A MANUAL OF PHYSIOLOGY. BY JOHN FULTON, M.D., M.R.C.S., Eng., L.R.C.P., London. PROF. OF DESCRIPTIVE AND PHYSIOLOGICAL ANATOMY, VICTORIA COLLEGE, TORONTO, MEMBER OF THE MEDICAL COUNCIL FOR UPPER CANADA, DOCTOR OF Medicine, victoria college, cobourg, bachelor of MEDICINE, TORONTO UNIVERSITY. “LABOR OMNIA VINCIT.” TORONTO: u ADAM, STEVENSON & CO.. BOOKSELLERS AND IMPORTERS. 1868. Entered according to Act of the Parliament of Canada, in the Year One Thousand Eight Hundred and Sixty-eight, by John Fulton, M. D., in the Office of the Minister of Agriculture. TORONTO: GLOBE PRINTING COMPANY, KINO STREET EAST. PREFACE. I have been induced to undertake this Work with a view to supply a want which has long been felt by the student of Physiology—of a condensed work which should embrace all the most import- ant facts connected with the subject. The limited amount of time at the disposal of the student of medicine is not sufficient to enable him to wade through the more elaborate treatises ; and although chiefly intended for the student, it is to be hoped that it may prove serviceable to many medical practitioners, more especially those who may have pupils under their instruction. In its construc- tion, I have availed myself of all the more impor- tant Works on Physiology. I am also indebted for many views expressed in this Work to the lectures on Physiology delivered by Prof. John N. Reid, M.D., of Victoria College, Toronto, during my academic course. It is my ardent hope that it' may effect the desirable object for which it is intended in a satis- factory manner; and if so, I shall feel greatly rewarded for my exertions. JOHN FULTON. Toronto, 1868. CONTENTb. Introduction 9 PAGE. CHAPTER I. Proximate Principles 10 Definition of a Proximate Principle 10 Classification of Proximate Principles.. 11 Proximate Principles of the First Class 13 Water 13 Chloride of Sodium 14 Chloride of Potassium 16 Phosphate of Lime 16 Carbonate of Lime 17 Carbonate of Soda 18 Carbonate of Potash 18 Phosphates of Magnesia, Soda and Potassa 18 Gases 19 Proximate Principles of the Second Class 19 Starch 19 Sugars 21 Oils and Fats 24 Proximate Principles of the Third Class....! 28 Albumen 28 Albuminose 30 Fibrin..... 31 Casein 34 Globulin e 35 Pancreatine 35 Pepsine 36 Mucosine 36 Musculine. 36 Cartilagine 36 Osteine 36 Elasticine 37 Keratine 37 Hematine 37 Biliverdine 38 Melanine 38 Frrosacine 38 VI CONTENTS. rAua. Elementary or Primary Forms of Tissue 39 History of the Animal Cell 39 Cytogenesis 43 Cause of Organization 47 Phenomena of Cells 48 Manifestations of Cell Life 49 Simple Fibres 50 Simple Membranes 51 CHAPTER II. Tissues 53 White Fibrous Tissue 53 Yellow Fibrous or Elastic Tissue 54 Areolar Tissue 56 Adipose Tissue 57 Cartilage 59 Bone 62 Muscle.... 68 CHAPTER III. Membranous Expansions 79 Serous Membranes 83 Synovial Membranes 84 Mucous Membranes 86 Appendages of the Mucous Membrane 88 Integument 93 Appendages of the Integument 97 CHAPTER IV. CHAPTER V. Digestion 106 Prehension 113 Mastication 114 Insalivation 119 Deglutition 122 Chymification 124 Chylification 128 Defecation ... 139 Absorption.... . 141 Villi and Lacteals 141 Lymphatic Vessels and Glands 142 Mechanism of Absorption 144 Absorption by the Villi and Lacteals 147 Absorption by the Veins 148 Absorption by the Lymphatics 149 Glandulse Solitaire 150 CHAPTER VI. CONTENTS. vii. CHAPTER VII. PAGE. O OD 151 Physical Character of the Blood 151 Microscopical Appearance of the Blood 152 Chemical and Structural Characters of the Blood 160 Difference between Arterial and Venous Blood 162 Conditions which Influence the Character of the Blood. 165 Vital Properties of the Blood 171 Coagulation of the Blood 171 Circumstances which Retard Coagulation 174 Circumstances which Promote Coagulation 176 Function of the Elements of the Blood .. 177 > Relation of the Blood to the Living Organism 182 CHAPTER VIII. Circulation 185 The Heart 185 Arteries 193 Veins 198 Capillaries 201 Fcetal Circulation 205 CHAPTER IX. Respiration 208 The Lungs 208 Action of the Lungs 211 Influence of Nervous Power in Respiration 213 Modifications of the Respiratory Movements 214 Changes in the Respired Air 215 Changes in the Blood during Respiration 218 CHAPTER X. Animal Heat, Light and Electricity 221 Heat 221 Theory of the Production of Heat 221 Light 224 Electricity 225 CHAPTER XI. Secreting Glands and their Secretions 229 The Liver 229 The Kidney 231 The Urine 234 The Mammary Glands 239 Milk 240 CHAPTER XII. Ductless Glands 244 The Spleen ....< 244 The supra-renal Capsules 247 The Tliymus Gland 248 The Thyroid Gland 249 VIII CONTENTS. CHAPTER XIII. PAGE. The Nervous System 250 Structure of the Nervous System 255 Ganglia of Nerves 257 Chemical Composition of Nerve Tissue 257 Function of Nerve Fibres 261 Development of Nerve Tissue 265 Function of Nervous Centres 266 Reflex action 267 Nervous force 268 Spinal cord .'.... 269 Encephalon 275^ Medulla Oblongata 275 Pons Varolii 278 Cerebellum 279 Cerebrum 281 The Mind and its relation to the body 289 Cranial Nerves 297 Sympathetic system 304 CHAPTER XIV. The Special Senses 308 Smell 308 Sight 310 Phenomena of vision 315 Accommodation of the eye to vision 317 Hearing 319 CHAPTER XV. The Voice 332 Larynx 322 Compass of the voice r. ... 323 Ventriloquism and Stammering .A.'.....’..... 324 CHAPTER XVI. Reproduction 326 Action of the Male i.W: 327 Action of the Female •••• •/ 328 Corpus Luteum . rtj 329 Action of the Oviducts i....,4 330 Development of the Ovum i. 331 Formation of the Amnion and Allantois 333 Formation of the Chorion A-CV/- 335 Preparation of the Uterus for the Ovram.. 336 Formation of the PJacenta TT’V. . 337 Umbilical Cord and Amniotic Fluid 338 General development of the Embryo 339 Parturition 339 HUMAN PHYSIOLOGY. Physiology, from cpvdi?, “nature,” and A.oyo%, “ a de- scription,” in its general sense, has for its province the investigation of the active phenomena presented by organized bodies, and is divided into two parts, viz:— Animal and Vegetable Physiology: the former treats of the laws that control the Animal Kingdom, the latter relates to those of the Vegetable Kingdom. Animal Physiology may also be divided into two parts, viz: Human Physiology, and Comparative Physiology, or the Physiology of the lower animals. Human Physiology treats of the vital phenomena of the human species, and is of much more practical impor- tance to the medical student than the Physiology of the lower animals, on account of its relation to Pathology and Therapeutics. The study of Physiology presupposes an intimate knowledge of Anatomy and Chemistry, in order that the student may be able to comprehend the character of the structure he is examining and the substance of which it is composed. Animal bodies are composed of solids and fluids: the former embrace the various textures and viscera; the latter the blood, chyle, lymph and glan- dular secretions. The same substance may be fluid in one part of the body and solid in another; for example, phosphate of lime is in solution in the albumen of the blood, but is solid in the bones. A law in Physiology is a certain phenomenon, always taking place in the presence of certain conditions. CHAPTEK I. PROXIMATE PRINCIPLES. Every animal tissue and fluid contains a number of proximate principles mingled together in various pro- portions. A proximate principle may be defined to be “ any substance, whether simple or compound, chemically speaking, which exists under its own form in the animal solid or fluid, and which can be extracted by means which do not alter or destroy its chemical properties.” But it must not be supposed that every substance which can be extracted from an organized solid or fluid by chemical means is a proximate principle; for example, chloride of sodium is a proximate principle : but chlorine is not, because it does not exist as such in the body. Phosphate of lime is a proximate principle of bone; but phosphoric acid is not, because it does not exist in a free state in the bony tissue; still less phosphorus, which is ob- tained only by the decomposition of phosphoric acid. Again, fibrous tissue, when boiled steadily for thirty- six or forty hours, yields a substance called gelatine; but this is not a proximate principle, since it is produced only by long-continued boiling. In extracting the proximate principles from the animal body, only the simplest chemical means should be employed. First, evaporate the substance, to extract and estimate the amount of water. The temperature should not be above 212QF., because a higher degree would change PROXIMATE PRINCIPLES. 11 some of the animal ingredients. Then dissolve out the salts with water. Coloring matter, or pigments, may be extracted by alcohol; oils and fats by ether. Some of the salts may be removed by double decomposition. Thus, glyko- cholate or tauro-cholate of soda may be precipitated by acetate of lead, forming glyko-cliolate or tauro-cliolate of lead, which may, in its turn, be decomposed by carbonate of soda, forming the original glyko-cliolate or tauro-cliolate of soda, Sometimes a proximate principle cannot be separated in an entirely unaltered state. Thus the fibrin of the blood can be entirely separated only by allowing it to coagulate ; lienee it loses its original char- acter of fluidity, and is permanently altered. The proximate principles are divided into three classes: 1st. Crystallizable substances of inorganic origin, as water, chloride of sodium, carbonate and phosphate of lime, &c. They are derived mostly from exterior sources. They are found in organized as well as in unorganized bodies, and have a definite chemical composition. (In this class may also be included the gases, as oxygen, hydrogen, nitrogen, carbonic acid, carburetted and sulphuretted hydrogen). 2nd. Crystallizable substances of organic origin, or non-nitrogenized substances, as starch, sugars, oils, and fats. They are found only in organized bodies, are crystallizable (excepting starch), and have a 'definite chemical composition. 3rd. Organic substances proper, “nitrogenized sub- stances,” “ albuminoid subst ances,” or “protein compounds,” as albumen, fibrin, casein, &c. They are exclusively organic in their origin, are not crystallizable, and are not definite in their chemical composition, that is to say, they do not always contain the same proportions of oxygen, hydrogen, carbon and nitrogen; but the relative quantities of these elements may vary, within certain limits, in different individuals, and in the same individual at different times, without changing in any material degree the peculiar properties of the substance which they form. This is characteristic of organic substances. They all closely resemble albumen, hence called albu- minoids. They were regarded by Mulder as compounds of a theoretical radical, which he called protein. This gave them the name of protein compounds. Mulder’s theory, however, is not generally received. Some of these organic substances are fluid, and others semi-solid, or solid, depending upon the amount of water which they contain. When subjected to evaporation they all lose water, and are reduced to a solid state. Their re- action is neutral. They have, in fact, no combining equivalent. The organic substances which are naturally fluid may be coagulated. Thus fibrin coagulates spontaneously when removed from the vessels; albumen, on the appli- cation of a temperature of 160°F.; and casein on being placed in contact with an acid. An organic substance, once coagulated, cannot be restored to its original condition. It may be dissolved by certain re-agents, as e, g., the caustic alkalies; but in this it only suffers a still further alteration; nevertheless it is necessary to resort to coagulation in some instances to remove an organic substance from the other proxi- mate principles with which it is associated, as for example, the fibrin of the blood. This is obtained by switching freshly-drawn blood with a bundle of twigs. Thus ob- tained it is in an unnatural condition, having lost its original character of fluidity. 12 HUMAN PHYSIOLOGY-. PROXIMATE PRINCIPLES. 13 These organic substances, when the vital force is removed, are liable to putrefaction. This process is peculiar to organic nitrogenized substances, and distin- guishes them from all other kinds of proximate principles. When in a state of putrefaction, they are capable of inducing in certain other substances a process of fermenta- tion, as for example, the decaying organic matters of the grape give rise to fermentation of the sugar, converting it into alcohol and carbonic acid. The putrescent body is called a ferment, and acts by catalysis, or by its mere presence, having nothing to do chemically with the process. PROXIMATE PRINCIPLES OF THE FIRST CLASS. Water, .—Water is tlie most important of the inorganic principles, and is found in all parts of the body. In the solids it does not exist in a fluid state, hut is incorporated with the substance of the tissue. It may be called “ water of composition,” in contradistinc- tion to what is called in chemistry “ water of crystalli- zation,.” It constitutes about two-thirds of the entire weight of the body. The following table shows the proportion of water per 1,000 parts in different solids and fluids In the Enamel of the Teeth, 2 “ Epidermis 37 “ Teeth 100 “ Bones 130 “ Tendons 500 “ Cartilage 550 “ Skin 575 “ Liver 618 “ Muscles 750 “ Ligaments 767 QUANTITY OF WATER IN 1,000 PARTS. Blood 780 Bile 880 Milk 887 Pancrecitic Juice 900 Chyle 904 Urine 936 Lymph 960 Gastric Juice.... 975 Perspiration 986 , Saliva 995 Solids. Fluids. 14 HUMAN PHYSIOLOGY. Origin and Discharge of Water.—It is introduced with the fluid and solid elements of the food. The amount of water taken into the system hy an adult, in the course of 24 hours, varies from 3| to 4 pounds. It is discharged from the body in four different ways—by the urine, faeces, perspiration, and breath,—about 48 per cent, being discharged by the urine and faeces, and 52 per cent, by the perspiration and breath. These propor- tions will vary according to circumstances; for example, in warm weather, when the skin is more active, and the perspiration more abundant, the quantity of urine is diminished. The quantity of water discharged by the lungs varies, also, with the state of the atmosphere and the pulmonary circulation. The water is not discharged pure, but is mingled with various salts, animal matters, and odoriferous substances. Function.—It holds in solution different salts and substances-of excretion, and gives fluidity to the blood and secretions. It is a most important article of diet, and is necessary both for the introduction of substances into the body, and their elimination from it. It gives to cartilage its elasticity, and to tendons their toughness find pliability. For, if water be ekpelled from a piece of cartilage by evaporation, it becomes dark in colour, semi-transparent, hard and inelastic. The same thing is true of muscles, tendons, &c. Chloride of Sodium, NaCl.—Chloride of Sodium is next in importance, and is found in all parts of the body except the enamel of the teeth. The entire quantity in the body has never been estimated. It exists in the greatest quantity in the fluids. In blood, for example, it is more abundant than all the other salines taken together. The following is a list of the quantities in the most important solids and fluids:— PROXIMATE PRINCIPLES. 15 QUANTITY OF CHLORIDE OF SODIUM IN 1,000 PARTS. In the Muscles 2 “ Bones 2.5 “ Milk 1 “ Saliva 1.5 “ Urine 3 “ Bile...; 3.5 Lymph 4.1 Blood 4.5 Chyle 5.3 Mucous 6 Aqueous Humor 11 Yitreous “ 14 Origin and Discharge.—It is introduced with the different kinds of animal and vegetable food and fluids, and as a condiment. Being soluble, it is taken up by absorption from the intestines, and is deposited in dif- ferent parts of the body. About | is discharged from the body in the urine, faeces, perspiration and mucus, the remaining \ being lost in the body by double-decom- position-with phosphate of potassa, resulting in the for- mation of phosphate of soda and chloride of potassium. It is also supposed to furnish the soda to all the salts that have a soda base. Function.—It regulates, to a certain extent, the phe- nomena of osmosis, for we know that a solution of chlo- ride of sodium permeates an animal membrane much less readily than pure water. In the blood it holds in solution the albumen and earthy phosphates, and pre- serves the integrity of the blood corpuscle. As an article of diet, it stimulates the secretion of saliva and gastric juice, and aids in digestion. The importance of chloride of sodium in this respect has been demonstrated by Boussingault in the fattening of animals. A small herd of animals were experimented upon, all of the same age, size and vigour. They were divided into two lots, and all supplied with an abundance of'nutritious food. One of these lots was deprived of this salt (except what was contained in the food), while the other received about 500 grains per day. No difference was observable for four or five months; from that time to the end of HUMAN PHYSIOLOGY. the year a marked difference was noticed. Those animals which received the chloride of sodium had a fine, sleek, healthy aspect, contrasting strongly with the listless and inanimate appearance of the others. Chloride of Potassium, KC1.—This substance is found in the muscles, liver, milk, chyle, blood, gastric juice, bile, saliva, mucus and urine. It is quite sol- uble in the fluids, and is more abundant in muscle than chloride of sodium. Origin and Discharge.—It is introduced with the food, and is also formed in the interior of the body by double-decomposition between phosphate of potassa and chloride of sodium, forming phosphate of soda and chlor- ide of potassium. This may be shown by feeding a considerable quantity of chloride of sodium to a sheep, and, upon examination of the urine, it will be found to contain an increased quantity of chloride of potassium, the proportion of chloride of sodium remaining un- changed. Chloride of potassium is discharged in the urine and mucus. Function.—Its function is probably identical with chloride of sodium. Phosphate of Lime, 3CaO,POs.—Phosphate of lime is found in all the solids and fluids of the body, but is more abundant in the solids, and increases as age advances. It exists in a solid state, as in the bones, and also in a fluid state, as in the blood. It is insoluble in water; but is held in solution in the fluids of the body by albumen and*the alkaline chlorides. In the urine, it is held in solution by the biphosphate of soda. In bone or cartilage, it does not exist as a granular powder, but is intimately united with the animal matter, and may be dissolved out by maceration in dilute muriatic acid, PROXIMATE PRINCIPLES. 17 leaving behind the animal substance. When a long bone like the fibula is immersed in this way for some time, it loses its brittleness, and may be bent double, or tied in a knot, without breaking. If immersed in a solu- tion of carbonate of lime, its rigidity may be again restored to a certain extent. Solids. ( Enamel 885. Dentine 643. -j Bone 550. ] Cartilage 40. I Muscle 2.5 QUANTITY OF PHOSPHATE OF LIME IN 1,000 PARTS. {Urine 25.7 Milk 2.5 Gastric Juice 4 Blood 3 Saliva 6 Fluids. Origin and Discharge.—This substance is derived exclusively from exterior sources. It is introduced with the food, and is eliminated by the urine, perspiration, and mucus; most by the urine, a small quantity by the fceces. Function.—Its use is to give consistence and strength to parts; for example, in the enamel of the teeth, which is the hardest tissue in the body, it is most abundant, and in dentine more abundant than in bone. Its absence is said by some to account for scurvy, as in long sea voyages; but it is more likely that it is due to the ab- sence of vegetables and their acids. Carbonate of Lime, Ca0,C02.—This substance exists in the bones, teeth, cartilage, blood, sebaceous matter, internal ear, and sometimes in the urine. In bone it is not so abundant as phosphate of lime, the proportion being about 113 parts in 1000. It is held in solution in the blood and urine by the free carbonic acid and chloride of potassium. Origin and Discharge.—It is introduced into our bodies with the food and drink. Spring water contains a variable amount, held in solution by the free carbonic acid which the water contains. 18 HUMAN PHYSIOLOGY. Function.—Its function is analogous to that of phos- phate of lime. Carbonate of Soda, FTa0,C02.—Carbonate of soda, is found in tlie bones, blood, lympli, saliva, and urine. It gives to the blood its alkaline reaction. Claude Bernard has shown that the alkalinity of the blood is necessary to life; for if a mineral acid be injected into the blood of a living animal, so dilute as not to coagulate the albumen, death takes place before its alkaline reaction has been completely neutralized. Origin and Discharge.—It is introduced in small (quantities in the food. It is principally formed within the body by decomposition of other salts, as malates, tartrates, and citrates of soda and potassa. These salts when introduced into the body in the food are decom- posed. Their organic acid is destroyed and replaced by carbonic acid, forming carbonate of soda and potassa. It is discharged in the urine and mucus. Function.—Its function is to maintain the fluidity of the fibrin and albumen, and to assist in preserving the form and consistence of the blood corpuscles. Carbonate of Potash, K0,C02.—This salt is found in nearly the same situation as the preceding—is produced in the same way, and its function is analo- gous. Phosphates of Magnesia, Soda, and Potassa.— These salts are found in small quantities in all the solids and fluids of the body. They are introduced in the food. Phosphate of soda and potassa are soluble in water. Phosphate of magnesia is dissolved in the fluids by the alkaline chlorides and phosphates, and in the urine by the biphospliate of soda. The fluids of the herbiverous animals contain a preponderance of the carbonates—the carnivorous a preponderance of the phosphates. The PROXIMATE PRINCIPLES. 19 latter is owing to the phosphates found in the animal tissues upon which the carnivora feed. They are dis- charged in the urine and faeces. The remaining proximate principles of this class are the sulphates of soda, lime, and potassa, and chloride of ammonium. The proximate principles of the first class exist in the animal tissues in the same form in which they occur in the inorganic world. Carbonate of lime in the bones is the same as that which is found in limestone rock; and chloride of sodium is similar to that which is found in solution in sea water. Gases.—Oxygen, nitrogen, hydrogen, carbonic acid, carburetted hydrogen and sulphuretted hydrogen, exist in a gaseous state, and also in solution in some of the fluids of the body. Oxygen is necessary to the respiratory process. It changes the shape of the blood corpuscle, rendering it biconcave, and giving to the arterial blood its bright-red colour. Arterial blood contains about 10 to 12| per cent, of oxygen. Nitrogen exists in very small quantity in the blood and lungs. It is also found in the intes- tines. Carburetted and sulphuretted hydrogen, also pure hydrogen, are found in the alimentary canal, and in small quantities in expired air. Carbonic acid is an excretion given off principally by the lungs. From 20 to 25 per cent, is found in venous blood. PROXIMATE PRINCIPLES OF T1IE SECOND CLASS. Starch, (C1:2 H, 0 O10) — This substance, though not crystallizable, is so closely allied to the others, in its general properties, and so easily converted into sugar, which is itself crystallizable, that it is naturally included in the proximate principles of the second class.. It is not amorphous, but assumes a distinct granular 20 HUMAN PHYSIOLOGY. form. It is found in nearly all the flowering plants, and is the principal ingredient in sago, tapioca, arrowroot, &c. TABLE OF QUANTITY OF STARCH IN 100 PARTS. In Pace 85 “ Maize 80 “ Barley Meal 67 “ Rye “ 61 “ Oat “ 59 Wheat Flour 56 - Iceland Moss 44 Kidney Bean 35 Peas 32 Potatoes 15 Physical Appearance of Starch.—It is a white powder, consisting of solid granules, which vary in shape, size, and physical appearance, in different vegetables. It produces a crackling sensation when rubbed between the fingers. The starch granule of potato varies from T 00 ()- to 4-00 of an inch in diameter, is pear-shaped in its out- line, and marked by concentric rings surrounding a minute pore, called the kilns, which is situated near the small extremity of the granule. The granules of arrow- root being smaller and more uniform, vary from 2 0’0 g to goo of an inch in diameter, and are oval in shape. The hilus is in the shape of a circular pore or transverse slit. The starch grains of wheat vary from 70000 to 7 J 0 of an inch in diameter, nearly circular in form, with a round or transverse hilus, but without any distinct laminar appearance. The granules of Indian corn are the same size as the preceding; they are irregular in shape, and present a crucial or (T) shaped pore. Origin and Properties.—It is found in most vege- table substances used as food, and in that way is intro- duced into the body. It is also found in the animal body in the lateral ventricles of the brain, fornix and septem Incident. It was first observed by Purkinje, and afterwards by Kolliker and Virchow. The granules are called corpora amylaeea. They vary in size from ? 7V0 to TT00 of an inch in diameter. They are transparent, softer than in vegetable starch, irregularly rounded, and PROXIMATE PRINCIPLES. 21 present a faint laminar arrangement, having a circular pore (near the centre), with lines radiating from it— star-shaped. Starch is insoluble in cold water, but the granules swell out, become gelatinous, and are readily dissolved in boiling water. It is then said to be hydrated. This is simply a mechanical change. Starch may be con- verted into sugar in three different ways. First, by boiling in dilute nitric, muriatic, or sulphu- ric acid for 36 or 40 hours. The starch is gradually converted into sugar, at the same time losing its property of responding to the iodine test. Secondly, by' contact with an animal or vegetable substance, at a temperature of 100°F. Boiled starch mixed with the saliva is converted into sugar in -a few minutes. Thirdly, by the process of nutrition and digestion in animals and vegetables. The starch found in seeds and roots must first be converted into sugar and thus rendered soluble before it can be taken up to nourish the plant during its growth. Function.—Its office in the animal economy is to form sugar. Starch is converted into sugar during di- gestion by the action of the pancreatic and intestinal juices. Tt is necessary for the process of development and nutrition at all periods of life. Test.—In whatever state it exists, its presence may be detected by its reaction with free iodine, giving a blue color. Sugars.—These substances are soluble in water, crys- tallize on evaporation, and are converted into alcohol and 22 HUMAN PHYSIOLOGY. carbonic acid in the process of fermentation. The ordi- nary varieties of sugar are the following: VEGETABLE SUGARS. Cane Sugar, C12 H41 041 Grape “ C12 H14 014 ANIMAL SUGARS. Milk Sugar, C12 H18 012 Liver “ C12 H14 0l4 Sug’rof Starch or Glucose Cl 2II14014 Sugar of Honey A mixture of Cane and Grape Sugar. Cane sugar is more soluble than any other variety and is therefore sweeter. Liver sugar and sugar of honey crystallize only with great difficulty; some of the sugars, as grape and liver sugar, ferment very easily; while others, as cane and milk sugar, do so with difficulty. In Figs 62.50 “ Cherries 18.52 “ Peaohes 16.48 “ Tamarinds 12.50 “ Pears 11.52 “Beets 9.00 “Barley 5.21. TABLE OF QUANTITY OF SUGAR IN 100 PARTS. Wheat Flour 4 to 8.48 Rye do 3.28 Ind’nCorndo 1.45 Peas 2.00 Cow’s Milk 4.77 Asses’ do 6.08 Human do 6.50 Origin and Function of Sugar.—It is an im- portant article of diet. It is introduced with the milk in the food of the child. In the adult it is introduced partly in the food as sugar; but mostly in the form of starch, which is converted into sugar during digestion by the action of the pancreatic and intestinal juices. It is also formed in the interior of the body, in the liver, mammary gland, and in the placenta of the foetus during the first three months of foetal life. It is found in the portal and hepatic veins, but disappears from the blood in its passage through the lungs, being probably con- verted into lactic acid. It is necessary in the process of nutrition at all periods of life, and is also supposed to assist in maintaining the animal heat of the body. Sugar is never discharged from the body in health (except in the female during lactation); but in certain diseased con- PROXIMATE PRINCIPLES. 23 ditions of the system, it is rapidly produced in the liver, and is discharged in the urine, constituting diabetes nullitus. Tests.—First, Tiiommer’s Test.—To the suspected liquid add one or two drops of a solution of sulphate of copper; render it alkaline by the addition of a solution of caustic potassa. The vdiole solution then assumes a blue color. Then boil it for a few minutes, and if sugar be present, the suboxide of copper is thrown down as a yellowish or reddish-brown precipitate. If no sugar be present, the liquid remains blue. The principle of this test depends upon the power sugar has in reducing the protoxide to the suboxide of copper. The alkali is added to liberate and neutralize the sulphuric acid. This test is not applicable to cane or beet sugar; but by.boiling them in dilute sulphuric acid they are converted into glucose, which responds readily. Sugar of honey, grape, glucose, liver, and milk sugar, all act promptly with Trommer’s test. Care should be taken that only a small quantity of sulphate of copper be added, as there might not be sufficient sugar in the solution to reduce it. Organic substances, as albuminose, interfere with this test. This substance may be precipitated by alcohol, and removed. Albuminose will be described in the proximate principles of the 3rd class. Fermentation Test.—Add a few drops of fresh yeast to the saccharine liquid, and keep it at a temper- ature of from 70° to 100° F. In this way the sugar is converted into alcohol and carbonic acid; the latter should be collected in a vessel and examined. Every cubic inch of carbonic acid is equal to about one grain of sugar. The presence of carbonic acid may be proved by introducing into the vessel a lighted taper, which will lie immediately extinguished, or by agitating with lime 24 HUMAN PHYSIOLOGY. water, which will be rendered turbid by the formation of insoluble carbonate of lime. Torul/E.—This is a vegetable growth presenting a number of growths or joints, oval in shape, and connected together, which may be observed on the surface of diabetic urine, and are called “ Toruhe Cerevisiae. ” They break up after a time and fall to the bottom of the vessel, in minute oval spores. Moore’s Test, or, the Potash Test.—A little caustic potash in solution is added to the suspected liquid, and boiled in a test tube. Tf sugar be present, it acquires a brownish color. Barreswill’s Test.—The principle is the same as in Trominer's test. The solution is prepared according to the following formula, given by Bernard: Potass Bitart 383 grains. Soda Cart) 309 “ Cupri Sulph 231 “ Caustic Potassa 309 “ Aqua 18 oz. mix. Add to the suspected mixture enough of the solution to give it a blue tinge, and boil. If sugar be present, the yellow suboxide of copper is thrown down, as in Trommer’s test. Bottger’s Test.—This is also analogous to Trommer’s test. To the suspected liquid add a few drops of a weak solution of nitrate of bismuth in nitric acid; render it alkaline by a solution of carbonate of soda, and boil; a dark precipitate will be produced, if sugar be present. Maumene’s Test.—Saturate strips of woollen in a solution of bichloride of tin, and dry; then dip them in the suspected liquid, and dry quickly; if sugar be present, the strips assume a brown color. Oils and Fats.—These substances are found in both animal and vegetable tissues. Fat exists in the animal PROXIMATE PRINCIPLES. 25 economy in three varieties, viz: Oleine—C94 II87 015; Margarine—C?6 H75 012; and Stearine—CJ42 H141 017 . By the chemist these bodies are considered as salts, formed by the union of fat acids with the base— glycerine—thus:— Oleine Oleic Acid (C36 H34 04) and Glycerine (C6 H8 06 .... Oleate of Glycerine. Margaric Acid (C34 H34 04) and Glycerine (Ce H8 06) Margarine Margarate of Glycerine. Stearine.. Stearic Acid (C3c H35 04) and Glycerine (C6 H8 06) ..Stearate of Glycerine. Saponification.—When oleine, margarine, or stearine, is boiled in a solution of caustic alkali, it is decomposed into a fat acid, as oleic, margaric, or stearic, and a sweet- ish viscid fluid called glycerine. The acid unites with the alkali and forms soap, and the glycerine is set free. The fat acid may be separated from the base glycer- ine by passing steam through fat at a temperature of 572 ° y The human body, when immersed in water for a length of time, becomes changed into a substance called adipocere, or saponified fat. This is supposed to be a process of saponification, caused by the union of margaric, stearic and oleic acids with ammonia, which is developed during the process of decomposition. Physical Appearance and Properties of Fat.— It exists in two forms in the body. First, in the form of large cells or vesicles, varying in diameter from to 3^a of an inch, as in adipose tissue. Secondly, in the form of oil globules, varying from on00 f° Woo of an inch, as in the chyle, in which it is said to be emul- sified. This is a mechanical subdivision of the fat cells, and is the only form in which it can be absorbed. Fats may be emulsified in mucilage and white of egg. The HUMAN PHYSIOLOGY. fat cell is characterized by a dark border surrounding a bright centre. It does not possess a nucleus or nucleolus at maturity. It is generally rounded in shape, but is found irregular in outline, depending on pressure. The small globules appear as minutely dark granules, so as to give the fluid in which they float an opalescent ap- pearance. In cow’s milk, the oil globules are 0 of an inch in diameter, have a pasty consistence, which is due to the margarine they contain; and when churned, are converted into butter, from their tendency to cohere. Oleine, margarine, and stearine, are always found min- gled together in the body; but they are never associated with any of the other proximate principles of the body, as water, sugar, &c. The only exception is the nerve tissue, in which they are combined with albumen, and also in the bile dissolved in the salts. They are united with phos- phorus, constituting the pliospliorized fats of nerve tissue. This union is supposed to take place in the lungs, under the influence of oxygen. In the living body, the fats are fluid, or nearly so, being held in solution by oleine; but after death, they assume the solid condition. Stearine and margarine are crystallizable, and sometimes present a very beautiful appearance. The crystals are needle- shaped, and are deposited in a radiated form, but some- times curved and branching. Stearine predominates in hard, margarine in soft, and oleine in liquid fats. The melting point of stearine is 143 0 F., margarine 118 0 F., and oleine 100 0 F. They are insoluble in water, but are soluble in ether and hot alcohol. - TABLE OF QUANTITY OF FAT IN 100 PARTS. In Filberts 60 “ Walnuts 50 “ Cocoa Nuts 47 “ Linseed 22 ‘ ‘ Indian Corn 9 “ Yolk of Egg 28 Ordinary Meat 14. SO Liver of Ox 3.89 Cow’s Milk 3.13 Human “ 3.55 Asses’ “ 0.11 Goats’ “ 3.82 PROXIMATE PRINCIPLES. 27 Origin and Function.—It is found in all parts of the body except in the compact tissue of the bones, teeth, tendons, beneath mucous membranes, in the cutis, be- tween the rectum and bladder, beneath the epicranial aponeurosis in ligaments, scrotum and eyelids. It is introduced in the food, and is emulsified by the pan- creatic juice during digestion and previous to absorption. It is also formed in the interior of the body. This has been proved by experiments on geese, the result of which showed more fat in the body than could be ac- counted for by that which existed in the food. Another proof is, that it has been found in the form of globules in the interior of the costal, laryngeal, and tracheal car- tilage cells, and also in the muscular fibre cell of the uterus during involution. It also exists in the form of globules in the hepatic cells, sebaceous glands, corpus luteum, and uriniferous tubes of the carnivora. In the marrow of bones, it exists both in the form of oil globules and fat cells, forming adipose tissue. In some parts, it is formed from blastema supplied by the blood vessels, as in adipose tissue; in others it is formed as the result of a retrograde metamorphosis, as in the muscular fibre cell of the uterus. It accumulates in excess in certain diseased condi- tions, as in fatty degeneration of the heart, liver, kidney. Its function in the form of adipose tissue is to give ro- tundity to the body, form a nidus for delicate organs, fill up spaces otherwise unoccupied, and from being a bad conductor to prevent the too rapid escape of the animal heat of the body. As an article of diet, it is necessary in the process of nutrition. It supplies animal heat, and is a store of food in case of emergency, as in the hyber- nating animals. Certain kinds of food favor the for- mation of fat; for example, Negroes employed in making 28 HUMAN PHYSIOLOGY. sugar grow fat from the quantity of sugar they eat. It is said to accumulate more rapidly when the animal is fattened in a darkened room. Fat is absorbed from the body in some diseases, and its place supplied with serum, as in consumption. It is discharged by the sebaceous glands of the skin, and in the milk of the female during lactation. Albumen, from “Albus,” wliite, on account of its appearance when coagulated. It exists both in the fluid and solid state in the body—fluid in the blood, lymph, chyle, serous and synovial fluids, and milk,—solid in the brain, spinal cord and nerves. It is also found in mu- cous membranes, muscular tissue, and in the aqueous and vitreous humors of the eye. It exists in the white of the egg, and can be easily coagulated or made to assume a solid form. Composition and Properties.—It consists of C54 8 H7.1 O21.3 S.6 P3 in 100 parts. The sulphur and phosphorus are in small quantities. The presence of the former may be detected by the blackening of silver that has been in contact with it. It does not co- agulate spontaneously, but may be coagulated by any of the following re-agents, viz., by heat at 160°F., alcohol, mineral acids, as nitric, sulphuric, &c., tannic acid, fer- rocyanide of potassium in an acid solution, and the metallic salts. It is very readily coagulated by bichlor- ide of mercury, and hence it is used in cases of poisoning from that salt. It unites with it to form the so-called albuminate of mercury. The white of one egg is suffi- cient to neutralize four grains of the bichloride. Albumen coagulates at the negative pole of the battery, if not too strong a current, and at both poles when a strong battery proximate principles of tiie third class. PROXIMATE PRINCIPLES. 29 is used. It is not coagulated by the vegetable acids (except tannic). When albumen is evaporated at a temperature of 120°F., it becomes solid and brittle, but otherwise un- changed, and may be re-dissolved in water. When coagulated by heat or the mineral acids, &c., it cannot be re-dissolved or made to resume its original condition. It is held in solution in the body, by chloride of sodium, earbonate and phosphate of soda, which give it an alka- line reaction. It exists in a neutral state in diseased blood, the egg, renal, splenic and hepatic veins. It parts with some of the soda in passing through the spleen, kidney, and liver. Origin and Function.—It is derived from the albuminoid elements of the food, by a catalytic process during digestion It is the nutrient element of the blood, and the pabulum of all the tissues. When it is withheld from the food, or withdrawn from the body in disease, as in albuminuria, the nervous and muscular tissues suffer most. It is converted into fibrin through the agency of the blood-cells and oxygen; this is pro- bably a chemico-vital process. There are some physiolo- gists who hold the opinion that fibrin is not formed from albumen, but that it is effete matter formed from the worn-out elements of the blood and tissues. It is by no means a settled question; but it is not the object of this work to discuss questions of this kind. Albumen is never discharged from the body in health (except during lactation). In a diseased state of the kidney it is found in the urine, as in albuminuria. Tests.—These depend on its property of coagulation. First. Heat.—When a solution containing albumen is heated in a test tube to 167° F., a precipitate, more or less abundant, is formed. If, however, the liquid be HUMAN PHYSIOLOGY. alkaline, the albumen will not coagulate; hence an acid should be used to neutralize it. The earthy phosphates of the urine, when in excess, are thrown down by heat; but these may be distinguished from albumen by the addition of a few drops of hydrochloric acid, which clears up the phosphates, but has no action on the albumen. Secondly. Nitric Acid.—When this is added to a solution containing albumen, a precipitate is instantly formed. When the urates are abundant in the urine, nitric acid causes a deposition of uric acid, but this may be re-dissolved by an excess of nitric acid. Albuminose.—This substance is found in the chyle and blood. It differs from albumen from the fact that it is not coagulated by heat, and only very imperfectly by nitric acid. It is coagulated by alcohol, acetic acid, and the metallic salts. When in solution in the gastric juice, it interferes with Trommer’s test for grape sugar. It is found in the stomach only during digestion. When Trommer’s test is applied to a saccharine liquid contain- ing albuminose, a purple color is produced on the addition of the re-agents, and when boiled, the color changes from red to yellow, but no suboxide of copper is thrown down. This test may be made to apply, by evaporating the solution to dryness, and making an alcoholic extract, then a watery solution of the sugar contained in the extract will respond as usual. It also interferes with the mutual reaction of starch and iodine, no blue color being produced. Origin and Function. — It is formed from the organic nitrogenized elements of the food, as fibrin, albumen, and casein, &c., by the action of the gastric juice during the process of digestion. It is absorbed in this state, and is converted into albumen in the blood. It is much more easily absorbed than albumen, on PROXIMATE principles. 31 account of its superior osmotic, properties. It is the soluble principle of fibrin, albumen, casein, &c. Fibrin.—iibrin (C54.3 H6,g O22.X S. 3 P3) exists in the blood, lymph, and chyle as found in the lacteals. When blood is removed from the vessels, it soon separates into a solid portion, or clot, and a fluid portion, or serum. The clot consists of coagulated fibrin, containing red and white corpuscles entangled in its meshes. When inflammation is present, the corpuscles have a tendency to cohere, and sink to the bottom of the vessel, hence the fibrin is more abun- dant at the top, and from the peculiar color it presents, is called the “huffy coat.” Fibrin is difficult to obtain free from corpuscles. It may be obtained nearly pure by switching freshly-drawn blood with a bundle of twigs. It coagulates on the twigs, and may be freed from impurities by washing. It is first washed with water, to remove the salts, then with alcohol, to remove the pigment, and ether, to remove fatty matters. Another mode is to filter frogs’ blood, the corpuscles of which, being large, are kept back; but the liquor sanguinis passes through, and the fibrin coagulates, and may be washed as above. A little thin syrup, or a weak solution of an alkali, should be added to retard coagulation during filtration. It is sometimes found in a tolerably pure state in the cavities of the heart and large arteries, after death. It is also found arranged in laminte in the sacs of aneurisms. Physical Appearance and Properties.—Fibrin is a greyish-white, tough, elastic and stringy substance, composed of microscopic fibrils. It possesses the pro- perty of “ spontaneous coagulation” (or fibrillation), and is a constituent of “ cocigulable lymph” which is deposited in the process of inflammation. This substance, which 32 is thrown out on some tissues of the body, as the pleura, forms fibrous bands, which unite the surfaces together. These are called “true membranes.” In low forms of inflammation, however, it is liable to degenerate and form pus. This is also the case when it is thrown out on mucous surfaces, the epithelium and the elements of the mucus having the power of destroying the property of coagulation and subsequent organization. This is a wise provision of nature, to prevent the agglutination of those surfaces. The only apparent exception is the exudation in inflammatory croup and diptheria; but even in these cases it is so far deteriorated, as not to form a “ true membrane.” Fibrin is insoluble in water, alcohol, and ether, but is soluble in the alkalies. Three-fourths of its weight is water. When treated with acetic acid, it swells out, becomes soft and gelatinous, and slightly soluble in water. It may be dissolved in cold concentrated hydro- chloric acid, and after a time the solution acquires a blue color. When dissolved in the potash salts, it resembles albumen in its properties and reactions. When boiled in water, it forms binoxide and teroxide of protein. When boiled in hydrochloric acid, it yields “ leucine” and “ tyrosine.” It is held in solution in the blood by the alkaline chlorides and carbonates. By some writers, it is said to be held in solution by ammonia, and that coagulation depends upon the evolution of that substance. Fibrillation.—The coagulation of fibrin is a process of fibrillation. When the process of fibrillation in an organizable blastema, as in the repair of wounds, or in inflammation, is viewed with a microscope, the blastema at first appears as a homogeneous mass; then it assumes a distinctly granular appearance, some of the granules being developed into cell-nuclei, and others are arranged HUMAN PHYSIOLOGY. PROXIMATE PRINCIPLES. in a linear manner, to form fibres, which extend in every direction between the cell-nuclei. These cell-nuclei seem to have the power of determining the arrangement and direction of the granules, which are subsequently deve- loped into fibres. When fully organized, it is distinctly fibrous in structure, and presents a number of cell-nuclei, some of which remain and others disappear after a time. The completion of this process depends upon the pre- vious elaboration of the fibrin, and the character of the tissue upon which it is deposited, whether serous or mucous, strong or flabby, dead or living. In the coagulation of the blood under the microscope, a granular appearance is first noticed; some of the gra- nules become star-shaped by the addition of other granules, the arms being directed towards the corpuscles, which are ultimately included in the meshes. It will be seen, therefore, that the blood corpuscles exercise the same influence over coagulation of the blood that the cell-nuclei do over the fibrillation of the blastema in the repair of wounds, &c. Coagulation of the fibrin will proceed, though more slowly, in the absence of the cor- puscles, as in filtered blood. This is due to the vitality which it carried with it from the corpuscles. Origin and Function.—Fibrin is a liistogenetic substance. It is formed from albumen, by the influence of the corpuscles and oxygen ; in other words, it is albu- men in a higher state of organization. It gives to the blood its property of coagulation, and it is through this property that “ natural hremostasis” is effected. It builds up the fibrogelatinous or connective tissue, repairs wounds, and prevents the blood from exuding through the coats of the vessels. A summary of the arguments in favour of the view HUMAN PHYSIOLOGY. that fibrin is effete matter, formed from the worn-out elements of blood and the tissues: 1st. It is too small in quantity to be of any great service in building up the tissues. 2nd. It is increased by repeated bleeding and starv- ation. 3rd. That in the improvement of the breed of animals it is diminished. 4th. That there is none found in the renal veins, it having been discharged by the kidneys, and in the hepatic veins it is considerably diminished. 5th. That there is less fibrin in the blood of the carnivora than the lierbivora. iry 6th. Defoliated blood injected into the veins within twenty-four hours after death, will remove the cadaverous rigidity, and the blood returned by the vein is coagu- lable. 7tli. That the blood of unborn infants contains less fibrin than that of adults. 8tli. That there is very little fibrin in the blood of the foetus, none in the egg, none in the chyle until it enters the lacteals, and then only as the result of the additions made to it from the blood or lymph. Casein. (Cgg.i H6.9 N15.9 CDi.g S.3) j.s the organic principle of the milk. It is held in solution by the alkaline carbonates, and may be coagulated by any of the acids. When any of the acids is ad- ded, the alkali is neutralized, and coagulation of the casein follows. It is also coagulated by rennet. This is obtained from the abomasus, or fourth stomach, of the young of ruminants. The pepsine contained in the stomach has the power of converting the sugar of the milk into lactic acid, which neutralizes the alkali, and a precipitate of casein. This is a catalytic PROXIMATE PRINCIPLES. 35 process. Casein is also coagulated during a thunder storm. A substance called ozone is developed in the atmosphere; this acts on the casein and decomposes it. The decaying casein acts as a ferment, and converts the sugar of milk into lactic acid, which precipitates the casein. Casein differs from albumen; it contains no phosphorus, is not coagulated by heat, and is precipitated by acetic acid. The precipitate of casein may be re-dissolved by a solution of caustic alkali. It is insol- uble in water and alcohol. Origin and Function.— It is formed from the albumen of the blood by a catalytic process in the mammary gland. It has been found in the blood of puerperal women. Casein may be obtained in nearly a pure state, by precipitating it with acetic acid, and then washing the precipitate with alcohol and water. It is the chief aliment of the young of the mammalia, and the substance from which all the tissues are formed. Globuline, (C54.6 H6.9 N16.2 02i.9 S.a), in a semi-solid state, is found in the crystalline lens, in the blood globules, and in the structure of cells generally. It is coagulated by heat, alcohol, and the mineral acids. It is soluble in water, but not in the liquor sanguinis of the blood. The coagulum of globuline is partly soluble in hot alcohol; this distinguishes it from albumen. Acetic acid causes it to swell out and become transparent. The globuline of the crystalline lens is called by some “ Crystalline.” It is more easily coagulated than globu- line. Pancreatine.—This is the organic principle of the pancreatic juice. It is a viscid fluid, coagulable by heat, alcohol, and strong acids. It is coagulated by sulphate of magnesia; this distinguishes it from albumen. It has the property of emulsifying oils and fats, and of convert- 36 HUMAN PHYSIOLOGY. ing starcli into sugar during the process of digestion. It is formed from the albumen of the blood in the pancreas. Pepsine.—This is the organic principle of the gastric juice. It is coagulated by heat and alcohol, and is with difficulty distinguished from albumen. It exists in the gastric juice in the proportion of fifteen parts per ‘thousand. It may be precipitated and extracted from the gastric juice by means of alcohol. The solvent power of the gastric juice depends on the presence of pepsine. This will be discussed in the chapter on digestion. Mucosine. — The organic substance of mucus is termed mucosine. In some of its properties it resembles albumen. It is coagulated by heat, strong acids, and the metallic salts. It lubricates the free surface of mucous membranes, being formed from the blood by the agency of the cells, which line the free surface of the membrane and its follicles. This substance, together with casein, urrosacine, and biliverdine, are the only proximate prin- ciples of this class that are discharged from the body in health. Musculine is a semi-solid organic substance peculiar to muscular tissue. It is insoluble in water, but is soluble in a mixture of ten parts of water with one of hydro- chloric acid, and may be precipitated again by neutral- izing with an alkali. It is a most important element of animal food, and is the great source of albumen and fibrin. Cartilagine is the organic ingredient of cartilage. By prolonged boiling, it is transformed into a substance called “ chondrine.” It is precipitated by acids and some of the metallic salts; this distinguishes it from “ gelatine.” Osteine.—This substance, peculiar to bone, is natur- PROXIMATE PRINCIPLES. ally solid. It constitutes tlie principal part of the animal matter. By prolonged boiling, it is converted into “ gelatine” or “ glue,” and is then soluble in water. Elasticine.—This is the organic principle of the yellow elastic tissue. It is soluble in nitric, sulphuric and hydrochloric acid, and these solutions are not preci- pitated by alkalies. Keratine.—This is an organic substance, found in the nails and hair. Unlike the other substances of this class, it is decomposed by potash. The remaining substances of this group are*the color- ing matters of the body. They all contain iron in a molecular state. They are hematine, biliverdine, mela- nine and urrosacine. Hematine (C44 II2.2 X3 06 Fe.) is the coloring principle of the blood, and exists in the interior of the blood corpuscles. The presence of iron may be detected as follows:—Add a drop of nitric acid to a small cpiantity of blood in a watch glass, evaporate slowly over a lamp. The iron absorbs oxygen, and is converted into peroxide, and nitrous acid fumes are given off. Then add a drop of the sulphocyanide of potassium, and a red color will be produced characteristic of the sul- phocyanide of iron. The color of hematine is supposed to be due to the iron. It exists in the blood in the proportion of one part of hematine to seventeen parts of globuline. When the red blood corpuscles are broken down from any cause, the hematine is set free, and the walls of the vessels and tissues are stained. This has been mistaken for arteritis. When the hema- tine is deficient in the blood, as in anemia, &c., it may be restored by the administration of iron. Hematine is soluble in ether and hot alcohol, but is insoluble in water and acids when removed from the blood. 38 HUMAN PHYSIOLOGY. Biliverdine is the greenisli-yellow coloring matter of the bile. It contains iron in the same proportion as hematine. It is insoluble in water, but is soluble in ether and alcohol. No doubt it is formed from hematine. It is discharged from the body in the faeces. Melanine is a brownish-colored substance, found in those parts of the body where pigment exists, as in the choroid coat of the eye, iris, epidermis and hair. It is very abundant in the epidermis of the negro. It is formed from hematine, but contains less iron. The color- ing matter is the same in all situations, the different shades being produced by the arrangement of the pig- ment cells among the fibres and capillaries of the tissue. In some cases it is entirely absent, as in the “ albino.” It is insoluble in water and dilute acids, but is soluble in caustic potassa. Urrosacine is a yellowish-red coloring matter pecu- liar to the urine. It is found, also, in urinary calculi. It is probably the worn-out hematine of the blood, which is being discharged by the kidney. Urrosacine and biliverdine are both discharged from the body, the one in the urine, and the other in the ffeces. CHAPTER II. ELEMENTARY OR PRIMARY FORMS OF TISSUE. The elementary or primary forms of tissue are cells, simple fibres, and simple or basement membranes. Of these, the cells are the most important, since they are the active agents in the performance of all the functions of the animal body, as digestion, absorption, selection, assimilation, respiration, secretion, excretion and repro- duction. They also constitute the fundamental elements of all the tissues, and are the active agents in all the catalytic and chemico-vital changes which take place in the animal economy. The agency of cells is not only exhibited in the healthy actions of the body, but may also be seen in the development of various morbid growths, as fibroid tumors, cancer, &c. Hence cellular physiology and pathology are the most important sub- jects which can engage the attention of the intelligent physician and surgeon. History of the Animal Cell.—The form which organic matter takes when it passes from the condition of a proximate principle to that of an organized struc- ture, is that of a cell, a simple fibre, or a simple mem- brane. Definition.—A cell is a membranous sac enclosing a cavity, which contains matters of variable consistence, appearance and properties. Variation in Shape.—The cells are generally glob- ular, but may assume various shapes, depending on internal and external circumstances, and the growth of the cell; for example, cells which are originally rounded, as the fat cell, may become polygonal, as the result of mutual pressure. The specific gravity of the contents will also affect the shape to a considerable extent. When water is added, they have a tendency to swell out and finally burst. When evaporation or dessieation takes place, they become flattened and hardened, as in the epidermis. The shape of the cell may also be changed by the absorption of gases and vapors, e.g., the blood corpuscle presents a distinctly biconcave disk under the influence of oxygen, and becomes rounded again when exposed to the influence of carbonic-acid gas. The vapor of ether, when inhaled, produces an irregular appearance of the blood corpuscles. Chloroform vapor causes a serrated outline, and alcohol renders them oval, with an indentation on one side. Cells may also assume different shapes, depending on their growth ; for example, the pig- ment cell, which is at first spheroidal, throws out arms or projections in different directions, and becomes stellate during its growth. The nerve cell becomes caudate; nonstriated muscular cell, fusiform. Epithelial cells are either cylindrical (columnar), or squamous (tesselated or pavement). This peculiarity of shape is due to the plastic power of the cell, which causes a molecular current of plasma to set to that part of the cell which is to be enlarged or prolonged. There is also, through the vital power of the cell, a condensation of the plasma at that particular part. In some instances, growths take place on the free surfaces or extremities of cells, as is seen in the cilite of epithelial cells. Variation in Size.—Cells vary in size from of an inch in diameter, the size of the largest fat cell, to f ouoo of an inch, the size of the fat globule. The aver- HUMAN PHYSIOLOGY. .age diameter of tlie blood corpuscle is about 3 d0 0- of an inch. Xerve cells vary from 355 to 4 do 0 °f an inch in diameter. Muscular fibre cell 4 do0 to of an inch, &c. In order to facilitate the general description of a cell, it may be divided into a cell wall, nucleus, nucleo- lus and contents. Cell Wall.—The cell wall is substantially the same in all cells. It is a simple homogeneous membrane, com- posed of globuline; and although no pores can be seen by the highest magnifying power, yet it possesses the property of osmosis. It lias also the power of choosing and refusing from the particles of nutrient fluid or cyto- blastema in its neighbourhood, incorporating some of them into the substance of its wall, and converting others into new substances in its interior. For example, the blood corpuscle has the power of forming globuline and hematine from the albumen and fibrin of the blood. I't is contended by some physiologists that this power resides solely in the nucleus; but it must be borne in mind that this property belongs also to those cells which are entirely destitute of a nucleus, as the fat cell at maturity, blood corpuscle, germ cells of the vegetable kingdom, &c., &c. When the cell-wall is acted on by acetic acid, it swells out and becomes transparent, so as to bring into view the nucleus, when that exists. Nucleus.—In the interior of most animal cells is seen a collection of granular matter, which is called the nucleus. It exists in three forms: First, as a minute granular body; secondly, as a well-defined granule; and thirdly, as a small cell, containing a granular body or nucleolus. The nucleus is generally situated in or near the centre of the cell; but may be attached to the wall, or ELEMENTARY OR PRIMARY FORMS OF TISSUE. 42 HUMAN PHYSIOLOGY. imbedded in it (as in the fat cell). It is generally rounded in form, but may be found elongated, as in the nonstriated muscular fibre cell. The size of the nucleus varies from jQp to goVo of an inch in diameter. It is more regular, both in shape and size, than the cell itself. When two or more nuclei are found in one cell, it is generally an evidence of rapid growth, as in fibro-cellular tumors, cancer, pus, &c., &c. They are, in these cases, formed by the subdivision of the original nucleus. Those cells which are not destined to reproduce their kind, do not possess a nucleus at maturity, as the blood corpuscle, fat cell, &c. The nucleus in substance is analogous to the cell-wall. Nucleolus.—When the cell-wall is acted upon by acetic acid, it swells out and finally bursts, and the acid coming into contact with the nucleus clears it up, and brings into view the nucleolus, when that is present. It is situated in the interior of the nucleus, and may consist of a single granule or a number united together. In some instances it is highly refracting and not readily acted upon by most chemical re-agents, as in the hepatic cell. Contents.—Every cell lias the power of generating in its interior a substance peculiar to itself, which is the result of its own secretion; one secretes bile, another milk, another mucus, another gastric juice, &c., &c. The contents of the cell may be either solid, as in bone, nails, epidermis, &c., or fluid, as in blood, chyle, mucus, &c. The contents of all cells are originally fluid, but become hardened by secondary deposit, as in bone, dentine, &c. This takes place by the deposition of solid particles on the inside of the cell-wall, and the outside of the. nucleus. Colok.—The color of the cell depends partly on its ELEMENTARY OR PRIMARY FORMS OF TISSUE. refracting power, and partly on the hematine, melanine, &c., which it contains. Pabulum, or Cytoblastema.—This is derived either from the fluid in which the cell floats, as blood, chyle, &c., or from the capillaries near the seat of growth. When the cells are situated on a basement membrane, as the epithelium of mucous and serous membranes, it is found surrounding them, having passed through the basement membrane from the capillaries immediately beneath. In all these cases the cytoblastema contains material not only to supply the wants of the present brood of cells, but also for the development of the new brood which is destined to take the place of the old. Laws of Cytogenesis. 1st Lem.—In all tissues composed of cells, the new cells which are being developed must resemble the parent cells in all their distinctive features and properties. When the young cell deviates in its character from the parent cell, abnormal growth may be said to have commenced. 2nd Lem.—Cell growth can only take place in or near its appropriate pabulum, and on living surfaces. Cytogenesis.— (kvto?, “cell,” yevedi?, “generation.”) Cells may be developed in two different modes;—either “de novo,” in the midst of an organizable blastema, or from a pre-existing or parent cell. Of the first mode, there are two varieties. First. The formation of the nucleolus from a collection of granules, and the subsequent development of the nucleus and cell-wall; and seconelly, the formation first of the cell-wall, and subsequently the nucleus and nucleolus. Of the second mode, there are also two varieties. First. Multiplication by subdivision of the original cell; and secondly, by the development of new cells within the parent cell. 44 HUMAN PHYSIOLOGY. First Mode—The Development of Cells “denovo” in the Midst of an Organizable Blastema.—In the first variety, when examined under the microscope, the blastema, when first effused, presents a homogeneous, semi-fluid appearance. As it solidifies, a number of molecules or minute granules show themselves. Some of these cluster together, and form a well-defined granule. This constitutes the future nucleolus. This nucleolus seems to have the power of arranging the granules around it at a certain radial distance, to form the nucleus; and around the nucleus thus formed is arranged concentric- ally a second series of granules, which constitutes the cell wall. The growth of the cell wall and nucleus takes place by the interstitial deposit of granules between those already arranged, and by additions on the outside and inside of their walls. In some instances this growth is irregular, and gives rise to those peculiarities of shape which have already been mentioned. This mode of cytogenesis may be demonstrated by experimenting on wounds. In the second variety, the cell is formed by the ex- pansion of granules. The molecules aggregate to form a well-defined granule. This enlarges, and presents a nebulous appearance; it then clears up in the centre, so as to resemble a cell nucleus. This expands and forms the cell wall, which allows the plasma to pass through for the subsequent formation of the nucleus and nucleo- lus. The nucleus is formed within the cell by a col- lection of granular matter (developed from the plasma), which clears up in the centre; and in the interior of the nucleus a few granules collect to form the nucleolus. This variety of cytogenesis may be observed in the primary development of nerve tissue. Second Mope—The Development of Cells from ELEMENTARY OR PRIMARY FORMS OF TISSUE. a Pre-Existing or Parent Cell.—Of the first variety, viz., multiplication by subdivision, the development of the cartilage cells furnishes a good example. The cell is originally rounded; but when the process of subdivision commences, it becomes oval, and subsequently presents a sort of hour-glass contraction, or—first of the nucleus, and afterwards of the cell wall. This continues until there is a complete separation, first of the nucleus into two parts, and then the cell wall, each part of the nucleus drawing a portion of the cell wall around it. This process may be again repeated in each part, either in the same direction or transversely, so as to form four new cells, and so on until a large mass has been pro- duced. At the point in which division of the original cell wall and nucleus is taking place, granular matter may be noticed, which is used in the process of recon- structing the new cells. In the second variety the nucleus appears to separate at once into several parts, each of which is developed into a new cell, and in this way the parent cell may be filled by a whole brood of young cells. This variety of cell development may be observed in structures of very rapid growth, as in cancerous tissue, &c. It is probable that these new cells may be formed by the expansion of granules. A compound cell consists of a cell within a cell, as the graafian vesicle. Conditions necessary to Cytogenesis.—The con- ditions necessary to cytogenesis are the presence of pabu- lum upon a living surface, a certain degree of animal heat, a requisite amount of water, oxygen, light and elec- tricity. The dynamic agency of heat cannot be dispensed with; too much would be injurious. The mysterious 46 HUMAN PHYSIOLOGY. influence of light is necessary to healthy action, and a certain amount of water is required to preserve the in- tegrity and promote the growth of the cell; hut too much would destroy it. Changes which Deprive a Cell of its Indivi- duality.—Cells may lose their individuality : 1st. By coalescence of the cell wall with the inter- cellular substance of temporary cartilage, as in the deve- lopment of osseous tissue, the nuclei of the cells forming the lacunas. (See development of bone.) 2nd. By the process of multiplication by subdivision, which has already been described. 3rd. By the coalescence of cells, in a linear manner, to form a fibre, as in fibrous tissue. The cells are origi- nally round; but in the process of forming fibres they become, first oval, then elongated, and in some instances fusiform. They are then arranged end to end, sometimes slightly overlapping each other, and by their fusion or coalescence a fibre is formed. * 4th. By the coalescence of cells, in a linear manner, to form tubes. In this instance the opposing walls of the cells, as they are arranged in a line, break down, the cavities of the cells communicate with each other, and in this way a continuous tube is formed, as in the devel- opment of nerve tissue, and in the formation of the vascular tract from the germinal vesicles.—See chapter on blood. Spontaneous Change in the Shape of Cells.— Spontaneous changes in the shape of cells give rise to motion. The cause of motion in the vegetable king- dom was for a long time a matter of speculation. It was finally discovered that this phenomenon was due to the spontaneous change in the shape of the cells when irri- tated, as in the mimosa or sensitive plant, the fly-trap of the Dionoea, and the Berberis. ELEMENTARY OR PRIMARY FORMS OF TISSUE. In the animal economy, muscular contraction is due to this spontaneous change. It occurs in both the striated and non-striated muscular tissue. In contrac- tion of the fihrillae the sarcos elements become shorter and broader; the same is true of the non-striated muscu- lar fibre cells. Spontaneous changes in the shape of the cells take place in the uterus during gestation. The cells are largely developed during pregnancy, in order to give enlarged accommodation for the development of the foetus, and increased power for the act of parturition. After birth the uterus undergoes the process of involution, by which the cells are diminished in size and number and changed in their physical appearance. When ex- amined by the microscope, oil globules may he seen in their interior at this stage. The movements of the ciliae are no doubt produced by the spontaneous change in the shape of the cells from which they spring. It is probably caused by the alter- nate contraction and relaxation of the opposite sides of noli -urn'll XV Ol U'W C i the cell wall. tUx. . Cause of Organization, Vitality, &c.—This is a purely speculative subject. Many theories have been advanced from time to time, to endeavour to explain the phenomena of organized bodies. Some suppose that it is due to an “ animating principle ” which pervades every organized structure and regulates its functions, and by which the new organism for the production of the species is moulded into shape, from materials furnished by the parent. This “ principle ” is supposed to he regulated and controlled by the Deity himself. This was the theory of Aristotle, and was afterwards advocated by Harvey. Hunter attributes the organization of living beings, and the vital actions manifested by them, to a “materia HUMAN PHYSIOLOGY. vitee ” diffused throughout the solids and fluids of the body. Abernetliy supposes this materia vibe to be a species of electricity. Muller supposes that the cause of organization is due to an “ organic force ” which resides in the whole organism, and possesses the property of generating each part. This “ organic force ” exists already in the germ, and is creative, as is seen in the aggregation of granules by the primary germ to mark the different parts of the new organism. It is not under the influence of the mind, for instinct is as capable of reproducing the species as higher intelligence. Prout advocates the existence of an “organic agent,” which possesses extraordinary powers in controlling and directing the organization and development of the living- being. This is very similar to the preceding hypothesis. There can be no doubt, however, that organic matter derives its vital properties from a previously existing vital organism. While these organic matters retain a perfect organization, and are supplied with their proper stimuli, as light, heat, moisture, &c., vital actions go on perfectly: for example, the fecundated egg, “ ornne vivum ex ovo,” acquires its vital properties while in the body of the mother; and when laid, if supplied with vital stimuli, and the organization remain perfect, it is developed into a new being. But as soon as the structure is destroyed, or the vital stimuli withheld or withdrawn, the organism dies, and its elements form new compounds, most of which are of an inorganic character. Organic life is presided over by the cerebellum and spinal cord; intelligence by the cerebrum. Phenomena of Cells.—The phenomena of cells are exhibited in the plastic and metabolic, or vital and chemi- cal power of the cell. The plastic power of the cell is ELEMENTARY OR PRIMARY FORMS OF TISSUE. 49 seen in the preparation of material for the formation of new cells; in the organization of this material into granules; in the arrangement of these granules in a certain order, to form the nucleus, nucleolus and cell wall; and in the subsequent growth and development of the ceil. The metabolic power of the cell is shown in the pro- perty it has of chemically changing the plastema within and without the cell. It is confined to the conversion of special substances, as in the formation of globuline and liematine, by the blood corpuscle, bile by the hepatic cell, and pepsine by the epithelium of the stomach. The cell of the yeast plant lias also the power of converting sugar into alcohol and carbonic acid. These two forces (plastic and metabolic) may act together; in fact, it is difficult to separate them, and the change which they produce is called a chemico-vital change, as the formation of fibrin from albumen, &c. Both these forces act together in harmony, and through their united action the different secretions and excretions are formed. These forces are affected by nervous impressions, as fear, joy, grief, anger, &c. For example, the character of the milk is changed by a fit of anger, and the secretion of the gastric juice is arrested by fear. The plastic and metabolic power* of the cell may be arrested by powerful chemical re-agents, as arsenic, cor- rosive sublimate, acids and alkalies. The latter will pre- vent the conversion of albumen into fibrin, and should be administered in cases of inflammation. It is also arrested by strong nervous shocks, as a stroke of light- ning or a powerful battery, and by septic poisons. Manifestations of Cell Life.—These are exhibited: First. In cell growth from the germ. 50 Second. Multiplication by subdivision. Third. Chemical transformation of the blastema. Fourth. Permanent change in the cell. Fifth. Temporary change in the cell. Sixth. Production of nervous force (vis nervosa.) And Seventh. Vitalization of the pabulum. A cell is a living organism, and like all living bodies? lias its period of growth, maturity and decay. It has the power of selecting matters from the blastema—assi- milating and organizing them into the new substances found in its interior. This property resides in the cell as a whole, and not exclusively in any single part of it. The granules from which the cell was originally developed are supposed to be a transition state between albumen and the substance which it is destined to form. The duration of the life of a cell depends on its activity— those of slow development are long-lived, and vice versa. When a cell begins to decay, granular matter is first noticed in its interior; the cell wall finally gives way, and the granular matter escapes. “Granules thou art, and unto granules slialt thou return.” HUMAN PHYSIOLOGY. SIMPLE FIBRES. A simple fibre is formed by the arrangement and coalescence of granules in a linear manner. They are found only in repair of tissue, as in wounds (and in in- flammatory exudations), and are formed under the influence of cell-nuclei by the process of fibrillation. Schwann maintains that “ all the tissues of the body are formed from cells.''’ All the tissues of the body were originally formed from cells ; but in the course of recon- struction or repair of wounds, and in inflammation, the process of fibrillation takes place. The plastic matter thrown out to heal the wound, or upon the inflamed ELEMENTARY OR PRIMARY FORMS OF TISSUE. surface, at first presents a homogeneous appearance, and as it solidifies it becomes granular. Some of the granules are developed into cell-nuclei, by the process of cytoge- nesis, and the remaining granules are arranged in a linear manner, radiating from the cell-nuclei, so as to form a network, including the cell-nuclei in its meshes. The cell-nucleus consists of a thin-walled nucleus, and a well-defined granule in the centre—the nucleolus. They never proceed any further towards organization, and are therefore called free cell-nuclei. They may be demonstrated by exposing a portion of the newly-formed tissue of a wound to the influence of acetic acid, which clears it up and brings into view the free cell-nuclei, and also the simple fibres which surround them. These are formed like the simple fibres already de- scribed, directly from the nutrient fluid or blastema, by a certain arrangement of granules peculiar to themselves. They exist under three different forms, which vary some- what in microscopical*appearance. In the first variety, it is a simple pellicle'of homo- geneous appearance, and shows no sign of organization, as in the cell wall. A good example may be seen in the lining membrane of a bivalve shell. In the second variety, the membrane is not homoge- neous in its character, but presents a number of minute granules irregularly scattered through the transparent substance. In the third variety, the membrane presents a num- ber of distinct spots or nuclei, and is capable of being torn up into portions of nearly equal size, each contain- ing one of these spots or nuclei. From this it would appear that the first variety is formed by the condensa- SIMPLE OR BASEMENT MEMBRANES. tion of a thin layer of blastema, the second by the con- densation of a thin layer of blastema in which granules had been formed, and the third by the condensation of a thin layer of blastema in which nuclei had been formed. The last two varieties of membrane above described have been called by some basement membrane, because it is the foundation or resting place for the epithelial cells; by others primary, germinal, or maternal mem- brane, because it furnishes the germs of those cells. The basement membrane is found on all the free sur- faces of the body, giving support to the epithelial cells. It forms the outer layer of the true skin, and the inner layer of mucous, serous and synovial membranes, blood- vessels and lymphatics. It is prolonged into all the ducts, follicles and tubuli connected with the mucous membranes. In all these examples its free surface is covered with cells, which receive their nutriment by osmosis, through the membrane, from the capillaries on its attached sur- face. Its office is to limit the nutrient fluid, and to modify it in its passage. It also supports the cells, and probably furnishes the germs of all the cells which are developed on its surface. In all probability, the granules and spots, or nuclei, seen in the basement membrane are the germs of cells, which spring from them as from a centre. HUMAN PHYSIOLOGY. CHAPTER III. TISSUES. WHITE FIBROUS TISSUE. This tissue enters into the formation of ligaments, tendons, aponeuroses and membranes. 1st. As ligaments, it connects the bones together and preserves the integrity of the joints in their various movements. The ligaments assume three different forms: Funicular, which consists of rounded cords of fibrous tissues, as the ligamentum teres. Fascicular, which consists of flattened bands, as the ligaments of the ankle, knee, and elbow; and Capsidar, which form tubular expansions, as in the shoulder and hip joints. 2nd. As tendons, it serves to connect the muscles to the bones and other structures to which they are occasionally attached; some of these are rounded— Funicular, as the tendon of the semi-tendinosus; others flattened—Fascicular, as the semi-membranosus. The tendons, at their insertion into the bones, blend with the periosteum. 3rd. As aponeuroses. These are tendinous expansions of considerable extent, as in the abdominal muscles- They serve to enclose cavities, and protect the contained organs. 4th. As membranes, it is used to cover, protect, and attach various organs, as the dura mater, sclerotic coat of the eye, pericardium, tunica albuginea testis, periosteum, perichondrium, fascia, lata, &c. Physical Appearance and Properties.—It presents a beautiful, silvery-white appearance, when freed from extraneous substances, and is composed of bundles of fibres, which are parallel to each other in some cases, and cross or interlace in others. Examined under the microscope, it is found to consist of wavy bands about of an inch in diameter. They appear to be formed of numerous fib rilin', varying in size from y f° 2 or! 00 of an inch. This is not the case, however. The bands are not capable of being separated into fibril be; but they present parallel streaks, which have a tendency to slit up in a longitudinal direction. When a portion is exposed to the action of acetic acid, it swells out and becomes semi-transparent, the streaks are entirely oblit- erated, and a number of cell-nuclei make their appearance, showing that it has been developed from cells. At the same time some wavy transverse lines may be seen at regular distances, which somewhat resemble striped muscular fibre. These lines mark the junction of the cells from which the tissue was originally formed. This tissue is perfectly inelastic, and allows of a slight degree of extension from long-continued force. It possesses no contractility, and its force of cohesion is very great. It is said that the tendo-achilles is capable of supporting a weight of nearly 1,000 lbs. It contains few vessels and nerves. The actual presence of nerves has not, as yet, been satisfactorily demonstrated, and its sensibility is very low. The division of a tendon is attended with very little pain. It yields gelatine, on boiling. HUMAN PHYSIOLOGY. YELLOW FIBROUS OR ELASTIC TISSUE. It is found in the ligamenta subflava, ligamentum nuchas of quadrupeds, internal lateral ligament of the lower jaw, stylo hyoid and pterygo-maxillary ligaments, chordae vocales, cricothyroid and thyrohyoid membranes, posterior wall of the trachea, arteries, veins, thoracic duct, and in areolar tissue. Physical Appearance and Properties.—This tissue, unlike the preceding, is of a yellowish color, highly elastic, and consists of long, single, brittle fibres, which show a disposition to curl upon themselves when broken. They vary in size from to of an inch, the average diameter being about 7 of an inch, and are round or flattened—depending on their situation or pressure. They anastomose with each other, and are mingled in various proportions with the white, to form areolar or filamentous tissue. It does not gelatinize on boiling, is not acted on by acetic acid, and is not readily dissolved by the gastric juice. It resists the approach of disease longer than any other tissue in the body; e. g., an artery will remain intact in the interior of an abscess after the other structures are destroyed, and when the artery gives way, the walls present a honeycomb appearance, on account of the destruction of the white fibrous and muscular tissues with which it is associated. It consists of C4 8 H36 014 +2 Ho., or one part of protein and two parts of water (Scherer). Its elasticity is due to the presence of water. It is sparingly supplied with blood vessels and nerves. The fibres are marked by transverse lines, in the lower animals, which shows that it is developed from cells. Its elasticity is impaired by age. Mode of Development.—This is nearly the same in both white and yellow. They were supposed by Henle to be developed by the process of fibrillation. Their real mode of growth was first pointed out by Schwann, to be from cells. The cells are developed from the plasma in the ordinary way. (See chapter on tissues. 55 cells.) They are at first round, and possess a nucleus, nucleolus and granular contents. They then become oval, then elongated, and finally fusiform ; and being applied or spliced end to end in a linear manner, coales- cence takes place, and a fibre is formed. At the same time the cells clear up, the nuclei become elongated, and finally disappear, until brought into view by means of acetic acid. In the white fibrous tissue, the bands are formed by the juxtaposition of several rows of cells .thus arranged. Areolar Tissue, (Syn., Cellular, connective or fila- mentous.)—This tissue is found in all parts of the body except the brain, compact tissue of bone, teeth, cartilage, hair, nails, epidermis, &c. It consists of a network formed by a combination of white fibrous and yellow elastic tissue. Where great strength is required, the white predominates ; and where motion is required, the yellow, as in the tissue of the lungs. The proportion of each may be easily demonstrated by acting on it with acetic acid, which swells out the white, while it pro- duces no change on the yellow. The interstices or meshes (improperly called cells) of areolar tissue com- municate with each other. This tissue, therefore, may be inflated with aii (the butchers take advantage of this circumstance in inflating their meat), or the meshes may be filled with fluid, as in anasarca. The interstices, especially in the subcutaneous areolar tissue, are par- tially filled with adipose tissue, and contain a small quantity of serous fluid of an alkaline reaction, composed of water, albumen and chloride of sodium. When the fat is absorbed by the demands of the system, its place is filled with serous fluid, as in phthisis, &c. Function.—Its function is to surround and connect various organs, and retain them at certain distances; at HUMAN PHYSIOLOGY. TISSUES. the same time allowing a certain amount of motion. It also forms a nidus for the vessels and nerves, fills up spaces between different organs, and when the meshes are filled with fat, gives rotundity to the body. In some parts of the body it is very dense, and has received the name of a fibrous membrane, as in the pharynx, sheaths of vessels, &c. It forms sheaths for the muscles, and the bundles and fasciculi of which they are formed. It also forms sheaths for the vessels and nerves. It attaches the membranous expansions, as the mucous, cutaneous, serous and synovial membranes, to the structures which they surround and embrace, and receives the name of submucous, subcutaneous, subserous and subsynovial areolar tissue, respectively. This was formerly described as nothing more or less, than areolar tissue, with fat cells imbedded in its meshes. This is not the case, however, for it exists in parts in which not the slighest trace of areolar tissue can be found, as, for example, in the cancelli of the bones. On the other hand, the areolar tissue in many parts of the body is entirely destitute of fat, as, e. g., beneath mucous membranes, in the cutis vera, between the rectum and bladder, in the eyelids, epicranial aponeurosis, scrotum, penis, &c., but in other parts of the body they are associated together. Physical Appearance and Properties. — It is composed of cells or vesicles containing fat, which vary in size from to 5 which generally indicates a high state of inflammation The coagulation of the blood is also retarded, or alto- gether destroyed, by keeping it at a temperature of ISO0!1., while the natural heat of the body (98°F.) promotes it. It is also retarded by cold, but is not destroyed, even by freezing; for, if frozen as soon as it is drawn from the vessels, it will coagulate on being thawed. Gulliver con- siders this fact as conclusive against the vital character of coagulation; but it is a well-known fact that seeds, eggs, lizards, &c., may be frozen or kept in a state of dormant vitality for an unlimited period. Continued agitation will retard the coagulation for a time; but it ultimately takes place in the form of shreds, or strings. Blood while still contained, in the living vessels, or effused in the living tissues, may continue in a fluid condition for a long period. Gulliver states that the blood included between two ligatures in a living vessel remained fluid three, four, or five hours. He also mentions one remark- able case, in which blood effused in the tissue of the loin, was found fluid when let out twenty-eight days, afterwards. In all these cases it coagulated in from fif- teen to thirty minutes when withdrawn from the living parts. Exclusion from the air retards coagulation, as may be seen by covering the blood with a stratum of oil so as to exclude the air. The neutral salts, added to fresh blood, have a tendency to retard, and sometimes to prevent coagula- tion ; and the same effect is produced by many vegetable substances, especially those of the narcotic and sedative class, as opium, hyoscyamus, belladonna, aconite, digi- talis, &c. Gulliver mentions that he has kept horses’ blood in a fluid state for fifty-seven weeks, with solution of nitrate of potash, and that it still coagulated, when diluted with water. It is for this, among other reasons, that physicians administer the potash salts in inflam- mation. The presence of bile retards the coagulation of the blood; and animal poisons, as the virus of serpents, may retard or entirely destroy its coagulating power. HUMAN PHYSIOLOGY. CIRCUMSTANCES WHICH PROMOTE COAGULATION. The natural temperature of the body, from which the blood is taken (in man 98° to 100° F.) is most favorable to coagulation. Best favors coagulation, but is not the cause, as some have supposed; for, although at rest, if air be excluded, as when it is within the living vessels, or covered with oil, coagulation is retarded for a consider- able time. Exposure to air accelerates the process of coagulation; also, the multiplicity of points; as in a lacerated, ragged wound, coagula are more readily formed than in clean, incised wounds. A low state of vitality of the vessels, from whatever cause, favors the formation of clots, or emboli a, as they are called. These are, no doubt, frequently formed dur- ing life, as grooves, marked out by the current of blood, may be observed in clots found in the heart after death. BLOOD. 177 The contact of a dead substance promotes coagulation, even in the living vessels. Simon carried a single thread, by means of a fine needle, through a contiguous artery and vein, and allowed it to remain from twelve to twenty-four hours. A coagulum was formed in both artery and vein; that in the artery being pyramidal in shape, the base directed towards the heart, while that in the vein was larger and more irregular, the clot being chiefly collected on that side of the thread most remote from the heart. The contact of dead animal matter accelerates coagu- lation in a remarkable degree, either within or without the living vessels. The presence of pus will produce coagulation in healthy blood, in from two to five minutes, and when injected into the veins, it produces instantaneous death. When an artery gives way in the interior of an abscess, the hemorrhage is restrained, to a certain extent, by the presence of the pus which sur- rounds it. FUNCTION OF THE ELEMENTS OF THE BLOOD. Function of Fibein.—It was formerly supposed that fibrin was that element of the blood which was directly drawn upon in the process of nutrition. This opinion was based on the then current theory that fibrin and muscle were identical in chemical composition; but it has since been shown, by Liebig, that, so far from this being the case, the evidence is precisely the other way. On the other hand, there are both structural and chemi- cal indications that fibrin is in a state of transition towards the fibro-gelatinous, or connective tissues, and may be regarded, therefore, as their special pabulum. Besides, there is no evidence whatever that fibrin is used in the formation of the cellulo-albuminous tissues; while, HUMAN PHYSIOLOGY. on the other hand, there are negative evidences that their formation and growth do not depend upon its presence. Firstly, the general purposes of nutrition may be served by a fluid which does not possess the property of coagulating spontaneously. Secondly, in nearly all exudations in which inflammation is absent, the fluid is albuminous. Thirdly, the small amount of fibrin found in the chyle is simply the result of elaboration in the lymphatics. Fourthly, the vegetable cell, which is essen- tially the same as the animal cell, is formed from an albuminous fluid, there being no fibrin in the juices of the plant. The plant is also deficient in the fibro- gelatinous tissues. Hematine and globuline are also formed from fibrin and albumen. As a component of the blood, fibrin is of importance in giving it its proper degree of plasticity, and in this way facilitating its passage through the vessels. It also prevents the blood from exuding through the coats of the vessels, and arrests hemorrhages by plugging up the mouths of the open vessels. The want of the coagulating power of the blood is strikingly seen in cases of purpura hemorrhagica, in which the blood is not able to form a clot sufficient to close the mouth of the smallest vessel, or to form a barrier to surround abscesses, and prevent the infiltration of pus in the tis- sues. The same thing may be seen in the hemorrhagic diathesis, in which there is almost an entire absence of coagulable material. Again, the consequence of the excess of fibrin in the blood is seen in inflammatory diseases, in which it is poured out and forms bands and false membranes, which, in some cases, by their adhesions, tie down and inter- fere with the functions of important organs; but this, though injurious in some cases, may be highly beneficial BLOOD. 179 in others—by securing perfect rest in the affected part, as, for example, in penetrating wounds of the intestines, &c., &c. The fibrin is also the material of the blood which is used in the healing of wounds, and this would appear to be one of its most important functions. Some physiologists and pathologists, among whom are Zimmerman, Simon, Jones, and Sieveking, &c., have advanced the idea that fibrin should not be regarded as an ingredient prepared for the nourishment of certain tissues, but as among those substances which have arisen from the decay of the blood, or the effete matter thrown into it from the tissues. In support of this view, they advance the following arguments. First, that fibrin is increased in bleeding, starvation, anemia, and other states of exhaustion, while, at the same time, the red corpuscles are rapidly reduced by the same means. This view is also favored by the fact that in improvement of the breed of animals the red corpuscles are increased, and the fibrin diminished. Secondly, there is also a small quantity of fibrin in foetal blood, none in the egg, or the chyle, until it enters the lacteals, and it is also smaller in quantity in the blood of the carnivora than in the herbivora. (See Fibrin.) Function of the Eed Corpuscles.—One great function of the red corpuscles is to elaborate the mate- rials of the blood which are to be used in the nutrition of the tissues, more especially those which supply the muscular and nerve tissues. They also assist in convert- ing the albumen into fibrin, and in forming globuline and hematine from the albumen and fibrin of the blood. They are also carriers of oxygen to the tissues, and de- porters of carbonic acid from the tissues to the lungs, where it is eliminated. This is .due to the power the corpuscles have of absorbing gases, and not, as was formerly supposed, to the presence of iron in the hema- tine, which was supposed to be converted into a perox- ide, as it passed from the lungs to the tissues, and then into a protoxide, or carbonate of the protoxide, as it returned to the lungs. The amount of red corpuscles bears a close relation to the amount of respiratory power in the different classes of vertebrata: both of these are also found to be greatest in birds, less in mammals, and very low in most reptiles and fishes. The proportion of the corpuscles is greater among the carnivora than the lierbivora. The want of red cor- puscles in the invertebrata is compensated by the introduction of air through their tracheal apparatus, directly to the tissues themselves. Function of the White Corpuscles.—These are, no doubt, also concerned in the elaboration of nutrient material for the tissues of the body, more especially in the invertebrate classes of animals. These corpuscles, which are oat-sliaped in the larvoe of insects, are found more numerous just before each change of skin, at which time a larger supply of nourishment is required. After these changes have taken place, they are again dimin- ished. The white corpuscles also contain a small quantity of iron, thus showing that the characteristic color of the red corpuscles is not due to this substance. In the vertebrata, on the other hand, the excess of color- less corpuscles is an evidence of unhealthy action; for example, they are very abundant in the blood of frogs that are young, sickly, or ill-fed. In the human subject, they are increased in the disease called leucocythemia, in anemia, and also in inflammation according to some, although, in all probability, this only occurs in sickly, scrofulous, or tuberculous patients. When the circula- HUMAN PHYSIOLOGY. BLOOD. tion of the blood is examined in a hat’s wing, or frog’s foot, under the microscope, the white corpuscles may he observed running outwards and inwards, from the centre of the current to the circumference, and hack again, occasionally adhering to the sides of the vessels. They are therefore looked upon, in the present state of our knowledge, as carriers of nourishment to the tissues. It has already been stated that they are considered by some physiologists as intermediate in development, between the chyle and red corpuscles. Function of Albumen.—This substance is the ori- ginal pabulum, from which all the tisssues of the body are formed. It is also used in the formation of the fibrin, globuline, and hematine of the blood itself. Al- bumen by itself, however, is incapable of organization, and its conversion into the various tissues must depend on their own power of appropriation. It also assists in holding in solution in the bood many of the metallic salts which exist in that fluid, or which enter the system. The albumen is derived from the food, and when any excess is taken into the system, it undergoes a retro- grade change, and is eliminated by the liver and kidney. It is not excreted in health, but may be found in the urine in certain diseased conditions, as morbus Brightii, scarlatina, &c., &c. Its presence in the urine may be detected by heat and nitric acid, which cause a precipi- tate in the form of flakes. It may also be found in the vomita and dejecta, in cholera and yellow fever. Fats.—The fatty matters taken into the system are intended, in part, for the supply of the nerve tissue, and fat cells; but their chief use, however, is to afford mate- rial for that combustive process which is necessary for the maintenance of animal heat. That which is stored up in the body may be looked upon as the surplus. Fat HUMAN PHYSIOLOGY. is often detected in the faeces, and such cases indicate a diseased condition of the liver or pancreas. The other organic compounds which have been found in the blood, as sugar, lactic acid, urea, uric and hippuric acid, creatine, creatinine, fatty acids and odorous sub- stances, but which do not properly form a part of it, are the result of a retrograde metamorphosis, either of the alimentary substances or of the tissues themselves, and are rapidly eliminated by the lungs, kidneys, liver, skin, &c. The uses of inorganic salts are not positively known; but such as have been investigated were referred to in the chapter on the proximate principles of the first class. The alkaline salts, as carbonate and phosphate of soda and potassa, are necessary to give the blood its alkalin- ity, to hold in solution the albumen, and to facilitate the passage of the blood through the capillaries. The salts of potash are necessary also for the proper nutrition of the muscular tissue. Phosphate of lime, carbonate of lime, fluoride of calcium, silica, &c., are required to build up the solid tissues, as bone, teeth, &c. The phosphate of lime, in particular, may be regarded almost as a histo- genetic substance,as it seems to be almost invariably present in newly-forming tissues, but more especially in the bone and teeth. Iron is an essential ingredient of the blood itself, entering into the formation of the hematine. Water exists in large quantities, and is liable to con- siderable variation. RELATION OF THE BLOOD TO THE LIVING ORGANISM. The normal proportions of all the substances found in the blood are maintained partly by the selective power of the tissues in the process of nutrition and growth, and partly by means of the excretory apparatus, which BLOOD. 183 removes the surplus materials. Each part of the body takes from the blood the peculiar substance which it re- quires for its nutrition, aud thereby acts as an excretory organ, by removing that which, if allowed to remain in the blood, would act injuriously in the nutrition of the body generally; for example, the phosphates and carbon- ates which are deposited in the bones are as effectually removed from the blood as those which are thrown off by the urinary organs. Again, the rudimental organs, as the hair in the foetus, the mamma in the male, &c., may be looked upon as excretions serving a useful purpose in the animal economy, by removing certain materials from the blood which might interfere with the proper nutrition of other parts of the body. Although the blood may vary slightly in its composi- tion and properties at different periods of life, yet we find that, taken as a whole, it presents such a constancy in its leading features, that we cannot fail to recognize in it some capacity for self-development, similar to that which the solid tissues possess. It retains its identity through life, just as a leg, an arm, or an eye. It has the power of maintaining itself from the new materials supplied to it from the food, and goes through the suc- cessive phases of growth, maturity, and decay, similar to all vital organisms. The self-maintaining power of the blood is forcibly exhibited in the phenomena of disease, especially those of a febrile class, as the exanthe-rt mata, typhus, typhoid, &c. In all these cases the “ morbid poison” would be eliminated by nature, if time were allow- ed to do so, the blood replenished, and the patient would resume his wonted health. In some instances, when a poisonous substance has entered the blood, the life may be saved by keeping up artificial respiration until nature has time to eliminate the poison from the system. In nearly aE the toxic diseases of the zymotic class, there is a natural tendency to the self-elimination of the poison, and of the products of its action on the blood, either by the agency of the excretory organs, or by the local lesions which occur in these cases; and this occurs with such regularity that we are able to predict witli certainty when the changes may be expected to take place. From the very nature of the action of these poisons on the blood, it is evident that no reliance what- ever can be placed on the action of antidotes in checking its course—the objects of treatment lie wholly in pro- moting the elimination of the morbid poison, in subdu- ing local action, and supporting the vital powers of the patient during the continuance of the disease. HUMAN PHYSIOLOGY. CHAPTER VIII. CIRCULATION. The object of the circulation of the blood is to carry to every part of the body the materials for its nutrition and growth, together with the supply of oxygen neces- sary for its vital actions; and also to carry away the effete substances which are formed as a result of the waste of the tissues. The organs concerned in this process are the heart, arteries, veins, and capillaries. THE HEART. The heart is the great central organ of circulation, situated in the middle mediastinum of the thorax, being placed obliquely, the base upwards and to the right side, on a level with the upper border of the third costal cartilage, and corresponding to the interval between the fifth and eighth dorsal vertebrae ; the apex corresponding to the interspace between the cartilages of the fifth and sixth ribs, one inch to the inner side, and two inches below the left nipple. The heart is a hollow, muscular organ, which, like a forcing pump, drives the blood through the vascular system. It varies in size and shape, in different classes of animals, from a simple, muscular tube, as in insects, to the complex double heart of man. In all animals the organs of circulation are adapted and modified in structure to correspond with the organs of respiration. In the lower order of animals, as insects, the heart consists of a simple muscular tube, provided with certain valves at short distances apart. HUMAN FHYSIOLOGY. Corresponding to the situation of these valves, there are distinct constrictions in the tube, so that it has the appearance of a series or chain of hearts. As we ascend the scale, we first observe the subdivision of the heart into two cavities, the auricles and ventricles, in the acephalous mollusks. In fishes, also, the heart consists only of two cavities, the auricle, into which the blood is received from the veins, and a ventricle, which drives the blood into the main artery which supplies the gills. In reptiles, there are two auricles and one ventricle. One of the auricles receives the blood from the lungs, the 'pulmonic; and the other, the blood from the veins of the body, the systemic auricle. They both open into a single ventricle, which propels the blood throughout the body, and also to the lungs. In birds and mammals (including the human species) the heart consists of two auricles and two ventricles, separated by a complete septum, each auricle communi- cating with its corresponding ventricle, and each ven- tricle communicating with an arterial trunk. The course of the circulation is as follows:—The venous blood is returned from the body by the superior and inferior venae cavae, and poured into the right auricle; thence it passes into the right ventricle, being prevented from returning by the closure of the tricuspid valves; from the right ventricle it passes to the lungs, through the pulmonary artery, the opening being closed behind it by the coaptation of the pulmonary semilunar valves. The blood being aerated in the lungs, is returned to the left auricle through the pulmonary veins; this constitutes the pulmonic circulation. It then passes through the auriculo-ventricular opening into the left ventricle, being prevented from returning by the closure of the mitral valves; it is then propelled with consider- CIRCULATION. able force into the aorta, the opening being closed behind it by the coaptation of the aortic semilunar valves, and is thence distributed to the various parts of the body, to be again returned by the veins to the right side of the heart. The latter constitutes the systemic circulation. (For the anatomy of the heart, see Descriptive Anatomy.) Muscular Structure of the Heart.—The heart consists of striated, muscular fibres, and fibrous rings, which serve for their attachment. The fibres interlace with each other in an intricate manner, and adhere closely together, there being little or none of that areolar tissue which exists in the external muscles. The dispo- sition of the fibres of the heart may be best demonstrated by prolonged boiling, which hardens the fibres and facilitates their separation. The fibrous rings are four in number; the right and left auriculo-ventri'cular, the aortic and pulmonary. The former serve for the attach- ment of the muscular fibres of the auricles and ventricles, and also for the tricuspid and mitral valves ; the latter for the attachment of the arterial vessels, semilunar valves, and muscular fibres of the ventricles. The Fibres of the Auricles.—These are divided into two sets or layers, a superficial, common to both, and a deep layer, proper to each. The superficial fibres run in a transverse direction across the bases of the auri- cles, and are most distinct on the anterior surface. The deep fibres consist of two sets, looped and annular. The looped fibres commence at the ariculo-ventricular rings in front, pass upwards over the auricle, and return to the rings on the posterior part. The annular fibres sur- round the auricles in a circular manner, and are conti- nuous with the circular fibres of the veins which open into them. The Fibres of the Ventricles.—These are also divided into two sets, superficial and deep. The super- ficial fibres are, in some parts, longitudinal; in others, oblique or spiral; the deep fibres are circular, and in some parts oblique. In front the superficial fibres run obliquely, from right to left, and from above downwards, coil inwards at the apex of the heart, around which they are arranged in a whorl-like form, called the vortex; they then pass upwards, interlacing with those of the opposite ventricle in the intermuscular septum, and ascend on the right side as far as its base. If these fibres are carefully uncoiled in a heart previously boiled, the cavity of the left, and then that of the right ventri- cle, will be exposed at the vortex. On the back of the ventricles, the superficial fibres are directed nearly verti- cally. All of the superficial fibres are reflected inwards at the apex, pass upwards, and spread out to form the inner walls of the ventricles, the septum and columnse carnem, and some of them are finally inserted directly into the auriculo-ventricular and arterial rings; while others are inserted indirectly through the chordae tendi- nece. The deep or circular fibres are situated deeply in the structure of the heart, between the superficial and deep, or reflected portion of the superficial fibres; these fibres pass around each ventricle in a circular direction, some at right angles to its axis, and others obliquely. They form a sort of hollow conical cylinder for each ventricle, which is attached by its base to the fibrous zone of the auricles, and is open below towards the apex. Some of the fibres pass across the septum, and surround both ventricles. Vessels and Nerves.—The heart is supplied by the anterior and posterior coronary arteries; the nerves are derived from the superficial and deep cardiac plexuses, 188 HUMAN PHYSIOLOGY. CIRCULATION. 189 which are formed partly by the spinal, and partly by the sympathetic system. Action of the Heart.—The blood is propelled in its course by the alternate contraction and dilatation of the muscular walls of the auricles and ventricles of the heart. The two auricles contract together, and after- wards the two ventricles; and in each case the contrac- tion is immediately followed by a relaxation. The con- traction is called systole, the dilatation, diastole. During contraction the heart appears to become longer and narrower, although, in reality, it becomes shorter and narrower, owing to the simultaneous con- traction of the longitudinal and circular fibres of the ventricles. This may be demonstrated by placing the heart of a recently killed animal, as a frog or rabbit, on the table, and transfixing the base by means of a large needle, and inserting another at the apex, so as merely to touch it. If the organ is then stimulated to contrac- tion by pricking it, the apex will be observed to recede from the needle, while the heart at the same time becomes narrower and shorter. 'Sounds of the Heart.—The action of the heart is accompanied by sounds. These are two in number; the first, or systolic, and the second, or diastolic. They follow each other in quick succession, and are succeeded by a -pause, or period of silence, after which the first sound again recurs. The duration of the first sound is double that of the second, and the second is equal to the pause. Thus, if the whole period be divided into four parts, the first two would be occupied by the first sound, the third by the second sound, and the fourth by the pause, thus: 2 parts occupied by the first sound 1 part occupied by the second sound 1 part occupied by the pause Rythm. 190 HUMAN PHYSIOLOGY. A very short pause must also exist between the first and second sound, otherwise the distinct sounds could not be heard. This order of succession is called the rythm of the heart, which, in a state of health, is re- markable for its regularity. The first sound of the heart is a heavy, prolonged sound, synchronous with the impulse of the heart, and is most distinctly heard over the apex; the second is a short, distinct sound, best heard over the base. These sounds somewhat resemble the sounds of the words “come” “up” whispered in rapid succession, the former representing the first sound, the latter the second. Causes of the Sounds.—The first sound is, in all probability, a compound sound, chiefly produced by the closure of the tricuspid and mitral valves, and the col- lision of the blood against the walls of the ventricles. It is also partly attributed to the contraction of the ven- tricles, and the impulse of the heart against the walls of the chest. The second sound is undoubtedly due to the closure of the aortic and pulmonary semilunar valves. They are forced back by the recoil of the blood, as one unfurls an umbrella—with an audible click as they tighten. This may be demonstrated by fastening one of the valves, by means of a hook or ligature, to the side of the aortic and pul- monary arteries respectively, in some animal, as a calf, so as to allow regurgitation to take place: when it will be ob- served that a bellows murmur takes the place of the second sound; but as soon as the valve is allowed to resume its play, the natural sound returns. It is thought by some that both sounds of the heart are produced by the same cause, viz; the tension of the valves. Disease of the valves gives rise to murmurs which interfere with the distinctness of the sounds. Impulse of the Heart.—Tlie impulse of the heart is produced by the contraction of the spiral muscular fibres of the ventricles, which produces a tilting of the apex against the walls of the chest. In its movement the apex describes a spiral curve from left to right, and from behind forwards. That the impulse of the heart is not due to the tendency of the arch of the aorta to straighten itself when distended with blood, and the elastic recoil of the parts about the base of the heart, is shown by the fact that the tilting movement of the heart will take place even when the apex has been cut off. Dr. Stille maintains that the impulse is due to the dila- tation or diastole of the ventricles. The force of the impulse varies in different individuals, and in the same individual at different times, and is most dis- tinctly felt in the space between the fifth and sixth ribs. It is very distinct in emaciated persons, and especially in hypertrophy of the heart, The impulse of the heart corresponds with the pulse in the arteries, consequently the actions of the heart may be counted by the pulse, at the wrist, or in any of the arteries. Frequency of the Heart’s Action.—In a healthy adult, the pulsations vary from seventy to seventy-five times per minute. The frequency of the heart’s action diminishes from the commencement to the end of life, as will be seen from the following table, which repre- sents The Average Number of Beats in a Minute:— In the fcetus 150 At birth 140 In infancy 120 In youth 90 Adult age 75 Old age 60 to 65 Posture exercises a remarkable influence on the fre- quency of the heart’s action. It is most frequent in the. CIRCULATION. HUMAN PHYSIOLOGY. erect posture, next to that, in the sitting, and least in the recumbent position. The pulse is also most fre- quent in the morning, becomes slower towards evening, and is very much diminished during the night. In health there is a nearly uniform relation between the frequency of the heart’s action and the respirations, the proportion being about four of the former to one of the latter. Force of the Heart’s Action.—A certain rate of movement must be maintained in the circulation, and the impediment produced by friction must be overcome by the muscular force of the heart; and, since the left ventricle propels the blood through the whole system, while the right sends it only to the lungs, the walls of the former are twice as thick as the latter, and the force of the one is double the force of the other. The force of the heart’s action may be estimated either by ascertaining the height of the column of blood which its action will support (Hales’ method), or by causing the blood to act on a column of mercury (the method of Poisseuille and Volkman). Hales introduced a long pipe into the carotid artery of a horse, and found that the blood rose to the height of ten feet. From this and other experiments, on the lower animals, he concluded that the human heart would sustain a column of blood seven and a half feet high, the weight of which would be about 4| lbs. Poisseuille’s experiments were made with a glass tube, bent so as to form a horizontal and two perpendicular portions, the latter being shaped like the letter U. It is called the hcemadynamometer. The horizontal portion is adapted by a tube to the arteries or veins, and the perpendicular branches are partly filled with mercury, the rise and fall of which can be measured on scales placed behind them, and as the rise and fall are equal, the double of either will give the weight of the CIRCULATION. column which the force of the stream is able to main- tain. The results corresponded closely with Hales’ estimate, being about lbs. Yolkman passed a solution of carbonate of soda into the horizontal branch to prevent the blood from coagu- lating on the sides of the vessel. From his experiments it appears that the force of the stream is capable of sup- porting a column of mercury about eight inches in height, or a column of blood about nine feet. But the force which the walls of the heart must exert in order to impart such a pressure to the blood which it propels, is equal to a weight of about 13 lbs. ARTERIES. The arteries are cylindrical tubes which convey the blood to the different parts of the body. They are found in nearly every part of the body, except the hair, nails, epidermis, cartilages and cornea, They were formerly supposed to contain air, because they were found empty after death, hence the name arteries. Structure.—They consist of three coats, internal, middle, and external. The internal is the thinnest, and consists of two layers, the inner or epithelial, and outer, or elastic. The former consists of a single layer of tessel- ated epithelium, with round or oval nuclei; the latter is a delicate, transparent, fenestrated membrane, which in medium-sized arteries is strengthened by several laminae of elastic tissue. The middle coat is thicker than the preceding, and consists of muscular (nonstriated) and elastic tissue, dis- posed chiefly in the transverse direction. In the largest arteries the muscular tissue forms only about one-third or one-fourtli of the thickness of the middle coat, while in the medium-sized arteries it predominates, and in the smaller arteries it is purely muscular. 194 HUMAN PHYSIOLOGY. The external coat is the thickest, and consists of areo- lar and elastic tissue. In arteries of medium-size, this coat is composed of two distinct layers, an inner or elastic, and an outer or areolar. In the large arteries both these coats are very thin, and in very small arteries the elastic coat is entirely absent. The arteries are supplied with blood-vessels like the other organs of the body. They are called the “rasa vasorum.” They are derived from some of the smaller arterial branches, ramify in the loose areolar tissue, con- necting the artery with its sheath, and are distributed to the external and middle coats, probably also to the inter- nal. They are also supplied with nerves, derived chiefly from the sympathetic system, but partly from the cerebro- spinal. Function of Elastic Tissue in Arteries.—It pro- tects them from the suddenly exerted pressure to which they are subjected at each contraction of the ventricle. Under this force, which might burst a brittle tube, their elastic walls dilate, and by thus yielding, break the shock of the force impelling the blood, and exhaust it before they are in danger of bursting, from being over- stretched. Again, by their recoil, which occurs during the diastole of the heart, they exert a pressure which in some degree replaces the action of the heart. This pres- sure is equally diffused in every direction, and tends to drive the blood either onwards, or backwards to the heart; but the latter is prevented by the closure of the aortic valves; hence they equalize the current of blood by maintaining pressure upon the stream during the diastole of the ventricles, and also moderate the jetting movements given to the blood by the systole of the ventricles. In this we cannot but admire the beautiful simplicity and harmony in the laws of nature. There is no loss of the force of the ventricles, for that part of tlieir force which is expended in dilating the arteries is restored in full, according to the law of action of elastic bodies, by which they return to the state of rest with a force equal to that by which they were moved. The elasticity of the arteries also gives them a capa- city for receiving, under certain circumstances, more than the average quantity of blood, and it enables them to adapt themselves to the various movements of the differ- ent parts of the body. In consequence of their elasticity, the arteries are not only dilated, but also elongated. This is most apparent in arteries which are curved. Function of Muscular Tissue in Arteries.—When an artery is cut across, its divided ends contract, and the orifices may be partially or completely closed, owing to the contraction of the muscular tissue. This con- traction is greater in the young than in the aged, and in animals than in man, and continues many hours after death. It is also increased by the application of cold, styptics, galvanism, irritation, or by twisting the cut ends of the artery. Owing to their contraction after death, the vessels cannot be injected until the rigor mortis passes off. The muscular tissue of the arteries can in no way assist in propelling the onward current of the blood. The manner in which the arterial trunks taper towards their distal extremities, renders it mechanically impos- sible that the contraction of circular fibres would drive the blood onward; in fact, the tendency would be in the opposite direction. The principal use of the muscular tissue is to regulate the supply to different parts of the body, according to the activity of the function of each part at different times; for example, the brain does not require so much blood during sleep as during mental CIRCULATION. HUMAN PHYSIOLOGY. labor; the stomach does not require so much blood dur- ing fasting as during digestion, &c., &c. It is evident that the heart cannot regulate the supply to each part at particular periods; but it may be regulated by the contraction of the muscular coat of the arteries, or their passive dilatation, so as to diminish or increase the sup- ply of blood according to the demand. Again, the con- traction of the muscular coat of a wounded artery, first limits and then arrests the escape of the blood, when assisted by the formation of a clot of fibrin in the mouth of the wounded vessel. This is nature’s mode of arrest- ing hemorrhage (natural hemostatics). The contraction of the arteries is determined chiefly by the influence of the great sympathetic system. Function of the Arteries.—From what lias been already stated, we may infer that the, function of the arteries is—first, to convey and distribute the blood to the different parts of the body ; second, to equalize the current, and moderate the jetting movements given to the blood by the ventricles; third, to regulate the supply to the different parts of the organism according to the demand. Anastomoses of Arteries.—The arteries have a remarkable tendency to communicate with each other in their course, in order more fully to supply the organs to which they are distributed. These are called anasto- moses. One of the simplest modes is the union of two arteries to form one, as the union of the vertebral to form the basilar. Another mode is, where two branches unite to form an arch from the convexity of which other branches are given off, which may in their turn form arches, and this may be repeated until the resulting branches are reduced to a very small size, when they terminate in the capillaries, as for example, the mesen- CIRCULATION. teric arteries. A third mode, which is the most remark- able, is, where two adjacent vessels communicate by a distinct vessel passing from one to the other, as in the circle of Willis. Here the anterior cerebral arteries are united by a short cross branch, the anterior communi- cating, and the carotid on each side is united to the posterior cerebral by the posterior communicating. In this way the brain is protected in all its parts against loss of blood, if the circulation in any of the main chan- nels should be arrested. The most common form is found in the limbs, where the main trunk usually divides into two branches, from which smaller branches are given off, which communi- cate with each other at various points, especially around the joints. These branches also communicate with others from adjacent arteries, as for example, the deep femoral with the sciatic, &c. By such an arrangement, the proper nutrition of the limb is secured by collateral circulation in the event of the main trunk being liga- tured, or otherwise occluded. In the application of a ligature, the surgeon should always make allowance for the anastomoses in the vicinity of the wound. In con- sequence of the free anastomoses between the adjacent branches, it is always necessary, when the artery is wounded, to apply a ligature both above and below the wound, in order to prevent the recurrence of secondary hemorrhage. Pulse.—When the finger is applied the wrist, or any of the arteries of the body, it is felt to beat or pul- sate in correspondence with the systole of the heart. The sensation communicated to the finger is due to the dilatation and elongation of the part, caused by the jetting movements of the current of blood in the vessel. Each jet of blood creates a wave, which moves along the whole arterial system. A certain time will be required for the wave to travel from the heart to distant arteries, so that although the wave corresponds with the systole of the heart, yet it is not in exact synchronism with it; the difference varying according to the distance from the heart. The longest interval is about one-sixtli to one- seventli of a second. The character of the pulse will depend—1 st, upon the force of the heart; 2nd, upon the integrity of its valves and orifices: 3rd, upon the quantity and quality of the blood in the system; and 4th, upon the condition of the walls of the arteries, whether rigid or yielding, tense or flabby, &c. The qualities of softness or fulness, of hardness or wiryness, of compressibility or incompressibility, &c., which are familiar to the practical physician, are deter- mined by the yielding or the resisting condition of the arterial walls. Kapidity of the Circulation in Arteries.—The velocity of the circulation in the arteries may be ascer- tained by an instrument similar to that used for measuring the force of the heart. Volkman estimates the velocity with which the blood moves in the carotid arteries of warm-blooded animals, at about twelve inches per second. HUMAN PHYSIOLOGY. VEINS. Tlie veins return the blood from the various tissues and organs to the right side of the heart. They are more numerodS* and, with the exception of the pulmonic veins, more capacious than the arteries. They com- mence in the capillaries, and uniting form trunks, some of which are superficial, and others deep, accompanying their corresponding arteries. Structure.—In structure they consist of three coats. These resemble the of the arteries, with ttie excep- CIRCULATION. tion of the outer, which contains some muscular tissue. Muscular tissue is, however, entirely absent in the sin- uses of the dura mater, uterus, and corpora cavernosa, cerebral veins, retinal veins, and the veins of the can- cellous tissue of bones. Most veins have valves which prevent the reflux of blood. They are more numerous in the superficial than in the deep veins, and in those of the lower than the upper extremity. The valves are formed by reduplications of the lining membrane, are semilunar in form, and are attached by their convex margins to the walls of the veins. They are generally arranged in pairs, occasionally there are three, but some- times only one. In very small veins they are absent; also in the venae cavae, pulmonary veins, hepatic veins, portal vein, renal, uterine and ovarian, the cerebral and spinal veins, veins of the cancelli of bones, and in the umbilical vein. The veins are supplied, like the arteries, by little vessels (vasa vasorum); but the nerves are not so easily detected upon them. CmcuLATiON in the Yeins.—In the veins, the blood moves in a continuous stream, and the velocity of the venous current is considerably less than the arterial. The circulation in the veins is produced by the vis d tergo of the heart, the action of the capillaries, the contraction of the voluntary muscles, the inspiratory move- ments of the thorax, and the vis d frontc or suction power of the heart (Mulder); the latter, however, is extremely small. The vis d tergo of the heart may produce, in certain conditions of the system, a distinct venous pulse, corres- ponding with the impulse of the heart, the wave having passed through the capillaries. This may be called the communicated or systolic venous pulse, and must be care- fully distinguished from the regurgitant venous pulse, HUMAN PHYSIOLOGY. 200 wliich is caused by the regurgitation which takes place, in some persons, into the venous trunks, during the sys- tole of the right auricle. In health, the regurgitation is very small and indistinct; hut when the right cavities of the heart are dilated, a large quantity of blood is re- gurgitated, and a distinct venous pulse is visible in the superficial and deep veins of the neck. The inspiratory movements of the thorcyc, by enlarging the capacity of the chest, tend to create a vacuum, which is chiefly filled by the rush of air into the chest; but' partly by the afflux of blood, which must be principally venous, since the closure of the aortic valves would op- pose any reflux in the aorta. This may be demonstrated by introducing a bent glass tube into the jugular vein of an animal, the vein being tied above the point where the tube is inserted, and the other end of the tube im- mersed in some colored fluid. It will be observed that at each inspiration the colored fluid will ascend in the tube, while during expiration it will either remain stationary or sink. Or it may be shown by the hccma- dynamometcr. The effect of inspiration on the veins is only observable in the larger ones. Forced expiratory movements, on the other hand, retard venous circu- lation, as may be seen by holding the breath for a few seconds, or by straining, when the veins about the face and neck swell up, and become distended, but immedi- ately return to their former size when the breathing is restored. The contraction of the voluntary muscles has a most marked effect in favouring the circulation of the blcod in the veins, as may be seen in cases of venesection, when the patient is directed to move his fingers freely. During muscular action a portion of the veins is com- pressed, and the blood is prevented, by the valves in the veins, from passing backwards in the small vessels; it is necessarily forced onwards towards the heart. As the muscles are relaxed the veins again swell out, to be re-com- pressed by .the renewal of the muscular force, and so on. This force is an important agent in maintaining the cir- culation, since the voluntary muscles are more or less active in nearly every position of the body, and the veins liable to be compressed by them. The vis a fronte or suction 'power of the heart, (Mulder), if there is such a thing, can exert very little influence in the general circulation. It is regarded by some as extremely small, by others as impossible. Rapidity of the Circulation in Veins.—The ve- locity of the venous current is to that of the arterial as two to three, or about eight inches per second, as near as can be ascertained by approximation. CIRCULATION. 201 CAPILLARIES. They are so named on account of their small size. They are the connecting link between the arteries and veins, and are found in all parts of the body except the uterine placenta, corpora cavernosa of the penis, nails, epidermis, hair, &c., &c. In structure they appear, under the microscope, to consist of a homogeneous mem- brane with cell nuclei which adhere to or are imbedded in their walls, at certain distances apart. It is quite likely, however, that the capillaries consist of all the coats which belong to the arteries, but are very much attenuated. The capillaries vary in diameter, from Tsiio to 4 the average being about gy’yy of an inch, and their length is about of an inch. The smallest are those of the brain and mucous membrane of the intestines; the largest are those of the skin and marrow of bones. They form meshes, which vary in different 202 tissues; for example, they are rounded in the lungs, elongated in muscles and nerves, and looped in the pa- pilhe of the tongue and skin. The closest network is formed in the lungs and choroid coat of the eye. As a rule, the more active the function of an organ, the closer is its capillary net-work, and the larger its supply of blood. In the compound tissues the capillaries do not ramify among the ultimate particles of the tissues; thus in muscle the vessels lie between the fibres, but do not pierce the sarcolemma. In nerves, in the same way, they are separated from the nervous matter by the tubu- lar membrane. In mucous and serous membranes they are imbedded in the sub-areolar tissue, which forms a nidus for them. Circulation in the Capillaries.—The current of blood flows through the capillaries with a constant equable motion, as may be seen under the microscope in the frog’s foot or bat’s wing. In the central part of the current in the larger vessels, may be seen the red cor- puscles; while near the edges of the vessel there is a transparent stratum of clear plasma, in which may be seen some white corpuscles. In the smaller vessels the corpuscles pass along in a single file, and sometimes be- come bent and otherwise distorted in order to accommo- date themselves to the curvatures of the capillaries. Whenever the current is obstructed or retarded in any way, the white corpuscles accumulate in the affected part, and become more numerous in proportion to the red. The circulation of the blood in the capillaries is partly due to the vis d tergo of the heart, and recoil of the arteries, and partly also to the attractive or selective power of the tissues. The former has been already referred to in connection with the heart and. arteries. With HUMAN PHYSIOLOGY. CIRCULATION. 203 regard to the latter, it is in the capillaries that those chemical and physical changes between the blood and the tissues take place, in which the phenomena of nutri- tion essentially consist. A certain force is generated by this interchange, which promotes the circulation of the blood through the capillaries. It is termed the attrac- tive or selective power of the tissues (or by Carpenter capillary force.) It may be explained as follows:—As the blood charged with oxygen and nutritious substances for the supply of the tissues approaches the capillaries, a rapid imbibition takes place with such energy, that it pushes before it, into the veins, the blood from which the nutritious elements had been previously removed, and which also contains the effete matter. This force resembles that by which the circulation is maintained in plants, and in some of the lower order of animals. The capillaries are under the influence of the nerves. Their contraction on the application of certain irritating substances, and from fear, and their dilatation during blushing, may be referred to the influence of the nerves, for in these cases the changes are so rapid that the heart has not time to effect them. Under one kind of nervous emotion the vessels contract, and empty themselves, and the countenance becomes deadly pale, as in anger, fear, &c. Under another kind of nervous emotion the vessels dilate, become filled with blood, and the cheek is suf- fused, as in blushing. Rapidity of the Circulation in the Capillaries.— The rate of movement of the blood in the capillaries may be determined by the microscope. It is slower than in either the arteries or veins, being, on an average, about If inches per minute. The combined forces by which the blood is propelled throughout the body, are, first and chiefly, the muscular 204 HUMAN PHYSIOLOGY. force of the heart; second, the recoil of the elastic walls of the arteries; third, the attractive or selective power of the tissues; fourth, the pressure of the muscles among which some of the veins lie; fifth, the inspiratory move- ments of the chest. Rapidity of the Circulation in the Body.—It is estimated that the ventricles and auricles are each capa- ble of holding about three ounces of blood, and that this quantity is propelled by either ventricle at each systole, and that the whole amount of blood in the system is about eighteen pounds. This would require ninety-six pulsations for its passage through either side of the heart, and allowing seventy-two pulsations to a minute,, the time occupied in transmitting the whole would be 11 minutes. But it has been ascertained by experiments on animals, as the horse, that substances in solution, such as prussiate of potash, nitrate of baryta, &c., may be detected in the blood drawn from the carotid artery within fifteen to twenty seconds after it had been intro- duced into the jugular vein of the opposite side. In the dog, the heart’s action may be arrested in eleven or twelve seconds, by the introduction of a solution of nitrate of potash in the jugular vein; in the rabbit in about four seconds, and in fowls, in about six. Hence, it appears that the rapidity of the circulation is under- rated in the estimate founded upon the capacity of the heart, and the number of pulsations in a minute. It has been estimated by Volkman, that in man the -whole cir- cuit is completed in considerably less than one minute. Peculiarities of the Circulation.—These are observed in the lungs, liver, brain and erectile organs. The chief peculiarity in the pulmonic circulation is, that the artery carries venous blood to the lungs, and the veins return arterial. The portal circulation is peculiar CIRCULATION. 205 in being a kind of offset from the general circulation. The peculiarity of the circulation in the brain is, that it is provided with a uniform supply of blood. This is secured by the number and tortuosity of the vessels, and their large anastomoses in the formation of the circula- tion of Willis. It is also stated by Dr. Kellie, that in bleeding animals to death, the brain does not become exsanguine, owing to atmospheric pressure, unless an opening is made in the cranium. But this is disputed by Dr. Burrows, who concludes, from careful experiments, that the brain may become exsanguine without any apparent aperture in the cranium, and that, in health, slight variations may occur in the quantity of blood sent to the brain. The erectile tissues are the penis, the clitoris, the erectile tissues of the vagina, and the nipple in both sexes. The venous plexuses of the erectile tissue become filled with blood, which swells and distends the organ, causing it to assume an erect condition. This influx of blood may be caused by local irritation, or by certain emotions of the mind communicated through the great sympathetic system. Erectile tissue consists of a plexus of veins with varicose enlargements enclosed in a fibrous envelope, with trabecular partitions. There are also some nonstriated muscular fibres, which are connected in some way with the process of erection. They may either by their con- traction prevent the due return of blood from the parts, or by their relaxation allow the plexuses to fill with blood, and remain so until the stimulus to erection subsides, when they contract and gradually expel the excess of blood. Fcetal Circulation.—In the foetus the course of the circulation is modified in consequence of the inaction of the lungs. The aeration of the blood is effected by the placenta, through which also the foetus is nourished, so that the placenta serves the double purpose of a respiratory and nutritive organ, or in other words, it per- forms the office of the lungs and stomach in the foetus. The course of the circulation in the fcetus is as follows:— The arterial blood is carried from the placenta to the fcetus, along the umbilical cord, by the umbilical vein. It then enters the umbilicus, and passes upwards along the free margin of the longitudinal ligament of the liver to its under surface, where it gives off two or three branches to the left lobe, and others to the lobus quadratus and spigelii. At the transverse fissure it divides into two branches; the larger is joined by the portal vein and enters the right lobe; the smaller passes onwards, under the name of the ductus venosus, which joins the left hepatic vein, where the latter empties .into the inferior vena cava. Hence the blood reaches the vena cava in three different ways; most of it passes through the liver with the portal venous blood, and is returned to the vena cava by the hepatic veins; some passes through the liver directly, to be returned also by the hepatic veins; and the smallest quantity is carried on by the ductus venosus to the vena cava. In the inferior vena cava the blood is joined by that which is being returned from the . lower extremities and viscera of the abdomen, it then enters the right auricle, and guided by the eustachian valve, passes through the foramen ovale into the left auricle, where it is mixed with a small quantity return- ing from the lungs. From the left auricle it passes into the left ventricle, from the left ventricle into the aorta, to be distributed cliiefiy to the head and upper extremi- ties—a small quantity passing into the descending aorta. From the head and upper extremities the blood is re- turned by the superior vena cava to the right auricle, 206 HUMAN PHYSIOLOGY. CIRCULATION. 207 where it is mixed with some from the inferior vena cava. It then passes into the right ventricle, and from the right ventricle into the pulmonary artery, hut the lungs of the foetus being almost impervious, only a small quantity is distributed to them by the pulmonary arteries, and is returned to the left auricle by the pulmonary veins; the greater part of the blood from the right ventricle passes through the ductus arteriosus into the descending aorta, where it is mixed with a small quantity of blood trans- mitted by the left ventricle into the aorta. It then descends along this vessel to supply the viscera of the abdomen, pelvis, and lower extremities—the greater portion, however, being conveyed by the umbilical arte- ries to the placenta. When the child is born, and respiration established, an increased amount of blood is sent to the lungs, and the placental circulation is cut off. The foramen ovale gradually closes up, being completed about the tenth day. The ductus arteriosus contracts as soon as respiration is established, and is completely closed from the fourth to the tenth day. The umbilical arteries, between the umbilicus and the fundus of the bladder, become obliterated between the second and fifth days. The umbilical vein and ductus venosus also become obliterated between the second and fifth days. In some instances the foramen ovale does not close readily, and the blood continues to pass through into the left auricle after birth, giving rise to a bluish color of the surface of the body. This condition is called cyanosis or morbus cceruleus, and may be remedied by keeping the child on its right side for a few days. CHAPTER TX. RESPIRATION. As the blood circulates through the different parts of the body, it is deprived of its nutritive elements and oxygen, and becomes loaded with impurities, resulting from the wear and tear of the tissues; hence it becomes necessary, not only that fresh supplies of nutriment and oxygen should be continually added to the blood, but also that provision should be made for the removal of the impurities. One of the most important and abun- dant of the impurities is carbonic acid, the removal of which, and the introduction of fresh quantities of oxygen, constitute the chief purpose of respiration. THE LUNGS. The organs of respiration are the lungs. They are two in number, situated one in each of the lateral cavi- ties of the chest, separated from each other by the mediastinal space. They are provided with a single air tube, the trachea, which is divided into two branches, the right and left bronchus, one for each lung. (See Descriptive Anatomy). Minute Structure.—The lungs are surrounded by a serous membrane, the pleura-pulmonalis, which is con- nected to the lung tissue by the subserous areolar tissue. The parenchyma, or lung tissue, is composed of lobules, which are held together by areolar or connective tissue. They vary in size and shape; those on the surface are large, of a pyramidal form, the base turned towards the surface; those in the interior are smaller, and of various RESPIRATION. 209 forms. Each lobule is a miniature representation of the whole organ of which it forms a part—being composed of one of the smaller bronchial tubes and its corresponding air cells, vessels, nerves, and lymphatics, all of these being held together by areolar tissue. The bronchus, on enter- ing the hilus of the lung, divides and subdivides dichoto- mously throughout the entire organ until the branches terminate in the lobular bronchial tubes. Each lobular bronchial tube, on entering the substance of the lobule, divides into from four to nine branches, according to the size of the lobule, diminishing in size until they reach a diameter of 51ff to of an inch. They are then contin- ued onwards, their sides and extremities being closely covered by numerous saccular dilatations—the air cells —in consequence of which the tubes lose their identity, as cylindrical tubes, and present the character of irregu- lar canals or passages (these are the so-called intercellu- lar passages). The air cells are small, alveolar recesses, which vary from to 3(j0 of an inch in diameter, and are separated from each other by their septa. They communicate with the terminal bronchial tubes, which they surround, by large circular openings; but do not communicate with each other except through the tubes. In the terminal bronchial tubes and air cells, the cartilaginous and mus- cular tissues are absent, and the mucous membrane is lined by squamous epithelium, while the trachea and broncliii are lined by columnar or ciliated epithelium. Vessels and Nerves.—'The pulmonary artery conveys the venous blood to the lungs for aeration. It divides into branches, which accompany the bronchial tubes, and terminates in a dense capillary plexus beneath the mucous membrane of the terminal bronchial tubes and air cells. The blood, purified during its passage through HUMAN PHYSIOLOGY. the capillaries, is returned by the pulmonary veins to the left auricle of the heart. The bronchial arteries sup- ply the blood for the nutrition of the lung. They arise from the thoracic aorta., and divide into several branches, some of which accompany the bronchial tubes to which they are distributed, and terminate in the deep bronchial veins; others are distributed to the areolar tissue, and terminate partly in the superficial, and partly in the deep bronchial veins; whilst a few ramify upon the walls of the terminal bronchial tubes and air cells, and termi- nate in the pulmonary veins, the blood having been purified in its passage through the capillaries. The bronchial veins, superficial and deep, unite at the root of the lung, and empty on the right side into the vena azygos major, and on the left in the superior inter- costal. • Nerves.—The lungs are supplied by the anterior and posterior pulmonary plexuses of nerves formed chiefly by branches from the pneumogastric and sympathetic nerves. Lung tissue has an acid reaction; this is due to the presence "of pulmonic acid. This substance is crystalli- zable, soluble, and is formed in the lung tissue, similar to the formation of sugar in the liver. This acid is sup- posed by some to decompose the alkaline carbonates of the blood in the lung, and in this way favor the deve- lopment and elimination of carbonic acid in the lungs. In corroboration of this it lias been shown by Bernard that a solution of bicarbonate of soda, injected into the jugular vein of a rabbit, is followed by so rapid a deve- lopment of carbonic acid in the lungs, lung tissues, and cavities of the heart, as to cause instant death by the arrest of the circulation. RESPIRATION. 211 ACTION OF THE LUNGS. The movements by which fresh air is taken into the lungs, and by which it is again expelled, are those of inspiration and expiration. This is called the mechani- cal act, in contradistinction to the chemical, which relates to the changes which take place between the blood and the atmospheric air. Inspiration.—During inspiration the chest is en- larged in every direction, but chiefly in the vertical. This is effected principally by the contraction of the diaphragm, and its consequent descent towards the abdomen. The ordinary muscles of inspiration are the diaphragm, external intercostals, levatores costarum, serratus magnus, and serratus posticus superior. But in extraordinary or forced inspiration, as during a par- oxysm of asthma, &c., the shoulders are fixed by the patient seizing something firmly, and the serratus mag- nus, pectoralis major and minor, trapezius, subclavian and scaleni muscles are called into action. The scaleni muscles fix the upper ribs, from which the external in- tercostals act, as from a fixed point, and elevate the lower ribs, by which the cavity of the chest is en- larged laterally. This action is also promoted by the action of the other muscles previously mentioned. The act of inspiration is slow, and occupies about two-thirds of the time consumed in the complete act of respi- ration. Expiration.—Expiration succeeds inspiration, after a brief interval, and is accomplished, in ordinary respi- ration, by the elastic recoil of the lungs and walls of the chest, after they have been dilated; and partly by mus- cular action. The ordinary muscles of expiration are the abdominal muscles, internal intercostals, except in front, serratus posticus inferior, and triangularis sterni. The extraordinary are the quadratus lumborum, latissi- mus dorsi, sacrolumbalis, and those which assist in fixing the spine and pelvis. In difficult breathing, almost every muscle in the body is made subservient to the action of respiration. It is stated that the power of expiration exceeds that of inspiration by one-third. Frequency of Respiration and Ratio to the Pulse.—The number of respirations in a healthy adult varies from sixteen to twenty in a minute. The pro- portion of respiratory movements to the pulsations of the heart is about one to four, and when this proportion is departed from, there is reason to suspect some obstruc- tion to the aeration of the blood, or some derangement of the nervous system. Any disproportion between the number of respiratory movements and the number of pulsations, or the amount of blood sent to the lungs to be aerified, is attended with dyspnoea. When the action of respiration is confined to the diaphragm and abdom- inal muscles, the breathing is said to be abdominal; but when the muscles of the thorax are called into action, it is then said to be thoracic. Quantity of Air Respired.—The quantity of air taken in at each inspiration varies from twenty to thirty cubic inches; this is called breathing or tidal air. The quantity which an adult of average size (five feet eight inches) can inhale in a forced inspiration is about 280 cubic inches; the excess being called complemental air (250 to 260 cu. in). After ordinary expiration, such as that which expels the breathing or tidal air, a certain quantity remains in the lungs, which may be expelled by a forcible expiration. This is called reserve or supple- mental air. But a quantity still remains, which cannot be forced out; this is called residual air. The respiratory capacity of the chest is called the 212 HUMAN PHYSIOLOGY. RESPIRATION. 213 vital capacity, and it varies according to stature, weight, and age. The vital capacity of an adult, five feet eight inches in height, is about 280 cubic niches; and for every inch in height above this standard, the capacity is increased about eight cubic inches. The influence of weight is not so marked as that of height; but it tends to diminish the respiratory power, when beyond a cer- tain limit. The vital capacity increases from fifteen to thirty-five years of age, and from thirty-five to sixty-five it decreases nearly one and a half cubic inches per year. The total quantity of air which passes through the lungs in twenty-four hours varies from 300 to 400 cubic feet, depending on the state of the health, bodily exer- tion, &c. Experience has shown that the minimum quantity of air which ought to be allowed for each per- son confined in prisons, hospitals, schools, &c., is about 800 cubic feet. Influence of Nervous Power in Respiration.— The movements of respiration are presided over by the medulla oblongata, into which may be traced the princi- pal excitor nerves, and from which proceed the princi- pal motor nerves. The chief excitor of the movements of respiration is the pneumogastric nerve. When this is divided on both sides the number of respirations is diminished about one-half, and irritation of its trunk is followed by an act of inspiration. The respiratory movements are supposed to be caused by the presence of blood, loaded with carbonic acid, in the capillaries of the lungs, which makes an impression on the periphery of the pneumogastric nerve. The other excitors are the nerves distributed to the general surface of the body, but especially to the face. A current of cold air, or cold water dashed on the face, is sufficient to cause a deep inspiration; and a similar impression on the chest HUMAN PHYSIOLOGY. or body, or a slap on tlie buttocks, will excite inspiratory movements when they would not otherwise commence, as in the new-born infant or in asphyxia. The first plunge into water, as in swimming, is usually accom- panied by a deep inspiration. It is quite probable also that the sympathetic nerves, which receive filaments from the spinal nerves and communicate with the pneu- mogastric, may be excitors of this function. The motor nerves concerned in the function of res- piration are the phrenic, intercostals, facial and spinal accessory. The motor power of the respiratory nerves is exercised, however, not only in the muscles of respi- ration, but also on those which guard the entrance to the windpipe. The respiratory movements, though partly voluntary, are in ordinary respiration essentially independent of the will; for example, during sleep or coma the respira- tory function is carried on, although the person is entirely unconscious of the movements. At the same time, it is necessary that the respiratory actions should be partly under the direction of the will, since they are subser- vient to the production of those sounds by which indi- viduals communicate their ideas to each other. Modifications of the Respiratory Movements.— These are coughing, sneezing, sighing, yawning, laughing, crying, sobbing and hiccup. Coughing is caused by any source of irritation in the throat, larynx, trachea or bronchial tubes. This act consists, first, in a full inspi- ration, the glottis is then closed and a violent expiration takes place, by which a sudden blast of air is forced up the air passages, forcing open the glottis and carrying before it any substance that may be present. The dif- ference between coughing and sneezing is, that in the latter the blast of air is directed more or less completely RESPIRATION. 215 through the nose, in order to remove any irritating sub- stance present there. Sighing is simply a deep inspira- tion, in which a larger quantity of air than usual is made to enter the lungs. Yawning is a still deeper inspiration, and is accompanied by a contraction of the muscles about the jaws. In laughing, the muscles of expiration are in convulsive movement, and send out the air from the lungs in a series of jerks, the glottis being open. Crying is very nearly the same as laughing, although occasioned by a different emotion. When the emotions are mixed, an expression is produced “between a cry and a laugh.” Sobbing is caused by a series of short convulsive contractions of* the diaphragm, the glottis being closed. Hiccup is caused by a sudden convulsive contraction of the diaphragm, the glottis suddenly clos- ing in the midst of it; the sound is produced by the impulse of the column of air against the glottis. Changes in the Respiked Air.—The air consists of a mixture of 20.81 parts oxygen to 79.19 of nitrogen, in 100 parts by volume; carbonic acid from .3 to .6 parts in a thousand; a variable amount of aqueous vapour, and a trace of ammonia. The changes produced on the atmospheric air by are—1st, an increase in the temperature equal to that of the blood; 2nd, an increase in the quantity of carbonic acid and aqueous vapour; 3rd, a diminution in the quantity of oxygen. The nitrogen remains nearly the same, and a small quantity of animal matter is eliminated by the lungs. The air is heated by contact with the interior of the lungs to a temperature of about 98° F. Exhalation of Carbonic Acid and Water by the Lungs.—The presence of an increased amount of carbo- nic acid in expired air, may be demonstrated by breath- ing through lime water, which becomes milky by the 216 HUMAN PHYSIOLOGY. formation of insoluble carbonate of lime. It has been ascertained that there are about 4.35 parts of carbonic acid in 100 parts expired air, and subtracting the quan- tity in the air when inspired, leaves about 4.30 parts per cent, by volume, which is eliminated from the lungs at each ordinary expiration. This would amount to about sixteen cubic feet per day of carbonic acid, or about ounces of carbon. The elimination of carbonic acid may be modified by a number of circumstances. Digestion has been observed to be attended with an increased exhalation of carbonic acid, most distinct about an hour after eating; while fasting, on the other hand, diminishes it. Alcohol, ether and chloroform intro- duced into the system, are followed by a diminution in the quantity of carbonic acid exhaled. Exercise increases the exhalation of carbonic acid to about one-third more than it is during rest. During sleep, on the other hand, there is a considerable diminution in the quantity of this gas evolved, owing probably to the tranquility of the breathing; but directly after waking, the amount is increased. Age and sex influence the quantity of carbo- nic acid exhaled; in males it increases from eight to thirty years of age; remains stationary from thirty to forty, and then diminishes to extreme age. In females, the quantity exhaled is always less than in males of the same age; it is increased from the eighth year to the age of puberty, and remains stationary as long as they con- tinue to menstruate, but when menstruation ceases, from whatever cause, the exhalation of carbonic acid again augments, after which it diminishes to extreme age. The temperature of the external air has an important influence on the exhalation of carbonic acid. Observa- tion made at various temperatures between 38° F. and 75° F. show that between these points every rise equal to 10° F. causes a diminution of about two cubic inches in the quantity of this gas exhaled per minute. Cold, on the other hand, within certain limits, increases it. The respiratory movements also influence the exhalation of this gas. When the respirations are increased in frequency more carbonic acid is exhaled, although the per centage in proportion to the amount breathed is less. If the air has been previously breathed, the quantity of carbonic acid exhaled is very much diminished. It should also be borne in mind, tha£ the continued respira- tion of an atmosphere charged with the exhalations from the lungs and skin is a most potent predisposing cause of disease, especially of the zymotic class. The amount of aqueous vapour exhaled from the lungs in twenty-four hours may be estimated, in temperate climates, at from twelve to twenty ounces. A certain amount of carbonic acid and water is also eliminated by the integument. Amount of Oxygen Inhaled.—The quantity of oxygen in respired air is always less than in the same air before respiration. Some of the oxygen unites with the carbon in the lungs to form carbonic acid; some is used in the chemico-vital changes which take place in the blood and tissues, and some is also used in oxidizing other substances besides the carbon, as for example, sul- phur and phosphorus, which are eliminated in the urine in the form of sulphuric and phosphoric acid. The quantity of oxygen consumed varies in different persons, and in the same person at different times. It is increased by food, especially of the farinaceous kind, and is diminished during fasting. The interchange of gases in the lungs does not accord with the law of “ diffusion of gases,” otherwise the proportion between the oxygen consumed and the carbonic acid exhaled should never RESPIRATION. 217 HUMAN PHYSIOLOGY. vary. Besides, the law requires that both gases should be free, and under equal pressure; while, in reality, the gas in the blood is dissolved, is under pressure, and is also separated by a membrane from that into which it is to be diffused. The nitrogen of the atmosphere nerves only to dilute the oxygen, and moderate its action in the system. Under ordinary circumstances there is very little differ- ence between the quantity of nitrogen inspired and exhaled. The absorption of nitrogen is increased by fasting; while, under opposite circumstances, it is diminished. There is also a small quantity of nitrogen given off in the form of ammonia. Changes Produced in the Blood by Respiration. —1st, its color is changed; 2nd, it absorbs oxygen; 3rd, it exhales carbonic acid and aqueous vapour, small traces of ammonia and animal matter. The most obvi- ous change is that of color, the dark venous blood being exchanged for the bright scarlet of arterial blood. The supposed causes of this change have been already dis- cussed in the chapter on blood. It is chiefly due to the exhalation. of carbonic acid which exists in the blood, and the absorption of oxygen which is taken up princi- pally by the corpuscles, and partly by the plasma, and carried to the tissues. The presence of oxygen in the corpuscles causes them to assume a biconcave disc, which reflects the light in such a way as to change their color. With reference to the oxygen, it was formerly sup- posed that it combined with the carbon of the venous blood in the capillaries of the lungs, and was exhaled in the form of carbonic acid; but it has since been estab- lished beyond doubt that only a small amount is formed in the lungs—the principal part being already formed in the venous blood before it enters the lungs, and the oxygen which is absorbed during respiration is mostly carried off in a free state with the arterial blood. Both the oxygen and carbonic acid exist in the corpuscles and plasma of the blood, partly in a state of solution, and partly in a state of chemical combination. The chief agents concerned in the absorption of the gases in the blood are the corpuscles. The exhalation of carbonic acicl is favored by the moist condition of the membranes of the lung, which liquefies the gas. This fact may be demonstrated by filling a bladder with carbonic acid, and then placing it in water; it will soon be found to collapse and become completely emptied. Carbonic acid is being constantly generated in the blood, and is removed by exhalation from the lungs as fast as it is produced; but if respira- tion is obstructed or seriously impeded, it accumulates in the blood, and may cause death by its poisonous effects on the nervous system. Carbonic acid is formed in three different ways in the system: 1st, in the blood, by the action of oxygen on certain elements introduced in the food, as starch, sugar, and fats, giving rise to a certain amount of animal heat; 2nd, in the capillaries, by the union of oxygen with the carbon produced in the disintegration of the tissues; 3rd, in the lungs, by the decomposition of the alkaline carbonates by the acid of the lung (pulmonic). Respiration is partly a physical and partly a chemi- cal process; c.g., the introduction of oxygen and the exhalation of carbonic acid is a physical process; while the formation of the carbonic acid itself is essentially a chemical one. The great object of respiration is to introduce oxygen into the blood, and remove the deleterious matters, as carbonic acid, animal matter, ammonia, &c., by the sur- face of the lungs. RESPIRATION. 219 220 HUMAN PHYSIOLOGY. Effects of the Arrest of Respiration.—When respiration is interfered with by any obstruction, or from whatever cause, the circulation of blood through the lungs is retarded, and at length arrested. This prevents the exit of blood from the right ventricle, and is followed by venous congestion of the nervous centres, and all the other parts of the body. Besides, only a very small quantity of blood finds its way into the left side of the heart, and this is venous also. Hence, in death from asphyxia, the left side of the heart is nearly empty, while the lungs, right side of the heart, and veins are gorged with venous blood. The cause of the reten- tion of blood in the lungs is due to the non-elimina- tion of the carbonic acid; for blood loaded with this gas does not pass freely through the capillaries. The fatal result is due, to some extent, to the weakened action of the right side of the heart, in consequence of its over-distension; and also to the venous congestion in the medulla oblongata and nervous centres. The time which is necessary for life to be destroyed by asphyxia varies from one and one-half to four minutes. In drown- ing, very few persons recover who have been submerged more than four minutes. Cases have been recorded in which recovery took place after the lapse of from fifteen minutes to half an hour, and even longer; but in these instances it is probable that a state of syncope had come on at the moment of immersion. CHAPTER X. ANIMAL HEAT, LIGHT, AND ELECTRICITY. Heat.—This is closely connected with the process of respiration. The average temperature of the human body varies from 98° to 100°E.; birds, from 106° to 111°F.; fishes and reptiles, about 51 °F. In mammals and birds the temperature of the blood and internal organs is always very much above the external air, and they are therefore called “warm-blooded animals.” In fishes and reptiles, on the other hand, the temperature of their bodies differs but little from that of the medium which they inhabit, hence they are called “cold-blooded animals.” In both classes, however, there is an internal source of heat, but it is more active in the one than the other. Even in vegetables a certain amount of heat- producing power is occasionally manifest, as for example, in the flowering of plants, malting of barley, &c. In disease, the temperature of the body may deviate some- what from the natural standard, as e.g., in scarlatina and typhus it rises as high as 106° or 107°F. In cholera, on the other hand, it often falls as low as 78° or 79 °F. In some cases of yellow fever, a remarkable rise takes place very soon after death, in one instance as high as 113°F., fifteen minutes after death. The temperature of the body in health, is about 1|°F. lower during sleep than while awake. It is raised by exercise, and also after eating. Theory of the Production of Animal Heat.— There have been many theories regarding this subject. 222 HUMAN PHYSIOLOGY Lavoisier supposed tliat the oxygen taken into the lungs combined with the carbon of the blood and formed car- bonic acid, which was at once eliminated, the same amount of heat being produced as if the oxidation of a similar quantity of carbon in wood or coal had taken place, and that the heat thus developed radiated to the different parts of the body. This view was, however, soon ascertained to be incorrect, inasmuch as the heat of the lungs was found to be no greater than the rest of the body. It was also shown that the carbonic acid is formed principally in the blood and tissues, and that tftie oxygen is taken up by the blood corpuscles and carried away in the general circulation. According to Liebig, the heat of the animal body is produced by the oxidation or combustion of certain elements of the food, while circulating in the blood, as starch, sug'ar, and fats. He therefore divided the food into two classes,— 1st, The plastic elements of nutrition, which are used in the building up of the tissues, as albumen, fibrin, casein, muscular tissue, &c. 2nd, The elements of respi- ration, as starch, sugar, and fats, which are chiefly used in the production of animal heat, being oxidized in the circulation, and eliminated in the form of carbonic acid and water by the lungs. This theory, slightly modified, is the one which is most generally received. The production of animal heat, then, is a phenome- non which results partly from the oxidation, or combus- tion, of the respiratory elements of the food, and partly from the chemico-vital changes which take place in the blood and the different organs of the body. Every change in the condition of the organic constituents of the body, in which their elements enter into new com- binations with oxygen, must be a source of the develop- ment of heat; and the amount of oxygen consumed ANIMAL HEAT, LIGHT, AND ELECTRICITY. bears a certain relation to the amount of heat produced— the same amount of heat being produced, whether the union be rapid or slow. It is also found that the quan- tity of heat generated in the body is, “cceter is paribus” in direct proportion to the activity of the respiratory process. For example, in birds, whose function of respi- ration is very active, the animal temperature is very high (111°F.), while in mammals, whose respiration is less active, it is less (98° to 102°F). In fishes and rep- tiles, both the respiration and the animal heat are much lower than in either of the preceding (51°F). Besides, the quantity and quality of the food used are different in different climates and seasons; for example, larger quantities of fats and oils are used in the food in cold than in warm climates, in order to supply material for the maintenance of animal heat. Even in temperate climates, more fats are used in winter than in summer. Influence of tiie Nervous System in the Pro- duction of Animal Heat.—It has been observed that after the division of the nerves of a limb the tempera- ture falls, and this diminution of heat is still more decidedly marked in cases of paralysis; e. g., the hand of a paralyzed arm was found to be 70°F., while that of the sound side had a temperature of 92°F. Again, when death is caused by a severe injury, or removal of the nervous centres, or in poisoning by woorara, &c., the temperature of the body rapidly falls, even though arti- ficial respiration be kept up. On the other hand, severe injuries of the nervous system are sometimes followed by the effect. This is supposed to be due to the dilatation of the arteries, in consequence of which the blood reaches the part supplied by those serves in larger quantities; the nutrition is therefore more active. Certain emotions of the mind may cause a 224 HUMAN PHYSIOLOGY. momentary increase of temperature, while others cause a diminution. These circumstances, however, do not prove that heat is produced by mere nervous action in- dependent of any chemical change. All the functions of the organism, as nutrition, secretion, excretion, &c., are under the influence of the nerves, and when they are divided, or otherwise injured, or paralyzed, chemico- vital action is in a great measure suspended. Loss of Heat by Evaporation.—The temperature of the body is rendered uniform by the evaporation which is continually taking place on its surface. Evapo- ration produces cold, on the principle that “when a fluid passes into a state of vapour heat becomes latent,” and hence the loss of heat will depend upon the amount of evaporation. When the atmosphere contains much moisture the evaporation is partly suspended, and all the effects of excessive heat are made more apparent than in a dry atmosphere, in which a greater amount of evaporation takes place, and consequently a greater amount of heat is removed from the system. Persons have been known to remain for several minutes in a dry atmosphere heated to 250°, without injury, the evapora- tion being sufficient to keep the temperature of the body within certain limits. Such a degree of heat in a moist atmosphere would be certain to cause serious injury. In fevers and inflammation, the skin is hotter than in health, and is also dry; this is owing to the arrest of the natural secretion or perspiration, in consequence of which there is little or no evaporation to produce cold. LIGHT. The evolution of light from the living human body, is a phenomenon of rare occurrence. Luminous exhala- tions have been frequently observed in burial grounds, ANIMAL HEAT, LIGHT, AND ELECTRICITY. 225 and a luminous appearance has been sometimes noticed in newly dissected subjects in the dark. This is due to the development of phosphoretted hydrogen during decomposition of the tissues. A luminous appearance has been observed in old sores in the living subject, which were in a state of decomposition. It is also said that an evolution of light has been noticed, in two or three instances, in patients in the last stage of phthisis. The light, in these cases, was observed to play around the face, and, in all probability, proceeded from the breath, which had a peculiar smell, and was probably charged with phosphoretted hydrogen. The urine also, in some instances, has a luminous appearance, depending on the presence of unoxidized phosphorus which it con- tains. The breath of an animal may be rendered dis- tinctly luminous by injecting phosphorus dissolved in olive oil, in the proportion of two grains to the ounce, into the veins. ELECTRICITY. This is generated by chemical union or decomposition, heat, and motion or friction. There are no two parts of the body (except probably those of opposite sides) whose electrical condition is precisely the same. This depends on the difference in the functional activity of the parts; e. g., the skin, and most of the internal membranes, are in opposite electrical states. Electrical currents exist in muscles and nerves; this may be demonstrated by means of the galvanometer. The direction of the current is con- stant in each muscle; but different muscles have differ- ent currents, e. g., in the gastrocnemius of the frog, the direction is from the foot towards the body; while in the sartorius it is the reverse. But, taking all the muscles of the limb together, the different currents are so unevenly 226 HUMAN PHYSIOLOGY. balanced, that a constant current is established in one direction of the limb, and this, in the frog, is from the foot towards the body. The current of a man’s arm is from the shoulder to the fingers. When the two cut ends of a muscle are placed against the electrodes of a galvanometer, a very slight deflection of the needle is observed, and the same is the case with two points of a longitudinal section which are equally distant from the middle of the muscle. But the most powerful influence on the galvanometer is produced when the surface of a muscle is placed on one of the electrodes, and the cut end of it brought in contact with the other. These results may be obtained with small portions of the muscle, even with a single fasciculus. Hence, it would appear, that each integral particle or sarcos element is a centre of electromotive action, and contains within it positive and negative elements, the arrangement of which represents a galvanic pile thus: It is supposed by some, that the light spots in the muscular fibrilloe are electro-positive, and the dark spots electro-negative. It has also been observed, that during contraction of the muscle the electric current is diminished. This may be exemplified by means of a common battery. It will be observed, that when the poles are held tightly in the hands, and the muscles firmly contracted, the shock is not so readily transmitted as when they are held gently. Since elec- tricity is transmitted both by the muscles and nerves, it is probable that contraction of the former alters slightly the relative position of some of the positive or negative elements, and in this way the power of conducting by the muscles is, to a certain extent, destroyed. There is also an electric current in nerves, similar to that in the muscles. When a small piece of nerve, ANIMAL HEAT, LIGHT AND ELECTRICITY. 227 recently obtained from the living body, is placed so that its surface rests on one of the electrodes, and its cut extremity touches the other, a considerable deflection of the needle is produced in a direction which indicates that the current is from the interior to the exterior of the nerve. If the cut ends are applied to the two electrodes respectively, no marked effect is observed. The most powerful effect is produced by doubling the nerve in the middle, and applying both ends to one electrode, and the loop to the other. The nervous current, like the muscular, is due to the electromotor action of the mole- cules of the nerve. The body would become surcharged with electricity were it not that the equilibrium is maintained by the free contact which is continually taking place between it and surrounding bodies. It is only when the body is insulated that it becomes apparent. The electricity of man is generally positive; of women, more frequently negative; and irritable men, of sanguine temperament, have more free electricity than phlegmatic persons. In some individuals, a crackling noise is produced when articles of dress, worn next the skin, are being removed, especially in dry weather. A case of a lady is men- tioned in the American Journal of Medical Sciences (1838), in whom the generation of electricity was so great, that whenever she was insulated by a carpet, or any other feebly conducting medium, sparks passed between her body and any object she approached. As many as four sparks per minute would pass from her finger to the brass ball of the stove, at the distance of one and a half inches. This phenomenon was accom- panied with a good deal of pain. Some animals possess organs in which electricity may be generated and accumulated in large quantities, HUMAN PHYSIOLOGY. and from whicli it may be discharged at will. The most remarkable examples are to be found in certain species of fishes, the best known of which are the torpedo, or electric ray, and the gymnotus, or electric eel. The shock of the gymnotus is sufficiently powerful to kill small animals; that of the torpedo is less severe, but is suffi- cient to benumb the hand that touches it. Sparks of electricity may be produced in most animals having a soft fur, by rubbing the surface, especi- ally in dry weather. This may be easily demonstrated by rubbing the back of a cat with the hand, in a dark- ened room, or by rubbing the horse, in a dark stable. CHAPTER XI. vSECRETING GLANDS AND THEIR SECRETIONS. THE LIVER. This is the largest gland in the body, situated in the right hypochondriac region, and extending across the epigastric into the left hypochondrium. It measures from ten to twelve inches from side to side, and from six to seven from before backwards, and weighs about three to four pounds. It is intended mainly for the secretion of bile, and is also supposed to effect important changes in certain constituents of the blood in its passage through the gland. (See Descriptive Anatomy.) Minute Structure.—The liver is surrounded by a reflection of the peritoneum, which constitutes its serous covering. This is attached to the substance of the. gland, except at its point of attachment to the dia- phragm, and in the bottom of the different fissures, by fine areolar tissue. The substance of the liver consists o.f lobules held together by delicate areolar tissue, the ramifications of the portal vein, hepatic artery and ducts, hepatic veins, nerves, and lymphatics. The lobules (acini) are small, granular bodies, about as large as a millet seed, varying in size from ytj to 2,o of an inch in diameter. They surround the small sublobular branches of the hepatic vein, to which each is connected at its base by a small intralobular branch. "When divided longitudinally, they present a foliated margin, and on a transverse section, they have a polygonal out- line. When one of the sublobular hepatic veins is laid 230 HUMAN PHYSIOLOGY. open, the bases of the lobules may be seen through the thin walls of the vein on which they rest. The base of each lobule presents a polygonal outline, in the centre of which may be seen the orifice of the intralobular vein. This gives them the appearance of a layer of tesselated or pavement epithelium. Structure of the Lobules.—Each lobule is a min- iature representation of the whole gland of which it forms a part. It consists of' a mass of cells, a plexus of biliary ducts, an intralobular vein (which is the com- mencement of the hepatic vein), arteries, nerves, and lymphatics. The hepatic cells form the chief mass of the substance of a lobule; they lie in the interspaces of the capillary plexus, so as to form rows, which radiate from the centre to the circumference of the lobule. They are generally spheroidal in shape, but may be polygonal from mutual pressure, and vary in size from to 2q1(JU °f an inch in diameter. Each cell contains a distinct nucleus, some- times two, and in the interior of the nucleus a highly- refracting nucleolus, and some granular matter. The contents of the cell are viscid, and contain yellow particles of coloring matter, and some oil globules. Biliary Ducts.—These commence within the lobule by a minute plexus of ducts with which the cells are in immediate contact. The ducts then form a plexus between the lobules (interlobular), and the interlobular branches unite into vaginal branches, which lie in the portal canals. These branches finally join into two large trunks, which leave the liver at the transverse fissure, and joining form the hepatic duct. Portal Vein.—The portal vein, on entering the trans- verse fissure of the liver, divides into two branches, one. for each lobe, which are situated in the portal canals, SECRETING GLANDS AND THEIR SECRETIONS. 231 together with the branches of the hepatic artery and duct, nerves and lymphatics. These vessels are sur- rounded by areolar tissue continued inwards from the transverse fissure of the liver (called Glisson’s capsule). The portal veins, in their course in these canals, give off vaginal branches, which form a plexus. From this plexus, and from the portal vein itself, small branches are givefi off, which pass between the lobules and cover their external surface (called interlobular); these then pierce the lobules, and form a capillary plexus within each, from which arises the intralobular vein. Hepatic Artery.—This takes precisely the same course as the portal vein and hepatic duct. It is intended chiefly for the nutrition of the tissue of the liver. It gives off in the portal canals its vaginal branches, which supply the coats of the portal vein and hepatic duct, and also interlobular branches, which pass between the lobules; the latter pierce the lobules, and terminate in the radicles of the intralobular vein. They are supposed by some to terminate in the radicles of the portal vein, but this is improbable. Hepatic Veins.—The hepatic veins commence in the interior of the lobules in the intralobular veins, which arise in the centre of the lobules, and leave them at their bases to join the sublobular veins. The sublobu- lar veins unite to form larger branches, and these join again to form the large hepatic veins, which terminate in the inferior vena cava. (For the secretion of the bile, and its function, see chapter on digestion.) KIDNEY AND ITS SECRETION. The kidneys are intended for the secretion of urine. They are situated in the hack part of the abdominal 232 cavity, one in each lumbar and hypochondriac region, extending from the eleventh rib to within two inches of the crest of the ilium. They are invested by a thin, smooth, fibrous capsule, which is very easily removed from tire surface of the gland. Structure.—The kidney consists of two different substances, an external or cortical, and an internal or medullary substance. The cortical substance fortns about three-fourths of the whole gland, is reddish in color, soft, granular, and friable in texture, and presents nu- merous reddish bodies (the malpighian bodies) in every part of it, excepting towards the free surface. It is composed of the convoluted tubuli uriniferi, blood-ves- sels, nerves and lymphatics, held together by a small quantity of areolar tissue, containing a transparent granular substance, and some small granular cells. The cortical substance is about two lines in thickness oppo- site the base of each pyramid, and it sends numerous prolongations inwards towards the sinus between the pyramids. The malpighian bodies are found only in the cortical substance. They are small round bodies, of a deep red color, and of the average diameter of T;l0 of an inch. They are nothing more or less than capsular dilatations of the tubuli uriniferi, and are divided into lateral and termi- nal, according as they are situated in the continuity of the tubes, or in their extremities. Within each body or capsule may be observed a vascular tuft, which consists of the ramifications of a small artery, the afferent vessel, which, after piercing the capsule, divides in a radiated manner into several branches, which ultimately termi- nate in a finer set of capillaries. The blood is returned from these by a vein, the efferent vessel, which pierces the capsule near the artery and forms a venous plexus HUMAN PHYSIOLOGY. SECRETING GLANDS AND THEIR SECRETIONS. with other efferent vessels around the adjacent tubuli. The capsules are lined by a layer of epithelium which, in all probability, is prolonged over the tuft of vessels. The medullary substance, which forms about one- fourth of the gland, is pale-red in color, dense in texture, and presents a striated appearance on account of the number of diverging tubuli uriniferi. It consists of conical masses (the “ malpighian pyramids”), which vary in number from eight to eighteen, their bases being di- rected towards the circumference of the organ, and their apices towards the sinus, in which they terminate by smooth rounded extremities, called the papilla3 of the kidney. The conical masses consist of the tubuli urini- feri, blood-vessels, nerves, and lymphatics, held together by areolar tissue. The tubuli uriniferi commence at the apices of the cones by small openings, which vary from t-0 sin of an inch in diameter; as they pass tovvards the base they divide and sub-divide, and diverge until they reach the cortical substance, when they become convoluted and anastomose freely with each other. The number of orifices on a single papilla is about 1,000; from 400 to 500 large, and as many smaller ones. The tubuli ifriniferi are lined by spheroidal epithelium, and pour their secretion into the sinus. Sinus of the Kidney.—This is a large cavity in the interior of the kidney which communicates with the tubuli uriniferi, on the one hand, and the ureter on the other. It consists of three prolongations, the infundi- bula, one situated at each extremity of the organ, and one in the middle. Each infundibulum is divided into from seven to thirteen smaller portions, the calyces, each of which surrounds, like a cup, the base of one or more of the papillie. It is lined by spheroidal epi- thelium. 233 234 Secretion of Urine.—The secretion of urine from the blood is effected by the agency of cells. It is pro- bable, also, that the malpighian bodies furnish chiefly the fluid portion of the urine, for it has been observed that in those animals which pass the urinary excrement in a semi-solid state, the tufts of the malpighian bodies are very small. The secretion of urine is rapid in com- parison with other secretions. It passes through the ureters and enters the bladder drop by drop; this may be seen in some cases of ectopia vesicoe. Some substances pass very rapidly from the stomach through the circula- tion, to be eliminated by the kidney; e.g., a solution of ferrocyanide of potassium passed in one minute, while, some vegetable substances, as rhubarb, occupied from sixteen to thirty-five minutes. The transit is slower when the substances are taken during digestion. HUMAN PHYSIOLOGY. URINE. Healthy urine is a clear, limpid fluid, of a pale straw or amber color, with a peculiar odor, and saline taste. When first voided, it lias an acid reaction, but after a short time it becomes alkaline from the development of ammonia during decomposition. In some instances the urine may become turbid on cooling, although clear and transparent at first. The specific gravity of urine varies from 1015 to 1025, depending on the time at which it is secreted, the kind of food, drink, &c. In consequence of this, the secretion has been divided into three varieties:—1st, urina potus, or that which is secreted after the introduction of fluids into the body; 2nd, urina cibi, or that secreted after the introduction of solid food; 3rd, urina sanguinis, or that secreted from the blood when neither food nor drink lias been taken. For purposes of investigation, the whole of SECRETING GLANDS AND THEIR SECRET 235 the urine passed during a period of twenty-four hours should be taken. In disease, as albuminuria, the spe- cific gravity is diminished to 1004; while in diabetes it may be increased to 1050 or 1060. The whole quantity of urine secreted in twenty-four hours varies, according to the amount of fluid drank, and the quantity secreted by the skin, from thirty to forty ounces. The secretion of the skin is more active in warm weather than in cold, and consequently the quantity of urine secreted during winter is greater than in summer. Chemical Composition of the Urine.—The urine consists of water, holding in solution certain animal matters, salts, coloring matters, &c. Its composition is as follows, in 1000 parts. Becquerel: Water ..967.00 Urea .. 14.23 Uric acid .. .47 Animal and extractive matter (creatine and crea- j • 10.17 tinine), coloring matter and mucus < Chloride of sodium and potassium S Sulphate of soda and potassa Biphosphate of lime, soda, magnesia & ammonia ] Hippurate of soda 1- 8.13 Fluate of potash 1 Silica . Traces. 1000.00 Water.—Tlie quantity of water varies in different seasons, and according to the drink, exercise, action of the skin, &c. In some diseases it is very much increased, as in hysteria, diabetes, &c. In other diseases, as albu- minuria, diarrhoea and dysentery, it is very much diminished. In fevers, and in inflammation also, the quantity of water is almost always diminished. Urea.—C2 H4 N2 02 (NII40 C2N0.) This con- stitutes nearly half of the solid matter of healthy urine. The quantity is increased by exercise, or by a purely animal or highly nitrogenous diet. An excess of urea is 236 HUMAN PHYSIOLOGY. often found in rheumatic and gouty patients. Urea exists already formed in the blood, and is simply removed by the kidneys. It is formed from the decomposition of the nitrogenous elements of the food, and from the disintegration of the azotized tissues. It may be readily obtained by evaporating urine to the consistence of honey, and acting on it with four parts alcohol; then evaporating and crystallizing. It crystallizes in acicu- lar crystals, which appear, under the microscope, as four- sided prisms. It may also be obtained in the form of nitrate of urea (C2 H4 N2 02, N05) by evaporating urine to one-half, and then adding an equal quantity of nitric acid, and crystallizing. Urea is identical in com- position with cyanate of ammonia (NH40 C2N0==C2 H4 N2 02), and may be prepared artificially by the chemist, by double decomposition from cyanate of pot- ash, and sulphate of ammonia. Urea is colorless when pure, and destitute of smell, neutral in its reaction to test paper, and soluble in water and alcohol. When urine stands for some time, the urea is decomposed, and forms carbonate of ammonia, It is also decomposed, in some cases, before it leaves the bladder, as in paralysis, and some low forms of disease. Nearly half an ounce of urea is excreted from the body in twenty-four hours, when the kidney is in a healthy condition; but in some diseases, as, e. g., in desquamative nephritis, Bright’s disease, or congestion of the kidney from any cause, a certain portion of the urea is kept back, and circulating through the system may, by its poisonous effects on the cells, give rise to dropsies in different parts of the body, or from its deleterious effects on the nervous system, occasion uremic convulsions and coma. It is supposed by Frerichs, that this substance is resolved, while in the circulation, into carbonate of ammonia, the presence of which produces those effects usually attributed to the presence of urea. Uric or Lithic Acid (C10 H4 At4 06). This sub- stance is rarely absent from healthy urine. It is com- bined with soda and ammonia in the form of urates. It predominates in the urinary excrements of birds, ser- pents, and other reptiles; while urea predominates in the mammalia, especially the The quantity of uric acid, like that of urea, is increased by the use of animal or highly nitrogenized food, and decreased by food which is free from nitrogen. It is increased in all febrile conditions, and in gout it is deposited in and around joints, in the form of urate of soda, and consti- tutes the (so-called “chalk stones”). Uric acid has been detected in the blood of healthy persons, and in con- siderable quantity in gouty patients. It is supposed to be formed in the system from the disintegration of the azotized tissues. Uric acid may be readily obtained by adding a few drops of hydrochloric acid to a portion of urine in a watch glass; after a few hours, it is found crystallized on the sides and bottom of the vessel. In larger quantities it may be obtained from the thick, white urinary excrement of serpents or birds, which consists almost entirely of urate of ammonia. This substance is dissolved in warm water, and then decomposed by nitric or hydrochloric acid. The crystals of uric acid assume very various and somewhat fantastic shapes, most fre- quently rhombic or diamond shaped. It is insoluble in alcohol and ether. Hippuric Acid (Cj 8 H8 N05 HO.)—This acid exists in small quantity in human urine, probably in the form of hippurate of soda, but is very abundant in the urine of cows, horses, and other herbivorous animals. It is closely allied to benzoic acid (C!7 II5 02 O HO), and SECRETING GLANDS AND THEIR SECRETIONS. HUMAN PHYSIOLOGY. this substance, when taken into the system, is excreted in the form of hippuric acid. Hippuric acid is chiefly formed from vegetable articles of food, and may be pre- pared from the urine of cows by precipitation with hydrochloric acid. It has a bitter taste, is slightly solu- ble in cold, but very soluble in hot water and alcohol. Animal Extractive and Coloring Matters.— Under this head are included certain substances, some of which, as creatine, creatinine, and urrosacine, have been separated, while others have not. Creatine—(C8 II9 hT3 04) occurs in very small quantity in the urine. It is a colorless crystalline body, with a pungent taste, soluble in water, but almost inso- luble in alcohol. It may be obtained from the flesh of animals. It is most abundant in the flesh of fowls, and in the heart of the ox. Creatinine—(C8 H7 N3 02) is also found in the urine. It crystallizes in colorless crystals, has a hot, pungent taste like caustic ammonia, and is soluble in water and alcohol. It may be formed from creatine by the action of hydrochloric acid. It is probably formed from creatine in the system. Urrosacine, the coloring matter of the urine, has; been already described, (see proximate principles). Salts.—The salts of the urine constitute about one- fourth of the solid ingredients; some of them are similar to the salines found in other parts of the body; others are peculiar to the urine. Chlorides of sodium and potassium form a large proportion of the salines of the urine, the former being more abundant than the latter. They are derived in part from the food, and also partly from chemical decom- position within the body. They may be readily precipi- tated by a solution of nitrate of silver, after the urine has been acidulated by nitric acid. When nitrate of silver is added to healthy urine, a whitish precipitate of chloride of silver and phosphate of soda is thrown down; the latter may be dissolved by the addition of a little nitric acid. The chloride of< silver is readily dissolved j by a little ammonia. The sulphates are more abundant in the urine than in the fluids and tissues of the body. They are increased by exercise, and in diseases accompanied by muscular exertion, as in chorea and delirium tremens, &c. The sulphuric acid is formed by the oxidation of sulphur which is derived from the decomposing proteine com- pounds. The phosphates are more numerous, though less abundant than the sulphates. In the urine they are acid salts, as biphosphate of soda, lime, magnesia, &c., and these are supposed to give the urine its acidity. Phosphorus is derived from the decomposition of nerve substance, albumen and fibrin, and like sulphur, is oxi- dized at the lungs, and then unites with the bases to form salts. The phosphates are increased by great men- tal exertion, and in phrenitis, while they are diminished in delirium tremens. Fluate of potash and silica are not constant ingredi- ents in the urine. SECRETING GLANDS AND THEIR SECRETIONS. 239 MAMMARY GLANDS AND THEIR SECRETION. These are the organs which secrete the milk. They are large and hemispherical in the female, but are quite rudimentary in the male. They are situated in front of the pectoralis major, between the third and sixth ribs, and extending from the sides of the sternum nearly to the axilla. They are enlarged at puberty, increased during pregnancy and lactation, and diminished in old HUMAN PHYSIOLOGY. age. The outer surface of the mamma presents, a little above the centre, a small conical eminence—the nipple— the surface of which is dark-colored, and surrounded by an areola, which has a rosy hue in the virgin, but becomes very dark-colored during pregnancy. Its sum- mit is perforated by numerous openings, the orifices of the lactiferous ducts. It is also provided with a number of sebaceous glands situated near its base, and upon the surface of the areola, which secrete a peculiar fatty sub- stance for the protection of the nipple during sucking. The nipple consists of numerous bl#od-vessels, nerves, lymphatics, ducts, erectile tissue, and nonstriated, muscu- lar fibre-cells, and is capable of slight erection during sexual excitement or irritation. Stkuctuiie.—The mamma consists of numerous lobes, which are made up of small lobules, connected together by areolar tissue, blood-vessels, and ducts. Each lobule, which is a representation of the whole gland, consists of a cluster of rounded vesicles, which open into the smallest branches of the lactiferous ducts, and these, uniting, form larger ducts—the tubuli lacti- feri. These vary in number from fifteen to twenty, and converge towards the areola, beneath which they form dilatations, or ampullae, which serve as reservoirs for the milk; they then become contracted, and continue on- wards to the summit of the nipple, where they open by separate orifices, which are narrower than the ducts themselves. The entire surface of the gland is invested by fibrous tissue, from which numerous septa are de- rived, which pass between the lobes. The fibrous tissue, also, contains some adipose. Milk.—The secretion of milk is usually limited to the period succeeding parturition, yet this is not invari- ably the case. Numerous instances are on record where young women who have never borne children, and even old women, have been able to act as wet nurses. In some rare cases, the male has been known to secrete milk in the breasts. A fluid resembling milk may frequently be expressed from the mammary glands of infants. The chemical composition of human milk is as follows, in 1000 parts: SECRETING GLANDS AND THEIR SECRETIONS. 241 Water 890 Butter 25 Casein 35 Sugar and Extractive 48 Fixed Salts 2 1000 When milk is examined with the microscope, a large number of minute particles may be seen, termed “oil globules,” which vary in size from to 721100 °f an inch. They are soluble in ether and alkalies, when agitated. In the colostrum, or first milk secreted after labor, large, yellow, granulated corpuscles may be seen; they appear to be composed of small granules or glob- ules of a fatty nature, being for the most part soluble in ether. They are supposed to be exudation corpuscles, by some; while others regard them as transformations of the epithelial cells of the lactiferous ducts, the result of fatty degeneration, depending on the activity of the mammary gland during pregnancy. The colostrum has a purgative effect on the child, which is useful in clear- ing the bowels of the meconium which they contain at birth. The oleaginous matter of milk chiefly consists of the ordinary constituents of fat, together with a sub- stance called “butyrin,” to which the taste and smell of butter are due. When this substance is treated with alkalies, or suffers decomposition, the following volatile acids are produced, viz.: butyric, caproic, caprylic, and capric. These are called butter acids. 242 HUMAN PHYSIOLOGY. The casein of human milk is not so readily precipi- tated as cows’ milk. It requires a large amount of acid, and rennet does not seem to take effect upon it, unless an acid he present. Lactin, or sugar of milk (C24 II24 024), may he obtained from whey by evaporation and crystallization. It strongly resembles glucose, into which it may be con- verted by the addition of dilute sulphuric or hydrochloric acid. The action of a ferment causes lactin to undergo the lactic acid fermentation; and when lactic acid, or the lactate of lime is allowed to stand for some time, it is changed into butyric acid, or butyrate of lime, having undergone the “butyric acid fermentation.” The saline matter of the milk is nearly identical with that of the blood, with an increase in the phosphate of lime and magnesia. From what has been already stated, it will be observed that milk contains the four classes of principles which are required for human food, viz.: The aqueous, the albuminous, the oleaginous, and the saccharine, consequently it is well adapted to the nourishment of the young animal. Certain medicinal agents, when administered to the mother, may pass into the milk, and in this Avay affect the child. As a rule, salines pass more readily than vegetable substances. Medicine may be administered to the mother, instead of the child, when it is desired to act upon the latter. Certain emotions of the mind, as anger, grief, fear, &c., may produce peculiar changes in the quantity and quality of the milk; for example, anger produces very irritating milk, which causes griping in the child, and green stools. Grief diminishes the secretion, and fre- quently vitiates it. Fear also diminishes the secretion, and that which is secreted under these circumstances is highly irritating. Violent exercise, or great anxiety of mind, has also a bad effect on the secretion of milk. Cases are recorded in which children have had convul- sions and died shortly after sucking milk secreted under the foregoing circumstances. SECRETING GLANDS AND THEIR SECRETIONS. 243 CHAPTER XIT. DUCTLESS GLANDS. These are so named from having no excretory ducts; they are the spleen, supra-renal, capsules, thymus and thyroid glands. THE SPLEEN. The spleen is situated in the left hypochondriac region, embracing the cardiac end of the stomach. It is of an oblong shape, highly vascular, very brittle, and of a bluisli-recl color. It measures five inches in length, three or four in breadth, and one and a half in thickness, and weighs from four to six ounces. Structure.—It is invested by two coats, an external serous, and an internal fibrous elastic coat. The serous coat is derived from the peritoneum, and is intimately adherent to the fibrous coat. It covers nearly the whole organ, being reflected from it at the upper end on to the diaphragm, and at the hilus on to the great end of the stomach, forming the gastro-splenic omentum. The fibrous coat consists of white fibrous and yellow elastic tissue. It covers the exterior of the organ, and sends prolongations inwards in the form of vagi nee or sheaths, which surround the vessels. From these sheaths, and from the inner surface of the fibrous coat, numerous trabeculae or bands pass in all directions, and these uniting form the areolar framework of the spleen. The presence of the elastic tissue permits of the great enlargement of this organ which is sometimes seen. The spaces or areolae between the bands are filled with a soft pulpy mass, of a dark brown color, consisting of colorless and colored elements, the proper substance of the spleen, and some rounded vesicles (the malpighian bodies). The colorless elements form about one-half or two- thirds of the entire pulp, especially in well-fed animals, and consist of granular matter, free nuclei, about the size of red corpuscles, and a few nucleated cells, about of an inch in diameter. The colored elements consist of unchanged red blood corpuscles, and blood discs in various stages of decay. Besides these may be seen a number of granular bodies or crystals, which in chemical composition resemble the hematine of blood. The malpighum bodies are rounded vesicles, from one- third to one-sixth of a line in diameter; of a semi- opaque whitish color, and are more distinct in early life than in adult age. Each consists of a membranous cap- sule, homogeneous in structure, and derived from a pro- longation from the sheaths of the small arteries to which the bodies are attached. They are surrounded and em- braced by the radicles of the arteries, and present a resemblance to the buds of the moss rose. Each capsule contains a soft wdiite substance consisting of granular matter, nuclei, and nucleated cells, similar to the color- less elements of the pulp. The splenic artery is large in proportion to the size of the gland, tortuous in its course, and divides into from four to six branches, which enter the hilus. Each branch runs transversely from within outwards, and di- vides into smaller branches; these ultimately terminate in tufts or pencils, which lie in direct contact with the pulp. The most striking peculiarity is, that each of the larger branches supplies chiefly that part of the organ to DUCTLESS GLANDS. HUMAN PHYSIOLOGY. which it is distributed, having no anastomosis with the adjoining branches. The capillaries terminate either directly in the veins, or open into csecal or lacunar spaces, from which the veins arise. The veins are much larger and more numer- ous than the arteries, and by their junction form from four to six branches which emerge at the liilus, and uniting form the splenic vein, the largest branch of the portal. From this it will be seen that the blood of the spleen passes through the liver before it enters the general circulation. Function of the Spleen.—In consequence of the large amount of elastic tissue which this organ contains, permitting it to undergo great changes in volume, and from its peculiar position in reference to the portal cir- culation, it would appear to serve as a diverticulum to the liver, so as to relieve its vessels from undue turges- cence, and prevent congestion of the liver, stomach, and bowels. Enlargement of the spleen is apt to occur from any obstruction to the hepatic circulation, or from internal venous congestion, such as occurs in the cold stage of inter- mittent fever. AVhen intermittent fever is long-continued, the spleen is generally very much enlarged, constituting what is commonly called “ague cake.” The spleen is larger four or five hours after food is taken than at any other time, and therefore it is supposed that this organ is the receptacle for the increased quantity of blood formed from the food, and which cannot be admitted into the system generally, without danger, until the volume of the circulating fluid has been reduced by secretion. In support of this theory, it has been stated that animals from which the spleen has been removed, are very liable to die of apoplexy, after taking large quantities of food. It would therefore appear to be a DUCTLESS GLANDS. storehouse of nutrient material, which may be drawn upon as the system requires. The increase of the fibrin in the splenic vein would show that the nutrient mate- rial is elaborated during its withdrawal. The spleen is also supposed to promote the disinte- gration of the red corpuscles. The pain in the region of the spleen, so common in chlorotic patients, is probably connected with an excess of the disintegrating action of this organ. The supra-renal capsules are situated upon the upper extremity of the kidney, somewhat triangular in shape, the base being applied to the kidney, and the apex directed upwards. Each gland is about one and one- half to two inches in length, rather less in width, about one-fourth of an inch in thickness, and weighs from one to two drachms. Structure.—Like the kidneys, they are divided into a cortical and medullary portion. The cortical 'portion, which forms the principal part of the organ, is of a deep yellow color, and consists of narrow, columnar masses, arranged perpendicularly to the surface, and held together by areolar tissue. These columnar masses measure about of an inch in diameter, and consist of closed parallel tubes, containing nucleated cells, dotted nuclei, granular matter, and oil globules. The granules are of various sizes, and are not changed by the action of most chemical reagents. The medullary substance consists of a plexus of minute veins, having nuclei and granules in its meshes. It is soft and pulpy, very dark in color, hence the name atrabiliary substance, sometimes given to it. Function.—-Very little is known regarding their function. They are the diverticula of the kidney, and SUPRA-RENAL CAPSULES. 248 HUMAN PHYSIOLOGY. are supposed to be concerned in elaborating some of the materials of the blood. It was observed by Addison that disease of the supra-renal capsules was associated with anemia, general weakness, and a peculiar change of color in the skin, the patient resembling a mulatto. The disease is called morbus Addisonia. THYMUS GLAND. This is only a temporary organ. It reaches its largest size at the end of the second year, and then declines until puberty, when only a small part remains. It is situated partly in the anterior mediastinum, and partly in the neck, extending from the lower border of the thyroid gland to the fourth costal cartilage. It is some- what oval in shape, of a pinkish grey color, lobulated on its surface, and consists of two lobes. It is about two inches in length, one and one-half in breadth, three or four lines in thickness, and weighs about half an ounce. Structure.—Each lobe consists of a central cavity or reservoir, around which are arranged numerous lo- bules, held together by delicate areolar tissue. The lobules vary in size from a pin’s head to a pea, and each contains a small cavity from Tg to of an inch in diameter, which communicates with the central cavity or reservoir of the organ. Each lobule is surrounded by smaller or secondary lobules, the cavities of which com- municate with those of the primary lobules. The closed cavity of the organ contains a chyle-like fluid, consisting of granular corpuscles, and nuclei about t j/q 5 of an inch in diameter. Function.—This organ would appear to be the diverticulum of the lungs, and is connected with the preparation of matter for the pulmonary arteries in early life. It probably forms fibrin from albumen and other substances, by the action of its nuclei. DUCTLESS GLANDS. 249 The thyroid gland is situated at the upper part of the trachea, and consists of two lobes connected by a narrow band (the isthmus), which crosses the second and third rings. Each lobe is conical in shape, about two inches in length, and three-quarters of an inch in breadth, the right being the larger. The whole gland weighs from one to two ounces. It is of a brownisli- red color, larger in females than in males, and is increased during menstruation. It is occasionally very much hypertrophied, and constitutes bronchocde or goitre. Structure.—In structure it consists of lobules, held together by areolar tissue. Each lobule consists of a number of closed vesicles, oblong or spherical in shape, each containing an albuminoid substance, consisting of granules, oil globules, nuclei, and nucleated cells, the latter occupying the position of an epithelium within the vesicles. The vesicles vary in size from gb to 2 of an inch in diameter. Function.—The thyroid gland acts as a diverticulum to the cerebral circulation. When the brain is inactive, the thyroid gland takes on an increased action, and accommodates the blood that would otherwise go to that organ. This view is based on the fact that the arteries which supply this gland arise in close proximity to those which supply the brain. The vesicles also probably remove, and store up from the blood, certain constituents which are not required in its passive state, to be returned to it when it resumes its activity. THYROID GLAND. CHAPTER XIII. The nervous system consists of two portions, the cerebrospinal, and the sympathetic or ganglionic system. The former was distinguished by Bichat as the nervous system of animal life; the latter as the nervous system of organic life. The cerebrospinal system includes the brain and spinal cord, the nerves associated with them, and tlieif ganglia, viz:—The ganglia of the posterior root of the spinal nerves, the ganglion of the fifth nerve, and those of the glosso-pharyngeal and pneumogastric nerves. It includes the nervous organs in and through which are performed the several functions with which the mind is more immediately connected, as those relating to com- mon sensation, volition, and the special senses, as well as those concerned in many nervous actions with which the mind has no connection. The sympathetic or ganglionic system consists of a double chain of ganglia connected by nervous cords, which extend along each side of the vertebral column, from the cranium to the pelvis, and from which nerves, with ganglia upon them, proceed to the viscera in the thoracic, abdominal, and pelvic cavities. This system is more closely connected with the process of organic life than the cerebro-spinal, but is less immediately connected with the mind. In the lower orders of the animal creation the nerv- ous system is quite rudimentary. In its lowest and simplest form it may consist of but a single ganglionic THE NERVOUS SYSTEM. THE NERVOUS SYSTEM. 251 centre, with afferent, and motor or efferent nerves, whose function is essentially internuncial, impressions being made and responded to without any intervention of con- sciousness, the movements being purely excito-motor. A simple repetition of such ganglionic centres may exist to any extent without dissimilarity of function, or any essential departure from the mode of action just men- tioned. A higher form of nervous system is that in which there is a multiplication of ganglionic centres to correspond with the diversity of functions, as in the higher articulata and mollusca, in which ganglionic centres are set apart for the actions of deglutition and respiration, as well as for those of motion, but their modus operandi is still the same—the actions being all excito-motor. In all but the very lowest invertebrata, the nervous system includes, in addition to the above, certain ganglionic centres which preside over the organs of sight, smell, hearing, &c. These sensorial ganglia constitute the “brain” in these animals. The highest degree of psychical perfection, as in the class of insects, consists in the exclusive development of the instinctive faculty, or of simple automatic powers, by virtue of which each individual performs those actions to which it is prompted by impressions made upon its afferent nerves, without any self-control or self-direction, so that it may be regarded as entirely a creature of necessity. In the vertebrated series, on the other hand, the highest degree of psychical perfection, as shown in man, consists in the highest development of the reason and the supreme domination of the will, to which all the automatic actions—except those which are essential to the organic functions—are subject, so that each indivi- dual becomes not only a thinking and reflecting, but also a self-moving and self-controlling agent, whose ■ 252 HUMAN PHYSIOLOGY. actions are performed with a definite purpose in view. During the early period of life, however, the mental faculties are but little in advance of that of the higher invertebrata; for example, the infant is prompted to seize the nipple, not from any knowledge gained by experi- ence, that by so doing it will relieve the feeling of hun- ger, but in consequence of the impulse arising out of impressions made upon the afferent nerves. The super- addition of more elevated endowments in the vertebrated sferies is coincident with the addition of a peculiar gan- glionic centre, the cerebrum, to the sensori-motor appa- ratus. The superiority of the mind of man over the lower animals consists not only in the greater variety and wider range of his faculties; but also in that dominant power of the will which enables him to utilize them with the highest effect. When the thoughts and feel- ings of man are the mere result of the action of ex- ternal impressions upon a respondent organism, he may be considered irresponsible for his actions, his character having been formed for him, and not by him. But, whenever he can exert a volitional power of directing Ids thoughts and controlling his feelings, he is morally and intellectually responsible for his acts. Some per- sons, however, in consequence of the weakness of their will, are so much accustomed to act directly upon the prompting of any transient impulse, that they can scarcely be said to be voluntary agents; and others allow certain dominant ideas or habitual feelings to gain such a mas- tery over them as to usurp for the time the power of the will. The fundamental part of the cerebro-spinal system is the cranio-spinal axis, which consists of the spinal cord, medulla oblongata, and the sensory ganglia, the THE NERVOUS SYSTEM 253 latter consisting of those ganglia lying along the base of the skull in man, and in which the nerves of the special senses have their origin, viz., the corpora striata and quadrigemina, and thalami optici, &c. This cranio-spinal axis, which represents the whole nervous system of the invertebrata (except the rudimentary sympathetic they possess), exists without any super-addition in the lowest known vertebrated animal, as in the case of the little fish called the amphioxus. This condition may even be found in the human species, as in the case of acephalous infants, in which neither the cerebrum nor cerebellum is present; such have existed for several days, breathing, sucking, crying, and performing various other move- ments. In man, however, and in all the higher vertebrata, large ganglia, which form the principal mass of the en- cephalon, are found superimposed upon and embracing the sensor}" ganglia. These are the cerebrum and cere- bellum; the former is the seat of the will, and presides over, controls, and regulates all the actions and move- ments of the body, except the organic functions and automatic actions; the latter is concerned in the regula- tion and co-ordination of the actions of the spinal cord. The action of the cerebro-spinal system may be eluci- dated by the following diagram—Carpenter. Intellectual operations- The Will- Emotions. - Cerebrum. - Ideas. Centre of emotional and ideo-n;otor reflexion. Sensations- Centre of aensori-motor reflexion. -Sensory ganglia- Impressions- Centre of excito-motor reflexion. ■ Spinal Cord- Motor Impulse. In consequence of the peculiar arrangement of the nervous apparatus, excitor impressions travel in the up- 254 HUMAN PHYSIOLOGY. ward direction; so in the left-hand corner of the diagram the impressions are represented as passing upward. If they meet with no interruption, they travel upwards through the spinal cord until they reach the sensorium or sensory ganglia, where they make an impression on the consciousness of the individual, giving rise to sensa- tions. These, passing from the sensory ganglia to the cerebrum, form ideas. If these ideas are associated with feelings of pain or pleasure, they give rise to emotions; and either as simple or emotional ideas, they become the subject of intellectual operations whose final issue culminates in an act of the will, which may be exerted in producing or checking a muscular movement, or in controlling or directing the current of thought. If this ordinary upward course be interrupted, or if the action be automatic, the impressions will exert their power in the transverse direction, and a reflex action will be the result; for example, if the interruption be produced by division or injury of the spinal cord, below the sensory ganglia, reflex movements being produced without sensation will be purely excito-motor. So, again, if the connection between the sensory ganglia and the cerebrum be severed, or if the function of the cerebrum be in abeyance, they may react on the motor apparatus by the reflex power of the sensory ganglia themselves; such actions, being dependent on the promptings of sen- sation, are sensori-motor. Some Physiologists consider the afferent and efferent nerves, and their connection with the spinal cord, as an automatic nerve arc, and the spinal cord as consisting of a longitudinal series of automatic arcs, since an impres- sion may be made through the afferent nerve which produces action of the muscles supplied by the efferent nerve, the whole force being either consumed without THE NERVOUS SYSTEM. 255 leaving behind any impression on the nervous centre, or a part of it being left in the vesicular matter of the nervous centre. The nerve arc may be connected to a ganglion by means of a band or commissure, through which a portion of the nervous influence passes to be stored up. This is called a registering ganglion, as, for example, the corpus striatum, thalamus opticus, &c., and these, in their turn,- are connected to the cerebrum; this connection constituting what is called the influential arc. The registering ganglia are regarded as the sensorium, and correspond with the sensory ganglia. Their func- tion appears to be to receive and retain impressions of ideas, events or occurrences, the time, place, and order in which they occurred, and other circumstances which are usually ascribed to the faculty of memory. Structure of the Nervous System.—The organs of the nervous system are composed essentially of two different substances, fibrous nervous matter and vesicular nervous matter. The former, on account of its color, is often called the white or medullary substance; the latter, the gray or cineritious substance. Fibrous Nervous Matter.—This consists of two different kinds of nerve fibres, the tubular and the gela- tinous. They are intermingled in most nerves; the tubular fibres being more numerous in the cerebro-spinal system; the gelatinous predominating in the sympa- thetic. The tubular fibres appear to consist of tubules of simple homogeneous membrane, similar to the sarco- lemma of striated muscular tissue, within which is con- tained the proper nerve substance, consisting of two different materials. The central part is a transparent material called the axis cylinder; the outer portion which surrounds the axis cylinder is usually opaque, and dimly HUMAN PHYSIOLOGY. granular, and is called the white substance of Schwann. It is the predominance of this substance which gives the cerebro-spinal nerves their white appearance. The axis cylinder is probably the essential element of the nerve tube; the white substance of Schwann, and the tubular membrane or sheath, merely affording mechanical pro- tection, and serving to isolate it from the neighboring fibres. In the recent state the nerve tubes are cylin- drical, and contain a transparent and apparently homo- geneous material; but after death they present a dark double contour, the outer line being formed by the tubu- lar membrane or sheath, the inner by the white sub- stance of Schwann. At the same time the white sub- stance and axis cylinder, which now appear granular, collect into little masses which distend portions of the tubular membrane, while the intermediate spaces col- lapse, giving the fibres a varicose or beaded appearance. The contents of the nerve tubes are very soft, and readily pass from one part of the canal to another, or escape from the ends of the tube on pressure. The nerves vary in size from to u’oo °f an inch in diameter in the trunk and branches of nerves, but are smaller in the gray matter of the brain and spinal cord, in which they arc seldom more than To-JDo to t? unu °f an inch. The gelatinous fibres constitute the principal part of the trunk and branches of the sympathetic nerves, and are mingled in various proportions in the cerebro-spinal nerves. They differ from the preceding chiefly in their fineness, being only half or one-third as large (4 o’o u to et/ou °f an inch); in the absence of the double contour; in their apparently uniform structure, and yellowish gray color. These fibres appear to be formed exclusively of the substance which corresponds with the axis cylin- der of the tubular nerves, and differ from them in not possessing the white substance of Schwann. Vesicular Nervous Matter.—This, as its name implies, is composed of vesicles or corpuscles called nerve cells or ganglion coo'puscles, containing nuclei and nucleoli. They are found only in the brain, spinal cord, and the various ganglia mingled with nerve fibres, being imbedded in a finely granular substance, and giving to these structures a peculiar reddish gray color. They present different shapes, some being oval or spheroidal, others caudate or stellate; some of the processes being continuous with a nerve fibre, and they vary in size from 3-J-0 to 4 000 of an inch in diameter. Each cell contains a vesicular nucleus and nucleolus, the latter being generally clear and bright; and the contents are finely granular, and of a reddish gray color. Ganglia.—These may be regarded as separate and independent nervous centres, of smaller size than the brain, and less complex. They are found on the posterior roots of the spinal nerves; on the posterior root of the fifth nerve; on the facial, olfactory, glosso-pliaryngeal and pneumogastric nerves; along the base of the brain, as the corpora striata, corpora quadrigemina and thalami optici; on eafch side of the vertebral column forming the trunk of the sympathetic, and on some of its branches of distribution. In structure they are similar to other nervous centres, being composed of a collection of vesi- cular nervous matter, and tubular and gelatinous nerve fibres. They are of a reddish gray color. THE NERVOUS SYSTEM. 257 Chemical Composition of the Nerve Tissues.— (Lassaigne.) Constituents White. Water 85.2 73.0 Albuminous matter 7.5 9.9 Colorless fat 1.0 13.9 Red 3.7 0.9 Osmazone and lactates 1.4 1.0 Phosphates 1.2 1.3 12* 100.0 100.0 258 Nervous matter is a soft, unctuous substance, easily lacerated, and contains a large proportion of water. It would appear to consist of albumen dissolved in water, combined with fatty matters and salts. From the fatty matters may be obtained carbonic acid, cliolesterin, oleo- phosphoric acid, traces of oleine, margarine, and fatty acids. The spinal cord is said to contain a larger pro- portion of fat than the brain. Distribution of Nerve Fibres.—Nerve fibres consist of round or flattened cords, communicating on the one hand with the nervous centres, and on the other, distributed to the various textures of the body, forming the medium of communication between the two. They are divided into two great classes, the cere- brospinal, or nerves of animal life, distributed to the organs of the senses, the skin, and the muscles; and the sympathetic or nerves of organic life, distributed chiefly to the viscera and blood-vessels. The cerebrospinal nerves consist of a number of pri- mitive nerve fibres, enclosed in a simple membranous sheath, the neurilemma. These are called funiculi, and t if the nerve is of small size it may consist of only one funiculus; but if large, there may be several connected together by a common sheath formed of areolar tissue. Every nerve fibre pursues an uninterrupted course from its origin at a nervous centre, to its destination, whether this be the periphery of the body, in another nervous centre, or the same from which it issued. They anasto- mose or communicate with each other in their course, sometimes joining at acute angles with others proceed- ing in the same direction; but they never coalesce, or unite with the substance of any other fibre; for although they cross and mingle with each other, yet each separate nerve fibre retains its identity throughout. The nerves, HUMAN PHYSIOLOGY. THE NERVOUS SYSTEM. 259 in certain parts of their course, form plexuses in which they anastomose with each other, as in the cervical, brachial, lumbar, and sacral plexuses. In the formation of a plexus, the component nerves divide, then unite, and again sub-divide, and in this way the fasciculi be- come intricately interlaced. The object of such inter- change of fibres is probably to give each nerve a wider connection with the spinal cord, so that the parts sup- plied may have wider relations with the nervous centres, and also that groups of muscles may be associated for combined action. Origin and Termination of Nerves.—The point of connection of a nerve with the brain, spinal cord, or ganglia, is called, for convenience of description, its ori- gin, root, or central termination; the point of distribution its peripheral termination, or 'periphery. With reference to their origin, some of them may originate in nerve corpuscles, others probably form simple loops. As the nerve fibre approaches the nerve cor- puscle, the white substance of Schwann gradually dis- appears, the tubular membrane or sheath dilates, so as to embrace the nerve corpuscle, which occupies the dilata- tion; it then contracts, and either ends in the corpuscle, or is continued onwards, the sheath becoming filled again with the proper nerve substance. In some instances more fibres have been counted leaving than entering a ganglion, from which it may be inferred that some of them arise from the corpuscles. It has not yet been determined whether this relation of nerve fibres to nerve corpuscles is common to all kinds of nerve fibres. It does not appear, however, to belong exclusively to either the cerebro-spinal or sympathetic nerves. Some are of opinion that sensitive fibres alone are brought into this intimate relation with nerve corpuscles. 260 HUMAN FHYSIOLOGY. The peripheral termination is also exceedingly diffi- cult to determine, but examples of Jive different modes have been observed: 1st. In loops. In this so-called mode of termination, each fibre, after issuing from a branch in a terminal plexus, runs over or through the substance of the tissue; it then turns back and joins the same, or an adjacent branch, and pursues its way back to the nervous centre. This mode has been found in the internal ear, in the papilla? of the tongue, in the skin, in the tooth pulp, and in striated muscular tissue. 2nd. By branching. Each ultimate nerve fibre appears to divide into several branches, which spread out in the substance of the tissue, as is seen in the retina, and in the muscular tissue of the frog, and lower verte- brata. 3rd. In plexuses. This mode may be seen in certain serous membranes, as the peritoneum, arachnoid, &c. 4tli. By free ends. The Pacinian corpuscles afford a good example of this variety. They are small, oval bodies, situated on some of the cerebro-spinal and sym- pathetic nerves, especially the cutaneous nerves of the hands and feet. They are named after their discoverer, Pacini. Each corpuscle is attached to the nerve on which it is situated by a narrow pedicle, and is formed of concentric layers of fine membrane, with intervening spaces filled with fluid. A single nerve fibre passes through the pedicle, and after traversing the several layers of membrane, it terminates in the central cavity in a bulbous enlargement, or a bifurcation. 5th. In nerve corpuscles. This mode of termination may be seen in the retina, and in the lamina spiralis of the internal ear. Some nerve fibres appear to have no peripheral termi- THE NERVOUS SYSTEM. 261 nation. It has been shown by Gerber that nerve fibres occasionally form loops by their junction with a neighbor- ing fibre in the same fasciculus, and return to the nervous centre without having any peripheral termination. He considers these to be sentient nerves, for the supply of the nerve itself, the nervi nervorum, upon which the sensibility of the nerve depends. This is somewhat similar to those nerve fibres met with at the posterior part of the optic commissure, where a set of fibres passes from one optic tract across the commissure to the tract on the opposite side, without having any connection with the optic nerves—the inter-cerebral fibres. On the other hand, some nerve fibres appear to have no central connection with the cerebro-spinal centre, as in those forming the anterior fibres of the optic commissure—the inter-retinal fibres. These commence in the retina on one side, pass along the optic nerve, and across the com- missure to the retina of the opposite side. The sympathetic nerves consist of tubular and gelati- nous fibres, intermingled in various proportions in differ- ent nerves, and are enclosed in a sheath of areolar tissue. The mode of distribution of these nerves is essentially the same as that of the cerebro-spinal. The most strik- ing peculiarity is the frequent formation of ganglia in the course of the trunks, and their branches. They are chiefly distributed to the head and trunk, being very limited in their connection with the extremities. Function of Nerve Fibres.—The function of a nerve may be determined by comparing its anatomy in man with that of the lower animals; by experiments on recently-killed or living animals, and by clinical obser- vation. The office of the nerves is to convey or conduct nervous impressions. This function is of a two-fold kind—-first, they serve to convey to the nervous centres the impressions made upon their peripheral extremities, or on parts of their course; and, secondly, they serve to transmit impressions from the brain, and other nervous centres, to the parts to which they are distributed. These impressions are of two kinds, viz., those that excite muscular contraction, and those which influence the processes of secretion, growth, &c. Those nerves that convey impressions from the periphery to the centre, are called sensitive, centripetal or afferent nerves, or nerves of sensation, and those which transmit impulses to the muscles, are called motor, cen- trifugal or efferent nerves, or nerves of motion. The nervous force (vis nervosa) by which secretion, nutrition, &c., are influenced, seems to be conveyed along both sensitive and motor sympathetic nerves. This peculi- arity cannot be accounted for from any special variety of structure which the nerves possess, or the tissues to which they are distributed. Nerve fibres require to be stimulated, in order to manifest their peculiar endowments, since they do not possess the power of generating force in themselves, or of originating impulses to action. The property of con- ducting impressions is called excitability; but this is never manifested until some stimulus is applied. The stimuli by which the action of nerves is ordinarily pro- voked, are of tivo kinds, mental and physical; the former relates to the will, the latter to the influence of external objects, and chemical, mechanical and electric actions or irritations. These stimuli, when applied to parts endowed with sensation, or to sensitive nerves, produce sensations, and when applied to the nerves of muscles produce contractions. Nerves, though divided, when irritated or stimulated have, by virtue of their excita- HUMAN PHYSIOLOGY. bility, the power of exciting contractions in the muscles to which they are distributed; but when the continuity of the nervous matter, with the tubular fibres, is bruised, or seriously injured, the property of propagating nervous force is destroyed. Nervous action is also excited by temperature; for example, any very hot substance applied to the body produces muscular contraction, and a sensa- tion of pain is transmitted to the nervous centre; the application of a very cold substance has a somewhat similar effect. Chemical stimuli excite the action of both sensitive and motor nerves, when their effect is not so strong as to destroy the structure of the nerve to which they are applied. A similar manifestation of nervdus power is produced by electricity. Nerve force travels along the fibres with immense rapidity; its velo- city will probably never be ascertained. Laws of Action in Nerve Fibres.—All nerve fibres are mere conductors of impressions; that is, an impres- sion made on any fibre is transmitted along it without interruption, and without being imparted to any of the fibres lying near it. This is probably due to the fact that the contents of each fibre are isolated from those of adjacent fibres by the membrane or sheath in which it is enclosed. It is also supposed that the white substance of Schwann acts as an insulator. No nerve fibre can convey more than one kind of impression; for example, the motor nerve conveys only motor impulse; the sensi- tive nerve transmits only sensation when propagated to the brain, and the nerves of special sense, as the optic and auditory, convey only sensations of light and sound. Nerves of sensation are able to convey impressions only from the parts to which they are distributed, towards the nervous centre with which they communicate; for example, wdien a sensitive nerve is divided, and irrita- THE NERVOUS SYSTEM. 263 264 HUMAN PHYSIOLOGY. tion is applied to that portion still connected with the nervous centre, sensation is perceived, or a reflex action ensues; but when the distal portion is irritated no effect is produced. When the trunk of a nerve is irritated, the sensation is felt in all the parts which receive branches from it; for example, if the ulnar nerve be compressed behind the internal condyle of the humerus, a peculiar tingling sensation is felt in the little finger, and in the ulnar half of the ring finger. Even when part of a limb has been amputated, any pressure or irri- tation to the remaining portions of the nerves which ramified in it, gives rise to sensations which the mind refers to the lost part, as well as to the stump, and ting- lings and pains are complained of in the lost finger, toe, hand or foot, as the case may be. Again, when the relative position of the peripheral extremities of sensi- tive nerves is changed artificially, as in the restoration of the nose from the integument of the forehead, the new nose thus formed, while connected by its isthmus, when touched, the sensation produced is referred to the forehead. This peculiarity may be exemplified by the following experiment:—Cross the middle finger of the hand behind the index finger so that the extremity is on the radial side of the latter, then roll the two fin- gers over a pea or marble, and a sensation will be pro- duced which leads the mind to suppose the existence of two distinct bodies. This is owing to the impression being made at the same time on the sides of the fingers most removed from each other in the natural position. Generally, however, the mind discerns the exact part of a nerve fibre that is irritated, and even when, as is the case in the retina, two or more impressions are made at the same instant on different parts of the same fibre, the mind can discriminate and perceive each, and compare the one with the other. THE NERVOUS SYSTEM. 265 Several of the laws of action in motor nerves are simi- lar to the foregoing. For example, motor influence is transmitted only in the direction of the fibres going to the muscles, and irritation of a motor nerve excites con- traction in all the muscles supplied by the branches given off below the point of irritation; but those supplied by branches given off above this point are never directly affected. Again, since motor nerves are isolated as com- pletely as sensitive, the irritation of a part of the fibres of a motor nerve does not affect the motor power of the whole trunk, but only that of the portion to which the stimulus is applied. Development of Nerve Tissue.—Nerve fibres ap- pear to be formed in the same manner as muscles. The primitive nerve cells arrange themselves in a linear manner, the contiguous walls break down, and a tube (or secondary nervous cell) is formed, in which are con- tained the nuclei and granular contents. At this period, as in muscle, a deposit of a whitish, fatty substance, formed from the granular matter, takes place on the inner surface of the tube. This is the white substance of Schwann. The nuclei become gradually absorbed, and the remaining cavity of the tube is filled, constituting the axis cylinder, or “band of Eemak.” In the vesicular nervous matter the cells remain in their primitive state, the only change being that they increase in size, and develop in their interior some pig- mentary granules. In the process of regeneration, after incision or injury, the extremities of the nerves are united at first by fibrous tissue, which after a time is replaced by nerve tissue, if the cut extremities are not too far removed. Perfect restoration of the action of the nerve, however, does not generally take place, owing probably to the want of exact 266 HUMAN PHYSIOLOGY. coaptation between the cerebral and peripheral portions of the same fasciculi; for example, the cerebral portion of a motor filament might unite with the peripheral por- tion of a sensitive one, and in this way the action of each would be neutralized. Vascular Supply.—The blood-vessels supplying a nerve terminate in a minute capillary plexus, disposed similarly to those of muscles, running parallel to the nerve fibres. They are connected together by short transverse branches, forming narrow oblong meshes. Function of the Nervous Centres.—The nervous centres embrace all those parts of the nervous system which contain nerve corpuscles, as the brain, spinal cord, and the ganglia of the cerebro-spinal and sympathetic system. Their function is that of variously disposing and transferring the impressions received through their several sensitive nerves. Nerve fibres, as already stated, are simple conductor's of nervous influence. Nervous centres are not only conductors, but also communicators of nervous impressions. The brain conducts, communicates, and perceives or takes cognizance of impressions. Conduction.—When an impression is produced on the periphery of a nerve, as, e. g., in the mucous mem- brane of the intestines by the presence of a portion of food, it is conducted to the adjacent ganglia of the sym- pathetic, from which a motor impulse returns to the intestines and produces a movement of the muscular coat. If, however, any irritant substance, as a drastic cathar- tic, be mixed with the food, a stronger impression is produced, and this is conducted through the nearest ganglia to others more remote, and from all these motor impulses proceed, which excite a more forcible and widely extended action of the small intestine; or the impression may be conducted through the ganglia of the THE NERVOUS SYSTEM. 267 spinal cord, from which motor impulses may proceed to the abdominal and other muscles, producing cramp. Besides, the same morbid impression may be conducted through the spinal cord to the cerebrum, where the mind can perceive and take cognizance of it. Communication.—Impressions made on the nervous centres may be communicated from the fibres that brought them to others, and in this communication they may be either transferred, diffused, or reflected. The transference of impressions may be seen in disease of the hip joint. The impression made by the disease on the nerves of the hip is conveyed to the spinal cord; it is thence transfer- red to the central termination of the nerve fibres of the knee joint; through these the impression is conducted to the brain, and the mind, referring the sensation to the part from which it is accustomed, through these fibres, to receive impressions, feels as if the pain were in the knee. In the same way, when the sun’s rays fall strongly on the retina, a tickling may be felt in the nose, causing sneezing; or irritation in any part of the respira- tory organs gives rise to a sensation of tickling in the glottis, and produces coughing. The diffusion of im- pressions is exemplified when an impression received at a nervous centre is diffused to many other fibres in the same centre, the sensation extending far beyond the part from which the primary impression proceeded, as is seen in toothache, in which the adjoining teeth and surrounding parts are similarly affected. The pain caused by the presence of a calculus in the ureter or bladder, is diffused far and wide. Reflection or Reflex Action.—The reflection of impressions exhibits an important function common to all nervous centres, and is the source of all reflex move- ments. The preceding examples are all instances of 268 HUMAN PHYSIOLOGY. reflection, or reflex action, for the manifestation of which three conditions are necessary. First, sensitive nerve fibres, to convey an impression. Secondly, a nervous centre, to which the impression may be conveyed, and in which it may he reflected. Thirdly, motor nerve fibres, upon which this impression may be conducted to the contracting tissue. If any of these conditions be absent, a proper reflex action cannot take place. They are all involuntary, and in health they have a distinct purpose to subserve in the animal economy, as in the movements of the intestines, the respiratory organs, contraction of the pupils, closure of the glottis, &c.; but in disease many of them are irregular and purposeless, as in chorea, convulsions, &c. Nerve Force (vis nervosa).—The special endowment by which nerves act and manifest their vitality is a peculiar one inherent in the structure and constitution of the nervous substance. It manifests itself in its effects on the muscles, in sensation, secretion, excretion, nutrition, &c. Nervous force, though not identical, pre- sents many points of resemblance to voltaic electricity. For the production of the latter, the ordinary requi- sites are two dissimilar metals, as zinc and platinum, or copper and an interposed compound fluid, as dilute sulphuric acid. When these metals are placed in con- tact with each other, chemical action commences, and a current sets in a definite direction, a state of polarity or electrical tension being produced. The production of nervous force, or nervous polarity, may have as analogues two kinds of nervous matter, vesicular and fibrous, and the presence of a fluid. From the structure and peculiarity of the nervous centres, there is much to justify the opinion that each nerve vesicle, and fibre connected with it, together with THE NERVOUS SYSTEM. 269 the blood-vessels and fluid surrounding them, is a distinct apparatus for the development of nervous polarity. The whole nervous system is therefore in a constant state of nervous polarity, and is prepared at any moment to receive, conduct, or communicate impressions, or convey motor impulses. A slight mechanical or chemical stim- ulus to a nerve, is capable of producing in it a state of polarity, and rendering it capable of conducting impres- sions or motor impulse; e.g., pain is excited by touching a sensitive nerve, and contractions may be produced by irritating the motor nerve of an amputated limb. The Spinal Cord.—The spinal cord is a cylindrical column of nerve substance, connected above with the brain, through the medulla oblongata, and terminating below—about opposite the first or second lumbar verte- bra—in a slender filament of grey substance, the filum terminate, which lies among the leash of nerves forming the cauda equina. It presents two enlargements, one in the cervical region, extending from the third cervical to the first dorsal vertebra, and the other in the lumbar, opposite the last dorsal or first lumbar. The spinal cord consists of two symmetrical halves, united in the middle line by a commissure. They are separated in front and behind by a vertical fissure, the posterior fissure being deeper, but narrower than the anterior. On each side of the anterior fissure, a linear series of foramina may be seen, from which emerge the anterior roots of the spinal nerves; this is the so-called anterior lateral fissure of the cord. On each side, near the posterior part of the cord, and corresponding with the posterior roots of the spinal nerves, may be seen a delicate fissure, the posterior lateral fissure. On each side, and near the posterior fissure, is a slight longitudinal furrow—the posterior medio-lateral fissure. These fissures divide each 270 HUMAN PHYSIOLOGY. half of the cord into four columns, anterior, lateral, poste- rior and posterior median columns. The anterior column. is situated between the anterior median and the ante- rior lateral fissures. It is continuous with the anterior pyramid of the medulla oblongata, in which decussation of the anterior columns takes place. The lateral column is situated between the anterior lateral and posterior lateral fissures, and is continuous above with the lateral tract of the medulla. The posterior column is situated between the posterior lateral and the posterior medio- lateral fissures, and is continuous with the restiform body of the medulla. The posterior median column is a narrow segment situated between the posterior medio- lateral and the posterior median fissures, and is continu- ous above with the posterior pyramid of the medulla oblongata. Structure of the Cord.—The cord consists of fibrous and vesicular, or white and gray nervous sub- stance ; the former is more extensive, and situated exter- nally ; the latter occupies the centre, and consists of two crescentic masses, connected together by a transverse band, the gray commissure. Both in front of and behind the gray commissure is a transverse band of white sub- stance, the anterior and posterior white commissures ;• these connect the white substance of each lateral half of the cord, and form the floor of the anterior and posterior median fissures respectively. Each crescentic mass of: gray matter presents an anterior and a posterior horn ; the former is short and thick, and does not quite reach, the anterior lateral fissure; the latter is long and slen- der, and extends to the posterior lateral fissure. The anterior roots of the spinal nerves are connected with the. anterior horn, and the posterior roots with the posterior horn. The white substance of the cord consists of trans- verse, oblique, and longitudinal nerve fibres, blood-ves- sels and areolar tissue; and the gray substance consists of smaller nerve fibres, nerve cells, blood-vessels, and areolar tissue. Spinal Nerves.—The spinal nerves consist of thirty- one pairs, issuing from the sides of the whole length of the cord. Each nerve arises by two roots, an anterior or motor, and a posterior or sensitive. The posterior root is larger than the anterior root, (except the first), and has a ganglion developed on it. Immediately beyond this ganglion the two roots coalesce, and the trunk thus, formed passes through the intervertebral foramen, after which it again divides into two branches., an anterior, which supplies the anterior surface of the body and the extremities, and a posterior, which supplies the posterior part of the body, each branch containing fibres from both roots. The anterior roots arise from the antero- lateral columns, and are also connected with the anterior horn of the gray substance; and the posterior roots arise from the postero-lateral columns and the posterior horns of the gray substance; the former consist exclu- sively of motor fibres, and the latter exclusively of sen- sitive fibres. Function of the Spinal Cord.—The spinal cord transmits impressions from the periphery to the brain, and also enables the latter to bring into action the motor nerves. Division of, or injury to the spinal cord, causes an interruption of voluntary motion and sensation in those parts supplied by nerves below the part affected, while the functions of the parts above remain unim- paired. But though the influence of the brain in receiving sensation, and exciting voluntary motion is cut off or interrupted, the portions of the coTd below the affected part still possess an automatic power, and hence THE NERVOUS SYSTEM. 271 272 HUMAN PHYSIOLOGY. the cord may be regarded as a nervous centre; for exam- ple, in cases of paralysis, muscular action may be excited by tickling the palms of the hands, or soles of the feet with a feather. It has been shown, by experiment, that irritation to the anterior columns of the cord is followed by convulsive movements of all the parts supplied with motor nerves below the irritated part., but no signs of pain are manifested; while irritation of the posterior columns appears to cause excruciating pain, without pro- ducing any muscular movement besides such as may be produced by the will or reflection. Again, when the spinal cord is completely severed, irritation of the posterior col- umns of the severed part produces no effect; but irritation of the anterior columns is followed by violent movements. On the other hand, irritation of the posterior columns of the portion of the cord connected with the brain causes acute pain and reflex movements; while irritation of the anterior columns of the same produces no effect. Again, when both anterior columns alone are divided, the power of voluntary motion is lost in parts below, the sensibi- lity remaining perfect; and when both posterior columns are divided, sensation is lost in the parts below, the power of motion remaining unimpaired. From this it would appear that the anterior columns are motor, and the posterior sensitive; nevertheless, the results of inju- ries, and diseases of different parts of the cord, are not always in accordance with it, but in some instances directly contrary to it; for example, cases have been seen in which complete loss of motion occurred without any impairment of sensation, as the result of lesion of the posterior columns of the cord, the anterior being wholly intact. The spinal cord has a crossed action for both motion and sensation; for example, in cerebral apoplexy the THE NERVOUS SYSTEM. 273 paralysis and loss of sensation is always on tlie side opposite to that on which the effusion has taken place. The decussation of the fibres of motion occurs between the anterior pyramids of the medulla oblongata, and may be seen with the naked eye. The discovery of the crossed action for sensation is due to Brown-Sequard. His experiments show that a decussation of sensitive impressions takes place between the posterior columns throughout the whole extent of the cord. The sensitive impressions reaching the cord, either ascend or descend for a short distance, the majority probably descend, and ultimately pass across to the opposite side of the spinal cord to reach the brain, so that if the posterior column of one side be impaired, sensation is lost on the opposite side of the body. The spinal cord, as an aggregate of many nervous centres, has the power of communicating impressions from fibre to fibre by transference, diffusion and reflection. This has been already referred to. (See Function of Nervous Centres.) The reflex function of tfie spinal cord is essentially similar to that of all the other nervous centres, and may or may not be under the control of the will. In health the will can, in a great degree, control and prevent the development of reflex actions in the extremities. If one Of the legs be paralyzed, as in hemiplegia from disease of the brain, and a stimulus be applied to the sole of the foot in the paralyzed limb, reflex actions are readily produced; but on applying the same stimulus to the sound limb, no such movements occur, the patient being able to resist the tendency to action which it produces. In cases of paraplegia from disease of the spinal cord, even where the loss of motion and sensation is complete, patients are sometimes tormented with involuntary 274 HUMAN PHYSIOLOGY. movements of the lower extremities at night, which not only prevent sleep, hut also occasion pain and distress. It is no doubt caused by irritation at the seat of the lesion. Some reflex movements are partly voluntary, and partly involuntary; for example, the respiratory move- ments may be performed while the mind is fully occu- pied, or during sleep; yet, in an emergency, the mind can direct and strengthen them, and adapt them to the several acts of speech, effort, &c. Again, other reflex actions are entirely involuntary, as for example, the con- traction of the pupil, the movements of the intestines (except defecation), the action of the uterus in parturi- tion, &c. When the limb is pinched or pricked, it is involuntarily withdrawn from the instrument of injury, and the eye is involuntarily closed when a blow on the face is threatened. The phenomena of spinal reflex action in man are more marked in disease than in health; e. g., in tetanus a slight touch on the skin, or a breath of air, is sufficient to throw' the whole body into convulsions; a similar state is induced by the introduction of strychnine or opium. In these instances, the spinal cord is in a state of polar excitement, and is kept so by the constant irri- tation propagated to it by the wounded part, on the one hand, or the poisonous substance circulating in the blood, on the other, there being no inflammatory or con- gested condition either of the cord or its membranes. . The spinal cord, with its encephalic prolongation, may be said to supply, by its reflex power, the condi- tions requisite for the maintenance of the various mus- cular movements wrhich are essential to the continuance of the organic processes; and, as Marshall Hall has pointed out, it especially governs the various orifices of ingress and egress. Thus, the act of deglutition is entirely dependent on the spinal axis (medulla), and the nerves proceeding from it. The action of the cardiac and pyloric orifices of the stomach is wholly regulated without the consent of the will. The movements of the intestines are influenced by the spinal cord through the sympathetic system. The external sphincter which sur- rounds the orifice of egress, is also under its influence, although partly subject to the control of the will. The reflex action of the spinal cord is also exhibited in the expulsion of the generative products, as the semen, in defecation, micturition, and in parturition in its second stage. The spinal cord is constantly in activity; in all periods and phases of life, the movements which are essential to its continued maintenance are kept up with- out sensible effort, “The spinal system never sleeps;” it is the brain alone which is torpid during sleep, and whose functions are affected by this torpidity. THE NERVOUS SYSTEM. ENCEPHALON. The encephalon is situated in the cranial cavity, and consists of the medulla oblongata, pons varolii, cerebellum and cerebrum. Medulla Oblongata.—The medulla oblongata is the cephalic prolongation of the spinal cord, and con- nects it with the brain. It is larger than the spinal cord, and is divided into segments, which are continu- ous with the columns of the spinal cord below. It is separated into two lateral halves by fissures, which cor- respond with the anterior and posterior fissures of the cord, and each lateral half is again subdivided by minor grooves into four columns, the anterior pyramid, lateral tract and olivary body, restiform body and posterior pyra- • HUMAN FHYSIOLOGY. mid. These are continuous with the anterior, lateral, posterior and posterior median columns of the spinal cord respectively. Structure.—The anterior pyramid is composed entirely of white fibres derived from the anterior column of the cord of its own side, and from the lateral column of the opposite half of the cord, and is continued upwards into the cerebrum and cerebellum; the decussation between the anterior pyramids may be distinctly seen with the naked eye. Some of the fibres enter the pons varolii in their passage upwards to the cerebrum. The lateral tract is continuous with the lateral column of the cord. Its fibres pass in three different directions; the external join the restiform body, and pass to the cerebellum; the internal pass forwards, pushing aside the fibres of the anterior column, and form part of the opposite anterior pyramid, and the middle fibres ascend to the cerebrum, forming the fasciculi teretes in the floor of the fourth ventricle. The olivary body presents, on a transverse section, a whitish substance externally, and a grayish-colored body in the interior—the corpus denta- tum—which presents a zig-zag outline, and contains some white substance in the interior, which communi- cates with that on the external surface by means of an aperture in its posterior part. The restiform body is continuous below with the column of the cord, and receives some fibres from the lateral and anterior columns; superiorly, it divides into two fasciculi; the external one enters the cerebellum, the internal one joins the posterior pyramid, and blends with the fasciculi teretes as it passes up to the cerebrum. The posterior pyramid joins the restiform body, and ■passes with it up to the cerebrum. THE NERVOUS SYSTEM, 277 In the lower part of the medulla the gray matter is arranged as in the cord; but in the upper part it becomes more abundant, and is disposed apparently with less regularity. Function of the Medulla Oblongata.—The gen- eral function of the medulla oblongata is similar to that of the spinal cord. It may be regarded as a conductor of impressions, in which respect it has a wider extent of function than any other part of the nervous system. In consequence of the decussation of the anterior pyramids, motor impressions proceeding from the brain pass across to the opposite side of the spinal cord; for example, in injury to one side of the head, producing paralysis, the loss of motion is always on the side opposite to that on which the injury was received. Besides the function of conduction, the medulla oblon- gata, acting as a nervous centre, presides over the func- tions of respiration and deglutition. The brain may be wholly removed above, and yet life may continue, and the respiratory function be carried on. The same is the case when the spinal cord below the phrenic nerve is removed; and even when both the brain and spinal cord are re- moved the function of respiration maybe continued ; but whenever the medulla is wounded the function is in- stantly arrested, and the animal dies as if asphyxiated. The medulla ablongata may continue to discharge its functions as a nervous centre after the part which is only a conductor has ceased to act; thus, in coma from apo- plexy or compression, and in anesthesia from ether or chloroform, patients continue to breathe, although they are wholly insensible. The medulla oblongata also exhibits the property of reflex action, and is peculiar from having a very wide range of connection. The principal centripetal nerves HOMAN PHYSIOLOGY engaged in respiration are the pneumogastric; but that these are not the only ones may be shown by their divi- sion when respiration becomes slower, but is not arrested. The wride range of connection which belongs to the medulla is further shown by the fact that impressions on the surface of the body may induce respiratory move- ments, as, e, g., dashing cold water on the face or body is instantly followed by a deep inspiration. From the medulla also arise the movements required in the act of deglutition. This may be shown by the persistence of the power of deglutition after removal of the cerebrum and cerebellum, and by its complete arrest when the medulla is injured. The reflex power of the medulla in deglutition is much simpler and more restricted than in respiration. — Pons Vaeolii.—The pons varolii is the bond of union between the cerebrum, cerebellum, and medulla oblongata. In structure it consists of longitudinal and transverse fibres, intermixed with gray matter. The longitudinal fibres are continued up through the pons from the anterior pyramids, olivary bodies, lateral and posterior columns of the cord. The transverse fibres con- nect the two hemispheres of the cerebellum, forming the transverse commissure, and are divided into a superficial and deep layer; the former passes across the surface of the pons, and the latter, situated deeply, decussates with the longitudinal fibres. Function of the Pons.—Its function is two-fold; it acts as a conductor, and also as a nerve centre. As a conductor it is the channel through which impressions are conveyed from the spinal cord to the cerebrum and cerebellum, and also between the two hemispheres of the cerebellum. As a nervous centre, it may be regarded as the connecting link between the different portions of THE XERVOU3 SYSTEM. 279 the encephalon, for when the cerebrum and cerebellum are removed the mind may still have sensation of im- pressions, or exercise the will. At all events, it is a nervous centre for higher and more definite reflex acts than the medulla or any part of the spinal cord. - r Cerebellum.—The cerebellum consists of two lat- eral hemispheres connected together by a transverse- commissure or band. It is situated in the posterior fossa of the cranium, beneath the posterior lobes of the cerebrum, from which it is separated by the tentorium cerebelli. It is oblong in shape, measuring from three and a half to four inches transversely; from two to two and a half from before backwards, and two inches in thickness, and weighs from five to six ounces. Each hemisphere is divided into several lobes, of different sizes, and its surface is marked by numerous curved fur- rows or sulci, which vary in depth in different parts. Structure.—It consists of gray and white matter; the former, darker than that of the cerebrum, occupies the surface; the latter the interior. When divided ver- tically it is seen to consist of a central stem of white matter, which contains in its interior a grayish mass—the corpus dentatum. The central stem of white matter sends forth laminae towards the surface, which are surrounded by the gray matter so that the cut surface of the organ presents a foliated appearance, to which •the name of arbor vitcc has been given. The cerebel- lum is connected with the rest of the encephalon by processes or prolongations, called peduncles. They are three in number, the superior, middle, and inferior. The superior peduncles connect the cerebellum with the cerebrum. They pass upwards beneath the testes to the crura cerebri and optic thalami, each peduncle forming part of the lateral boundary of the fourth ven- tricle. Beneath the corpora quadrigemina the inner- most fibres of each peduncle decussate with each other, some fibres from one side of the cerebellum communi- cating with the opposite side of the cerebrum. The middle peduncles, the largest of the three, con- nect together the two hemispheres of the cerebellum, and form the transverse fibres of the pons varolii. The inferior peduncles (crura cerebelli) connect the cerebellum with the medulla oblongata. They pass downwards to the back part of the medulla, and form part of the restiform bodies. Function of the cerebellum,—The cerebellum is itself insensible to irritation, and may be cut away without causing pain; but if any of the crura be touched, pain is instantly felt. Its removal is not attended with any loss or disorder of sensibility; the animal can see, hear, smell, &c., as before its removal; but he has lost the power of springing, flying, walking, standing, &c., and his actions are like those of a drunken man. If one- half of the cerebellum be removed, the animal exhibits a tendency to roll over upon its longitudinal axis, and from the side injured. From the above circumstances it would appear that the function of the cerebellum is to regulate and coordinate the voluntary movements of the body. The influence of each half of the cerebellum is directed to muscles on the opposite side of the body. The cerebellum is supposed by some to be the organ of sexual instinct, or of amativeness; this view is gen- erally received by Phrenologists. The facts in favor of it are—1st, cases in which atrophy of the testes and loss of sexual passion have resulted from injuries to the cere- bellum ; 2nd, disease of the cerebellum has been attended with almost constant erection of the penis, and frequent seminal emissions ; 3rd, that it has seemed possible to humax physiology estimate the degree of sexual passion in different per- sons by an external examination of the region of the cerebellum. In reference to the first class of facts, the loss of sexual passion may have been the consequence of the loss of the testes, and hence these facts have little bearing on the question, unless it can be shown that the loss of sexual passion followed the injury of the cerebel- lum, before the testes began to diminish. Disease of the cerebellum proves nothing, because the same thing more generally occurs in disease of the medulla and spinal cord. On the other hand, cases are recorded in which the whole of the cerebellum has been disorga- nized, or completely absent, without loss of the sexual passion. Besides, among animals there is no proportion between the size of the cerebellum and the development of the sexual passion, and castration in early life is not followed by any diminution of the cerebellum. From all that has been observed, it would appear that no other office is manifest in it than that of regulatiug and co- ordinating muscular movements. The Cerebrum.—The cerebrum occupies the upper part of the cranial cavity, resting upon the anterior and middle fossae of the base of the skull, and is separated posteriorly from the cerebellum by the tentorium cere- belli. It is ovoidal in shape, and is divided into two lateral hemispheres, which are connected together by a broad transverse commissure of white matter—the car- pus callosum. The average weight of the brain is about fifty ounces in the male, and forty-five in the female. The weight of the brain increases rapidly up to the seventh year, more slowly up to twenty, and still more slowly up to the fortieth year. When it reaches the maximum, it remains stationary for a few years, and then declines as age advances, about one ounce for each THE NERVOUS SYSTEM. 281 282 HUMAN PHYSIOLOGY subsequent decennial period. As a rule, the size of the brain bears a general relation to the intellectual capacity of the individual. Cuvier’s brain weighed rather more than sixty-four ounces; Dr. Abercrombie’s, sixty-three; Dupuytren’s, sixty-two and a half. The brain of the late D’Arcy McGee, the celebrated Cana- dian statesman, weighed fifty-nine ounces. On the other hand, the brain of an idiot seldom weighs more than twenty-three ounces. In only two animals is the brain larger than in man, viz., the elephant and the whale. The mere comparative size of the brain, however, does not always give an accurate measure of the amount of mental power, for not unfrequently men possessing large and well-formed heads are seen, whose mental capability is not greater than that of others whose crania have the same general proportion, but are much smaller. Large brains, with deficient activity, are commonly found in persons of a lymphatic temperament; whilst small brains, and great activity, characterize Uie sanguine and nervous temperaments. The quality of the nerve tissue, and the number and extent of the convolutions, also bear a certain relation to the intellectual capacity of the indi- vidual. Structure.—The cerebrum consists of two kinds of nerve tissue, the gray and the wh$e; the former is situ- ated externally, the latter interiially. The surface of the cerebrum presents a number of convolutions or fold- ings, separated from one another by depressions or sulci of various depths. The outer surface of each convolu- tion is composed of gray matter, which is sometimes called the cortical substance, and the interior consists of white matter. The convolutions are admirably adapted to increase the extent of surface or amount of gray mat- THE XEHVOlTS SYSTEM. ter, without occupying much additional space. The gray matter of the convolutions, when closely examined, however, appears to consist of from four to six layers of gray and white tissue placed alternately, from two to three layers of gray substance, and an equal number of white; the latter occupying the surface. The sulci are generally about an inch in depth; but they vary in dif- ferent brains, and in different parts of the same brain, being usually deepest on the outer surface of the hemis- pheres. The number and extent of the convolutions, and the depth of the sulci, bear a close relation to the intellectual power of the individual. They are entirely absent in some of the lower orders of mammalia, and increase in number and extent as we ascend the scale. The largest and most constant convolutions of the human brain are the convolutions of the corpus callosum, supra-orbital convolutions, and the convolutions of the longitudinal fissure. The convolutions of the brain are the centre of intellectual action. The white matter con- sists of three kinds of fibres: diverging or peduncular, transverse and longitudinal commissural fibres. The diverging or peduncular fibres connect the cere- brum with the medulla oblongata and spinal cord, and constitute the crura cerebri. Each crus consists of two bundles, superficial and deep, separated by a dark gray mass in the interior—the locus niger. The superficial fibres are continued upwards from the anterior pyramids to the cerebrum. The deep fibres are contined upwards from the lateral and posterior columns of the medulla and the olivary bodies. As the peduncles of the cere- bellum enter the hemispheres, they diverge from one another to enclose the interpeduncular space, and the fibres of each pass through two large masses of gray matter, the ganglia of the brain, called the thalami optici and corpora striata, which project from the upper and inner side of each peduncle. Above these masses is situated the great transverse commissure—the corpus callosum—which connects the hemispheres together. The space bounded by the peduncles and ganglia on the sides, and the corpus callosum above, forms the general ventricular cavity. The upper part of the cavity is divided into two lateral ventricles by the septum lucidum, and the lower part constitutes the third ventricle, which communicates above with the lateral ventricles, and behind with the fourth ventricle. The fifth ventricle is situated in the space between the two layers of the sep- tum lucidum. The transverse fibres connect together the two hemispheres. They form the corpus callosum, and the anterior and posterior commissures. The longitudinal fibres connect together distant parts of the same hemisphere. They form the fornix, tenia semicircularis, peduncles of the pineal gland, striae longitudinales, gyrus fornicatus, and the fasciculus unci- natus, which connects together the anterior and middle lobes. Vascular Supply.—The blood-vessels of the brain are numerous and capacious, it being supplied by four large arteries; the two internal carotids and the two ver- tebral arteries. These vessels, in their passage, pursue a winding course to reach the brain, the object of which is to increase the extent of surface over which the blood passes, and thus add to the amount of impediment produced by friction, in order that the supply may be more equable and uniform. These curvatures in the vessels also tend to moderate the force with which the blood may be sent to the brain under certain circumstances, as during great excitement, violent exercise, and the like. These vessels also anastomose freely with each other after entering the HUMAN PHYSIOLOGY. THE NERVOUS SYSTEM. 285 cranial cavity. This takes place not only between the smaller branches, but also between the primary trunks; the former is seen all over the surface of the encephalon; the latter constitutes the well-known Circle of Willis. This is formed in front of the anterior cerebral and ante- rior communicating arteries, on each side, by the trunk of the internal carotid and the posterior communicating, and behind by the posterior cerebral and point of the basilar. These vessels divide and subdivide upon the surface of the brain, until they terminate in very small arteries, which are connected together by some areolar tissue, constituting the pia mater, from which smaller vessels are given off which pierce the brain substance. No medium-sized vessels pierce the cerebral substance except at the perforated spaces; but prolongations of the pia mater, carrying with them the blood-vessels, pass into the interior of the brain at the transverse fissure, to form the velum interpositum and choroid plexuses which are situated in the ventricles. Function of the Cerebrum.—From its anatomical relation the brain does not appear to be one of the essen- tial or fundamental portions of the nervous system, but is a superadded organ, receiving all its impulses to action from the parts below, and acting upon the body at large through them. But its great size, its position at the summit of the cerebro-spinal system, and the vesicular substance of its convolutions affording a termination to the fibres in connection with it, mark it out as the high- est in its functional relations, and as the organ through which all the processes of thought, reason, and intelli- gence are carried on. There is a very close correspondence between the relative development of the cerebrum, in the several tribes of vertebrata, and the degree of intelligence they HUMAN PHYSIOLOGY. respectively possess. In the lower animals it is difficult to say what part of their actions may be regarded as instinctive, and what as intelligent. Intelligent actions are exhibited : 1st, in the variety of means used to accom- plish the same ends by different individuals, and by the same individual at different times ; 2nd, in the improve- ment in the mode of accomplishing the object, which re- sults from experience ; 3rd, in the adaptation of means to altered circumstances. The difference between the intelligence of lower animals and pure instinct, is well seen in comparing birds with insects. Their instinctive propensities are nearly similar; but in the adaptation of their operations to peculiar circumstances birds display a certain degree of intelligence. Certain tribes of birds, especially the parrot and its allies, are capable of being taught to perform tricks and to pronounce words, in which they exhibit simple acts of reasoning, similar to those of a child when first learning to talk. Some of the domestic animals, as the dog and the horse, manifest a considerable degree of intelligence. There is no evi- dence, however, that any of the lower animals have the power of directing their mental operations in obedience to the will. With reference to the sensibility of cerebral matter, it has been ascertained by experiment that neither sensa- tion nor motion is produced by irritation of the vesicular or fibrous substance. In fracture of the skull, accom- panied by protrusion of the cerebral matter, it may be separated without exciting either sensation or convulsive motion. When one of the hemispheres is removed from an animal, it is followed by temporary weakness of the limbs on the opposite side of the body, and a loss of sight in the opposite eye, but the pupil remains active. When both hemispheres are removed, the animal appears THE NERVOUS SYSTEM. to be in a sleepy state, from which it cannot be fully aroused, but consciousness still remains, the persistence of which proves that the cerebrum is not its exclusive seat. In this state a reptile or a bird may survive many weeks if its physical wants be supplied. The influence of dis- ease on the cerebrum is somewhat anomalous. In some instances extensive disease lias occurred in one hemi- sphere, without any obvious injury to the mental pow- ers, or interruption of the influence of the mind on the body ; but morbid phenomena are invariably present when both hemispheres are affected. On the other hand a sudden lesion, although of a trifling character, may occasion very severe symptoms; for example, a slight effusion of blood in or around the substance of the cor- pus straitum is followed by paralysis in the opposite side of the body. Some of the muscles of the face are also paralyzed on the side opposite the injury as a general rule; but in a few exceptional cases, the side corresponding to the injury is affected. This appears very singular, when it is borne in mind that the nerves which supply the muscles of the face are given off above the place where the anterior pyramids decussate. The exceptional cases may be explained by the fact of a double injury having been sustained; the paralysis of the limbs resulting from injury to one side of the brain, and the paralysis of the face from injury to the other. When the corpora quadrigemina, or the part below, are involved in the injury, the paralysis is accompanied by convulsions on the same side. The conclusion to be drawn from wliat has been already stated is, that the cerebrum is the organ of intellectual action, emotion, ideo-motor action and voli- tion, the seat of which is the gray matter of the convo- lutions. The crura cerebri are the principal conductors of im- 287 HUMAN PHYSIOLOGY. pressions to and from the cerebrum. Wben one of them is divided, the animal moves round and round on a ver- tical axis from the injured to the sound side; this is caused by a partial paralysis on the side opposite the injury. The corpora, quadrigemina are the representatives of the optic lobes in birds, reptiles and fishes, and may be considered as the centres of the sense of sight, since their removal or diseased condition is accompanied with blind- ness. Injury or disease on one side is followed by blindness of the opposite eye, and a slight rotatory motion, as after division of the crus cerebri; the pupil is also dilated. They are not only the centres from which the optic nerves arise in part, but also the organs in which the mind perceives the sensation of light. The thalami optici are also concerned to a certain extent in the function of vision, for part of the fibres of the optic tracts may be traced to their surfaces. In persons born blind, the optic thalami, and also the cor- pora quadrigemina, are found extremely small. Destruc- tion of one of them produces effects similar to those of division of the crus cerebri; the animal remains stand- ing, and turns continually round. The corpora striata were supposed by Magendie to be the centres of motor power for backward movement, and that fmacard movement was excited by the cerebellum, these two powers being exactly counterbalanced, and hence division of the corpora striata caused an irre- sistible tendency to run forwards. This, however, has not been confirmed by other experimenters. Longet and others assert that animals remain stupid and immovable after division of the corpora striata, and it is only when irritated by pinching or pricking that they exhibit any disposition to move. THE NERVOUS SYSTEM. 289 The corpus callosum connects together the two hem- ispheres of the cerebrum. It is entirely absent in birds, reptiles and fishes. Its division is followed by severe general injury. It probably enables the two sides of the brain to act in concord in the performance of its highest functions. The Mind and its Relation to the Body.—With reference to the relation of mind and matter, and the nature and source of mental phenomena, there are two theories, that of the materialist and the spiritualist. The materialist supposes that all the operations of the mind are but “expressions of material changes in the brain;” that thus man is but a thinking machine, his whole conduct being determined by his original consti- tution, his character being formed for him and not by him, his actions being simply the result of the reaction of his cerebrum upon the impressions which called it into play. According to this doctrine, the highest elevation of man’s psychical nature is to be attained by proper attention to those circumstances which promote his physical development. The arguments in support of this theory are:—1st, the dependence of the normal activity of the mind upon the healthy nutrition of the brain, and its proper supply of pure blood; 2nd, the peculiar effects of lesions of the brain upon the intel- lectual operations, as is seen in loss of speech, memory, &c., after severe injury to the head; 3rd, the produc- tion of mental imbecility as a result of disease in the parents, or defective nutrition in the offspring during childhood; and—4th, the complete perversion of the mind and moral feelings which is produced by intoxi- cating agents. Now, though this doctrine recognizes some great facts regarding the dependence of mental operations upon the organization and functional activity 290 HUMAN PHYSIOLOGY. of the nervous system, yet there is beyond and above all this a self-determining 'power which can rise above tho promptings of external suggestions, and which can suit external circumstances to its own requirements, instead of being completely subjugated by them. The spiritualist regards the mind in the light of a separate immaterial existence connected with the body, but not in any way dependent upon it, except as deriving its knowledge of external things through its agency, and as making use of it to execute its determinations so far as these relate to material objects. According to this theory, the operations of the mind, having no relation to those of the body, are never affected by its irregularities or defects of functional activity; and the mind, thus in- dependent of the body, is endowed with a complete power of self-government, and is responsible for all its actions. But nothing can be more plain than that the introduction of intoxicating agents into the system really perverts the action of the mind, and occasions many strange results at variance with its normal action. So that, however true it may be that there is something in our mental constitution beyond and above any agency which can be attributed to matter, the operations of the mind are in a great degree determined by the material conditions with which they are so intimately associated. The whole system of education recognizes the import- ance of external influences in the formation of the character; and it is the duty of every teacher to foster the development and promote the right exercise of that power by which each individual becomes the director of his own conduct. Hence it will be seen that any attempt to bring mind and matter into the same category is attended with difficulty, since no relation of identity can exist between TUB NERVOUS SYSTEM. 291 them. But although no relation of identity or analogy subsists between mind and matter, a very close relation may be shown to exist between mind andforce, or between mind-force and nerve-force. In the phenomena of volun- tary movement the will operates upon the nervous matter, and developed nerve-force, the transmission of which along the nerve trunks is the determining cause of mus- cular contraction. Here is evidence of the excitement of nerve-force by mental agency. The converse of this is equally true, viz., that mental activity may be excited by nerve-force. This is the case in every act in which the mind is excited through the instrumentality of the sensorium; the impression is first conveyed to the senso- rium (or sensory ganglia), in which it produces a certain active condition of the nervous matter, which is the im- mediate antecedent of all consciousness—whether of emotions or ideas. And since the will can develope nerve-force, and as nerve-force can develope mental ac- tivity, there must be a correlation between the two forces, •not less intimate than that which exists between nerve- force and electricity. The nervous matter of the cere- brum is the material substratum through which the metamorphosis of nerve-force into mind-force, and mind- force into nerve-force is effected, and like all other changes, every act of the. mind involves the disintegra- tion of the nervous substance which ministers to it. When impressions are made upon some part of the body that is supplied with afferent nerves, they are transmitted through them to the sensorium, and occa- sion affections of the consciousness, which are called sensations. Every impression which affects the consci- ousness produces some change in the nervous centre, by which that impression is perpetuated in such a manner as to permit of its being again called up before the mind 292 HUMAN PHYSIOLOGY at any future time. The nature of the change by which sensory impressions are thus registered is not understood, and probably never will be. The acuteness with which particular sensations are felt depends on the degree of attention they receive from the mind; for example, ordi- nary impressions are not felt during sleep, or when the mind is engaged in some deep subject of study. On the other hand, impressions which are in themselves very slight may produce painful sensations, when the mind is directed strongly towards them. They are also much modified by the influence of habit. Sensations not attended to become blunted by frequent repetition; whilst sensations attended to become much more readily cogni- zable by the mind. Every student knows that the effluvia of the dissecting room becomes tolerable after the nose has become habituated to it. In some instances, sensations may be produced by internal causes; these are called subjective sensations, in contradistinction to objective, which are caused by a real material object. The most common cause of these sub- jective sensations is congestion or inflamation; e, g., con- gestion in the nerves of common sensation gives rise to pain or uneasiness; in the retina or optic nerve, it pro- duces “flashes of light;” and in the auditory nerve it occasions “a noise in the ears.” Again, subjective sen- sations may be produced by sensations originating in objective impressions on other parts, as e. g., a calculus in the bladder gives rise to pain in the glans penis; disease of the hip occasions pain in the knee. The mental recognition of the cause of sensation is called 'perception. For the production of a sensation a conscious state of the mind is all that is required; but for the exercise of the perceptive power, the mind must be directed, towards the sensation, and hence, when the THE NERVOUS SYSTEM. 293 mind is inactive, or engaged in. study, the sensation may not he perceived or remembered. The perception of sensation gives rise to ideas; some of these partake of the nature of feeling; others relate to knowledge. An idea.is a mental representation of an object which has been perceived by the mind—something grasped by the mind, and held up before it as an intelligible object of contemplation. Ideas may be communicated and ren- dered intelligible to other minds by means of visible signs, or by spoken language, in which certain combina- tions of sounds are used to express ideas; and the nearer the signs or sounds employed are to the natural expres- sions of the ideas which they represent, the more readily are they comprehended. When ideas are associated with feelings of pain or pleasure, they give rise to emotions. These, unlike ideas, cannot be communicated or expressed in language to others; they are unutterable. Those emotional states of the mind which determine a great part of the conduct of individuals, are the result of the attachment of the feelings of pleasure and pain, and of other forms of emotional sensibility to certain classes of ideas. Thus, grief is the painful contemplation of loss, misfortune, or evils of any kind. Joy is the pleasurable feeling which accompanies success, good fortune, or good prospects, &c. Fear is a painful emotion excited by an expecta- tion of future evil. Hope is the pleasurable expectation of future enjoyment. Benevolence is the pleasurable con- templation of doing good to others. Malevolence is a positive pleasure in the contemplation of the misfor- tunes of others, and so on. The emotions are partly under the control of the will, and partly independent of it. The capacity for performing mental acts is known as 294 the intellect, or the reasoning power ; and the capacities for those various forms of intellectual activity which pertain to the mind are called the intellectual faculties. They are 'perception, imagination, memory and judgment. It is, however, quite erroneous to suppose that the entire intellect can be split up into a certain number of facul- ties, since each faculty expresses only a mode of activity in which the whole mind is engaged at once, just as the whole power of the steam engine may be employed in propelling the vessel forwards or backwards, according to the direction given to the power. It is also quite absurd to attempt, with the phrenologist, to parcel out the cerebrum into distinct organs for these respective faculties, the whole of it being called into operation and acting as a unit in every kind of intellectual process which occupies the attention at the time. The empi- rical method by which Gall first lived upon certain parts of the brain as the seat of certain faculties, is exposed to the serious fallacy that a part on the surface of the brain may appear largely developed in consequence of the large size of some subjacent or neighboring part,—for example, a thick neck and large occipital region may indicate a large pons and medulla more frequently than a large cerebellum. Again, with respect to the cranium itself, large prominences just above the eyebrow's may- indicate large frontal sinuses rather than a large develop- ment of “certain organs” on. the anterior lobes of the cerebrum. Gall divided the -whole cerebrum into twenty-seven different organs to represent different facul- ties, and Spurzheim divided it into thirty-five. The determining power of the will acts both upon the body and the mind; but the only sensible effect which the strongest effort of volition can produce on the bodily frame is that of contraction of the voluntary muscles. HUMAN PHYSIOLOGY'. The immediate operation of the will is not upon the muscles, but upon the brain, in which it excites nerve foroe, which is transmitted along the nerves, and stimu- lates the muscular tissue to contraction. With refer- ence to the action of the will upon the mind, it may be said that it possesses the povTer of recalling ideas which are present in the mind, excluding some and bringing others more prominently before it. This is effected by the power of voluntary attention, which is the chief means through which the sequence of our thoughts is directed by the will. When the will is most strongly exerted, it causes the consciousness to be so completely engaged by one train,of ideas that the mind is, for the time, incapable of receiving any other idea or impression, the individual being as insensible as if he wrere in a pro- found sleep. This powder of concentration of the mind on the subject of study, is of very great importance and advantage in the acquirement of knowledge and the pur- suit of truth, and one which is capable of cultivation to a considerable extent by habitual exercise. The influence of the mind over the body is a most remarkable phenomenon, and one w7ell worthy of atten- tion. Many of its effects are quite familiar; for example, fear or great anxiety of mind produces a desire for fre- quent micturition, and not unfrequently the bowels are moved also. The announcement to the patient of the arrival of the accoucheur, suspends for a time the labor pains. The sight, or even the thought of very unpala- table medicine, produces nausea, and sometimes vomiting, Under the influence of the mind, opium pills have been known to produce catharsis, when the patient supposed that he had taken a cathartic. In this way also, persons have been much benefited, and in some instances en- tirely cured, by the simplest remedies. Much of the TEE NERVOUS SYSTEM. HUMAN PHYSIOLOGY. success of the Homoeopathist is no doubt due to this fact. In all modes of treatment, therefore, it is abso- lutely necessary to have the entire confidence of the patient. It has also been observed, that when the mind is directed to any tumor or growth of the body, its in- crease is greatly accelerated. In consequence of the waste of nerve tissue during its activity, it is necessary that a periodical suspension should take place in order to permit of nutritive regene- ration; this is called sleep. In deep sleep there is a state of complete unconsciousness, and the body may remain for a considerable time motionless ; but the indi- vidual is capable of being by external impres- sions. In this it differs from coma, which is generally the result of some pressure upon the brain, in which the patient is incapable of being aroused. The tendency to fall asleep is favored by a succession of dull, monotonous sounds, as a dull, prosy speech or sermon; or by sounds accompanied by gentle movements, as is seen in putting infants asleep. Another method is to close the eyes and fix the attention upon some object, or repeat a certain word until the mind becomes completely lost or uncon- scious. The average amount of sleep required by a healthy adult is about eight hours in twenty-four; children re- quire more. On some occasions the sleep is more or less disturbed by dreams. These generally refer to some- thing that has engaged the attention previously ; but in some instances they would appear to indicate things that are to happen; at all events, there is in many instances a singular coincidence between dreams and occurrences which follow them. An uneasy or anxious state of mind is unfavorable to sleep. It is said that criminals under sentence of death sleep badly while they have THE NERVOUS SYSTEM. 297 hopes of a reprieve, but as soon as they are assured that their death is inevitable, they usually sleep more soundly. Derangement of the digestive organs, or a disturbed state of mind, in' some instances, gives rise to a dreaming state called somnambulism. In this state the indivi- dual acts as if he were awake, and as if all the pheno- mena presented to him were real. He answers questions rationally and with readiness; he walks with precision and avoids obstacles; yet, not unfrequently, accidents happen which show that he has not full command of his senses. A state remarkably analogous to somnambulism may be induced in some persons, Avhich has been called mes- merism. The production of this state requires the apparent influence of another individual, who looks directly in the face of the person experimented upon, and makes certain movements before him called passes; or the person is required to gaze steadfastly upon a piece of metal or other substance held in the hand, until a state of unconsciousness is induced. Remarkable statements have been made, implying that in these cases the facul- ties are very much exalted, and the person acquires powers of a superhuman kind. Such statements, how- ever, are made by those interested in such seances, or by those who are ignorant of the deception resorted to in order to obtain notoriety. CRANIAL NERVES. The cranial nerves include those nerves which arise from some part of the cerebro-spinal centre and are transmitted through foramina at the base of the brain. There are nine in number on each side, and they are 298 HUMAN PHYSIOLOGY. arranged in pairs in the following order from before- backwards: 1st Olfactory 2nd Optic 3rd Motor Oculi 4th Pathetic 5th Trifacial or trigemini 6th Abducens 7th Facial or portio dura Auditory or portio mollis Glosso-pharyngeal. Pneumogastric. Spinal accessory. 8 tli 9tli Hypoglossal. They may be subdivided into four groups, according to the peculiar function of each, viz., 1st, nerves of special sense, as the olfactory, optic, auditory, the lingual branch of the trifacial, and part of the glosso-pharyngeal; 2nd, nerves of common sensation, as the greater portion of the fifth, and part of the glosso-pharyngeal; 3rd, nerves of motion, as the motor oculi, pathetic, part of the tri- facial, abducens, facial, and hypoglossal; and 4th, mixed nerves, as pneumogastric and spinal accessory. The olfactory nerves arise from the cerebrum by three roots, and present a bulbous enlargement which rests upon the cribriform plate of the ethmoid bone, from which delicate filaments are given off which supply the nose. They are the nerves of the special sense of smell. In structure they differ from the other nerves, in being soft and grayish in color, and destitute of the white* substance of Schwann. The optic nerves are distributed to the eye, in which they expand to form the internal layer of the retina, and are the nerves of the special sense of sight. Division* of the optic nerve produces total blindness and dilatation of the pupil, but does not destroy ordinary sensibility or paralyze muscular action. The auditory nerves, are the special nerves of the sense of hearing. They convey to the brain the sensa- tion of sound, and are incapable of transmitting any other, being entirely destitute of ordinary sensibility. THE NERVOUS SYSTEM. 299 The filaments are distributed to the cochlea, semicircular canals and vestibule. The motor-oculi is a nerve of motion, and is distribu- ted to all the muscles of the eyeball, except the superior oblique and external rectus. It also supplies motor fila- ments to the circular fibres of the iris. In paralysis of this nerve, the upper eyelid falls down over the eye, so that it appears half closed, the pupil is dilated, the movements of the eyeball are nearly suspended, and the eye is directed outwards, owing to the action of the external rectus. This condition of the eyelid is called ptosis. The stimulus of light on the retina produces contraction of the circular fibres of the iris and partial closure of the pupil. This is a reflex action, the stimu- lus being conveyed by the optic nerve to the brain, and thence reflected through the third nerve to the iris; con- sequently the iris ceases to act when either the optic or third nerve is divided or destroyed, or the nervous centre injured or compressed. The radiating fibres of the iris are probably supplied by filaments from the ophthalmic or ciliary ganglion. The pathetic nerve, the smallest of the cranial nerves, is also a nerve of motion distributed to the superior oblique muscle. When the nerve is irritated the muscle acts spasmodically, and its division causes paralysis and a loss of rotary motion of the eyeball on its axis, and sometimes double vision. The abducens supplies the external rectus with motor power. Irritation of this nerve produces an effect simi- lar to the preceding. Division or injury is followed by convergent strabismus. The trifacial nerve closely resembles the spinal nerves. It arises by two roots, an anterior, smaller or motor, and a posterior or sensory, which has a ganglion developed 300 HUMAN PHYSIOLOGY. on it. The functions of this nerve are various; it is the great sensitive nerve of the head and face; the motor nerve of the muscles of mastication (except the bucci- nator), and its largest branch is one of the nerves of the special sense of taste. This nerve, within the cranium, is divided into three branches—the ophthalmic, which passes through the sphenoidal fissure, the superior max- illary, which passes through the foramen rotundum, and the inferior maxillary, which passes through the foramen ovale. The first and second divisions are purely sensi- tive; the third division contains filaments of special sense, sensation and motion. It is the most intensely sensitive nerve in the body; its irritation is followed by intense pain. Any irritation to this nerve, or any of its branches, as e. g., a carious tooth, may give rise to neural- gia of the corresponding side of the face, and in many instances one-half of the tongue is found covered with a white fur, while the other half is perfectly clean. Divi- sion of the fifth nerve produces loss of sensibility, and motion in the parts supplied by it, and is followed by inflammation of the corresponding eye, which usually goes on to complete and permanent destruction, and sloughing of the organ. Injury to the fifth nerve, or some of its branches, is sometimes followed by total blindness in the corresponding eye. The blindness is probably the result of defective nutrition to the retina. Paralysis of the third nerve may also follow neuralgia of the fifth nerve. The facial nerve supplies all the muscles of the face, the platysma, buccinator, the muscles of the external ear, digastric and stylo-hyoid, the palate, lingualis, sta- pedius, and laxator tympani muscles. It is a nerve of motion, and not of sensation, and therefore its division, which was formerly resorted to in cases of tic doloureux, THE NERVOUS SYSTEM. 301 is incapable of relieving neuralgic pains, but is followed by paralysis of the muscles which it supplies. Division or paralysis of the facial nerve also prevents the eye from being closed, and its continued exposure to the air, and particles of dust, is apt to produce inflammation. The sense of hearing and taste may also be impaired. In facial paralysis there is an absence of expression on the affected side, the angle of the mouth is lower, and the eye has an unmeaning stare. In drinking, the fluids flow out at the corner of the mouth, and the food lodges between the cheek and gums. When the tongue is protruded it is drawn to the sound side, in consequence of the paralysis of the muscles on the affected side. The glosso-pharyngeal nerve is distributed to the tongue and pharynx, being the nerve of sensation to the mucous membrane of the pharynx, the fauces and tonsil; of motion to the pharyngeal muscles, and a special nerve of taste to the posterior part of the tongue. The tongue is therefore supplied by two special nerves—the lingual branch of the fifth, and the glosso-pharyngeal; the former supplies the anterior and lateral parts of the superior surface, and the latter the posterior and lateral parts. This may be proved by division of either of these nerves, when the sense of taste is lost in the part supplied by the injured nerva The hypoglossal nerve is a nerve of motion, and is distributed to the muscles which belong to the hyoid bone and tongue. Irritation of this nerve produces muscular contraction, and is sometimes attended with pain, the sensibility having been borrowed from the nerves with which it communicates. The pneumogastric nerve is one of the most remark- able and important in the body. It supplies the larynx, pharynx, oesophagus, heart, lungs, stomach and liver. It 302 HUMAN PHYSIOLOGY. possesses motor, sensitive and sympathetic or ganglionic nerve fibres, and is therefore regarded as a triple-mixed nerve. The pharyngeal branch supplies the muscles of the pharynx; the superior laryngeal is chiefly sensitive, and supplies the mucous membrane ; the inferior is for the most part motor, and supplies the muscles; the branches to the oesophagus supply its muscular tissue; the cardiac branches constitute a channel through which the influence of the central organs and the emotions of the mind are transmitted to the heart; the pulmonary branches form a channel through which the impressions on the lungs are conveyed to the medulla oblongata ; the motor filaments of the pneumogastric nerve supply the motor influence by which the function of deglutition is performed. In the functions of the larynx, the sensi- tive filaments supply that acute sensibility by which the glottis is guarded against the ingress of foreign bodies or irrespirable gases. These are instances of “ reflex action.” Division of the pneumogastric nerves is at once fol- lowed by a diminution of the frequency of the respiratory movements. In young animals it is often quickly fatal, owing to the closure of the glottis, which is due to the yielding nature of the cartilages; but in older animals death ensues more slowly, owing to the rigidity of the cartilages which surround the glottis. Death takes place in from one to six days after the operation, and is caused by the engorgement of the lungs. They are commonly very much congested, nearly solid, and the bronchial tubes are filled with a frothy, bloody fluid and mucus. This is due in part to the slowness of the respi- ratory movements, the imperfect aeration of the blood, and the accumulation of carbonic acid in the air cells, and also in part to the paralysis of the blood-vessels THE NERVOUS SYSTEM. 303 themselves. Sjnee respiration is still carried on after division of the pneumogastric nerves, it is evident that though they are the chief agents by which the respira- tory stimulus is conveyed to the medulla oblongata, they are not the only ones. The sensations of hunger and thirst still remain, and the secretion of gastric juice continues after division of the pneumogastric nerve; but the digestive function is more or less disturbed in various ways. In many instances the food taken by the animal never reaches the stomach owing to the paralysis of the oesophagus, but is regurgitated in a few moments afterwards^—this action being excited by the influence of the sympathetic nerves. The muscular coat of the stomach is also para- lyzed by section of this nerve. Division of the pneumogastric nerve also interferes with the proper function of the liver, and aziy irritation in the course of the nerve is followed by the rapid devel- opment of sugar in this organ. The spinal accessmaj nerve arises partly from the medulla oblongata, and partly from the spinal cord. It is essentially a motor nerve; but it also con- tains sensitive fibres, and is connected with the gang- lion of the pneumogastric. From these circumstances it may be regarded as a mixed nerve. It supplies the sterno-mastoid and trapezius muscles, and it is also con- nected with the vocal movements of the glottis. If the spinal accessory nerve be divided on both sides, or its branch of communication with the pneumogastric nerve, the voice is instantly lost, the animal being incapable of uttering a single sound. It may be stated as a general law, that when any part of the body receives nervous filaments from two different sources, it is for the pur- pose of enabling it to perform two different functions. This is exemplified in the muscles of the larynx. These muscles are concerned in the respiratary movements, the nervous stimulus for which is conveyed by the facial, hypoglossal, and pneumogastric nerves; but they are also concerned in the formation of the voice, the nervous influence for which is conveyed by the spinal accessory. HUMAN PHYSIOLOGY. SYMPATHETIC SYSTEM. The sympathetic system consists of a series of gang- lia connected together by intervening cords extending on each side of the spinal column from the base of the skull to the coccyx; some of the ganglia may also be traced into the cranium. These two gangliated cords lie parallel with one another as far as the coccyx, where they communicate through a single ganglion—ganglion impar. It is also stated that they communicate at their cephalic extremity through a small ganglion, situated on the anterior communicating artery—the ganglion of Eibes. They are arranged as follows:—In the cephalic re- gion there are four ganglia on each side (and the gang- lion of Eibes); in the cervical region, three; in the dorsal region, twelve; in the lumbar region, four; in the sacral region, five; and in the coccygeal region, one—the ganglion impar. Each ganglion may be regarded as a distinct centre from or to which branches pass in various directions, as follows:—1st, communicating branches be- tween the ganglia; 2nd, communicating branches to the cerebral or spinal nerves; 3rd, primary branches of dis- tribution to the arteries in the vicinity of the ganglia, to the viscera, or to other ganglia in the thorax, abdo- men, or pelvis. The latter consist of two kinds of nerves, the sympathetic and spinal, and have a remark- able tendency to form intricate plexuses which surround the blood-vessels, being conducted by them to the vis- THE NERVOUS SYSTEM. 305 cera. Many of these primary branches, however, pass to a series of ganglia in the thorax and abdomen, the chief of which are the cardiac and semilunar ganglia. It was named the sympathetic system, because it was thought that through it was carried the several sympa- thies in morbid action which distant organs manifest. The sympathetic system is endowed with sensibility and the power of exciting motion; but in the exercise of these functions it is less active than the cerebro-spinal system. When irritation is applied to a sensitive nerve in one of the extremities, the evidence of pain or motion is acute and instantaneous; while, on the other hand, irritation to the sympathetic nerve is felt distinctly enough, but is only responded to after somewhat pro- longed application. This comports very much with what is known of these organs, supplied chiefly by the sympa- thetic. system, e.g., the movements of the stomach and intestines are not felt under ordinary circumstances; but any excessive or prolonged irritation may cause them to become exceedingly painful. The ganglia of the sympathetic system are regarded by some writers as reservoirs of nervous force, which they equalize and correctly balance, by storing up all transi- ent excesses it, and furnishing all transient deficien- cies. Complex as the whole sympathetic system .appears, however, each of its parts exhibits a wonderful simplicity; for each ganglion with its afferent and effer- ent nerves forms a simple nervous system, and might serve for the illustration of all the nervous actions with which the mind is unconnected. The general processes which the sympathetic system appears to influence are those of involuntary motion, secretion, and nutrition. Parts supplied with sympa- thetic nerves are usually capable of only involuntary 306 HUMAN PHYSIOLOGY. movements, as, c.g., the heart, stomach, and intestines, and these parts may still continue to move for a short time after the death of the animal. Thus, in the mam- malia the heart continues to heat for one or two minutes after it is taken from the body; in reptiles and amphibia, for hours; and the peristaltic action of the bowels con- tinues under the same circumstances. Division of the sympathetic nerve produces imme- diately a vascular congestion in the parts supplied by it. This was first pointed out by Bernard; he divided the sympathetic nerve of a rabbit in the middle of the neck, and he found that congestion of the corresponding side of the head immediately followed, which was most dis- tinctly marked in the ears, and the venous blood return- ing from the part had a ruddy hue. The pupil is also contracted and the eye partially closed, owing to the in- creased sensibility of the retina from vascular congestion of the parts. The congestion appears to be caused by the dilatation of the vessels and consequent increased rapidity of the circulation, for when any irritation is applied to the divided end of the nerve, the vessels con- tract and the congestion disappears. The vessels there- fore appear to be under the influence of sympathetic nerves, which accompany them in all their varied distri- butions and minute ramifications. They supply the muscular coat of the vessels, the function of which is to regulate the supply of blood to the various organs. The congestion of the vessels caused by division of the sympathetic nerve is also accompanied by an elevation of temperature in the affected part; this increase of heat has been found as high as 8° to 9°F., and like the vascu- lar congestion, to which it is due, may last a consider- able length of time. THE XERV0U3 SYSTEM. AYitli reference to the influence of the sympathetic nerve in the processes of secretion and nutrition, little is known except that it is in great measure connected with the supply of blood to the parts. It serves as a medium of reflex action between the sensitive and motor poitions of the digestive, excretory and generative organs, and it also takes part in reflex actions which may be referred to the cerebro-spinal system; for exam- ple, the contact of food in the intestine excites, through the medium of the sympathetic nerves, a peristaltic movement in the muscular coat. The irritation pro- duced by undigested food in the alimentary canal may give rise to diarrhoea, or it may produce, through the medium of the sympathetic and cerebro-spinal systems, epileptic convulsions, especially in children. CHAPTER XIY. THE SPECIAL SENSES. The special senses are five in number, smell, sight, hearing, taste, and touch. The last two have been already casually referred to. Smell.—The sense of smell is limited to the nasal cavity, and is confined to that portion on which the olfactory* nerves are distributed, viz., the roof, the septum, and the upper part of the lateral walls. The nasal cavity is lined by mucous membrane, called also the pituitary or Schneiderian membrane; it is lined by columnar ciliated epithelium, except in the upper part and the roof, in which they are non-ciliated. The fila- ments of the olfactory nerves pass through the foramina in the cribriform plate of the ethmoid bone, and are dis- tributed beneath the mucous membrane; they convey the sensitive impressions made by the odoriferous par- ticles upon the mucous membrane to the sensoriuiu, which give rise to the sense of smell. The sense of smell is confined to the olfactory nerves, as has been shown by their division, after which the sense of smell was completely lost, while sensibility still remained, and their irritation .is not followed by any muscular action, either of a direct or reflex character. The sense of smell may be impaired by division of the fifth nerve, or some of its branches, which supply the nose. It cannot be inferred from this, however, that it is a nerve of the special sense of smell; the re- sult is to be attributed to the dry and otherwise deranged THE SrECIAL SENSES. 309 state of the mucous membrane, occasioned by the al- tered nutrition of the parts. The meatuses and sinuosities of the nasal cavities are well adapted not only to increase the extent of mucous surface, but also to impede the air and odoriferous par- ticles which it may contain, in their passage through them, so as to bring them into more immediate contact with the mucous surface, by means of which their pecu- liar characters are more fully impressed on the olfactory nerves. The frontal sinuses are supposed to assist in the exten- sion of the sense of smell; but since they do not receive filaments from the olfactory nerves, and are largely devel- oped in some animals, as the grey-hound, in which the sense of smell is by no means acute, it is highly improba- ble. The sense of smell varies much in different individuals, and, like all the senses, may be improved by frequent practice. But the sense of smell may become blunted by long-continued exposure to one kind of smell, as, for example, the effluvia of the dissecting room. Various odors also affect it differently, as musk, asafcetida; and some produce nausea and even fainting. The irritation produced by the contact of substances which act mechanically or chemically on the mucous membrane, as ammonia, nitrous acid, &c., must not be confounded with the sense of smelling. These impressions are conveyed to the sensorium by the fifth nerve, which is the nerve of sensation. The sense of smell may be impaired or destroyed by the obstruction of the air passages, as in the case of polypi; by chronic inflam- mation, as catarrh, ozscna, &c.; by the frequent use of snuff, &c., which tends to blunt its acuteness and cover the surface with its particles. Besides the olfactory and fifth nerve, there are some HUMAN PHYSIOLOGY. filaments from the spheno-palatine ganglion distributed to the nose. The function of these is not very well known; but from the connection with the fifth nerve and the sympathy between the senses of smell and taste, they are probably nerves of associate function. SIGHT. The eye is the organ of the special sense of sight, and is situated in the cavity of the orbit. It is spheri- cal in form, having the segment of a smaller and more prominent sphere engrafted on its anterior stirface. It measures about an inch in the antero-posterior diameter, and a little less transversely. It consists of three coats; an outer, consisting of the sclerotic and cornea; a middle, consisting of the choroid coat, ciliary processes, and iris; and an internal, the retina; and three refracting media — the aqueous humor, the vitreous humor, and the crystalline lens and capsule. The sclerotic is a dense, fibrous membrane, which covers the posterior five-sixths of the eye, and is con- tinuous in front with the cornea, and behind with the sheath of the optic nerve, which is derived from the dura mater. Behind, it is pierced, a little to its nasal side, by the optic nerve, around which are openings for the passage of the ciliary vessels and nerves. The cornea projects forwards, somewhat resembling a watch-glass, and covers the anterior sixth of the globe. It is concavo-convex, the degree of curvature varying in different individuals, and in the same individual at dif- ferent periods of life, being generally more prominent in youth than in advanced life. This difference in the curvature influences considerably the refractive power of the eye, and is the principal cause of long and short- sightedness. The cornea, in health, is perfectly transpa- THE SPECIAL SENSES. 311 rent, and consists of five layers,—the cornea proper, a central fibrous structure; in front of this, the anterior elastic lamina, covered by the conjunctiva; behind, the posterior elastic lamina, covered by the lining mem- brane of the anterior chamber of the eyeball. The choroid is a thin, highly vascular membrane, of a dark color, which covers the posterior five-sixths of the globe, and is situated between the sclerotic and retina. It is pierced behind by the optic nerve and terminates in front of the ciliary ligament, where it bends inwards and forms the ciliary processes. It is composed of three layers,—the external, which consists of the larger brandies of the ciliary arteries, but chiefly the veins and some star-shaped pigment cells; the middle, which con- sists of a fine capillary plexus (tunica Kuyschiani); and the internal or 'pigmentary layer, which is made up of a single layer of hexagonal cells, loaded with pigment granules, so arranged as to resemble tesselated epithe- lium. In perfect albinoes the cells contain no pigment. The ciliary processes are formed by the folding in- wards of the middle and internal layers of the choroid around the margin of the lens, behind the iris. They vary in number from sixty to eighty, and are about one- tenth of an inch in length. They are similar in structure to the corresponding layers of the choroid. The iris (zpzS, a rainbow) is a thin, circular-shaped contractile curtain, suspended in the aqueous humor behind the cornea and in front of the lens, and present- ing, at the nasal side of its centre, a circular opening, the pupil, for the transmission of light. It separates the cavity for the aqueous humor into two parts, the ante- rior and posterior chambers. It consists of muscular tissue, fibrous tissue, and pigment cells. The muscular tissue consists of circular fibres which surround the 312 HUMAN PHYSIOLOGY. pupil, and radiating fibres which converge from the circumference of the iris to the margin of the pupil; the former contract the pupil, the latter dilate it. (See motor oculi.) The fibrous tissue forms a delicate mesh in which the pigment cells, vessels and nerves are con- tained. The pigment cells are found in the stroma, and also as a distinct layer on the anterior surface. On the posterior surface of the iris there are several layers of round cells filled with pigment granules. These are called the uvea, from their resemblance in color to a ripe grape. The iris is connected to the choroid and to the external coat of the eyeball at the junction of the scle- rotic and cornea, by means of a circular band of white fibrous tissue, the ciliary ligament. The middle coat of the eye is also connected to the external by means of a circular band of nonstriated muscular tissue, the ciliary muscle. It is about one- eighth of an inch broad, thicker in front than behind, and is attached anteriorly, or arises at the point of junction of the sclerotic and cornea, and passing back- wards is inserted into the choroid in front of the retina. By its action it draws the ciliary processes towards the line of junction of the sclerotic and cornea, and com- presses the vitreous humor which pushes forward the lens, and in this way adjusts the eye to the vision of near objects. The retina is the delicate nervous membrane upon the surface of which the images of external objects are received. Behind, it is continuous with the optic nerve; in front it terminates by a serrated margin, the ora ser- rata; its inner surface is in contact with the hyaloid membrane which surrounds the vitreous humor; exter- nally it is in relation with the choroid. In the centre of the posterior part, corresponding to the axis of THE SPECIAL SENSES. 313 the eye, is seen a round, yellowish spot called the limbeus luteus, or the yellow spot of Sommering. The retina in this part is very thin, and the sense of vision is most perfect. About one-tenth of an inch to the inner side of this spot is seen the entrance of the optic nerve; here the power of vision is entirely absent. The retina is composed of three layers, together with blood-vessels and areolar tissue; the external or columnar, consisting of solid columnar rod-like bodies, with hollow cones interspersed at regular intervals; the middle or granular layer, consisting of two laminae of rounded particles, the outer globular, the inner flattened, and look- ing like pieces of money seen edgeways, called the nummular layer; the internal or nervous layer, consisting of an expansion of the terminal fibres of the optic nsive and the nerve cells. The aqueous humor occupies the anterior part of the globe, and completely fills the anterior and posterior chambers of the eye. It is a clear, thin fluid, having an alkaline reaction, which is due to the presence of chloride of sodium. In the adult, the anterior and posterior chambers communicate through the pupil; but in the foetus, before the seventh month, the pupil is closed by the membrana pupillaris. The persistence of this mem- brane sometimes occasions congenital blindness. The vitreous humeri' occupies the posterior four-fifths of the globe. It is perfectly transparent; of the consis- tence of jelly, and is surrounded by the hyaloid mem- brane. It is hollowed out in front for the reception of the crystalline lens. The vityeous humor contains some salts and a little albumen. In the foetus, a minute artery passes through the centre to the posterior part of the capsule of the lens, but it disappears in the adult. The crystalline lens, enclosed in its capsule, is situated HUMAN PHYSIOLOGY. in front of the vitreous humor and behind the pupil. The capsule is a transparent brittle membrane, highly elastic, and is disposed to curl inwards upon itself when ruptured. It surrounds the lens, to which it is connected by a layer of nucleated cells, and is held in position by the suspensory ligament, which connects it to the anterior margin of the retina. The suspensory ligament consists of two layers blended together; the outer, a milky, granular layer, comes in contact with the inner surface of the ciliary processes; the inner, is an elastic transpa- rent membrane. This ligament forms part of the boundary of the posterior chamber of the eye ; its poste- rior surface is separated from the hyaloid membrane by a triangular interval—the canal of Petit. This canal is about one-tentli of an inch wide, bounded in front by the suspensory ligament, behind by the hyaloid membrane, and the base is formed by the capsule of the lens. The lens itself is a transparent double convex body, being more convex behind than in front. It measures about four lines transversely and three lines from before backwards. It appears to consist of concentric laminae., like the coats of an onion, the central ones forming a hardened nucleus. It also appears to consist of three triangular segments; this is readily demonstrated by boiling or immersing it in alcohol. There are therefore two forms of the lens in the human eye,'viz., the concavo-convex or meniscus, as the cornea; and the double-convex, as the crystalline lens. The essential parts of the eye, then, appear to be: 1st, a dark coat to absorb thQ rays of light—the choroid; 2nd, a nervous expansion to receive and transmit to the brain the impression of light—the retina; 3rd, a concavo- convex lens to collect the rays of light from the object and direct them inwards, and a double convex lens to THE SPECIAL SENSES. collect the rays of light and bring them to a focus, so as to form a correct image on the retina—the cornea and lens; 4th, a contractile curtain with a central opening, to regulate the quantity of light entering the eye—the iris. The eye is thus a simple optical instrument, en- dowed with vitality, and acting as required without assistance. Phenomena of Vision.—In order fully to under- stand the physiology of vision, it will be necessary to refer briefly to some of the laws which regulate the transmission of light. 1st,—light travels in parallel rays through a me- dium of uniform density. 2nd,—When the rays meet with a medium of in- creased density, they become refracted, or changed in direction, towards a line which falls perpendicularly to the surface of the body which they enter. 3rd,—When the rays of light meet with a medium of diminished density, they are refracted from the per- pendicular line. 4th,—When the rays of light fall upon a convex lens, they are collected; and if this be a double convex body, they come to a point or focus at a certain distance, depending on the greater or lesser convexity of the lens; the greater the convexity the shorter the distance, and vice versa. The image formed by the refraction of the rays of light in coming to a point or focus will be an inverted one. Those rays which pass through the lens towards its circumference come to a focus earlier than those that pass through the central axis, and thus a cer- tain amount of spherical aberration is produced. 5tli,—If the convexity of the lens be too great, the focus will be formed in front of the mirror or reflecting body. If too slight, the focus will be formed beyond it. 316 HUMAN PHYSIOLOGY. Vision is accomplished by the formation of an image of the object looked upon, on the internal surface of the retina. The impression made upon this produces a sen- sation, which is conveyed to the sensorium by the optic nerve, and the mind takes cognizance of it. The image is formed in the following manner:—The rays of light are reflected from the object, and impinge on the outer convex surface of the cornea, through which they pass, becoming refracted towards the perpendicular. Those which fall on the circumference of the cornea im- pinge upon the iris, and are reflected, showing the color of this structure; those which pass nearer its centre, converge and enter the pupil. They now penetrate the crystalline lens, by means of which they are still further converged, their convergence being completed by their passage through the vitreous humor, and are brought to a focus on the inner surface of the retina. Since rays of light come from all points of the object, and are re- fracted in their passage, they must cross each other, and thus the image of the object on the retina will be in- verted. The angle of crossing is called the visual angle. The inversion of the image may be shown by means of an eye of a recently killed animal, on which the image is distinctly formed in an inverted position. The inver- sion of the image is corrected by the sensorium. When there is too great a degree of curvature of the cornea and lens, or of either of them, the rays of light are brought to a focus before they reach the retina, and the image is unseen. This condition is called myopia, or near-sightedness, and is most common in early life. On the other hand, if either or both of these bodies are preternaturally flattened, the rays of light are brought to a focus beyond the retina, as it were, and the image is imperfect; this is called presbyopia, or farsightedness, and is more common as age advances. Both these con- ditions may be corrected by the use of artificial lenses, which supply the natural defect. Accommodation of the Eye to Vision.—It is quite evident that some arrangement of the refractive parts of the eye is necessary to adapt it to the vision, of near and distant objects. The precise manner in which this accommodation is effected is a disputed point; some maintain that it is due to an alteration in the position of the lens; while others regard it as being due botl; to an alteration in the shape and position of the lens. The eye, in its normal state, is accommodated for distant vision under the guidance of the recti muscles; this may be called its 'passive condition. The active accommoda- tion of the eye for the vision of near objects is caused by the advance of the crystalline lens towards the cor- nea, and probably, also, by its increased convexity. It is advanced towards the cornea chiefly by the action of the ciliary muscle and partly by the compression exer- cised upon the posterior three-fourths of the eyeball by the recti muscles. It may therefore be inferred that the recti muscles adapt and adjust the eye for ordinary vision; while the ciliary muscle may be regarded as the fine adjuster, which regulates the eye for the vision of near or very small objects. The formation of distinct and correct images on the retina is favoured by the action of the pupil, which pre- vents the rays of light from passing through any part of the lens but its centre, and thus preventing any ten- dency to spherical aberration. It is also further secured by the black coating of pigment on the inner surface of the choroid, which absorbs any rays of light which may be reflected within the eye, and prevents them being THE SPECIAL SENSES. thrown back again upon the retina, so as to produce dazzling of the image there formed. The eye, in the uneducated state, cannot comprehend the properties of the objects seen, as color, form, &c., or the distance of the object; this is acquired by experience. Impressions once produced on the retina remain for a short time afterwards; their duration depends on the intensity of the impression they have left; a momentary impression of moderate intensity continues about one- eiglith of a second. This is the reason why the act of winking does not interfere with the continuous vision of surrounding objects. There is in front of the eye a cer- tain space within which objects are perceived, and be- yond which nothing can be distinctly seen ; this is called the circle of vision. For example, if the eye is intently fixed upon one word in the middle of the page, this, word and those that immediately surround it, which are in the circle of vision, are distinctly visible, while those at the circumference are imperceptible while the eye remains fixed. Simultaneous action of the two eyes.—Although an image of the object is formed on each retina, yet the impression of the object conveyed to the mind is single. This is, no doubt, owing to the fact that the image is formed on identical points of both retinae, giving rise to but one sensation, and the perception of a single image— the result of a mental act. This unity of action may be favoured by the continuation of the optic filaments across the part of the chiasma of the optic nerve, but is not dependent on it; for, if the visual axis of one eye be altered, objects are seen double. This may be demonstrated by pressing the eyeball on one side with the finger in order to rotate it upon its axis, while the eyes are fixed upon some object, as a book or lamp. HUMAN PHYSIOLOGY. THE SPECIAL SENSES. 319 The ear is the organ of hearing, and is composed of three portions, the external, middle and internal ear. The external ear consists of an expanded portion, the pinna, and the meatus auditorius externus, or canal. Its use is to collect the vibrations of the air, and conduct them to the membrana tympani, or drum of the ear. This structure separates the external from the middle ear. The middle ear or tympanum is situated in the petrous portion of the temporal bone, between the membrana tympani externally, and the internal ear or labyrinth in- ternally. It is filled with air, and communicates with the pharynx through the eustachian tube. It is crossed by a chain of movable bones, which receives the im- pressions from the membrana tympani, and serves to transmit them to the internal ear, upon which the audi- tory nerve is distributed. The bones of the ear are the malleus, incus, and stapes; the handle of the malleus is received between the inner and middle layers of the membrana tympani, and the stapes is implanted in the fenestra ovalis. The internal ear or labyrinth consists of the cochlea, semicircular canals, and vestibule. It consists of a series of cavities hollowed out of the petrous portion of the tem- poral bone, communicating externally with the middle ear through the fenestra ovalis and fenestra rotunda, and internally with the cranial cavity through the meatus auditorius internus, which transmits the auditory nerve. Within the osseous labyrinth is contained the mem- branous labyrinth upon which is distributed the fila- ments of the auditory nerve. The membranous labyrinth is filled with a transparent fluid, and is the essential part of the organ of hearing. HEARING. 320 HUMAN PHYSIOLOGY. Sounds are produced from vibrations of the external atmosphere, which are collected by the external ear and transmitted to the membrana tympani. They are here modified by the tense or lax state of this membrane, produced by the action of the laxator and tensor tympani muscles. The modified vibrations from the membrana tympani are thence conducted along the chain of bones, and through them transmitted to the auditory nerve which is distributed to the labyrinth. The auditory nerve receives the impressions, and conveys them to the sensorium. From various experiments which have been performed, it appears that tension of the membrana tympani is unfavorable generally to the propagation of sounds, especially those of a low pitch. This may be shown by making a continuous effort of expiration or of inspiration, while the mouth and nostrils are closed by the hand. The effort of expiration causes the air to be forced into the tympanum through the eustachian tube, the membrana tympani is made to bulge out and become tense, and the hearing is indistinct. The effort of inspi- ration exhausts the air from the cavity of the tympanum, and the pressure from without causes the membrana tympani to bulge inwards and become tense, and is fol- lowed by temporary deafness. The action of the chain of bones, as conductors, is enhanced by the presence of air in the cavity of the tympanum. It serves to isolate the bones so as to pro- pagate the vibrations with concentrated intensity, and prevent the dispersion of sound. The air is supplied through the eustachian tube, which communicates with the pharynx just behind the posterior nares. When persons are listening very intently, the mouth is usually partly open, in order to allow a free current of air to pass through the eustachian tube. THE SPECIAL SENSES. 321 The vestibular 'portion of the membranous labyrinth would appear, from its persistence in the lower animals, to he the essential part of the organ of hearing. It con- tains a fluid through which the impressions are finally communicated to the auditory nerve. A fluid substance seems best adapted to convey the impressions, in conse- quence of the soft condition of the structure of the nerve itself. Any irritation or excitement of the auditory nerve, as congestion, cerebral disease, &c., may give rise to ringing or buzzing sounds in the ears. They are called subjective sounds, because they are produced by internal causes. The sense of hearing- varies much in different indivi- duals, and in the same individual at different times; some will discern the most delicate sounds without the least difficulty, whilst others are wholly incapable of receiving similar impressions. Hearing may be impaired by a preternaturally dry state of the membrana tympani, or the partial closure of the external meatus by collec- tions of wax, particles of dust, &c. In some of the lower animals the sense of hearing is very acute. CHAPTER XV. VOICE. The organ of voice is the larynx, which is situated at the upper part of the air passages. It is in this organ that the sounds are originally produced; hut they may he modified during and after their production, constituting, in man, the faculty of speech. The larynx, in man, is situated between the trachea and base of the tongue, at the upper and anterior part of the neck; it is narrow and cylindrical below, but is wide and triangular at the upper part. It is composed of cartilages, held together by ligaments, moved by numerous muscles, and is lined by mucous membrane. The upper part of the larynx presents a triangular-shaped orifice, wider in front than behind—the glottis. This opening is guarded by the epiglottis, which is situated in front, between the opening and the root of the tongue. The epiglottis closes the orifice during the passage of food or fluids, and prevents their passage into the larynx. Within the cavity of the larynx, on each lateral wall, may be seen two elevated bands, the superior and inferior vocal cords, separated by an elliptical depression—the ventricle of the larynx. Of the two vocal cords, the inferior consists of a band of yellow elastic tissue, covered by mucous membrane, and is called the true vocal cord; while the superior, wfiich is formed entirely by a folding of the mucous membrane, is called the false vocal cord, because it is not concerned in the production of the voice. The interval between the true vocal cords in the me- dian line is called the rima glottulis, or chink of the VOICE. glottis, the narrowing or widening of which, and the ten- sion or laxity of the cords, produce those variations of sound which are characteristic of the human voice. The narrower the opening and the tenser the cords, cccteris paribus, the higher the pitch of the note. The tension of the vocal cords and the size of the aperture are regu- lated by muscles which are situated in the larynx. It has been proved by observations on the living subject, as well as by experiments on the larynx of the dead body, that the sound of the voice is caused by the vibration produced by the currents of expired air passing over the margins of the true vocal cords. For example, if a free opening be made in the trachea, the sound of the voice ceases, but returns as soon as the opening is closed. Again, distinct vocal sounds may be produced in the dead subject by forcing a current of air through the larynx, and this will occur even when all the struc- tures above the vocal cords are removed. The compass of the voice varies from one to three octaves, and some singers may even exceed three octaves. Before puberty, the pitch of the male and female voice is nearly the same; but at this period the larynx under- goes certain changes, during which the voice is said to “crack,” and the pitch falls about one octave. This change does not take place in eunuchs, and they retain the puerile character of voice. The different pitch of the male and female voice depends on the different length of the vocal cords in the two sexes. There are two kinds of male voice, the bass and tenor, and also two kinds of female voice, the contralto and soprano, all differing from each other in tone. The bass voice reaches lower than the tenor, and its strength lies in the low notes; while the soprano reaches the highest in the scale. The essential distinction between the different voices, however, con- 324 HUMAN PHYSIOLOGY. sists in the tone which distinguishes them when they are singing the same note. Most persons have the power of modulating their voices through a double series of notes of different characters, viz.: the notes of the natural voice, or chest notes, and the falsetto notes. The former are produced by the ordinary vibrations of the vocal cords ; the latter, in all probability, by the vibra- tion of only the inner border of the vocal cords. The voice is principally used in man in the formation of speech. The tone of the speech depends much upon the state of the chordae vocales, and the development of the larynx; but articulation, or modification of the sounds, is effected by the lips, teeth, mouth, tongue, fauces and nose. The sounds produced in speech, or articulate sounds, are commonly divided into vowels and consonants; the former are sounded by the larynx, while the latter are produced by the interruption of the current of air above the larynx. All vowel sounds can be expressed in a whisper, without vocal tone—mutely. The consonants cannot be sounded except consonantly with a vowel, hence the name. Ventriloquism appears to consist in the varied modi- fication of the sounds produced in the larynx, so as to imitate the voice as heard from a distance. It is accom- plished by taking a full inspiration, then keeping the muscles of the neck and chest fixed, and speaking with the mouth almost closed and the lips motionless, while air is slowly expired through a narrow glottis, care being taken that none of the expired air passes through the nose. The attention of the audience is at the same time gene- rally directed to that part of the room from which the sound is expected, a circumstance which adds materially to the success of the performance. Stammering, in most instances, is an affection of the VOICE. 325 nervous system, and not of the articulating organs. It consists in an imperfect power of co-ordinating the muscles of speech, associated with a spasmodic action of certain muscles concerned in the formation of the voice. Some stammer only on attempting to articulate certain letters; others do so at every attempt to speak. It is much increased by any mental excitement, surprise, &c. Females seldom stammer, although more subject to nervous disorders generally than males. The cure of stammering is best effected by training the muscles in the production of the sounds most easily formed, and thence proceeding to the most difficult; to avoid all causes of excitement to the patient, and prevent him from thinking about his condition as much as possible. Some have recommended the use of pebbles in the mouth, or small pieces of ivory; but it is very doubtful whether or not these can be of any great service. CHAPTER XVI. REPRODUCTION. Tiie process of reproduction comprises the several provisions made for the multiplication of individuals and the propagation of the species. There are three modes by which the multiplication of individuals takes place in the lower orders of organized beings, while in the higher forms it is restricted to one of these types. The first and simplest mode consists in the division of the being into two, each of these again subdividing into two others, and so on. This is multiplication by subdivi- sion; or, fissiparous multiplication. It is seen in the lowest plants, as in the cells of fungi and lichens, and also in cartilage cells. The joints of the common tape-worm multiply in this manner. Some organizations, as the polyp, when divided artificially into segments, have the power of developing into a perfect form from each segment. The second mode takes place by a process of gemma- tion, or budding from the parent stalk. These buds, which consist of a mass of cells, are at first entirely nourished by the parent stalk, but gradually become less dependent, and at last detach themselves and maintain a separate existence. This is termed multipli- cation by gemmation or gemmiparous multiplication The hydra affords a good example of this variety. The first change which is observed is a slight elevation on the surface, which assumes a globular form; a cavity is then formed in the interior, which communicates REPRODUCTION. with the parent. After a time this channel of com- munication closes, the newly-formed polyp drops off, and a new creature is formed. The third mode is called true generation, and consists in the union of the contents of two different cells, the sperm cell and the germ cell, from which is produced a new being differing from both. The simplest form of this process is seen in the Algae in conjugation. At first the opposite cells of two filaments form a process on the sides next each other; these at length meet and fuse, the contents of the two cells becoming mixed and form- ing a new body termed a spore or sporangium, from which the new plant is formed. In the higher plants and animals distinct organs are set apart for the formation of the sperm cells and germ cells; the former are produced by the male organs of generation; the latter by the female. Through the action of the contents of the sperm cell the ovum be- comes impregnated, and an embryo is formed from which the adult animal is gradually developed. In some instances, however, as in the class of insects, several distinct changes or metamorphoses are passed through before the animal is fully developed, as the larva, chry- salis, and perfect animal. In other instances the embryo, instead of being developed into the perfect animal, only attains a sort of larval condition, and there may be several series of these imperfect or larval forms, each larva producing other larvae, until at last they give rise to perfect forms, which propagate only by the produc- tion of ova. This is called by Prof. Owen metagenesis and parthenogensis. Action of the Male.—The male furnishes the spermatic fluid or sperm, which is secreted by the testes. This fluid contains the sperm cells in which are developed HUMAN PHTSIOLOGT. the spermatozoa. These are the essential elements of the spermatic fluid, and are set free by the breaking down of the parent cell. They are transparent filament- ous bodies, about of an inch in length, and from Woo to to3oo of an inch in thickness, being thicker at the anterior extremity or head than the posterior or tail. Their movement is accomplished by the constant vibra- tion of the tail; they are said to move at the rate of one inch in seven and one-half minutes. Their movements may be suspended, and their power of impregnation destroyed by the action of solutions which act chemi- cally upon them, as solution of nitrate of silver, sulphate of zinc, chloride of zinc, &c. In the female organs of generation the movements continue longer than in any other situation. In the act of coition the seminal fluid is deposited in the vagina, and the spermatozoa make their way into the uterus and meet the ovum at or soon after its dis- charge from the ovary. The fecundation of the egg may take place either in the uterus, fallopian tube or ovary, in each of which situations spermatozoa have been found after coition. The high degree of nervous excitement which attends the act of coition is followed by a correspond- ing amount of depression, and the too frequent repetition of it is very injurious to the general health. This is still more the case with that solitary vice which it is to be feared is practised by too many youths. Nothing is more certain to reduce the powers both of body and mind than excesses in this respect. Action of the Female.—The essential parts of the female organs of generation, and counterpart of the testes, are the ovaries, in which the ova are developed. The ovary is partially invested by peritoneum, beneath which is the proper covering of the organ—the tunica albuginea REPRODUCTION. 329 —which is a dense, firm membrane, enclosing a highly vascular fibrous structure—the stroma. In the meshes of this tissue are imbedded the Graafian vesicles, which contain the ova. They vary in size from a pin’s head to a pea, and are from fifteen to twenty in number. Each Graafian vesicle consists of an external vascular and an internal serous coat, named the dvicapsule. The inter- nal coat is lined internally by a layer of nucleated cells, called the membrana granulosa, and within this is situated the ovum. The cells of the membrana granu- losa are accumulated in large numbers round the ovum, forming a granular zone, the cumulus, discus proligcrus retinacula or chalaza. The ovum is a small spherical body, about to of an inch in diameter. It consists externally of a trans- parent envelope, the zona pellucida, or vitelline membrane, and within this is the yelk or vitellus. Imbedded in the substance of the yelk is a small vesicular body, the germinal vesicle, and within the germinal vesicle is the germinal spot. The latter varies in size from f° 3503 of an inch. At the approach of the menstrual period one or more of the Graafian vesicles enlarges, approaches the surface of the ovary, and when mature, forms a small projection on the surface. It finally bursts and the ovum escapes, being caught by the fimbriated extremity of the fallopian tube, and by it conducted to the uterus. Corpus Luteum.—As the ovum escapes it leaves behind it the external vascular and the internal serous coat of the Graafian vesicle, the cavity of which is im- mediately filled with a bloody fluid which soon coagu- lates, and the cicatrix presents a yellowish appearance; hence it has been called the corpus luteum. After a short time the coagulum contracts, and the membranes 330 HUMAN PHYSIOLOGY. become convoluted and hypertrophied, so that when the corpus luteum is divided transversely, about three weeks after its formation, it is seen to consist of a central firm •coagulum surrounded by a convoluted wall of a reddish yellow color. Corpora lutea are divided into true arid false; the former are found only when conception has taken place; the latter are met with in the unimpregnated state. They are both produced in the same way, and for the first three weeks there is no distinction between them; but the true corpus luteum becomes larger and remains longer than the false, in consequence of the increased vascularity of the parts after impregnation. At the end of the third week they each measure about one-half or three-fourths of an inch in diameter. After this the false corpus luteum begins to diminish, and entirely dis- appears in the course of about two months, while the true increases in size until about the third or fourth month, and then gradually declines until after parturi- tion, when it rapidly disappears. Action of the Oviducts.—In the human subject the oviducts commence by a wide-fringed expansion—the fimbriated extremity of the fallopian tubes. The ovum, in passing through the fallopian tube to the uterus, absorbs a certain quantity of fluid, increases in size, and if impregnated soon presents a number of minute villi on its surface which give it a shaggy appearance. This is called the chorion. In fowls, as the ovum leaves the ovary it enters the oviduct, and in passing the first portion, which is about two inches in length, it absorbs fluid and becomes more flexible and yielding. In the second portion, which is about nine inches in length, the mucous membrane is thick and glandular. In the upper part it secretes a REPRODUCTION. 331 viscid fluid which surrounds the yelk and forms a gelatinous deposit around the vitelline membrane, and from the rotation given to the egg by the oviduct the two ends become twisted in opposite directions from the poles of the egg and form the chalazce. The membrane which connects the chalazce is called chalaziferous mem- brane. In the rest of this portion an albuminous secre- tion is poured out to form the albumen or white of the egg. In the third division, which is about three inches in length, a material is poured out which condenses and forms three fibrous membranes, an internal, middle and external. The egg then passes into the fourth division, which is about two inches long. This pours out a secre- tion containing calcareous matter, which is deposited in the meshes of the external membrane of the egg, forming the shell. After the expulsion of the egg, evaporation of some of the watery ingredients takes place through the pores of the_ shell, its place being filled with air. The air cavity is situated between the internal and mid- dle membranes at the large end of the egg. The vitellus is the essential part of the egg, the white simply con- tributing to the nourishment of the chick until it leaves the shell, and the membranes and shell affording the pro- tective coverings. Development of the Ovum.—After the ovum is impregnated a remarkable change takes place, which is known as the spontaneous division or segmentation of the vitellus. A furrow first shows itself surrounding the vitellus in a vertical direction, which gradually becomes deeper until it has divided into two portions. Each of these portions is again subdivided into two, and the four segments thus produced are divided into sixteen, and sixteen into sixty-four, and so on, until the whole mass has assumed a mulberry appearance, and is finally 332 HUMAN PHYSIOLOGY. converted into “true animal cells,” which, adhering together, form the blastodermic membrane. These cells are sometimes called the primordial or primitive cells, or germinal vesicles. The albuminous matter liquefies and gradually passes by osmosis through the vitelline membrane into the interior of the egg. The blastoder- mic membrane then divides into two layers, the external blastodermic, serous or animal layer, and the internal blas- todermic, mucous or vegetative layer, both of which are composed of cells. The former produces the spinal col- umn and organs of animal life; the latter the alimentary canal and organs of vegetative life. Up to this stage the process is the same in all animals, birds, fishes, reptiles and mammalia. The simplest form of development is seen in the egg of the frog. The egg, when discharged from the body and fecundated, is deposited in the water, sur- rounded by a layer of albuminous matter, and is freely exposed to the light and heat of the sun. The first sign of organization is the thickening and condensation of the external blastodermic membrane in one part, form- ing an elongated oval spot with opaque edges. This is called the embryonic spot. Enclosed within this is a narrow transparent space, the area pellucida, in the cen- tre of which is a longitudinal line, the primitive trace. On each side of the primitive trace in the area pellucida the blastodermic membrane rises up in two plates, called the dorsal plates, which at last meet and enclose a foramen, the spinal canal, in which nervous matter is deposited to form the spinal cord, being enlarged anteriorly to accommodate the brain. At the same time the external blastodermic membrane grows outwards and downwards, to form the abdominal walls which embrace the internal blastodermic membrane and the fluid in its cavity. Be- REPRODUCTION. 333 neatli the spinal canal is formed a cartilaginous cord, which is called the chorda dorsalis, from which the ver- tebrae are subsequently developed. As the whole mass grows rapidly, the head becomes thick and voluminous, while the tail begins to project backwards, and the embryo assumes an elongated form. The internal blas- todermic layer forms the alimentary canal, the mouth and anus being developed by atrophy and perforation of the external layer of the blastodermic membrane at these points respectively. The young tadpole then ruptures the vitelline membrane and escapes, after which the extremities are developed by a process of budding or sprouting, and when fully formed, the tail atrophies and disappears. The animal at first breathes by gills; but these are subsequently replaced by the lungs. In the fish, the internal blastodermic membrane is divided into two parts by a constriction, one of which forms the intestinal canal, while the other, remaining outside, forms the umbilical vesicle, which is surrounded by a portion of the external blastodermic membrane, and is gradually atrophied as development proceeds. In the human embryo the umbilical vesicle becomes more completely separated, and forms a cord by its con- striction, at the distal extremity of which is situated the vesicle, which contains a clear transparent fluid. The umbilical vesicle may continue until the end of the third month, after which it gradually disappears in the advancing development of the adjacent parts. Formation of the Amnion and Allantois.—These are two accessory organs which belong to the higher order of animals. The amnion is formed from the exter- nal layer of the blastodermic membrane, and the allan- tois from the internal; the former forms a cavity or sac containing fluid in which the foetus floats; the latter is a 334 HUMAN PHYSIOLOGY. vascular structure destined to bring the blood of the embryo to the external sources of nutrition and atmos- pheric influence. These are not necessary to the devel- opment of the egg of the frog and fish, since absorption can readily take place through the vitelline membrane from the media by which they are surroundud. The amnion is first formed; this takes place by double foldings of the external blastodermic membrane, which pass upwards from the abdominal surface on all sides of the embryo, until they meet at a point over the back which is called the amniotic umbilicus. Fusion then takes place at this point, the inner layer of the fold forming the amnion, the outer, blending with the vitelline membrane, forms the external investing mem- brane of the ovum. A shut sac is thus formed between the amnion and the foetus called the amniotic cavity, which is filled with a clear fluid—the liquor amnii. About this time the allantois commences as a pro- longation or diverticulum from the posterior part of the intestinal canal, and follows the course of the amniotic fold which preceded it, lying between its two layers. It gradually increases in size until it covers the body of the embryo, together with the amnion; it then meets and fuses over the back as did the amniotic folds. It therefore lines the whole internal surface of the invest- ing membrane of the ovum with a flattened vascular sac, the vessels of which come from the interior of the body of the embryo. The cavity of the allantois is con- tinuous with the cavity of the intestines. The umbilical vesicle is situated between the amnion and allantois. In the chick the allantois comes immediately in con- tact with the shell membrane, taking the place of the albumen which has been liquefied and absorbed, and through the pores of the shell an interchange of gases REPRODUCTION. 335 takes place, oxygen being absorbed from the air, and carbonic acid exhaled from the blood-vessels of the allantois. It will be seen, therefore, that a true respira- tion takes place by means of the allantois through the external covering. When the chick arrives at maturity, it breaks open the shell and escapes from its confinement, the allantoic vessels are torn off at the umbilicus, and the allantois remains behind in the abandoned egg shell. Formation of the Chorion.—In the human embryo the obliteration of the cavity of the allantois takes place very early, so that it does not enclose a cavity, but fuses together, and uniting with the outer fold of the amnion and the vitelline membrane, constitutes the chorion. Hence there are two membranes in the foetus, the amnion and the chorion, and the umbilical vesicle is situated be- tween the two. The chorion in the human subj ect is iden- tical with the allantois of the lower animals, its chief peculiarity being that its opposite surfaces are adherent instead of enclosing a cavity. The next peculiarity of the chorion is that it becomes shaggy, owing to the num- ber of minute villi or “villosities” which are found on its surface. The villi may be distinctly seen as soon as the ovum has reached the uterine cavity, even when it is still very small. They continue to grow and elongate, and divide into a number of branches by the process of sprouting, each filament terminating in a rounded ex- tremity. The whole tuft bears a certain resemblance to some varieties of seaweed. The vessels of the chorion pass into the villosities, forming loops like the vessels in the villi of the small intestines. The villi of the chorion therefore bear a slight resemblance to those of the small intestines; but are unlike any other structure of the body, and their presence in the uterus or its discharges may be considered as a proof of pregnancy. 336 HUMAN PHTSIOLOGT. The villi are the organs through which nourishment is supplied from without, at this stage of existence. At about the end of the second month the villi become atrophied, except at the part which corresponds with the insertion of the foetal vessels, and the chorion becomes partly bald. Those villi which remain continue to grow, and ultimately form the placenta, which attaches itself to the uterus. Preparation of the Uterus to Receive the Ovum.—As the impregnated ovum is about to descend into the cavity of the uterus, the mucous membrane be- comes greatly hypertrophied, tumified, and vascular, and projects in rounded eminences into the uterine cavity. The tubules or follicles are elongated and enlarged so that their open mouths may be seen with the naked eye. The hypertrophied mucous membrane* is called the de- cidua vera. When the ovum reaches the uterus it insin- uates itself between the opposite surfaces of the mucous membrane, and becomes lodged in one of the depressions between the projecting eminences of the decidua, where it subsequently becomes fixed. At this point a rapid development of the mucous membrane takes place, and a folding or prolongation of the decidua surrounds and envelopes the ovum, called the decidua rejlexa. It was formerly supposed that the decidua was an entirely new product thrown out by exudation from the surface of the uterus, similar to the inflammatory exuda- tion of croup, &c. This surrounded the whole internal surface of the uterus, and was called the decidua vera, and as the ovum passed from the fallopian tube into the uterus it pushed before it a folding of the decidua vera, which formed the decidua rejlexa. The closure of this folding behind the ovum was called the decidua serotina. This was the theory of William Hunter. It is now REPRODUCTION. 337 known to be no other than the mucous membrane itself, very much thickened and hypertrophied. Formation of the Placenta.—The placenta is formed partly by the vascular tufts of the chorion, and partly by the hypertrophied mucous membrane to which they are connected. About the commencement of the third month the villi which are destined to enter into the formation of the placenta continue to elongate, and peneti ate or are pushed into the follicles of the mucous membrane (like the fingers into a glove), which are en- larged for their reception. The growth of the villi and that of the follicles go on simultaneously, and keep pace with each other. The capillaries of the villi are enlarged and become tortuous, and those on the exterior of the folli- cles enlarge excessively and become dilated into wide sinuses, which are filled with blood derived from the arteries of the uterus, so that two membranes intervene between the capillaries of the villi and the sinuses of the uterus, viz., the covering of the villi and the lining membrane of the follicles. These afterwards fuse to- gether and blend with the walls of the capillaries on the one hand, and the walls of the sinuses on the other. The tufts of the villi are prolonged into the sinuses, pushing before them the walls, and are everywhere bathed with the blood of the mother. The process of osmosis takes place through the thin fused membrane, there being no direct communication between the foetal and maternal vessels. The placenta is fully formed about the com- mencement of the fourth month, and constitutes the channel through which nourishment is conveyed from the mother to the foetus. The nutritive material passes from the blood of the mother through the intervening membrane" by osmosis, and enters the blood of the foetus. Besides, the placenta is an organ of exhalation as well as HUMAN PHYSIOLOGY. of absorption. The impurities circulating in the blood of the foetus are here discharged into the maternal ves- sels, to be removed by the excretory organs of the mother; so that the placenta may be said to fulfil the double office of the lungs and stomach in the foetus. In consequence of the intimate relation existing between the mother and the foetus, there is no doubt that nervous impressions experienced by the former, such as fear, anger, disgust, &c., which disturb the circulation, may occasion deformities and deficiencies of various kinds, nsevi, warts, &c., in the latter. The circulation in the foetus has been already described. (See page 205.) Umbilical Cord and Amniotic Fluid.—The umbili- cal cord, or funis, is the connecting link between the foetus and placenta, In early life it is very short, and consists of that portion of the allantois or chorion next the abdomen. The umbilical vesicle is situated between the amnion and chorion, the rest of the space being filled with a gelatinous fluid. The amnion continues to expand, the quantity of liquor amnii increases, and about the beginning of the fifth month the amnion comes in contact with the chorion, the umbilical vesicle and gelatinous fluid gradually disappearing. The umbilical cord at the same time elongates in proportion to the increasing size of the amnion, and towards the close of gestation the amnion and chorion blend together and constitute what is commonly called the “membranes.” As the cord lengthens it twists from right to left. It consists of the two umbilical arteries, the umbilical vein, the urachus, and the remains of the umbilical vesicle, imbedded in a gelatinous material and surrounded by a folding of the amnion. The cord at full term varies in length from one to three feet. REPRODUCTION. 339 General Development of tiie Embryo.—The de- velopment of the different parts formed by the external blastodermic membrane have been already casually refer- red to. The internal blastodermic membrane forms the intestinal canal and organs of vegetative life. The intes- tinal canal is formed at a very early stage, and is at first straight, but after a time it becomes convoluted. The bladder is next developed from the urachus; this is a hollow tube which connects the posterior part of the intestines with the allantois. As the abdomen closes at the umbilicus, the part of the urachus outside the body forms part of the cord, while the portion included in the abdomen becomes dilated and fusiform at the lower part, and forms the bladder. The liver is also developed at a very early period, and is of large size in proportion to the body; it secretes a substance which is thrown into the intestines, termed the meconium. The Wolffian bodies are developed about the end of the first month. They take the place of the kidneys, by which they are replaced about the end of the second month. The ducts which connect the Wolffian bodies to the bladder become the vasa deferentia or fallopian tubes as the case may be. The development of the heart has been referred to, (page 156). The lungs are developed by small tuber- cles in front of the oesophagus, and gradually extend laterally to fill the thorax, and a growth extending upwards forms the trachea. Parturition.—The discharge of the ovum is termed parturition. This is effected by the contraction of the muscular fibres of the uterus, assisted in the second stage by the contraction of the diaphragm, abdominal, and other muscles of the body. The placenta is separated from its attachment to the inner surface of the uterus, during which the sinuses are lacerated and a certain 340 amount of liemorrhage occurs, which, however, is soon arrested by the contraction of the uterus and consequent closure of the mouths of the vessels leading to the sinuses. After parturition the uterus undergoes the process of involution. This consists in a diminution in the size of the uterus, and a change in the appearance of the muscular fibre cells. The muscular fibres of the uterus, during gestation, are very much increased in size, and granular in appearance. After parturition they appear to undergo a fatty degeneration; fat globules make their appearance in the interior of the muscular fibre cells; the tissue becomes soft and is gradually absorbed, its place being supplied by new cell fibres. HUMAN PHYSIOLOGY. FINIS. INDEX. A PAGE. Abdueen3 299 Absorption 141 Mechanism of 144 by villi and laeteals 147 by veins 148 by lymphatics 149 Acini of liver 229 Adipocere 25 Adipose tissue 57 Appearaneejnid properties of.. 57 Function of*. 58 Air, Changes in respired 215 Quantity respired 212 Breathing or tidal 212 Complemental 212 Supplemental 212 Residual 212 Air Cells. 209 Albinoes 38, 96 Albumen 28 Composition of 28 Function of. 29, 181 Tests for 29 Albuminose 30 Origin and function of 30 Albuminoid substances 11 Alcohol 110 Amnion and allantois 333 Ampullae 240 Aponeuroses 53 Apophysis 66 Aqueous humor 313 Area pellueida 332 Areolar tissue 56 Function of 56 Arrectores pilorum 71, 96 ArUriei 193 Structure of 193 Function of 196 Elastic tissue of 194 Muscular tissue of 195 Vasa vasorum of.. 194 Anastomosis of 1% Pulse of 197 Rapidity of circulation 198 Articulation 324 Asphyxia 220 Associate function of Nerves 310 Auditory nerves 298 Automatic action 251, 254 Axis-cylinder 255, 299 B Basement membranes 51 Function of 52 PAGE. Bernard on the function of the liver. 135 “ " action of the lungs,.. 210 Bile 131 Appearance and properties of 132 Chemical composition of 132 Biliary salts of. 133* Function of 130 Tests for 137 Biliverdine 38, 132 Blastodermic membrane 332 Bleeding, effects of, on blood 165 Blood 151 Elements of 151 Quantity of 151 Physical character of. 151 Specific gravity of 152 Color of 152 Microscopical appearance of .. 152 Red corpuscles of 153 White corpuscles of 155 Origin of Corpuscles of 156 Development of Corpuscles of. 157 Chemical composition of 160 Chemical composition of cor- puscles of 161 Chemical composition of liquor sanguinis of 161 Difference between arterial and venous 162 Gastric, hepatic, mesenteric, and splenic venous blood 163 Gases of 163 Causes of Color of 165 Influence of venesection on .. 165 “ starvation on 166 ‘ ‘ Iron and flesh diet on 167 “ Age and sex 167 “ Disease on 168 Poisons'of 170 Vital properties of 171 “ Elements of 171 Coagulation of 171 Time required for coagulation. 172 Cupped and Buffed'condition of 173 Coagulation of retarded 174 “ promoted 176 Function of fibrin of 177 “ red corpuscles of.. 179 “ white corpuscles of 180 “ albumen of 181 “ fats of 181 “ salts of 182 Relation of, to living organism. 182 Globuline of 161 Hematineof 161 Increase of fibrin of 168 342 INDEX, PAOE. Blood Circulation of 186 Changes of in respiration .... 218 Bone 62 Appearance and properties of.. 63 Chemical Constituents of 63 Structure of 63 Haversian canals of 64 Lacunas and canaliculi of 65 Articular lamella of 65 Development of 66 Growth of 67 Repair of 68 Brain 281 Average weight of 281 Structure of 282 Vascular supply of 284 Ventricles of 284 Function of, &c 285 Bronchocele or goitre 249 Brown-Sequard on crossed action of spinal cord 273 Brunner’s glands 92 Bursae 85 Butter acids 241 C Callus of bone 68 Canaliculi 65 Canal of Petit 314 Capillaries 201 Structure of 201 Circulation in 202 Influence of nerves upon 203 Rapidity of Circulation in 203 Carbonate of lime 17 Soda 18 Potassa 18 Cartilage 59 Appearance and properties of. 59 Vascular supply of 62 Temporary 59 Permanent 60 Articular 60 Costal 60 Membraniform 61 Cartilagine 36 Casein 34 Origin and function of 35 Cauda Equina 269 Cause of Organization 47 Cells, history of. 39 Definition of 39 Variation in shape of 39 “ “ size of 40 Color of 42 Cell wall 41 Cell contents 42 Cell nuclei 51 Phenomena of 48 Spontaneous change of 46: Manifestation of life 491 Secondary deposit in 42 j Plastic and metabolic power of. 491 Growth, maturity and decay of. 50 Individuality of, lost by 46 Cerebellum ' 279; Structure of 279! Peduncles of (crura) 280; PACK. Cerebellum Function of 280 Not the organ of sexual in- stinct 281 Cerebrum 281 Average weight of 281 Structure of 282 Convolutions of 282 Sulci of 288 Ventricles of 284 Vascular supply of 284 Function of 285 Crura cerebri of 287 Ceruminous glands 102 Chalaza '. 331, 329 Chloride of potassium 16 Chloride of sodium 14 Cholesterine 133 Chondrine 36 Chorda Dorsalis 338 Chorion, formation of 335 Choroid 311 Chyle 142 Molecular base of 147 Composition of 142 Color of, in thoracic duct 142 Chylification 128 Chymification 124 Ciliary Ligament 312 Muscle 312 Processes 311 Cilise 81 Growth and motion of 47, 82 Ciliated epithelium 83 Circulation 185 Course of, in the adult 186 Peculiarities of. 204 Rapidity of- 204 Foetal 205 Coagulable lymph 31 Coffee in Colostrum 241 Coldblooded animals 221 Coma 296 Compound cell 45 Corrugation 327 Corium or cutis vera 96 Cornea 310 Corpora amylacea 20 Corpora striata 288 Corpora quadrigemina 288 Corpus luteum 329 Corpus callosum 289 Corpuscles of the Blood 153 Origin of. 156 Development of 157 Coughing 214 Cranio-spinal axis 252 Cranial nerves 297 Creatine and creatinine 238 i Crying 215 ; Crystalline lens and capsule 313 ; Cumulus 329 ; Cyanosis 207 jCytoblastema 43 Cytogenesis 43 Laws of 43 Modes of 44 Conditions necessary to 45 INDEX. 343 D PAGE. Decidua Vera 336 Reflexa 336 Serotina 336 Decussation of Medulla 276 Defecation 139 Deglutition 122 Mechanism of 123 Dentine 115 Development of 117 Development of cells 44 of the embryo 339 “ intestinal canal 339 “ bladder 339 “ liver 339 “ Wolffian bodies 339 “ lungs 339 Digestion 106 Rate of 127 Artificial 128 Movements of stomach in 128 Digestive fluid 128 Discus Proligerus 329 Dorsal plates 332 Dreams 296 Drink 110 Ductless glands 244 Diaphysis 66 E Ear 319 Structure of 319 Bones of 319 Elastic tissue 54 Elasticine 37 Electricity 225 Currents of 225 Phenomena of, in man 227 “ “ animals 228 Elementary forms of tissue 39 Embryo, development of 339 Embryonic Spot 332 Emotions 293 Enamel 115 Development of 118 Encephalon 275 Endosmosis and exosmosis 145 Epidermis 94 Epiglottis 322 Epithelium 79 Tesselated 80 Columnar 81 Ciliated 83 Erectile tissue 205 Excretine 140 Expiration 211 Muscles of 211 Eye 310 Structure of 310 Accommodation to vision.... 317 Simultaneous action of 318 Essential parts of 314 F Facial nerve 300 Division of, for tic doloureux.. 300 Paralysis of 301 PAGB. Faculties, intellectual 295 Faeces 139 Analysis of 139 Ashes of 140 Fats and oils 24 Physical appearance of 25 Functions of 27, 181 Fenestra ovalis and rotunda 319 Fibrous tissue 53 Fibrocartilage 61 Fibrin 31 Physical appearance of 31 Fibrillation of 32 Function of 33, 177 As effete material 34, 179 Filum terminale 269 Fine adjuster of the eye 317 Foetal circulation 205 Changes in, after birth 207 Follicles 90 Food 106 Classification of 106 Histogenetic substances of 107 Quantity of 108 Quality of 109 Force, nervous 268, 291 Frontal sinuses 309 Gr Galvanic pile 226 Ganglion impar 304 Ganglion of Ribes 304 Ganglia of the Nervous System 257 Ganglia of the Sympathetic 304 Structure of 304 Gases 19 163 Gastric juice 125 Physical Appearance of 125 Chemical Composition of...... 126 Function of 127 Gelatine 10, 37 Generation, True 327 Germ Cell 327 Germinal Vesicle 329 Germinal Spot 329 Germinal Membranes 52 Germinal or Primitive Vesicles 332 Glands, Secreting 229 Glands, Lymphatic 143 “ Ductless 244 Globuline 35, 161 Glottis 322 Glossopharyngeal Nerve 301 Glycogenic function of Liver 135 Granules or Molecules 44, 50 Graafian Vesicles 329 Growth of Bone 67 “ of Nails 99 “ of Hair 100 H TTo.it* QQ Hair follicle I!”””".!!!!"!".""" 100 Haversian system 64 “ canals 64 Heart 185 Structure of ... 1S7 344 INDEX. PAGE. Heart Vessels and Nerves of 188 Action of 189 Rythm of 189 Sounds of 189 Cause of sounds of 190 Words representing sounds of.. 190 Impulse of 191 Frequency of action of 191 Force of action of. 192 Hearing 319 Sense of, impaired 321 Heat 221 Theory of production of 221 Influence of nerves in produc- tion 223 Loss of, by evaporation 224 Latent 224 Development of, in muscular action 76 Hematine 37, 161 Hepatic cells 230 Hiccup 215 Hippurie acid 237 Histogenetic substances of food 107 Elements of blood 151 Humor, aqueous 313 Vitreous 313 Hunger 112 Hypoglossal nerve 301 I Ideas 293 I deo-motor action 253, 287 Inanition 112 Image formed on the retina 316 Impulse of the heart 191 Impressions 291 Registration of 255, 292 Insalivation 119 Inspiration 211 Muscles of. 211 Instinct and intelligence 286 Intellect 294 Intellectual faculties 294 Integument 93 Epithelium of 94 Color of 95 Corium of 96 Appendages of 97 Papillae of 97 Function of 103 Intestine (large) 138 Intestinal juice 129 Appearance and properties of.. 129 Function of 129 Intestines, villi of 92, 141 Inter-cellular passages in lungs 209 Involution of the uterus 47, 340 Iris 311 Structure of 311 K Keratine 37 Kidney 231 Structure of 232 Malpighian bodies of 232 PAGE. Kidney Papillae of 233 Sinus of 233 Function of 234 L Labyrinth 319 Vestibular portion of 321 Lacteals 141 Absorption by 147 Laetin or sugar of milk 242 Lacunae 65 Larynx, organ of voice 322 Structure of 322 Vocal cords of 322 Ventricles of. 322 Laughing 215 Laws of cytogenesis 43 of nerve action 263 Law of Physiology 9 Laws regulating transmission oflight. 315 Law of nervous distribution 303 Lenses 314 Lieberkiihn’s follicles 91 Light 224 Ligaments 53 Limbeus luteus 313 Liquor Amnii 334 Liver 229 Structure of 229 Use of 131 Hepatic cells of 230 Function of 135 Vessels of 230, 231 Lungs 208 Structure of 208 Air cells of 209 Vessels and nerves of 209 Reaction of tissue of 210 Action of 211 Exhalation by 215 Inhalation by 217 Lymph 144 Composition of 144 Lymphatic vessels 142 Structure of 148 Absorption by 149 Lymphatic Glands 143 M Mammary Glands 289 Structure of 240 Milk of 240 Chemical composition of milk. 241 Colostrum of 241 Effect of medicinal agents on.. 242 “ of emotions on 242 Margarine 25 Marshall Hall on spinal cord 274 Mastication 114 Muscles of 119 Maternal membranes 52 Materialist doctrine 289 Meconium 339 Medulla oblongata 275 Structure of 276 Function of 277 Decussation of 276 INDEX. 345 PAGE. Melanine 38 Membranous expansions 79 Membranes (simple) 53 Membranes of the foetus 338 Membrana Granulosa 329 Membrana Tympani 319 Mesenteric Glands 141, 143 Mesmerism 297 Metamorphosis in animals 327 Metagenesis 327 Mind-force 291 Mind, and its relation to the body.... 289 Morbus Cseruleus 207 Mind, Influence over the body...... 295 Morbus Addisonia 248 Motion, cause of 46, 74 “ ciliary 46, 82 Motor oculi 299 Mucous Membranes 86 Structure of 87 Appendages of 88 Mucus 86 Chemical constituents of 87 MucineorMucosine 36, 87 Mulberry Mass 331 Multiplication by subdivision.... 45, 326 “ by gemmation 326 Muscle 68 Striated 69 Primitive fibres of 69 “ Fibrillae of 70 Non-striated 70 Mode of Development 71 Attachment of, to tendons.... 72 Chemical composition of 73 Vaseular and nervous] supply.. 73 Properties of. 74 Sound in contraction of 76 Heat in contraction of 76 Rigor mortis of 76 Lever power of 77 Musculine 36 Myolemma 70 Myopia 316 N Nails 98 Nervous power in respiration 213 System 250 Of lower animals 250 Cranio-spinal axis of 252 Diagram of action of 253 Structure of 255 Ganglia of 257 Chemical composition of 257 Distribution of nerve fibres.... 258 Origin and termination of.... 259 Function of nerve fibres 261 Afferent and efferent nerves.. 262 Excitability of nerve 262 Laws of action of nerves 263 Development of nerve tissue.. 265 Regeneration of 265 Vascular supply of 4266 Reflex action of 267 Automatic action of 251, 254 Nerve cells or corpuscles 2571 PAGE. Force (vis nervosa) 268, 291 Nervous polarity 268 Nervi nervorum 261 Nerve arc 254 Centre, function of 266 Conduction 266 Communication 267 Nitrogenous substances 11 Notes, chest 324 Falsetto 324 Nucleus 41 Nucleolus 42 O Odoriferous glands 102 Oils and fats 24 Oleine 25 Olfactory nerves 298 Optic nerves 298 Chiasma of. 318 Optic thalamus 288 Ora serrata 312 Organic substances 11 Putrefaction of. 13 Osmosis 145 Osteine 36 Ovanes 328 Ovicapsule 329 Oviducts, action of 330 Ovum 329 Development of 331 Segmentation of 331 Oxygen 19 P Pabulum 43 Pacinian Corpuscles 260 Pancreatic juice 130 Appearance and properties of.. 130 Chemical composition of 130 Function of 131 Pancreatine 35, 130 Papill® 88, 97 Parthenogenesis 327 Parturition 339 Pathetic nerve 299 Pavement epithelium 80 Pepsine 36, 127 Peptic follicles 90, 125 Perception 292 Perspiration 104 Chemical constituents of 104 Function of 104 Peyer’s Glands 93 Phosphate of lime 16 Phosphates of magnesia, soda and potassa 18 Phrenology, absurdity of 294 Pigment cells 95 Placenta, formation of 337 Plastic elements of nutrition.... 107, 222 Pneumogastric nerve 301 Function of 301 Division of 302 Pons varolii 278 Structure and function of 278 346 INDEX. page. \ Prehension 113 Presbyopia 316 Primitive trace 332 Primitive or primordial cells 332 Primary forms of tissue 39 Primary membranes 52 Protein compounds ’.. 11 Proximate principles 10 Definition of 10 Mode of extraction 10 Classification of 11 First class of 13 Second class of. 19 Third class of 28 Pulse 197 Venous 199 Ptosis. 299 Ptyalin 121 R Red blood corpuscles 152 Function of 179 Size of, in different animals.... 154 Color of 155 Reflex action 267 Registering ganglia 255 Reproduction 326 Three modes of 326 Action of male in 327 Action of Female in 328 Respiration 208 Frequency of. 212 Quantity of air respired 212 Breathing air of 212 Complemental air 212 Reserve air 212 Residual air 212 Influence of nervous power in.. 213 Modification of movements of.. 214 Changes in air during 215 Changes in the blood by 218 Effects of the arrest of 220 Elements of (Liebig) 107 Retina 312 Structure of 313 Impressions on. 318 Retinacula 329 Rigor mortis 76 Rima glottidis 322 Rythm of the heart 189 S Salivary glands 120 Structure of 120 Saliva 120 Composition of 121 Function of 121 Saponification 25 Sarcos elements 70 Sarcolemma 70 Sclerotic 310 Sebatine 101 Sebaceous glands 101 Secondary deposit 42 Secreting glands 229 Secretion of bile 131 * PAGE. of urine 234 of milk 240 Segmentation 331 Semen or spermatic fluid 327 Sensations 2S>1 Attended to 29? Not attended to 292 Subjective and objective 292 Serous membranes 83 Structure of 85 Sight 310 Sighing 215 Simple fibres 50 Membranes 51 Sleep 296 Smell 308 Sneezing 214 Sobbing 215 Solitary glands 93, 150 Somnambulism 297 Sounds, subjective 321 Articulate 324 Muscular 76 Special senses 308 Sperm cell 327 Spermatozoa 328 Spherical aberration 315 Spinal accessory nerve 303 Function of 303 Spinal cord 269 Structure of 270 Spinal nerves of 271 Function of 271 Reflex function of 273 Crossed action of 273 Brown-Sequard’s views on.... 273 Marshall Hall’s views on 274 Constant activity of 275 Spiritualist doctrine 290 Spleen 244 Structure of 244 Malpighian bodies of 245 Fimction of 246 Peculiarity of splenic artery... 245 Spore or sporangium 327 Stammering 324 Starvation 112 Starch 19 Physical appearance of 20 Conversion of into sugar 21 Function of 21 Tests for 21 Stcarine 25 Steatozoon folliculorum 102 Stercorine 140 Stomach 124 Mucous membrane of 90, 124 Follicles of 125 Movements of 128 Sudoriferous glands 102 Sugar 21 Function of 22 Tests for 23 Supra-renal capsules 247 Structure of 247 Function of 247 Disease of 248 ! Suspensory ligament of capsule.... 314 INDEX. 347 PAGE. Sympathetic system 304 Nerves of 261 Function of 305 Division of 306 Synovial membranes 84 Structnre of 85 -Synovia 85 T Taste, seat of 88, 301 Tea Ill Teeth 114 Structure of 114 Development of 115 Eruption of ;... 118 Temperature of the body 221 in disease 221 of animals 221 how produced 222 Tendons 53 Attachment of 72 Tesselated epithelium 80 Tests— Trommers’ 23 Fermentation 23 Torulse 24 Moore’s 24 Barreswill’s 24 Bottger’s 24 Maumene’s 24 Pettinkoffer’s 137 Thalamus opticus 288 Thirst 112 Thymus gland 248 Structure of 248 Function of 248 Thyroid gland 249 Structure of 249 Function of 249 Tissues 1 - 53 Attractive or selective power of 203 Tobacco Ill Tongue, Papillae of 88, 119 Trifacial nerve 299 Division of 300 Irritation of 300 Trochlear nerve 299 Tympanum 319 Air in 319 Tympanitis 140 U Umbilicus amniotic 334 Umbilical vesicle 333 Cord 338 Urachus 339 Urine 234 Secretion of 234 • Specific gravity of 234 Chemical composition of 235 Urea 235 Uric or lithic Acid 237 Hippuric Acid 237 Extractive matters of 238 Creatine of ,, 't... 238 PAGE. Creatinine of 238 Salts of 238 Urrosaeine 38 Uterus, preparation for ovum 336 Involution of 47, 340 . Muscular fibre cells of 47, 340 Y Valvulee Conniventes 91 Vasa vasorum 194 Vasa deferentia 339 Veins 198 Absorption by 148 Structure of 198 Valves of 199 Circulation in 199 Rapidity of circulation in 201 Ventricles of the larynx 322 Ventriloquism 324 Vemix Caseosa 102 Vice, solitary 228 Villi of intestines 92, 141 ‘ ‘ of chorion 335 ‘ ‘ Structure of. 92 “ Absorption by 147 Vis a fronte 201 Vis k tergo 199 Vis nervosa 268 Vision, phenomena of 315 Circle of 318 Vital elements of the blood 171 Vital capacity of the chest 213 Vitelline membrane 329 Vitreous humor 313 Vocal cords 322 Voice 322 Compass of 323 Modifications 324 Voluntary attention 295 Vomiting 123 Mechanism of 124 Vowels and Consonants 324 W Warm-blooded aninnls 221 Water 13 Function of 14 White fibrous tissue 53 Appearance and properties of.. 53 Development of 55 White blood corpuscles 155 Function of 180 White substance of Schwann.... 256, 265 Will, power of 294 Willis, circle of 197, 285 Wolffian bodies 339 Y Yawning 215 Yelk 329 Yellow elastic tissue 54 Appearance and properties of.. 55 Development of 55 Zona pellunida 329