THE BACTERIOLOGY AND PATHOLOGY OF DIPHTHERIA.

   By Simon Flexuer, M. D., Associate in Pathology,
             Johns HLopkins University.
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[From The Johnt Hopkins Hospital Bulletin, No. 48, March, 1895.] 
 
[From The Johns Hopkins Hospital Bulletin, No. 48, March,' 1895.]
THE  BACTERIOLOGY AUD PATHOLOGY OF DIPHTHERIA.*

     By  Simon  Flexner, M. D., Associate in Pathology,
                 Johns Hopkins University.

   The results of the researches of Loeffler published at the
close of  the year 1883 may be said to mark the beginning of
the new era  in  the  study of diphtheria, and  whatever doubt
surrounded  his  first  publication regarding  the  relation to
diphtheria of the micro-organism which now bears his name,
has now been finally dissipated.   The isolation of the Loeffler
bacillus  by workers  in different parts of  the world from the
local lesions of  the disease in many thousands of cases would
seem to  afford irrefutable evidence of  the constancy of the
relationship existing between the bacillus and  the pathological
process.   Hence it is  that  attention has been  directed  to a
consideration of other aspects of the subject than  that of the
presence or absence of the Loeffler bacillus in primary diph-
theria.
   The wide divergence of opinions regarding diphtheria which
existed  prior to the  discovery of  the bacillus  diphtherias
illustrates with  what difficulty every advance in the study of
a disease is accompanied  so long  as its astiological factor is
still unknown.   It had long been a well-established fact that
by a variety of agents, pseudo-membranes which offered more
or less the appearances seen in diphtheria could be produced
upon mucous surfaces in  man and in animals;  but it was at
the same time recognized that none of  these  agents could
reproduce  the  symptom-complex of diphtheria;   and none
of us are likely to  forget .the almost interminable discus-
sion which arose as  to whether  it was primarily a local  or a
constitutional disease.  Nor did the  study of its  pathology
give much assistance in the solution of this question, and  only
  * Being the substance of an address delivered on January 8,1895,
before the Alumni Association of the  Jefferson Medical College,
Philadelphia. 
2
after the specific  micro-organism had been obtained  in  pure
culture did it become possible, by a study of its properties out-
side the body and of its occurrence under natural conditions
in human beings, to establish a rational  basis for a classifica-
tion of the disease.
  First of all, then, it is important to distinguish between the
anatomical and the astiological significance of the term " diph-
theria," and it will  be found that a limitation of the term to
a disease characterized by the presence of  the bacillus diph-
therias in the affected portion of the body will do much to
eliminate the  confusion  of  pathological  conditions which,
while anatomically resembling one another, are otherwise quite
distinct.
  The first  question to which I would direct your attention
regards the proportion of cases of pseudo-membranous inflam-
mations of the  throat which are due to the Loeffler bacillus.
In the first series  reported by Loeffler himself, a certain num-
ber of the cases examined did not yield the diphtheritic bacil-
lus ; but of  these, several were recognized as  not having been
cases of primary diphtheria.  This failure to find the Loeffler
bacillus in all pseudo-membranous inflammations in the throat
and air-passages  has been confirmed by later investigators.
Thus in a table prepared  by Escherich,  in 679 examinations
collected from  Paris, Berlin and  New York,  the bacillus
diphtherias was found in  427, or in  62  per cent, of all  the
cases.  In a  series  studied by Morse of  Boston, of  301  cases
examined, the Loeffler bacillus was found in 217, i. e., it was
present in 72 per cent, of the cases.   Park and Beebe report
that of 5611 cases  examined, positive results were obtained
in 3255 (58 per  cent.).  The bacillus was absent in 1540 cases
(27 per cent), while 816 cases were doubtful. The doubtful
cases represent those in which  for  some  reason or  another
satisfactory  cultures were not supplied.   If these, then, be
disregarded altogether—although it may not be entirely fair to
do this—we find that out of 4795 cases of suspected diphtheria,
68 per cent,  were  instances of true diphtheria.
  It is acknowledged that the pseudo-membranous anginas
which  are associated with the  acute exanthemata are com-
monly not caused by the Loeffler bacillus, but are due in most
cases to the invasion of  the  streptococcus  pyogenes.  In a 
3
series of bacteriological examinations made by Booker in such
cases,  the  bacillus diphtherias  was constantly absent; and
Escherich, who studied fourteen cases  of  scarlet fever, states
that the Loeffler bacillus is  never present in the early days of
the disease, but that in several of these cases they were found
to be present later on, a fact which he attributes to the imper-
fect separation of  diphtheria and scarlet fever patients in the
Munich hospital, where his studies were carried on.   He also
found the Loeffler bacillus in  certain cases of measles and
whooping-cough, and  he  agrees with  other investigators  in
holding that the acute exanthematous diseases predispose to
infection with the bacillus diphtherias.
   It had  been observed by the  older  clinicians that during
epidemics of diphtheria, pseudo-membranous inflammations of
the throat in the course of typhoid fever were more frequent.
Morse reports four cases  of typhoid fever complicated with
diphtheria; at least three of which developed diphtheria after
admission to the hospital.
   A purely local and perhaps non-contagious  inflammation of
the larynx has, by the bacteriological examination of a consid-
erable number of cases of membranous croup, been shown  to
occur unassociated with  diphtheria.  These cases, however,
are quite  exceptional.  Of  88 cases of membranous croup
studied by Martin, 59, or 67 per cent., were of diphtheritic
origin.  The statistics of  Park indicate that in  New York
fully 80 per cent, of  the cases of the same disease are caused
by the Loeffler bacillus.  Of 229 of Park's cases, in 167 no
membrane  or exudate  was found above the  larynx.  Welch
and Abbott, Booker, Williams, Kolisko and Paltauf, Concietti
and Fraenkel have reported cases of laryngeal diphtheria  in
which the pseudo-membrane was confined to the  larynx and
lower air-passages.
   It is an undoubted fact that a case of so-called membranous
laryngitis has not infrequently been the first of a series  of
cases of genuine faucial diphtheria.
   Among the most important results  of the bacteriological
study of the  inflammations of the throat and air-passages has
been the discovery that cases which present the features of a
mild catarrhal angina  or of a lacunar tonsillitis may be  asso-
ciated with the presence of the bacillus diphtherias, and that 
4
from  these can  arise other cases  in which membrane is
found on the fauces.
  This class of cases has been studied by Escherich and Feer,
and especially by Koplik.  Within the past few weeks I have
seen two such instances in the practice of Dr. W. D. Booker,
and from them obtained the Loeffler bacilli in cultures.  The
first was a girl of 16 years, who came to the surgical dispen-
sary of the Johns  Hopkins Hospital for enlarged glands of the
neck. Upon examination she was found to have a lacunar ton-
sillitis.  She suffered no inconvenience other than that result-
ing from the swollen glands.  The plugs  from the crypts of
the tonsils contained the Loeffler bacillus.  She made a rapid
recovery.
  The second was a child one and a half years of  age whose
tonsils were greatly swollen and almost meeting in the middle
line of  the throat.  There was no  visible membrane.  Cul-
tures  from the throat showed the  presence  of  the  bacillus
diphtherias.  The  local treatment recommended by Loeffler
was used, and by the third  day all  symptoms of the  disease
had disappeared.
  Heubner  has  just published a short  series  of  cases, in
which he calls attention to what he describes under the title
of latent diphtheria.   These were secondary to other diseases
than scarlet fever and measles, and occurred in the young in
the course of wasting affections, such as  rickets,  tuberculosis,
etc., in hospital practice.  The symptoms were fever, gastro-
intestinal  disturbance, and slight bronchial and nasal catarrh.
Heubner says that diphtheritic infection  is not apt to be sus-
pected in these cases until laryngeal stenosis suddenly develops,
or the fact is revealed at autopsy by the finding of a false mem-
brane in the pharynx or larynx.*
  Roux and Martin have found in the course of their inocula-
tion experiments  for the preparation of the anti-toxin, that
animals which had been  previously inoculated with other
bacteria or their poisons, from  which they had recovered, were
more susceptible to the diphtheria toxin ; and, similarly, that
pregnant animals or such as  had just given birth to young
exhibited  a similar diminution of resistance.
  *See Flexner and Pease, Johns Hopkins Hospital Bulletin, Feb-
ruary, 1895. 
5
   The mucous membrane of the nose affords a favorite rest-
ing-place for the Loeffler bacillus.  In pharyngeal diphtheria
these bacilli are commonly present in the nasal secretion, even
in the absence of membrane in the nose.  Primary diphtheria
of the nasal mucous membrane sometimes occurs.   Such cases
have been  reported  by Stamm, Baginsky, Abbott, Ravenel,
Czemetschka, Townsend and Park.  Of  the last  two writers
the  membrane was  confined to  the nose  in 4 and  9 cases
respectively.  Escherich has seen one case in which the infec-
tion of the nasal mucous  membrane took place through the
tear-duct in  a case of diphtheritic conjunctivitis.  Katz has
just reported a case of faucial diphtheria which developed in
a child exposed to  infection from another  child suffering
from fibrinous rhinitis due to the Loeffler bacillus.
  Babes first cultivated the Loeffler bacillus from  the pseudo-
membrane in diphtheritic conjunctivitis, and reproduced the
disease by the inoculation  of the organism upon the conjunc-
tivas of rabbits.  A number of cases of  pseudo-membranous
conjunctivitis have since been found to be associated with the
bacillus diphtherias,  although it must be stated that not all
are caused by this  organism.  In two cases which  I examined
for Dr. Hiram Woods the  Loeffler bacillus was not found in
the  exudate,  but  streptococci  were present in  both.  The
results of Councilman's investigations would go to show that
certain cases of otitis media are due to this bacillus.
  The skin surfaces of the body would appear to  be immune
to the action  of the Loeffler bacillus in the absence of any loss
of continuity.  Thus Wright cultivated the diphtheria bacillus
from excoriated or ulcerated surfaces of  the skin in 7 cases of
diphtheria;  and Park  found  this  organism in  wounds  of
the finger received  by physicians while performing intubation.
Cases of wound diphtheria associated with the Loeffler bacillus
are reported by Brunner, Neisser, Treitel and Abel; but it is
probable that most cases  of so-called wound diphtheria are
caused by  other  micro-organisms.  The relative insuscep-
tibility of  the external surfaces  of  the body to  infection
with the bacillus  diphtherias is illustrated by  the behavior
of tracheotomy wounds,  which  only exceptionally become
infected with this  organism.  Faltonek examined  953  trache-
otomy wounds without succeeding in a single  instance  in
isolating the  Loeffler  bacillus.  Other  observers  have been 
6
more successful, but in these cases the possibility of the con-
tamination of the wounded surfaces with the tracheal secretion
cannot be excluded.
  Having now passed in rapid review the situations of common
localization of the Loeffler bacillus upon the surface and in
the cavities of the body, I  would ask your attention to its
distribution within the  viscera.   At  the time  of  Loeffler's
first publication he expressed a belief that the bacillus diph-
therias was to be found only at the local site of  the  disease,
and that it did not invade the tissues at  all, or at least  only
exceptionally.   He had cultivated it, however, in one  case
from the lungs;  and later  Kolisko and Paltauf and Babes
isolated in rare instances a few organisms from the internal
organs.   The  observations  of Frosch,  since  confirmed by
others, have shown that  not uncommonly a few bacilli enter
the circulation and may be cultivated from the internal organs
at autopsy.  They are not  however only small  in number,
but their distribution is irregular, and it is necessary to trans-
plant considerable quantities  of  material  in  order to grow
them.  Frosch cultivated the bacillus from the blood of the
heart, the brain, pleural and pericardial exudates, pneumonic
areas in  the  lungs, spleen, kidneys, bronchial and cervical
lymph glands  and  liver.  Booker  has also  obtained  the
organism from the  internal  organs.  At  the autopsy of a
child of three years which had both pharyngeal and laryngeal
diphtheria I obtained the bacillus diphtherias in pure culture
from the heart's  blood, cervical lymph glands, liver, spleen,
lungs and kidneys, but, contrary to Frosch's experience, they
were present,  in  this  case, in large numbers  in the blood,
glands and spleen.  In this as well as  in a later instance I
was  able to  cultivate the  Loeffler  bacillus from broncho-
pneumonic areas, and also to demonstrate them in sections from
the bronchi and lung tissue.  The predominating organism,
however, was the micrococcus lanceolatus.   Kutscher has just
shown that the Loeffler bacillus exists at times in  consider-
able numbers  and may be  the predominating organism in
cases of  broncho-pneumonia associated with diphtheria, and
he  inclines to  the view  that it is capable of causing both
bronchitis and consolidation of the lung  substance.  Wright
has found the bacillus  diphtheriae in the internal organs in
cases of  human diphtheria, and he  has also cultivated them 
7
from the liver, spleen, heart's blood and kidneys in a small
number of experimental guinea-pigs.  Abbott and G-hriskey
found  that after  inoculating cultures of diphtheria bacilli
into the testicle of guinea-pigs, small nodules containing  this
organism sometimes appeared in the omentum; and this bacillus
has also been cultivated from the ecchymotic  patches in the
stomach and from the surface of the  membrane in croupous
gastritis.  Of especial interest is the case reported by Howard,
in which a bacillus  in all  respects resembling the bacillus
diphtherias, except that  it did not possess  pathogenic proper-
ties for guinea-pigs, was cultivated in large numbers from the
heart-valves in a case of acute ulcerative endocarditis and from
the infarctions in the spleen and kidneys.
  Notwithstanding the results  of later and more  searching
studies which have necessitated  a modification of  the earlier
views regarding the relation of the Loeffler bacillus to diph-
theria, and  notwithstanding the fact  that it is now known
that the Loeffler bacillus can develop not only locally upon
the affected  mucous  membrane, it must be  considered as
proven that only a few organisms  penetrate into  the  body;
and there are  undoubted  instances  in  which the disease has
pursued a typical, severe and even fatal course in which the
bacilli have  remained localized  in  the mucous membrane.
Hence the local process is still  to  be regarded as the chief
seat of the activity of bacillus diphtheriae.
  The study of the properties of this bacillus as it exists  out-
side the human body  and the results derived from  the inocu-
lation  of susceptible  animals would indicate that the effects
which it produces upon the body are due to a  soluble poison,
a toxin, proceeding from its growth and multiplication.  By
means of this toxin, separated from the living bacilli, all the
constitutional effects  of diphtheria can be induced.  For the
production of the false membrane the presence of the bacillus
itself is necessary.
  The growth  and multiplication of  the  bacilli in the false
membrane in  the pharynx, larynx and  nose are  associated
with the formation of  this toxin, which,  entering the body,
causes the symptom-complex of  the disease.   Sidney Martin
has extracted from the pseudo-membrane  an  albumose which
possesses the poisonous  properties of the toxin. 
8
  We owe especially  to  Roux and Yersin and  Brieger and
Fraenkel our knowledge of the nature and properties of this
toxin.   According to their researches  it  belongs  to a class of
substances of albuminous nature, possessing poisonous proper-
ties, for which  the name tox-albumens  has been proposed.
Up to the present time the tox-albumen of diphtheria has not
been obtained in a pure form, but in  its impure state it is
found to possess extraordinary potency.   Susceptible animals
(rabbits, guinea-pigs, kittens) inoculated with it exhibit all
the symptoms of  diphtheria, not excepting the post-diph-
theritic paralysis.
  The study of the action of this bacillus upon  animals has
shown a material  difference in the virulence exhibited by
cultures derived from different colonies, those obtained from
a single case showing at  times wide variations in virulence.
The guinea-pig  being the  animal most  susceptible  to its
influence, is generally employed for testing these variations.
  No less striking  are the  differences in the potency of the
toxin produced  by the bacillus, and it  has been found that
there exists a direct  relation between the virulence of the
organism  and the  intensity of the poison which it is capable
of yielding.
  It cannot be said  that  any such relation between the viru-
lence of the organism and  the severity of the symptoms has
been shown to exist for  human beings.   Indeed, contrary to
the results arrived at by Roux and Yersin—which seemed to
indicate that a progressive diminution in the virulence of the
bacilli corresponding with the mildness  of  the  attack took
place, and that the same thing happened during convalescence
from a severe attack—Escherich, Tobiesen, and especially
Wright, have  shown  that no such diminution of virulence
occurs.  Fully as virulent organisms may be found in cases
which  are mild from a clinical  standpoint  as  in those  of
severer grade.
  The question  of individual predisposition or of resistance
to the invasion of the bacillus diphtheriae  and to the effects of
its toxic products has therefore to be considered in this as in
the case of other infectious diseases.  What the physical basis
for  this distinction really  is we  are probably still far from
having discovered.  A few of the conditions which  favor  or 
9
   inhibit infection in human beings and in animals seem clear.
   Hence it is that the results of the recent studies of Wasserman
   and Abel  upon  the  action of the blood-serum of healthy
   human beings upon  animals previously inoculated with the
   Loeffler bacillus are suggestive, as they indicate that the serum
   of certain  individuals contains some protecting substance, the
   power possessed  by the serum of adults being greater  than
   that of children.
     It  is quite established  that the  bacillus diphtheriae may
   possess all grades of  virulence down to complete absence of
   pathogenic power, and some confusion has arisen by the intro-
   duction of the term " pseudo-diphtheritic " bacillus to denom-
   inate an organism which,  while it resembles the true bacillus
   diphtheriae, is devoid of  virulence  for guinea-pigs.   This
   bacillus was first isolated by  Hoffmann, who regarded  it as
   identical with Loeffler's bacillus.  Roux and Yersin advanced
   the view that this so-called "pseudo-diphtheritic" bacillus
   represents an  attenuated form of the true bacillus diphtheriae,
   and the work of Abbott,  Park, Koplik and Escherich lends
   support to this  position.   On the other hand, it is suggested
   that  the name " pseudo-diphtheritic"  should be reserved to
   designate  bacilli which, though resembling the true diphthe-
   ritic bacillus, show certain cultural differences and are devoid
   of pathogenic effect  for guinea-pigs.  Such a  pseudo-diph-
   theritic bacillus has  been found in a few cases of genuine
'   diphtheria associated with the true bacillus diphtherias.
     It must  be confessed that our knowledge of the relation of
   the Loeffler bacillus to diphtheria and associated pathological
   processes  has  been much extended in the past  few years.
   Thus this organism  has been found in a large proportion of
   all cases of pseudo-membranous inflammation of the throat,
   and is the probable causative agent in  all cases  of true diph-
   theria.   Those  pseudo-membranous  anginas in  which  the
   Loeffler bacillus is not found are characterized  in themselves
   and distinguished from cases of true diphtheria  by the mild-
   ness  of their course, their slightly contagious character and
   their low mortality;  in Park statistics, excluding those  asso-
   ciated with scarlet fever, the death-rate was 1.7 per cent.
     That virulent  diphtheria bacilli may be  present upon the
   mucous membrane of the pharynx without giving rise to a 
10
false  membrane is proven by those cases  of  pure laryngeal
diphtheria from which the bacilli have been cultivated from
the pharynx.  Loeffler found in the throat of a healthy child
a bacillus which was identical with the true bacillus diphthe-
rias ; later Hoffmann, Fraenkel and Feer found it under simi-
lar circumstances.   In 330 healthy persons examined by Park
and Beebe, who gave no history of contact with diphtheria,
they found the non-virulent organisms in 24, virulent bacilli
in 8, and pseudo-diphtheritic bacilli in 27.  The examinations
included for the most part children.   Of the 8 cases in which
virulent  bacilli  were found 5  were children  in an  asylum
where from time  to  time true  diphtheria occurred.   Of the
remaining three, one was from a house where a supposed case
of croup had  existed three weeks before.  Two of the 8 chil-
dren  developed  diphtheria some days  later;  the  other six
remained healthy.   Loeffler recently examined the throats of
60  school children and found diphtheria bacilli in  four.  Of
these  two subsequently  developed  diphtheria, one a slight
inflammation of the throat, the fourth remaining well.
  The study by Park of the throats of persons exposed to
diphtheria has shown that in 50 per  cent,  virulent Loeffler's
bacilli are present.  Of these 40 per cent, developed later the
lesions of the disease.  Park states  that in the families from
which his statistics covering this point were obtained the con-
ditions for the transmission  of the disease were most favor-
able.   On the  other hand, in families where the patient suffer-   '
ing from diphtheria  had been well isolated, the bacilli were
found in less than 10 per cent, of the  healthy children.
  Considered  in the  light of our present  knowledge of the
common existence of  pathogenic  micro-organisms, such as
streptococci, staphylococci and pneumococci, in the mouths of
healthy persons without necessarily doing harm there, these
facts  of the  occasional  occurrence  of virulent  diphtheria
bacilli in the  throats of  healthy persons are less surprising.
Doubtless it is necessary that a certain  susceptibility  to their
action—a predisposition, if you prefer, must exist before their
peculiar  effects can  be  exerted.   I  beg  to  recall  in  this
place the experimental results obtained from healthy human
blood-serum as bearing upon this point. However, the figures
furnished by Park and Loeffler would indicate that the pres- 
11
ence of the bacillus  diphtherias in the throat is  far  more
significant even for the individual himself, to leave out of
consideration for a moment those with whom he may come in
contact, than are the other pathogenic organisms mentioned.
  The bacteriological study of convalescent cases shows that
virulent bacilli may persist for a time after the  disappearance
of the false membrane.  They are  not  uncommonly present
after  2 to 3  weeks,  and in a few  instances they have been
found after a  much  longer  period.  In a case reported by
Park, and one  also by Abel, they were still demonstrable on
the 56th and 65th day respectively after the membrane had
entirely gone.
  The severity  of the case has no influence upon the duration
of the presence of the bacilli; the occurrence of nasal diph-
theria as  a  complication  seems to favor this  persistence.
Tezenas found  in 12 cases complicated with nasal diphtheria
that for a long time after the membrane had  disappeared a
serous exudation from the nose  continued.  In ten of  these
cases  Loeffler bacilli were demonstrable so long as the secretion
persisted, although they had  long ceased to be present in the
throat.  Hence where cultures cannot be made it  is recom-
mended to continue  the isolation of the patients for at least
three weeks after the disappearance of the membrane.
  It  is probable that the bacillus diphtherias is capable of
increasing only within the body of  infected persons or in the
seat of inoculation of susceptible animals.  The bacilli are,
however, able to remain  alive and  in a condition capable of
causing infection  for  a considerable time when outside the
body.  Conditions which promote the drying of the organism
and exposure to strong light  are  unfavorable for the preser-
vation of its vitality.   The individual Loeffler bacilli quickly
die when  allowed to become  air dry.  But  in  bits of mucus
or membrane, particularly if protected  from the light and
preserved in  a  damp  place, they may remain alive for a long
time—upon old cultures  from 5 to 15  months;  in bits of
membrane from 4 to 17  weeks.   They  have been cultivated
from  tableware and toys; from  soiled linen which  had been
in contact with the sick; from the shoes and hair of nurses,
and from the broom  used to  sweep the floor of a diphtheria
ward.  In view of these  facts it is  unnecessary to  point out 
12
the importance of thorough disinfection and of the rigorous
care that should be observed in disposing of the excreta of the
sick.
  The association of other micro-organisms with the bacillus
diphtherias in the false membrane is by no means uncommon,
although  cases  of  pure  diphtheritic  pseudo-membranous
inflammations  are said to exist.   The organisms  usually
associated with the Loeffler bacillus are the pyogenic cocci,
strepto-, staphylo- and  diplococci.  Their presence  is  now
known  to be of great clinical and  pathological significance,
especially if they enter the deeper tissues, as they are wont to
do.   While the bacillus diphtheriae is found only exceptionally
in the adjacent lymph glands and internal organs, there exists
a group of casea of poly-infection, especially with streptococci,
in which the latter enter the  circulation  and  invade  the
organs.  Since  the introduction of the anti-toxin treatment
of diphtheria this class of cases has attracted especial atten-
tion.  These cases had been recognized and studied by a number
of investigators, and in  this country especially by Council-
man and his associates.   Broncho-pneumonias, suppurations
of lymph glands and septic forms of diphtheria are attributed
to these associated bacteria, particularly to the  streptococcus.
Roux and  Yersin first  pointed out the  importance  of  this
poly-infection, and subsequently Schreider, Mya, Barbier and
Martin confirmed their observations.  Funk, Roux and Martin
and Bernheim have recently made careful experimental studies
on this subject.  The latter employed only organisms which
had  been associated in  the diphtheritic membrane,  and he
found  that the virulence of the Loeffler bacillus is  increased
both by being grown with the streptococcus or  in the  filtrate
obtained from streptococcus cultures.  A limited number of
experiments with staphylococci did not show a similar increase
in  the virulence  of  the bacillus diphtherias, a result con-
firmatory of Mya's earlier experiments.   On the other hand,
in human beings, according to Morse's statistics, cases of poly-
infection with staphylococci run a more unfavorable  course
than those with streptococci.  Welch has criticized his con-
clusions and shown the improbability of their correctness.
  The natural  variation  in virulence of the bacillus diph-
therias led first unintentionally, and later purposely,  to  the 
13
rendering of animals immune to subsequent inoculation to
the Loeffler  bacillus.   But it  was soon  observed  that  this
method of securing immunity was capricious and unreliable.
The use of cultures of bacilli attenuated by chemical  agents,
the injection of tissue fluids into another of an animal  dead of
a previous  inoculation of  the  bacilli, the employment of
sterilized bouillon cultures and of cultures grown in infusions
of cellular organs, such as the thymus gland, while attended
with  success  in  some  cases,  were found  to  be precarious
methods of securing  immunity, and not at all adapted to large
animals.   The use of a virus obtained from bouillon cultures
several weeks old  by filtration has been successfully  employed
by  Behring,  Ehrlich and Wasserman, Roux and  others, to
render even large animals such as the  horse immune to large
doses  of diphtheria cultures.  And one of  the surprising  and
significant facts  which has resulted  from the  study  of the
changes induced  in  the body fluids of the immune  animal
consists in the discovery that they contain  a substance which
is capable of rendering other animals, and even human  beings,
immune from diphtheria and also of curing the disease after
its development.
  This anti-toxin obtained from the  blood of immune animals,
though antidotal to the poison of the bacillus diphtherias,
exerts no power  over the  poison produced by the bacteria
associated with the Loeffler bacillus in the pseudo-membrane,
and thus it becomes clear why cases of poly-infection  are less
influenced  by the anti-toxin treatment than those of  pure
diphtheria.
  It is but a confirmation of an intuitive belief to find  that in
the blood of  human  beings well of  diphtheria there exists a
body similar to that found  in immune animals.   The  experi-
ments of Klemenciwicz and Escherich proved the correctness of
this supposition, and Abel has just furnished a large series of
observations with confirmatory results.  In animals a  certain
time elapses after the inoculation of  the toxin before the anti-
toxin  appears, and it is only after repeated doses at intervals
that a high grade  of anti-toxic power is developed in the blood-
serum.  In human beings the blood taken on the 5th or 6th
day after infection shows no protective action; the protecting
power appears from the 8th to the 11th day, and it persists  a 
14
variable time.   Sometimes  it fails  to appear  at  all.  After
some months it may be still present, though in a diminished
degree,  or it may  have entirely  disappeared.  The longest
periods  of its persistence yet observed are 150 and 200 days.
  These facts bear out the experience of  physicians who have
noted that diphtheria is not one of those diseases one attack
of which affords protection to subsequent infection.  Perhaps
the individual  differences observed are  to be explained by
the variation in the amount of healing  and protecting sub-
stances  formed in any case.
  In cases of genuine diphtheria the Loeffler bacilli are found
in large numbers in the pseudo-membrane,  there being less in
the deeper than in the older and more superficial parts. A
lesion of the surface provides  a condition  favorable to  their
settlement and increase, a fact also borne out by experiments
on susceptible animals.   Where no previous defect exists it is
probable that the toxin itself can  cause  a  superficial lesion.
The tonsils, which are the starting-points of many cases of
diphtheria, afford an excellent nidus for the bacilli, on account
of the incompleteness  of their epithelial  covering, even in
health.  The depth and extent of the necrosis of the mucous
membrane vary in different  cases; and the character of the
pseudo-membrane is affected by the nature  of the underlying
structures; in the pharynx it is firmer and less easily separable
than in the larynx and trachea,  where a  distinct basement
membrane is found in the mucosa.
  The earlier workers in the field of experimental diphtheria
failed to find in the internal  organs the  lesions which had
been described by Oertel in the tissues of human beings dead of
diphtheria.  These lesions consist of foci of cell-death  char-
acterized by extensive  destruction and fragmentation of cell
nuclei.  In such areas of necrosis fibrin may be deposited.
Dr. Welch  and I confirmed and  extended these  results of
Oertel by experiments upon guinea-pigs, kittens and rabbits.
Subcutaneous inoculation of cultures of  the organism  or of
the filtrate in a bouillon culture 4  or  5 weeks old, produces,
besides the local lesion peculiar to each, foci of cell-death in
the adjacent lymph glands and in the lymph glands through-
out the body;  in the  spleen, liver, lungs, heart muscle and
intestinal mucosa.   The kidneys show degenerative changes. 
15
When the dose is small and the animal lives several weeks the
paralysis which belongs to  the  disease may develop.  This
phenomenon, first  observed  in animals by Roux and Yersin,
was noticed among our  animals.  Interesting changes have
been described  in  the peripheral nerves  under these condi-
tions by Sidney Martin.   In some cases he observed defects in
the myeline sheaths, which stained poorly in osmic acid, while
in certain severe cases the sheaths had entirely disappeared.
The axis cylinders  were either intact  or had  undergone
granular degeneration, and the continuity of some of the fibres
had become broken.  At times the muscles supplied by these
nerves  showed  signs of fatty degeneration.  These changes
agree  with  those  found by Gombault, Meyer, Leyden  and
Arnheim in human beings who had suffered from diphtheritic
paralysis.
  Albuminuria is a not infrequent complication of the disease,
and casts may appear in the urine.  In some cases  the urine
may be much diminished in  amount, but uraemia is unusual;
and hydrops, which seldom occurs, is, when present, of a mild
grade.   The  heart is  not  uncommonly involved,  and the
lesions described  are either parenchymatous degeneration,
in the  severer grades, associated with fatty degeneration, or
interstitial myocarditis.   The lymphatic glands of the neck
become swollen, but show a  slight tendency  only to suppura-
tion. Various complications due to the invasion of  secondary
micro-organisms occur.