  lets it  out in
 short interrupted jets, the muscles of the throat, neck and chest,
 especially the diaphragm, being convulsively agitated.   And if
 the laughter  be strong and continued, he holds his sides, which
 become really sore, from  the violent action of the  respiratory
 muscles in this expression  of his emotions.  In weeping too,
 these same muscles are affected.  The diaphragm acts spasmod-
 ically, the  breathing is cut short by sobbing, the inspiration is
 quick, and the expiration is slow,  and often with a melancholy
 note.   But it is not alone in these marked cases that the respi-
 atory muscles are seen to act, but  you can observe their action
 in many of the slighter expressions of feeling.
    351. There are certain effects  produced by emotions  upon
 the circulation, which heighten the expression  resulting from
 muscular action.   I have already referred to the blush of mod-
 esty, and the  paleness of fear.   In both laughter and  weeping
 the spasmodic action of the  muscles of respiration impedes the
 flow of  blood  through the lungs; and hence the countenance
 becomes flushed or suffused with the blood of the impeded cir-
 culation.  This is very different from common blushing, which
 has nothing to do with the state of the general circulation, but
 is entirely  a local effect, confined to the capillaries of the part,
 where it occurs.  These capillaries are affected  by the  emotion
 through nervous connections, just as the minute secreting vessels
 in the tear glands are excited to unusual action.
 _  352. From the views which I have presented of the capabil-
 ities of the human countenance in expression, you must  be as
 much  struck with its  adaptation to the mind that moves it, as
 you were with the hand in this  respect.   Both are instruments
 of the mind, by which it accomplishes  its purposes; and  they
 would be out of place in any other animal, even one of a higher
 order, because he has not a mind capable of using such instru-
 ments to advantage.  Man needs the face, with all its endow-
ments, to express his thoughts and  feelings, and the hand  to do
the handiwork which his mind designs; and  the Creator has 
240               HUMAN PHYSIOLOGY.
    Training of the muscles of expression. Beauty depends much on their action.

proportioned the capabilities of these instruments to the necesi-
ties and the mental powers of man.
   353.  As the muscles of the face perform such high  functions,
as the instruments of the mind  in expression, it is important
that they should be well trained  in these functions.   Much is
often said about the importance of  grace  in  the  attitudes and
movements of the body, while seldom is a thought given to the
attitudes and  movements of  the  countenance.   Muscles are at
work in the one case as well  as in  the other, and the muscles
of the face  can be trained to work skillfully and gracefully as
well as the muscles  of  any  other  part of the  body.   Indeed,
grace of action is much more important in the  face than in the
body generally, because the  muscles  there are used so much
more  for  expression  than  in any  other  part.   And yet  the
speaker, who aims to gesture  gracefully with his arms, is often
very careless in regard to the gestures, for so we may call them,
which  are  made  by his  face.  So  too  the  parent, who takes
unwearied pains to make the gait and attitudes of her child grace-
ful, often allows most uncouth attitudes of countenance to grow
into a habit.   Many a child that has been drilled most  faithfully,
in order to overcome  awkwardness of movement, is suffered to
become incurably  awkward in the  face, as some one  has aptly
expressed  it.  Sometimes even a habit of making grimaces is
unconsciously contracted, which utterly prevents the countenance
from accompanying the words  that are  uttered with  any thing
like appropriate expression.
   354.  Beauty depends  much upon the attitudes and  move-
ments of the face, and not alone upon the shape of the features.
We often see a face which  is  beautiful in  repose, that becomes
ugly the moment that it is in action, because  the movements of
the muscles  are so ungainly.  And,  on the other hand, we often
see faces which are quite at fault in the  shape of the features,
display great beauty when in  action, from the movements which
play so easily and  gracefully  among the muscles.   It  is a great
triumph of the spiritual over the physical, when  the mind within
thus puts  its impress of  beauty upon a material  form which is
destitute of symmetry.   When it  does  this, there is more to
challenge  our admiration,  than when the  sculptor chisels the
marble into beauty.   And if  he were  to undertake, in imitation
of what we  often  see in living nature,  to put beauty into  ill-
shapen features, he would signally fail.  This can be done only
by the active mind within, moving plastic features by the subtle
agency of nerves  and muscles.   In relation to the inadequacy 
THE LANGUAGE OF THE MUSCLES.         241
               Skill in the use of the muscles of expression.

of mere symmetry of form to meet our ideas of beauty in the
living countenance, Addison has justly said, "No  woman  can
be handsome by the force of features alone, any more than she
can be witty only by the help of speech."
   355. There is nearly as much difference  in skill in the use of
the muscles of the face, as in the use of those of the hand.   And
we need not go to the accomplished orator or actor, as furnish-
ing us alone with the higher examples of this skill.  It is often
seen  exhibited in the ordinary intercourse  of life, in those who
have  great capacity of expression, together with a mind uncom-
monly refined and susceptible.  In them every shade of thought
and feeling is clearly and beautifully traced in the countenance.
While this is the result of education of the muscles of expres-
sion,  an  education of which  the  individual is for the most part
unconscious,  no direct attempt in the training of  these muscles
will succeed, unless  the mind itself be of the right character.
Intelligence  and kindness cannot  be made to beam  from the
countenance, if they do  not  exist in the moving spirit within.
They are often awkwardly counterfeited, the one by the bustling
air assumed  by the face of the shallow pretender, and the other
by the smirk of him who smiles only to get favor or profit from
others.  The counterfeit is often  mistaken for the reality ; and
in relation  to the truly intelligent and kind, there is often much
error  in the estimate  put upon their intelligence and  kindness,
from  the different degrees in which these qualities, when exist-
ing in the same amounts, are exhibited in the expression of the
countenance.  In some, the muscles of expression respond more
readily and aptly to the  thought and  feeling within, than they
do in others.
   356. I know not of any more beautiful and striking exempli-
fication of the influence  of the mind and heart upon the expres-
sion of the countenance,  than is to be seen in those institutions
where juvenile outcasts from society are redeemed from their
degradation  by the hand of benevolence.  You can often note
most  clearly  the  progress of the  mental and  moral cultivation
in the lineaments of the face, as lively intelligence takes  the
place  of stolid indifference, and refined sentiment  that of brutal
passion.  Sometimes a few weeks  suffice to change the whole
character of the  expression.   The dull eye becomes bright, not
from any change  in the  eye itself, but from the intelligence and
sentiment which now play upon the muscles in its neighborhood.
Those muscles which impart  a lively and  pleasant cast to the
countenance when they are in action, are awakened from their
                              21 
242
HUMAN PHYSIOLOGY.
            The habitual expression of the countenance after death.

long continued dormant state by the magic wand of benevolence,
and thus give outward expression to the thoughts and feelings,
which genial influences are producing in the mind and the heart.
The change is often as great in a little time, as it would be in
the face of an idiot, if he could  be suddenly brought  into the
full possession of the mental faculties.
   357. The habitual expression of the countenance, depending
as it does upon the habitual  condition  of  the muscles, is seen
after  death.   In the  state of relaxation  which immediately
occurs at death the face is very inexpressive, because its muscles
are, together with those of  the whole body, so entirely relaxed.
But very soon  they  begin  to contract,  and  they assume that
degree of  contraction  to which they were  habituated during
life, and therefore give to the countenance its habitual expres-
sion.   It is when this has taken place—when  the muscles, recov-
ering from the relaxation of the death-hour, resume their accus-
tomed attitude, as we may  express it, that the countenance of
our friends appears so natural to us, and we are  held, as if by a
charm, gazing upon the intelligence and affection beaming there
amid  the awful stillness of death, till  it seems as if those lips
must  have language.   And this expression is retained through
all the period of rigidity, till it is  dissolved  by the  relaxation
which  succeeds  this state  and ushers in the process of decay.
It is thus that the soul, as it takes  its flight, leaves its impress
upon  the noblest part of its tabernacle  of flesh; and it is not
effaced till the  last vestige of life is gone, and the laws of  dead
matter take possession of the body.   The state  of countenance
which I have described is thus beautifully alluded to by Byron.
           He who hath bent him o'er the dead,
           Ere the first day of death has fled,
           The first dark day of nothingness,
           The last of danger and distress,
           (Before decay's effacing fingers
           Have swept the lines where beauty lingers),
           And mark'd the mild angelic air,
           The rapture of repose that's there,
           The fix'd yet tender traits that streak
           The languor of the placid cheek,
           And—but for that sad, shrouded eye,
           That fires not, wins not, weeps not, now,
           And but for that chill, changeless brow,
           Where cold obstruction's apathy
           Appals the gazing mourner's heart,
           As if to him it could impart
           The doom he dreads yet dwells upon;
           Yes, but for these,  and these alone, 
THE VOICE.                    243
Superiority of the vocal apparatus to musical instruments.

Some moments, aye, one treacherous hour,
He still might doubt the tyrant's power;
So fair, so calm, so softly sealed,
The first, last look by death revealed!
                   CHAPTER  XIV.

                         THE VOICE.

  358.  The apparatus of  the voice is truly a musical instru-
ment.   We can see therefore, in its construction and arrange-
ment, the application of those principles, which usually  regulate
the production of musical sounds, and which man observes in
makino- the various instruments which his ingenuity has invented
to delight the ear.  It is, however, a much more perfect instru-
ment than any which man has invented.  Almost every musical
instrument, it is true, has a greater compass than that of the
human voice;  but it is by no means the chief excellence of an
instrument that it  can command a great extent of the scale.
The apparatus of the voice can execute enough of  the  scale for
all common purposes.  It is wonderful  that its compass  is so
great as it is, for it is a very small instrument, occupying a space
of less  than an inch square where the vibrating ligaments are
situated.  In every respect besides  compass this instrument far
excels all others.   Listen to a good voice  which has  been
well educated.   Its transitions have an ease and a grace which
the workmanship of man can not equal; the richness and sweet-
ness of its tones are  above all  imitation with the most perfect
instruments; and utterance is given to its various notes with so
little apparent  effort, with so little show of  machinery, in com-
parison with  the instruments made by man, that  we are tilled
with wonder at the effects  produced by so simple, delicate, and
beautiful a piece of mechanism.  But the most important cir-
cumstance to be noticed  is, that there are parts connected  with
this apparatus, which  give articulation  to  the  voice  as it
comes from.the vocal chords, thus  making it the principal me-
dium of communication  between man  and man.   This distin-
guishes it from every other musical instrument, aud constitutes 
244
HUMAN PHYSIOLOGY.
         Voice of conversation and song. Voices of the brute creation.

its crowning excellence.   When  I  come  to  speak particularly
of the articulation of  the voice, you will see how really compli-
cated is  the apparently simple mechanism  that produces the
varied articulations, and thus makes the voice the chief medium
of mental  communication.   And if you  try to measure, with
the utmost stretch of conception, the endless  variety of thought
and  feeling, which this apparatus conveys daily, hourly, every
moment  from heart to heart in the intercourse of  life, you will
be able to estimate in some good  degree the  value of those or-
gans, which, though we seldom spend a thought upon them, are
so constantly ministering to our enjoyment.
   359. Such being the high uses for which the voice is designed,
when it possesses a rich and flowing melody, and its articulation
is  graceful and  easy, its  powers  of fascination  are wonderful.
Such a voice is a fit medium of communication  for "thoughts
that  breathe and words that burn."   This is more often true of
the voice of conversation than that of song.  It is in the hourly
intercourse of life that melody of voice is most valuable to us as
a source of enjoyment, and here its influence is often astonishing.
It will sometimes give a charm, not to say beauty, to an ordinary
face ; while on the other hand, the fascination of beauty is often
destroyed by the utterance of a voice harsh and without melody.
And it may be remarked that a rich and finely modulated voice
of conversation, and a melodious voice  of song, do not always
go together.  The voice which  has delighted the ear of multi-
tudes at  the public concert, may  be divested of all its charms,
when used  in conversation;  and on the other hand, there are
many who  sing unskillfully, and yet in conversation give utter-
ance to genuine and varied melody.
   360. There is music not only in the human voice, but in the
voices also  of the brute creation.  And  the varied forms of the
apparatus by which it is produced show the impress of the same
power.   What variety there is in the sounds  which come  from
the multitudes of different animals on our globe, and how diversi-
fied is the handiwork exhibited in their vocal organs  !  The pow-
er from  which springs this  endless variety is the same as that
which gives such diversity to the human countenance, and I
know not which  is the  most wonderful  display of it.   And it
may  be remarked, that although the voices of some animals are
harsh and  discordant, those  which we most frequently hear are
melodious.   Even some of those  which are unpleasant to the
ear, become in some degree  pleasant when  occasionally heard
at the right time and in the right place, from the addition which 
THE VOICE.
245
  Two kinds of wind instruments—reed, and those having an inflexible mouthpiece.

they make to the variety of sounds that we hear, and from the
associations which become connected with them.   A goose on  a
common, says Cowper, is no bad performer.
  With  these  preliminary remarks I proceed to the investiga-
tion of the subject.   I shall speak  first of  the voice as it is pro-
duced in  the  larynx by the vibration  of  the  vocal  chords or
ligaments, and  then treat of the articulation  of the voice.
  361.  As  the apparatus of the voice is  really  a wind instru-
ment, I will first develope the principles on which wind instru-
ments produce the various musical notes,  and
then  show you the resemblance between these        no. 135.
instruments and  the  set of organs which  are         £
engaged in producing the notes of the voice.
Wind instruments  are of two  kinds—those
that have an inflexible  mouthpiece, and those
in which the sounds  are produced  by a vibrat-
ing reed.   The horn, trombone, trumpet, flute,
fife, flageolet, flute-stop and  other stops of the
organ, &c,  are instruments of the first kind.
The cause of the variation of notes produced
in these instruments may be thus explained.
The column of  air contained in the tube is the
vibrating body from which proceeds the sound.
Any thing then that  affects the column of air
affects the  note.  The length,  the breadth,
and the mode of producing the vibrations are
the causes of the variation of the  note.   The
holes which are in the side of a flute  are for
the purpose of  altering the length  of the con-
fined column of air.   In the trombone this  is
done  by sliding  one part of the  instrument
upon the  other.  The general  rule is,  the
longer is the column of air the more grave  is
the  note.  Thus in the flute, the lowest note
that can be produced by the instrument is
made by covering all the holes, so that  you
have a column of confined  air the whole length
of the tube.  The highest note, on the other
hand, which the instrument is capable of pro-
ducing is made by so arranging the fingers as
to allow the air  to  escape  at the first hole.
In this case the length of the confined vibra-
ting column of air extends only from the mouth
                             21*
 
246
HUMAN PHYSIOLOGY.
          Size and width of vibrating column of air affecting the note.

hole to the hole from which the air escapes.  I take another
illustration from the organ.   Fig. 135 is a representation of one
of the pipes of the flute-stop of the organ, which is a wooden
box, made  very  much  after  the  manner  of a boy's chesnut
whistle.   At a is the passage for the introduction of the air ; b
is the inclosed column of air, the vibration  of which produces
the sound ;  c is the place of escape for the air; and d is a mov-
able plug, by means of which the vibrating column of air can
be  made  longer  or shorter, according to the note desired.   In
tuning the organ, if the  pipe gives too low a note the plug is
moved  downward, thus shortening the column of inclosed air,
but if too high a note, the plug is raised up.
  362.  The same rule applies to the .width of  the vibrating
column of air.  The wider the column the graver the note,  and
vice versa.  I  would observe, that in a long, slender  column of
air, as in the trombone, by giving the current of air from  the
mouth  a  great  velocity  a high note  may  be produced;  but
where, as  in the ophicleide, the column is both wide and long,
it is difficult to do this, because it is difficult to produce a quick
vibration in  so large a body of air, with all the suddenness  and
force with which  we can move it.
  363.  In those instruments which have no  expedient for alter-
ing the length of the column of air, such as the common horn,
the various  notes are produced by narrowing or  widening the
orifice  by the  agency of the lips, as  the  case requires, at the
same time giving, by the varied velocity with which the air is
forced  into the instrument, a quicker or slower vibration to the
air.  Grave  sounds are produced by  a wide, and acute by a
narrow opening.  In playing the flute the opening of the  lips
is thus varied  in  order to produce a vibration which shall  cor-
respond with  the length of the column of air.  If the flute
player, with his fingers arranged for a high note, should blow
into the mouth  hole with his  lips forming a large orifice, he
would  not produce the desired note.   To produce the   proper
vibration in a short column of air, the orifice from which the air
issues to move this column must be small enough to corres-
pond, and with it there must  be the requisite velocity in the air
as it comes from the mouth.   You have a  good  illustration of
the influence of size of orifice on the note of sound in common
whistling.   The  higher  the note produced the more narrow is
the outlet  from the mouth.  The size  of it is regulated by both
the lips and the tongue.
  364.  In reed instruments the variations in note are produced 
THE VOICE.
247
         Reed instruments. Principles.  Tube connected with the reed.

in a different manner.   The clarionet,  hautboy, bassoon, the
reed stops in the organ, &c, are instruments of this sort.   It is
the vibration of the thin plate  called the reed that causes the
sound.   The longer this plate is, the slower are  the vibrations,
and therefore the graver is the note, and vice versa.   The prin-
ciple can be well illustrated in the reed stops of the organ.   The
reeds in the different pipes are made of different lengths, accord-
ing to the notes which they are to produce.   In  a reed  instru-
ment pla}'ed by the mouth, as the clarionet for example, the
rapidity of the vibrations is regulated by the pressure of the lips.
In producing a high note the lips press firmly on the reed  and
leave but a  small portion of it to vibrate;  while in producing a
low note the lips press less firmly on the reed, and leave a large
portion of it to  vibrate.
   365. You see that the same principles apply to the reed as
to the column of air in the other kind of wind  instruments.  In
both cases the longer and thicker the vibrating body the coarser
is the vibration, and the graver  the note.   This same principle
also applies  to  stringed instruments.  Thus in the piano, the
grave notes come from long and large strings,  while the higher
notes come  from slender and  short ones.   In  the violin the
strings are all of the same length, the larger strings giving the
graver notes, and  the smaller the  higher ones.  The notes are
varied also  in the case of each  string, by varying the tension.
They are varied too while playing on the instrument by varying
the length of the vibrating strings by the pressure of the fingers.
   366. The reed is  always  connected with a tube.  Has  this
any influence upon the note produced by the reed ?  It contains
a column of air through which  the sound caused  by the vibra-
tion of the reed must pass.    Unless, then, the vibration of this
column of air corresponds with  the vibration of the reed, it will
alter the note.   It  does alter the note to some extent always.
It never raises  it, but  always  makes it  more grave.   That is,
the vibration, in  passing from  the  reed to the  column of air,
becomes less rapid  and coarser, as is always the case when vi-
bration passes from any  substance to another.  But the tube is
so arranged that there may be as little  change in this respect
as possible, and yet have the combined effect of a  reed and wind
instrument secured.   Holes are  therefore  properly placed in the
side of the tube, so that with the fingers the column of confined
air  may, in the case of every  note, be placed in correspondence
with the vibration of the reed.   Suppose the tube to be long
and without holes; in this case low notes could be easily pro- 
248
HUMAN PHYSIOLOGY.
      Description of the organ of the voice. Hyoid bone.  Larynx. Trachea.

 duced, but attempt a high note and you would fail.  The reason
 is obvious.  The low note is caused by a low and coarse vibra-
 tion of the reed, for the transmission of which a long column
 of air is  fitted.  But if a  high note be attempted, the slow
 vibration  of the long column of air disagrees with the quick
 vibration  of the reed, and flattens very much the sound after it
 comes from the reed, as it passes through the tube.  As I have
 already hinted, the object of the tube is to secure in the instru-
 ment the  combined effect of a  reed  and a wind instrument.
 The tube  makes the reed speak, as it is expressed; that is, it
 gives intensity and an agreeable character to the sound.  If
 you disconnect the reed of the hautboy or bassoon, for example,
 from its tube, and blow upon it, you can produce all the variety
 of notes,  but the sound is disagreeable;  but by connecting the
 tube with the reed you produce a compound sound, as we may
 call it, which has a sweet and  rich melody.
   We will now examine the apparatus of the voice, and see how
 far the  principles which I have developed in  relation to common
 musical instruments are applicable to this instrument.
   367. Just at the root of the  tongue, as described  in the Chap-
 ter on the Bones, § 282, is a small bone, shaped so  much like
 the Greek letter v that it is  called the hyoid or  U-like bone.
 The round end of this bone is towards the  root of the tongue,
 and its two ends point backward  toward  the pharynx.   To
 this bone  is connected a long cartilaginous  tube extending to
 the lungs, called the trachea, or windpipe.   It is  through this
 tube, as you have  already learned, that the air goes back and
 forth from the lungs  in respiration and speech.   It is  not one
 solid tube, but is composed of a great number of rings of carti-
 lage connected together by membranous parts. The rings are
 not perfect circles.  They are deficient behind, and this deficiency
 is supplied by a membrane.   The object of  this arrangement is
 evident. ^  The part of  the tube where the rings are deficient is
 directly in front in its whole  length of the oesophagus or gullet,
 the tube through which the food passes.  If the rings had been
 made entire, it is manifest that  their pressure would interfere
 somewhat with swallowing.  But  it is the  upper part of the
 windpipe,  that part which is immediately below  the U-like bone,
 which claims our, attention as the seat "of the formation of the
voice.   This part is called the  larnyx.   It is formed of five car-
tilages, the arrangement of  which I will now show you.  The
largest of  these cartilages, the  one which forms the most of the
body of this music-box, as we  may call it, is the thyroid.  It is 
THE VOICE.                    249
Thyroid, cricoid and arytenoid cartilages.
FIG. 136.
 the pomum Adami, or Adam's apple, which  is so easily felt in
 the top of the neck.   This cartilage forms the front and sides
 of the larynx, but it is open  behind.   The cricoid  cartilage  is
 shaped very much like a seal ring, and this resemblance  gives
 it its name.   The narrow part  of it is situated directly under
 the thyroid cartilage, in its front and at its sides, but the broad,
 seal-like part of it is  behind, projecting upward and filling up a
 part of the open space left by  the deficiency of the thyroid in
 in its rear.  A side view of these parts
 is given in Fig. 136, in which 1 is the
 the U-like bone ;  4 is the thyroid car-
 tilage;  and  6 the cricoid.  At 8 is
 the back  part of the cricoid, filling up
 a part of the space in  the open rear
 of the  thyroid;  3 is a horn shaped
 projection of  the  thyroid, and  5  is a
 smaller one below, projecting over on
 to the  outside of the cricoid;  2 is a
 strong membrane or ligament connect-
 ing the hyoid or U-like bone with
 the top of the thyroid; 9 is  the epi-
 glottis,  drawn up  by a hook ; and at
 7 are the rings of the trachea.   The
 epiglottis is composed in part of car-
 tilage.  It is, as I have already told
 you, in the Chapter on Digestion, § 78,
 the lid of the music box, the larynx,
 shutting  down when  we swallow, so
 that the food or drink may pass over
 it,  and  being raised up  when  we
 breathe or speak.
   368.  There are two small  cartilages which are not  seen in
 this figure, called  arytenoid cartilages,  from  two  Greek words,
 meaning ladle and shape, because they bear some resemblance
 in form to a ladle.  They stand in the open  space  in the rear
 part of  the  thyroid, on the top of the  cricoid  cartilage.   They
 are the pillars to which the vocal chords or ligaments are attached
 behind.   These two  cartilages  are  movable,  having a regular
joint with the upper edge of the cricoid.  There are small mus-
cles which pull them in different directions, and thus change
the degree of tension  and the  position of the vocal ligaments,
and of course vary the note of the sound produced by their vibra-
tion.  That you  may understand how this is done, I give you
  Side view of

THE  LARYNX. 
250
HUMAN PHYSIOLOGY.
Vocal ligaments.  Mode of their action.
Diagram showing the action of the
 VOCAL LIGAMENTS.
FIG. 138.
in Fig. 137 a diagram showing the arrangement of these liga-
ments.   It  represents a view of them  as  you look down into
the larynx, in which a is the front of the thyroid cartilage, and bb
are the two arytenoid cartilages.   To
these you see are attached two sheets
of membrane, which are  also fastened
all around to the  inside of  the thy-
roid.   If these movable parts, as we
may call  them, to which the ligaments
are  thus attached,  be drawn back-
ward, it  is obvious that it will make
the ligaments  more  tense.   If they
are  separated  from  each  other, the
opening  between  the  ligaments  will
be  widened.   If  they  are  brought
nearer together, this  opening will be
narrowed, and  the forward  part of the free edge of each liga-
ment will be prevented from vibrating, because it is here brought
in contact with the other ligament.
Now there are small muscles which
are attached to the arytenoid car-
tilages for the purpose of moving
them as  I have pointed  out.  The
figure which I  have presented is a
mere diagram, to show the arrange-
ment of  the ligaments for the pro-
duction of the various notes of the
voice.  In Fig. 138 is represented
the actual appearance of the  liga-
ments and the arytenoid cartilages,
as you look down upon them.  The
ligaments you observe are thicker at
their free edges than any where else.
   369. In Fig. 139 you have a view of the larynx and trachea
from behind, in which are shown two of the muscles that move
the arytenoid cartilages.  At h  is the hyoid bone;  t  t,  the
posterior   margins  of  the  thyroid cartilage; between these
stands the  broad rear  part of  the  cricoid   cartilage, the
middle line of which  you  see at  c; at r are the rear ends
of the rings of the  trachea;  I is the membranous part  of the
trachea,  which  lies in front of the oesophagus  or gullet;  a
marks  the top of one of the arytenoid cartilages, and you see
also  the  top of the other ;  e is  the  epiglottis represented as
THE VOCAL LIGAMENTS. 
____________THE VOICE.                    251
Muscles regulating the tension of the vocal ligaments.
FIG. 139
       REAR  VIEW  OF THE LARYNX  AND  THE TRACHEA.

raised up as when we  are speaking  ; b is  a muscle, which, be-
ginning at the middle line of the cricoid cartilage, runs forward,
and is fastened to  the outside of the arytenoid  cartilage, there
being one like it on  the other side, as you see; s is  another
muscle going from the cricoid to the arytenoid cartilage, which
also has its fellow on the other side.   You can see that the muscle,
s, and its fellow, if contracted would bring the arytenoid cartilages
nearer together, and so diminish the opening between the vocal
membranes which are fastened to these pillars.  The muscle, b,
and its fellow, on the other hand, when they act, so draw upon
the outer edges of  the arytenoid cartilages as to  separate these
cartilages from each other, and therefore  enlarge the openings
between  the  ligaments.   There  are  other muscles not seen in
the figure, that alter  the size of the orifice between the vocal
ligaments and their degree of tension, and thus affect the notes
of the voice.
   370. I have described the true vocal ligaments.  But there 
252              HUMAN PHYSIOLOGY.
Interior view of the larynx and epiglottis.
is  another pair of ligaments directly above  them, the space
between which is the real opening into the larynx,  upon which
the epiglottis  shuts  down when we swallow.   You will get a
good idea of the arrangement of the two pairs of ligaments from
Fig. 140.   This is a representation of an inner view of one

                          FIG. 140.
INTERIOR  OF THE  LARYNX.
half of the larynx, the  division being made  directly down, and
from front to rear.  At t is the front of the  thyroid  cartilage
with its cut edge; at c c, are the two cut edges of the cricoid,
showing how narrow is its front part compared with its broad
rear portion ; a  is the left arytenoid cartilage, c  showing the
place where it is united by a joint to the top of the cricoid ; / is
the trachea; r  is  the true vocal ligament or chord;  v is the
space between this and the upper ligament; and e is the epig-
lottis which is shut down upon  the upper ligaments as a cover
by the contraction of the muscle b, just when this is  needed. 
THE VOICE.                    253
Upper and lower ligaments.  The lower the true vocal chords.
In Fig. 141 is a diagram represent-
ing the plan of these two pairs  of
ligaments, as shown by a perpendic-           FIG- 141-
ular section from side to side.   B B
represents the vocal ligaments, C C
the upper ligaments, and V V, the
two recesses between them.
   371. We know that  it  is the
lower  ligaments  that are the true
vocal  chords,  because  the  parts
above  these, even the  upper  liga-
ments, may be all cut away, and yet
a  vocal sound may  be produced ;
while if an opening  be made into
the  larynx  below the  lower  liga-
ments  the voice will  be destroyed.
Magendie,  a French physiologist,
speaks of a man, who on account of
an opening in the larynx  was never
able to speak without pressing his
cravat  tightly against  this opening,
in order  to prevent the air from  escaping  through it.   Many
experiments have  been  tried with the larynx after death to
verify the results  above stated.  The lower  ligaments are then
the  vocal chords,  by the vibration of which  all the different
notes of the voice are produced.   And the  other parts of the
vocal apparatus serve  only to modify the sound caused by the
ligaments.  The lungs act merely  as the " wind-chest," to hold
the  air which being forced out strikes on  the ligaments, and
makes  them to vibrate.
   372. Let us now  apply to this  apparatus  the principles
which I  have developed in the beginning of this  chapter, as
regulating the  variation  of note  in  common musical  instru-
ments.  The size of the  aperture,  through which the sound is
thrown out,  influences the note,  of which we have a familiar
example in whistling.   And  as you have seen that the  size of
the  opening between  the vocal  ligaments  is varied by  the
muscles  moving  the  arytenoid cartilages, this must have  an
influence upon the note of the voice.   But this is not the only
cause of the variation of the note.   As I showed in  relation to
the reed,  and to the  strings  of stringed instruments, so also
here the larger and less tense are the vibrating bodies, the vocal
chords, the graver is the note, and vice versa.   You have seen
                              22 
254              HUMAN PHYSIOLOGY.
        Principles of musical instruments applied to the vocal apparatus.

how these chords or ligaments are varied in tension  by the
action of the muscles that move the arytenoid cartilages.  You
have  also seen that, as these  cartilages are brought near  to-
gether by the muscles, the extent of the free vibrating edges of
the ligaments is shortened, because their edges  are  brought to-
gether in their  anterior part  (Fig. 137).  Magendie  verified
this by observation.  He  opened  the throat of a noisy dog in
such a way that he could look directly upon the vocal ligaments.
When the sounds were grave,  he  observed that the ligaments
vibrated in their whole  length, and that the air passed out in the
whole  length of the  chink between them.  But when the
sounds were on  a high note, the ligaments did not vibrate in
their anterior part, but only in  the posterior, and the air passed
out only  at the open vibrating part.   It is manifest that in pro-
ducing the various  notes, the muscles that move the arytenoid
cartilages act upon the ligaments just as the lips do upon the
reed of the hautboy or bassoon, regulating the extent and the
rapidity of the vibrations.
   373. There has  been much discussion as to the kind  of
musical instrument the larynx most resembles.  From the facts
above stated it appears clear that  it most resembles reed instru-
ments, though its analogy to stringed instruments is also quite
apparent.   There is also a resemblance to some small extent to
common wind instruments, as the  size of the orifice between the
vocal  ligaments  must  have some  influence  upon the  note.
Whatever  we may  think as to  the  degrees  in  which  these
analogies exist, we can  see  that the great principle of  musical
sounds is regarded in all the arrangements of the vocal appara-
tus, viz.,  that coarse and slow vibrations produce  grave notes,
while rapid and fine vibrations  produce high ones.
   374. I will trace  the resemblance between the instrument of
the voice and common musical instruments still farther.  The
sound as it comes from  the  larynx passes through  a tube, just
as the sound coming from  a  reed does  in a reed instrument.
In other words there is a body of inclosed air extending from
the larynx to the outlets of the  mouth and nose, which vibrates
in transmitting the sound from  the larynx.   This body of air is
not as simple in its form as that is which is inclosed in the tube
of common reed instruments.   It  has three outlets, the mouth
and the two nostrils.  The sound  of the voice, however,  seldom
comes out from the orifices  of  the nostrils, but almost always
from the mouth.   In humming it comes  altogether from the
nostrils.   In  ordinary speaking  and singing the cavities  of the 
THE VOICE.                     255
          Tube of the vocal apparatus like that of a reed instrument.

Qose act as reverberating cavities, the sound which reverberates
there issuing  from the  mouth.  This  fact will  be illustrated
when I come  to  speak of the articulation of the voice.   The
curtain of the palate  answers as a sort of swing  door between
the cavity of the mouth, and the cavities of the nose, to direct
the  air the one way or  the other.   When a  sound  is to be
reverberated in the cavities of the nose, it hangs in such a  way
that the  communication  between the mouth and these cavities
is open.
   375. You have seen that the tube  connected with  the  reed
in the reed instrument is so arranged, that the  length of the
confined  column  of air can  be changed,  in  producing the
different notes, the vibration of the air  thus being brought into
correspondence with that of  the reed.   How is the same thing
effected  in the  vocal  apparatus ?   It is  done  in  two ways.
First,  the  length of the tube is  altered.   If  you place   your
finger on the front of the larynx, and then sound various notes,
you will feel the larynx  rise when you sound a high note, and
fall when you sound a  grave one.   The  object of this move-
ment is to alter the distance from the larynx to the outlet of the
mouth, in  other words, to alter the length of the column of air
in the tube, so that it may correspond  in its vibration with the
vibration of the vocal chords.  But the size of this column of
air is altered in  another way.  It is altered in its width, which,
as I have remarked in relation to musical instruments, § 362, is
quite as  effectual in changing the vibration as an alteration of
length.  The tube of the vocal instrument you readily see can
be  altered in its width by the  muscles  of  the throat and
mouth.
   376.  The object of the tube of the reed instrument is, I  have
stated in § 366, to make the reed speak, as it is termed ; that is,
to give intensity and an  agreeable character to the sound.   The
tube in the instrument of the voice  undoubtedly does the  same
thing.  If the voice should  come directly from the larynx with-
out passing through the tube attached  to it, it would be as dis-
agreeable  as the sound of a  reed when separated from  its  tube.
The  voice gets most of its melody  after  it  is made in the
larynx, as  it passes out through the column of air in the throat
and mouth.   And it is the variations of this tube produced by
the muscles  that surround  it that give to the voice  its variety
of  tone  as well  as its  melody, thus  constituting one of the
great excellencies of the vocal  instrument in  comparison  with
all common musical instruments.   If  the voice  of Jenny  Lind 
256
HUMAN PHYSIOLOGY.
          Seat of hoarseness.  Influence of the epiglottis on the voice.

could be made  to come directly from the larynx, notwithstand-
ing its great compass, it would  lose all its charm, and would be
better  fitted for the performances of Punch and Judy, than for
the public concert.
   377. It is a very common  popular notion, that a hoarseness,
or a loss of voice, indicates disease in the lungs.   But you have
seen that the lungs are the mere bellows, or the " wind-chest" of
the organ of the voice, and that the voice is produced by the vi-
bration of the vocal ligaments  as the air forced from the wind-
chest strikes them,  and is modified by the tube which  extends
from the larynx to the outlet of the mouth.  Any alteration of
.the sound therefore, as hoarseness,  must be caused by difficulty
either  in the ligaments, or the tube, or  in both, and an  en-
tire loss of the voice can be caused only by an affection of  the
ligaments.   Disease in the lungs, it is true, is very apt to  affect
the  larynx  and the throat by  extension or by sympathy, and
thus alter the voice ; but it often does not.  Consumptive per-
sons sometimes have a clear voice almost to the last.
   378. The epiglottis, besides acting as a lid for the larynx, for
the  food to pass over it into  the  oesophagus, also  has an in-
fluence upon the voice in two  ways.   First it can be made  to
narrow more or less the passage of air from the  larynx.  And
secondly, some experiments of M. Grenie  on reed instruments
show,  that it has an influence upon the intensity of the  voice.
When experimenting on some reed instrument, he wished  to in-
crease  the intensity of sound without changing the  reed.   For
this purpose he gradually increased the force of the current of
the air; but this not only augmented the  sound, but raised its
note.   He at length obviated the difficulty, by placing obliquely
in the  tube, just under the reed, a supple elastic tongue.   He
could  now give greater  intensity to the sound without raising
its note.  The epiglottis seems to perform the same  office in
our vocal tube, for it is  elastic and supple  like the little tongue
which  M. Grenie placed  in  the  tube of  his instrument.  Its
situation is similar  also, it being  directly over  the double reed
of the  larynx, as we may call its ligaments.  There are  muscles
to move it, so that it  may be at the  right  inclination  in all
cases.   One of these is seen in  Fig. 140 at b.
   379. I have thus traced the analogy between the apparatus
of the  human voice, and musical  instruments.  How nicely ad-
justed  are all its parts !   With what precision must the  muscles
that move them act in those who are able to produce the most
delicate, as well as the most striking variations of note !   Every 
THE VOICE.
257
       Delicacy of the action of the vocal muscles. Gliding from note to note.

 modulation of the voice,  however  slight, requires muscular ac-
 tion to effect it.   The vocal  ligaments must be  put  in just such
 a state, or the wrong sound will be  produced.   So too, the
 muscles of the mouth and throat must  put the  tube of the
 vocal instrument into the right shape, in order to  have the con-
 tained  column  of air correspond  in  vibration  with the  vocal
 ligaments.  To have some  conception  of the variety  of the
 motions of the muscles  concerned in the  modulation  of the
 voice, listen to some singer whose voice can command with ease
 and freedom  a great extent  of the scale.   For every note that
 you hear there is a distinct and  particular adjustment of the
 vocal  ligaments, and of course a particular degree of contrac
 tion of the little muscles that move them.   Let  us see how deli-
 cate the action of these parts is.   It is calculated  that the liga-
 ments vary in length only about the -^ of  an inch in producing
 all the  notes  of the voice.   Now  the natural  compass of the
 voice (that is its range from  its lowest to its highest note) in
 most  singers is  about  two  octaves or 24 semitones.  Within
 each semitone a singer of ordinary capability can produce 5 or
 6 distinct notes; so that for  the whole number  of notes that he
 can sound distinctly  120 is a moderate estimate.  He therefore
 produces 120 different states of tension in the vocal ligaments.
 And as the variation in their length for passing  from the lowest
 of these 120 notes to the highest is only the -£-th of an inch, the
 variation required to pass from one note to  another will be only
 the iroTth of an inch.   A very expert singer  can  produce a
 much  more delicate action  than this, and  distinctly appreciate
 the  result by his ear.   How great  the contrast between the
 minute contractions of the little muscles that move these vocal
 ligaments,  and the contractions of the large muscles in the arm
 that wield the ax and the sledge-hammer!
   380. It is proper to notice here one very marked difference be-
 tween the vocal apparatus and common musical  instruments.   I
 have spoken in the previous  paragraph of  distinct notes as exe-
 cuted by the voice.  Most instruments execute only these distinct
 notes.   But the voice can also glide from one note  to another
 with a continuous sound.   In this respect the vocal  instrument
 is superior to  common  musical instruments.   There is one
 instrument, however, the violin, in which this gliding movement
 can be to a great extent imitated.   It  is  done by  sliding the
 finger on the string, as it vibrates under the bow.  A peculiar
use of this gliding movement distinguishes the  voice of speech
from that of song, as I shall  show you  in  another part of this
                             22* 
258
HUMAN PHYSIOLOGY.
  Training of the muscles of the voice.  Importance of keeping the chest full of air.

chapter.   It is by an imitation of this, by sliding the finger on
the string, that the violin can be  made to imitate  so well the
tones of conversation.
  381.  The muscles, by which all the variations in the tension of
the vocal ligaments are effected, receive nerves from the brain, and
are under the guidance  of the will.   When the mind therefore
wills to produce  a certain  sound, these muscles  immediately
place the  parts in such  a state as to cause that sound.   This is
true of the muscles that put the  tube in correspondence with
the larynx, as well as of those which produce the right state of
tension in the ligaments.  It is also true of  the  muscles which
articulate  the voice, of which I am yet to  speak,  and of those
which work the chest, the bellows or "wind-chest''  of the organ
of the voice.   The muscles of this  apparatus are in the same con-
dition with other voluntary muscles; and therefore, like them,
the more  they are trained in  the exercise of their powers, the
more perfect  will be their action.  The muscles in  the arm and
hand of the infant learn to  execute the motions of which they
are capable gradually.  Just so  it  is with  the  muscles of the
voice—from our infancy they are  trained under  the ear as an
instructor.  The  muscles  which  regulate the adjustment of the
vocal ligaments, in producing the different  notes, cannot do it
accurately without the education of exercise, any more than the
lips of one just beginning to play on the hautboy  or  clarionet,
can regulate their pressure on the reed, so as to sound the dif-
ferent  notes  correctly.   The  analogy is perfect, for  it  is the
muscles moving the vocal chords that vary the note of the voice,
and it is the muscles moving the  lips  that vary their  pressure
on the reed, and  of course vary  the note of the instrument.
  382.  The skillful  singer  or  speaker  exhibits  much skill  in
managing the  muscles of the " wind-chest."  He keeps it all
the time well supplied with air,  so  that but a comparatively
slight action of the  expiratory muscles will suffice  to throw the
air  against the vocal ligaments with  the requisite force.  But
an  unskillful singer or speaker  much of the time  has his chest
poorly supplied with air, and so speaks or sings, as it is expressed,
from the top of the chest.   It costs him, therefore, so much labor
to throw out the  air with sufficient  force, that he is soon tired
out.  The necessity of  keeping the chest full of  air, in order to
work the  vocal apparatus easily, may be illustrated by reference
to the bagpipe.   If the  bag containing the air be well filled, a
slight pressure of the arm upon it will force the air through  the
pipe with sufficient rapidity to produce the sound.  But if  the 
                        THE VOICE.                   259
           Tiring out the vocal muscles.  Vocal apparatus in birds.

bag be flaccid, from the little quantity of air in it, a very strong
pressure of the arm will be required to produce  the same effect.
   383.  But it is not the muscles of the chest only that are tired
out in the  unskillful singer or speaker, but  also the muscles of
the larynx  and  the  throat.  And a frequent  tiring of these
muscles weakens the force  of  the parts, and  often at length
produces disease.  Much of the throat-disease of public speakers
comes from this  cause, and is a nervous disease, the affection of
the lining membrane of the throat being often a mere accompa-
niment.  This result is  more apt to occur when the nervous
force  of the system generally is impaired, than when there is a
state of vigor.  It is also more apt to occur in those who speak
in a uniform and somewhat monotonous manner, than in those
who have much  variety in their mode  of speaking.  A continua-
tion of precisely  the same muscular effort for any length of time is
apt to produce painful exhaustion, while a much greater amount
of varied muscular effort may  be put forth without weariness,
or even with pleasure.
   384.  It would be interesting to trace  the differences in the
arrangement of  the vocal apparatus in different animals, but I
will only notice  the arrangement which we  find in birds.  The
voice  of birds is formed not, as in us, at the top  of the wind-
pipe,  but  at  its  lowest portion.   Like  the human voice, it is
produced  by the vibration of sheets of membrane.  These are
placed just at the division of the trachea, where its two branches
go off to supply the two lungs with  air.   The voice is formed
by these ligaments, and is then  transmitted through the column
of air contained  in the whole  length of  the windpipe.   This
column of air must have some influence on the note of the voice,
according to its  length and diameter.   Birds, therefore, in sing-
ino- different  notes change its length in some measure.   This is
easily done, as the windpipe is composed  of rings of cartilages,
connected together by membranous substance.  There are mus-
cles indeed up and down the tube, for the  purpose of shortening
it by  approximating these rings to each other.   As the turkey
gobbles he throws his head up and  down, and thus shortens
and lengthens the  trachea.  This movement is quite obvious
also in the  canary bird.
  385. Having  "thus treated of  the  formation  and  the mod-
ulation of  the  voice,  I  come  now to its articulation, which
makes it the  grand medium of intercourse between man and
man.   I will first describe the parts engaged in articulation, and
then speak of the agency of each of them. 
260              HUMAN PHYSIOLOGY.
               Tarts engaged in the articulation of the voice.

   386. The vocal tube, which I have  described  as extending
from the larynx to the outlets of the mouth and  the nostrils,
produces all the variety of pronunciation in all the different lan-
guages of our globe.   It is all one cavity, though it is partially
divided by  partition walls.   If you recur  to Fig.  10, on  page
48, you will see a representation of this compound cavity.  At
the top of the trachea d you see  the epiglottis c, which shuts
down upon  its  orifice when we are  swallowing.   Above this is
a large space  called the pharynx.   It is  the back part of the
throat, which  we  can see  behind the arch of the palate on
looking at it through  the open mouth.  Its communication with
the mouth and the cavities of the nose is regulated  by the palate
g, which is moved by muscles into the different positions required.
The cavities are very complicated, having several partitions par-
tially dividing them, as seen in Fig. 89, and they  communicate
with cells in the  bones by small orifices.   That very movable
organ, the tongue, and  the teeth  and lips, I need not describe.
   387. We will  now observe  the agency which  the different
parts of this compound vocal tube have in the articulation of the
voice.   Every letter, whether it be a vowel  or  a consonant, re-
quires a particular position of the different parts of the vocal tube.
In some letters the tongue is the chief agent in articulation, in
others the lips, in others the teeth, in others the palate, and there
are some in the formation of which the cavities of the nose have
an important agency.   I will notice the different parts separately.
   388.  The tongue has been considered so essential to  speech,
that tongue and language  are often used synonymously.   But
though it does  perform an important part  in articulation, it is
not absolutely essential.  Though it assists in the formation of
many of the alphabetical  elements, it is the principal agent in
but  two of them, I and r.  The loss  then of this busy little
organ does not necessarily  produce dumbness, nor  even  impair
to any great extent, in some cases at least, the power of speech.
To  prove  this I will  cite a few facts which appear to  be well
authenticated.  The Emperor Justin says that he had seen ven-
erable men who, after their tongues  had been cut off at the root,
"complained bitterly of the  torture they had suffered."   He
says also in  another place that some prisoners, who were pun-
ished in this barbarous manner by Honorichius, King of the
Vandals, " perfectly retained their speech."  But there are cases
more thoroughly attested, having been examined and reported
upon by scientific observers.  A boy, who  lost his tongue by
disease at the age of eight years, was exhibited publicly because 
THE VOICE.
.261
         The tongue less essential than commonly supposed.  Dentals.

he could talk without a tongue.   At the request of the members
of the University of Saumur, the boy was brought before them
by his friends.   After a strict examination they were  perfectly
satisfied as  to  the  facts in the  case, and recorded their official
testimony to that effect.   A very interesting  account is given
of another  case in'the Philosophical Transactions, in  several
papers  published  from time to time  between the years 1742
and  1747.  It is  the  case of a girl who  lost from disease the
whole of her tongue,  together with the uvula, (the little round
body which hangs down from  the middle of the arch of the
palate,) and yet  could talk and swallow as well as any one.
So perfect was her articulation,  that she  could pronounce with
exactness those letters which commonly require  the  agency of
the tip of the tongue.  She could sing finely, articulating with
the same clearness as when she talked.   The sockets of the teeth
too were so much injured, that  there were few teeth,  and these
rose so little above the gums, that  they could not render much
assistance, if any, in articulation.   This case was  investigated
very thoroughly.   The account  was given to the Royal Society,
attested by the minister of the parish, a physician  of repute,
and  another respectable  person.   The Society, not wishing to
give too easy a credence to so strange a case, requested another
report from another set of  witnesses appointed by themselves,
and  they gave them a series of questions to guide them in their
investigations.  The report which they made out  coincided very
minutely with the  account first given.  The case excited so
much interest that the young woman was at length brought to
London, and appeared before the Royal Society to satisfy them
that she could really talk and sing, although she had no tongue.
  389. Some of  the letters are  formed principally by the teeth,
as c, t, s, z.   They are therefore called Dentals.   It is the  too
frequent and bungling employment of some of these which con-
stitutes lisping.  Those who have a tongue too large for the
mouth are apt to lisp.  In  advanced age, when the teeth are
lost,  we find  this  defect  of lisping.  The reason is obvious.
When the teeth are gone,  the sockets gradually become oblit-
erated, and  that part of the jaw-bone where the  teeth were, of
course diminishes in size, making  the  mouth too small for the
tongue.
  390. The letters, in  the  articulation of which the lips take
the lead are b, p, m,f, v, w, &c, and are  called labials.  Chil-
dren, when  they first begin to talk, use  labials freely, because
they can see in others  the motions necessary for their pronunci- 
262
HUMAN PHYSIOLOGY.
          Labials.  Reverberation in some letters in the nasal cavities.

ation, and then imitate them.   Hence the endearing terms used
by the  child to the parent are, I believe, in all  languages, or
nearly all, composed of labials and vowels.  And too, it is from
the delight which the child  takes in repeating over and over
these terms, that we  have the word  papa and mama, instead
of pa and ma.   The  same  thing can be observed in other lan-
guages  as well as  the  English.  If  we teach a child to say
father instead  of papa, he  finds little difficulty in articulating
the first syllable, because  it begins with a labial,/;  but in the
last syllable he will at first substitute  for th the labial v, making
it faver.  Intoxicated persons,  their  lips being weak  and  trem-
bling, are apt to make an awkward use of the labials, as well as
of those letters in which  the  tongue  has much agency.   Per-
sons with large lips also are apt to use the dentals unskillfully.
Sometimes one labial is used for another,  as / for v, andja for
b.  This is very common  among the  Welsh.   Shakspeare gives
us an amusing case of this sort in Sir  Hugh Evans in  the Merry
Wives  of Windsor.  " Ferry  goot,''  says  he,  " I will  make  a
prief of it in my note  book."  And so he says prains  for brains,
peings for beings, petter for better, &c.  The labial  w  is  some-
times used for v, thus, winegar,  indiwisible, werry  wigorous.
   391.  The  nasal  cavities, it is  obvious,  must  have  a  great
influence in articulation.   The letters  m and n are partly  nasal.
In pronouncing m  at the end of a syllable, as am, em, or om,
we close the lips, and the sound issuing  from the larynx  rever-
brates in the cavities of the nose.   You can perceive  this  rever-
beration by pressing  gently upon the nostrils  with  the fingers
while pronouncing  this syllable.   The same  can be  said of n,
except that in pronouncing it we press the tip of the tongue
against  the roof of the mouth just behind the front  teeth, pre-
venting the passage of the air out through  the mouth in this
way, instead of doing it by closing the lips, as in articulating
m.  When m and n begin syllables, as in mo and no,  the mouth
is opened after  the m  or n is pronounced, in order  to  give  utter-
ance to the next letter.  These are  two  distinct acts, but the
one succeeds the  other  so quickly, that they appear  to  be  a
single act.  The nasal sound ng is the one which we  employ in
humming.  Hence, the mouth  is kept closed and the sound  issues
from the orifices of the nostrils.
   392.  A reverberation of sound in the back part of  the mouth
and the cavities of the nose constitutes a distinguishing peculi-
arity of many of the  consonants.  Thus, in pronouncing  b and
p, the  lips are placed precisely in the  same manner,  and the 
THE VOICE.
263
           This reverberation in some consonants and not in others.

only difference  between them is that b has the reverberation
spoken of, but p has not.   If you pronounce these two letters
in the syllables  ap and ab, for example, while you press on the
nostrils with your fingers, you can feel the vibration occasioned
by this reverberation  in pronouncing b, but there is obviously
none in pronouncing^.  This reverberation is heard in the follow-
ing alphabetical elements, B, D, G, V, Z (the sound of s in the
word as), Y, W, Th (as in thou), Zh (the sound of z in azure),
Ng, L, M, N, R.  Those which have not this reverberation are
P, T, K, F, S (as heard in  sun), H, Wh (as heard in which),
Th (as heard in thing), Sh (the sound of s in sure).  That you
may contrast these two sets of alphabetical elements individually,
I place them here in two rows.   B is like P, except that it has
a reverberation, and so on through.
    B,  D, G,  V, Z,  Y,  W,  Th, Zh,  Ng,  L, M, N, R.
    P,  T, K, F,  S,  H,  Wh,Th, Sh.
   393. In what is commonly called speaking through the nose
the reverberation mentioned  above is disagreeably strong.   The
popular idea of it  is  incorrect, for this fault occurs in those who
have some obstruction to the free passage  of the air  through
the nose.   This obstruction acts like the pressing of the nostrils
with  the  fingers,  confining  more or less the  body of air con-
tained in the nasal passages.  It is the vibration of this air thus
partially confined in tortuous passages that produces the nasal
twang.  Any thing therefore  which prevents the free outlet of the
air from the nose will  occasion it.   Pressing the fingers on the
nostrils while  speaking, as already hinted, will  produce it.  A
common example  of it we have in what  is  called a cold in the
head.   The snuff-taker has this twang, because by such constant
stimulation of  the  lining  membrane it becomes thickened.
Those  who have this fault of " speaking through the nose," do
not like others  breathe ordinarily through the nose alone, but
you see them sitting with their mouth constantly open, showing
that there is so much  obstruction in the nasal passages that
they7 are not able to  transmit sufficient air to the lungs.
   394. I  have  thus far spoken of articulation  as employed in
ordinary speech, that  is  with a vocal sound.   But when no
sound is produced by the ligaments of the larynx, as is the case
in  whispering, the noise  produced by the  passage of the air
through the cavities of the vocal apparatus can be so articulated,
as  to be heard distinctly at a considerable distance.   Persons,
therefore,  who have entirely lost the voice can converse.  In 
264              HUMAN PHYSIOLOGY.
      Variation of note in whispering. Contrivances to imitate articulation.

whispering the vocal  ligaments are relaxed as they are when we
simply breathe.  But the sound of whispering has its high and
low notes like the vocal sound.   The variation of note is caused
by variation of the size of  the column of air contained in the
vocal tube.  This is effected chiefly by the tongue.   In the high
notes of whispering the tongue is nearer the roof of the mouth
than in  the low notes.  The distinction between many of the
letters as to reverberation noticed in § 392 holds in whispering
as it does in ordinary vocal speech.
   395.  You can  observe the mechanism of the parts  that is
necessary for any one  of the alphabetic elements, by pronoun-
cing some  syllable which it  ends, prolonging the sound of the
letter in  question.  And in doing this you will readily see the
incorrectness of the common  definition of consonants, viz., that
they are letters which cannot be sounded without the aid of a
vowel.    Take, for instance, the  lettter  m in  the  syllable  am.
After getting  an  idea of  the  mechanism necessary for it by
sounding it with a, you can readily sound it alone.   It is proper
to remark here, that in observing the distinctions between the
alphabetical elements, you  must bear in mind that the names
which are given to the letters in the alphabet  do not represent
their sounds.  For example, H  (aitch)  and W (double-u)  are
nothing like the sound of these letters in have and wave.
   396.  Various attempts have  been made to imitate the artic-
ulation of sounds by mechanism, but with very limited success.
In 1779 a prize was  offered  by the  Academy of Science at St.
Petersburg, for the  best dissertation  on the  theory of vowel
sounds, and it was awarded  to  G. R. Kratzanstein, an account
of whose experiments was  published in the Transactions of  the
Academy.   He found that the sound of the four vowels, A, E,
0 and U, might be  produced  by blowing through a reed into
tubes, the forms of which are represented in  Figures 142, 143,
144 and 145, and that the sound of I, as pronounced by  the
FIG. 142.  FIG. 143.    FIG. 144.      FIG. 145.    FIG. 146.
 
THE VOICE.
265
           Accurate adjustment of vocal and articulating muscles.

French and other European nations can be produced by blowing
into the tube, Fig. 146, by blowing at a without using the reed.
M. Kempelen, of Vienna, the inventor of Maelzel's automaton
chess-player, carried  the imitation  of the human  voice still
farther.   He produced an instrument capable of uttering certain
words and short phrases in  Latin  and  French.   But it is not
known exactly bow he accomplished this, as he kept the matter
secret.  A gentleman of Cambridge,  England, investigated this
subject, and among other things found that by blowing through
a reed into  a conical cavity, the vowel  sounds  could be pro-
duced by altering the size of the aperture for the passage of the
air from the cavity, by means of a sliding  board.  I have alluded
to these  attempts  to  imitate  the  voice, to show by contrast
the wonderful completeness and perfection of the vocal  appa-
ratus.   Kempelen's instrument, a box three feet long,  could
produce only a  few  words, but  the instrument of the  voice,
although  it occupies so little  room in the  body, can  utter all
words in all languages.
   397. We have  now examined the whole of the vocal  appa-
ratus.   You will observe that I have  spoken of it as having two
parts, the larynx, which is the reed of the instrument, and the
vocal tube, which you have  seen is  quite  complicated, for the
purposes of articulation.  Every action in both parts of the in-
strument  is  produced by  muscles.   You  have seen  that the
action  of muscles is  requisite  to cause any, even  the slightest,
variation  of note.  So it is with the articulating  apparatus, as
it may be called.   Every alphabetical element, (and in our lan-
guage Rush  makes 35 in the whole,) requires a particular ad-
justment  of the articulating apparatus.   This adjustment  is
effected by muscles that move the tongue, lips, palate,  &c.  As
these muscles then perform such varied movements, to produce
this variety of note and articulation, it is no wonder that they
require  such long and diligent training.   The child begins this
lone course  of  education  the  moment  he  utters  an  articulate
sound.   Observe him as he  pronounces  the syllable pa or ma,
the first which children generally learn. He  looks at his mother's
lips, and  imitates the motion  as well as he can.  Cheered by
his success, and by her approving smile,  he is constantly repeat-
ing these  first lessons in pronunciation to every  one that comes
near him.  Being as yet without skill in the use of these organs,
he gives much  more force than is  necessary to  the mechanical
motions of articulation.   For example, in pronouncing  the word
pa, he closes his lips strongly, and  not slightly as we do, and
                               23 
266
HUMAN PHYSIOLOGY.
              Training of the muscles in speech.  Skill in their use.

   when he opens it for the utterance of the word he does it with an
   explosive force, at the same time quickly bowing his head.  The
   energy of his whole frame  seems to be  concentrated  upon the
   effort.  Day after day he strives to add to his stock of words,
   but his progress is slow ;  and as a sort of compensation for the
   leanness of his stock he repeats those which he has learned, and
   so of his own accord he says papa and mamma instead of using
   the words of  a single  syllable.  In this education of the organs
   of  the voice the ear  is the principal instructor, but the eye, as
   you see, is also of great assistance.   The little pupil, on hearing
   a sound which he wishes to utter  himself, tries  to imitate the
   motion which he sees is  used in producing it, and he continues
   to try till his ear  assures  him that he  has  actually  mastered
   the sound.    Soon  he is  able to utter two  different articulate
   sounds in succession ;  and he  goes on learning year after year,
   till  at length he can command all  the sounds  of his native
   tongue.  And I may  remark that it is in childhood and youth
   alone, that we can learn accurately and thoroughly the pronun-
   ciation of  a language that  is at all difficult in  this respect.
   Hence a foreigner, however long he  may live in a country, to
   which he goes  in  adult  life, cannot wholly conceal his  native
   accent.  And we  know how much  such sounds  as that of th
   trouble the German  and the  Frenchman, unless they begin to
   learn the English language early in life.
     398.  If we observe different persons while  speaking or sing-
   ing, we shall see that  some manage the vocal apparatus, or play
   on the vocal  instrument,  as we may express it, with more skill
   than others.  Listen  to two persons  in conversation,  the one
   modulating and articulating his voice with a graceful  melody,
   the other having an  utterance harsh and awkward; and the
   contrast is  as great  as that  between two instruments, one of
   which is well and the other badly played.  In some you can al-
   most imagine that you hear the creaking of the machinery; while
4  in  others you do not once think of the mechanism of the voice,
   but your ear feasts upon its  richly modulated  and gracefully
   articulated  sounds.   It is as  true of the muscles of  the vocal
   apparatus as of those  of any other part of the body, that skill in
   the management of them can be very much increased  by exer-
   cise.  The  rope-dancer, by training his  muscles, gives them a
   wonderful precision of action.  The same thing can be done
   with the muscles that regulate the modulation and articulation
   of the voice.   And in the most noted singers  the little muscles
   which  move  the vocal ligaments and those which adjust the 
   _^^^              THE VOICE.                   267
              Stammering.  The ear the instructor of the voice.

 parts of the vocal tube, must have a precision  of action incom-
 parably more  accurate  and delicate than the large muscles in
 the limbs of the rope-dancer.   If we compare the  limited and
 bungling  operations of  the vocal apparatus in  a little child just
 beginning to talk, with its infinitely  varied but precise  move-
 ments in a voluble speaker, or a skillful singer, we  shall have
 some conception of the delicacy of motion, of which the muscles
 of this apparatus become capable by long continued  exercise.
    399.  There is a defective action of  the muscles  of the vocal
 apparatus, called stammering or stuttering, which  I will just
 notice.  It is an irregular spasmodic action of these muscles, very
 much like that which we  see  in the  muscles  of other parts of
 the body in the disease called St. Vitus' dance.   It is very much
 influenced by habit, and mental  agitation aggravates it.   Shak-
 speare gives the following accurate description  of it.  "I would
 thou wouldst stammer, that thou mightest pour  out of thy mouth,
 as wine comes out of a narrow mouthed bottle, either too much
 at once, or none at all."  It is a singular and  instructive fact,
 that many who stutter in  ordinary conversation can read and
 sing as well as others.  Dr. Good remarks that one of the worst
 stammerers he ever knew was one of the best readers of Paradise
 Lost that he ever heard.  Such facts suggest some valuable
 principles in the treatment of this difficulty, which can be more
 easily overcome than is commonly supposed.
   400. Not only is the ear the educator of the muscles  of the
 voice, but the dependence upon the ear is entire.  The deaf and
 dumb therefore are  in almost every  case dumb because they
 are deaf.   Their vocal organs  are in a good condition, and the
 muscles  are all  there with their nervous  connections.  But the
 machinery does not work, for there  is  no guiding power to
 direct it.   That this is the true view, is proved  by those cases in
 which hearing has been restored, for such restoration is followed
 by that of the power of speech.   Magendie relates an interest-
 ing case  of this kind.   It was the case of a young  man deaf
 and dumb from  birth, who had his hearing restored  by M. Itard.
 He first  heard  the sound of  the neighboring  bells,  which not
 only caused very lively emotions, but even headache and dizzi-
 ness.   The next day he  heard the sound of the small bell  in
 the room, and shortly after he could hear the  voice of  persons
speaking.   His  delight was then extreme,  and he was  so ab-
sorbed in his  new enjoyment that, says  Professor  Percy, " his
eyes seemed to search the words  even  on  our  lips."  His voice
was soon developed.  The muscles of  the vocal organs,  so long 
268
HUMAN PHYSIOLOGY.
  Absolute dependence of the voice upon the hearing.  Seen in the deaf and dumb.

inactive, began to wake up under the tuition of their instructor,
the ear.  Only vague sounds were formed at first, and, although
after a while  he  could pronounce  some words, he did it awk-
wardly as children do when they are beginning  to talk.   He
learned to talk very slowly.   It would have been very interest-
ing to have watched  this case in its progress, but this was pre-
vented by a disease which proved fatal.
  401. Few cases  occur like that which  is related above, but
there are many cases in which the  dependence of speech upon
hearing is proved in another way.  I  refer to those cases in
which the loss of  the power of speech  is obviously the conse-
quence of the loss of the hearing.   This is the case with children
that become entirely deaf after  they have made some progress
in learning to talk.   They cease to talk, and very soon forget
the motions which they had  learned  to make in articulation.
Sometimes some of these  motions are remembered, and the
individual  can  pronounce some words.   But he  does it very
awkwardly, and  the consciousness of this makes him very averse
to trying it.  A friend mentioned to me the case of a man who
became deaf just after  he had  learned  the alphabet.   He re-
membered the mechanical effort necessary to produce each letter,
but he had no control over the loudness or note of the voice, so
that some of the letters  he sounded very high, others low,  some
very loud, and  others soft, making of course some laughable
contrasts.  It is  undoubtedly possible to teach deaf and dumb
persons to talk to some extent, if we begin  early enough; but
the power of speech, after the most persevering training,  must
be  awkwardly  mechanical, and exceedingly  limited.  Accord-
ingly all  such efforts have been very soon  given up.
   402. The question has probably arisen in your  minds  as to
what the difference is between the voice  of speech and the  voice
of song.   The common  notions on  this subject were very indefi-
nite until recently.  But Dr. Rush, in his admirable work on the
voice, has developed the  true principles  in regard to it.  He
has shown that  we use the same notes in  speech and song, and
that the  difference lies in the mode of using  them.  I will en-
deavor to place  before you  the  most prominent and material
points in his  view of this subject.
   403. If you pronounce the sound a as heard in day, you will
observe that it ends in another sound, that of e.   The voice in
pronouncing it rises  through the interval of a tone, the sound
at the same  time gradually  diminishing.   So of other  letters.
Thus, a as sounded in awe, ends or vanishes in e as heard in err; o 
THE VOICE.                    269
               Voice of speech and of song.  Explanation of emphasis.

    as heard in old vanishes in oo as heard in ooze;  and ou as heard
    in our vanishes also in oo.  The vanishing sounds are of course
    rather obscure and feeble.   The first sound he calls the " radical
    movement of the voice," and the subsequent diminishing sound
    its " vanishing movement."  The rise of the voice during the van-
    ishing movement is not always through the interval of a tone,
    but it may be only a semitone, or it may be  even through the
    interval of an octave.  In singing the movement is very differ-
    ent.   We pass " quickly and faintly through the radical move-
    ment to dwell with greater time and fullness on a note or level
    line of sound at  the extreme place  of  the vanish."   Both in
    song and speech there is also a downward as well as an upward
    movement on the scale.  The gliding of the voice on the scale,
    and its gradual vanish cannot be imitated on instruments.  They
    may be  imitated to some  extent however on the violin if the
    finger moves along the string while the bow is drawn.  The
    difference  between the voice of speech and song is thus repre-
    sented by Dr. Rush:

             VOICE OF SPEECH.                 OF SONG.






    At 1 is represented the vanish on the interval of a tone; at 2
    on that of a third; at 3 on that of a fifth, and at 4 on that of
    an octave.
      404. I will notice very briefly the use  of the vanishing move-
    ment  in speech.   In simple  narrative the vanish never rises
    above the interval of a tone, as at  1.  Whenever it rises higher
    it is either  for  emphasis or interrogation.   The vanish on the
*   interval of a fifth, as at 3, is the most common mode of interro-
    gation.  That of  the octave, 4, is used when the question  is
    asked with great vehemence, or is accompanied with sneering,
    mirth, contempt, or raillery.  Thus when the Jew in the Mer-
    chant of Venice asks,
                   Hath a dog money ?  Is it possible
                   A cur can lend ten thousand ducats ?
    there is a rise  through the interval of an octave on the words
    cur and dog.   You observe that the rise is on the words which
    are emphasized.   Thus we can make four entirely  different
                                 23* 
270              HUMAN PHYSIOLOGY.
        Use of the semitone in speech. Difference in capability of singing.

sentences of  the question, do you ride to town to day ?  accord-
ing as we make the rise on  you, or ride, or town, or day.   By
the use of this rising  vanish we can make a question of  the
most positive assertion,  even  of the blunt negative, no.
   405. The vanish on the interval of a semitone gives the voice
a plaintive character, and it is therefore  used for the expression
of love, grief, supplication, &c.   It is  sometimes used so much
as to give a  general  character of plaintiveness  to  one's whole
conversation.   As a very clear  and striking illustration of  the
power of the semitone  we will take the  cry  of fire.  Divide  the
word into two syllables, fi-yer, and ascend the scale thus :
           Fi-yer.   Fi-yer    Fi-yer.      Fi-yer.

The two places of the  semitones, indicated by the braces, will
give  the  cry of fire as we commonly hear it.  Sometimes we
hear  it cried in sport upon one note, and the sound is discordant
and ludicrous.  So also, the two words, "0 dear" sound like a
mere mockery  of grief, if uttered  on one  note, or any other
interval than the semitone.
   406. Every one learns  to  talk, but there are many who do
not learn  to sing.  Now as the same  notes are used in the two
cases, what is the reason of the difference?   The  reason is not
in an absolute inability to appreciate  the variations of note in
sound, for these are practically appreciated in  the use of the
vanishing rise in conversation.  There  are  two  reasons  for the
difference.   One is this.  As  the  transitions of the voice from
one part of the scale to another are much more varied in song
than in speech, and are made by leaps  instead of slides, song
requires greater skill than  speech does in the action of the mus-
cles.  Another  reason  is, that speech is a necessity, and song
is  not.  We learn to speak therefore as a matter of course, but
singing is a mere  accomplishment.   If it were learned  as uni-
versally as speaking is, there would be nearly  as  much good
singing as good speaking.  We  can realize the truth of this
assertion, when we observe the results of very early training in
singing.   And we should  realize  it still more if singing were
universally considered, as it should be, as an  essential part of 
THE EAR.
271
           Ventriloquism.  Difference between a sound and a noise.

the education of children.  And I may remark in  this connec-
tion, that all have  some measure of musical talent, though in
some it is exceedingly small in amount.   The difference in this
respect in different  persons is the same  as the difference in re-
gard to any other talent, as that of drawing for example.  Skill
is acquired in the same  way in both cases, and its degree  de-
pends to  the same extent, and in the same manner upon natural
endowment.
  407. Some  persons  possess extraordinary powers in the.  use
of the vocal organs.  I refer to ventriloquism.  This is a purely
imitative art, and is not to be attributed to any peculiar forma-
tion of the  parts in the individual who possesses the  power.
The ventriloquist must have the  faculty  of appreciating with
great accuracy the almost infinite variety of tones, articulations,
and inflections of the voice, and  must be  able to imitate them
with but  little motion of those parts of the articulating apparatus
which appear in view.   He at the same time makes skillful  use
of those  circumstances, which  will favor the false impressions
in the  minds of his audience, in  relation to the locality of  the
source of the sounds.  This is the simple explanation  of this
wonderful power.
                   CHAPTER  XV.

                         THE EAR.

  In the last chapter I treated of the  production of sound by
the vocal  apparatus.   In  this  chapter I propose  to  show you
how the impression  of sound is  transmitted to the  brain, in
order to produce the sensation of  hearing.
  408.  That you may the better understand the arrangement
of the   apparatus of hearing, I will first notice  some  of  the
principles  that govern  the transmission of sonorous vibrations.
Sound   may be  produced by the  vibration of any substance;
though  some are better fitted to produce it than others, and are
therefore called  sonorous  bodies.   When the vibrations which
cause sound are equal,  a musical sound results;  but if thev are 
272               HUMAN PHYSIOLOGY.
            Reflection of sound. Speaking tube.  Ear trumpet.

unequal, we have a  discordant sound, or what we  ordinarily
call a  noise.  Sound is transmitted from  the  point where  it
originates, in all  directions.   And its vibrations gradually les-
sen, just as the ripples lessen which  are produced by dropping
a stone  into the water.   The  vibrations of sound are reflected
by objects against which they strike.   For this reason the voice
can be heard at a much greater  distance if it  be transmitted
along a wall than when it is uttered  in an open  space.   This
may be illustrated on Fig.  147.  Let A B represent a wall, and

                           FIG. 147.
C the  position of the  ear.  If the bell at D be  rung, besides
the vibrations which come  to the  ear  at C in  the direct  line
C D, a vibration striking the wall at F will come to the ear in
the line F C, and the same can  be said of other  points  along
the wall.  An accumulation of vibrations, therefore, comes to
the ear at C, which therefore receives a louder  sound from the
bell than it would  if the  bell were rung in a perfectly open
space.   For the same reason a speaker can be heard much more
easily within walls than he can be in the open air.  The  sound
is reflected, and, therefore, in some measure concentrated by the
walls.  In speaking tubes this reflection and concentration  are
carried to a  still greater  extent.   Sound can  in this way be
heard at a great distance from its  source.   M. Biot found that
when  he spoke in a whisper at one end of a tube, over three
thousand feet in length, he was distinctly heard  at the other
end; so  entirely do the walls of the tube  prevent the diffusion
of the vibration in the air around.  Speaking tubes are  there-
fore used to a great extent in large manufactories, where direc-
tions need to be given  continually to workmen in different parts
of the  establishment.  The flexible tube, now so commonly
made  use  of by  deaf persons, furnishes another  illustration.
The vibrations of the voice received by  the trumpet-shaped end
are transmitted through the tube to the ear. 
                         THE EAR.                     273
      Difference in the transmission of sound through solid, liquids, and gases.

   409.  Sound  may be transmitted  through  any substance,
 whether it be solid, liquid, or  gaseous.   It  cannot be trans-
 mitted through a vacuum, for there is nothing there to vibrate.
 Sound differs in this respect from light, which passes as readily
 through a vacuum as it does  through any transparent substance.
 The fact that sound cannot be transmitted through  a vacuum
 is often illustrated by an experiment with  the air-pump.   If a
 bell be put under the receiver, and be set to ringing, as the air
 is exhausted by the pump, the sound becomes more and more
 faint, and at  length it is not heard at all.   For the same reason,
 a pistol fired on the summit of a mountain, gives nothing like
 so loud a report as when it is fired in the valley below.  The
 more  solid the  medium is for the transmission of sound, the
 more readily is it transmitted.   The scratching of  a pin at the
 end of a long log may be heard by the ear applied  to the other
 end, although it  cannot be heard through the air, at  even the
 distance of a few feet.  Savages are  in the habit of putting
 the ear to  the ground to hear the  step of their  enemies when
 they apprehend  their  approach.  A  deaf gentleman, resting
 the bowl of his pipe on  his daughter's piano-forte as he smoked,
 found that he could hear the music with great distinctness; and
 many deaf persons can hear conversation, by holding a stick
 between their teeth, while the other end rests against the teeth
 of the  person speaking.  A knowledge  of the ready transmis-
 sion of sound through solids suggested the examination of the
 chest in disease by the  ear.   If  the  ear be applied to the chest,
 the various sounds produced by the air, as  it passes through
 the bronchial tubes into the  air cells, can be heard  through the
 solid walls of the chest, and thus the state of the lungs can be
 discovered.   Water is  a much  better  conductor  of sonorous
 vibration than air, though it is not as good an one as a solid
 substance.   The force of the vibration is lessened more gradu-
 ally in water than  in air, and  its  rate of progress in water is,
 according  to Chladni, 4,900 feet in a second, or between four
 and five times as great as in  air.
   410. Sonorous vibration  does not pass  readily from  one
medium to another.  Thus, although the scratch on  the log is
heard  so  easily by the ear  at  the other  end,  if the ear be
removed a  little  from  the  log,  it  does not  hear  the sound,
because the vibration is so  much lessened  in  passing from the
solid wood to the air.  It is clear that the more unlike the two
substances  are, when sound  passes from  one to the other, the
more will the vibration be lessened;  for the more unlike they 
274
HUMAN PHYSIOLOGY.
           Hearing a compound process.  Only in part mechanical.

 are, the  less easily will  the  one take  the vibration  from the
 other.  For this reason, a sonorous  vibration, produced in a
 solid body, may be transmitted to water with much less loss of
 intensity or force, than occurs when it is transmitted to air.
 And it  may be  remarked  in this connection, that when vibra-
 tions are transmitted to  a  fluid, from air or from a  solid, the
 intervention of a  membrane is of essential service, for it pre-
 sents a firm surface upon which the vibrations can be received.
   411.  The principles which I have thus noticed will be seen
 to  apply to the  arrangement of the apparatus  of hearing, as
 we proceed in the examination of it.  It has various parts for
 the different portions of the process which we call hearing.  I
 will premise a mere general description of this process, before
 entering upon the examination of the apparatus in detail.  The
 vibrations of sound, passing into the ear  by a  tube, strike at
 the bottom of that tube  upon a drum.   The air  can go no far-
 ther, for this drum is perfectly air-tight.   It communicates its
 vibrations, however, to the drum, which transmits them to a
 chain of four little bones, the  last of which transmits them to
 another  drum, covering  an opening into various winding pas-
 sages in solid bone.  In these passages is contained  a limpid
 fluid, which is put in motion by the vibrations of  the drum last
 mentioned.  So  much for the mere mechanical part of the pro-
 cess.  In the winding passages are spread out the minute fibres
 of the nerve of hearing.   The vibrations of. the  liquid in these
 halls of audience, as we  may call them, make an impression
 upon these nerves, which is communicated to the  brain through
 the trunk of the  nerve, and this  completes the whole process
 necessary to the  production of the sensation of hearing.
   412.  The parts of the apparatus of hearing may be seen in
 Fig. 148.  The internal portions are made rather larger  than
 natural, in order that the arrangement may be more clear.  At
 a b c is the external ear;  at d is  the entrance  to the tube of
 the ear/; g is the drum of the  ear at the  end of this tube,
 called the membrane of the tympanum; h is the cavity of the
 tympanum, the chain of  bones which it contains being left out,
 so that the plan of the apparatus may be more  clear to you;
 k is the Eustachian tube,  which  makes a communication be-
 tween the back of the throat and  the cavity of the tympanum;
 n is a part of the winding passages, shaped like a snail's shell,
 and is therefore called the cochlea; at m are three other wind-
ing passages, called, from their form, semi-circular canals; and
at I is the vestibule, or common  hall of entrance to  all these 
THE EAR.
275
The parts of the apparatus of hearing described.
FIG. 148.
VERTICAL SECTION OF THE ORGAN OF HEARING.
winding passages.  In the cavity of the tympanum, on the side
opposite to the  drum of the ear, you see  two holes.  These
open into the winding passages, the larger one into their vesti-
bule or entrance hall.  Both of these holes are covered by a
membrane, and to the membrane of the  larger one is attached
the last of the chain of bones.  At o is the trunk of the nerve
of hearing, and at e e is the bone that  incloses  these parts,
which  is so hard that it is called the petrous, or rock-like bone.
  Having given you this general view of the apparatus, I shall
now speak of each part more particularly.
  413. The object of the external ear is to collect the waves of
sound, and direct them into the tube of the ear.   There have
been many speculations in regard to the use of the prominences
and ridges of the external ear, but they are fanciful and ground-
less ; and its  surface is thus  diversified, probably for the sake
of making this organ a comely one.  If the object were to give
it the best shape and arrangement for collecting the vibrations
of sound, it would have had a different shape  altogether, and 
276              HUMAN PHYSIOLOGY.
            External ear. Tube.  Ear-wax.  Drum and bones.

would have been  arranged with muscles which could  turn it in
different directions, as is the  case with  many animals.   The
shape of the external  ear is much better in many animals than
it is in  man, if we consider its  object to be merely the collec-
tion of  the waves of sound.   The endowment is in this case, as
well as  in every other, according to the necessities of the case.
The bat is guided so  much in  its  movements by the sense of
hearing, that it has of necessity very large ears, and they are
so shaped as to collect, in the  best  possible manner,  the vibra-
tions of the air.  With proportionably large, and similarly shaped
ears, man could hear much better than he now does, but he  has
no need of such ugly appendages.   In  regard to the motions
of the ears in  animals, it  is worthy of remark, that animals of
prey can turn  their ears forward with  the most facility, while
timorous animals turn their ears backward to keep  warned of
danger.
   414.  The tube of the ear is about  an inch long in  the adult.
It is formed of cartilage like the external  ear, and ends at the
drum.  At its entrance are hairs which  afford some  protection
against intruders.   But the chief protection  is the bitter wax,
which is secreted  by  little glands, situated in  the  skin of  the
tube.   The odor from this secretion so effectually keeps out the
bisects from this open entrance, that it is quite a rare occurrence
to have an insect get into the ear.   And when one does get in,
the wax envelopes him, and commonly soon destroys  him.
   415.  The drum of the ear,  which makes the closed end of
the tube above described, as  seen  at g, Fig. 148, is very  thin
and transparent.   On the other side  of it  is the cavity of  the
tympanum h.   In this  cavity are  the four bones.  These  are
represented in Fig. 149, enlarged
so that  you can see their shape
distinctly. They are named from         /^
their shapes.  They are the mal-        1aYl
leus or hammer m;  the incus      ^&X
or anvil i;  the os orbiculare, or   ^^^\\
round bone o,  the  smallest bone           \
in the body;  and  the stapes or          /J
stirrup-bones.  The long  handle
of the hammer  h is fastened to
the middle of the  drum of the ear.   The  little round bone is
fixed between the slender end of the anvil, and the top of  the
stirrup-bones.   In Fig. 150 you  have a representation of these
bones, together with the drum of the  ear.  While the end of
 
THE EAR.                     277
           Eustachian tube. Winding passages of the internal ear.

the handle of the  hammer is fastened to        FIG- 15°-
the middle  of the  drum, the  base of the
stirrup is fastened to another drum, cover-
ing the hole  or window, opening into the
vestibule of the winding passages.   There
are three very delicate  muscles which move
these  bones.   One of  them  relaxes the
drum  of the  ear   and another  makes  it  DRUM QF THE EAR
more tense; and thus the drum is put into      wilh ibtbm„
the right states of tension, to accommodate
it to the various kinds of vibration that come to it.  This is a
matter of some importance, for it is plain that while a  relaxed
drum can vibrate properly to grave sounds that  enter  the ear,
it must be  tense, in order to respond properly to the vibrations
of the air in the higher notes.
   416. The cavity  of the tympanum (h  Fig. 148) in which the
little bones are, and which is beyond the drum,  communicates
with the mouth by the Eustachian  tube  g.   If you shut your
mouth, and close the nostrils with the fingers, and then perform
the action of blowing, you will  feel the air enter the Eustachian
tubes, and fill  the  cavity of the tympanum.  The chief object
of this communication is to have air on the inside  as well as
the  outside of the  drum, so that  it may vibrate freely.   The
cavity of the  tympanum  might  indeed have  been a  closed
cavity, containing air.   But it would then have been very much
like a common drum, with  the  hole in  its side closed.   This
would very much impair the vibration.
   417. We  now  come to another part of the  apparatus of
hearing—the winding passages.  These  are inclosed, as I have
already stated, in the most solid bone in the  body.   They are
called together, very  appropriately, the labyrinth, sometimes
the internal ear.   This is really the essential part of the appara-
tus.  Here are the  true halls of audience, where the  nerve  is
posted, which  receives  the messages from  without, and trans-
mits them  to the brain.  The  drum of the ear and the chain of
little  bones may be  destroyed, and yet, if  these winding  pas-
sages remain entire, with the membranes over the two  windows
that open into tbem, the hearing will not  be  lost; though  it
will be less perfect  than it  is when the whole of the apparatus
is there, and in good order.  Sir Astley Cooper relates the case
of a gentleman, who  lost the  drums of both ears by disease.
By shutting his mouth, he could blow the air  out through his
ears, with such force as to make a whistling noise, and to  move
                           24 
278              HUMAN PHYSIOLOGY.
           Description of the winding passages. Their importance.

the hair that huno- from his temples.   Yet he was not only able
to hear with ease all  common conversation, but he  had a nice
appreciation of musical  sounds.   Sir Astley  says that " he
played well on  the flute,, and had frequently borne a part in a
concert;  and he sung with much taste, and perfectly in tune."
   418. The labyrinth  is represented much  magnified in Fig.
151.  The middle part of it, v, is the vestibule.   From this go
out the  semi-circular canals,
x, y, z, on the upper side, and
on the lower the winding pas-
sages of  the cochlea, k.  At o
you see the opening called the
fenestra  ovalis,  or  oval win-
dow.   This is  covered  by a
membrane, on  which presses
the base of the stirrup-bone.
You  see another opening r,
which is called the fenestra
rotunda,  or round  window.
This is  covered with a mem-
brane.   Both  of these open-
ings you see  in Fig. 148, in
the cavity of  the tympanum,
opposite  to the  drum of the
ear.   In  these  winding pas-
sages is  a watery fluid,  the vibrations of which, acting  upon
the branches of the nerve distributed there, cause the sensation
of hearing.  Of course, if either of the membranes covering the
openings into these  passages be destroyed or broken, the fluid
will run  out from the ear, and there can be no more hearing,
although the rest of the apparatus is perfect.   The drum will
continue to vibrate as  sounds strike upon it,  the little  chain of
bones will  repeat the vibration, but it will stop at the end of
the chain, the stirrup-like bone.   So too, although the  mem-
branes may be entire, and the whole  apparatus may be perfect
as a piece of mechanism, so that the succession of vibrations
from the air without through the drum and the chain of bones,
to the fluid of the labyrinth, is  uninterrupted, if the  nerve of
hearing be paralyzed, so that it  cannot be impressed with the
vibration of the fluid that bathes its  branches, there can be no
hearing.   Partial deafness is  undoubtedly often  owing  to a
thickening of the fluid in these  passages, or  to a partial failure
of the nerve distributed in them.
 
THE EAR.
279
        Principles of transmission of sound observed in the arrangement.

  419.  It will be proper to say a word here in relation to the
choice of a fluid, instead of a solid or an aeriform substance, as
the medium through which, the impression of the vibration of
sound is communicated to the nerve.  ^ is better  than a  solid
would  be, so far as we can see, because no arrangement of a
vibrating solid with the minute fibres  of the branches of the
nerve could be effectual, and at the same  time so little  liable
to derangement, as the arrangement of nervous fibres immersed
in a liquid, and the whole  inclosed in solid walls  of bone.  It
is better than air would be, for at least two  reasons.   1st. The
vibrations of sound, as stated in § 409, are communicated with
much more ease and rapidity through water than  through air.
This we see to be a consideration of some importance, when we
look at the complicated and winding passages that contain the
fluid.   2d. There is not as much loss in the force  of the vibra-
tion in the transmission from the solid stirrup-bone through the
membrane to the fluid, as there would be  if the  transmission
were to air.
   420. The whole arrangement in regard to material we can
see to be admirable, if examined in relation to the known prin-
ciples of the transmission of  sound.   We can see  the object of
the chain of bones.  If these were left out of the arrangement
we could hear, but not so well as we do now.  For it has been
ascertained by experiment, that the transmission 4s much  more
perfect when the vibration  passes,  as in  the case of the ear,
through a tense membrane, then through  a chain of  solid sub-
stances, and  from  them through  a second membrane to  the
fluid, than  it is when the chain of solid bodies is  omitted, and
air is made to take their place.  And when the vibration has
arrived at the fluid in the labyrinth, there is a contrivance  there
for increasing its intensity.  There are two little chalky con-
cretions suspended in  this fluid  by nervous fibres.  These  are
found in all mammalia, and in fishes they are quite  large and
hard.   This being the case, it was inferred that  these bodies
have some important  influence upon  the transmission; and it
has been found by experiment that hard bodies thus situated
in a fluid increase the sonorous vibrations in  their neighborhood.
   421. You will remember that there are  two openings  into
the  labyrinth, from  the cavity of  the  tympanum.   Both  are
covered by membranes, one  of which is  pressed  upon by the
stirrup-bone, while the other is free.  It was formerly supposed
that the second  opening was absolutely essential  to the vibra-
tion of the  fluid  in  the labyrinth.   For, as fluids are incom- 
280
HUMAN PHYSIOLOGY.
           Mode of vibration of the fluid in the winding passages.

pressible,  it was  inferred that, as the  stirrup-bone communi-
cated its vibration to the membrane of  the fenestra ovalis, the
fluid in the labyrinth would not vibrate, unless there was another
opening  some where, ^he membrane of which would yield to
pressure.   This, however, has been ascertained to be not strictly
true.   It has been proved by experiment that a sonorous vibra-
tion can be transmitted through a confined fluid.  Indeed there
are some animals in which there is only one  opening into  the
labyrinth.  But, although this second opening is not essential to
the vibration of the liquid, it undoubtedly makes that vibration
more  perfect.   Although  the second opening  is so near  the
first, as seen in the  cavity of the  tympanum, (Fig.  148) yet in
relation to the  arrangement of the  winding passages of the
labyrinth, as you will  soon see, it  is  really quite  at the other
end of it.  The vibration then may be considered as communi-
cated through a  long tube, which  has a membrane  at both
ends.   And it is  obvious that a vibration  communicated to the
membrane at one end, will more readily move the fluid through-
out all the tube, from the yielding of  the  membrane  at  the
other end.   This will  be more obvious, as  I describe more par-
ticularly  the arrangement of the passages  in the labyrinth,
which I will now do.
   422. To recur to Fig.  151, the vestibule v, into which  the
fenestra ovalis o  opens, is, as before stated, a sort of common
entrance hall  to all  the  passages  of the labyrinth.  I have
spoken of  the  semi-circular  canals x, y, and z, that lead  out
from this.  These are simple canals.  But the passages of the
cochlea, k, are  very complicated, and it is  this fact that  has
given the name of labyrinth  to the whole of the internal  ear.
The vestibule opens into  the cochlea at  its base.  Now, the
cochlea is so divided, that the passage into which the vestibule
opens, runs around the pillar in the middle of it  to  its top,
making just two turns and a half.   It there opens into another
passage, which makes two turns and a half back to  the base of
the cochlea.  This passage does not end in the vestibule where
the other began, but it ends  in the  round  hole r, which opens
into the cavity of the tympanum.   This  disposition of the
parts of the cochlea may be seen in Fig. 152, which represents
it as opened to  show the arrangement of the walls  of the  two
winding  galleries.  The pillar in the middle, around which
these  dividing walls are fastened, expands  in the top into what
is called a cupola, where the two spiral  galleries  communicate
together.   With this  description, you can understand  in what 
THE EAR.
281
Distribution of the nerve of hearing in the cochlea.
FIG. 152.
THE  COCHLEA OPENED.
directions the vibration is transmitted, when it is received from
the stirrup-bone, at the door of the labyrinth, by the membrane
which covers it.  It travels one way up the fluid  in  the three
semi-circular canals.  It  travels another way through one spiral
gallery in the cochlea to the cupola, and  then down  the other
spiral  gallery, reaching at length the membrane of the fenestra
rotunda., or round window.
   423. I will now describe  to you  the arrangement of the
branches of the nerve of hearing in these passages.   The ar-
rangement is different in the  vestibule and  the  semi-circular
canals from what it is in  the cochlea.   In all the cavities of the
labyrinth, there is a thin, delicate lining of  membrane, which
secretes  a watery  fluid.  In  the  vestibule  and  semi-circular
canals, there is a second  membrane.  This is  separate from the
first membrane, and lies  loose in the cavities.   It makes a close
sac, and  as it extends from the vestibule into the semi-circular
canals, it is very irregular in its form.  This sac contains a fluid,
and the fluid secreted from the membrane which lines the bone
bathes the outside of the sac.   Now, it is on the delicate mem-
brane which forms  this sac,  that  the fibres of the  nerve  are
distributed,  so that  they  may  receive the  impression of the
vibration of the fluid.  In  Fig. 153, is  a  representation of this
sac, with  the distribution  of  the nerve.  At  1, 2, and 3, you
see the parts of this sac which  line the semi-circular  canals.
At 4  is a junction of two of these canals, for what purpose we
know not.   At 6, 9, 10, and  11, are seen the terminations of
branches of the nerve.   At 8 and 13  are two of these branches,
                              24* 
282
HUMAN  PHYSIOLOGY.
Distribution of the nerve in the semi-circular canals.
FIG. 153.
and at 14 is the branch of the nerve which goes to be  distrib-
uted in the cochlea.   In Fig. 154 is  represented one of the parts
 
THE EAR.
283
          Beautiful arrangement of the nervous fibrils in the cochlea.

where the nerve terminates, as at 10  in Fig. 153, much more
highly magnified.  You see the loop-like  termination  of  the
nervous fibrils.   You  can readily see that  every vibration of
the fluid would make an impression  upon  these  nervous fibrils
thus distributed upon  this delicate  membrane, which has  the
fluid upon both sides of it.
   424.  The distribution of the nerve is after a different man-
ner in the cochlea.   Here there is no loose membrane, with the
nerve distributed upon it,  and the fluid each side of it, as in
the vestibule and the semi-circular  canals.   But  the  nerve is
distributed upon the  division wall  of the  galleries in  a very
beautiful manner.   This is represented in Fig. 155, in which 2

                          FIG. 155.
is the nerve, and  3, 3, 3, show its distribution.   These fibrils
lie in little channels in a lamina, or leaf of solid bone.   But the
bone  extends only to  4, 4, and the remainder of the division
wall is made of membrane, represented at 5, 5, 5.   At 7 is the
opening in the cupola, by which the  two spiral galleries com-
municate.  At 1 you have these parts of the natural size.  We
know not  exactly how this mechanism works, but the  proba-
bility is, that the nerve receives impressions from the vibrations
of the fluid in two  ways—directly from the fluid itself, and also
from  the vibration  of the membrane  to which the extremities
of the nerve are attached,  this  membrane  being shaken  of
course by the vibrating fluid.
  425.  Having thus described the parts of the organ of hear-
ing, I will  trace for you, with  some particularity, the steps of 
284
HUMAN PHYSIOLOGY.
             Steps of the process of hearing given in their order.

 the process of hearing, as it  must  occur in  the case of every
 sound that produces that sensation.  The vibrating  air enters
 the tube of the ear, and, reaching the drum, produces a vibra-
 tion  there.  This vibration is communicated to the  chain of
 bones, which, as Dr. Paley very aptly  says, like  a  repeating
 line of frigates pass it on.  It is  transmitted from  the  last of
 this chain  of bones, the stirrup-bone, to the membrane covering
 the fenestra ovalis, and from  this to the fluid contained in all
 the passages of the labyrinth.  The vibration goes through all
 the semi-circular canals in one direction, and  in another up one
 gallery of  the cochlea, and down the other.   In all these cavi-
 ties, are spread out in various ways, the  filaments of the nerve
 which receive the impression of the vibration.  This impression
 is  transmitted from  the extremities of the  nerve,  through its
 trunk, to the brain, where the mind receives it.   All this to-
 gether constitutes hearing; and all of it  occurs in  the case of
 any sound which we hear, however closely it  may follow any
 other sound.
   426. Most  of our hearing is  done  precisely in  the way
 described,  but  not  all.   We  sometimes  hear directly through
 the bone  surrounding the labyrinth.   If you place a  watch
 between the teeth,  you hear the ticking; and  it gives  a very
 different sound from what  it  does when held  to  the ear, be-
 cause the  sonorous vibration is transmitted directly  throuo-h
 the solid bones of the skull from the teeth.   In  the same way
 was the sound  transmitted in  the case of the deaf  old gentle-
 man, (§ 409)  who  heard  his  daughter's  music through the
 stem of his pipe, as  he  rested the bowl of it on  the  piano.
 The fact thus  illustrated is often made use of by physicians, in
 detecting the nature of the difficulty in cases of deafness.  Thus,
 if a watch  held between the teeth communicate a very distinct
 and loud sound to the ear, we infer that the internal ear is in a
 good condition, and that the difficulty is  in  some of the other
 parts connected with it, the  drum, or  the cavity of  the tym-
 panum, or  the Eustachian tube.
   427.  I have  described the apparatus of hearing as we  find it
in man.  But  it varies in different animals,  according to the
circumstances  in which they  are placed, and their necessities.
Animals that live  in water of  course have  a  different  appa-
ratus of hearing from those that live in air.   In most fishes the
semi-circular  canals exist, but  there is nothing like a cochlea.
As sounds  are  transmitted so easily through  water, (§ 410,)
fishes have  no need of so complicated and perfect an apparatus 
THE EAR.
285
    Hearing in other animals. Only a part of the process of hearing understood.

as animals that live in air.   They are fitted to hear in their own
element, and probably the moment that a fish is taken out of
the water he becomes quite  deaf,  because his hearing apparatus
is so poorly fitted to receive and transmit vibrations from the
air.  But in  many animals  that  live in air the ear differs from
that of man in its arrangements.  The cochlea in birds is nearly
straight  instead of being spiral.  Such facts lead to the  infer-
ence, that  the  peculiar arrangements in the hearing apparatus
of man have  regard, not merely to the medium in which he is
placed, but to peculiar uses which are necessary in his case, as
the determination  of the direction of sound, the appreciation
of its pitch and its  character, the power of hearing very slight
sounds, &c.  The simplest form of apparatus found in animals,
is a cavity excavated in bone, with a fluid shut in it by a mem-
brane, and nervous filaments distributed so as to be impressed
by the vibrations of the fluid.   And this is all that is absolutely
essential to hearing.
   428. Many speculations have been broached in regard to the
special offices of  particular parts of the labyrinth.   Thus, it has
been supposed that the semi-circular canals have an agency in
informing us of the direction of sounds;  for it is observed that
they are  always arranged  in  the  same  relative angle to each
other.  It has been supposed also, that the cochlea gives us the
idea of the note of  sounds, because it is noticed that the devel-
opment of this part in different  animals is in proportion  to the
variety of note which they produce.  These suppositions, though
quite probable, require farther investigation in comparative anat-
omy to test their truth.
    429.  In the process that makes up the sensation of hearing,
there  is  one  part which we can in some measure  understand,
 and to which we can apply the known principles which govern
the transmission of sonorous vibrations.   But there is another
part, that which links the process to the immaterial mind, that
we cannot understand.   We can trace  the vibration  received
from the air through the several parts to the fluid in the laby-
 rinth, but here we  come to  a stand  in  our  knowledge.  The
 vibration stops here, and what is transmitted (jjrough  the nerve
 to the  mind we know not.   We call  it an impression; but this
 is  only an indefinite word, implying  simply that something  is
 transmitted, without defining what it is.   Neither do we know
 how  the transmission is made.   All that we do know is, that
 the nerve is essential to the completion of the sensation of hear-
 ing, and that it spreads  out its minute  fibrils or tubuli  in the 
286              HUMAN  PHYSIOLOGY.
      Ear equal to the eye in delicacy, beauty, and complication of structure.

halls of audience, in order to receive  impressions from the vi-
brations that come there, and transmit them to the brain where
the mind takes cognizance of them.  Every part of the appa-
ratus  may be  mechanically perfect, so  that the  vibrations
may be  transmitted  to  the fluid which  bathes the  nervous
fibrils, but if the nerve be paralyzed, or if the communication
between its extreme  fibrils and the  brain  be in any way inter-
rupted, the mind knows  nothing of the vibration, and there is
no hearing.
  430. The eye has generally been spoken of as being more
wonderful than any other organ in the body, in view alike of
the delicacy, the beauty, and the complication of its structure.
But the apparatus of hearing presents a combination of these
qualities  quite as wonderful.  There is nothing more delicate,
and beautiful, and  complicated than the arrangement of the
nervous fibrils in the winding labyrinthic  passages of the halls
of audience.   And as we  trace the  steps of the  process of
hearing,  from  the drum  of the ear where  the sound  strikes, to
the gray substance  of the brain where  the mind receives the
impression, and  think of each sound  as  sending a  vibration
through membranes and a chain of bones  to the fluid in which
the nervous fibrils are immersed, and of these fibrils as catching
from every vibration of the fluid  a  definite  impression and
transmitting it to the mind, we see a mingling of the purely
mechanical with the  spiritual, which greatly enhances our ad-
miration  of the mechanism.  Though the apparatus is compli-
cated, the mechanical result is  a  simple one—it is a mere
trembling of a fluid inclosed in winding cavities of bone.  But
simple as the result is, it is made, through the beautiful nervous
connections of the ear with the brain,  one  of the chief inlets of
knowledge to the mind, coming to it from nature's multitudinous
voices, and is a constant  medium of communication for thought
and feeling between  man  and  man.   Thus intimately in the
human body are the simplest mechanical results connected with
the complicated and diversified operations  of the mind.  In the
process of hearing the drum of the  ear is  to be considered one
end of the apparatus, and  the  gray portion  of the brain the
other.  The drum  simply  vibrates;  and instantaneously the
mind receives a distinct impression from the vesicles of the gray
matter.   And  thus is the communication established  between
the immaterial mind, and the vibrations  of the material sub-
stances with which it is surrounded. 
THE EYE.
287
Seeing a compound process.  Refraction of light.
                   CHAPTER   XVI.

                          THE EYE.

   431. The sensation  of sight is the result of a compound
 process, which may be  divided into two  distinct parts, as I re-
 marked in relation to the sensation of hearing, in § 429.  The
 one part is purely mechanical, and the apparatus for it is con-
 structed according to  the common principles, which we find
 illustrated in optical instruments.  The object of its arrange-
 ments is to form distinct images of objects in the back part of
 the eye.  The other part of the process is executed by the nerve
 of -vision, called  the optic nerve.  This nerve, expanded upon
 the membrane where the  images are formed, transmits impres-
 sions from the%e images to the brain, just as the nerve of hearing
 transmits to the brain the impressions which come  from the
 vibration  of the fluid of the labyrinth.
   Before  proceeding to an examination of the eye as an optical
 instrument, I will call your attention to certain principles, which
 we shall find  illustrated more  beautifully and perfectly in the
 eye than  in  any optical instrument which  man has ever con-
 structed.
   432. The rays of light coming  from any  luminous point go
 in straight lines in all directions, just as the vibrations of sound
 do, and, like  them, become  less  intense  the farther they are .
 diffused.  But they move in straight lines only so long as they
 remain in the same medium.   When they pass from one me-
 dium, into another they are  bent  out of their straight course,
 or refracted, as it is termed, unless they pass from one  to the
 other in lines perpendicular to the
 surface of the medium  which they          fig. 156.
 enter.  This  may be illustrated by                  ,
 the  following  experiment.  Place                 /
 a coin, a,  in the bottom of a basin,       i       /     rf
 as represented in Fig. 156, and then              /    .^ &
 withdraw  from  it so far  that the            /  ..-^
 coin may  be hidden from  your eye           /-''sy
 by the edge of the basin,  as rep re-    fijli&o
sented in the figure.  Keeping your    Ijjp
eye fixed in that position, pour some       a 
288
HUMAN PHYSIOLOGY.
     Refraction as light passes from a rarer into a denser medium, and vice versa.

water into  the  basin  up to the level, c.   The coin will again
become  visible  to  your eye.  The reason is, that  the rays of
light, as they come from the water  into the rarer medium, the
air, are refracted or bent downwards, that is from  the perpen-
dicular.   The effect of this may be seen in the figure.  A ray
of light, coming from  the coin in the direction a, d, does not
pass to d, but is bent downward, and so passes  to  the- eye at
e.  And so of other rays  coming  from the object.   The  coin,
therefore, is seen by the eye at e, but it is not seen in its true
direction from the eye which is in the line e, c, a.  The only point
in which the eye can see  the coin  in its true position is when
the eye is at b,  in a perpendicular line directly over it.  A ray
that passes  from one medium to another in  a line perpendicular
to the surface  of the  medium  into which  it passes is not bent
out of its course.  All other rays  are, and  the  more so the
farther they are from the perpendicular.
   433. While rays that  pass  from a  dense medium  into  a
rarer, as from water into air, are bent from the*perpendicular,
those on the other  hand, which pass from a rarer medium into
a denser, as from air into water,  are bent towards the perpendic-
ular.   Thus if in  Fig.  156 a be the position  of the  eye  of  a
fish, and where  the eye is, at e, there be an insect, the fish can
see it, because the ray that strikes the surface of the water, c,
is refracted  or bent towards  the perpendicular line,  b, a.   And
so of other rays.  He  does not see the insect, however, in its
true direction, a, c, e, but it appears to him to be at d.  For we
always judge of the place of an  object by  the direction in
which the rays from it  strike the eye.
   434. When light passes from  one medium into another which
presents  a convex  or  concave surface, instead of a flat one,  a
very  great  change  is produced in the  direction  of its rays.
Thus suppose, as represented in Fig. 157, three diverging rays
coming from a point, a, through the air,  enter a convex surface
of glass,  b, b'.  The central ray  a, c enters the glass in a direc-
tion perpendicular  to  its surface, and  therefore  does not bend
from its course.   But the ray a, d, enters very obliquely, and is
bent towards the perpendicular  at  that  point, e, and passes on
in the direction /.  So likewise the ray, a, g, is bent towards
the perpendicular h, and passes on  in  the  line i.   These  rays
diverging in the air have become converging in  the glass, and
the point at which they meet is called the focus.  To this point
all the other rays entering the convex glass converge also.
  435. But if the surface of the  glass be concave, as represented 
THE EYE.
289
Refraction by convex and concave lenses.
FIG. 157.



      \    I   .......-A
in Fig. 158, the diverging rays which enter it will be made to
diverge still more.   The ray, a, c, being perpendicular to the sur-
face is unchanged in its course;  but the ray, a, d, is bent towards
the perpendicular, e, into the line /, and the ray, a, j, is bent to-
wards the  perpendicular h into the line i.   In the case of both

                           FIG. 158.
the concave and the convex lens, the greater the curvature, the
greater is the change of direction in the rays.  The greater the
curvature, therefore, the sooner  are the rays brought to a focus
in the case of the convex lens.
   There are other optical principles illustrated in the apparatus
of vision, that  will be  brought out in  the description of the
eye, which I will now proceed to give.
   436.  The arrangement of the different  parts of the eye you
can understand by Fig. 159, which is a mere map of a section
of the eye, through its middle part from  front to rear.   It is
intended  merely to represent the arrangement of the parts dis-
tinctly, without strict regard to proportion.  The eye has three 
290              HUMAN PHYSIOLOGY.

                  Description of the parts of the eye.
FIG. 159.
DIFFERENT PARTS OF THE EYE.
coats, as they are called.  At a is the thick strong white coat,
called the sclerotic  coat, from  a Greek  word  meaning hard.
This, which is commonly called  the white of the eye, gives to
the eyeball its firmness.   Into it the cornea, e, fits, like a watch-
glass into its case.  The sclerotic and cornea then make one coat
of the eye, the outer one.  Next comes the choroid coat, b.  This
is a very vascular coat, containing the minute branches of blood
vessels which nourish other parts of the eye.   It is of  a dark
color^ for reasons which I will state in another place.  Its color
is owing to coloring matter contained in  pigment cells, which
lie along on the inner  surface of this coat, next to the inner
coat of the eye, the retina, c.   The retina is a thin membrane,
being principally composed of the expansion of the optic nerve,
d.  The eye  has three humors, as they are termed.  The first
is the aqueous or watery humor,/, which is in  a chamber be-
tween  the  transparent cornea, e, and the  crystalline humor, or
lens, h.  This chamber is divided into two parts by the iris, g,
g, the  pupil  being the circular  communicating door between
them.   The  part of  the chamber which  is in front of the iris
is much larger  than  that which is behind it.   The crystalline
humor, or lens, as it  is  more  often called, has  the consistency
of half dissolved glue.   At * is the vitreous humor, filling up
a large part of the cavity of the eye.  It is called vitreous from
its glassy appearance.  It is a clear, jelly-like substance, having
about the tenacity of white of  egg.  It is contained in an ex- 
THE EYE.
291
               Arrangement of the front part of the eyeball.

ceedingly thin  and delicate sac, and this is divided into  cells
which contain the liquid.
  437. Fig. 160 is a map of the front part of the eye, in which
the parts are more minutely delineated than in Fig 159.  At 2
is the sclerotic coat; 3, the  cor-
nea ;  6, the crystalline lens ;  a, a,
a,  the aqueous  humor;  7, 7, the
iris; 4, the choroid coat; 8, the
retina; c, c,  the vitreous humor,
and  9,  the  sac   containing  it.
Around the  inside of  the  cham-
ber containing  the aqueous  hu-
mor  is a very thin membrane,
(represented as you see by a line,)
which secretes  the humor.   In
this membrane, as  in the case of
every other closed sac in the body,   3
there  are  both exhalents and ab-
sorbents, so that the fluid may be
changed  as  necessity  requires.
There is another thin  membrane
of the eye which I have not  yet
described.   It is represented by a
line, 1, in the figure.   It  is  the
conjunctiva, so called  because it
unites or  conjoins the ball  of the
eye with  the eyelids.   It  covers
the cornea, passes back  a  little way on  the white of the eye,
and then turns forward to line the eyelid.  It is the seat of the
most  common form of inflammation in the eye.  It is very vas-
cular, as is shown by its distended vessels when it is inflamed.
It is exceedingly sensitive,  and hence the  great pain which is
occasioned by any thing, even the smallest mote, that gets into
the eye.   The  object of  having it so sensitive I have spoken
of in  the Chapter on the Nervous System, § 242.
  438. At 6 in Fig. 160, is one of the ciliary processes, as they
are called, from their resemblance to the eyelashes.  There is a
circular row of them,  numbering from sixty to eighty, so  ar-
ranged as to resemble the disk of a radiated flower.   In Fig.
161 they are represented as they appear  in looking at them
from behind, the back part of the eye being  removed.  At 1
is the divided edge of the three coats; 2, the pupil; 3, the iris;
4, the ciliary processes.   At 5 is the anterior edge of the retina,
 
292              HUMAN PHYSIOLOGY.

        Object of the apparatus to form images of objects on the retina.
FIG. 161.
CILIARY PROCESSES.
which stops at the beginning of these processes, presenting, as
you see, a  scalloped appearance.  The processes, however, do
not arise from the retina, but come from the choroid coat, and
are united  at  their origin  by a ring of ligamentous substance
to the sclerotic  coat.  The exact operation of this beautiful
arrangement is  not  known, but it is  pretty well ascertained,
that muscular fibres  are so connected with these processes, that
when they contract they  draw the crystalline lens  forward.
This,  as you will see in another part of this chapter, is a very
important  movement in the adaptation of the eye to seeing at
different distances.
   439.  The object of all  this apparatus, which  I- have de-
scribed, is to have images of objects formed in  the back part
of the eye  upon the retina, so  that the optic nerve expanded
there  may  carry impressions from  them to the brain.   This is
done  in this way.  The rays  of light  coming from an object
pass  through  first the cornea, then  the aqueous humor, then
the crystalline lens, and lastly the vitreous humor to the retina,
where they, so to speak, daguerreotype the object.   The fact
that such an image is formed has been  often proved by obser-
vation on  the eyes of animals.   If the eye of  a rabbit be
cleansed from the fat and muscles at its back part, and a candle,
be held in front of it, you can  see the image of the candle
through the sclerotic coat, formed upon  the  retina.  So if you
take the eye of  an ox, and carefully pare off the back part, so 
           THE EYE.

Images on the retina inverted.  Camera Obscura.
293
as to leave it very thin, a distinct image of any thing placed in
front of the eye may be seen at the back  part.  The image
however will be inverted, as represented in Fig. 162.   For the
FIG. 162.
sake of  clearness two rays only are represented as coming from
each of  the two ends of the object, a, c.   These rays cross each
other in the middle of the eye, those  from a being brought to
a focus at b, and  those from c at d.   As  all the other rays,
comin-r from  other  points in the object, are  refracted  m  the
same manner, a complete inverted picture of it is thus formed.
The same thing is seen in the instrument called the camera ob-
scura   If light be  let into a darkened  room through a small
aperture in a window  shutter, an inverted picture  of  objects
without can be seen on a screen, as  represented m *ig. 163.

                           FIG. 163.
This experiment, which can be performed by any one, illustrates
in a rude way the principle of the camera obscura.  The real
instrument has a tube with a double convex lens, so as to collect
together the rays from  objects, and concentrate them upon a
small space, thereby making  a  very  distinct small image of
them   The eye is a very beautiful and perfect instrument ot
this sort   The space filled by the vitreous humor is the  dark-
ened room; the pupil answers to the hole in the window shut-
                            25* 
 294               HUMAN PHYSIOLOGY.
  ---------*_____________________,_____._.___.__
           Cornea.  Iris.  Its radiated and circular muscular fibres.

 ter, or the tube of the more perfectly constructed camera;  the
 crystalline humor is the lens; and the retina is the screen  on
 which the images are formed.
   We will now attend to the agency which the different parts
 have  in producing  the result, for which the apparatus is con-
 structed, observing the perfect  adaptation  of each of them  to
 the particular part which it performs in the process.
   440. The cornea, as it lets in the light, requires to be trans-
 parent, and, as it is very much exposed to injury, it also  re-
 quires to be very firm  and  hard.   Both of  these objects  are
 secured in an admirable manner.  Its transparency is secured
 in this way.   It is  made of different layers, which  are kept
 moist by a delicate transparent fluid.   It is  this which  in health
 makes the eye so clear and  sparkling.  Disease often so lessens
 it, as  to give  this window of the eye a dull appearance.  The
 cornea is, as you see by Fig. 159, more convex than the sclerotic
 coat, so that it may act with some power as  a lens in making
 the rays converge.
   441. The iris is a circular curtain with a round opening  in
 its centre, the pupil, which can be varied in size to a  consider-
 able degree.   On  the  iris depends what is called  the color  of
 the eye, which is various, as blue, nearly black, grey, hazel, <fcc.
 The color is owing to the pigment which is  in cells on its inner
 surface.   The chief  office of the iris is to regulate the quantity
 of light that  enters the  eye.   When the  light is obscure the
 opening in the iris is widely dilated;  but when there is much
 light it is contracted; and if the light be  excessive, it  is con-
 tracted almost to  a point.   Its motions, therefore, considering
 ing its small extent, have a very wide range.   You can realize
 this if you look at the eye of some one in a dim light,  and then
 suddenly bring a lighted candle very near to it.  These motions
 are effected by a  peculiar arrangement of muscular  fibres,  of
 which the iris is in part composed.   There are
 two sets of fibres, the circular  and radiated, as
 represented in Fig.  164.   When  the circular
 fibres  contract, the pupil is contracted; and when,
 on the other hand, the radiated fibres  contract,
the pupil is dilated.  There must be a very nice
adjustment of the fibres, to enable them to di-
late the pupil  as widely as  they sometimes do,
without producing any puckering of the surface of
the iris.  The opening in the iris is always  round in man ; but
in animals whose range of vision requires  to  extend widely in
 
THE EYE.
295
       Crystalline lens.  Seat of cataract. Choroid coat.  Why dark.

a horizontal direction, (as the herbivorous animals,) it is in the
form of an ellipse, with the long diameter horizontal.  In ani-
mals, on the other hand, that leap up and  down in pursuit of
their food, as the cat and other carnivorous animals that seek
their prey in the  same manner,  the pupil has  the  elliptical
form, but with the long diameter vertical.
   442. The crystalline lens is the chief agent in the eye in con-
centrating the rays of light by refraction.   In Fig.
165 you have a side  view of it.   Its anterior part,   FIG- 165-
1, is less convex than its posterior, 2.   In Fig. 166
is  a magnified view of the lens hardened in spirit
and cut open, so as to show the different layers of
which it is formed.   The layers are more and more
hard as you go  towards the centre.  The object of
this arrangement and of the peculiar shape  of  the  Crystalline Len'-
lens,  is  not  as yet  understood.
This lens is the  seat of the disease           FIG- 166-
called cataract.   In this disease
the  lens  becomes  opake  so as to
prevent the rays of light from pass-
ing to the retina.   There are three
ways of getting rid of the difficulty.
One is to introduce an  instrument
shaped like a needle  into the side
of the eyeball, with which the opake
lens is pushed off one side  in the
vitreous  humor, so as to be out of
the way of the rays of light.  An-
other is to break  up  the  lens with the needle, so that its frag-
ments may be  absorbed.  The third method is to make  an
opening in the cornea, and to extract the lens through it.
   443. The choroid  coat (b, Fig. 159) contains quite  a large
share of the  minute  bloodvessels, and nerves of the eye, and
serves for a medium by which they pass to other parts of this
organ.  But it serves another  important purpose by means  of
its dark pigment.   It makes a dark chamber of the  back part
of the eye where  the optic nerve is expanded.   The object  of
this is to  secure distinctness in the images formed  upon the
retina.  If the choroid coat were of a light color, there would be
so much reflection  of the rays of light back  and forth in  all
directions in the eye,  that the pictures formed  upon the retina
would be confused.   There would be a glare of light, such  as
we experience in a room where the walls are all of a very light
 
296
HUMAN PHYSIOLOGY.
          Want of pigment in the choroid of the albino.  The retina.

color.  There is the same reason for having the chamber of
the eye of a dark color, as for  having that of the  camera ob-
scura so.   In the albino there is a  deficiency of the  pigment of
the choroid;  and, therefore, in a bright light there is in his case
a defect  of vision, from the cross reflection to  which I have
alluded.  During the day  his vision is very indistinct; and it is
only when twilight  appears  that he can see well, or with com-
fort.  The pigment  is also  deficient in the  iris of the albino;
and the bright red or pinky hue of the iris in his case is owing
to the blood in the minute  bloodvessels, with which  this part
is so well supplied.   Those  animals that use their eyes mostly
in daylight  have the pigment of the choroid of the darkest
color;  wbile, on the other  hand,  those that need  to see most
clearly at night, as the owl,  either have none of  this pigment,
or have it of a very  light  color.
  444. The retina is a soft greyish delicate  membrane, formed
chiefly of the expansion of  the optic nerve.   Here the images
are formed, and the  minute fibres of nerve in this membrane
receive impressions from these images, which are transmitted to
the brain by the trunk of  the  nerve.  This  nerve has the same
relation  to light  that  the nerve of hearing has to sound, the
nerve of  smell  to odors, or  the nerve of touch to the qualities
of bodies that we feel.  And  it is curious  to observe that the
termination of the nerve of sight  on  the  surface of the retina
is arranged in papilla, just  as  the terminations  of the nerves
of touch  are.  In Fig. 167 is represented
a portion of the retina of  a  frog magni-         fig. 167.
fied  three hundred  times.  The  upper
rows of papilla?, which are without dots,
are seen  sideways.
  445. The superiority of the eye, as an
optical instrument, is seen in  a striking
manner  in several particulars, in  which
difficulties and  defects to  which all opti-
cal instruments are  liable are removed.   There is, for example,
a defect in the operation of lenses in optical instruments, which
is termed spherical aberration.   This  can  be explained on  Fig.
168, which represents a lens, L, I/, with  some of  the rays as
they pass through it.  Now the rays R, R", R"',  are brought
to a focus at F;  while the rays R, L and  R"", 1/ come  to  a
focus much nearer, at I.  It  was found by experiment, that if the
central portion of the lens be covered, so  that the rays R', R",
R'", cannot pass, a distinct  image will be formed on a screen
 
THE EYE.
297
Spherical and chromatic aberration. How remedied in the eye.
put at I.  And, on the other hand, if the outer portion of the
lens be covered, so that the outer rays are intercepted, then the
middle rays, R' R" R/7/ will form an image  on a screen at F.
But if the whole lens be used, no distinct image is formed, wher-
ever you  may place the  screen.  If you place it at I, it will
receive with the rays that come to a focus there, rays that have
their focus at F.  And so of other points.
   446. It is in view of such experiments, that  a contrivance
has been adopted in the construction of telescopes and micro-
scopes, for  the purpose of remedying the  difficulty above de-
scribed.  What is called a diaphragm, or stop, is  put in against
every lens.  It is a perforated partition which permits the light
to pass only through the central portion of the lens.   The lines
D, D', in Fig. 168, cutting off all rays in the neighborhood of
R and R"", show the operation of the stop.   In the eye the
iris acts as the diaphragm or stop to the crystalline lens which
is behind it, as you can see by recurring to Fig. 159.  Ordina-
rily, by means  of this stop, the  rays pass through only the
central part of the lens.
   447.  Another difficulty attending the operation of a common
lens is what is termed chromatic aberration.  Every ray of white
light consists of a mixture of  rays  of seven different colors.
Some of these colors  are more easily refracted than  others, and
therefore on passing through a lens will come to a focus sooner.
This of course is apt to make some confusion in the color and
the distinctness of objects, when seen through a single lens, or
through several if they are alike.  The difficulty has been rem-
edied, although Sir Isaac Newton thought that it never would
be.  And it is said that the hint of the remedy was  taken from
the arrangement of the eye.  At any rate, the defect is avoided 
298              HUMAN PHYSIOLOGY.
            Adjustment of the eye to objects at different distances.

by having lenses made of different materials, just as is the case
in the eye.   Thus  if two lenses be used, one of which is made
of flint and the other of common glass, the difficulty disappears.
In the eye it is perfectly avoided by the passage of the rays
through so many different materials, before it reaches the retina.
The stop has been  found a  partial remedy in the case of optical
instruments; and the iris, the stop of the eye,  of  course acts in
the same way.  But the  full remedy was not found, till another
step was taken in imitation of the eye, the most perfect of all
optical instruments.
 „ 448.  There is another arrangement in the eye, which the
optician can imitate only in a comparatively bungling manner.
It is that by which the eye adapts itself to different distances in
looking at objects.  If we  look through a telescope at a near
object, and then turn it towards one  at a distance,  we cannot
see it distinctly until we  adjust the lenses to suit the distance.
But in  the eye how quickly the  adjustment  is  made!  It is
done ordinarily, without any effort on our part of which we are
conscious.   It  is  done so  easily that we do not think of the
change.  We look at an object at a few inches distance, and in
an instant turn the eye and see  an object afar off with almost
equal distinctness.   There  has been much discussion in regard
to the means by which this adjustment is effected.  One of the
means undoubtedly is, a change in the relative position of the
crystalline lens, which is  effected by the muscular fibres spoken
of in § 438.  These fibres when they contract,  draw the lens to-
wards the front of the eye, and  away from the retina.  This is
done whenever we look a„t a near object.  If it were not, the rays
which come from the object, as they diverge considerably, would
not be brought to  a  focus when they reach the  retina.  The
iris also has some agency in  adjusting the  eye for seeing at
different distances.  When the eye is turned to a near object
the pupil always  contracts,  thereby shutting out those rays
coming from it which are the most divergent.
FIG. 169.
 
THE EYE.                     299
              Difficulty in the near-sighted and the far-sighted.

  449.  In some cases  this power of adjustment is counteracted
by defect in the arrangement of  the eye.  Thus, in the near-
sighted, either the  cornea or the crystalline  lens, or both, are
too convex; or, the crystalline lens is  too far from the retina.
The result is, that the rays of light coming from a distant ob-
ject come to a focus before they reach the retina, as represented
in Fig.  169.   All objects, therefore, are seen indistinctly except
those which are brought near to the eye.  This defect is rem-
edied by the use of a concave lens, which counteracts the effect
of the too highly refractive  power  of the eye  by making  the
rays divergent, instead of parallel, before entering the eye.  By
an habitual adjustment of the eye for seeing near objects, near-
sightedness may be produced.   Hence  it is  that engravers,
watch-makers, students, &c, are so liable to become near sighted.
   450. In the far sighted the difficulty is of an opposite char-
acter.   The  refractive power of the eye is too feeble.   This is
owing either  to  too little convexity of the cornea, or of the
crystalline lens,  or of both; or,  to too great  nearness of the
crystalline lens to' the retina.   In this case  the rays coming
from a near object do not come  to a focus soon enough.   The
focus of the rays coming from any point of the object is behind
the  retina, as seen  in  Fig.  170,  in which  the rays from  two

                          FIG. 170.
points are represented as prolonged till they meet at their focus
behind the retina.   This defect is palliated by the use of convex
glasses.   It is quite common in persons who have passed middle
age ;  while near-sightedness appears mostly in younger persons,
the full compliment of the humors of the eye in their case
making the front part of the organ prominent.
   451.  There has  been much  discussion of the question why
we see every thing in its real position, while the images of ob-
jeots  are, as you have seen in § 439, reversed on the retina.  It
has been  supposed by some that we really see  every thing re-
versed,  and that our  experience with  the sense of touch, in
connection with that of vision, sets  us  right in  this particular. 
300
HUMAN PHYSIOLOGY.
      Why we see things erect, though their images on the retina are reversed.

And this, it is supposed, is the more readily done from the fact,
that our own limbs  and bodies are reversed as pictured on the
retina, as well as objects that are around us, so that every thing
is relatively right in position.  But if this  be the true explana-
tion, those who have their  sight  restored, after having  been
blind from birth, should at first see every thing wrong side up,
and should be conscious of  rectifying  the  error  by iooking at
their  own  limbs and bodies.  But this is  not so.   In the case
related  by the  anatomist Cheselden,  of the boy who was blind
from  birth, and who at about the age of thirteen had his sight
restored by an operation, there was no complaint that he did not
see things erect at the first.  If this difficulty had existed, he would
have complained of it quite as readily as he did of the difficulty
in estimating the size  and the distance of  objects.  The above
explanation of erect vision, and other explanations of a similar
character, are  based  upon a  wrong idea of  the office which the
nerve performs  in  the process of vision.  It  is not the image
formed  upon the retina which is transmitted to  the brain, but
an  impression  produced by that  image.   The mind does not
look in  upon the eye and see the  image, but it receives an im-
pression from  it  through the nerve; and this impression is so
managed that the mind gets the right idea of the relative position
of objects.   Of the way in which this is done we know as little
as we know of  the nature of the impression itself.
  452.  It  is an interesting and wonderful fact, that as we look
at an object with  both  eyes, although  there  are two images
formed, and therefore two impressions are carried to the brain
by the  two nerves, yet a single impression is  produced in the

                          FIG. 171.
 
THE EYE.
301
              Correspondence of action between the two eyes.

mind.   To produce this single effect at the end of the process
of seeing, it is manifest that there must be a very exact corres-
pondence in  the two  eyes as optical  instruments.  The two
images  must be similar, and must be formed on corresponding
parts of the  retina in both eyes.   Thus, if there be a range  of
objects,  as at A, B, C, in Fig.  171, the impression will be a
single one in  the mind, because the picture of these objects is
on the same  part of the retina in both eyes, a, b, c, and a!, b', c''.
But  if you press with your finger  one of the  eyes a little out
of its place, all these objects will  appear double, because their
images  occifpy different parts of the retina in  the  two eyes.
  453.  It is  essential, therefore, that the muscles which  move
the  eyes, as  we direct  them  towards different objects, should
harmonize in their action.   They  must move  together with
great exactness, or there will be disarrangement of vision.  If the
want of correspondence  be  slight, the vision will  be merely
confused.  But if  it be  considerable, so that the  images are
formed on quite different parts of the retina, in  the two eyes,
every object  will be distinctly double.   You can verify this,  by
pressing one of  your eyes with the finger with different degrees
of force, while you look at the objects.  The  intoxicated man
often sees indistinctly, and sometimes even  double, from this
want of correspondence in the action of  the muscles moving
the eyes.  This is one of the causes of double vision, as we  see
it occurring in disease.   I will cite  a  case  which has recently
come under my care, in illustration.  The  patient could see as
usual, so long as  he  looked directly in front, or towards^ the
left.   But when he turned his eyes to look towards the  right,
he saw every thing double, and the farther he looked in that
direction, the farther apart were  the two images of every  ob-
ject.  The reason  was obvious.   In looking to the right, the
left eye turns towards the nose, while the  right eye turns from
it outward.  The failure in this case was  in  the action  of the
muscle  that  turns  the  right  eye from the nose.   The  conse-
quence was, that as he attempted  to turn  his eyes to look to
the right, the right eye did not correspond in its motion with
the left, but  remained nearly stationary, presenting  therefore a
squinting appearance.  In common squinting, there is a per-
manent-contraction of one of these straight muscles, similar to
that which we see in  wry-neck,  as stated in §  308.  When
this  difficulty exists, the  images of objects are formed in two
different parts of the retina in the two eyes, as in the case  which
I have just related.  We should  therefore expect that there
                               26 
302              HUMAN  PHYSIOLOGY.
       The two images of an object in the two eyes not always exactly alike.

would be double  vision, but ordinarily there is not.   Why is
this?  It is because the mind acquires the habit of attending
to the impression that comes from one eye alone, the sound one.
If the squinting occur suddenly there is double vision at first,
because it takes a little time for the mind to acquire the habit
referred to.   But  it generally comes on  gradually, and there-
fore  there is  no difficulty in  the  acquisition of this  habit, to
meet the exigency of the case.
   454. While it is  necessary to single vision when both  eyes
are used, that the image of the object should  occupy corres-
ponding portions of  the retina  in the  two eyes, it is  not true
that these two images are in all cases exactly alike.  They are
so when the object presents a  plane surface, or one, every line
of which can  be seen equally well  by both  eyes.   But if the
object be such that some  lines  or surfaces of it are seen by one
eye alone, while other lines and surfaces of it are seen  only  by
the other eye, two different images  are obviously formed in the
two eyes.   You can verify this  by a simple  experiment.   If
you hold a book  before your eyes,  with  its  back in a vertical
direction, you see the back of the book and its sides at once, as
a single  object.  If now, still  holding  the book in the same
position, you shut one eye, you see  but one side of  the cover of
the book—that one which is  on the same side with the open
eye.   And so with the other eye.   The plain inference is, that
when you look at the  book with both eyes,  the image formed
in the right eye is composed of the  back  of the  book and  the
cover of the right side, while the image in the  left eye  is com-
posed of the back of the book and  the cover of the left  side.
From these two distinct images, of course, two distinct impres-
sions  are sent  to the brain;  and yet but a single impression' is
recognized there by the mind, for the book is seen  as a single
object.  This  single  impression  must, therefore, result in some
way  from a mingling of  the  two impressions transmitted along
the two optic  nerves.  Were it not  for this mingling of the two
impressions, we should see double, that is, see two things, when-
ever  we look  at any solid projecting object,  and  should  see
single only when we look at plane surfaces.   Indeed, one who
has but one eye can  not acquire from sight  alone  any idea of
solidity.   Every thing would appear to him to  be  on  a plane
surface, till he finds it to be otherwise  by the use of the sense
of touch, in connection with that of sight.
   455. The statements  in the last paragraph are  beautifully
illustrated by the instrument contrived by Professor Wheatstone, 
THE EYE.
303
                   Explanation of the stereoscope.

which he calls the stereoscope.  In using this instrument, you
look at two pictures of the same  object with the two eyes, and
yet you see but one thing—that is, but  one impression is pro-
duced in the  mind, although two different pictures are made in
the two eyes, and of course two different  impressions are con-
veyed to the  brain.  Suppose  the object represented is a book,
as described  in the  experiment alluded to, in § 454.  In  the
right half of the instrument is a  representation of  the book, as
seen by the right eye, and in the left half  is a representation of
it as seen by the left eye.  As you  look at them you  see  but
one book, just as you do in holding the book before your eyes.
The two different images formed in the two eyes are the same
in the two experiments.  The same  thing is  done with  other
objects.   Thus, the two representations of a dog, seen in Fig.
172, are seen in the instrument as a single dog.  You observe

                          FIG. 172.
that they are  shaded differently.  They are representations of
the two pictures, which a dog  in this position would make on
the retina in  both of the eyes of a person  looking at him.
When you look at them in the instrument, the single dog that
you see stands out more than either of the two representations,
as seen when they are not in the  instrument.  The reason is
obvious.   In the  two images formed  in the  eyes, as you look
into the instrument, are all  the  lines of  light and  shade, which 
304
HUMAN PHYSIOLOGY.
Rude imitation of the stereoscope.
you would see in looking at a  real dog with both eyes;  while
either one of these representations contains only a part of these
lines.   You  can imitate in some good degree the effect of the
stereoscope,  by placing the end of a small book  between these
figures, and letting the  other end rest against the nose and fore-
head, thus separating the eyes from each  other.  If now you
look intently at the two figures, you will in a few  moments find
them  approximate  each  other, till at length  they mingle to-
gether, and you will see but a single dog  standing  out like  a
statue.   The same thing can be shown by mathematical figures.
Thus, if two figures a  a, represented in Fig. 173, be  placed in
the two apartments of the instrument, on  looking  into it you
will see a  single figure, shaped  like b.   You can  imitate the
stereoscope here also, by placing the end of a book in such  a
way as to cover the middle figure, the other end being between
the  eyes.  The  two figures will run together, and  the  union
will represent the figure of a truncated, four-sided figure, stand-
ing out in bold relief.   But such experiments afford  only a rude
imitation of the  stereoscope, for in  this instrument  the separa-
tion  between the eyes is entire, so that the effect is  produced
at once.   There  is no running together of the two  figures, but
the moment that you look into the instrument they are blended
in one.
   456. The harmony which we have seen to exist in the  action
of the eyes  is very wonderful.   It  must be remembered that
the eyes  are  optical  instruments,  endowed with self-adjusting
powers, to accommodate the  different distances of objects, and
the varying degrees of light.  And thus  must both be just
alike  in  all these diversified adjustments,  that the images in
both may correspond.  And besides all this adjusting machinery
inside of  the eyes, so delicate and so correspondent in its  action
in both, there is muscular machinery outside, to move the eye- 
THE EYE.
305
    Correspondence not only between the two eyes, but also between their nerves.

balls in all directions;  and in these movements also, as you
have seen, there is an exact correspondence.   All  these motions
for adjusting this complicated machinery within and around the
eyes, are regulated by the nerves.   How astonishing the accu-
racy with  which  they  do this!   How exact are the different
impressions transmitted  through them, in producing the various
degrees,  and  multiplied  combinations  of action, in  the little
muscles of these organs!
  457. There is correspondence not only in  the  machinery of
the eyes, as optical instruments, but also in that  portion of the
process of seeing which is not mechanical.  The  nerves of vis-
ion must be exactly correspondent in the two eyes, that similar
impressions may go from the retina to the brain in both.  And
the correspondence is in this case the more wonderful from the
fact, that  the impressions transmitted  are, as you have seen,
not always precisely alike.  How the harmony is preserved in
connection  with  this variation is  a great mystery.   We can
readily conceive how a single impression can result in the mind,
from two impressions transmitted to the brain from two images
which are exactly  alike.  But we  cannot conceive how confu-
sion can be avoided when the images and the consequent impres-
sions are in some measure different.  In  this connection I will
notice a  peculiarity  in the  arrangement of the  optic nerves.
They are not entirely separate as they go from the eyes to the
brain.   At one point in  their  course they unite together, and
then  separate  again.   In doing so, some fibres from  both the
nerves communicate  together, and some  cross  each  other, so
that a portion  of each  nerve passes  over to  the other before
they go to the brain.   Undoubtedly this arrangement  has some
reference  to  the harmony of action of  the two nerves, but we
know  nothing of the way in which it  exercises  its  agency in
this respect.
   458. The power of perceiving the size, distance, and figure  of
objects, is wholly an acquired power.  The case already referred
to, in which Cheselden restored the sight by an operation, shows
this to be true.   "When he first saw,"  says Cheselden  of his
patient, " he was so far from making any judgment  about dis-
tances, that he  thought that all objects whatever touched  his
eyes  (as he expressed  it,) as what he felt  did his  skin, and
thought no objects so  agreeable  as those which were smooth
and regular, though he could form no judgment of their shape,
or guess what it was  in any object that was  pleasing to him.
He knew not the shape of any thing, nor any one  thing from 
306              HUMAN PHYSIOLOGY.
       Power of perceiving the size, distance, and figure of objects acquired.

another, however different in  shape or magnitude; but  upon
being told what things were, whose form he  before knew from
feeling, he would carefully observe, that he might know  them
again; but having too  many objects to learn  at  once, he forgot
many of them;  and (as he said),  at first  he learned  to know,
and again forgot a thousand things in a day.  At first he  could
bear but very little light, and the  things  he saw he thought
extremely large ; but upon seeing  things larger, those first seen
he conceived  less, never being able to imagine any lines beyond
the bounds that he saw;  the room he was in, he said, he  knew
to be but part of the house, yet he could not conceive that the
whole house  could  look bigger."   Every infant, if it  could ex-
press its ideas, could give  us a narrative of a similar experience,
in its first lessons in seeing.  It is  obvious  that seeing is a pro-
cess which we learn to do, as really as  we  learn to talk or  walk.
The confused vision of the infant  bears the same relation to
the accurate vision of the adult,  that its uncouth noises and
awkward motions bear to the adult's harmonious utterances and
graceful movements.   In  order to  acquire  definite and correct
ideas of objects, we are obliged to learn how to use those  opti-
cal instruments, the eyes.   The infant  manifestly does not  know
how to use them to any great advantage.   He does not at first
know how to use the muscles that direct the eyes towards any
object, and there is, therefore, an obvious  awkwardness in their
movements.  As he reaches out his  hands towards  objects, it
is plain that he does not appreciate their distances.  He reaches
out for the moon, or any  other distant object, just as he does
for the toy that is held before him.  It is by a continued com-
parison of experiences that he  learns the  sizes, shapes, and dis-
tances of objects.   And  in doing this, the sense of touch acts
as the educator of the vision, very much, as the ear educates the
voice.   And  even the adult, with  all the training which he has
bestowed upon his eyes, often makes mistakes, especially in rela-
tion to magnitude and distance.   There are various degrees of
skill in seeing; and he is the most skillful seer who makes the
fewest of the mistakes referred to.
   459. Let us look now at the means by which we gain the
experience  that is necessary to  correct vision.  One  means  is
the appreciation of the space occupied by objects in the field
of vision.  This  is measured by  what  is termed the  visual
angle—that is, the angle  which is formed by two  lines coming
from the extremities of an object, and meeting in the eye, as
represented in Fig. 174.   In this way we get the  idea of mag- 
THE EYE.
307
Visual angle. Distance of objects estimated by their distinctness.
FIG. 174.
nitude.  But it is manifest that it cannot alone give us this idea
correctly.  It would do so,  if all  objects  were at an  equal
distance from the eye.  But you can see by the figure, that if
they are at  different distances, you  must know something of
those distances, to estimate the magnitude  of the objects by
the visual angle, which  they subtend.   The  arrow at A, B will
appear just as large as the larger one at A', B', because it will
occupy  the same space a, b on the retina, and subtend the same
angle.  But  if  you know that the one  is  nearer  to you than
the other, you make allowance for this in the estimation of the
size.  Your hand, held  up to keep  the rays of the sun from
your eyes,  would look to you as large as the sun itself, if you
did not know how near it is to you; and the sun  and  moon
appear  to us  to have about  the same magnitude, because we do
not keep in mind the fact that the sun is ninety-six  millions of
miles from us, while  the moon is only  two hundred and forty
thousand.                                  ,
   460.  Another means which we use in getting  a correct idea
of objects  by vision, is the degree of distinctness in their lines,
and shadows, and  colors.   The  fact is learned very early by
the child, that the nearer objects are, the  greater  is their dis-
tinctness';  and he  makes use of this fact  continually in estim-
ating both their distance and their  magnitude.   He estimates
the Tatter less directly than  he does the former by this means.
He makes use of his notion of the distance of an object, gained
by its degree of  distinctness, in forming an  idea of its magni-
tude    Many mistakes are  made in  the use of this means  of
 imlobio- of objects.   Thus,  a very bright light will often  appear
to be nearer  than one that is  less bright.   When the atmos-
phere is very clear, mountains and other objects  appear nearer
to us than they do when the atmosphere is thick and hazy.
   461  Another  means of making a  correct estimate of the
distance and magnitude of objects is,  comparison with other 
 308               HUMAN PHYSIOLOGY.
       Size of objects estimated by comparison. Muscular sense in the eye.

 objects which are familiar to us.   Thus, we  get  our  ideas of
 the size of animals from  objects in  their neighborhood.  The
 artist makes use of this means of communicating ideas of  size
 in pictures and  engravings.  Figures of men are placed near
 large buildings for "this purpose.   A notion of the great size of
 the elephant is given by placing his keeper at his side.   I need
 not  multiply instances  of this sort.  We  are not ordinarily
 aware how dependent we are  upon  such  comparisons, in esti-
 mating the magnitude of objects.   An occasional mistake  re-
 minds us  of it however.   For example, I once turned  my  eye
 suddenly from a giddy height, upon some huts below at a river's
 side; they appeared to me to  be dog kennels, till  a man issued
 from  the door of one of them, and  thus dispelled the  illusion,
 by affording me a means of comparison.  So complete was  the
 illusion, and so sudden was the dissipation of it, that it seemed
 as if  there was an instantaneous  swelling of dog  kennels into
 huts.   Every one must have noticed how large the full moon
 appears as he sees it  rising, while the higher it  rises the smaller
 it becomes to the eye, although it is really at no greater distance
 than  it was when it first rose.  The reason is, that when it first
 rises you see it in  a range with other objects,  with which you
 instinctively compare it.  And, therefore, it appears larger when
 you see it rising in the direction of some distinct object, as a
 large building, or a high hill, than it does when you see it rising
 over a level plain.
   462. Another  means of judging  of the magnitude  and  dis-
 tance of objects is, the muscular  sense (§ 323)  exercised  in
 adjusting  the eyes in  seeing  them.   Thus, consciousness   of
 the amount of muscular action, in passing the eye up and down
 a tall object, helps to give us an idea of its height.  So too, in
 looking at near objects, consciousness of the amount of effort,
 in turning the two eyes towards the point looked at, helps  us
 to estimate  the distance of  the object.  Commonly we do  not
 distinctly  think of this effort, because it is so  easily made; but,
if after looking at an object held at some distance from the eyes,
we suddenly bring it  very near, the effort to make the  axes* of
the eyes converge enough to see  it  distinctly is very manifest,
 producing a straining effect, which, if it be repeated many times
successively,  wearies  the eyes.  You  can discover how very
dependent you are upon this  sense of the convergence of  the

  * The axis (plural axes) of the eye is a line drawn through the centre of the cornea
and pupil backward through  the eye to the central point of the retina. In Fig. 171 the
axes are B b,  and B b'. 
                         THE  EYE.                     309
       Seeing is in part a mental process. Really complicated and difficult.

eyes,  in  accurately  estimating  comparative distances  in  near
objects, by  attempting to thread a needle, or  nib  a pen, or
snuff  a candle  with  one eye shut.   The change in the converg-
ence of the  eyes, on looking at objects at different distances, is
very manifest to us when we  observe the eyes of others.   We
perceive thus not only the direction, but the distance of the objects
at which they are looking.  We do this so continually from our
infancy, that we very early acquire  great accuracy in judging,
at what distance the point is towards which  the eyes are turned,
or in  which, in other words, the axes of the eyes meet.
   463. From the facts presented  in the few last paragraphs, it
is obvious that what we include in the word seeing is, to a great
extent, a  mental process.   That  is,  there  are certain  mental
efforts which are  absolutely essential  to correctness  in vision.
Without these mental efforts or processes, we  could not  see
things as  they are, as it  is  expressed very properly, but we
should see them  as  the boy operated upon by Cheselden  did,
when he first began to see.   Seeing is  commonly supposed to
be a  very simple process.  The idea is, that one has merely to
open his eyes,  and he sees.   But, as you have seen, the whole
process is both a complicated and a difficult one; and  in order
to be able to do it, the eyes have to  go through a  course of
training in  the case of every infant, just as was  the  case with
the boy whose  sight Cheselden restored.  We should be  con-
scious of  this, if we could recollect  the experiences of infancy.
But not being  able to do this, it is  only when we make  some
extraordinary effort  in vision, that we are  at  all sensible  that
there is any acquired skill in the process.   After the training
which the eyes have in infancy, ordinary seeing is  done with
so much facility, that we are  not  conscious of any effort either
bodily or mental.  This appears very wonderful, when we  con-
sider that the eyes are two  optical instruments,  which need, as
you have seen, a most careful  and  nice change of adjustment
continually, to see  in  different directions, and at different dis-
tances, and that there is also  considerable and  complex mental
effort in getting the right impressions from the objects which
are pictured upon the retina.
   464. But there is another  view in which the  mental part of
the process of  vision appears  strikingly prominent.  When it is
said that images of objects are formed upon the retina, and that
impressions are transmitted from them  to the brain, this  is far
from  stating all  that is  true on that point   Many of  the
images pictured upon the retina do  not transmit  impressions to 
310
HUMAN PHYSIOLOGY.
        All images on the retina do not produce impressions in the mind.

the mind.  The sensation of seeing is, therefore, in relation to
them incomplete—the beginning only of the process is effected.
This you have  seen  to be true in the  case of strabismus  or
squinting.  The faulty eye in this case is not used—the  mind
takes no cognizance of the images formed in it (§  453).   But
it is true of ordinary vision also, that the mind takes no cogni-
zance of many of the  images formed on the retina.  This can
be verified by a simple experiment.  If you  hold a finger near
the eyes (at some ten  or  twelve inches from them), and a fin-
ger of the other hand  at  a  greater distance, but in the  same
direction, and then look  at the near  finger, you will perceive
that the other finger appears double.   So, on the other hand,
if you look at the  distant finger, the near  one appears double.
The reason of this can  be made clear to you by Fig.  175.  The
two eyes, L and R, being direct-
ed so that their axes converge
on  the object A,  the middle
points of  the two images cor-
respond with the middle points
of the retina in the two eyes, a
and a'.  The images  thus cor-
responding in their place on the
retina, the impressions carried
from  them  by the  two  optic
nerves to the brain correspond
also, and so the vision is single.
But the image of the  object B
is formed in the two  eyes, in
parts of the retina that do not
correspond, b and b'.  They are
both on the  inside of the mid-
dle points, a  a', that is towards
the  nose;  whereas the outward
part of the  retina  in  one eye
corresponds  with  the  inward
part in the other eye,  and vice versa.   This you will see to be
true  by recurring to Fig. 171, in  which is shown  the way in
which a row  of objects is  pictured  on the  retina in  the two
eyes.   There you see  that the image  of the object A, for  ex-
ample, is in the left eye, L, on the inner side of the middle point,
b of  the retina; while  in the right eye, R, it is at the outer side
of the middle point, b'.   In the case of the object B, then, in Fig.
175, it is clear  to you that the images of it in the two eyes are
 
THE EYE.
311
         Some of the images on the retina are not attended by the mind.

formed in parts of the retina that do not correspond, and there-
fore it appears double.
   465.  The  application of all  this to the  point in  hand you
can readily see.   As  the  images of all objects  in  the field of
vision of the two eyes are pictured on the  retina, it is plain,
according to the facts developed above, that whenever the  eyes
are directed  together to  any one object, other objects in the
same direction, but at a different distance, must make images
on the retina in the two eyes that do not correspond.   We are
therefore  continually  seeing  double, so far  as that part of the
process  of seeing, which  consists  in the formation of the im-
ages, is  concerned.   But we  are  not ordinarily conscious of
seeing double.   How is this ?   How is the  difficulty  (for it is a
real  difficulty in the eyes, as a  pair of optical instruments,  aris-
ing from the non-corresponding images) remedied ?   It is done
obviously in  the other part of the process of seeing, the mental
part.  The mind  regulates  vision  by the  varying  degrees of
attention it bestows on objects.  Ordinarily it does not attend
to non-corresponding impressions that come from the non-cor-
responding images, but it  attends only to those which  are corres-
pondent.  As in squinting, it disregards, as  you have seen, the
impressions that come from the faulty eye, so in ordinary vision
it disregards many of the impressions that come from both of
the eyes.  By an effort of the will it can attend to the impressions
which it ordinarily disregards.   When this  effort is  not made,
it disregards  them,  as we  may say, instinctively.  To  make this
obvious,  I will  recur  to the experiment with the  two fingers,
held at different distances.  When  you first attempt the experi-
ment, you do not for  the moment perceive that you see one
finger double, because you  change  the direction of  your  eyes
from  one finger to  the other,  so easily and so unconsciously,
that  you seem to see them both singly at once.   But by a little
mental effort you fix your  eyes  on one, at the same time attend-
ing to the images and consequent impressions produced by the
other, and then the experiment succeeds.  From all  this it  is
obvious  that  the reason that you do  not  see very near objects
double, when looking  beyond them to distant ones, or see distant
ones double when looking at near ones in the same  direction,
is simply that the mind ordinarily attends only to those images
and impressions which are correspondent, while  it with an ha-
bitual instinct disregards  those which are  not so.
   466. In connection with this subject of the influence of mental
attention on vision, it is proper to notice the fact, that vision is most 
312              HUMAN  PHYSIOLOGY.
        Point of distinct vision. Minuteness of the images on the retina.

distinct at the central part of the retina—that part where the axis
of the eye strikes, as seen in Fig. 171,5, b'.   This is commonly
called the point of distinct vision.   The mental attention makes
use of  this point continually.   Thus, if we are looking intently
at a minute object, the eyes are so directed, that their converg-
ing axes meet on the object.  So when we are reading, although
the whole page may be pictured on  the retina of each eye, only
the letter  on which the axes of the eyes meet is  seen  with per-
fect distinctness.  And  the point of union  of the  axes moves
from one letter to another along the lines, so that each letter is
successively pictured on the central part of the retina.  The
process is so  rapid  that  we  are not conscious  of it, until
we take pains to observe what the  process  is.  So, in looking
at a prospect, the  eyes at each moment see some  one point
more distinctly than  any other part of all that fills the field of vis-
ion.   We are unconscious of this, just as in  the  case of read-
ing, because the axes of the eyes are so continually moved by a
slight but exceedingly quick motion from one point to another.
We in this way take into the central part of the retina so many
points  with such rapidity, that, by  a mingling of the impres-
sions upon the mind, we seem to see the whole  prospect at the
same  moment, with  nearly  equal  distinctness.  The  successive
impressions from the images on the retina, occupy so little time,
that they appear to be simultaneous, unless we watch the process.
   467. But although some  one letter on a  page, or  some one
point in a prospect, is at each moment seen with much more
distinctness than what is all  about it, yet there  is some vision
of the page  and of the prospect as a whole, of course being
less distinct the farther it is from the central  point.   It is pic-
tured as a whole on  the  retina, and the impression from it as a
whole goes by the nerve to  the brain.   The  picture  is a very
minute one, as it occupies a small space, and  yet it is very dis-
tinct in all its lines, and  shades, and colorings.   On  this point
Dr. Paley remarks that " in considering vision as  achieved by
the means of an  image formed at  the bottom of the eye, we
can never  reflect without wonder upon the smallness, yet correct-
ness of the picture, the subtility of the touch, the fineness of
the lines.   A landscape of five or six square leagues is brought
into  a space of half an  inch diameter; yet  the multitude of
objects which it contains are all preserved;  are all discriminated
in their magnitudes, positions, figures,  colors.   The  prospect
from Hampstead Hill is  compressed into the  compass of a six-
pence,  yet is circumstantially represented." 
THE EYE.
313
            Our judgment of the motion of objects often erroneous.

  468.  We form a judgment of  the  motion of bodies, in part
by the movement of the images of them upon the retina.  The
perception of this movement must  be exceedingly delicate,  for
even when a body passes over  a  considerable space, its image
moves over a very small space on the retina.  "A stage-coach,"
says Dr. Paley,  " traveling  at its ordinary speed for  half an
hour, passes in the eye  only  over one-twelfth of an inch, yet is
this change of place in the image distinctly perceived through-
out the  whole progress;  for  it is only by means of that per-
ception  that the motion of the coach  itself is made sensible to
the eye.  If any thing can abate our admiration of the small-
ness of this visual  tablet, compared with the  extent of vision,
it is the reflection which the  view of nature leads us every hour
to make, viz :  that in the hands of  the Creator, great and little
are nothing."
   469.  Many of our impressions in regard to  motion, as we
look at  objects, are erroneous.  When we are moving ourselves,
for example, stationary objects appear to  move.  As we  ride
rapidly, the objects  that we see  seem  to  fly by us.   This is
especially the  case, if the  motion to which we are subjected be
an even one, as when we ride in a rail-road car.  And if we
look at  distant and  near objects at  the same time, while  the
near objects seem to fly back, the distant seem to go along with
us.  This is owing to their  relative change of position, as  can
be made clear by Fig. 176.  Suppose that  when  at a you  see

                          FIG. 176.
 
314
HUMAN PHYSIOLOGY.
        Rapidity of succession of images on the retina.  How measured.

two objects, c and d, in the same direction.  If you pass rap-
idly to b, the object c appears to have moved backward in rela-
tion to the object, d, while the object, d, appears to have moved
forward in relation to c ;  and the line, d, e, represents the rela-
tive change of positions in the images of the two objects  upon
the retina.
   470.  As every object  that we see is daguerreotyped, as we
may say,  upon  the  retina, the  rapidity with which these pic-
tures change, and the distinctness with which the nerves trans-
mit impressions from  them  to the brain, are very wonderful.
The time required for each  transmission is very small—only the
fraction of  a second.  The  length of time  has been estimated
by experiment.  Thus, if it is found that a burning coal, whirl-
ing around at the rate of six  times in a second, produces a
continuous circle of light, but that the circle  is broken when it
whirls  round  only  five times in a  second, we  know that the
length of time required for a  distinct and  separate  impression
is  the  one-fifth of  a  second.   The same experiment  can be
tried with a wheel.   In this case we observe what is the largest
number of revolutions in a second, that  can be  made without
blending the  visual impressions of the  spokes into one con-
tinuous impression.  By such experiments, it has  been found
that the time required for a distinct visual  impression varies in
different individuals, and in the same  individual at different
times, from  one-fourth to one-tenth of a second.   This differ-
ence in the rapidity of succession of the impressions is of course
not owing to any difference in the rapidity  of the formation of
the images; for they are formed by  the light, and light always
moves  with the same velocity.  It must be  owing manifestly to
a  difference of facility on  the part of the mind, in receiving
impressions from the images.   In other words, the mental  ac-
tivity in the use of the optical  instruments, the  eyes, differs in
different individuals, and in  the same  individual  at different
times.   If one sees more quickly than another, it is a  mental
quickness.   It is a difference  analogous to that which we see in
relation to the use of other instruments of  the mind, the  mus-
cles for example.   Some use  these instruments much  more
readily and rapidly than others.  We see  this in the motions
of the eyes themselves, and the  eyelids also.   Some wink more
quickly than others, and there was wisdom  in  the decision of
the blacksmith who dismissed a workman,  because  he did not
wink quick enough, and  was  therefore always getting sparks in
his eyes. 
THE EYE.                     315
         Thaumatrope.  Defenses of the eye.  Bones.  Cushion of fat.

  471.  The blending  of  impressions in vision, produced by
rapid motion, has  been made use of in the contrivance of an
amusing optical toy, called the Thaumatrope.  In making  this,
you cut a circular card, and  make two different figures  on its
two sides.   If you attach two silken strings to opposite points
in its diameter, and  then twist  the strings, so  that when  the
card is left to go free, it will  revolve with considerable rapidity,
the two figures will  be mingled  together  as seen by the  eye.
In Figs. 177 and 178, are represented the two sides of  a card,
FIG. 177.                            FIG-  178.
prepared in this way.  In this case, the figures as they mingle
together appear to the eye as a cross.   If a  bird  be drawn on
one side of the card, and a cage on the other, the mingling of
the two figures, as the card revolves, will show you the bird in
the cage.
  There are many other points in regard to the phenomena of
vision, which it would be interesting to notice.  But it would
make this chapter too long.
  472. The means by which so delicate an  organ as the eye
is protected  from injury, are worthy of notice.   Observe first
its  situation.   Parapets of  bone surround it,  and receive the
force of  most of the  blows that come upon that part of the
face.   Above  is the  strong  arch of bone,  forming  the  lower
part of the forehead.  Then there are the cheek bones, and the
bones  of the nose.   Thus, walled  in, in  all directions by these
prominences, the eye is seldom hurt, except by a direct  thrust.
And besides  being  thus protected by surrounding  bones, it re-
poses  upon  a soft  cushion of fat, which yields, if the eye be
pushed backward by violence.  Indeed it is thus pushed back-
ward effectually by the muscle that closes the eyelids, whenever
an impending blow is seen, and it is thus sunk farther back m
its cushioned" recess, amid the projectingparapets, and of course
receives less of the force of the blow  than it otherwise would.
This  muscle,  also,  by its instantaneous  action, prevents  many 
316              HUMAN PHYSIOLOGY.
       Eye defended by the eyebrows, eyelashes, and lids.  The tears wash it.

light articles from flying into the eye.  Such articles  are  also
often prevented from  entering the eye, by being  intercepted by
the  eyelashes.   The  eyebrow, beside being  an ornament,  pro-
tects the  eye from harm, by preventing the  salt perspiration
from running down into the eye, and irritating it.   It acts  as a
thatched roof, projecting from the arch over the eye, and letting
the perspiration from  the  forehead evaporate from it, when it
is small in amount, or drop from it down upon the cheek, when
it is abundant.   The  eyelashes also serve to keep the perspira-
tion of the eyelids from entering the eye.  The structure of the
eyelids is  such, that  the freest  motion  is allowed, while  they
afford by their  firmness considerable protection  to the organ.
They derive their firmness from  a fibrous cartilage, which makes
the body of  each  lid.   You can readily see that this  cartilage,
making an even pressure on the surface  of the eye, must often
prove an effectual  defense against direct thrusts.  If the weapon
hit this cartilage,  it acts as a firm shield, to ward off the blow
from the eye behind it.  And  even that part of the lid which
is intended by  its  laxness to allow free  motion to the lid, the
skin, is often an  effectual  defense.   If  an impending  blow be
seen, and  the  eye be instantaneously  and  forcibly shut, the
wrinkled skin forms a soft cushion  over  the  eye, and thus  not
only covers it up, but serves materially to deaden  the force of
the blow.
  473. The  tear  apparatus
affords the  eye   material              FIG- 179-
protection. The bland tears
keep  the  organ  properly
lubricated, so that its con-
stant motions  occasion no
irritation.   And if  any thing
gets into the eye,  the tears
are  manufactured abund-
antly,  for  the   purpose of
washing out the  intruding
substance, which is generally
effected.    Fishes  have no
need of a tear  apparatus, as
their eyes  are  washed con-
stantly by the  water in
which they  live.   In  Fig.
179  is represented the tear-                         e
apparatus.   The tears are          tear  apparatus.
 
                        THE EYE.                     317
                 Tear apparatus.  Oiling the eyelashes.

secreted by a small gland, called  the lachrymal gland, situated
at a, in the orbit under the arch of the forehead, and near the
outer angle of the eye.   At b are the  ducts which empty the
tears in upon the surface of the eye on the inside of the upper
lid.  By the constant motions of the organ the tears are diffused
over its whole surface, and thus continually wash the eye.  The
arrangement for carrying off the fluid is this.   It flows through
a tube, d, e, into the nose.  This  tube has at its beginning in
the eye two branches, c, c, which open on the edges of the two
lids at the inner corner of the eye.  These  open mouths, that
drink up  the tears as they flow to them, you can very readily
see.   The drain of the eye, which thus conveys the lachrymal
fluid to the nose, is ordinarily capable of taking  care of all the
tears that the  gland makes.  But when an uncommon amount
is made,  as in weeping, it cannot receive all the tears, and they
therefore overflow their banks, the edges of the  eyelids.  And
sometimes there is a constant overflow from obstruction of the
drain by disease.  The continual weeping of the eye, when this
obstruction exists, will give you some idea of the amount of fluid
which the lachrymal glands make.
   474. Along on the edge of each eyelid are some very small
glands which secrete an oily substance.  This serves two pur-
poses.   It oils  the eyelashes.   It also prevents the tears, when
they are  only in  ordinary quantity, from being diffused over
the edges of the  eyelids in  the constant motions of  the eye.
This exceedingly  small quantity  of oily  substance  suffices to
keep  the tears  in  the  eye where they are  needed.  There  is
also a curious provision for directing the tears
to the mouths of the ducts when the lids are
closed.   When  brought together their edges
unite in such a manner as  to  form with the
surface of the eye a triangular channel for the
tears to run in.   This is made  clear by the
diagram  in Fig.  180, in which the line b rep-  a<[
resents the surface of the eye, and a the edges
of the lids, showing a section of the canal be-
tween them.
   475. I had  intended to notice some of the
peculiarities of the eyes of  different classes of
animals,  but this  chapter  is already so long  that I will notice
but  one — the  nictitating  membrane in the eyes  of birds.
When not in use it is gathered  up in the inner corner of the
eye.   When it is stretched over  the  organ it is a thin translu-
                            27*
 
318
HUMAN PHYSIOLOGY.
                Nictitating membrane in the eyes of birds.

cent membrane.  It is very elastic, so that
as soon as the  muscles that sweep it so
quickly over the eye are  relaxed, it flies
back  at once  to the  corner where it is so
snugly folded.   In Fig. 181 it is represented
as half way over the front of the  eye.  In
Fig. 182 are seen  the  curiously  arranged
muscles that move it.   One of the muscles,
g, arises from the ball of the eye at its up-
per part, and running back forms  by the
trunk of the optic  nerve  a  tendon with a
loop, through which the tendon of the other
muscle, p, works.  This muscle  arises from
the lower  part of the ball of the eye, op-
posite to the origin of the first muscle.  Its
tendon, t, is fastened into  the edge  of the
nictitating  membrane.  It  acts  through
the loop as a pulley, and you can see that
the muscle, g, assists it materially in effecting
the very quick motions of  the membrane.
                  CHAPTER  XVII.

            CONNECTION OF THE MIND AND THE BODY.

  476.  In the Chapter on the Nervous System I gave you a
general  view of its functions and its arrangements.  You saw
that it is to the mind the grand  means of communication with
the world of material and immaterial things around it.  In the
Chapters on the Senses and the Organs of Locomotion, we have
considered the modes in which this communication is maintained,
through organs subordinate to the nervous system.  And you
have  seen that through  the senses all knowledge of external
things is  communicated  to the  mind, where  it  is used as the
material of thought and  reflection and feeling; while, on the
other hand, through the  muscles the mind produces all its im-
pressions  upon  the things and beings on which it acts.  You
FIG. 181.
FIG. 182.
 
      CONNECTION OF  THE MIND  AND THE  BODY.   319
          The brain the organ of the mind.  Facts which prove this.

are now therefore  prepared to look more  thoroughly into the
connection which  the  nervous system establishes between the
mind and the body, and to observe some of the higher and more
intricate  phenomena which result from it.   It is  to views upon
these points that I shall  devote this and the following chapter.
   477. The brain is the organ of the  mind.  In this life there
can be no mental  manifestations except through  the agency of
this organ.  The mind and the brain always act together as one
thing.  This is manifest in regard to motion and  sensation.   It
is  equally  true  of thought.   The  mind can think and excite
motion in the muscles only through the brain.   The proofs of
this are various  and abundant.   If a man by a blow upon his
head  have a portion of the skull driven in upon the brain, so  as
to press upon it considerably, all sensation and power  of motion
are suspended.   His mental  connection with the world around
him is completely cut  off.  And  not only so, but all mental ac-
tion is arrested.   The  mind, thus shut in from the world around
by the suspension of sensation, does not go  on to act indepen-
dently of the compressed brain.  The man does not think; for
if thinking did occur in such cases,  there would occasionally be,
as after dreaming, some recollection of what passed through the
mind, after the pressure is taken off from the brain by the tre-
phine and elevator of the surgeon.  He lives, because  the invol-
untary muscles,  connected by their nerves with the top of the
spinal marrow, (§  229,) which is uninjured, carry on the breath-
ing and the circulation.  But  though  he lives, he is not now a
moving,  or a  sentient, or  a  thinking  being.  His  mind is  as
dormant as life is in a  state of hibernation.
   478. The same state of things occurs in apoplexy, and in the
senseless state which  accompanies  most convulsions.   And  it
may  be  remarked, that  the  degree of the suspension  of the
mental functions depends  upon  the degree of effect  produced
upon  the  brain.  If,  for example, in the case of injury, the
pressure of the bone driven in  upon the brain be not very great,
the suspension will be  partial;  but if the pressure be considera-
ble the suspension will be complete.
   479. The dependence of the  mind upon the brain is mani-
fested in  a great variety of diseases.  The delirium of fever and
of inflammation of the  brain, and insanity resulting from chronic
disease in  this  organ,  show this  absolute and inseparable con-
nection of the mind with the material organization in our present
state of being.   We sometimes see the mind gradually blotted
out by the progress of disease in the brain, so that a man of 
320
HUMAN PHYSIOLOGY.
         Insanity a disease of the organization. Situation of the brain.

even high  mental powers  becomes a drivelling idiot.  So, too,
a  bad formation of the brain,  or early  disease of  this organ
often prevents mental development.  Insanity is always the re-
sult of disease  in  the organization.  This is so even when it is
produced by moral causes  acting directly upon the mind.   The
insanity in such  a case is an indirect effect—the organization
affected by the  mind is thrown into a diseased state and reacts
upon the mind, influencing  its manifestations.  " If the  mind
thus acted upon were a spirit, separated from the body, the
result would  be merely the feelings, which the motives applied
would naturally produce, and not the  unnatural feelings of
insanity.  It is  not strictly proper then  to speak of  a ' mind
diseased.'  Let  me not be understood to mean that  mental de-
rangement in every case is to be attributed to disease  that leaves
such palpable traces, that the dissecting knife would  reveal it if
death were to take place.  There  are diseased  operations of the
body, that are hidden from our view—so hidden, that they not
only leave no traces, but often develop no characteristic bodily
symptoms."*  I shall recur to this subject of the dependence
of the mind upon the  brain in another part of this chapter, and
shall endeavor to point out definitely what are the teachings of
physiology, of our consciousness, and of revelation respectively
in regard to it.
   480.  Observe for a moment the situation and the  immediate
connections of the brain, the organ of the mind.   Its situation
in the human structure is appropriately a commanding one.   It
is fitly placed at the summit of the structure,  inclosed by that
noble dome which I described  to you in the Chapter on the
Bones.   And then observe that in its immediate neighborhood
are the  organs of four of the  senses, sending their messages
continually to the mind.  Especially you notice that under the
jutting  arches  of the front  of  the dome are the ever-moving
eyes, looking out from their elevated place of observation ; and
at the sides of the base of the dome are the halls of audience,
ever open and ready to transmit the messages  that come to the
soul through the  vibrations  of the air.   And  there,  too, in the
very front of this habitation of the mind is the face, indicating
by the delicate, quickly changing play of its muscles the thoughts
that are at work within.  And  lastly, there is the mouth, the
outlet for the voice, the  chief agent of the outward  manifesta-
tions of the  mind.  Here then are clustered  together in this

                  * "Physician and Patient," page 292. 
      CONNECTION  OP  THE MIND AND THE BODY.   321
         Rapidity of communication between the mind and the body.

small space, in the immediate neighborhood of the mind's hab-
itation,  its principal instruments of communication  with the
world around.   When we  are listening to eloquence, whether
it be in the  public assembly, or in  the social circle, or in- the
more private intercourse of friendship, and observe, as the rich
tones proceed from the mouth, the  elevated and changeful ex-
pressions of  the countenance, we are impressed with the idea,
that, if it be the  mind which constitutes the image of God in
man, the face of man  thus situated in the front of the mind's
habitation, is the fitting outward emblem of that image.
   481. It is interesting  to observe how exceedingly  rapid are
the communications  of the mind with the different parts of the
body.   Notice what the  process is,  or rather what the processes
are, when you withdraw your hand  from any thing that hurts it,
as heat for example.  An  impression is produced upon the ex-
panded nerve in the part—this  impression  is sent along the
nervous tubuli  to the brain—the  mind there receives the im-
pression—the mind in return  communicates an  impression to
the brain—this  impression goes by  another set of nervous tubuli
to the  muscles—they act, and the hand is  withdrawn.   If it
took  as long to do all  this as it has for me to describe  it, the
hand would be very thoroughly burned before it is drawn away.
The same set of processes is gone  through  with, when in ex-
ecuting music, either with the voice or an  instrument, a mis-
take  is immediately heard  and corrected.  And so of  other
cases.
   482. In the Chapter on the Muscles I spoke of the great va-
riety in the motions of the body.  In executing these motions
the  individual  commonly  knows nothing of the muscles with
which he does it.  Even the anatomist, who is familiar with the
situation  and arrangement of the muscles,  seldom  thinks of
them while he works them in  the  production of different mo-
tions ; and if he does think of them it affords him no  assistance
in their use.  Great skill can be  acquired  in the use of the
muscles, without any knowledge in the individual of the fact that
he has such organs.   In muscular  action men commonly  move
a machinery of  which they know nothing.   They have only to
will any particular motion, and  the nerves  are so  arranged at
one  end with the muscular fibres  that will do it, and with the
brain  at  the other, that the message from the mind goes to
exactly the right  fibres,  and the result is produced.^  For the
infinite variations of motion in the  body what complicated and
intricate arrangements are needed!  These  variations, it is  to 
322              HUMAN PHYSIOLOGY.
           Skill in the use of the muscles.  Variety in their action.

be  remembered, do not result  merely from  combinations of
movements, but are  rendered  vastly more extensive  from the
varying degrees of contraction in the muscles.   If each muscle
always acted just  so much  and no more, there would be even
in that case  great variety of motion, from  its combination in
various ways  with  other muscles.  But the variety is made to
be endless from the endless variation in the degree of  their con-
traction.   And for each one of these variations, both  in degree
and combination of  action, there must be a different message
sent from  the  mind  along  the  nerves.   In every motion the
muscles that produce it must, so to speak, be  told to act, and not
only so, but they must be told just how far to  act.  In motions
that are very compound, and at the same time exceedingly del-
icate  in  their  variation, the accuracy and variety of the mes-
sages thus sent from the brain along the  nerves are not only
wonderful,  but are beyond  our conception.  We realize this
fully, when with the views above expressed in  the  mind, we
watch a skillful balancer, as he executes his endlessly varied but
exact movements.   So, too, when we hear from Ole Bull's one
violin such a mingling of sounds, that we feel  that there must
be a half a dozen violins played upon at once, how inconceivably
rapid and numerous and complicated must be the messages that
fly from his brain along the nerves to the muscles, and yet there
is not a failure in one of them—not a fibre that does not con-
tract at the right moment, and in the right  degree!
  483.  The use which the mind makes of all the machinery of
the senses and of the organs of  locomotion  does not come to it
at the outset.   It comes by training, and in some cases by very
long training.  The  child at first uses its  muscles bunglingly.
It does not see or hear skillfully.   It knows nothing at the first
of the colors, or shapes, or distances of objects.  It knows nothing
of the direction or distance of sounds.   It  has all these things
to learn.  And for  this purpose the  organs  of sense and the
muscles are put into exercise at once, and the child begins its
long process of learning on the day of its birth.   Few have any
conception of the  amount of knowledge which is acquired in
the first of the child's life.   He is born not only with  absolutely
no  knowledge of the world  of things  around him, but he has
no  skill  in the use of the instruments, the  muscles and the
senses, by which he is to  obtain  his  knowledge.  These give
him at first no very definite information; but  by the constant
exercise of them, and by comparisons between the reports of
the different  senses he soon adds rapidly to  his stock  of knowl- 
      CONNECTION OF  THE MIND AND THE BODY.   323
      Learning to use the muscles. Their action at first aimless and awkward.

edge, and becomes skillful in the use of his means of gathering
it.  But let us see a little more particularly how this is done.
  484.  I will speak first of the progress of the child in learning
how to  use his muscles.   When he first  puts them into action
you see that  he has no skill in using them.  The action is aim-
less and awkward.  You see in his movements none  of  that
native grace  of which so much is said.   This is to be acquired,
and all  that is native  about it is the power of acquiring it.   He
learns to execute very many motions  before he comes to that
complicated  movement of so many muscles, creeping, and  then
the no less complicated  but more  difficult one  of walking suc-
ceeds.  How awkwardly he  does  this  in his first  attempts to
preserve his balance,  and how many failures must he encounter
before he can perform this  motion even  decently well!  The
same thing can  be said of learning to talk or to sing, for this is
but a training of the  muscles.  It is thus gradually that all the
voluntary muscles become educated.   It is true  even of the
muscles of the face.  At the first  how expressionless ordinarily
is the face of a child.  You  see nothing of those delicate move-
ments of the muscles which  in after years express every varying
shade of thought and feeling.  When he cries there is an  awk-
ward over action of the muscles,  as  represented  in Fig. 183.
FIG. 183.
He learns to use these muscles  partly at least, by imitation.
His first lesson ordinarily is in smiling, which he soon learns
by imitating the smile of his  mother.  But even this, simple 
324              HUMAN PHYSIOLOGY.
  Skill in the use of the senses and the muscles. Comes later in man than in animals.

as it is, he does awkwardly at first, and he must go through a
long process before he  can master all the capabilities of ex-
pression in these  little "muscles.
   485. Skill in the use of-the muscles varies quite  as much as
any other acquirement in different individuals.  It is wonderful
in the juggler, the rope dancer, the skillful player on a musical
instrument, and the accomplished singer.   You will have some
conception of  what education can do for the muscles, if vou
contrast the awkward  balancing of the child in walking with
the agile  and delicate  balancings of  the  rope  dancer, or the
aimless and uncouth movements of the infant's hands with the
rapid and varied  execution of the player on an instrument, or
the monotonous  and coarse sounds uttered in  a child's first
attempts at singing with the varied melody of a  skillful singer.
   486. The senses are  educated as well as the  muscles.  As
you see an infant reaching  out his little hands awkwardly with
his unskilled muscles towards an object, it is manifest that he
knows not at what distance the object is  from  him, and that
he does not readily adjust  his eyes to its distance, so as to see
it clearly.    He after a while by practice acquires the power of
doing  this.  The  same may be said  of  hearing.  The little
muscles which I  described to you as so nicely adjusting the
eye for seeing at  different  distances, and  the ear for  hearing
various notes of sound, require training, just as the muscles do
with which  we walk or talk.
   487. It is a singular fact that most  other animals are born
with so much more skill  in  the use of  the muscles and the
senses  than  man.   While man is " in the  nurse's arms," the
chicken, for example, walks about as soon  as  it is  hatched.
He does it at first awkwardly, it is true, but he soon learns all
that is to  be learned about it.   He is assisted materially, it is
to be remarked, by the fact that  his  feet  spread  out over so
large a space, that he has no hard lessons to learn in balancing
as the  child has.   But this is evidently not all the difference.
If it were, the child should  be able to creep at the first, or even
walk on its  hands and feet, for  in  performing these motions
there is no difficulty in supporting the  centre of  gravity.   The
same s difference  exists  also in  regard to the  senses, for  the
chicken seems to understand distances at  once.   As it runs
about to pick up  its food it makes no mistakes on this score.
But while man is thus at the first the most helpless of animals,
in regard  to both his muscles and his senses, by his process of
learning he ultimately  acquires vastly greater  range  and va- 
     CONNECTION OF THE MIND AND  THE  BODY.  325
          The senses and the muscles mutual teachers.  Exemplified.

riety of motion than other animals.   And  the same thing can
be said of his acquirements through the senses.
  488. The  senses and the  muscles are  mutual  teachers in
this education which  I have described.  Thus, in singing, the
accuracy of the  sense of hearing in estimating  sounds is ac-
quired through  the action of the muscles of the voice while
the ear is listening.   And on the other hand, skill in executing
sounds is acquired by these muscles under the  tuition of the
ear.   The dependence of the  senses upon the muscles is not as
absolute,  however, as that of the  muscles  upon the senses.
The ear can be trained in the accurate appreciation of sounds
without  any corresponding  exercise  of the muscles of the
voice, though the two processes are ordinarily to a greater or
less extent connected, and are  corrective of each other.   But
even  when the  ear is trained  without any aid from the mus-
cles of the voice, the training is  in  some  measure a train-
ing  of muscles.  For, as you  saw in the Chapter on the Ear,
§ 415, there are certain little muscles that regulate the tension
of the drum of  the ear, which undoubtedly go through a pro-
cess of training when we are learning to distinguish accurately
between different notes of sound.   While the dependence of
the senses upon  the  muscles is thus a partial one, the depen-
dence of the muscles'upon  the senses is, on the other hand,
complete.   Although  the  muscles  have a sense of their own,
a muscular sense, as  Bell  calls it,  this is  not adequate  to be
their sole guide in action, but it serves as a mere auxiliary in
this respect.  This absolute dependence of  the muscles upon
the  senses is very strikingly shown in the fact, that the deaf
and dumb are dumb  simply because they are deaf.   The voice
in them has no  teacher.   The  muscles which regulate the ten-
sion of the vocal ligaments,  and  those which  articulate the
voice do not act, because, as stated in the Chapter on the Voice,
§ 400, they have no guide in their action.
   489. Although I have spoken of the education of the mus-
cles and  the senses, this language is not strictly correct.  For
the education is an education of the mind that operates through
these muscles and senses.  It is the  training of the mind in
the  use  of these instruments.   This  is very clearly shown in
cases of idiocy.   In  these cases the defect in talking is pro-
portioned to the mental deficiency.  It  arises  from an inca-
pacity on  the part of the  mind  in using  its instruments, the
muscles  and the apparatus of the senses, and  not from any
defect in the construction of  these instruments.  The larynx
                              28 
326              HUMAN PHYSIOLOGY.
              The involuntary muscles not educated.  Why,

and the articulating  organs of the voice are perfectly  well
formed in the idiot, as I have stated that they are in the deaf
mute.   While, in the case of the deaf  mute they are not used
at all as vocal organs, because  the mind, through the absence
of hearing, has  no power of regulating them; in the case of
the idiot they are  used to a  limited extent, and in a very
bungling manner, because the capability of regulating them is
limited  by the deficiency of the directing intellect.  And what
I have said of the muscles of the voice in  the idiot is equally
true of  the  muscles of the face.  There is no defect of  con-
formation, nor  is there any  lack  of lustre in  the eye,  as  is
commonly supposed.   The limited range of expression and its
awkwardness  arise from an incapability on the part of the
mind of using the muscles of expression with facility and skill.
The muscles have an  incompetent teacher, and so learn to do
but  little, and  do that little bunglingly;  or, to speak more
correctly, the deficient mind is not capable of learning to use
them properly.
   490.  The education of the muscles does not extend to those
which are involuntary.  Though respiration, for example, is a
very complicated act of many muscles, these  muscles require
no education to do their part skillfully.  We have no need to
superintend them, for their constant  action is secured by an
arrangement for nervous influence which is independent of the
mind, as stated in  the Chapter on the Nervous System.  So,
while the mind sleeps, or when it is locked up  in the stupor
of disease, these muscles continue to  perform their  duty, as
well as  when we are  awake.   The same substantially can be
said of the muscles which perform  the act of swallowing.  Al-
though this  is a very compound, and, mechanically considered,
a very difficult act, as shown in the Chapter on Digestion, § 78,
it is performed  as well in the first hour of the child's life as it
is at any future  period.  The muscles  that  execute it need no
training.  And  yet it is only after long and diligent training
that the purely voluntary muscles,  as for example those of the
hand, execute movements which are no more complicated and
difficult.   The reason for this difference is obvious.  The move-
ments which are performed by the involuntary muscles, such
as breathing and swallowing, are  immediately essential to the
preservation  of life,  and it is therefore necessary that  they
should be well executed from the first.   Their perfect action is
therefore secured by a nervous arrangement, which is indepen-
dent of  the mind.   The voluntary  muscles, on  the other hand, 
      CONNECTION OF  THE MIND  AND THE BODY.   327
          Association of action in the muscles without mental action.

instead of being devoted, like the involuntary, to the main-
tenance of life, act as the instruments of the mind, and there-
fore the mind acquires  the  power of using them  skillfully by
dint of long-continued training.
   491. In the education of the muscles, it is  to be observed,
that although during the  process of learning  the mind takes
distinct cognizance  at first of every movement, it after a while,
as the education becomes complete, takes little or no notice of
many of the movements, except  when some  error occurs, or
some obstacle arises.  Thus,  when  one is learning to sing or
play a tune, the mind at first through the ear takes a definite
and distinct notice of every sound, and makes a palpable ex-
ertion in every movement.  »But  after the tune is learned, this
ceases to be the case, and the movements seem to be associated
together, iQ some measure independently of mental  action.  So
in learning to walk the  child notices each of his  movements
very  distinctly.  But  when he  has  fully learned, but  little
thought seems to be expended upon the motions, except when
some obstacle appears which interrupts their regular succession.
When one walks in a reverie, the mind is most  of the time
wholly abstracted from the associated movements which make
up the compound  act of  walking.   In learning to read the
child makes a distinct mental effort in regard to  each letter,
resorting  to  every  aid which will help to make  the effort a
successful one, even to the putting the finger on each letter as
he looks  along  the line.  But as he becomes more and more
skilled, the association of action of which I have spoken comes
more and more into play.  I will refer you to a partial expla-
nation of the facts above alluded  to, given  in  §  262, in the
Chapter on the Nervous  System.
   492. It has been stated in § 325 and § 476 that the mind
receives  impressions  only through the senses, and  imparts
them only through  the muscles.   These act as the  instruments
of the nervous  system,  the  senses being the inlets  and the
muscles the outlets of communication.  And it has been gen-
erally considered as a settled point,  that these are  the sole
channels through which the interchange of thought  and feeling
is  effected in our  present state of  being.  But it has been pre-
tended that other mysterious modes of communication have in
these latter days of progress been discovered.  The  phenomena
presented  by animal magnetism, as it is called, are  claimed by
some to demonstrate, that there  is in some cases a peculiar
means of communication, distinct  from those which  are usually 
328              HUMAN  PHYSIOLOGY.
               Animal magnetism.  Simple tests expose it.

employed.   It has  been fancied  that something analogous to
magnetism is the medium  of connection in  such cases, and
hence the name of animal magnetism.   Through this medium,
it is asserted, that thoughts and sensations pass from one person
to another, independent for the most part at least, of the ordi-
nary conditions on which communication  depends.  The phe-
nomena have been presented at different times under different
phases,  and the  theory framed  to  account  for them varies
somewhat from  time to time, according to the  varying char-
acter of the phenomena, and  the tastes and  imaginations of
the believers in this so called science.  Amid all the  various
forms which it. has  thus assumed, with its corresponding di-
versity of names, one thing has  always been true of it,  viz.,
that whenever any efficient tests have been applied, it is shown
to be a large superstructure of falsities built upon a very few
facts.   And in view of the uniform  results of these tests, we
may confidently say, that as yet there has been no satisfactory
proof, that there  are any other channels of mental communi-
cation, than the ordinary ones furnished by the senses and the
muscles.   Most minds are bewildered by the strange, and some-
times  inexplicable  things, which appear in  the exhibitions
which they witness, and  are ready to adopt any plausible ex-
planation which may be offered.   But some simple yet  search-
ing tests have thus far, whenever applied, always sufficed to
expose the delusion.
  493. In illustration of  the  manner in which these tests de-
molish the  lofty  pretensions  of this  so  called  science, I  will
give a single example.   The exhibitor asserted that  whatever
was in his mind, realized  distinctly and vividly,  had  its image
in the mind of the  subject whom he magnetized, by  means of
the peculiar connection thus established between them.  Any
decided sensation, therefore, which he felt, the subject felt also;
and if he fixed his thoughts upon any thing, the subject thought
of the same thing.   I observed that whatever was said by the
subject, in relation to any sensations or thoughts in the opera-
tor, was generally  in reply to questions on the part of the
operator himself.  And  as  these questions were sometimes
repeated in various  forms before correct answers could be ob-
tained, I suspected that the information requisite for the answers
was communicated  to the subject in this way.   I,  therefore,
proposed to  the  exhibitor to  try some  experiments without
questions, as these,  according  to  his theory, were clearly  not
necessary;  for, if there were such a channel of communication 
CONNECTION OF THE  MIND AND  THE BODY.   329
Mental phenomena of animal magnetism.
between his  mind  and that of his subject as he asserted, the
aid of the voice was not required.   The proposition was man-
ifestly so fair an one that he could not refuse to comply with
it.  But his experiments performed in this way failed altogether,
and the audience, caring less for a strict search for truth than
for the continuance of their amusement, showed  little relish
for the  interruption, and the pseudo-scientific exhibition went
on.   I  applied other tests as I had opportunity, which developed
the evidence of imposture here and there in the exhibition, and
though many sober and intelligent citizens were deluded with
the belief that they had enjoyed a rational  and truly scientific
amusement,  I  had no  doubt that the whole  was a piece of
jugglery.  There was  one feature in the exhibition, which of
itself was enough to condemn it as a ridiculous imposture.  The
operator  claimed to have  a sort of absolute control over the
 subject, so that at will he could hold him in a  connection with
 himself so insulated that no impressions could  be imparted to
 him by any  other  person, and yet could dissolve this connection
 and put him into connection with  some one else, with as much
 facility as a  locomotive can be switched off from one track on to
 another.   And ridiculous as this shifting of mental connections
 is, this was  quite  as successful with the audience as any part
 of the  exhibition.                                ■,•,■•     <?
    494. Some  of the phenomena presented in the exhibitions ot
 animal magnetism afford interesting illustrations  of the influ-
 ence exerted upon  the  body through  the  mind.  The mental
 influence, exerted by the operator upon his subject, often causes
 a condition of the  nervous  system, which is analogous to som-
 nambulism, or to  some of  the forms of hysteria.  The manip-
 ulations  practiced, the looking the subject intently in the eye,
 the holdino- of a piece of metal in the hand with  the eye fixed
 upon it,  and other expedients, help to  produce the impression
 in the mind of the subject, that a mysterious  and resistless in-
 fluence is coming  from the operator upon  him, and is stealing
 over his system.  It  is not strange  that this  should occasion
 such physical results  as we often see, when the  mind and the
 nerves are very susceptible.  This is the simple explanation of
  all that is positive in what such exhibitions present to us.  1 here
  is no such thing as a magnetic influence, and animal magnetism
 is a misnomer.                                    .
    495 The state  of nervous  system often  produced is not in-
  consistent with imposture any  more than hysteria is.  As in the
  nervous states exhibited by this  disease there is often a strange
                             28* 
330              HUMAN PHYSIOLOGY.
               Alliance to hysteria.  Suggestive influences.

perversion of the moral mingled with that of the  physical, so
there is also in the state  produced by the mental  influence of
the magnetizer.  Accordingly his most available  subjects  are
women found here and there in every community, who, through
this  mingled moral and  physical perversion, have acquired a
permanently morbid state of mind, that makes them like to be
thus petted, and to be the wonder of a  gaping multitude.   There
is often in the exhibitions of animal  magnetism self-imposition
at the same time that  there is imposition upon others.   In  the
case of travelling exhibitors there has  always  been collusion
enough to stamp the character of jugglery upon the exhibition.
And  in  other  cases, where both  the operator and the subject
are honest, there  is delusion in both, and they impose not only
upon themselves, but upon  each other, as well  as  upon  those
that witness the performance.
   496.  One of the peculiarities of the state of  somnambulism
which is  induced by the magnetizer,  is the ready obedience of
the mind of the  subject to suggestive  influences.  It is  alive to
any suggestions which come  from the mind to which it supposes
itself bound by a magnetic spell, and  is often in fact shut up to
influences from that source alone, so  as to be insensible to in-
fluences from any other quarter.   The somnambule  is possessed
with one idea, and  that an  all-absorbing one, because invested
with such mystery.  His insensibility to all that  is not in ac-
cordance with this  idea is to be accounted for in the same way
that we  account  for the fact, that a wound  received in battle
is often unfelt till the excitement of the battle is over, and other
similar facts, as alluded to in  § 226.  This state is often quite
successfully imitated by impostors; and sometimes there is a
mixture of a partial real somnambulism with imposture, similar
to that which occurs in the case of  the  hysterical condition.
Of course when this mental connection is so easily shifted from
the operator to bystanders as was described in § 493, there must
be sheer imposture.  Whether there be full somnambulism alone,
or this in a partial degree and  mingled with deception, the in-
fluence of the principle of suggestion is very apparent. Nothing
can  be  done without  questions.   Leading  questions  suggest
ideas to  the mind of the subject, and an  audience led on by
love  of the marvellous and the exciting, are readily satisfied by
the coincidences that occur in the exhibition, while the failures
are disregarded and forgotten.
  497. In the  state of somnambulism induced artificially by
the so-called magnetizer, as well as  in that which  occurs from 
      CONNECTION OF  THE MIND AND THE BODY.  331
  Clairvoyance a false pretension.  Little thnt is true in so called animal magnetism.

other causes, there is  often an exaltation of the  powers of the
senses.   Thus, sometimes a somnambule can read  through en-
velopes  of even  many thicknesses, from  an exaltation of the
sense of vision.*   But all pretensions to reading through bodies
that have no pores or interstices, as metallic substances, or to
reading from other parts  of the body, as the pit of the stomach,
or the back of the head, are  impostures.   So  too are  all the
pretensions to seeing what is going on in other places, or inside
of the  body.  This clairvoyance, as it is called, has  precisely
the same claim upon our  confidence that  fortune telling has,
and no more.   Real  searching tests have always sufficed to ex-
pose its imposture.
   498.  I have introduced the above views of what is generally
called animal magnetism, in order that  you may be prepared to
apply the  proper tests, whenever such  popular  delusions claim
your  confidence.   I have  introduced them, also, because, what-
ever real phenomena do appear in the  exhibitions presented to
us under this name, afford some  interesting illustrations of the
influence of the mind upon the body.   They add another chap-
ter to our view of the mysterious connection of the physical with
the spiritual, secured by means of that wonderful apparatus, the
nervous system.   It is from this consideration  merely that they
claim the  attention of the physiologist.  The so-called animal
magnetism, when thoroughly sifted is dissipated, and there are
left as a residuum only a few phenomena, which offer  nothing
particularly new, but are  chiefly interesting from their analogy
to phenomena with which we were already familiar.   And  its
boast of the discovery of a new medium of mental communica-
tion is, as  you have seen, entirely groundless.
   499.  In the Chapter on the Nervous System I spoke of the
different offices of the different  central organs of this  system.
The brain, as you have seen, is more especially  connected with
the mind,  and is the  great instrument through which mental

  • Many of the statements, however, of such cases, could have been found to be
false if the proper tests had been applied. The failure in testing, so common in these
cases I will exemplify by a single case, which made some noise in its time.  It is a
case reported by Col. Stone in his famous pamphlet. He gave the clairvoyant, a
sea'ed  packet with a  very odd sentence in it, which she  read, as the Colonel sup-
postd, without, opening it.  But how did he know that she did not open the packet?
Simply because she returned it  to him a clay or two after apparently in the same
state as he gave it to  her, accompanied with  a copy of the sentence contained in
it.  This he considered good proof, but it is defective in its most essential point.
If she could read the  packet without  opening it, why did she not do it in his pres-
ence 1  There is  not a particle of evidence that any one saw her do it. The true
test was an easy one, but it was not applied. There is such a thing as skill in open-
in"-seals and replacing them so as to avoid detection, and until we have proof that
thfs was not done we  are not called upon to believe that the clairvoyant read through
the envelopes. 
332
HUMAN PHYSIOLOGY.
                 Offices of the cerebrum and cerebellum.

 manifestations are made.   But it is only a certain  part of the
 brain, the cerebrum, a, Fig. 72, that has this special connection
 with the mind.   The cerebellum, b, Fig. 72,  it is supposed, is
 especially devoted to the motions of the body, for it is found in
 animals that it is developed in proportion to the range  and va-
 riety of motion.   From  extended observations on this  point in
 comparative anatomy there seems to be good reason to conclude,
 that the cerebellum is the  great central apparatus for combining
 the various compound  motions of the body.  It is uniformly
 found to be larger in those animals  that have great complica-
 tion in their muscular movements, than in those in which these
 movements are of a simple character.   Thus,  in animals whose
 most complicated  motion is walking, as the hoofed quadrupeds,
 the cerebellum is much smaller, than in those animals that climb
 and that take hold  of things with their paws.   In man it is
 much  larger than in  any other animal, for  he walks erect, and
 thus brings into action a very large number of muscles in this
 delicate  balancing  movement (for such it is),  and then, in the
 individual parts of the body, especially the hand, he executes a
 great range of very complicated movements.  It is more devel-
 oped in monkeys and apes than in any other of the  inferior
 animals, because,  with  their capability of extensive variety of
 posture, and their power of seizing objects with their extremi-
 ties, they obviously come nearer to man  than any other animal
 in the varied combination of their muscular action.
   500. The conclusions,  thus  arrived at by comparative obser-
 vations in animals have been confirmed by experiments.   It has
 been found  by physiologists, that if the cerebellum  be removed
 in an animal, with as little disturbance as possible to other parts,
 although the  sensibilities remain, and motions are  performed,
 the power of combining  muscular actions in definite compound
 movements, such as flying, walking, &c, is lost.
   501. These conclusions  have  also been to some extent con-
 firmed by observation of the phenomena of disease.  The testi-
 mony from this source, however, has not as yet been very decided
 for two reasons.   First, because disease  in the brain is not apt
 to be confined to one  portion of  the organ.  And secondly and
 chiefly, because we have not had a sufficient number of observa-
 tions of cases on this point.  It has been observed, however in
 some interesting cases of chronic disease in the cerebellum, that
deficiency in the performance of the compound movements of
the body was a prominent  symptom.   An unsteadiness of gait
was remarked in these  cases.  -The  negative testimony which 
     CONNECTION  OF  THE MIND  AND THE  BODY.   333
          CJrny part of the cerebrum proportioned to the intelligence.

disease gives us in regard to  the office of the  cerebellum is very
conclusive.  The mental phenomena of disease, when it is fast-
ened upon this particular portion of the brain, show that this is
not that part of the  organ where the thinking is  done.
   502.  It is chiefly,  as you see, by observing the different de-
velopments  of  the nervous system in various  animals, in con-
nection  with the different functions performed by this system,
that we can discover the  uses of its different parts.   In pursuing
observations of the animal kingdom in this way, we find a more
and more complicated  nervous  apparatus, as  we proceed from
the lower animals up to man.   We find part after part added,
and with  every addition of a part we find new functions.   And
as  we study any particular  part in relation  to  the functions
which appear as connected with it, we see  that these functions
are prominent  in proportion  to the amount of the development
of the part.  Thus, as before  stated, we find-the size of the
cerebellum  is in proportion to the variety and complication of
motion  in the animal,  while  that of the cerebrum is in propor-
tion to the amount of intelligence.  And  in relation  to the
cerebrum itself we find that  the amount of intelligence depends
on the amount of  its gray portion, the vesicular substance.  In
man, therefore, this  part of  the cerebrum is very much greater
than it is in any other animal.  It is the difference in the amount
of the  gray substance which constitutes the grand distinction
between the brain of man, and that of any of the higher  orders
of animals, for in all other respects his  brain  differs very little
from  theirs.
   503. In  looking at  representations of the brain, as in Fig. 74,
it would seem  at first  view that the gray substance, the working
part  of the cerebrum, is much less  in amount than the white
portion, which serves only for transmission.  But this is not so.
The eye is  deceived, because the white substance is all together
in one  central mass,  while  the gray substance is spread out in
an external layer.   This is very plainly illustrated by Fig. 184.
Here the area, a, contained in the inner circle, strikes the  eye as
being larger than the area, b, included between the two circles,
and yet these  areas  are  precisely equal.
   504. Observe for a moment in this connection the concurrent
evidence, by which  we determine what the function of the gray
substance of the  brain  is.  It comes from  two sources.   The
first is that which is furnished to us by the structure of the cere-
brum.  As stated in § 206 and §  232, the gray portion is
made up of cells, while the white portion is composed of tubuli. 
334              HUMAN PHYSIOLOGY.

           Quantity of the gray substance. Phrenology considered.
FIG. 184.
These tubuli are such as we find in the nerves, and in fact are
continuous with them.  We very properly infer, therefore, that
as the nerves serve only for transmission, the white part of the
brain does the same.   Is has,  therefore, nothing to do with the
thinking, and  yet  this we know from  other  facts, (§ 477 and
499,) is done in  some  part  of the cefebrum.   So  we  infer
necessarily that it must be done  in the  gray substance.   And
here, to confirm the  truth of this inference, comes in one other
source  of evidence, viz., the comparison between  different ani-
mals in regard to the  correspondence  between the  amount of
the gray substance and the amount of  intelligence.   This I re-
marked upon in § 502, and need not dwell upon it farther.
   505.  This dependence of the mental faculties upon the gray
substance, the outer part of the brain, seems to give some coun-
tenance to the doctrine of phrenology.   But there is no evidence
from an examination of this substance that it is arranged at all
in separate organs, as instruments or seats  of different faculties.
And all the facts which  have been collected in regard to the
external conformation, as indicating the comparative prominence
of different organs with their faculties, go to show, when properly
examined,  that the mapping out of the  brain which phrenology
does so definitely is altogether a fiction.   The question  in re-
gard to  this is wholly a  question  of evidence.  For although
we can see no division of the cortical substance into organs, yet 
CONNECTION OF THE  MIND AND THE  BODY.  335
Observations opposed to phrenology.
if the pretensions of phrenology in regard to the results of the
external  examination of heads  are well founded, we must ac-
knowledge such  divisions to exist, though even the microscope
cannot reveal to us their boundaries.
   506.  It would lead me into too long a discussion to examine
fully the evidence in regard to these pretensions of phrenology.
Besides stating the general fact, that the failures in describing
mental and moral character from external examinations of the
head are such, when  the examination is conducted  fairly,  as to
exhibit the falsity of these pretensions, I will only allude to one
or two particular facts, and  dismiss the  subject.   In the phre-
nological map of the cranium  there are  located  some half a
dozen organs along in the region  of  the eyebrows.  Now, you
will remember that  the frontal sinus extends along in this lo-
cality.   This sinus varies very much  in size in different individ-
uals.  It is obvious, therefore, that an external examination
can give us  no  accurate idea of the quantity of brain in that
locality.  Take another point.  Phrenologists have always in-
sisted that there was the most positive evidence, from examina-
tions of the head in man and in  animals, that certain faculties
 or propensities  have their  organs  in the locality where the
 cerebellum lies.   But all this mass of vaunted evidence is swept
 away by the discovery stated in § 499, that  the cerebellum is
 chiefly concerned in effecting the compound motions of the  body.
 I might go on to examine in this way the  rest of the  evidence
 adduced in favor of the  truth of  phrenology,  and show that
 there is no satisfactory evidence of the correct localization of any
 one of the  organs paraded with such definiteness on the cranial
 map of this so called science.  But it would occupy too  much
 space.
    507.  The only fact which seems to  give any  countenance to
 phrenology is that general fact, which is matter of common ob-
 servation, that the front and upper portion of the brain—that
 which occupies the forehead—is commonly developed in pro-
 portion to  the development of  the  intellect.   This would  seem
 to show that the  intellectual faculties  have their seat in this
 part of the brain.   But it is  far  from proving this  to  be so.
 For it may be, that a general  enlargement of the cerebrum  is
 for some reason accommodated  by having the forehead enlarged,
 in preference to other portions of the cranium.   For it is evident
 that a brain which is larger alike in all  its  parts than  usual,
 can, as it is a soft yielding organ, be equally well accommodated,
 whether the cranium be made of unusual size in only one direc- 
336               HUMAN PHYSIOLOGY.
             Size of the front part of the brain.  Facial angle.

tion, or in all directions.  The fact that in the child the forehead
is  more  prominent than  in  the adult, is inconsistent with the
supposition that the intellect  has its seat especially in the front
part of the brain, for  the  child has more of the instinctive and
less of the intellectual  than the  adult.   I may remark in this
connection, that the phenomena presented by injuries and by
disease in this part of the cerebrum, have  not, as  thus far ob-
served, seemed to show that it is the peculiar seat of the intel-
lectual faculties.
   508. The size of the anterior portion of the brain, above re-
ferred to, may be estimated by the  measurement of the facial
angle,  so termed,  proposed  by  Camper,  a Dutch naturalist.
This angle is formed  by drawing  two lines as  represented  in
Figures 185 and 186.  The line, a, b, is drawn from  the most
FIG. 185.                       FIG. 186.
prominent part of the forehead to  the front of the upper jaw.
The line, c, d, is intended to represent the line of the base of the
brain, and runs from the orifice of the ear along on the floor of
the cavity of the nose.   It is manifest that the less prominent
is the forehead, that is, the less brain  there is in the front part
of the head,  the more acute will the angle be that is formed by
these lines.   In Fig 186, which represents the skull of a negro,
this angle is  more acute than in the skull of the European, Fig.
185.   In  animals this facial angle is much more acute than in
man.  In the monkey tribe it varies from 65° to 30°, while in
man its average is about 75°.   The ancient Greeks, wishing to
give the aspect of great intellectual superiority to  their statues
of deities  and heroes, made it in them as high as 90°.
  509.  It is  proper to remark here, that while it is clear that,
as a general rule, the  amount of intelligence is to some extent
proportioned  to the amount of the  cerebrum, both in man and
in animals, the rule is not an  invariable one.   Size is far from 
      CONNECTION OF  THE MIND  AND THE  BODY.  337

     Mental difference between man and animals.  Little difference in the brain.

being the only measure of power in  this  case.  What differ-
ences there may be in intimate structure, to compare with the
mental differences, we know not.  Even where the  rule  stated
above holds good, the difference in mere bulk is far from being
proportionate to the mental difference.  The mind of a Newton
or a Shakspeare is gigantic compared with any common mind,
but the brain  in  such cases is not very much  larger than ordi-
nary  brains.
   510.  In relation  to the evidence drawn from  a  comparison
between different animals, in regard  to the  functions of the
nervous system, there is one significant fact which must not pass
unnoticed.  Though, as we rise in the scale  of animal  life in
our observations, we find every new addition of functions coupled
with some  new  additions of structure,  until  we come to the
higher animals,  we do not find  this to be so when we pass from
them to man.   The brain, it is  true, is larger  in man than it is
in them, and has much more of the gray substance; but there
are no essential differences of structure in  his brain, to corres-
pond with the added mental qualities which so decidedly dis-
tinguish him from the brutes.   These qualities constitute some-
thing more than a difference of degree.  It  is a difference of
kind.   And, therefore, it is a great and  a significant fact, that
there is no corresponding difference of kind in the organization
of the bran.
   511. The qualities to which I  refer I have alluded to in the first
part of this book  (§ 40).  They are possessed by  every hu-
man being  to   some extent,  however  debased he may be;
and, on the other hand,  they are never possessed by any of the
inferior animals, however high their mental manifestations may
be,  and  however  much  they  may be  improved  by training.
Though there be so wide a distance between  such minds  as
Newton, and Milton, and Shakspeare, and the lowest representa-
tive of our race, yet in him are contained the elements of the
excellence to which they  arrived.   But no one dare assert this
to be true of  the very wisest of the inferior animals.
   512. The distinction  between man and animals is a definite
one.   It is as  definite as it would be if it were  based upon  differ-
ence of organization.  The barrier is  fixed ; and not a step over
it has  any animal advanced, with all  the training which may
have been expended upon him.  No animal,  however intimate
has his intercourse been with  man, has ever acquired  man s
habit of abstract reasoning, or  manifested any real knowledge
of  the difference between right and  wrong.   Prof.  Guyot does
                               29 
338
HUMAN PHYSIOLOGY.
              Intimate connection of the mind and the body.

not speak  too  strongly when he says, "I will  even go farther
than is ordinarily done, and I will say, that there is an impassa-
ble chasm between the  mineral and the plant, between the plant
and  the  animal; an impassable chasm  between the animal and
many  Surely if the  impassable chasm between  minerals and   \
vegetables, and that between vegetables and animals, are worthy
of note when we take a comprehensive view  of  the material
world, so  also is that which is much  more manifest as existing
between animals  and  man.  When, therefore, the  comparative
physiologist, in his examination of mental manifestations in con-
nection with physical  developments  finds, as he comes to man,
that in him are  peculiar  and distinctive mental manifestations
with no corresponding physical developments,  he should  deem
it to be an important fact in science, which should not be slurred
over,  or passed  unnoticed, as is often the case.   I shall allude
to certain bearings of this fact in another part of this chapter.
   513.  In looking at the facts  presented in this  chapter and
in that upon the Nervous System,  you must have been contin-
ually struck with the intimacy of the union between  the mind
and the body.   On this subject I thus remark in another work.
"There are various figures used  to illustrate this connection.
The  most  common  one is that in  which the mind is spoken of
as dwelling in  the  body as a habitation.  In  a certain  sense
this is true.  This tabernacle of flesh, as the Bible aptly terms
it, is in its present state a habitation, which the mind is to leave
in a  short  time, to return to it, however, at  length, rebuilt and
refitted in a more glorious, an incorruptible form, to dwell in it
then  forever.   But  this  illustration  of the mysterious connec-
tion  of the mind with the body is  but a partial one—it does
not express the  extent  nor the intimacy of that connection.
The  mind  is not a mere  dweller put into this  habitation.  Its
union with it is not thus  loose and easily severed.   It is bound
to its every nerve and  fibre, so that the least touch  of  the body
at any point affects the mind.  Instead of being put into the
body, it has, being -thus interlaced,  as we  may say, fibre with
fibre, grown with its growth and strengthened with  its strength.
In the feebleness of infancy the mind is just as feeble as the
body, and they both  grow together up to the vigor and firmness
of manhood, and both decline together in old age.  So close is
their union through  all the stages of life, and so equally is each
affected by the joys and sufferings of the other, that  we might
justly conclude  that at death, when the tabernacle   crumbles
into  dust, the  mind  falls  with it never to rise again, had not a 
      CONNECTION OF THE  MIND AND THE  BODY,  339
         Sources of evidence in regard to the nature of the connection.

divine revelation told  us  that, indissoluble  as this  connection
appears during life, Almighty power will dissever it, and release
the soul from the thousand ties that bind it to its habitation, at
the very moment of its  destruction.  Were it not for this assur-
ance of our immortality, we could look  forward in the uncertain  I
future to nothing but blank, drear annihilation, as awaiting our
minds, just as it does the minds of the  brutes that perish.
   514. In our carefulness to avoid materialism, we are too apt
to look upon the mind  and the body as two separate and  inde-
pendent things.  At death they do indeed become so,  but who
of us  knows that they would, were it not for the fiat of the Al-   '
mighty ?   Who knows that there is  not a  necessity for  the
putting forth of his power in each individual case at the time
of death, to prevent the mind of man from dying with his  body,
just as the mind of the brute does with his?  The very preva-
lent notion  that the mind  is essentially indestructible, and that
it is put into the body  as  a separate thing, having  the power
of itself to  leave the  body whenever it dies, rests  on no sub-
stantial proof.   That it is destined thus  to  leave the body is
quite  another thing."*
   515. The nature of the  connection of the mind and the  body
is a great mystery.  Still,  there are many things which we can
know in relation to it.  The sources of our knowledge on this
subject are three, viz.,  the  investigations of Physiology, the tes-
timony of  Consciousness,  and that  of Revelation.   Each of
these  kinds of evidence  throws light upon the others.  If,
therefore, we use all of them, giving to each its due limits and
force, we  shall come to some  certain and valuable conclusions.
But if we take any one of them alone, we shall be liable  to be
led into gross error.
   516. There is in some physiologists  a disposition to rely upon
physiology alone, to the exclusion of the  other  sources of evi-
dence, in  the investigation of  this subject.  In doing this they
are driven  to  this  alternative.  Either they must be content
with a very limited knowledge of the subject, or they must rely
upon  mere presumptive evidence for many of their  conclusions.
And  commonly  the latter  is  the course which they pursue.
They  are not content with  the very limited conclusions  to which
they are shut up by the absolute proof furnished by physiology.
They   boldly reason, therefore,  upon  what  they deem  to be
  * i; Physician and Patient," from the Chapter entitled " The Mutual Influence ot
rhf Mml ;i'i-l Rndy in Disease." 
340
HUMAN PHYSIOLOGY.
             Endowments of matter, is intelligence one of them t

  probable.  And they are invariably led into error.  This I pro-
  pose now to show.
    517. In order  to  get  definite ideas of the manner in which
  the erroneous conclusions  are  arrived at, let us view matter in
  its various states and connections.  Unorganized dead matter
  you see to be entirely different in some important respects from
  living  organized  matter.   The distinction is a definite one.  It
  is easily recognized,  and none  but dreamers  in  science have
  failed to see it.  Though Robinet and others of his class have
  sought to obliterate it, in  carrying  out  their fanciful notions,
  (§ 48,) and though some have supposed that there was a latent
  life in  all unorganized matter, ready to be called into action on
  the application of the appropriate excitants, it is considered by
  all rational observers  as a settled point, that there is an essential
I  distinction  between  common dead  matter  and living  matter.
S  The latter is endowed with  certain properties that the  former
!  has not.   They are termed vital properties.   They control to a
  certain  extent the  mechanical  and  chemical  properties which
  both forms of matter have  in  common.   Some  suppose that
.  what we call life is a single  principle;  but others  suppose the
  endowment to be compound, made up of different principles or
  properties.   But  this question we need not discuss.  All that
  concerns the view I am presenting is the mere fact of  the en-
  dowment.
    518. Let us go a step farther.   Some living beings have more
  endowments than others.  All  have those of  organic  life in
 common (§ 32).  But there is  an animal life also, which  by
 means  of the  nervous system  is  superadded to  the organic.
 And, as we trace  the animal kingdom from the lowest animal
 up to man, we find the endowments connected with this  system
 multiplied as we advance, till in him  they are more complicated
 and extensive than in any other animal.  This is especially true
 of intellectual  endowments, those which  are merely instinctive
 being  more  developed in many, perhaps we may say most, of
 the inferior animals.  And  in  man we find  special  mental
 endowments, of which other animals  present not the faintest
 trace.
   519. Now the question  arises,  whether intelligence  is like
 life, a  mere endowment  of matter, or whether it is in some
 measure  independent of  it.  In  other words, whether  it is a
 principle or set of principles with which matter  is endowed, or
 an immaterial  something which acts through matter as its in-
strument.  How  much does  bare physiology teach us on this 
      CONNECTION  OF THE  MIND AND THE BODY.   341
  _________Reliance on evidence from physiology alone leads to materialism.

question ?   It has often been claimed that it can teach us much,
and the most  bold conclusions have sometimes been ventured
from this  quarter.  But mere  speculation has in all  such cases
been deemed to be proof.  Physiology  does show us, as I have
before said, that the spiritual is in this world  always  connected  ■
with the material, and  that  mind never acts independently of
the  matter with which it  is connected in the brain.  But it
gives us no light  upon the nature of this connection.   It is
well for us to know how deficient are its teachings on this point.
For all that it can teach us, we know not but  that  the  mind  .-
may be a mere result of action in matter.  It  neither tells us
that it is so, or that it is not.  It  leaves us entirely in the dark
on  this point.  Indeed so far as it affords presumptive evidence,
it appears to teach, that mental phenomena are results of mat- f
ter, acting in consequence of certain endowments or tendencies
imparted to it, just as secretion is  in living substances, or chem-
ical action  in those which  are not living.  Accordingly those ;
who have  relied upon physiology alone  on this subject, have |
adopted various forms of  materialism.  Some  have supposed
that thought is a mere product of matter, and  that  the brain
secretes it as the liver secretes  bile.   Others have taught that
the mind is " a bundle  of instincts," each residing in  some par-
ticular part of the brain as its organ.   This has been the doc-
trine of some prominent phrenologists.
  520. Let us look at  living matter in another  point of view,
and see to what physiology alone, if at all venturesome in draw-
ing  conclusions, will  lead us.  Let us  look at  the  origin and
growth of  the thinking animal.   Take, for example, an animal
the formation of which we traced  in  the Chapter on Cell-Life,
§210.  The beginning of the bird as it forms in the egg is a
simple cell filled with a fluid.  This produces other  cells, and
soon the organs and the limbs  of the animal  are formed.   At
length the  animal  bursts the  shell, and comes out not only a
living and sentient being, but a thinking being.  It has a mind
which  feels desires and emotions, and  prompts the muscles to
action to effect  its purposes.   Organization here precedes the
development of mind so far as we can see, and therefore it would
seem that  mind  is a result of organization.  Especially does
this appear to be so, when we find that the amount of mind in
different animals is proportioned to the amount of a certain part
of the organization, the brain.  All this is  as true of man as it
is of other animals.   And  besides, we see in man  that as the
organization becomes perfected, the intelligence is proportiona- 
342
HUMAN PHYSIOLOGY.
         Action of formative vessels like instinct, and even intelligence.

bly increased.  In infancy, when the organization of the brain
is imperfect, the intelligence is small in amount, and grows with
the growth, and  strengthens  with  the strength of the  brain.
And as the mind thus grows with the body, it appears to perish
with the dissolution of the organization, and in the case of the
inferior animals undoubtedly does so.
  521. But it may be said, that the physiologist observes that
the mind designs, and devises means to carry out its designs, and
this shows that there is an immaterial principle that moves the
machinery  of the material organization.  This  is a  plausible
view of the subject, but it is only plausible.   Physiology alone
cannot prove it to be a correct view.  For, if we  limit ourselves
to her teachings alone, it can be made  to  appear  by the same
line  of argument, that mind is at  work in all the phenomena
that we see in living beings.  In the formation of any part, as
you saw in § 163, in the Chapter  on  Formation  and Repair,
the formative vessels work after a fixed  plan, and cooperate to-
gether to accomplish the object.  They seem to act intelligently,
as if they had a mind by which  they designed,  and devised
means for carrying out their designs.  And the  formative and
other vessels thus act together, proportioning  means accurately
to ends, not only  under fixed and regular circumstances, but they
do so  under varying circumstances, to meet exigencies.   Thus,
when an artery supplying a limb is tied, § 169, the formative ves-
sels enlarge the arteries in the neighborhood, in order that the
blood  may be supplied to the limb in suitable quantity.   That is,
they construct after a larger pattern to meet the new  want, just
as if  they were informed of it and  acted accordingly.  Take
another example  afforded by the formation and discharge  of an
abscess,  as  described  in  § 170.  In this case, as the abscess
forms, various operations are going on, with different sets of
vessels cooperating together to effect a common purpose.   And
when  the abscess has  made its way to the  surface, and dis-
charged itself at an outlet, a change comes over the operations,
in order  to restore  the part to its usual state.   The different
vessels accommodate themselves to this change, as if they were
intelligent workmen, acting in conformity to  a design  or  plan
of their  own, upon which they had agreed.  Other  examples
might be cited, both from vegetable  and animal life, all stowing
design and cooperation in effecting purposes.
  522. In such phenomena we see a striking  analogy to  those
of instinct,  and even  to  those  of intelligence also.  It is this
analogy which has led some  in their speculations to adopt the 
     CONNECTION  OF  THE MIND  AND THE  BODY.  343
                  Conflicting evidence of Physiology.

idea that life and soul are  the same thing.   Hence, too, many
phenomena in vegetable life are in common language  often
called  instinctive.   Thus, it is. said, that when a seed sprouts,
the roots instinctively seek the ground, and the stalk and branches
instinctively seek the air and the light.  This is even the case
sometimes when the  seed  is placed at some little distance from
the  ground.  So, too, if a plant  that  naturally  grows in wet
ground is put into dry soil, but in  the  neighborhood of a wet
spot, it shoots forth roots  abundantly towards this spot, rather
than on the other side.
   523. But the evidence  from  physiology does not all tend to
materialism.  There is  some  negative evidence which has a
different bearing.  I refer to the fact stated in § 510, viz., that,
while man differs  in  his spiritual  nature so  widely and so spe-
cifically from the inferior animals, his brain  exhibits no corres-
ponding specific difference in structure, but  only  a difference in
amount   The difference in degrees of intelligence in the animals
below  man is marked  by a corresponding  difference in  the
amounts of the gray substance.   And if it were true that man,
as some think, differed from them  only in having a higher de-
gree of intelligence, we  should expect to find in him a mere
increase cf this substance.   But as his mind differs from theirs
not merely in degree, but  in kind also, we should have reason
to expect, if mind were  wholly dependent on organization, that
the anatomist would find  not only an increase in the quantity
of the gray substance, but also a difference in its structure.
   524. But strong as this evidence is, it appears to be  strongly
rebutted, perhaps almost overborne, by the other evidence which
I have cited from  physiology.   And  the  physiologist might
perhaps say that, although as yet no difference of structure has
 been found that corresponds with  the mental difference, future
investigations with the microscope  may discover  some  subtle
 difference of structure which now escapes our notice.   But this
 it must be allowed is not at all probable.  On the whole it may
 be remarked, that the fact of which I have been speaking, although
 significant and valuable as being coincident with evidence drawn
 from the other sources, yet considered simply in connection with
 the physiological evidence, the evidence from the other sources
 being wholly shut out, it is doubtful how much weight it ought
 to  have,   the physiological evidence, taken by itself is con-
 flicting and looking at the whole scope of it, the preponderance
 must be acknowledged to be towards materialism.
    525. It is quite clear then, that the physiologist cannot well 
 344               HUMAN  PHYSIOLOGY.
              Physiologist needs other evidence.  Consciousness.

 avoid materialism, if, in examining the connection between the
 mind and  the  body, he rejects  all evidence beside that which
 physiology furnishes.  He can be saved from this result only by
 being content with the narrow limits, to which he is shut up, if
 he confine himself to absolute proof.   As we  have already seen,
 the positive knowledge that physiology gives us on this subject
 is exceedingly narrow.   We soon come to the line that divides
 between the known and the supposed.  And if we attempt to
 go  beyond that,  our  conclusions as to what is probable will
 quite certainly lead us to the result which I have pointed out.
 The need,  therefore, of the evidence drawn  from  the other
 sources that I have mentioned is most  palpable.  The physiol-
 ogist must confess himself to be under the necessity of going
jmt-o£ his  physiology, in order to learn all that can be learned
 upon this subject.  At the best, there is much mystery in rela-
 tion to it which we cannot penetrate, with all the light that we
 can bring to bear  upon  it.   And the mystery is deep indeed,
 when we call to our aid only the dim  light of physiology.  It
 needs some other  light to deliver us from the  confusion of ideas,
 into which  we are introduced by the analogy existing  between
 the phenomena of life and instinct and intelligence, in relation
 to  their connection with the  organization of matter.  Let us
 look then  at the evidence which comes  from  the  other  two
 sources,  viz., our consciousness, and revelation.
   526. Every individual is conscious that, as he feels and thinks
 and acts, he, that is his mind or spirit, acts upon the structure
 of  his body, and is acted upon by it.   It is not a consciousness
 that he  as a material body does all this.   He feels that it is a
 power within that does it, and he instinctively separates in his
 ideas the power from the different parts of the body, and from
 the body as a whole.  He is conscious too of a responsibility in
 relation to the thoughts and acts of the spirit within.   He has
 a knowledge of right and wrong, and has self-reproach on doing
 wrong, and  self-approbation on doing right.  It is this conscious-
 ness of a self-acting immaterial spirit in this material  body, that
 constitutes the basis of all character, and of all the moral rela-
 tions of man to  his fellow man, and to his Maker.  Every body
 acts upon the testimony of this consciousness as being valid and
 certain testimony.  And, however the  physiologist may reason
 about matter and  mind,  as if the latter were a mere product or
 endowment of the former, yet as a man, as a member of society,
 as a subject of  government and  law, he  cannot avoid acting
 upon the ground,  that mind in a certain sense controls matter, 
      CONNECTION OF THE MIND  AND THE  BODY.  345
            Evidence from consciousness confirmed by Revelation.

and is responsible for its acts independently of the matter with
which it is connected.
   527.  Now the evidence which this consciousness affords us
should suffice to keep us from the materialism, into which phys-
iology taken alone  would be apt to lead us.   It shows us that,
although the mind  is developed with  the material organization,
and can  act only with it, it is not its  mere product, nor one of
its endowments.  It shows  us, on the  other hand, that it is in
some measure independent of matter, and that its  dependence
upon it  is only a dependence  of connection, matter being the
instrument of mind, through which it acts on external things,
and is acted upon  by them.  The  evidence from this source is
of a positive character.   We are driven by it to the alternative,
of believing that the  mind is  an immaterial, self-acting agent,
in some  measure independent  of matter, or of harboring the
impious  and monstrous belief, that  the Creator  has implanted
in the bosom of man a lie, and  that he is living a horrible farce,
acting in view of moral  relations and responsibilities that have
no existence.
   528.  This positive testimony of our consciousness is confirmed
by the testimony of revelation.   This is not done by any formal
array of proof.  The existence of the spiritual part of man as
a self-acting responsible  agent  is assumed as a fact that needs
no proof.  All the statements, and teachings, and appeals of the
Bible recognize it as a fact known to  the consciousness of every
man.  The Bible, therefore, may be considered as simply affirm-
ing that the  testimony of  our consciousness on this  point  is
valid testimony.   But the Bible goes farther  than  this.   It
gives us  one great fact of which neither  physiology nor  our con-
sciousness  could assure us.  I refer  to the mind's immortality.
Our  consciousness could, it is true, give  us presumptive evidence
to show  that the soul with its high powers and aspirations is to
live  after  the  death of the body.    But it could furnish us no
absolute proof of the fact.  And its presumptive evidence would
be effectually rebutted by the presumptive evidence from physi-
ology, which,  as you have  seen, points  in  another direction.
We are so familiar"with the mind's immortality as a known fact,
and we  so  uniformly think of it  in connection with the death
of the body, that we  are not aware  how absolutely dependent
we are upon revelation for all that we know in relation to it.
If there were no revelation, and death were to us an unknown
event and  we were  now for the first time called upon to witness
the death of a friend, how little should we know, and how con- 
346
HUMAN PHYSIOLOGY.
                Immortality revealed only by revelation.

fused would be our thoughts in relation to the great mystery
before  us!   "What is it?"  we should  ask.   "Is it sleep?"
No.   We never saw any  one  sleep  thus.  What is it ?   Who
can tell us ? "   And we should wonderingly watch to see some
signs of awakening, not giving up all  hope till decay begins its
ravages on the loved form before us.  Then, as  we should from
the dictate of nature,  consign to the  earth the friend who was
so recently among us a breathing, moving, speaking man, now
a mere mass of decaying matter, we should feel that we bury
there  not the body only, but all that belonged  to that body
during life—the whole man.   Thought and feeling, as  well as
life and  motion, would  appear to  us, untaught of God, to  be
extinguished in the grave.  Even if some one  should utter all
tremblingly the hope, that there might be a  subtle spiritual
part of our friend, that would  some  time in some form return
again to  our society, that hope would at  once  be  crushed  by
the reflection that whatever  it was in our friend that thought
and felt, it came  into existence with the body, was infantile
when  the  body was, grew with the  growth of the body, and
strengthened with  its  strength, and  therefore now, so far as  we
can see, has perished  with it.   Nature utters no voice to tell us
otherwise.   She emits no  light to  illumine the grave.  Dark-
ness and silence  rest there, till the  light of revelation shines
upon it, and God proclaims man's immortality.
   529. I have  thus spoken of the three sources of evidence in
regard to the connection  of the  mind and the body, and have
indicated the character of  the  evidence furnished  by each.  I
have  shown particularly that  if the  attention be confined to that
which is furnished by physiology, the  mind is apt to be led  into
materialism.  But  the attention should not thus be confined.
All the three kinds of evidence should be employed and should
be brought to bear upon each other.   If this be  done,  the dis-
crepancies in the  evidence from physiology are cleared up by
the evidence afforded by consciousness and revelation,  and we
see the true value and bearing of the fact, that the specific men-
tal difference between man and animals is not  attended with a
corresponding  structural difference.  Though this fact operates
merely as conflicting evidence, when taken simply in connection
with the rest of the  facts developed  by physiology; when, we
come  on the other hand, to take the whole range of evidence
from  the three  sources spoken of, it is exceedingly satisfactory as
concurring with the testimony of consciousness and revelation.
At the same time, those  physiological phenomena, which taken 
MAN  AND THE  INFERIOR  ANIMALS.       347
            Evidence from consciousness and Revelation positive.

by themselves seem to show so strongly that the mind is wholly
dependent upon organization, are so interpreted by the evidence
from  the other  sources, that the dependence is seen to be for
the most part a dependence of connection only, the brain being
the instrument of the mind.
  530.  The evidence from consciousness and revelation is of the
most  positive character, and  cannot be set aside by evidence
from any other source.  Other  evidence may serve to interpret
it, but cannot nullify it.   The attempt is sometimes made to set
it aside by urging the presumptive  evidence of  physiology, as
if it were absolute proof.   But most  physiologists engage in no
such futile and  unchristian efforts, but give due weight to the
testimony of consciousness  and  revelation in all their investiga-
tions of the mysterious connection  of the mind  and the body.
The influence of Carpenter,  an English physiologist, whose works
are  more extensively used  by students than those of any other
physiologist, is especially to be commended in this respect.   And
although skepticism occasionally utters its plausible falsities, de-
ceiving  the superficial and the speculative, we  have no  fears
from present indications that the votaries of physiological science
will, as  a body, be arrayed  in opposition to  Christianity.
                 CHAPTER  XVIII.

    DIFFERENCES BETWEEN MAN AND THE INFERIOR ANIMALS.

   531.  I have already treated somewhat of the differences be-
tween man and the inferior  animals  in different parts of this
book, and especially in the preceding chapter.  But it has been
done only incidentally, and the subject demands at our hands a
more thorouo-h and systematic investigation.   This I propose to
do in the present chapter.
   532.  Lord  Monboddo maintained  that man  is only an  im-
provement on the monkey, occurring as a result from the general
tendency to advancement claimed to exist in nature.  He seemed
to think that man bore a relation to the monkey somewhat like 
348               HUMAN PHYSIOLOGY.
              Lord Monboddo.  Nature of instinct a mystery.

that which the frog bears to the tadpole, as described in § J67,
and that as the tadpole  becomes the frog, so the  race of man
was produced by a change at some  remote period of the crea-
tion, of the monkey into a man.   This ridiculous notion of the
erudite but fanciful  Scotch philosopher  is really but another
phase of the more recent  theory of gradation, or development,
as it is sometimes called, which in different forms is  now advo-
cated by so many European philosophers.   And, although few,
comparatively, adopt this  theory definitely and fully, there  is
quite a disposition  among  many to  obliterate the distinctions by
which the Creator has  in so marked a manner separated man
from the inferior animals.   It is well, therefore, that we should
have a clear idea of these  distinctions.
   533. It is often  very loosely said that while man is governed
by reason, instinct  rules  in the animal.*  If it be meant by this
that, as a general rule, reason predominates in man, while in-
stinct does so in animals, the statement is a correct  one.  But
if it be meant that animals are wholly governed by instinct, and
that man is distinguished  from  them as a reasoning animal, it
is not correct.   For some  animals do reason, that is, if making
inferences be considered  as reasoning.  In tracing out the differ-
ences between  man and animals I  shall not attempt to  show
what the nature of instinct is.   This is a great mystery, and all
attempts to solve it have utterly failed.  I shall content myself,
therefore, with pointing  out some of the differences between in-
stinct and reason.   In  doing this it  is not always easy to say
just where the one begins and the other ends, so intimately are
their phenomena often mingled together.
   534. The actions  of  instinct  are more unaccountable  than
those of reason.  In  the operations of reason we see  something
of the processes by  which results  are reached.  But it is not
so with instinct.  For example, as a man travels over an unex-
plored country, we can understand by what means he obtains a
knowledge of the country, in order to guide him on his journey.
The processes of his  reasoning in regard to  this we can  com-
prehend.   But when an insect travels with unerring certainty
to its place of destination without any guide marks that we can
  * Some explanation may be well here in relation to the different uses made of the word
animal in different connections.  Here it is used in contra distinction to man.  So it is
used in the expression, man and animals.  But as  man is in certain senses an  animal,
whenever we wish to recognize this fact we speak of other animals as the inferior ani-
mals. And thus in regard to animals, we speak  of their higher and lower orders, the
higher of course being those that approximate nearest to man. 
MAN AND THE  INFERIOR  ANIMALS.        349
         Instinct governed by invariable rules.  Mysterious in its operations.


see,* or when a swarm of bees or a flock of birds wing their flight

to distant places, or when bees construct their honey-comb with

the exactness of mathematics in obedience  to the best principles

for such a structure, we cannot  understand the processes which

lead  to the  result.   It seems to  be produced by an impulse from

a cause extraneous to the animal,  guiding it as if it were a mere

machine.   The little  intelligence of the animal  seems to have

only an incidental  connection with  this impulse.    It, therefore,

merely controls somewhat  the  circumstances under which the

instinct acts.

   535.  So  little has the intelligence to  do with the instinct, and

so nearly mechanical therefore are the actions of the latter, that

they are  governed  by an  invariable  rule.   It is  as  invariable

almost as are  the  movements  of a machine.   For this reason

there are no improvements or alterations in the acts of instinct.

The  bird and the bee, for  instance,  have  no change of  fashion

in  their  architecture  from  age  to  age.    The  honey that fed

John the Baptist, or  that  which  was  found  by Samson  in the

carcase of the  lion, was deposited  in the  same hexagonal cells


  * I will introduce here as an illustration, a little incident recorded in my note book
many years ago.  The account of it runs thus: I wns much entertained to-day in watch-
ing the movements of a very small winged insect—about one-third of the size of a com-
mon fly. He was dragging a dead spider across the road.  Every now and then he would
drop his load, and run forward a little, springing about here and there, and then would
go back and take up his load again.  His movements in this way were so quick and ap-
parently so irregular, that they seemed to be  without an  object.   But I observed, that
although he thus ran about here and there, his course in its general bearing was a very
straight one.  Soon a waggon passed along directly over where the insect was, separating
him from his load, and disturbing the whole surface of the ground.  He, however, soon
found his load, and then with a good deal of apparent reconnoitering he went on again in the
same general course.  In the latter part of his journey he travelled over and amidst a heap
of stones.  Here he would occasionallv leave the spider and disappear, and then return
again to take his load.  Again a little farther  on I would see him emerge from  his con-
cealed pathway, and so on to the end of his journey.  His place of destination was a hole
in the sand beneath a flat stone.  Now, how did this insect  in his journey to his home,
(which to him was a long  one, though only three rods,) manage  to  keep so straight a
course1 Was it in the same way that men  manage in their journeys, guided by way-
marks, and by information  obtained  from others ■?  Following out this idea, suppose then
a man to be at the same distance from his home in proportion to Ins size that the insect
was from his home.  According to this supposition he must be over three thousand miles
from home.  Suppose the direct line to his home lay across an uninhabited country, so
that he can get  no information from others.   This makes his case  parallel with the in-
sect's  for we saw him meet no  other insects  on the road.  Now, if he knew the exact
direction in which his home  lay. he could not, without his compass, move with any pre-
cision towards it  And  if he  had wandered away from it without a compass, as the in-
sect did from his home, how would he know in what direction it lay 1  And yet the insect
travelled towards his home as if he preserved exactly amid all his wanderings the points
of the compass   The surface over  which he went was very irregular.   He had to cross
or wind around eminences, which were to him  as large as hills and mountains are to man
and vet he was not embarrassed; and when  he went among the stones he hud more and
greater difficulties to encounter than man meets with in passing through the wildest coun-
tries  A"ain suppose that the travelling man  should meet with some whirlwind or some
convulsio°n of nature, which should separate him from his burden, and disarrange in some
measure the face of  the country about him. just as the travelling insect was served by the
commotion of the horse's feet and the wheels of the waggon.  Would he find his load as
easily as the insect did, and go on his way with as little hesitation ?

                                 30 
350              HUMAN PHYSIOLOGY.

                  Contrivances in the nests of birds.

which are constructed by the  bees of the present  day. _  And
each bird builds its nest" precisely in the same way that its an-
FIG. 187.
NEST OF THE BAYA.
cestral birds have ever done.  Most birds'
nests are constructed after the same general
pattern.   But sometimes we observe strik-
ing peculiarities to subserve some special
purpose.  Fig. 187  represents the nest of
the Baya, a little bird of Hindoostan.   It
is in the shape of a bottle, and is made of
long grass.   It is suspended  from a slen-
der branch of a tree, so that  monkeys,
serpents,  &c, cannot reach it.   The  en-
trance to the nest is made on the under
side, so that these animals cannot enter,
while the bird itself  can readily fly in.  ^ It
is divided into apartments, in one of which
the female sits upon  the eggs, while in  the
other the male bird " solaces his companion
with his song whilst  she is occupied  in ma-
ternal cares."   In Fig. 188 is seen the nest
of another little  eastern  bird, which with
filaments of cotton taken from  the  cotton
plant, sews leaves together with its beak
and feet, so as to conceal the inclosed nest
from its enemies.
FIG. 188.
of the Tailor Bird. 
MAN AND  THE INFERIOR  ANIMALS.       351
     Contrivances in the honey-comb.  Mathematical principles exactly applied.

  536. While there  is  no change  in  the acts of instinct they
are marked by perfection.   That is, they are perfectly adapted
to the purposes to be effected and to  the circumstances under
which they are performed.   The  Creator, who  directs the im-
pulse that governs  the animal, in  this case  as well as in all
others, accurately fits the means to the ends to be accomplished.
There is nothing in which this  perfection  of instinct  is  better
shown than in the construction of the honey-comb.  The cells
are made hexagonal,  because in this way all  the space is occu-
pied—there is no waste of room.   If the  cells were made cir-
cular, there would  not only be a waste of room,  but a large
quantity of material would be needed to fill up the spaces be-
tween the cells.   The.difference can be seen in the two Figures
189 and 190.  Each comb, it is to be observed farther, has two
FIG. 189.                   FIG. 190
sets of cells, the ends of one set being arranged against the ends
of the other in a peculiar manner.   These ends are not flat, but
each one  has three plane surfaces, forming with each other a
particular angle soon to be noticed, and uniting  together at the
centre in a point.  In the arrangement of these  cells, therefore,
a cell of one set does  not lie end to end with a cell  of another
set.   Its three surfaces form a part of
the bottom  or end of three  cells of          FIG- 191-
the other set.  This is made clear by
Fig. 191, in which a cell  of one set is
represented  as it abuts against a cell
of the other set by one of its surfaces,
its other two surfaces forming  a third
part of the  ends of two other cells.  Now  it has been  found
that the an<rie formed at the edge of these surfaces between the
two sets of cells is  such as to secure the greatest strength with
the least amount of material.  It was at one time thought that
 
352
HUMAN PHYSIOLOGY.
         Wonderful operations of instinct in communities among animals.

 this was proved to be not exactly true.  The variation from the
 correct angle, made out  by the calculations of the mathemati-
 cians, was indeed a slight one, but still  it was variation enough
 to  show, if the calculations were correct, that the workings of
 instinct were  not perfect in this case.   But the investigations
 of  Lord Brougham have satisfactorily shown that the mathe-
 maticians were wrong in  their calculations, and that the bees
 are right.
   537. The perfection of the operations of instinct is shown in
 the most wonderful manner in the regulation of communities of
 animals.   Here we see  cooperation  to  produce results effected
 through an irrational, and  therefore  in  some measure  a  blind
 instinct.  This  social instinct  is  most  extensively exemplified
 among the insect tribes, as  for instance the bee and  the wasp.
 The structures, resulting  from the cooperation of multitudes of
 little laborers  guided by this instinct, are very interesting.  I
 shall allude  to  but a single familiar  example, the  construction
 of the nests of wasps.  These insects make their building ma-
 terial from the fibres of old wood.  These  they convert by mas-
 tication into a pulp, which made into a thin layer, becomes firm
 like paper.   It is indeed a process very much  like  the common
 process of paper-making invented by man, and the first rude
 inventor may have got  his idea  from  the insect.  With this
 substance  the wasps build  several  ranges of cells, which  are
 hexagonal, like the cells  in the comb of the bee.  These ranges
 of cells are placed parallel  to  each other, at regular  distances,
 with  little supporting columns between  them, as  seen in Fig.
 192.
  The number and variety of instincts of the ordinary hive bees
 are  very wonderful, but it would occupy too much space to de-
 scribe them.
  538. The wonderful cooperation of animals in  obedience to
social  instinct, in  the  building of habitations and  other struc-
tures is seen in several of the mammalia.   But it is most won-
derful in the beaver,  the  following description of whose habits
in this respect I take from Carpenter.   " During the summer it
lives solitarily in  burrows, which  it  excavates for itself on  the
bordere of lakes and streams; but  as the cold season approaches
it quits its retreat and  unites itself with its fellows, to construct,
in common with  them,  a winter  residence.   It is  only in the
most solitary places that their architectural instinct fully devel-
ops itself.  Having associated in  troops of from two to three
hundred each, they choose a lake or river, which is deep enough 
MAN AND  THE INFERIOR ANIMALS.       353
Exemplified in the beaver community.
FIG. 192.
NEST OF WASPS.
to prevent its being  frozen to the bottom; and they generally
prefer running streams, for the sake  of the convenience which
these afford in the transportation of the materials of their erec-
tion.   In  order that  the water  may be kept up  to a uniform
height, they begin by constructing a  sloping dam;  which they
form of branches interlaced one  with another, the intervals be-
tween  them being filled up with stones  and mud, with which
materials  they give  a  coat of rough-cast to the exterior also.
When  the  dam passes  across a running stream, they make it
convex towards the current; by which it is caused to possess
much  greater strength than  if it were straight.  This dam is
usually eleven or twelve feet  across at its base, and is enlarged
every year; and it frequently becomes covered with vegetation,
so as to form a kind of hedge.
   589  When the dam is completed, the  community separates
                           30* 
354              HUMAN PHYSIOLOGY.
                   Blindness of instinct exemplified.

into a certain number of families; and the beavers then employ
themselves in constructing huts, or in repairing those of a pre-
ceding year.  These cabins are built on the margin of the water;
they have usually an oval form, and an internal diameter  of six
or seven feet.  Their walls are constructed, like the dam, of
branches of trees; and  they are covered, on two  of their  sides,
with a coating of mud.   Each has two chambers, one above the
other, separated by a  floor;  the upper one  serves as the habita-
tion of the beavers, and the lower one  as the magazine for the
store  of  bark, which  they lay up for  their provision.  These
chambers have no other opening, than one by which they pass
out into  the water.   It  has  been said that the flat oval tail of
the beavers serves  them as a  trowel, and is  used by them in
laying on the mud of which their erections are partly composed;
but it does not appear that they use  any other implements than
their incisor teeth and fore-feet.  With their strong incisors they
cut down the branches, and  even the trunks of trees which may
be suitable; and by the aid of their mouths and  fore-feet, they
drag  these  from  one place  to  another.  When they establish
themselves on  the  bank  of a running stream, they cut  down
trees above the point where  they intend  to construct their dwell-
ings, set them afloat,  and, profiting  by  the current, direct them
to the required spot.  It is  also with their feet that they dig up
the earth they require for mortar, from the banks or from the
bottom  of the water.   These  operations are executed with ex-
traordinary rapidity, although  they  are only carried  on during
the night.   When the  neighborhood of man  prevents  the
beavers  from  multiplying to the degree necessary to form such
associations,  and from  possessing  the  tranquillity which they
require  for  the construction of the works just  described, they
no  longer build huts, but live in excavations in the banks  of the
water."
   540.  Instinct moves straight on  to  its result, and it does so
blindly.   It exercises no intelligence in regard to the  purpose
for which  the  result is intended, or the  circumstances  which
tend to defeat this  purpose.  It evidently in  some cases never
knows any thing of the purpose aimed at by its acts, as, for ex-
ample, when an animal makes provisions for a progeny  which
it is never to  see.  "It is  scarcely possible," says Carpenter,
"to point to any actions better fitted to give an idea  of the na-
ture of  instinct, than  those which are performed by various
insects, when they deposit their eggs.  These animals will never
behold their progeny;  and  cannot acquire any notion from ex- 
MAN  AND  THE  INFERIOR ANIMALS.      355
              Results of instinct mingled with those of reason.

perience, therefore, of that which their eggs will produce ;  never-
theless they have the remarkable habit of placing, in the  neigh-
borhood of each  of  these bodies, a supply of aliment fitted for
the nourishment of the larva that  is  to  proceed from it;  and
this they do, even when they are  themselves  living on food of
an entirely different nature, such  as would  not be adapted for
the larva.  They cannot be guided in such actions by any thing
like reason;  for  the data on which alone they could  reason
correctly, are wanting  to them; so that they would be led to
conclusions  altogether  erroneous  if they were not  prompted
by an  unerring instinct, to adopt  the means  best  adapted for
the attainment of the required end."
  541. The results of  reason  are  often  mingled with those of
instinct in such a way that  it is  difficult  to  distinguish them
from each  other.  But  instinct is of itself wholly irrational.
If it were not so, it would avoid acting whenever action  would
evidently be useless.  But instinct has  not the eyes of  reason
to see  when this  is the case.   It leads the animal  blindly on;
so that, although under all ordinary circumstances the  object
is accomplished definitely and in the best manner,  yet there is
no  capability of  making provision for  extraordinary circum-
stances.  Therefore, actions are occasionally performed,  which
do not at all answer the purpose which the instinct is designed
to effect. Instinct, though perfect in its action under the fixed
uniform circumstances under which it  is  destined to act, is a
kind of blunderer when irregular circumstances arise.  Instinct
is a strict routinist,  while  reason  readily accommodates itself
to endlessly varying  circumstances.   In  illustration   of  the
above  characteristic of instinct,  I will cite  a few  examples.
The hen will sit on pieces of chalk shaped like eggs, as readily
as she will on the eggs'themselves.  Her instinct is so blind
as to  be deceived by this general resemblance.  The flesh-fly
often lays its eggs in the carrion-flower, the  odor  of which is
so much like that  of tainted meat as to deceive the  insect.
An amusing  illustration  of  the   blind disregard  of circum-
stances in following out the promptings of instinct is given by
a gentleman, Mr. Broderip, in an  account of a beaver  which
he cauo-ht when very young.   As  soon  as it was let out of its
cage, and materials were  placed  in  its  way,  it began to build
after the fashion followed by these animals when they construct
their dam in a stream of water and build their habitations in its
banks.   "Even when it was only half grown," says Mr.  B., "it
would drag along a large sweeping-brush, or a warming-pan, 
 356               HUMAN PHYSIOLOGY.
               Blindness of instinct illustrated in the beaver.

 grasping the handle with its teeth, so that the load came over
 its shoulder; and would endeavor to  lay this with  other ma-
 terials, in the mode  employed  by the beaver when in a state
 of nature.  The long and large materials were taken first;
 and two of the largest were generally laid cross-wise, with one
 of the ends of each touching the wall,  and the other ends pro-
 jecting out into  the  room.  The area formed  by  the  cross-
 brushes and the wall, he would fill up with hand-brushes, rush-
 baskets, books, boots, sticks, cloths, dried turf, or any thing port-
 able.   As the work grew high, he supported himself on his tail,
 which propped him up admirably; and he would often, after lay-
 ing on one of his building materials, sit up over against it, ap-
 pearing to consider his work, or as the country people say, 'judge
 it.' This pause was sometimes  followed by changing the position
 of the material judged; and sometimes it was left in its place.
 After he had piled up his  materials in one part of  the room,
 (for he generally chose the same place,) he proceeded to wall
 up the space between the feet of  a chest of drawers which stood
 at a little distance from it, high  enough on  its legs to make
 the bottom a roof for him; using for this purpose dried turf
 and sticks, which he laid very even, and filling up the interstices
 with  bits of coal, hay, cloth,  or any thing  he could pick up.
 This last place he seemed to appropriate for his dwelling; the
 former work seemed to be intended for a dam.  When he had
 walled up the space between  the feet of the chest of drawers,
 he proceeded to carry in sticks,  cloths, hay, cotton, &c, and  to
 make a nest;  and when  he had done, he would sit up under
 the drawers, and comb himself with the nails of his hind feet."
 I simply remark in relation to this amusing narration, that you
 can see at once that if the instinct of this animal had been  at
 all rational, it would not have  impelled him to construct a dam
 and a dwelling in  a common  room, where  they would be  of
 no use to him.   Reason would have dictated the building  of
 a nest and  nothing more.
   542. The care which animals  exercise  in relation to their
 progeny seems to be governed  to a great extent, perhaps wholly,
 by a blind instinct.  All care is given up when  care is no longer
 needed, and with it what  appears to be  affection is given up
 also.   In animals there is no such lasting affection of the pa-
 rent for  the  progeny as there is in man;  for in them it  is
merely instinctive, and not rational and moral  in its character,
 and it, therefore, lasts only so long as it is needed to  carry out
the purposes for which  this  particular instinct  is  designed. 
MAN  AND THE  INFERIOR  ANIMALS.      357
        Difference between the intelligence of man and that of animals.

Indeed, in some cases there can be no affection in all the care
which is instinctively exercised by the parent, for it is put forth
for progeny which, as stated in §  540, the animal is destined
never to see.  And in those cases among animals in which the
family state exists, it is a mere temporary affair, and as soon
as the  offspring is able to take  care of itself it is no more to
the parent than any other animal of the same tribe is.
  543.  But some animals have intelligence as well as instinct.
When this intelligence is shown in the mere power of  imita-
tion it  is of a low order.   The parrot that learns to imitate
man in speech is nothing  like as intelligent as some animals
that have no such power.  Some animals have really a reason-
ing intelligence—that is, they make rational inferences.  Their
reasoning is sometimes, as before  remarked, so  mingled with
the operations of  instinct, that it is difficult to distinguish them
accurately.   In the case of the  beaver related in § 541, who
labored so faithfully in obedience to  a blind instinct, there was
some exercise  of reason, as, for example, when he  "judged"
his work.  But it is  difficult  to point out  definitely the line
between instinct  and  reason in such a case.  There are some
animals, however, in whom the workings of a reasoning intel-
ligence are to be  seen with perfect distinctness.   But their
reasoning differs  from that of man.   The inferences  which the
reasoning  animal makes are individual; while man goes be-
yond this, and makes  general  inferences, and  therefore dis-
covers general truths.   Newton's dog, Diamond, saw  apples
fall to the ground, as well as his master.   And he was capable
of making some  inferences in regard to  them;  but  they were
individual  inferences.    For  example, if an apple-tree  were
shaken, and  the  dog were hit  by  a falling apple, whenever he
saw other  apples falling he would infer that he might be hit
again, and would infer also that it was best for him to get out
of harm's way.   This would be the extent of his reasonings.
But his master inquired into the cause of the fall of the apple,
and by considering this and other similar phenomena,  he de-
duced general principles, which govern  the movements both
of the atoms, and the worlds of the  universe.
   544. The inferences which  are formed by animals are mere
results' of the  association  of ideas,  and the process, therefore,
really hardly merits  the appellation of reasoning.  Thus, in
the case of Newton's dog, supposed  above, the idea of the fall-
ing apples was associated in his mind with the hurt experienced
when he was hit, and prompted the  getting out  of harm's way. 
358              HUMAN PHYSIOLOGY.
         Reasoning in animals mere mental association.  Exemplified.

When such associations are extended and  complicated, it ap-
pears at first thought as if the animal acted in view of general
truths, arrived at by the same process of reasoning that man
employs.  But it is a  mere extension of mental  associations.
Thus, Newton's dog probably associated the idea of being hit
and hurt with  other falling bodies beside apples.   And so, too,
various circumstances might come  to be associated with the
falling of bodies, and thus complicate the mental process which
occurred when he saw any  object falling near him.
  545. To show somewhat the  extent to which this mental
association operates in  the brute mind, I will allude to some
examples.  A  wren built its nest in a slate quarry, where it
was liable to great disturbance from  the blastings.  It soon,
however, learned to quit its nest, and fly off to a little distance,
whenever the  bell  rang to warn the workmen  previous to a
blast.  As this was noticed, the bell was sometimes rung when
there was to be  no  blast, for the sake of the amusement in
seeing the poor bird fly away when there was no need of alarm.
At length, however, it ceased to be  deceived in this way, and
when it heard  the bell ring it looked out to see if the workmen
started, and if they did then it would leave its nest.  In this
case  the bird  merely learned to  connect in its mental  associa-
tions  two circumstances  with  the blasting,  instead of  the one
from which it at first took the warning.  The  operation of
this mental association is shown  in a little different manner in
the following case.  Some  horses in a field were supplied with
water in a trough which  was occasionally filled from a pump.
As the supply  was not always sufficient, one of the horses, more
sagacious than the rest, whenever he, on going to drink, found
the trough empty, pumped the water into it by taking hold of
the pump-handle with his teeth,  and moving his  head up and
down.  The other horses  seeing this, would, whenever  they
came to the  trough and  found it  empty, tease  the one that
knew how to pump, by biting and kicking him, till he would
fill the trough  for them.  In this case the  horse that did the
pumping associated in his mind the motion of the pump-handle,
as he had seen it done by his master, with the supply of water.
And  while  they associated this supply with his  pumping, he
knew what their teasing him meant, because he associated it
with  their motions about the trough, indicating so plainly that
what they wanted was water.  But I will give a still stronger
case.   A dog  belonging  to a Frenchman was observed to go
every Saturday,  precisely at two o'clock, from his residence at 
MAN  AND THE  INFERIOR ANIMALS.      359
          Relation between cause and effect learned from association.

Locoyarne to Hennebon, a distance of about three quarters of
a league.  It was  found that he went to a butcher's, and for
the purpose of  getting  a  feast of tripe which he could always
have at that hour  on Saturday, their day of killing.   It is also
related of this dog, that at family prayers he was always very
quiet, till  the  last paternoster was  commenced, and then he
would uniformly get up and take his station near the door, in
order to make his  exit immediately on its being opened.   The
narrator of these facts thinks that the first fact shows, that the
dog could measure time and count the days of the week.   But
this cannot be  so.  The  dog undoubtedly associated in his
mind the time at which he could get the tripe, with something
that occurred on Saturday at that hour  at his master's house,
just as  he associated  the concluding of family prayers with
something that  occurred as the last paternoster was read, per-
haps with some peculiarity in the manner of his master when
he came to that part of the service.
  546.  Animals learn the relation between cause and effect bv
this mental association,  and act upon the  experience  thus
gained.   This is manifest  in  the examples I have  cited.   And
it may be observed in  many acts that we witness occasionally
in the higher  animals.   Thus, for  example, as my horse was
cropping some grass, he took hold of some that was so stout,
and yet so loosely  set in  the ground, that  he pulled it up by
the roots, and, as  the dirt which was on it troubled him, he
very deliberately knocked it across the bar of a fence till he got
all  the  dirt  out,  and then  went on to eat it.  Here was a
knowledge of cause and effect which was derived from previous
experience through mental  association.  You see the same
thing when you see a cat jump  up and open  the  latch of a
door, or a horse unbolt the stable door to get out to his pasture.
But in all such cases the knowledge of cause and effect differs
from the same knowledge in man in one importaht  particular.
In the animal it is always an individual knowledge, that is, a
knowledge of individual facts; while in man it is often a knowl-
edge which has  relation to general truths or principles.
  547.  From the  facts stated in the last few paragraphs it is
clear, that Carpenter is not correct in saying, that " the mind
of man differs from that of the lower animals, rather as to the
degree in which  the reasoning faculties are developed in him,
than by any thing peculiar in their kind" While there is much
in common between them in  their modes of mental action, es-
pecially if man be  compared with other animals in  the period 
360
HUMAN PHYSIOLOGY.
        Abstract reasoning source of language and of a belief in a Creator.

 of his infancy and childhood, there is, as you  have seen, one
 attribute of the human  mind which is wholly peculiar to it,
 and never exists in any degree, in any other animal.   And this
 attribute, the power of abstract reasoning, or in other words,
 the power of deducing general truths or  laws from  collections
 of individual facts, constitutes the great superiority  of the hu-
 man mind, in distinction from the mind of the brute.
   548. It is this attribute which is  the source of language in
 man.  This  can be readily seen by observing what is the na-
 ture of language.  It is a collection of corresponding vocal
 and written  signs of an  arbitrary character, arranged accord-
 ing to certain general  rules  or  principles.   Other animals do
 have a kind of language of a very limited character.   It is
 the language of natural  signs.  It is  composed of cries  and
 motions, which vary in different tribes of animals, so that each
 tribe may be said to have its own  natural  language.  But an-
 imals never  invent and  agree upon any arbitrary signs, as is
 done continually by mankind in the construction and exten-
 sion of language.   This  they cannot do, because abstract rea-
 soning is required for such  an invention.   General  principles
 are observed in the construction and arrangement of arbitrary
 signs, and, as I have shown, brutes know nothing of principles.
   549.  This attribute  also is the source of man's belief in a
 Creator.  If he had not the power of deducing general truths
 from individual facts, he  could  neither  discover the  truth that
 there is a first great Cause, nor  appreciate  or  even  receive it,
 if it were communicated to  him.   Not the faintest shade of
 such an idea can be communicated to any of the inferior ani-
 mals, however high their mental manifestations may be,  and
 simply because the structure of their  mind is such that they
 know nothing of general principles.   Carpenter speaks of the
 disposition to believe in  the existence of  an unseen but pow-
 erful Being,  which is  found to be  universal even among the
 most degraded races of mankind, as  a natural tendency, which
 he  seems to think is  implanted in the human breast by the
 Creator.  But it appears clear, that it is a mere natural result
 of the exercise of  the power that I have just spoken of.
  550.  Man  differs from other animals also in having a con-
science, or, a  knowledge between right and wrong, and a sense
of obligation in relation  to it.  This moral sense  is supposed
by some to be a mere  result of the  exercise of the power of
abstract reasoning.  But others suppose that the sense is  im-
planted as a distinct quality or power, and  that the office of the 
MAN AND  THE INFERIOR ANIMALS.      361
        Conscience. None in animals.  Summary of mental distinctions.

reasoning power in relation to it is to bring the evidence before
it for its decision.   I shall not discuss this point, but will merely
remark in regard  to this subject, that there is no doubt as to
the existence of such a sense in man.  Some  attempt to throw
doubt over it by pointing to its perversions, maintaining that it
is a mere creature of circumstances, varying almost endlessly in
different parts of the world.   But it would be just as rational to
attempt  to  show, that there is no such thing as a sense of the
beautiful  in man, by appealing to the evidences of perversions
of taste, which ignorance, bad education, and foolish and nov-
elty-loving fashion have induced.
   551. In those cases in  animals in which this moral sense has
been supposed to exist, it is  nothing but slavish fear.   It has
been said by some one that man  is the god of the dog; but it
is sacred  trifling to compare the attachment of an animal to its
master and its fear of his  displeasure, with the intelligent regard
of man  for his Creator  as a holy and benevolent being.  We
ordinarily recognize the  distinction between man and animals,
as to the existence  of a  conscience, in the  language we use.
We never attach the idea of moral  character to the acts of an
animal except by the force of association, and.then only slightly
and loosely.   We are not apt to speak of punishing a dog, for
this word implies a moral fault as the occasion of the infliction.
We whip him, sometimes, simply to associate in his mind the
smart  with the act done, so as  to prevent  him from doing it
again, and sometimes to  vent our ill feeling for the  harm done
us on the poor dog that has so innocently done it.  It is related
of Sir Isaac  Newton that he had a favorite  little dog called
Diamond, who  being left in his  study, overset  a candle among
his papers, and thus burnt up the  almost finished labors of many
years, and yet the philosopher only said, "O  Diamond! Dia-
mond  ! thou little knowest the mischief thou hast done."  New-
ton was both a wise and a  good  man, and while he saw that
whipping the dog would do no good in preventing any similar
accident in future, he had no ill feeling to vent on poor Diamond,
who certainly had a better and more rational master than most
dogs have.
   552. The mental distinction between man and animals may
be thus summed up.  The animal  is governed  by instinct, and
in the higher orders bv a kind of reasoning which is based upon
mental association.  Man has, in addition  to instinct  and this
lower  order of reasoning, the power of abstract reasoning.   In
the lower orders of animals probably instinct rules alone.   In
                               31 
362              HUMAN PHYSIOLOGY.
             Experience gathered by animals, but not transmitted.

 them there is none even of the limited reasoning which we see
 in the higher animals.   They have a nervous system with cer-
 tain central organs, but have really no one great central organ
 that we can  call  the brain.  As we trace the animal kingdom
 upward, we  soon  find  that  a brain  appears, that is, such an
 organ as may be considered the chief centre of the nervous sys-
 tem.   And then, as we continue to trace upward in the  scale,
 we find  that the more intelligence  or  reasoning there is,  the
 more prominent is the brain in proportion to other parts of this
 system.  When we come to man the brain is much larger than
 in any other  animal, and his intelligence is not only greater,
 but it is of a different  character.  Not only is  the amount of
 his reasoning by association  greater than in other animals, but
 there is also  superadded, as  his grand distinguishing mark,  the
 power of abstract reasoning.
   553. Instinct, you have seen, cannot be improved by educa-
 tion.   It always acts in the same way throughout the life  of an
 animal, and through the succeeding generations of the  tribe.  It
 has no accumulated experience, either individual or traditional.
 But it is  otherwise with the  two kinds of reasoning power.
 These can be educated, and they have an experience.   But here
 there is a marked difference between the two kinds of  reason-
 ing.    The  lower kind  of reasoning,  that of mere  association,
 which is the only kind possessed by animals, is altogether in-
 dividual, and is not at all traditional.   However wise an animal
 may become, there  is  no transmission  of  his  wisdom to  his
 posterity.   No  animal  can  start  from a point of knowledge
 gained by his  ancestor, as a vantage ground, and thus make
 greater advances than  his predecessors.  Each animal, in  ac-
 quiring experience as to the relations of cause and effect, has to
 begin at the  beginning, and learn every thing for himself.  The
 higher form  of  reasoning,  that which man  alone possesses, is
 absolutely essential to the transmission of experience from one
 generation  to another.  It is necessary to the transmission even
 of that experience  which is  gathered by the other  power of
 reasoning, as well  as  that which is  gathered by itself.  The
 amount of improvement which  can  be  effected where  there
is only the lower  kind  of reasoning to act  upon, is very  won-
 derful  in the  case of some of the docile animals.   The dog, the
elephant, the monkey,  &c,  are  familiar examples.   By the
skillful and persevering  use of mental association  in the training
of animals, results can be obtained, that resemble very closely
those which  come  from man's power of abstract reasoning 
          MAN AND  THE INFERIOR ANIMALS.        363
         The power of generalization the basis of improvement in man.

And in some cases  the animal  accumulates quite a large indi-
vidual experience.  But his race is none the wiser for it.   It is
none of it transmitted to another generation.
  554. We see then  the  basis of improvement in man.   It is
not his power of  making inferences merely.  The  brutes do
this.   It is his power of making general inferences, or, in other
words, deducing general laws or principles from individual facts.
And as this power  distinguishes man from the inferior animals,
so a superior degree of it ordinarily constitutes the  intellectual
superiority of one man to another.  This is seen very readily in
inventions and discoveries.  In the case of almost every inven-
tion or discovery, the  individual facts  upon which  it is based
were known to many others, perhaps even a long time before
the invention or discovery was  made.  The merit of the in-
ventor or discoverer consists in having seen the available general
truth indicated by the facts, and traced out its  application  to
certain objects to be attained.  Thus, to take a single example,
dairymen and dairywomen in  great numbers  knew the  fact,
that a certain disease,  derived from the cow accidentally by in-
dividuals, prevented  them from taking  the small  pox; but
Jenner was  the first to see, that here was  developed  a great
general fact, capable of universal application.  And thus seeing
the wide scope of the fact, he collected  the proofs of it,  and de-
vised  the means by which  it could be made available to prevent
the ravages  of one of  the  great  scourges of the race.   It was
by the generalizing power of his reasoning that he went beyond
dairymen and dairywomen, and became the discoverer.
  555. It is interesting to observe  that while the  capabilities
of instinct are developed rapidly, sometimes almost instantane-
ously,  the  capabilities  of  the  reasoning power  are  developed
gradually.   Especially is this the case with the higher reasoning
power, that  distinguishes man from  the brutes.   The child is
governed at the first wholly by instinct; and  then as he gathers
knowledge of the world around him through his  senses, mental
association comes into play.   By the exercise of the lower kind
of reasoning, which he has in common with animals, he accumu-
lates experience of  the relation of cause and effect.   Thus far
he is on  common ground  with  animals, that is, those  of the
higher orders,  except that he adds more  largely to his experience
from  mental association than  they do.  Meanwhile the power
of abstract  reasoning  is gradually  developed, raising him up
from the level of the brutes, and introducing him into compan-
ionship with the whole intelligent creation, even with God him- 
 364              HUMAN PHYSIOLOGY.
    The wonderful power of abstract reasoning.  Slowness of development in man.

 self, whose image he bears in possessing  this attribute.  This
 power of generalizing facts is developed earlier than is generally
 supposed.   It  is of course feeble at first, and  has  a  narrow
 range; but it  very early shows itself sufficiently to  indicate to
 us clearly, that the child's mind differs essentially from that of
 the brute.   And when  disease or original  physical defect pre-
 vents  its development, we  see  the  mental deficiency, and  the
 consequent resemblance of the child in mental character to the
 inferior animals.
   556.  When this characteristic power of  the mind of man is
 fully developed, its achievements  are often so wonderful, that
 they give us some realization of the  great truth, that  man is
 created  in the image  of God.   As we witness the  demonstra-
 tion of such facts as Newton  discovered, or the unerring calcu-
 lations of an eclipse, or listen to a perfect argument as it develops
 grand truths, and leads us with  a  majesty of thought almost
 divine, straight on  to  mighty conclusions, we  take  in the  full
 meaning of the assertion, that "the soul is that side of our  na-
 ture which is in relation with  the Infinite," and we see the folly
 of those dreamers  in   science, that  look upon man as making
 merely the highest order in  the animal kingdom.  We see that
 the chasm between him and other animals is truly "impassable."
 We see that we are in a mental region of which the  most intel-
 ligent  of them know nothing—that though they live like us,
 having the same  senses, seeing the same beautiful things, and
 hearing the same voices of  nature, and like us have  thoughts
 and emotions and desires, they are shut out from an upper region
 of thought and feeling in which we freely roam, and from which we
 look with aspirations unknown to them to another world beyond.
   557. As the mental  capabilities peculiar to man are slowly
 developed,  so it is with  his physical frame, and the powers that
 belong to it.  Though man at  length so excels all  other animals,
 that they are subject to his power as their  master, he is at the
 first the most helpless of all animals.   He  is  a long time  "in
 the nurse's arms," and for years he is unable to obtain his own
 food.   He  does not reach  the full strength of his body and
 mind till he is  more  than twenty years of age.  He is  in strong
contrast with other animals in regard to this slowness of devel-
 opment, they generally reaching their full capabilities in a short
time.   But even among them, it is to be observed, that there is
a difference in this respect, in obedience to a general  law, that
the higher the capabilities are, the slower they are in  their  de-
velopment. 
MAN  AND THE  INFERIOR  ANIMALS.        365
         Difference between man and animals in physical endowments.

  558. The differences between the physical  endowments of
man, and those of the  higher orders of animals, are often very
minutely described.  But  though strongly marked, too much
prominence  is ordinarily given  to them.   They should be con-
sidered  as  subordinate  altogether to the  mental differences.
Thus, much is often said of the  superiority of man in regard to
the possession of a hand, on which I have remarked in various
parts of this book.   But why should he have such an instrument
given to him ?  Simply because  he has a mind which is  not
only capable of directing it, but which needs such an instrument
to produce  suitable  results  in  its action on the world around.
If other  animals  had a hand they could not use it properly.
They  have instruments of a different character, of less various
capabilities, but such as  are suited to their wants and powers.
The same thing can be said of other bodily endowments.  They
are always suited in range and  power to the wants and mental
capabilities of the animal.  As we  trace out this general idea,
we find that some animals have some bodily endowments which
far excel the same in man.  Thus, some have greater powers
of vision and hearing than he has, because they need them.
So, too, some have endowments  of  which we find no trace in
man,  as, for example, the power of flying.  For the same reason
most  animals have special natural means of defense against the
attacks of other animals; but man has not, because he has no
need of them, as by his ingenuity he  can contrive such means as
he may require.
   559. The physical  endowments of man in comparison  with
animals are indeed wonderful, and correspond with his spiritual
endowments, so far  as  gross matter can compare with subtle
immaterial  mind.  We have looked at these  endowments in
detail in various parts of this book.   Let us glance at the prin-
cipal  of them collectively.  As the  muscles are the organs by
which all  communication between  man  and man, and indeed
all action upon the external world is effected, it is in the endless
combinations  of  muscular action that man is mostsignally su-
perior to animals in physical  endowment.   This is shown, as
you have seen, in the human hand,  whether it be looked  at as
an instrument for work or for  expression.  The same thing we
see exhibited almost as strikingly in the muscles of the voice—
both  those which by their delicate and accurate action regulate
the vocal ligaments, and those which by their complicated action
give the voice all its variety of  articulation, especially the latter.
But let us look  at  the  body as a whole.   Man walks erect, a
                           31* 
366
HUMAN PHYSIOLOGY.
         Beauty of the human form.  Best shown when it is in action.

significant characteristic of him as differing from animals.  And
though there be grace of movement in many animals, it is not
in any case to be compared with that which we see exhibited by
the erect human form.   The extreme variety of combination in
the action of the muscles in man is one cause of this superiority.
But another and the chief cause is the impress of beauty given
to graceful  action  by the mind.   Almost all muscular action
speaks to us a  language  that comes from the thought and feel-
ing at work within, even when it is unintended ; and this is the
source of a large portion of the enjoyment that we receive, for
the most part unconsciously, from the graceful movements that
we witness in  our  fellow men.   And when in a beautiful and
graceful form we come to add to the ordinary movements of the
body, which are commonly, though improperly, considered as
meaningless, those movements which are distinctively expressive
of thought  and  emotion, we  are filled with admiration of the
wonderful capabilities of the human frame in graceful action.
   560.  The human form in repose, when in  its greatest perfec-
tion,  far transcends, as  a combination of varied  beauty, any
thing that we  see  in the inferior animals.   But its superiority
in this  respect is  best  seen  when the  intelligent and feeling
mind puts it into action.   And this is especially true  of those
parts which are most engaged in expression—the hand with its
endlessly varied  movements, but most of all the face.   It is in
this noblest part of the  human  frame that  the soul of man,
through the subtle agency of the nerves, most strikingly imprints
its  immaterial qualities  upon a material form, and exhibits the
highest graces of motion in the delicate and ever varying play
of the muscles.  And when in the impassioned speaker, while
the muscles of the voice and articulation are  executing their
exceedingly rapid and complicated movements, we see the whole
frame in its motions and attitudes brought into consonance with
the burning words  and the beaming countenance, we take in
the full idea of the adaptation of the human body to the mind
that tenants it.  Though the hand is commonly spoken of as
affording the best illustration of man's superiority to other ani-
mals in muscular action, it is far  from  being as impressive an
exhibition of it as  this  action of the whole frame.  It is when
the mind, through the  numberless  nerves that connect it with
every part of the body, brings them  all into  its service in ex-
pression, that we get the most exalted conception of the excel-
lence of the human organization. 
VARIETIES OF THE HUMAN RACE.        367
Mankind all the same species, but presenting very marked varieties.
                   CHAPTER  XIX.

                VARIETIES OF THE HUMAN RACE.

  561.  Although, as we look  at men of different nations, we
find that there is a general  agreement  in form and organiza-
tion, there are many points in which they strikingly differ from
each other.   " With those forms, proportions, and colors,"  says
Mr. Lawrence, " which we consider so beautiful in the fine fig-
ures of Greece, contrast the woolly hair, flat nose, thick lips, the
retreating forehead, advancing jaws, and black skin of the negro;
or the broad square face, narrow oblique eyes, beardless chin,
coarse straight hair, and olive color of the Calmuck.  Compare
the ruddy and sanguine European with the jet  black African,
the red man of America, the  yellow Mongolian, or  the  brown
South Sea Islander; the gigantic  Patagonian to  the dwarfish
Laplander;  the highly civilized nations of Europe, so conspicu-
ous in arts, science, literature, in all  that can strengthen and
adorn society, or exalt and dignify human nature, to a troop of
naked, shivering, and starved New Hollanders, a  horde of filthy
Hottentots, or the whole of the more or less  barbarous tribes,
that cover nearly the entire continent of Africa;—and although
we must refer them all to the same species, they differ so re-
markably from each other  as to admit of being classed into a
certain  number of great varieties; but  with  regard  to the pre-
cise number, naturalists have differed materially."  Cuvier ad-
mitted but three varieties, the Caucasian, Negro, and Mongolian.
The more commonly received  classification,  however, is that of
Blumenbach, who makes five varieties, viz., the  Caucasian,
Ethiopian,  Mongolian, American, and  Malay.
   562. The chief characteristic of  the  Caucasian variety is the
fine form of the head, it being nearly oval, as you view it from
the front.   It is also characterized by a great range of varia-
tions of the color both of the  skin and  the hair.   There has
been more  of civilization and improvement of every kind in this
race than in any of the others.  It is  mentally superior to the
other races.  It is  called Caucasian  from  Mount Caucasus, from
the  vicinity of which, it is supposed, it originated.  Even at the
present  day it is said that  the characteristics of this race are 
368              HUMAN PHYSIOLOGY.
            Blumenbach's classification—most commonly received.

most perfectly developed in the Georgians and Circassians, who
live in the neighborhood of this range of mountains, and who
are considered the handsomest people in the world.
   563. The Ethiopian variety  is  quite  in contrast  with  the
Caucasian.   The organization  has not the perfection and ele-
gance which the Caucasian presents, and it shows an approxi-
mation to the higher orders of the inferior animals.   The skull
is small.  The forehead is  retreating, while the face below is
projecting,  the  cheek  bones being prominent,  and  the  nose
broad.  The apparatus of the senses is  thus  fully  developed,
while the brain is less than in the Caucasian.  The hair is black,
oily, and frizzled.  It  is commonly said  to be woolly, but it is
really not so.   Dr. Carpenter  says that " microscopic examina-
tion clearly  demonstrates that the  hair of the negro has exactly
the same structure with that of the European, and that it does
not bear any resemblance to wool  save in its crispiness  and its
tendency to curl."  The skin  is generally black; but not so in
all the race, for the Caffirs and the Hottentots  are yellow.
   564. The Mongolian variety, of which the Chinese  race forms
the largest  family, is  characterized by prominent broad cheek
bones, flat  square face, small  oblique eyes, straight black hair,
scanty beard,  and olive skin.
   565. The American variety is  characterized  by high cheek
bones, a narrow low forehead, features large and bold, except
the eyes, which are  deeply sunken in  large sockets, hair gen-
erally  black, stiff and  straight, and complexion varying from a
crimson brown to a deep copper.
   566. The Malay  variety, which occupies the Islands south
of Asia, in the Indian and Pacific oceans, has not so well marked
characteristics as the other varieties.  The complexion is brown,
varying from  a light  tawny to almost black, the hair is black
and thick, the forehead is  low and round, the nose is full and  *-
broad, the nostrils wide, and the mouth large.
   567. Other classifications have  been made, in some of which
the  human race  is  divided into  many  more  varieties.  Any
classification must be in a great  measure arbitrary,  and must
be regarded rather as  a convenience, than as having the defi-
nite and invariable  character which  belongs to truly scientific
distinctions.   In each of  the  five  divisions  of Blumenbach
there  is great diversity.   Thus, in the Caucasian  variety, the
English, the French, the  German, the Irish, &c, are quite dis-
tinct from  each other.  And we sometimes  see very striking
characteristic marks separating single families from others.   The 
VARIETIES OF THE  HUMAN  RACE.       369
    Differences in individuals, families and nations—produced by similar causes.

varieties of the race are thus almost endless, the lesser differing
only in  degree from the larger.
   568.  The national differences  are  evidently  produced by
causes of  very much the same character with those which pro-
duce differences in individuals and families.   And the question
arises whether  such differences as those which Blumenbach de-
scribes  as marking the races, are not produced  in a  similar
manner.  This question has been much discussed, and there is
great difference of opinion in regard to it.   The great majority
of naturalists believe in the unity of the origin of the  human
race, and  hold that its varieties  are the results of the  various
circumstances by which  man has been surrounded.  But some
suppose that the different varieties come from  separate pairs
created by God in different localities, and hold that the  history
in Genesis is a history of the origin of only one of the varieties
of the race.  Those who advocate this doctrine are few in num-
ber ; but  it has  acquired greater  currency of late, because  one
of the  most eminent naturalists of  the present day, Professor
Agassis, has espoused  it.   His  doctrine on this subject I will
give as briefly as possible.
   569. All animals, he  asserts, like plants, have  particular lo-
calities, for  which  they are fitted, and to  which  they  belong.
These zoological  provinces, as  he terms them, are of unequal
extent,  some animals having a wider range than others.   From
this general law of distribution, which he illustrates with many
facts, he infers that the various animals on the face of the earth
were not  created in one part of  the earth and distributed from
this to  other parts, but were created in the provinces to which
they belong.   This view of the subject forces itself upon the
mind of the naturalist, as he  observes the arrangement of the
various tribes of animals on the earth's surface.   And  besides,
there are apparently insurmountable difficulties in the way of  a
diffusion of animals over the globe by means of migration.  For
example,  we cannot conceive how the polar  animals could have
migrated over the warmer tracts  of  land, which they would
have to cross according  to this  supposition, for it  is impossible
now  to keep  them alive  under such circumstances with the
greatest  precautions.   And farther, some animals of the same
species, sometimes presenting  varieties and sometimes  not, are
found in  different  localities which are  so cut  off from all com-
munication with each other, that it is impossible that these ^ani-
mals could migrate from some one locality to all the rest.    lo
assume" he remarks, "that  the geographical distribution ot 
370
HUMAN PHYSIOLOGY.
             Doctrine of the multiple origin of the human race.

such animals, inhabiting zoological districts entirely disconnected
with each other, is to be ascribed to  physical causes, that these
animals have been  transported, and, especially, that the fishes
which live  in  fresh water  basins  have been transported  from
place to place—to suppose that perches, pickerels, trouts, and
so many other species  found in almost every  brook and every
river  in the temperate  zone, have been transported from one
basin into another by freshets or by water birds—is to assume
very inadequate and accidental causes for general phenomena."
Not only then  were  different species  of animals created origi-
nally in different  localities, but it is also true to a considerable
extent, that animals of the same species occupying different lo-
calities were created in those localities.
   570.  All this he claims  to be  consistent with scripture, and
with very good reason.  The account of the preservation of an-
imals in the ark, interpreted according to the common license
of language, indicates really only such a preservation, as would
be necessary for the  stocking of that part of  the world where
Noah and  his family  were, after the waters  should  subside.
The number and  the variety of the  animals preserved for this
purpose would of course be very great, and would, according to
the common usage  of language  in  narration, be spoken of in
the terms used in the Bible.  This interpetation holds equally,
whether the deluge  be considered  as having been partial or
universal.
   571.  The case being  thus quite clearly  made out in relation
to animals generally, he proceeds to trace  an  analogy between
them and the races of man in  this respect.  He supposes  that
there are certain  zoological  provinces for the different human
races, as there  are for the  different species  and varieties of ani-
mals ; and  that  these races were separately  created in these
provinces with organizations suited  to their peculiar localities.
While he allows that  climate and  other influences affect the
varieties of  the human  race, he claims that they are not  com-
petent to produce them  alone;  and he infers, therefore, that
there must have been, as in the  case of animals, different original
creations  in the  different  zoological districts.   He  accordingly
claims that the history given in Genesis is a history of the origin
of only one branch of the  human family.  He  does not  sup-
pose that the different  branches constitute  different  species, but
are made varieties of one  species.*   He  characterizes mankind

  * The difference between species and varieties is this.  The distinction of species rests
upon specific characteristics, that cannot be changed by those influences which tend to 
            VARIETIES OF THE  HUMAN  RACE.        371
           Most naturalists believe that the race came from one pair.

as being every where essentially the same in mental character,
and alike the accountable  subjects of God's  kingdom, notwith-
standing  their  multiple origin.   It is  in this  respect that he
considers them as being of one brotherhood, and he looks upon
the expression in  the Bible, " made of one blood," as being en-
tirely figurative, and as referring to " the higher unity of man-
kind, and not to their  supposed connection by natural descent."
   I do not propose  to  go into a thorough discussion of  this
question.  This would not be possible in the narrow limits of
a chapter.  I  shall only present a general  view  of the chief
facts and arguments that bear upon  the point at issue.   And
let us look at this subject first in the  light of physiology  and
natural history.
   572. The great majority of physiologists and  naturalists, as
I have before remarked, have  thus  far been of the opinion that
the human race came  from one origin, and that the varieties of
it  have been  produced by the various influences to which man
has been subjected.   These are commonly included in the gen-
eral expression, climatic and other influences.  To  be more par-
ticular, they  are—climate, situation,  food,  clothing,  customs,
habits, way of life, state of civilization.   Too great prominence
has been undoubtedly given to the influence of climate.  Law-
rence very justly  remarks  in  his  general conclusions in rega/d
to the production of the varieties in man and animals, " that of
the circumstances which favor this disposition to the production
of the varieties in the  animal  kingdom, the most powerful is the
state of  domestication.,"  This word, as he uses it, includes all
those  social influences, which as manifestly affect the animals
which man domesticates as they do man himself.   The analogy
between man and animals in  relation  to the results of the influ-
ences referred to I shall soon  speak of more particularly.
   573. That climatic  and other influences do have a very great
agency in producing the varieties both individual and general,
that we see on looking  over  the human  family, no one doubts.
The  only  question is, whether they have  produced all these
differences—whether,  for  example, they  have  occasioned that
produce the differences that make varieties.  The characteristics of a species are orig-
inal, while those of a variety are acquired.  "The term species," says Prichard, "in-
cludes only the following  conditions, namely, separate origin and distinctness of race,
evinced by the constant transmission of some characteristic peculiarity of organization.
A race of animals or of plants marked by any peculiarity which it has ever constantly
displayed, is termed a species; and two races are considered specifically different, if they
are distinguished from each other by some characteristic which the one cannot be supposed
to have acquired, or the other to have lost, through any known operation of pnysical
causes." 
372              HUMAN PHYSIOLOGY.
         Color affected by climate.  Circumstances affecting the form.

very wide difference that we see between the Caucasian and the
Ethiopian.   My limits will not allow me to go into a full exam-
ination of the influence of these causes, and I can only touch
upon a few points in a very general way.
  574. That climate has a great influence upon the color of the
race is proved  by many clearly observed facts.   Tropical heat
always has a tendency to produce  a black skin.   This is shown
very decided^ in the case of the Jews, who have preserved their
characteristic features  amid varieties of climate, and yet have
their color altered.  Thus, while  the Jew of the interior of
Europe has a fair complexion and light hair, under the scorching
sun of India his hair is crisped, and his skin is black.  The ev-
idence of the influence of climate  is the stronger in this case,
because the change  from the original color has  been two-fold.
For the original Jew in Palestine had undoubtedly a dusky skin
and  dark hair, upon which the temperate climate  of the interior
of Europe, and the tropical climate of India have produced two
opposite  effects.
  575.  But in  the varieties of the human race there are differ-
ences of  form as well as of color.   That the various influences
to which man is subjected have a marked effect upon his phys-
ical  form is  universally acknowledged.  We see this  alike in
individuals, families,  and nations.  Intellectual and moral influ-
ences manifestly exert some  influence in moulding the shape of
the head in the individual.   The differences, which we so com-
monly see in  the shape of the head between the intellectual and
the  ignorant, are not  owing altogether to original difference
of capacity, but in part to education.  The brain, like all  other
organs in the body, is influenced  in its development by the
degree of activity to which it is stimulated.   It is not made an
exception to this general law of development.   Accordingly we
find  that depressing influences tend to make the top of the head,
the cerebral part, small, and the forehead retreating, while the
face, from the predominance of the sensual over the intellectual,
is rendered relatively too prominent.   The tendency of elevating
influences is of an opposite character.  And such influences, thus
operating in  the individual,  when repeated  and accumulated
from generation to generation, produce great and  lasting results.
It is thus that a race becomes either degraded or  elevated.  By
a continuance and  accumulation of influences it acquires either
a good or a bad fixed character.
  576.  I have thus spoken of one  class of causes  effecting
changes in the physical form, the influence of which is manifest. 
           VARIETIES  OF THE  HUMAN  RACE.       373
           Marked tendencies to three different forms of the head.

But  there  are changes  seen, the  causes  of which we cannot
clearly make out;  and yet we know that they  are occasioned
by the varying circumstances in which man is placed.   By the
compound  influence of many causes  combined  we continually
see differences in the shapes of various parts of the body intro-
duced.  Family and national peculiarities are thus occasioned.
The  influences to which I have thus referred, some of which are
little understood, are all  those which  Mr. Lawrence includes in
the term domestication, which, as I have before said, he applies
to man as well as to animals.
   577. Dr. Prichard has pointed out three different types of
form in the  head, occasioned by three distinct classes of influ-
ences.  One  he terms the prognathous, (a word derived from
two  Greek words meaning  before and  the jaw,) in which the
jaws project very prominently forward.  This formation is char-
acterized by the predominance of  the sensual  over the intel-
lectual, the apparatus of the  senses being  largely developed,
while the cerebrum is small, making the  forehead retreating.
The tendency to assume  this type is always in proportion to the
action of the' degrading influences.  " Want, squalor, and igno-
rance," says Carpenter, " have a special tendency to induce the
diminution of the cranial portion of the skull, and that increase
of the facial, which characterize the  prognathous type." It is
seen most strongly marked  in  the negroes of the Gold Coast.
In the pyramidal type, as it is termed, the cheek bones are very
broad, and the bones above are so shaped as to  give the top of
the head a sort of pyramidal form.   This type  we see in those
tribes that lead a wandering life—the nomadic races, as they
are  called.   The oval or  elliptical form, which is seen  so well
marked in the Caucasian variety, is manifestly the result of ele-
vating influences.   These types are convertible into each other.
Thus, the oval  mav be  degraded into the prognathous, or the
prognathous may be elevated into the oval.   The latter  change
is seen in the Ethiopian, when in successive  generations he is
subjected to  elevating influences,  in his intercourse  with the
Caucasian.   And it is interesting to observe that the form of the
head is more  readily changed than the color.   " Thus," says
Carpenter, " in  some  of the older West  Indian colonies, it is
not  uncommon to meet  with  negroes, the descendants of those
first  introduced there, who  exhibit  a very European physiog-
nomy ; and  it has even been asserted that a negro belonging to
the  Dutch portion of Guinea may be distinguished from another
belonging to the  British settlements, by the similarity of the 
374
HUMAN PHYSIOLOGY.
         Insensible gradations in diversity.  Fixedness of the varieties.

features and expression in each, to those which peculiarly char-
acterized his master's.  The effect could not have been produced
by the mixture of bloods, since  this would  be made apparent
by alteration of color."  In the same way is the pyramidal type
convertible with the others.   The pyramidal and  the  progna-
thous are often mingled together, by the influence of vagabond
habits and degrading causes.
  578.  The view thus given of the operation of influences in
producing  the varieties of mankind is  strengthened by the fact
that, as Humboldt says in his Cosmos, there are "many inter-
mediate gradations in the color  of the skin and in the form of
the skull."  If we look alone at  the extremes in varieties of color
and form, we are of course disposed to regard such great differ-
ences as marking a  distinction  of species.   But when  we see
these varieties passing into each  other  by such insensible grada-
tions, and at the same time observe the manifest influence of
causes upon these gradations, as in the cases referred to in the
last paragraph, the evidence is clear to us that the varied influ-
ences brought to bear upon man are competent to produce the
varieties of the race.
  579.  But it is objected that although climatic and other in-
fluences have a great effect, yet, so far as we can see, they only
produce  changes  that  approximate to those differences  that
mark the grand divisions of the race.   They cannot, for exam-
ple,  be  shown,  from actual observation, to  have effected the
entire change in any length of time of any portion of the Cau-
casian race into the  Ethiopian, nor, on the other hand, of the
Ethiopian  into the Caucasian.  It is  objected, farther,  that the
peculiarities of the principal varieties of man existed  in the early
history of  the race.  This appears in relation to the Ethiopian
variety in  the figures found on Egyptian monuments.   These
show "that  the peculiarities of the negro race were as strongly
marked nearly 5,000 years ago as they are now.  This fixedness
of character under such a variety of influences  continued so
long, it is claimed, indicates that the peculiarities were  original,
and not acquired.
  580.  In reply to both of these objections, I  will call your
attention to a general fact, which I deem to  be very significant
in its bearing upon the great point at  issue.   It is the fact that
when a variety is formed by any influences, either among plants
or animals, it is apt to remain in  spite of opposing influences.
It seems to be easier by far to produce a variety, than  to bring
it back to the character  of  the  original from which it came. 
VARIETIES OF THE HUMAN RACE.        375
          Influence of " domestication " both in man and in animals.

Domestication has  been continually producing varieties in the
animals that man has so largely appropriated  to his service, and
the varieties once produced, commonly remain.   And the same
thing is seen in the varieties  resulting  from the same class of
influences so continually in the human race.    It is  matter of
common observation that family and  national  peculiarities are
apt to be perpetuated.   And it  is not merely  from  a continu-
ance  of the causes from which  they result, for they are apt to
remain even when strong counteracting  influences are brought
to bear upon them.  Now the causes  which tend  to produce
varieties  in the human  race  acted  of  course  at  the first, and
were  competent to produce the most prominent varieties during
the first ages of the race.  And the tendency to fixedness, which
we see exemplified in so many  ways  in the varieties of both
plants and animals, is sufficient  to account for the perpetuation
of such marked characteristics as those  of the  Ethiopian and the
Caucasian.
   581.  The analogy then which is thus observed between  man
and the domesticated animals is  a  much clearer and stronger
one, than that which Professor Agassis has attempted to make
out between man and animals generally in regard to zoological
districts.  And the inference is a legitimate one, that the same
influences, that we see produce varieties in domesticated animals,
are competent to produce the varieties in the human race, which
are even less marked than some of those which we see in ani-
mals.   Varieties  are produced  more readily and  in greater
numbers in animals than in man, probably  because they have
less power of resisting influences that act upon them.  The va-
rieties of some of the domesticated animals are very numerous.
   582.  The analogy drawn between man and animals in regard
to  zoological  districts is weakened  by the consideration,  that    *-
there was no necessity for  man's being created in different lo-'
calities, because  he can  migrate  so  easily from one country to
another.  The necessity existed in regard to plants and animals,
but not to the same extent in all.   Migration  is easier in the
case of some  than in the case of others.  And this difference
seems to have been acted  upon  by  the Creator.   Accordingly,
the evidence is quite conclusive,  that those animals which  have
been  so universally appropriated by man  to his  service,  have
been  diffused from central  points  and  have gone  with  man,
instead of being created in many  localities.  This being the
case,  it is hardly  to be supposed that man, who  is capable,
through his  ingenuity,  and  skill, and daring, of going  every 
376              HUMAN PHYSIOLOGY.
      New causes occasionally introduced by the Creator.  Facts showing this.

where, would be unnecessarily created in different pairs at differ-
ent points on the earth's surface.
   583.  But suppose that in view of all the evidence we should
come to the conclusion, that the climatic and other influences
are not the sole causes of the differences in the races, are we of
course driven to the admission that, as Agassis and others teach,
there must have been created at the first, several, we know not
how many different pairs in different localities ?  By no means.
We are not to forget that the Creator, besides using influences
of which we have no knowledge, (which he is continually doing,)
can  effect new combinations of the causes already existing, or
introduce into operation  entirely new causes.  That he is from
time to time evolving new results in one  or the other  of these
ways, or both of them, is  manifest.   The  very common notion,
that at the creation all the causes which have produced all the
phenomena  that have  been observed to the present time, were
then set in operation, and have been left  to work out their
results,  seems to be  contradicted by many facts.   Most  of the
causes then  set in operation, it is true, have been at work ever
since.   Unless this were so, nature  would  not  exhibit the regu-
larity which  it now does, and  calculations could not be made
with such definitene"ss as to its processes from knowledge gained
by experience.  But changes and irregularities sometimes occur
which must have been the result of new causes.   I shall allude
to but a few examples.
   584.  The age of man before the flood was much greater than
it  has been since.   A change was  effected at that period.  It
was not a mere arbitrary change, but such a change in  the very
character of the human system, that  its capability  of  resisting
the tendency to decline was greatly reduced in the period of its
continuance.  It was not a change  resulting from the influence
of deteriorating causes, for in that case it would  have been less
suddenly induced.   To effect this change some new causes must
clearly have been  brought to bear upon  the system, making it
in  the post-diluvian a different system in some important respects
from what it was in the ante-diluvian.  Take  a fact of a differ-
ent kind, indicating a similar change of agency.   New diseases
from time to time  appear.  This could not occur without either
entirely new causes, or new combinations of elements heretofore
existing.  That very definitely  marked disease, the small pox,
we have the best of evidence, was not known to the  ancients,
and is  comparatively  a modern  disease.   It  is  impossible to
conceive of  its being introduced without some new cause of a 
VARIETIES OF THE  HUMAN  RACE.       377
       Supposition of new causes more probable than Agassis' supposition.

very definite character.   Take  now  another fact  of  a widely
different  kind from either  of those  to which I have alluded.
The earth is marked all  over with signs  of great  convulsions
that have occurred since its first creation.   It has been supposed
till  recently that these signs all refer  to  that great  event de-
scribed  in the Bible, the  Deluge of  Noah;  but  geological
researches have  demonstrated  pretty clearly that they point in
part at least to other previous convulsions.   Now these convul-
sions are not to be reckoned as a part of  the regular order of
nature.   They could not have resulted from the ordinary causes
that act continuously.   New causes must have been introduced
at the time, to produce  these unwonted results.
  585.  It matters not to the argument above indicated, whether
the new results  that are  occasionally developed, come from a
direct agency at the time, or come from a  chain of causes set in
operation a  long time before.   The results are new results, and
come from causes or  combinations  of causes, which differ from
those that have produced the ordinary and  regular results which
we  witness from day to day or from year to year.
  586.  Now in like manner can we suppose, if it be necessary,
that the  Creator  produced  the varieties of the human race, by
adding other and new causes to the ordinary influences to which
man is subjected.   This is  a much more  probable supposition
than that of the  advocates of the  multiple  origin of the race.
For besides  accounting satisfactorily for the facts, and at the
same  time  being consistent with  the  record in Genesis, it  is
more clearly supported  by analogical  facts  than the supposition,
(for it is a mere supposition,) that  the  human race was created
in different  localities.  And farther, this supposition avoids diffi-
culties which attend the  other.   For, if  we  suppose that the
race came  from  different pairs, it would  be difficult to decide
how many  pairs there  were.  Such  are the variations of the
race in different localities that there  would  be much disagree-
ment as  to  the  number of the  representative  pairs,  and  their
distinguishing characteristics.
   587.  But it may perhaps  be said in  objection, that I am
supposing a miraculous interposition.   Whether it may rightly
be  termed such  I will not stop to consider, but will  merely re-
mark, that it is just such an interposition, or rather, direct agency,
as is affirmed by the advocates of  a multiple creation, differing
from it  only in the time  of its occurrence.  They suppose the
direct  agency of God  to  be put  forth in creation at different
points, whether at different times they do  not say, and this is
r                           32* 
378               HUMAN PHYSIOLOGY.
             The testimony of the Bible to be received as evidence.

really quite immaterial;  and I suppose the same direct agency
to be put forth,  but  in  a  less  marked manner, to produce a
change in what has  been  already created.   In supposing the
direct agency of the  Deity at all, we go beyond mere physics;
and he surely has the power to  put forth  this  agency at such
times as he pleases.*
   588. But the supposition made  above  is not in  my view
needed.   I believe  that the regular, continuous, natural causes,
which have ever operated upon man, have been  competent  to
produce all  the varieties of the race.   And I only suggest this
supposition, as a  consideration  for those who  fail to see that
these  causes have been thus  competent;  and I  claim that
it is a  more  probable  supposition  than the one  offered  by
Agassis  and  others to meet the difficulty in the minds of such
persons.
   589.  Thus far I  have  treated  this subject  chiefly  as  one
of natural  history  and  physiology.   But  is  the  testimony of
the Bible not to be  received as a part of the evidence ?   Is
the  question to be  decided wholly  on considerations and facts
drawn from natural  history and physiology ?  This  seems  to
be the view of some  naturalists,  though the  great majority of
them are disposed to  admit the  statements of Scripture as evi-
dence.   It is true  that the Bible does not purport to be  a phi-
losophical book.   Its language is based upon the principles of
common  and  not scientific usage,  and  is so to  be interpreted.
And it should be thus interpreted in relation to the subject be-
fore us.   Its statements on this subject are of the  most explicit
character.  It purports to give an account of the  origin  of the
race, and portions of  its  history.   It ascribes the corrupt char-
acter of  the race to a fallen parentage.  This connection of the
general corruption of the race with the fall of its  original pair,
however divines and philosophers  may differ in accounting for
it, is recognized as a  fact throughout the whole book of revela-
tion.  The  testimony is  definite, and is  not to  be mistaken.
The question is,  whether it be valid  testimony.   And  if the
Scriptural record be established, as  it  is abundantly, by both
  * There seems to be in the minds of some naturalists a great reluctance to admit at all
the direct ngency of the Crentor, whether it be exerted in consonance with the order of
nature which he has established, or miraculously in  opposition to it.  And they would
smile skeptically at what they would deem the simplicity or superstition of Hugh Miller,
in referring some narrow escapes which he has had, in pursuing his geological researches,
to a particular Providence. The relation of the agency of the great First Cause to second
causes, it is true, is a mysterious subject; but it implies no disposition to fathom what is
unfathomable if we assert that the facts are far from warranting us in the belief, that this
agency has not been exerted since the period of the creation, but confined itself to that
time. 
VARIETIES OF THE  HUMAN RACE.        379
        The unity of the race recognized by the whole scope of the Bible.

internal and coincident evidence, its testimony in regard to the
origin of the race is to be received  by scientific  men.   It can
not be set aside by any mere presumptive and analogical evidence
drawn from physiology  and  natural  history.   If  actual facts
be  proved inconsistent with the Mosaic history,  as properly
interpreted, they will  of  course bring discredit  upon that his-
tory.   No  immunity  against  a strict investigation is to be
claimed for the Bible.  But there is  no fear of such an issue ;
and it is to be remembered  that mere analogies are not facts,
and are not to be deemed as having much force, especially when
there is a question in regard to  their value in comparison with
other analogies that point to an opposite conclusion.
   586. If the account given  in  Genesis be a correct account,
as is generally allowed by the advocates of the  multiple origin
of man, and if, as they claim, it is the account of the origin of
only one branch of the race, while  other pairs were created in
other  parts  of the world, they are  driven  by the  facts in the
case to this  alternative.  Either other pairs were created with
an  original  corrupt nature, or  they were created  innocent as
Adam and Eve were, and then were tempted in a similar man-
ner and with a similar result.   To  claim  that  the  other pairs
were made so like Adam and Eve  as to constitute with them
one species, alike physically, intellectually and morally, without
taking either  of the suppositions  just  given, is to admit the
truth of only'a small portion of the Mosaic account, and is also
inconsistent with the existence of the  great acknowledged  fact
 of the general  corruption of the  race.   So that it is evident
 that the unity of the race, and the truth of the Mosaic history,
 must stand or fall together.  And  it is not the truth of this
 history merely that is involved in  this  question, but the truth
 of the Bible as a whole.   For the corruption of the race, which
 the Bible seeks  to remove, as  before  remarked, is throughout
 this book distinctly referred  to  the  fall of man as recorded in
 the Mosaic history "as its origin.  The main facts of that record
 are recognized as  true by the whole  scope of the  Bible, what-
 ever may be thought of  the minute particulars of the narration.
 It matters not then, you will observe, to the argument, whether
 the  Mosaic account be received as true in all its minutiae, or
 whether it be  considered, as it is by some, as a mere myth.
 For the argument is based upon the recognition by the rest of
 the Bible of the main facts contained in the history.   And if it be
 a myth or fable, it must be based  upon these facts, or, in other
 words, it is these facts that it is the object of this myth to convey. 
380
HUMAN PHYSIOLOGY.
         Distinction between man and the higher animals very definite.

   587.  I have thus presented a summary (for it necessarily is a
mere summary) of what I deem to be the proper view of this
subject.,   In doing so, I have left out many facts and considera-
tions which  are important, if we intend to  go into a full and
thorough investigation.  I have selected for your consideration
those points which are  most  prominent and important.  I have
attempted to indicate as clearly as  I can the value of the differ-
ent prominent arguments, that have been  advanced  on both
sides of the  question.   And from the views and facts presented
I think  it very evident, that the  true interpretation of the pre-
sumptive evidence, drawn from natural history and physiology,
is entirely in accordance with  the  teaching of the Bible, viz.,
that God " made of one blood all the nations of men for to dwell
on the face of the earth."   We are all one brotherhood.  And,
therefore, however debased  our fellow man may be—to what-
ever degree of degradation the unrestrained corruption of his
nature  may have brought  him—we are  to look upon him as
containing the elements of that moral and intellectual elevation
which is attained  by the most gifted of men.  It is  this view
of the subject that imparts dignity,  and interest, and hope, to  all
philanthropic efforts to raise man  from the moral, intellectual,
and physical degradation, to which sin has reduced him.
   588.  Although there are perhaps none  at the present time
who distinctly advocate  the doctrine, that  the lower  races  of
men, as they are  termed, are half way between man  and such
animals as the monkey and ourang-outang, yet there is in some
minds an indefinite partial admission of this idea.  There is a
disposition in some naturalists to make the most of any resem-
blances  found between these races and animals.   The attempt
has been sometimes made to  show, that there is a decided  re-
semblance between the form of the Ethiopian and that of the
monkey tribe.  But it has always  failed:   It has been said that
the arm of the negro is longer than that of the Caucasian, and
that in  this  respect he approaches  to animals of this class.  But
the difference is so slight that  the  analogy fails entirely.   And
besides, the  hand of the negro, the most important part  of the
upper extremity,  bears no manner  of resemblance to the imper-
fect hand of the monkey,  but  is  essentially like  that of the
European.   It has been said, too, that the brain of  the negro is
like that of the  monkey.   The brain in any race or family of
men that are debased  and ignorant is smaller than in the ele-
vated, and in this respect alone does it approach to that of the
monkey and other higher orders  of animals.  And,  as I have 
LIFE AND  DEATH.
381
     Life, though various in its manifestations, in some senses always the same.

before said, there are certain mental characteristics in the most
debased which link them to the most  exalted of our race, creating
an " impassable chasm " between them and the most intelligent
of animals.
                   CHAPTER  XX.

                      LIPE AND DEATH.

  589. Life is very commonly spoken  of as being one thing,
although  its manifestations  are  exceedingly  various  in their
character.   In  the  simplest  growths that we see, both  in the
vegetable and  the  animal kingdoms, the operations of life are
in some respects very different  from the complicated' processes,
that we  witness in the human structure, which has been the
subject of your study in this book.  And yet, as you have seen
in the Chapter on Cell-Life, life in these  apparently  opposite
cases is essentially the same.  It is the same  in its_ origin.  It
begins always in a single  cell, whether the living being is to  be
minute or monstrous, simple or complex, a plant or an animal,
a creature of a day, or a  being destined to immortality.   Why
it is that from a simple cell  the vital force, as it is termed, can
evolve such a  range of diversified results  as we see in all ani-
mated nature, is one of the great mysteries of the Creator.   As
we see in the spring time a bud upon a tree unfold itself grad-
ually, and develop to us successively leaves and  flowers and
fruit, it  fills us with wonder, when we reflect how much has
come from that little  bud;  but when we go farther, and think
of the whole tree  as  having  come from a single cell, so small
that it can be seen only by the microscope, the mystery appears
passing  wonderful.  And it is a still  greater mystery^ when a
complicated animal organization is looked at as having been
developed by the vital force, alike with all other living things,
through a single "cell as its origin.                  _  >
   590.  Life is not only always  the  same in  its origin, but it
 continues essentially the  same in its processes.  All the various
 forms which it produces, both in the vegetable and  animal
 world are built and  kept in repair by cells.  All the  functions,
 too  are carried on through the  same agency.  The  secretions 
382               HUMAN PHYSIOLOGY.
         Difference between the vital force, and heat, light, and electricity.

 and  excretions, as you  saw in § 201, are effected by constant
 successive creations of numberless cells.   Even the intellectual
 operations in the mind of man are dependent upon cells so long
 as the mind is connected with the body.  In thinking, as well
 as in muscular motion, cells are  worn out, and must be replaced
 by other cells, which are continually supplied by the vital force.
   591.  Life being thus wonderful in its operations, the  inquiry
 arises, what can  this mysterious  agent be.   With curious eye
 we watch its workings, but although we  can learn some of its
 laws, its nature  eludes our search.  Then pressing the  micro-
 scope into our service, we trace  it back to its hiding place in a
 minute  round cell containing  a fluid; but simple as this prison
 is in which it is  confined, it  is  more of  a mystery than ever.
 The  vital force, which  begins here, and, enlarging more  and
 more the sphere  of its operations, developes gradually the simple
 or the  complicated  living form, as the case may be, has been
 classed  by  some with  other forces, the nature of which we do
 not understand, as heat, light,  and electricity.   But it differs
 from them  entirely in some important  points.   While they act
 in connection with matter generally, both  organized and unor-
 ganized, vital force is only seen acting in organized substances.
 While  they diffuse themselves through all kinds of matter with
 more or less rapidity, the vital force has no  power of diffusion,
 but is confined within certain  limits.  These limits differ in the
 different living substances.  The  vital  force has  the  power of
 appropriating matter to itself within  these limits.   It does this
 by assimilation, as described  in § 10.  It has  then the power
 of extension to a limited  degree;  while the  other forces men-
 tioned have the  power of diffusion, in some  respects limitless.
   592.  Another difference is this.  While these forces, light,
 heat, and electricity, are  lessened  in  power by being diffused,
 vital force is not lessened by  extension.  Heat, for example, if
 diffused is lessened at the  point of its diffusion; but life is as
 energetic at its starting point after its  extension as before, and
 even more  so.   It is,  so to speak, self-generating,  while  the
 other forces are mere products.   The vital force  stands peculi-
 arly alone  in  this respect.   The effects too,  which  this force
 produces, as  it  lays common matter  under contribution, and
.fashions it  in such  diversi6ed  forms,  have  an infinitely wider
 range of variety than the effects of the other forces.
   593.  We can  thus trace the differences between the  vital force
 or principle and other forces, but we  cannot, as I have before
 said, discern its nature.   We  know not whether it be one thing. 
LIFE AND  DEATH.
383
       Life in the blood. Vital laws control the chemical and mechanical.

It is convenient to speak of it as being so.   But we know not
but that it may be a compound of endowments, or tendencies
imparted to matter, and varying with the various forms of living
substances.   Some have supposed that the vital principle resides
chiefly in the blood, and that this is the meaning of the passage
in the Bible, " the  life of  the flesh  is  the  blood."   That the
blood has  some vital properties is  certainly true.  These prop-
erties are communicated to it as it is made from the food, and
fit it to be  the material for the  construction  and repair of the
organization.  And it is simply the fact, that the blood  is the  „
common material out of which all  the diversified parts of the
living structure are made, that is recognized in the language of
Scripture  on this subject.   The same fact is embodied in an-
other form in the remark of the French physiologist, that the
blood is chair coulante, or  running flesh.
   594.  When the  vital force  appropriates  to  itself common
matter in assimilation, it takes it away in  part from the opera-
tion of certain forces which have had entire control over it.  As
long as it  is common dead matter, it is wholly subject to the
laws of mechanics, and of chemical  action.   But when it be-
comes organized living matter, the laws of life  take possession
of it.  The laws of chemistry and  mechanics are not, it is true,
annulled in relation to it.   They still exert their influence, but
under the control of vital laws.  The force of gravity acts con-
tinually upon the body ; but the living muscles  are much of the
time acting in direct opposition to it.  The blood circulates  on
hydraulic principles; but  the vital force  furnishes  the motive
power, and keeps the blood from  becoming solid and stopping
up its channels.   Chemical changes are going on  in the stomach,
the lungs, and at every point in the capillary circulation;  but
they are modified, controlled, by  the  vital  principle,  and are   ,
properly termed ehemico-vital processes.
   595. The human body is made of materials that are exceed-
ingly prone to chemical  decomposition, and  the  degree of heat
which  is maintained is such as to favor this result; but the vital
force not only holds the chemistry of the  system in abeyance,  \  !
but even presses it into its service.   When life is destroyed, the
laws of chemistry assume  their full sway, and  the process  of
decay begins.  The very agencies which  served, while  under
the control of the vital principle, to maintain the living organi-
zation  now acting  alone  run  riot, and work  its destruction.
Thus,'that powerful agent, heat,  existing in the body  at the
point of  98°, is necessary to the carrying on of the processes of 
384              HUMAN PHYSIOLOGY.
         Change always attends life in action.  Life sometimes dormant.

life ; but let life be destroyed,  and the maintenance of this de-
gree of heat would ensure a very rapid putrefaction.  So too, a
degree  of heat  which would  rapidly  putrefy  a  dead egg by
quickening the chemical changes, would actively  stimulate in a
living egg those  curious vital processes that  produce at  length
the bird.  During incubation the egg of the  hen is kept for
three weeks at a  heat of 105°, and  yet when  the chicken is
hatched all of the yolk that is left is unchanged.   A dead egg
would soon putrefy under such a temperature.
   596. The vital force exhibits its  controlling  power in  an ex-
traordinary manner in connection with that great force of nature
to which I have  just  referred.  Heat is very diffusive, and is
exceedingly liable to change from varying circumstances.   And
yet the vital  force maintains  the heat of the body  quite uni-
formly at one  point, although the agencies which tend to  vary
it are very numerous and effective.   The  production of heat in
the system is a chemical operation, but the vital  principle  reg-
ulates  the quantity in the body very  accurately, by providing
for its escape in various ways, and perhaps by curtailing in some
measure its production.
   597. Continual changes are effected by the vital force in every
part of the body.  In one sense death  may be said  to be taking
place constantly, while life is as constantly generated,  as the
useless  particles are separated and taken away, and the new
ones  are deposited  in  their place.  While  these changes are
going on the vital force so  operates as  to  maintain  the peculiar
shape and plan of every part, even during its growth.  And as
we look abroad  over all the  diversified forms of animated na-
ture, the accuracy with which this force works  in  the  prescribed
mould of each is very wonderful.  This point I  have commented
upon in the first chapter, page 18, and will not  dwell  upon it
here.
   598. While the  vital force is in  action there is constant
change ; but sometimes it is dormant.   A seed in its quiescent
state has life in  it, ready to be waked  into action by  the proper
excitants, air, warmth, and  moisture.   Seeds that were found in
the excavations of Pompeii have shown that they retained their
life during all this time, by shooting forth their  germs as soon
as they were exposed to these natural excitants of their growth.
One of the most interesting cases of this kind  is  related by Dr.
Lindley.  " I have  now before me,"  he says, " three plants of
Raspberries, which have been raised in the gardens of the Hor-
ticultural Society, from seeds taken from the stomach of a man, 
LIFE AND  DEATH.
385
Mysterious connection of life with the soul.
whose skeleton was found  thirty feet below the surface  of the
earth, at the bottom of a burrow which was opened near Dor-
chester. - He had been buried with some coin of the Emperor
Hadrian, and  it is probable, therefore, that the seeds were six-
teen or seventeen hundred  years old."
   599.  A similar dormant condition of the vital force exists in
a greater or less degree, as you saw  in  § 158, in the state  of
hibernation.   So also, in  cold climates,  life is throughout al-
most the whole  vegetable world dormant during the period  of
winter, to wake  to greater  energy from the stimulating warmth
of spring.  In the human body, with the  exception  of some
few  very rare cases, life is always in an active state.  Some
portions, however, of the system are a part of the time dormant
for the purpose  of rest and repair.  The brain and the muscles
sleep ; but during their sleep life is busy in the formative vessels,
repairing their  energies, and we may say, their textures also,
which have been wasted by their labor.  I will not dwell longer
upon this interesting subject, but in leaving it I remark, that it
is a  very wonderful attribute  of the vital force that it can, as
in the case of the  hibernating warm  blooded animals, stop all
its active operations,  without damage to the machinery of life,
and  with such  facility resign itself into  a  state of temporary
inactivity.
   600. The most mysterious of all the circumstances in regard
to the vital force is its connection  in man with the immortal
soul.  The  life  and  the  soul are so intimately connected that
some have considered them to be the  same.  But they are two
distinct forces.  They are in some measure indeed antagonistic to
each other.   For the soul, in using the machinery of the nerves
and muscles occasions a wear and tear of the structure, which
it is the office of life with its numberless  cell-laboratories to re-
pair.  The  soul and the vital principle are both  present in  all
parts of the  system, but  not in  the same sense.  The vital
principle is seen equally at work every where.   It has no great
central organ from which  it sends forth its influence.  But the
soul is especially connected with the brain, and by means  of
the  complicated nervous  connections of this  organ, it affects
and is affected by all parts of the system. Its influence is thus
an all pervading one.  Every point of the living  organization
has  thus a sort  of telegraphic communication with the imma-

   601   But there is another view of this connection of the soul
 and the vital principle.  The soul is developed in and with the
                           33 
386              HUMAN PHYSIOLOGY.
                   Natural limits of life.  Decay.

living structure.   It is not created by itself and put  into the
body as a tenant.   Its powers  are  developed while  the vital
force developes the powers of the physical  organization.   The
two processes go on together.   Nay more, the development of
the soul is in a measure dependent  upon the  development of
the body.  The vital force exerts a manifest influence  upon the
soul's growth.   As it prepares the  organs  for the use of the
soul—those  organs by which it acquires knowledge from with-
out, and  thus  procures the  stimulus and even the material for
its growth—whenever  the vital force  fails  to construct  these
organs properly,  the powers  of the soul are not well developed.
This we see  exemplified in the idiot.  In this intimate connec-
tion of the soul with life we find a great mystery.   Life, a force
belonging to mere matter, an endowment of it, or a compound
of its endowments—life, that builds up all organized substances,
the humblest  and simplest  vegetable  growth, as well as that
most  complex of all  living structures, man—life, that so soon
perishes in the noblest of its works that it is likened to the dis-
solving vapor—is made by the  Creator an  agent in developing
an immaterial principle or being, that is to survive the dissolu-
tion of the  structure in which it is generated, and is to live
forever.   Strange that the immortal should be thus  produced
in the mortal—that the  unchangeable and imperishable soul
should be thus developed in such intimate connection with the
changeable  and  perishable  body.   It  is a mystery which we
cannot fathom.
  602. The vital force, that is so busy in building and repair-
ing so long  as it lasts, has in all cases its natural limit; and in
the case of the human system it seldom fully reaches this limit.
The diversified, and complicated, and beautiful structures which
it evolves, if saved from accident till the natural period of de-
cline  comes, lose their  vigor and beauty, and at length die and
are given up to the action of the common  laws of chemistry,
which the vital force has so  long resisted and controlled.   The
structures then decay, and the particles are dissipated, perhaps
to be  united again to other structures.
  603. The death  of  the body is  not ordinarily complete at
the moment when  what we term death occurs.   Though as a
whole, as a  system of organs, the operations of life  are at an
end, yet there is some degree of life in some  parts, and  there
may be in all parts  of  the body.   The beard and nails  even,
may grow.  Some of the organs may secrete their fluids—the
liver its bile, and the stomach its gastric juice.  Some of the 
LIFE AND  DEATH.
387
       Systemic and molecular death.  Death beginning in the heart, and in the lungs.

   properties of life, too, manifestly still remain.   The irritability
   of the muscles, which  is strictly a vital  property, as it never
   belongs to common dead  matter, still appears on the applica-
   tion of excitants.  It was the contraction of the muscles in the
   leg of a dead frog on the accidental  application of a stimulus,
   that led Galvani to  his grand  discovery.   And it is through
   this vital  property that the culprit who has been hung can be
   galvanized into apparent  life.   Death then may be said to be
   of two kinds—systemic, that is, the death of the body  as  a
   whole, a  system of  organs—and molecular, that  is, the death
   of the individual  molecules  or  particles  which  compose the
   body.   Death can be said  to be  complete only when the  laws
   of life have resigned their  power over these molecules, and the
   laws of purely chemical action have taken their place.   When
   this change  occurs, the process of decay, which  is strictly  a
   chemical  process, begins.
•     604, It will  be interesting to notice here the modes in which
   systemic  death occurs.  There  are three great systems in the
   body, each of which is immediately essential to the continuance
   of life—the  system of  the circulation, the respiratory system,
   and the  nervous system.   And  we may speak of death as be-   /
   ginning in any  one of these systems wrhen the cause of death
   acts primarily upon it.  I will notice some examples under  each
   head.
      605. If a large quantity of blood be lost, so large as to result
   fatally, death in this case  obviously begins in the circulation.
   The heart not  being supplied with the quantity of blood that
   usually flows  through  it, becomes more and more feeble in its
   action, till it at length ceases to beat.   When a large aneurism
   bursts, it is the sudden drain from the circulation that destroys
   life.
      606. Any thing which to any great extent prevents  the air
   from entering the lungs may cause death to begin in the respi-
   ratory system.  This may be done  by three classes of  causes.
   1st. Causes that act upon  the large  air passages.  Examples
   of  this class of causes are  strangling,  smothering, drowning,
   &c.  In  croup the  principal cause  of  death is the prevention
   of  the free passage of air through the windpipe into the lungs.
   2d. Causes which act upon  the walls of the chest.   If a  bank
   of earth fall upon a  man, though it leave his head clear, so that
   the air passages are unobstructed, he cannot breathe, because
   his chest is held as if in a  vice.   A man came near dying  from
   this cause, who was  having a cast  taken of the upper part of 
388              HUMAN  PHYSIOLOGY.
                Death beginning in the nervous system.

his body.   If the muscles of respiration were to be paralyzed,
death would ensue, just as it  does when they are prevented from
acting by  other causes.  3rd. Causes acting upon the lungs.
Disease may occasion  an amount of obstruction in the very
substance of the lungs sufficient to cause death.  It does so by
preventing the introduction of the air into the minute air vessels,
where the air revivifies the blood.  The obstruction is just  as
effectual in this case as it  is where  it occurs in the large air
passages.
   607.  When death occurs  from a blow upon the head as the
immediate  result of the shock, we have an example of death
beginning in the nervous system.   But the cause may act upon
this system in some  other quarter.  A blow at the  pit  of the
stomach, for example, may so shock the whole nervous system
as to stop at once the operations of life.  Some poisons, too, as
opium, destroy life by their  influence  upon this system.   Very
extensive burns give a shock to the nerves from which they do   •
not rally.   The same can be said of  other injuries when there
is no recovery from the first shock.   Powerful medicines, im-
properly given in cases of disease disposed to prostration, may
depress the nervous system to a point from which it may never
revive.  Cold destroys life mostly by the benumbing, paralyzing
influence which it exerts upon the nerves.
   608.  Though we thus  classify the  modes of death,  in  the
great majority of cases death is a  complex event, resulting from
a concurrence of causes.  It is so even when the disease is not
of a complicated character.   Take, for example, a case of pure
uncomplicated  consumption, in which all the organs but the
lungs are in a healthy  state to  the end.  The whole system
becomes at length exhausted by the disease.   If this exhaustion
alone be the cause of death, then we  may say that it is an ex-
ample of death beginning in the nervous  system.   But  if the
obstruction in the lungs to the admission of  air in the air-cells
be the cause, it is a case of  death beginning in the respiratory
system.  Generally in such  cases death  results from the two
causes combined, and it is often difficult to determine which is
the more prominent cause.
   609. The signs of death are so clear that there is, with very
few exceptions, no mistake in regard to the  occurrence of the
event.  The  stories  that are  related about burying alive are
most of them unfounded. The apprehensions created by them
in the minds of some persons have led them to insist, that no
body ought to be  committed to the grave, till the most infalli- 
                     LIFE AND  DEATH.                389
    The signs of death. Death as viewed by the Physiologist, and the Christian.

ble sign of death, putrefaction, has appeared.  That we should
wait for the appearance of this sign in all cases in which there
is a shadow of doubt, I will  allow.   But the cases are exceed-
ingly rare in which we cannot determine  the  reality of death
long before  this  sign shows itself.  Our decision is not made
up, it must be  observed, merely from the  signs of death.   All
the circumstances of the case are taken into  view—the disease,
its progress, its symptoms, and the events of the last hours of
the patient.   With this evidence before us, we absolutely know,
in all ordinary cases,  that  death  has occurred when the respi-
ration and the  circulation have  ceased.  And in the exceed-
ingly few cases in which  there is any reason to doubt on that
point, there is always something which will attract the attention
and excite the curiosity of some one, unless  there  be  stolid in-
difference and the most absolute lack of intelligence.   In such
cases there  is always something strange—the  circumstances
attending the cessation  of the respiration and  circulation are
singular, and the signs of death are  not complete and in  their
proper order of succession.   Whenever there  is for these reasons
any doubt as to the reality of the apparent death, the strictest
watch should be maintained till the signs of commencing putre-
faction appear.  With this simple rule of prevention burying
alive need never to occur.
  610. The investigations of physiology, as you have seen, end
with  the death of the  body.  It can  give  us no light on the
question  as to what may be beyond this  life.   Although the
physiologist studies the  human structure not merely as an or-
ganization instinct with life, but also as the wonderful machinery
through which a reasoning soul acts and is  acted upon in this
state of being, yet, as a physiologist, he knows not  that the
soul survives the death of  the  body.   He knows not but that
it is  a mere  endowment of matter, as  life probably  is, and so
perishes in the hour of dissolution.  He may indeed conjecture
that such exalted faculties which are in this world susceptible
of such high cultivation,  instead of  being destroyed with the
body, are destined to still farther development in another state
of existence.   But what is mere conjecture to him as a Physi-
ologist, is made fact  to  him as a Christian.   The eye of his
faith sees an  immortal spirit rise from the dying body, and he
realizes the truth of the  sublime declaration, that  "death is
swallowed up of victory."

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