TEXT BOOK OF PHYSIOLOGY. A TEXT BOOK OF PHYSIOLOGY, BY T. FULTON, M.D., M.R.C.S., Eng.; L.R.C.P., Lon, v** PROFESSOR OF PHYSIOLOGY AND SANITARY SCIENCE IN TRINITY MEDICAL COLLEGE, TORONTO; SURGEON TO THE TORONTO GENERAL HOSPITAL, AND PHYSICIAN TO THE HOME FOR INCURABLES, TORONTO. SECOND EDITION, REVISED AND ENLARGED, .. .. WITH NUMEROUS ILLUSTRATIONS. “LAUOR OMNIA VINCIT. ’ PHILADELPHIA: LINDSAY & BLAKISTON TORONTO: WILLING & WILLIAMSON 1879. Entered according to Act of the Parliament of Canada, in the Year One Thousand Eight Hundred and Seventy-nine, by J. Fulton, M.D., in the Office of the Minister of Agri- culture, at Ottawa, D.C. Entered according to Act of Congress, in the Year One Thousand Eight Hundred and Seventy-nine, by A. L. Fulton, M.D., in the Office of the Librarian of Congress, at Washington, D.C. Dudley & Burns, Printers, XI Colborne Street, Toronto. PREFACE TO THE SECOND EDITION, The science of Physiology has been so much advanced in almost every department of the subject, since the issue of the first edition, that the preparation of the present one has been no easy matter. The very favorable reception, however, which was accorded the first edition, has induced me willingly to undertake the self-imposed task. Many of the chapters have been re-written, and much new matter added ; but while every part has received careful revision, the original plan of arrangement has been rigidly adhered to, as that best adapted to the wants of those for whom it was written. My experience as a teacher in the department of Physiology during the last fifteen years, formerly in Victoria Medical College, and latterly in the University of Trinity College, has led me to the conclusion that Physiology can be best taught in connection with Histo- logy, and with this view I have endeavored to supply a prevailing want in the ordinary text books, by the intro- duction of a concise history of this interesting subject. It has been truly said that a knowledge of Anatomy is the keystone to Medicine, and it is equally true that a knowledge of Histology is the keystone to Physiology. Illustrations have been introduced wherever they ap- peared desirable, and in order to prevent the volume from being too expensive, such illustrations as did not appear necessary to the elucidation of the text have been omitted. vi. The illustrations are partly new and partly borrowed from recognized authorities, and special acknowledgment must be made of those obtained from James Campbell, Pub- lisher, Boston, U.S. It was not considered desirable, as a rule, in a work of this kind, to quote authorities for the statements in the text, as it would have required numerous references to home and foreign books and periodical litera- ture, which would have been not only useless, but confusing to the generality of readers. Notwithstanding the number of most excellent works on Physiology published, a well digested text book on this subject, adapted to the wants of the advanced medical student and the general practitioner, is still a desideratum in medical literature. This work is chiefly intended for medical students, but it is hoped that it may also prove serviceable to medical practitioners, more especially those who have students under their instruction. J. FULTON. Elgin Place, 303 Church St., Toronto. CONTENTS. page Ineroduction II CHAPTER I. Proximate Principles 14 Definition of a Proximate Principle 14 Classification of Proximate Principles 15 Proximate Principles of the First Class 16 Water 16 Sodium Chloride 17 Potassium Chloride 18 Lime Phosphate 19 Lime Carbonate 19 Sodium and Potassium Carbonates 20 Sodium and Potassium Sulphates 20 Magnesium Phosphate and Carbonate 21 Gases 22 Proximate Principles of the Second Class 22 Starch 23 Glycogen 25 Sugars 26 Oils and Fats 29 Proximate Principles of the Third Class 33 Albumen „ 35 Albuminose or Peptone 37 Fibrin 38 Casein 40 Globuline 41 Pepsine 41 Pancreatine 42 Ptyaline 42 Mucosine 42 Musculine 42 Cartilagine 42 Collagen 43 Elasticine 43 Keratine 43 Coloring Matters 43 Hemoglobine 43 Melanine 44 Bilirubine and Biliverdine 44 Urosacine or Urochrome 45 Luteine 45 ■Crystallizable Nitrogenous Matters 45 Lecithine 45 Cerebine 46 Leucme 47 CHAPTER II. PAGE Elementary or Primary Forms of Tissue 46 Protoplasm 47 Cells, shape, size and structure 47 Cytogenesis 51 Conditions necessary to Cell growth 53 Permanent Change in the Shape of Cells 53 Temporary Change in the Shape of Cells 54 Cause of Organization 55 Function of Cells 56 Manifestations of Cell Life 57 Granules 57 Simple Fibres 57 Simple Membranes 58 CHAPTER III. Tissues 60 White Fibrous or Connective Tissue 60 Yellow Fibrous or Elastic Tissue 62 Areolar Tissue 64 Adipose Tissue 65 Cartilage 66 Gelatinous and Reticular Tissue 71 Bone 72 Teeth 79 Muscle 83 CHAPTER IV. Membranous Expansions 96 Epithelium 97 Serous Membranes 101 Synovial Membranes 102 Mucous Membranes 103 Appendages of the Mucous Membrane 105 Integument 112 Appendages of the Integument 116 Digestion 125 Prehension 132 Mastication 132 Insalivation 134 Deglutition 137 Chymification 139 Chylification 144 Defecation 156 CHAPTER V. CHAPTER VI. Absorption 158 Villi and Lacteals 158 Lymphatic Vessels and Glands 159 Mechanism of Absorption 162 Absorption by the Villi and Lacteals 165 Absorption by the Blood Vessels 166 Absorption by the Lymphatics 167 Glandulae Solitarise .. 167 ix. CHAPTER VII. PAGE Blood j68 Physical Character of the Blood 168 Microscopical Appearance of the Blood 169 Chemical and Structural Characters of the Blood 176 Difference between Arterial and Venous Blood 180 Conditions which Influence the Character of the Blood 183 Coagulation and Vital Properties of the Blood 188 Circumstances which Promote Coagulation 191 Circumstances which Retard Coagulation 192 Function of the Constituents of the Blood 194 Relation of the Blood to the Living Organism 198 CHAPTER VIII. Circulation 200 The Heart and Circulation 200 Proofs of the Circulation 203 Action of the Heart 206 Arteries 21? Veins 219 Capillaries 222 Velocity of the Circulation 225 Fcetal Circulation 227 Respiration 230 The Lungs 230 Mechanism of Respiration 233 Influence of the Nerves in Respiration 237 Modification of the Respiratory Movements 238 Changes in the Respired Air 239 Changes in the Blood during Respiration 242 Effects of the Arrest of Respiration 243 CHAPTER IX. CPIAPTER X. Animal Heat, Light and Electricity 244 Heat 244 Theory of the Production of Heat 245 Regulation of the Temperature of the Body 247 Light.. 248 Electricity 248 Secreting Glands and their Secretions 252 The Liver 252 The Kidney 256 Secretion of Urine 259 The Mammary Glands 266 Milk 267 CHAPTER XI, CHAPTER XII. Ductless or Vascular Glands 270 The Spleen 270 The Supra-renal Capsules 273 The Thymus Gland ; 274 The Thyroid Gland 275 CHAPTER XIII. X PAGE. The Nervous System 276 Structure of the Nervous System 281 Ganglia of Nerves 284 Chemical Composition of Nerve Tissue 284 Origin and Termination of Nerves 286 Function of Nerve Fibres 289 Development of Nerve Tissue 292 Function of the Nervous Centres 293 Reflex Action 295 Nerve force 295 The Spinal Cord 296 Function of the Spinal Cord 299 Encephalon 303. Medulla Oblongata 303 Pons Varolii 306 Cerebellum 307 Cerebrum 310 The Mind and its relation to the body 324 Cranial Nerves 329 Sympathetic Nervous System 336 CHAPTER XIV. The Special Senses 340 Smell 340 Sight 343 Phenomena of Vision 351 Accommodation of the Eye to Vision 352 Defects of Vision 356 Hearing 358 The Mechanism of Hearing 362 Sense of Taste 364 Sense of Touch 366 CHAPTER XV. The Voice 370 Larynx 370 Compass of the Voice 373 Ventriloquism and Stammering , 374 CHAPTER XVI. Reproduction 375, Action of the Male. 377 Action of the Female 378 Corpus Luteum . 380 Action of the Oviducts 381 Development of the Ovum 382 Formation of the Amnion and Allantois 386 Formation of the Chorion 388- Preparation of the U terus for the Ovum 389 Formation of the Placenta 390 Umbilical Cord and Amniotic Fluid 391 Parturition 392 General Development of the Embryo 392 HUMAN PHYSIOLOGY. INTRODUCTION. Physiology, from (pvcng, “ nature,” and Aoyoc, a descrip- tion,” in its general sense, has for its province the investi- gation 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 Com- parative 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 importance to the medical student than the Physiology of the lower ani- mals, on account of its relation to Pathology and Therapeu- tics. The study of Physiology requires an intimate know- ledge of Anatomy and Chemistry, in order that the student may be able to comprehend the character of the structure he is examining, and the substances of which it is composed. Animate bodies, in contradistinction to inanimate, are possessed of organs, each of which has a special structure and distinct office to perform in the living organism. This action or office is called its function, for example, the func- tion of the liver is to secrete bile, the salivary glands to secrete saliva, &c. The functions of the different organs are also mutually dependent on each other. The aeration of the blood by the lungs, is dependent on its circulation by the heart and blood vessels, and the circulation of the blood 12 INTRODUCTION. is dependent on the influence of the nerves, and the continu- ance of life is the result of the continued normal and har- monious action of all the organs of the body. The different organs of the body are sometimes called systems, as the osseous system ; muscular system ; nervous system ; arterial system, etc. Each organ is made up of smaller parts or ultimate elements, which can only be seen and studied by the aid of the microscope ; these are called the “ anatomical,” “ histological,” or “ microscopical ele- ments ; for example, the primitive fibrillse are the ultimate or “anatomical ” elements of muscular tissue, the axis cylin- der and white substance of Schwann are the anatomical ele- ments of nerve fibres, etc. All living beings pass through the various stages of birth, growth, development, maturity, and decay. These are the so-called essentials of life. Birth means the separation from the parent, with power of independent life and existence, inherited from the parent. Growth is the power of increas- ing in size, but this is not limited to living beings. A stone or a crystal may also grow, but it is by the laying on of particles on the outside, or superficial, while the growth of living organisms is interstitial, and has definite limits. Living organisms absorb the material required in growth into their interior, and assimilate it into their own composition. De- velopment indicates the successive changes through which all living organs must pass, before they are capable of pro- perly performing their functions. The brain of the adult idiot has grown, but it is incapable of the proper perform- ance of its function, from want of proper development. Maturity is the attainment of complete growth, and is soon followed by decay or decline. In fact, decay may be said to be constantly taking place in our bodies, and life consists in making up for the loss attendant on it, by continual repair. The particles of our bodies die, and are replaced by new ones from day to day, although the individual remains the same, so that it may be said of our bodies “ in the midst of life we are in death.” INTRODUCTION, 13 Some have endeavoured to draw a distinction between the animal and vegetable kingdoms, but while this is a mat- ter very easy of accomplishment in the higher orders, it is very difficult to say where vegetable life terminates and animal life begins, lower in the scale. The distinction which is probably the most reliable, is the power of vegetables to live on inorganic matter, as water, carbonic acid, and am- monia, while animals cannot subsist without organic mate- rial. The distinctions sometimes given, based on the difference in chemical composition—the presence or absence of nitro- gen ; the power, or absence of movement, and the presence or absence of a stomach in animals and vegetables respec- tively, while of value so far as the higher orders are con- cerned, are valueless as a means of distinguishing between the two classes, low down in the scale of life. 14 PROXIMATE PRINCIPLES. CHAPTER I. PROXIMATE PRINCIPLES. Animal bodies are composed of solids and fluids : the former embrace the various textures and viscera ; the latter the blood, chyle, lymph and glandular secretions. The same substance may be fluid in one part of the body and solid in another; for example, lime phosphate is in solution in the albumen of the blood, but is solid in the bones. Every animal tissue and fluid contains a number of proximate principles mingled together in various proportions. A proximate principle may be defined to be any chemi- cal substance, which exists in the animal solids or fluids in its own form, and which may be extracted in an unaltered state by chemical process. But it must not be supposed that every substance which can be extracted from an organized solid or fluid by chemi- cal means is a proximate principle; for example, sodium chloride is a proximate principle; but chlorine is not, because it does not exist in its elementary form in the body. Lime phosphate is a proximate principle of bone ; but phos- phoric acid is not, because it does not exist in a free state in the bony tissue; still less phosphorus, which is obtained 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 does not exist as such in the body but 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 PROXIMATE PRINCIPLES. 15 amount of water. The temperature should not be above 100° (212°F.) because a higher degree would change 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, sodium glyko- cholate or tauro-cholate may be precipitated by lead ace- tate, forming lead glyko-cholate or tauro-cholate which may, in its turn, be decomposed by sodium carbonate form- ing the original sodium glyko-cholate or tauro-cholate. Sometimes a proximate principle cannot be separated in an entirely unaltered state. Albumen requires to be coagulated by heat or nitric acid ; the fibrin of the blood can only be separated by coagulation, which it does spontaneously; hence they lose their original character of fluidity, and are permanently altered. The proximate principles are divided into five classes: 1st. Crystallizable substances of inorganic origin, as water, sodium chloride, lime carbonate and phosphate, etc. 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 sulphur- etted 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. They contain carbon in large proportion but no nitrogen. 3rd. Organic substances proper, “nitrogenized substances,’7 “ albuminoid substances,” or “ protein compounds,” as albu- men, fibrin, casein, &c. They differ from the two former classes in the fact that they contain nitrogen. They are exclusively organic in their origin, are not crystallizable, and are not definite in their chemical composition. 16 PROXIMATE PRINCIPLES. 4th. Coloring matters, as hemoglobine, melanine, biliru- bine, biliverdine, etc. 5th. Crystallizable nitrogenous substances, as urea, crea- tine creatinine, lecithine, cerebrine, etc. PROXIMATE PRINCIPLES OF THE FIRST CLASS. Water, H20.—Water is the most important of the in- organic principles, and is found in all parts of the body. In the solids it does not exist in a fluid state, but is incor- porated with the substance of the tissue. It may be called “ water of composition,” in contradistinction to what is called in chemistry “ water of crystallization.” It con- stitutes 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 :— QUANTITY OF WATER IN 1,000 PARTS. Enamel of the Teeth 2 Epidermis . 37 Teeth 100 Bones 130 Tendons. 500 Cartilage.. 550 Muscles . 750 Ligaments 768 Blood 795 Bile 880 Milk... 887 Pancreatic Juice 900 Urine 936 Gastric Juice 975 Perspiration 986 Saliva 995 Solids. Fluids. Origin and Discharge of Water.—It is introduced with the fluid and solid elements of the food. It is also be- lieved to be formed in the body from the union of oxygen and hydrogen, as they are liberated from organic combinations. The amount of water taken into the system by an adult, in the course of 24 hours, varies from 3£ to 4 pounds. It is dis- charged from the body in four different ways—by the urine, faeces, perspiration, and breath—about 50 per cent, being dis- charged by the urine and faeces, 30 per cent, by the per- spiration and 20 per cent, by the lungs. These proportions 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 PROXIMATE PRINCIPLES. 17 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 sub- stances 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 and pliability, for, if water be expelled from a piece of cartilage by evaporation, it becomes dark in colour, semi-transparent, hard and inelastic. The same thing is true of musffes, tendons, etc. Sodium Chloride, NaCl.— Sodium chloride 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 been estimated by Dr. Lankester, at one-quarter of a pound, avoirdupois. 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.:— QUANTITY OF SODIUM CHLORIDE IN 1,000 PARTS, Muscles 2 Bones 7 Milk, 3 Saliva 1.5 Urine 5.5 Bile 3.1 Lymph 5. Blood 3.3 Chyle 5.3 Mucus 6 Aqueous Humor 11 Vitreous 14 Origix and Discharge.—It is introduced with the dif- ferent 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 different parts of the body. About f is discharged from the body in the urine, fleces, perspiration and mucus, the remaining i being sup- posed to be changed in the body by double-decomposition 18 PROXIMA TE PRINCIPLES. with potassium phosphate, resulting in the formation of sodium phosphate and potassium chloride, It is also sup- posed to furnish the sodium to all the salts of that metal. Function.—It regulates, to a certain extent, the process of osmosis, for we know that a solution of sodium chlo- ride permeates an animal membrane much less readily than pure water. In the blood it holds in solution the albu- men and earthy phosphates, and preserves the integrity of the blood corpuscles. As an article of diet, it stimulates the secretion of saliva and gastric juce, and aids in digestion. The importance of sodium chloride 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 vigor. 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 con- tained 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 the year a marked difference was noticed. Those animals which received the sodium chloride had a fine, sleek, healthy aspect, contrast- ing strongly with the listless and inanimate appeai'ance of the others. The animals of the forest, as the buffalo and deer have their “ salt-licks ” to which they resort from time, to time. Potassium Chloride, KC1.—This substance is found in the muscles,liver, milk, chyle, blood, gastric juice, bile, saliva, mucus and urine, associated with sodium chloride. It is quite soluble in the fluids, and is more abundant in muscle and milk, than sodium chloride, less so in blood, gastric juice and perspiration. Origin and Discharge.—It is introduced with the food and is also supposed to be formed in the interior of the body by double-decomposition as previously stated. Potassium chloride is discharged in the urine, mucus and perspiration. Function.—Its function is probably identical with sodium chloride. PROXIMATE PRINCIPLES. 19 Lime Phosphate, Ca3P408. — Lime phosphate is found in all the solids and fluids of the body, but is more abun- dant in the solids, and increases as age advances. It exists in a solid state, as in the teeth, 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, is is held in solution by the acid sodium biphosphate, so that when the urine is rendered alkaline the phosphates form a turbid precipitate. 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, 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 solution of lime carbonate, its rigidity may be again restored to a certain extent. QUANTITY OF LIME PHOSPHATE IN 1,000 PARTS. Solids. Enamel 885. Dentine 643. Bone 550. Cartilage 40. Muscle 2.5 Urine 7 Milk 2.7 Gastric Juice 4 Blood 3 Saliva 6 Fluids. Origin and Discharge.—This substance is derived ex- clusively from exterior sources. It is introduced with the food, in nearly all forms of which it is found, and is elimin- ated by the urine, perspiration, and mucus; most by the urine, a small quantity only by the faeces and perspiration. 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 presence in milk is subservient to the growth and development of bone in the young of the mammalia. Lime Carbonate, CaC03.—This substance exists in the 20 PROXIMATE PRINCIPLES. bones, teeth, cartilage, blood, sebaceous matter, internal ear (otoliths), and in the urine. In bone it is not so abundant as lime phosphate, the proportion being about 113 parts in 1000. It is held in solution in the blood and urine by the free carbonic acid and alkaline chlorides. 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. Function.—Its function is analogous to that of lime phos- phate. Sodium and Potassicm Carbonates, Na2C03, K2C03.— Sodium and potassium carbonates are found in the bones, blood, lymph, saliva, and urine. ' They give to the blood its alkaline reaction. Claude Bernard has shown that the alkalescency 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.—They are introduced in small quantities in the food, but are principally formed within the body by decomposition of other salts, malates, tartrates, and citrates of the alkaline bases. These salts when introduced into the body in the food are decomposed. Their organic acid is destroyed and replaced by carbonic acid, forming sodium and potassium carbonates. They are discharged in the urine and mucus. Function.—Their function is to maintain the fluidity of the fibrin and albumen, to give alkalescency to the blood and secretions and to assist in preserving the form and con- sistence of the blood corpuscles. Sodium and Potassium Phosphates, Na.,HP04, K2HP04, —These substances exist in all the solids and fluids of the body. They are soluble in water, possess an alkaline reaction and are known as the alkaline phosphates. These, together PROXIMATE PRINCIPLES. 21 with the alkaline carbonates are essential to the maintenance •of the alkaline character of the fluids of the body, all of which possess an alkaline reaction except the following, which are acid; 1 Gastric juice. 2 Perspiration. 3 Urine. 4 Mucus of the Vagina. The fluids of the carnivorous animals contain a prepon- derance of the alkaline phosphates; the herbivorous a prepon- derance of the carbonates. The former is owing to the phosphates found in the animal tissues upon which the car- nivora feed. Origin and Discharge.—They are introduced in the food, both animal and vegetable, and are also partly formed in the body by the oxidation of phosphorus and its union with the alkaline bases. They are discharged in the urine, perspiration and mucus. Function.—Together with the alkaline carbonates they give to the blood and secretions their alkaline reaction. This condition of the blood increases its power of dissolving car- bonic acid, and also favours the elimination of the latter by the lungs. A small proportion of sodium phosphate added to water, enables it to dissolve twice the usual quantity of car- bonic acid, and the other alkaline salts have a similar action. The acid sodium biphosphate, is found in urine, and gives to that fluid its acid reaction. It is formed from the sodium phosphate by the action of uric acid which combines with a portion of the sodium. 1 Sodium and Potassium Sulphates, Na2S04,K2P04— These exist in small quantity,—in some fluids only a trace, as in milk, saliva, Ac. They are found in blood, lymph, milk, saliva, mucus, perspiration, urine and fseces. They are more abundant in the urine, than in any other fluid, being a little more than half as much as of the phosphates. They are introduced by the food and drink. A certain amount is also formed in the body in a similar manner to the phos- phates, by oxidation of sulphur and its subsequent union with the alkaline bases. 22 PROXIMATE PRINCIPLES. Magnesium Phosphate and Carbonate, MgHP04, Mg C03.—These salts are found in small quantities in nearly all the solids and fluids of the body. Associated with lime phosphate, they are known as the earthy phosphates, They are introduced in the food. They are dissolved in the fluids by the alkaline chlorides and phosphates, and in the urine by the sodium biphosphate The salts of magne- sium are more abundant in muscles and brain, than the salts of lime. The}* are eliminated principally by the urine and fpeces. The proximate principles of the first class exist in the animal tissues in the same form in which they occur in the inorganic world. Lime carbonate in the bones is the same as that which is found in limestone rock ; and sodium chlo- ride is similar to that which is found in solution in sea water. Gases.—Oxygen, nitrogen, hydrogen, carbonic acid, car- buretted 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 corpuscles rendering them biconcave, and gives to the arterial blood its bright-red colour. Arte- rial blood contains about 10 to 12| per cent of ox}Tgen. Nitrogen exists in very small quantity in the blood and lungs. It is also found in the intestines. Carburetted and sulphuretted hydrogen, also pure hydrogen, are found in the alimentary canal, and in small quantities occasionally in expired air. Carbonic acid is an excretion given off prin- cipally by the lungs. From 20 to 25 per cent, is found in venous blood. The substances of this class are all of organic origin, and exist both in vegetables and animals. They consist of car- bon, hydrogen and oxygen only, and are therefore non-nitro- PROXIMATE PRINCIPLES OF THE SECOND CLASS. PROXIMATE PRINCIPLES. 23 genous. There are two divisions, the carbo-hydrates and fatty matters. In the former the hydrogen and oxygen are in the proportion to form water, and in the latter the carbon and hydrogen are in much larger quantity than the oxygen. Starch, C6Hio05.—This substance, though not crystal- lizable, is so closely allied to the others in its general pro- perties, and so easily converted into sugar, which is crystallizable, that it is naturally included in the proximate principles of the second class. It is not amorphous, but pos- sesses a distinct granular form. It is found in nearly all the flowering plants, and is the principal ingredient in sago, tapioca, arrowroot, &c. QUANTITY OF STARCH IN 100 PARTS. In Rice 88 “ Maize 67 ‘ ‘ Barley Meal 66 “ Rye “ 64 “Oat “ 60 Wheat Flour 57 Iceland Moss 44 Beans 33 Peas 37 Potatoes .20 Physical Appearance of Starch.—It is a white pow- der, consisting of solid granules, which vary in shape, size, and physical appearance, in different vegetables. It pro- duces a crackling sensation when rubbed between the fin- gers. Each starch granule consists of two substances min- gled together, granulosa and cellulose. The former, which is more abundant, is soluble in boiling water, the latter is insoluble. The starch granule of potato varies from TTr?rTFTr to tof of an inch (2.5 to 62.5 mmm.) in diameter, is pear- shaped in its outline, and marked by concentric rings sur- rounding a minute pore, called the hilum, which is situated near the small extremity of the granule (Fig. 1.) The granules of arrowroot are oval in shape, small, and more uniform, and vary from to -gihr of an inch (12.5 to 50 mmm.j in diameter (Fig.3). The hilum is in the shape of a circular pore or transverse slit. The starch grains of wheat vary from to T-J-¥ of an inch (2.5 to 35.5 mmm.) in di- ameter, nearly circular in form, with a round or transverse 24 PROXIMATE PRINCIPLES. hilum, but without any distinct laminar appearance (Fig. 2), The granules of Indian corn are the same size as the preced- ing ; they are irregular in shape, and present a crucial, (Y) or (T) shaped pore (Fig. 4). The granules of rice are very small,, uniform in size, polygonal in outline, and present a granular appearance (Fig. 5). Fig. 1 Starch granules of potato. (2). Starch granules of wheat. (3). Starch granules of arrowroot. (4). Starch granules of Indian corn. (5). Starch granules of rice. Origin and Properties.—It is found in most vegetable substances used as food, and in that way is introduced into the body. It is also found in the animal body in the lateral ventricles of the brain, fornix, and septum lucidum. It was first observed by Purkinje, and afterwards by Kolliker and Virchow. The granules are called corpora amylacea, and vary in size from to jtVo °f an inch (5.5 to 22.5 mmm.) in diameter. They are transparent, softer than in vegetable starch, irregularly rounded, and present a faint lam- inar 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 Fig6- Corpora Amylacea. PROXIMATE PRINCIPLES. 25 water. It is then said to be hydrated. This is simply a mechanical change. Starch may be converted into dextrine, by torrefaction—a dry heat of 210° ("400 F.) This sub- stance which is of a gummy nature, is so named because in solution it rotates the plane of a polarized ray of light towards the right. Starch may also be converted into sugar, in three differ- ent ways. Firstly, by boiling in dilute nitric, muriatic, or sulphuric acid for 36 or 40 hours. The starch is first converted into dextrine and then into sugar, and at the same time loses its property of responding to the iodine test. Secondly, by contact with an animal or vegetable sub- stance, at a temperature of 37.5° (100°F.) Boiled starch mixed with saliva is converted into sugar in a few minutes. Thirdly, by the process of nutrition and digestion in ani- mals and vegetables. The starch found in seeds and roots is converted into sugar by the presence of diastase, and thus rendered soluble before it can be taken up to nourish tho plant during its growth. Function.—Its office in the animal economy is to form sugar. Starch is converted into sugar during digestion by the action of the pancreatic and intestinal juices. It is necessary for the process of development and nutrition at all periods of life. It is the source of sugar in the vegetables. Test.—In whatever state it exists, its presence may be detected by its reaction with free iodine, giving a blue color. Ozone test-paper is prepared on this principle. White paper is first saturated in a solution of starch, and then in potassium iodide. When exposed to an atmosphere con- taining ozone, the latter oxidizes the potassium and liberates the iodine which reacts upon the starch, and stains the paper blue. Glycogen, C6H10O5—This is the name given to an amyla- ceous substance found in animal bodies. It exists in ther 26 PROXIMATE PRINCIPLES. liver of all vertebrate animals, also in the muscles and in- tegument at an early period of development. It gives a violet-red color with iodine, instead of blue. It is soluble in water and is easily changed into sugar or glucose, by boil- ing with a dilute acid, or by contact with an animal sub- stance. It is the source of sugar formed in animals, as starch is in vegetables. Sugars.—These substances are soluble in water, crystal- lize on evaporation, and are converted into alcohol and car- bonic acid in the process of fermentation. The ordinary varieties of sugar are : glucose or grape sugar, saccharose or cane sugar, and lactose or milk sugar. Saccharose is more soluble than any other variety, and is therefore sweeter. Glucose crystallizes with difficulty, but ferments readily ; while cane and milk sugar ferment with difficulty. Sugar 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. It is never discharged from the body in health (except in the female during lactation) ; but in certain diseased conditions of the system, it is rapidly produced in the liver, in the form of glucose and is discharged in the urine, constituting diabetes mellitus. TABLE OF QUANTITY OF SUGAR IN 100 PARTS. In Figs 62.50 11 Cherries 18.52 11 Peaches 11.61 11 Tamarinds 12.50 11 Pears 11.52 11 Beets 8.00 “ Barley 3.04 Wheat Flour 2.33 Rye do 3.46 Ind’n Corn do 3.71 Peas 2.00 Cow’s Milk 5.20 Asses do 6.08 Human do 6.50 It is an important article of diet. It is introduced with the milk in the food of the child. In the adult it is intro- duced partly in the food as sugar ; but mostly in the form of starch, which is converted into glucose during digestion by the action of the pancreatic and intestinal juices. Glucose, CcH1206—This variety is named grape sugar because it exists in large quantity in ripe grapes and PROXIMA TE PRINCIPLES. 27 sweet fruits. Glucose is found in the interior of the body, in the liver, blood, lymph, chyle, 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 readily soluble in water, and has a moderately sweet taste. It may be formed from starch bv boiling with a dilute acid, by contact with animal sub- stances at a temperature of 37.50° (100 F), or by the action of a nitrogenous substance in a state of decay, as vegetable diastase. Tests.—Trommer’s Test.—To the suspected liquid add one or two drops of a solution of copper sulphate; render it alkaline by the addition of a solution of caustic potassa. The whole solution then assumes a blue color. Then boil it for a few minutes, and if sugar be present, copper suboxide 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 copper protoxide to the suboxide, in the presence of an alkali, which is added to liberate and neutralize the sulphuric acid. This test is not applicable to cane or milk sugar; but by boiling them in dilute sul- phuric acid they are converted into glucose, which responds readily. Liver and milk sugar act promptly with Trom- mer’s test. Care should be taken that only a small quan- tity of copper sulphate 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 among the proxi- mate principles of the 3rd class. “ Fehling’s Liquor ” Test.—The principle is the same as in Trommer’s test, but it is a much more delicate test. The solution is prepared according to the following formula : Copper Sulphate, crystallized . . . 40 grammes ==( 617 grains) Potassium Tartrate, neutral . . . .160 “ =(2468 “ ) Sodiumhydrateinsolutionsp.gr. 1.12 650 “ =(10029 “ ) 28 PROXIMATE PRINCIPLES. The first two are dissolved in water, mixed with the alka- line solution and water added to make 11544 cubic centi- metres =(2 pints.) Add to the suspected mixture enough of the solution to give it a blue tinge, and boil. If sugar be present, the cop- per suboxide is thrown down, as in Trommer’s test. A single drop of this liquid will detect TfT of a milligramme =(yoV(T of a grain) of glucose. It should be kept excluded from light and air, otherwise it will become changed and unfit for use. Fermentation Test.—Add a few drops of fresh yeast to the saccharine liquid, and keep it at a temperature of about 25° (77°F,), in this way the sugar is converted into alcohol (C2HeO),and carbonic acid (C02); the latter should be collected in a vessel and examined. Every cubic inch of carbonic acid is about equal to one grain of sugar. The presence of carbonic acid may be proved by introducing into the vessel a lighted taper, which will be immediately extinguished; or by agitating with lime water, which will be rendered turbid by the formation of insoluble lime carbonate. The fer- mentation of glucose is due to the vegetation of a micro- scopic fungus, saccharomyces or torula cerevisice. The fun- gus is entirely cellular, the cells being rounded or oval, with one or two nuclei and about in’e of an inch, (10 mmm.) in diameter. They multiply by a process of budding, and occasionally two or three of them may be seen adhering together. They may be observed on the surface of diabetic urine, which has stood for some time. 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 pot- ash in solution is added to the suspected liquid, and boiled in a test tube. If sugar be present it acquires a brownish color. This is not a very reliable test. Saccharose, or cane sugar C12H22On.—Saccharose is very soluble, readily crystallized, and the sweetest of all the PROXIMATE PRINCIPLES 29 sugars. It exists in the sugar cane, maple, beet, parsnips, rarrots, turnips etc., and is chiefly used for culinary purposes. It is formed from glucose in the process of vegetation. It will thus be seen that starch and sugar are closely allied to each other in all their relations—and are mutually con- vertible, starch being the solid formation, and sugar the active liquid one. Cane sugar will not respond to Trom- mer’s test, nor ferment until it has been transformed into glucose by boiling it for a few seconds with a dilute mineral acid, or by adding yeast to it. Lactose, or sugar of milky C12H24012.—This form of sugar is found only in milk, and is a constant ingredient. It is less soluble than the other forms, and therefore not so sweet. It undergoes alcoholic fermentation slowly and in- completely, and when it takes place in milk a part of the sugar is transformed into lactic acid—known as the lactic acid fermentation. It responds readily to Trommer’s an I Fehling’s tests. It is supposed to be formed from glucose by catalysis in the mammary gland. Oils and Fats.—These substances are found in both animal and vegetable tissues. The three principal varieties of fat which exist in the animal economy are: Oleine— C57H10406; Margarine or Palmitine—C51H9g06 ; and Stearine —C57Hn0O6. By the chemist these bodies are con- sidered as salts, formed by the union of fat acids with the base—glyceryl—thus :— Oleine .. Oleic Acid (C18 H34 O2 ) and Glyceryl (C3 H5 ... Oleate of Glyceryl. Palmitine j Palmitic Acid (Ci6 H32 O2 and Glyceryl (C3 H5 .Palmitate of Glyceryl. Stearic Acid (Ci8 H36 O2 ) and Gylceryl C3 H5 ) Stearine. . Stearate of Glyceryl. These may be separated from each other by the process of saponification. When oleine, palmitine, or stearine, is boiled in a solution of caustic alkali, it is decomposed into a fat acid, as oleic, palmitic, or stearic, and a sweetish viscid fluid 30 PROXIMATE PRINCIPLED. the hydrate of glyceryl, or glycerine. The acid unites with the alkali and forms soap, and glycerine (C3H53HO.) is set free. The fat acid may also be separated from the base, gly- ceryl, by passing steam through fat at a temperature of 300° (572° F.) The human body, when immersed in water for a length of time, becomes changed into a substance called adi'pocere, or saponified fat. This is supposed to be a pro- cess of saponification, caused by the union of palmitic,, stearic, and oleic acids with ammonia, which is developed during the process of decomposition. Physical Appearance and Properties of Fat.—It ex- ists in two forms in the body. First, in the form of large cells or vesicles, varying in diameter from (1 to of an inch (31 to 83 mmm.), as in adipose tissue, (Fig. 9.) Secondly, in the form of oil globules, varying from llVJ55 to 47/00 of an inch, (1.2 to 6 mmm.) as in the chyle, in which it is said to be emulsified, (Fig 7.) This is a mechanical subdivision of the fat Fig. 7. Fig. 8. Fat globules of chyle. Fat globules of cow’s milk. cells, and is the only form in which it can be absorbed. Fats- may be emulsified by means of alkalies, serum of blood, muci- lage, or white of egg. The fat cell is characterized by a dark border surrounding a bright centre; usually no nucleus is seen,, but it may occasionally be found attached to the cell wall. 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 appearance. In cow’s milk, the oil globules are of an inch (6.25 mmm.) in diameter, have a pasty consistence, due to the palmitine they contain; PROXIMATE PRINCIPLES. 31 and when churned, are converted into butter, from their tendency to cohere. Oleine, palmitine, and stearine, are always found mingled 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 Fig. 9. Fat cells of adipose tissue. also in the bile dissolved in the salts. They are united with phosphorus, constituting the phosphorized fats of nerve tis- sue. 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 palmitine are crystallizable, and sometimes present a very beautiful appearance. The crystals are needle-shaped, and are deposited in a radiated form, but sometimes curved and branching. Stearine predominates in hard, palmitine in soft, and oleine in liquid fats. The melting point of stear- ine is 60°, (140° F.), palmitine 46°, (115° F.), and oleine 38°, 100° F. They are insoluble in water, but are soluble in ether and hot alcohol. TABLE OF QUANTITY OF FAT IN 100 PARTS. Linseed 22.00 Eggs 7-oo Liver of calf. . 5.58 Beef, average 5.19 Salmon 4.85 Goat’s milk 3.82 Cow’s milk 3.70 Human “ 3.55 Beans 2.50 Wheat 2.10 Potatoes ix Indian Corn 9 32 PROXIMATE PRINCIPLES. Origin and Function.—It is found in all parts of the body except in the compact tissue of the bones, teeth, ten- dons, beneath mucous membranes, in the cutis, between the rectum and bladder, beneath the epicranial aponeurosis, in the ligaments, scrotum and eyelids. It is introduced in the food, and is emulsified by the pancreatic juice during diges- tion and previous to absorption. It is also formed in the interior of the body. This has been proved by experiments on geese, the re- sult of which showed more fat in the body than could be accounted 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 cartilage cells, and also in the muscular fibre cell of the uterus during involution (Fig. 10,) It also exists in the form of globules in the hepatic cells (Fig. 11,) sebaceous glands, corpus luteum and uriniferous cubes 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 cer- tain diseased conditions, as in fatty degeneration of the heart, liver, kidney. Its function in the foim of adipose tissue, is to give rotundity to the body ;form a nidus for delicate organs; fill up spaces other- wise 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 Fig. 10. Uterine muscular fibre cells, two weeks after parturition Fig. 11. Hepatic cells. PROXIMATE PRINCIPLES. 33 supplies animal heat, and is a store of food in case of emer- gency, as in the hybernating animals. Certain kinds of food favor the formation of fat; for example, negroes employed in making 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. Cholesterine, C26H440.—Thissubstance may be described among the oils and fats. It is found in bile, blood, liver, nervous tissue, crystalline lens, and meconium. It differs from ordinary fat in the fact that it is not capable of saponi- fication, is volatile at a high temperature and rotates a ray of polarized light to the left. It crystallizes in thin trans- parent rhomboidal plates, is insoluble in water, but soluble in ether, chloroform, hot alcohol, and volatile and fatty acids. When treated with sulphuric acid and chloroform it produces a peculiar red color, which soon changes on exposure to air to violet, blue, green and finally fades away. It melts at 145° (293°F) and distils at 360°. (680° F). The substances belonging to this class are very important as they have an intimate connection with the active phe- nomena of living bodies. They are not crystallizable, and are not definite in their chemical composition ; that is, they do not always contain the same proportions of oxygen, hydro- gen, 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 pro- perties of the substance which they form. This is charac- teristic of organic substances. They all closely resemble albumen, hence called “ albuminoid substances”. Their re- \ action is neutral. They were regarded by Mulder as com- PROXIMATE PRINCIPLES OF THE THIRD CLASS. PROXIMA TE PRINCIPLES. pounds of a theoretical radical, which he called protein. This gave them the name of “ protein compounds”. The albuminoid substances are all hygroscopic. In some parts of the body they are fluid, and in others semi-solid, or solid, depending upon the amount of water which they contain. When subjected to evaporation they lose water, and may be reduced to a solid state. Advantage is taken of this fact in O the preservation of eggs,, milk etc., by evaporating at a low temperature and hermetically sealing in cans. When water is added, they again absorb it, and return nearly to their original condition. They are all capable of being coagulated. Fibrin coagu- lates spontaneously, when removed from the vessels ; albu- men, on the application of a temperature of 71° (160°F.); and casein on the addition of an acid. An organic sub- stance, 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 coagula- tion to remove an organic substance from the other proxi- mate principles with which it is associated. Fibrin is obtained by switching freshly-drawn blood with a bundle of twigs. Thus obtained it is an unnatural condition, having lost its original character of fluidity. These organic substances, when the vital force is removed, are liable to putrefaction. This process is peculiar to organic nitrogenized substances, and distinguishes them from all other proximate principles. When in a state of putrefac- tion, they are capable of inducing in certain other substances a process of fermentation, as for example, the decaying or- ganic 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. The conditions necessary to putrefaction are, the presence of oxygen, heat, and moisture. If oxygen PROXIMATE PRINCIPLES. be excluded by boiling, and the substance be placed in her- metically sealed vessels, in an atmosphere of carbonic acid, or nitrogen, putrefaction will not take place. The same is the case if the substance be dried, or if the temperature be kept near the freezing or boiling points respectively. During the process of putrefaction, there will be observed swarms of minute microscopic organisms floating about in the fluid, called bacteria and micr ococci, (Fig. 12); the former are so named from their rod-like form, and consist of two small cells placed end to end ; the latter are so called because of their minuteness, and appear like small specks. Both are in a state of inces- sant and rapid motion. Bacteria are in- creased by spontaneous subdivision of the cell into two, each of them again subdividing, and so on. The variety found in putrefying infusions is known as the bacterium termo. They are believed by some to be vegetable organisms, which are spontaneously developed in the albuminoid substance, and cause putrefaction to take place. By others, they are supposed to be derived from germs floating in the air, and which become developed in putrefying substances. Fie. 12. A.—Bacteria. B.—Micrococci. Albuminous matters are found in most substances used as food, the proportion according to Payen being as follows : QUANTITY OF ALBUMINOUS MATTER IN 100 PARTS. Beans 24.40 Mackerel 24.30 Peas 23.80 Beefsteak 19.50 Wheat 18.00 Oats 14-3° Oysters 14.00 Salmon 13.50 Indian corn 12.50 Eggs 12.30 Rice 7.50 Potatoes 2.50 Albumen.—This substance is named albumen from “Al- bus,” white, 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, cerebro-spinal fluid, serous and 36 PROXIMATE PRINCIPLES. synovial fluids, and milk,—solid in the brain, spinal cord and nerves. It is also found in mucous membranes, muscu- lar tissue, and in the aqueous and vitreous humors of the eye. It exists in the white of egg, and can be easily coagulated or made to assume a solid form. Composition and Properties.—The average chemical composition of the albuminous substances is as follows :— (Fremy,) Carbon . . . . 52.0 Hydrogen . . . .6.9 Nitrogen .... 15.6 Oxygen . . . .24.0 Sulphur .... 1.5 Albumen does not coagulate spontaneously, but may be coagulated by any of the following re-agents, viz., heat at 71° (160°F.), alcohol, mineral acids, as nitric, sulphuric, etc., tannic acid, potassium ferrocyanide in an acid solution, and the metallic salts. It is very readily coagulated by bichloride of mercury, and hence it is used in cases of poi- soning from that salt. It unites with it to form the so-called albuminate of mercury. The white of one egg is sufficient to neutralize four grains of the bichloride. Albumen coag- ulates at the negative pole of the battery, if not too strong a current, and at both poles when a strong battery is used. It is not coagulated by the vegetable acids, except tannic acid. The fresh juices of vegetables contain a substance coagu- lated by heat, called vegetable albumen. When albumen is evaporated at a temperature of 49° (102° F.) it becomes solid and brittle, but otherwise unchanged, and may be re-dissolved in water. When coagulated by heat or the mineral acids, &e., it cannot be re-dissolved or made to resume its original condition. It is held in solution in the body by sodium chloride, sodium and potassium carbonates and phosphates, which give it an alkaline reaction. It ex- ists 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. PROXIMATE PRINCIPLES. 37 Origin and Function.—It is derived from the albumin- oid 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 album- inuria, the nervous and muscular tissues suffer most. It is converted into fibrin through the agency of the blood-cells and oxygen ; this is probably a chemico-vital process. Al- bumen is never discharged from the body in health. In a diseased state of the kidney it is found in the urine,, as in Bright’s disease, also in scarlatina, diphtheria, and in the cold stage of cholera. Tests.—These depend on its property of coagulation. First. Heat.—When a solution containing albumen is heated in a test tube to 75° (167°F), a precipitate, more or less abundant, is formed. If, however, the liquid be alkaline the albumen will not coagulate ; hence an acid, as acetic 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 solu- tion 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 or Peptone.—This is a colorless liquid found in the chyle and blood. It differs from albumen from the fact that it is not coagulated by heat, nitric acid, or potas- sium ferrocyanide. It is coagulated by alcohol in excess, 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 and intestines, only during digestion. When Trommer’s test is applied to a saccharine liquid con- taining albuminose, a purple color is produced on the ad- 38 PROXIMATE PRINCIPLES. dition of the re-agents, and when boiled, the color changes from red to yellow, but no copper suboxide 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 reac- tion 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, etc., 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 account of its superior osmotic properties. It is the soluble principle of fibrin, albumen, casein, &c. Fibrin.—Fibrin exists in the blood, lymph, and chyle as found in the lacteals. When blood is removed from the ves- sels, it soon separates into a solid portion, or clot, and a fluid portion, or serum. The clot consists of coagulated Fig. 13. Coagulated fibrin containing white blood corpuscles. fibrin, containing red and white corpuscles entangled in meshes. When inflammation is present, the red corpuscles have a tendency to cohere, and sink to the bottom of the vessel, Jience the fibrin is more abundant at the top, and from the PROXIMATE PRINCIPLES. peculiar color it presents, is called the “ buffy coat.” Fibrin is difficult to obtain free from corpuscles. It may be ob- tained 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 some- times found in a tolerably pure state, in the cavities of the- heart and large arteries after death. It is also found arranged in laminae, in the sacs of aneurisms. It is regarded by some as formed by the union of two substances in the blood, fibrinogen and fibrinoplastin, and by others as resulting from the decomposition of a substance called plasmine. Physical Appearance and Properties.—Fibrin is a greyish-white, tough, elastic and stringy substance, composed of microscopic fibrils. It possesses the property of “ spon- taneous coagulation,” or fibrillation. It 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 con- centrated hydrochloric acid, and after a time the solution ac- quires 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 alka- line chlorides and carbonates. Coagulation.—The coagulation of fibrin is a process of fibrillation. When the process of coagulation is viewed with a microscope, a granular appearance is first noticed ; some of 40 PROXIMATE PRINCIPLES. the granules become star-shaped by the addition of other granules, the arms being directed towards the corpuscles which are ultimately included in the meshes. When fully organized it is distinctly fibrous in structure. Coagulation of the fibrin takes place more slowly in the absence of the corpuscles, as in filtered blood. Certain vegetable sub- stances as wheat flour, contain an albuminous matter very similar to fibrin, called gluten, or vegetable fibrin. Origin and Function.—Fibrin is formed from albumen, by the influence of the corpuscles ana oxygen; in other words, it is albumen in a higher state of organization. It gives to the blood its property of coagulation, and it is through this property that “ natural haemostasis” is effected. It gives to the blood its viscidity, and prevents it from, exuding through the coats of the vessels. It was formerly supposed to be the material which was thrown out, and sub- sequently became organized, in the repair of wounds, and in inflammation, under the name of “ coagulable lymph” Lymph is now generally believed to be the product of the white corpuscles, which have passed through the coats of the vessels by virtue of their amoeboid movement, supplemented by the proliferation of connective tissue elements in the wounded or inflamed parts. Fibrin was some considered as effete matter, formed from the worn out elements of the blood and tissues, and the arguments adduced in favour of that view were, that it was increased in bleeding and starvation; that there was none found in the renal veins, having been discharged by the kidneys ; that there was very little in the blood of the foetus ; none in the egg; none in the chyle until it entered the lacteals, and then only as the result of the additions made to it from the blood or lymph. Casein.—This is an albuminous principle found only in milk. It is held in solution by the alkaline carbonates, and when any of the organic or mineral acids, or magnesium .sulphate is added, the alkali is neutralized, and coagulation PROXIMATE PRINCIPLES. 41 of the casein follows. It is also coagulated by a solution of rennet, the abomasus, or fourth stomach, of the young of ruminants. The pepsine contained in the stomach has the power of converting the sugar of milk into lactic acid, which neutralizes the alkali, and causes a precipitate of casein. This is a catalytic process. Casein is also coagu- lated during a thunder storm ; a substance called ozone is developed in the atmosphere, which acts on the casein and decomposes it. The decaying casein acts as a ferment, and converts the sugar of milk into lactic acid, which precipi- tates the casein. Casein differs from albumen; it is not coagulated by heat, and is precipitated by organic acids. The precipitate of casein may be re-dissolved by a solution of caustic alkali. It is insoluble in water and alcohol. An albuminous substance called vegetable casein is found in beans, peas, &c. 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 a nearly 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.—This is a semi-solid substance 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 globuline. Pepsine.—This is the organic principle of the gastric juice. It is coagulated by heat and alcohol, and is with 42 PROXIMATE PRINCIPLES. difficulty distinguished from albumen. It exists in the gastric juice in the proportion of fifteen parts per thousand, from which it may be precipitated and extracted 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. Pancreatine.—This substance exists in the proportion of ninety parts per thousand in pancreatic juice. It is a viscid fluid, coagulable by heat, alcohol, and strong acids. It is coagulated by magnesium sulphate; this distinguishes it from albumen. It has the property of emulsifying oils and fats, and of converting starch into sugar during the pro- cess of digestion. It is formed from the albumen of the blood in the pancreas. Ptyaline is an ingredient in saliva, and gives it the pro- perty of converting starch into sugar. It is not coagulated by nitric acid or acidulated potassium ferrocyanide. This distinguishes it from albumen. It is precipatated by alco- hol and boiling, and in the latter case loses its power of con- verting starch into sugar. Mucosine.—The organic substance of mucus is termed mucosine. In some of its properties it resembles albumen. It is coagulated by alcohol and acids, but not by heat, or the metallic salts. It lubricates the free surface of mucous membranes, and is formed from the blood by the agency of the cells, which line the free surface of the membrane and its follicles. Musculine or Myosine is a semi-solid substance peculiar to muscular tissue. It is insoluble in water, but is soluble in a mixture of ten parts of water with one of hydrochloric acid, and may be precipitated again by neutralizing with an alkali. It is a most important element of animal food, and is the great source of albumen and fibrin. Caiitilagine is the organic ingredient of cartilage. By prolonged boiling, it is transformed into a substance called PROXIMATE PRINCIPLES. 43 “ chondrine.” It is precipitated by acids and some of the metallic salts ; this distinguishes it from “ gelatine.” Collagen.—This substance is peculiar to bones, tendons, ligaments, etc. It constitutes the principal part of the ani- mal 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 not soluble in water, alcohol, ether, or acetic acid, but is dissolved and decomposed in nitric, sul- phuric and hydrochloric acids, and these solutions are not precipitated by alkalies. Keratine.—This is an organic substance, found in the epidermis, nails and hair. It is not affected by boiling in water, alcohol, ether and dilute acids, except by continuous boiling in a Papin’s digester at 150° (302°F). COLORING MATTERS. The substances of this group give to the tissues and fluids their distinctive coloration. They are all supposed to be crystallizable, and formed from the coloring matter of the blood. The coloring matter may be removed from the fluids of the body by filtering through animal charcoal, which has the property of removing coloring matter from any fluid. Animal charcoal will also remove albuminous matter from any fluid containing it. The most abundant and important ■of the coloring matters is Hemoglobine.—It is analogous in many respects to chlo- rophyl in the vegetable kingdom, for while hemoglobine is the agent on the one hand by which oxygen is carried into the system, chlorophyl, on the other, is the agent by which carbonic acid and water are decomposed and oxygen set free in the vegetable. It exists in the blood corpuscles in the proportion of 25 to 30 per cent., and also in muscular tissue. It is soluble in water, dilute alcohol, and alkaline salts, but is insoluble in strong alcohol, ether and oils. It crystallizes out in rhombic or hexagonal plates or prisms* 44 PROXIMATE PRINCIPLES. differing in different species, and also in the same species under different circumstances. It is easily decomposed. Its characteristic property is its great power of absorbing oxy- gen, which it holds in a free state, until it yields it up to the tissues. When charged with oxygen it becomes bright red, and is called “oxidized ” or scarlet hemoglobine; when deoxi- dized,it assumes a purple color,and is called “reduced” or pur pie hemoglobine. It contains 4.2 parts iron per thousand, which is essential to the blood. This is not in the form of an oxide, but is combined with carbon, hydrogen, nitrogen, and oxygen of which it is composed. Iron is also found in the coloring matter of the hair, bile and urine. The blood of an ordinary sized man is said to contain 2.8 grammes (43 grs.) of iron. When the red blood corpuscles are broken down from any cause, the hemoglobine is set free, and the walls of the vessels and tissues are stained. This has been mistaken for arteritis. When the hemoglobine is deficient in the blood, as in anemia, etc., it may be restored by the administration of iron. 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 abun- dant in the epidermis of the negro. It is formed from hemoglobine, but contains less iron. The coloring matter is the same in all situations, the different shades being pro- duced by the arrangement of the pigment 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 alcohol, ether and dilute acids, but is soluble in caustic potassa. Bilirubine is formed from hemoglobine in the liver, and constitutes the yellowish-red coloring matter of the bile. It is crystal lizable, insoluble in water, but soluble in alcohol, ether, chloroform, and alkaline fluids. It responds readily to “ Gmelin’s bile test,”—nitroso-nitric acid. If a small quan- tity of nitric acid be dropped into a solution of bilirubine PROXIMA TE PRINCIPLES. 45 to which nitrous acid is previously added, a play of colors is produced in order as follows,—green, blue, violet, red, and yellow. Bilirubine, if rendered alkaline, and exposed to the air becomes changed into biliverdine. Biliverdine is the greenish coloring matter of the bile. It is more abundant in animals that feed upon vegetable food. It is insoluble in water, ether and chloroform, but is soluble in dilute alkaline solutions, alcohol, and acetic acid. It is believed to be formed from bilirubine. It is discharged from the body in the faeces. It is often found in gall stones, Urochrome or Urosacine is a yellowish-red coloring matter peculiar to the urine. It is found, also, in urinary calculi. It is probably the worn-out hemoglobine of the blood, which is being discharged by the kidney. Urosa- cine and the coloring of bile are both discharged from the body, the one in the urine, and the other in the faeces. It is soluble in water and in ether, but only slightly so in alcohol. Luteine is a yellow coloring matter found in yolks of eggs and the corpus luteum. It is crystallizable, insolu- ble in water, but soluble in alcohol, ether, chloroform, and oils. It is easily decomposed, and nitric acid added to it gives a blue color. The substances of this group are crystallizable, and with one or two exceptions are derived from the nitrogenous mat- ters of the body as the result of retrograde changes. They are lecithine, cerebrine, leucine, and the substances found in urine and bile, as urea, creatine, creatinine, urates and hippu- rates of soda, glycocholate and taurocholate of soda. The latter will be described with urine and bile respectively. Lecithine, formerly described as a phosphorized fat is found in blood, (.4 parts per thousand), bile, spermatic fluid, yolk of egg and nerves, also in certain vegetables. It is CRYSTALLIZABLE NITROGENOUS MATTERS. PRIMARY FORMS OF TISSUE. soluble in alcohol, ether, chloroform, and oils, and is easily decomposed. Water swells it up into a pasty mass, and gives rise to so-called “ myeline forms,” an appearance resembling “ myeline ” or medullary layer of nerve fibre. It contains phosphorus. Cekebrine exists only in brain and nerves, and is more abundant in the white than the gray substance. It is a whitish substance, insoluble in water and ether, but is solu- ble in boiling alcohol and deposits again on cooling. Heated in the air it turns brown and burns readily. Leucine is found in small quantities in the kidneys, spleen, liver, pancreas, brain and glandular system. It crys- tallizes in whitish glistening laminae, and is soluble in water and alcohol, but insoluble in ether. Little is known regarding the origin and physiological relation of these sub- stances. CHAPTER II. ELEMENTARY OR PRIMARY FORMS OF TISSUE. The elementary or primary forms of tissue are cells, granules, 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, assimi- lation, respiration, secretion, excretion and reproduction. They also constitute the fundamental elements of all the tis- sues, and are the active agents in all the catalytic and chemico-vital changes which take place in the animal eco- nomy. The agency of cells is not only exhibited in the healthy actions of the body, but may also be seen in the de- velopment of various morbid growths, as fibroid tumors, cancer, etc. The form which organic matter takes when it passes from the condition of a proximate principle to that of an organized structure, is that of a cell, a simple fibre, or a simple membrane. PRIMARY FORMS OF TISSUE. 47 In all animal and vegetable tissues, there exists a soft gelatinous or albuminous substance called protoplasm, sarcocle, cytoplasm or “ germinal matter.'’] It is transparent, of the same consistence in all parts of the body, and by the action of the vital forces may be formed into small rounded masses or cells, or thin hyaline membranes. It possesses properties and exhibits phenomena which are called vital, such as the movement of molecules in its substance, and the changes in the shape of the mass itself. CELLS. A cell may be defined to be a semi-solid rounded mass of protoplasm, or it may assume the form of a membranous sac enclosing protoplasmic or other contents. In the in- terior of most animals cells will be seen a small body termed the nucleus;^and within the nucleus, a nucleolus; or there may be two or more nuclei,each containing one or more nucleoli. Variation in Shape.—Cells are generally globular, but may as- sume various shapes, depending on internal and external circumstances, and the growth of the cell; for ex- ample, fat cells which are round when formed, may become poly- gonal as the result of mutual pressure (Fig. 9.) The specific gra- vity 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 desiccation takes place, they become flattened and hard- ened, as in the epidermis. The shape of the cell may also be changed by the absorption of gases and vapors, e.g., the blood corpuscles present a distinctly biconcave disk under the influence of oxygen, and become rounded again when Fig. 14. (a) — Nerve cell. (b)—Nucleolus, (c)—Nucleus, (d) Ganglion corpus- cle with two nuclei, (e)—Multi nu- clear giant cell from bone marrow, (Frey), (f) Blood corpuscle, (g) Fat globule. 48 PRIMARY FORMS OF TISSUE. 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 out- line, and alcohol renders them oval, with an indentation on one side. Cells may also assume different shapes, depending on their growth ; for example, the pigment cell, which is at first spheroidal, throws out arms or projections in different directions, and becomes stellate during its growth. The nerve cell becomes unipolar, bipolar, or multi- polar ; nonstriated muscular cell, fusiform. Epithelial cells are either cylindrical (columnar), or squamous (tesselated or pavement.) In some instances, hair-like growths take place on the free surfaces or ex- tremities of cells, as is seen in the cilia of epithelial cells. Some cells undergo a spontaneous change in shape, as the amoebae, white corpus- cles, etc. Fig. 15. Pigment Cells. Fig. IQ. (c) —Columnar epithelium of the intestines. (d) —Columnar ciliated epithelium of the nose. Variation in Size.—Cells vary in size from Wu of an inch (83.5 mmm.) in diameter, the size of the largest fat cell, to of an inch, (1.25 mmm.) the size of the fat globule. Some are so large as to be called giant cells, as those of bone marrow (Fig. 14, e.), and abnormal tumors, as cancer, sarcoma, etc. The average diameter of the red blood corpuscle is about t-Aou of an inch, (7 mmm). Nerve cells vary from toToioo of an inch (83.5 to 2.5 mmm ; muscular fibre cells aVfr f° Woo °f an inch, (5.5 to 10 mmm.) in diameter. The cell may be divided into a cell wall, nucleus, nucleolus and contents. Cell Wall.—The cell wall, when present, is substan- tially the same in all cells, and is formed by the consolida- PRIMARY FORMS OF TISSUE. 49 tion of the outer surface of the mass of protoplasm. It is a simple homogeneous membrane, composed of globuline, and although no pores can be seen by the highest magnify- ing power, yet it possesses the property of osmosis. In some instances it is extremely thin; in others dense and unyielding. 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 body exists. Nucleus.—In the interior of most animal cells is seen a small body, which is called the nucleus. It exists either in the form of a small vesicle, or as a small mass of proto- plasm, containing one or more minute particles termed nucleoli. The nucleus is generally situated in or near the centre of the cell, but may be attached to the wall, or 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 vobi) to enVo °f an inch to 4 mmm.) in diameter. It is more regular, both in shape and size, than the cell itself. In most instances each cell contains but one nucleus ; cartilage cells frequently contain two or more. 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, etc. In giant cells there may be a multitude of nuclei in each cell (Fig. 14 e.). They are, in these cases, formed by the subdivision of the original nucleus. The nucleus resists the action of acids and alkalies better than any other part of the cell. It is readily stained by ammoniacal solution of carmine, and hence is regarded by Beale as germinal matter in contra- distinction to the outer portion of the cell, which he calls formed matter. Nuclei are sometimes found disconnected from the cells, when they are said to be free. They may be found floating in fluid as in certain secretions, or imbedded in a homogen- eous pellucid substance, as in rudimental cellular tissue, or 50 PRIMARY FORMS OF TISSUE. on the surface of fibres, as in muscle and nerve fibres, in which they are either upon or immediately beneath the investing membrane. The nucleus is a most persistent little body, and retains its original form in many cases after the cell to which it belongs has ceased to exist as such. Nucleolus.—This is situated in the interior of the nu- cleus, and may consist of a single molecule, or a number united together. In some instances it is highly refracting, and not readily acted upon by most chemical re-agents. There may be one or more in each cell. Contents.—The contents of all cells consist of a certain amount of protoplasm mingled with other substances. Each cell has the power of generating in its interior a sub- stance peculiar to itself, which is the result of its own se- cretion ; one secretes bile, another milk, another mucus, another gastric juice, etc. The contents of the cell may be either solid, as in bone, nails, epidermis, etc., or fluid, as in blood, chyle, mucus, etc. The contents of all cells are fluid when formed, but become hardened by secondary deposit, as in bone, dentine, etc. This takes place by the deposition of solid particles in the interior of the cell.' Color.—Cells are generally colorless ; a few only have color which depends partly on their refracting power, and partly on the hemoglobine, melanine, or pigment which they contain, as the red blood corpuscles, pigment cells, etc. Protoplasm, or Cytoblastema.—This is the name given to the substance from which the cells spring, and is derived either from the fluid in which they float, as blood, chyle, lymph; 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. PRIMARY FORMS OF TISSUE. 51 The ceil has also the power of choosing and refusing from the particles of nutrient fluid or cytoblastema in its neigh- bourhood, incorporating some of them into its substance, and converting others into new substances in its interior. For example, the blood corpuscle has the power of forming globuline and hemoglobine from the albumen and fibrin of the blood. It 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 blood corpuscle, germ cells of the vegetable kingdom, etc. Cytogenesis.—Kvror “cell” and ymsis “generation.” Cells have their period of birth, growth, maturity, and decline. They spring up, perform their office, and then pass away. Some do so with great rapidity, while others are slower in their progress, or are longer lived. They are governed by certain laws, two of which we may here formulate. 1st Laiu.—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 Law.—Cell growth can only take place in or near its appropriate pabulum, and on living surfaces. The mode of origin of cells takes place in several ways. Schleiden and Schwann, as far back as 1838, asserted that cells were developed de novo in an organizable blastema. According to this theory the cell was developed by the for- mation of granules in the blastema, their subsequent ar- rangement to form the nucleolus, around which at a certain distance was formed the nucleus, and lastly the cell wall and contents ; or the order might be reversed by the for- mation, first of the cell wall, and subsequently the nucleus and nucleolus. This theory of free ceil formation still has its advocates among many French physiologists, especially Robin. 52 PRIMARY FORMS OF TISSUE. According to the modern doctrine, which was first advo- cated by Virchow in 1852, every cell must originate from a \pre-existing or parent cell (omnis cellula e cellula.) There are three different modes by which cells may be produced in this way. 1st. By Multiplication by sub-division, fission, or fissip- arous multiplication of the cell. This process has been seen in the amoeba, and in the blood corpuscles of the lower animals. The cartilage cell also 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, first of the nu- cleus, and afterwards of the cell. This continues until there is a complete separ- ation, first of the nucleus into two parts, and then the cell, each part of the nu- cleus drawing a portion of the cell or 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 number have been produced. This is the mode by which segmentation of the vitellus takes place. 2nd. By subdivision of the nucleus or contents of the cell only, the so-called endogenous mode. In this mode the nucleus appears to separate into two or more 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, the so- called daughter cells. This variety of cell development may be observed in bone cells, (Frey) also m structures of very rapid growth, as in cancerous tissue. 3rd. By gemmation or budding. In this case a node or swelling is seen on one side of the cell which gradually in- Fig. 17. A cell undergoing the process of multiplication by subdivision, (a)—Original cell, (b)—Oval, (c)—Hour-glass contraction and division of the nucleus, (d)—Division of the cell into two. Fig. 18. A cell containing a number of young cells. PRIMARY FORMS OF TISSUE. creasing, finally drops off by constriction at the base. The yeast cell is propagated in this manner. Dr. Beale accepts the modern doctrine, and the term “pro- toplasm " as the substance from which cells are formed, but makes a distinction between the nucleus, which is readily stained with carmine, and the rest of the cell. He terms the nucleus “ germinal ” or living matter, in contra- distinction to the outer portions of the cell, which he calls “formed matter,” designating by the latter, the various tis- sues formed from cells. Conditions necessary to Cell Growth.—The condi- tions necessary to cell growth are the presence of protoplasm upon a living surface, a certain degree of animal heat, a re- quisite amount of water, oxygen, light and electricity. The dynamic agency of heat cannot be dispensed with ; too much would be injurious. The mysterious influence of light is necessary to healthy action, and a certain amount of water is required to preserve the integrity and promote the growth of the cell; but too much would destroy it. Permanent Change in the shape of Cells.—Cells un- dergo changes in the formation of tissues, and in the pro- pagation of their kind, by which they lose their individuality as cells. This may be seen : 1st. By the process of cytogenesis, as in multiplication by sub-division etc., which has already been described. 2nd. By coalescence of the cell with the intercellular sub- stance of temporary cartilage, as in the development of osseous tissue. (See development of bone.) 3rd. By the coalescence of cells, with the intercellular substance to form fibres as in fibrous tissue. The cells are originally round ; but in the process of forming fibres they become elongated, and in some instances fusiform or stellate. They are then arranged longitudinally, sometimes slightly overlapping each other, and both the cells and the inter- cellular substance are broken up into fibrillre. 4th. By the coalescence of cells in a linear manner to form tubes. In this instance the opposing walls of the cells, as 54 PRIMARY FORMS OF TISSUE. they are arranged in a line, break down, the cavities of the cells communicate with each other, and in this way a con- tinuous tube is formed,as in the development of muscular and nerve fibres, also in the formation of small vessels; or the cells may assume the form of curved plates or segments, united or cemented together in such a way as to form a tube. Temporary Change in the Shape of Cells.—Tem- porary changes in the shape of cells give rise to motion. The cause of motion in the vegetable kingdom was for a long time a matter of speculation. It was finally discovered that this phenomenon was due to the change in the shape of the cells when irritated, as in the mimosa or sensitive plant, the fly-trap of the dionoea, and the berberis. In the animal economy, muscular contraction is due to this temporary change. It occurs in both the striated and non-striated muscular tissue. In contraction of the fibrillse the sarcous elements become shorter and broader ; the same is true of the non-striated muscular fibre cells. Temporary 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 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 examined by the miscroscope, oil globules may be seen in their interior at this stage. (Fig. 10.) In some instances the change in the shape of the cell appears to be entirely of a spon- taneous character, as in the amoeba and white corpuscles of the blood, in both of which, changes in shape are constantly occurring at certain periods, and under certain circum- stances. The movements of the cilia of epithelial cells are no doubt also produced by the spon- taneous change in the shape of the cells from which they Fig. 19. Amceba. In the centre is seen the nucleus, and sur- rounding it a num- mber of vacuoles. PRIMARY FORMS OF TISSUE. 55 spring. These movements are probably caused by the alternate contraction and relaxation of the cells, and also of the cilia. Cause of Organization, Vitality, &c.—This is a purely speculative subject. Many theories have been advanced from time to time, to endeavor to explain the phenomena of organized bodies. Some suppose that organization 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 was the theory of Aristotle, and was after- wards advocated by Harvey. Hunter attributed the organi- zation of living beings, and the vital action manifested by them, to a “ materia vitae ” diffused throughout the solids and fluids of the body. Abernethy supposed this materia vitae to be of a species of electricity. Muller supposed that the cause of organization was 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 production and arrangement of cells to form the different parts of the new organism. It is not under the influence of the mind, as instinct is as capable of reproducing the species as higher intelligence. Prout advocated the exist- ence 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 de- rives 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, etc., vital actions go on perfectly : for example, the fecundated egg, "omne vivum ex ovo,” acquires its vital properties while in the body of the mother; and 56 PRIMARY FORMS OF TISSUE. when laid, if supplied with the vital stimuli, and the organiza- tion remain perfect, it is developed into a new being. But as soon as the structure is destroyed, or the vital stimuli are withheld or withdrawn, the organism dies, and its elements form new compounds, most of which are of an inorganic character. Function of Cells.—The function of cells is exhibited in the plastic and metabolic, or vital and chemico-vital power of the cell. The plastic power of the cell is seen in its development from protoplasm; the proliferation, by multi- plication of new cells, their subsequent growth and de- velopment, and their transformation in the development of the tissues of the body. The metabolic or cliemico-vital power of the cell is shown in the property it has of chemically changing the protoplasm within and without the cell. It is confined to the conver- sion of special substances, as in the formation of globuline and hemoglobine, by the blood corpuscle, bile by the hepatic cell, and pepsine by the gland cells of the stomach, etc. The cell of the yeast plant has also the power of converting sugar into alcohol and carbonic acid. These two forces (plastic and metabolic) may act together : in fact, it is diffi- cult to separate them, for while the cell is growing it is already beginning to perform its office. Both these forces act together in harmony, and through their united action the different secretions and excretions are formed. They are affected by nervous impressions, as fear, joy, grief, anger, etc. 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, corro- sive sublimate, acids and alkalies. It is also arrested by strong nervous shocks, as a stroke of lightning, or a powerful battery, and by septic poisons. The function of the cell is also further manifested in the permanent change it under- goes in the formation of tissues already described. PRIMARY FORMS OF TISSUE. 57 Manifestations of Cell Life.—These are exhibited : First—In cell growth from protoplasm. Second—In the multiplication or production of new cells Third—In the chemico-vital transformation of protoplasm Fourth—In the permanent change in the cell. Fifth—In the temporary change in the cell. Sixth—In the production of nervous force (vis nervosa.) A cell is a living organism, and like all living bodies, has its period of growth, maturity and decay. It has the power of selecting matters from the nutrient elements, assimilating and organizing them into new substances found in its inte- rior. This property resides in the cell as a whole, and not exclusively in any single part of it. The duration of the life of a cell depends on its activity ; those of slow develop- ment are long-lived, and vice versa. When a cell begins to decay, granular matter is first noticed in its interior; the cell wall or outer portion dissolves, and the cell finally disappears. GRANULES. Granules or molecules are minute particles of matter from jotto iTToTr an (2-5 mmm) in diameter. Some appear as dark specks, while others present a dark outline with a bright centre; this latter is characteristic of fat globules. They may be found incessantly moving about in the interior of cells, or in the fluids, as the granules of pigment cells, called pigment granules. They may exist either in the free state, as in chyle, milk, blood etc.; in- closed in cells, or imbedded in the tissues as in bone, den- tine, cartilage. They are present in great abundance in chyle and give to that fluid its opalescent appearance (Fig. 7.) The molecules of chyle are of low specific gravity, readily soluble in ether, and are known as fat globules or granules. SIMPLE FIBRES. A simple fibre is formed by the arrangement and coal- escence of granules or molecules in a linear manner. They 58 PRIMARY FORMS OF TISSUE. vary in size from to Yshuv °f an inch (2.5 to 1.25 mmm.) in diameter, and are rounded or prismatic in shape depend- ing on pressure. They are formed in the coagulation or fibrillation of fibrin, and they constitute the primitive fibrillse of striated muscular tissue. As coagulation of the fibrin takes place, star-shaped points are first formed, and the granules arrange themselves in a linear manner from one point to another and coalesce to form fibres, until the process is completed (Fig. 13.) This was formerly believed to be the mode of healing or organization in woundsandadhesive bands in inflammation, from the coagulable lymph or fibrin which was exuded from the blood-vessels for that purpose. The modern view regarding this subject, is that “coagulable lymph ” is the product of the white corpuscles, which have passed through the coats of the vessels by virtue of their amoeboid movements, supplemented by the prolifera- tion of the connective tissue cells in the wounded or inflamed parts. SIMPLE OR BASEMENT MEMBRANES. These are formed directly from the nutrient fluid or protoplasm, by a certain arrangement of molecules peculiar to themselves. They are found in the walls of most cells, in the sarcolemma of muscular fibre, in the sheath of nerve fibre, in the covering of the vitreous humor, in the vitelline membrane of the ovum, and as the structure upon which the epithelium rests in membranous expansions. They exist under three different forms, which vary somewhat in micro- scopical appearance. In the first variety, it is a simple pellicle of homogeneous 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 presents a number of minute granules irregularly scattered through the transparent substance. In the third variety, the membrane presents a number of distinct spots PRIMARY FORMS OF TISSUE. 59 or nuclei, and is capable of being torn up into portions of nearly equal size, each containing one of these spots or nuclei. From this it would appear that the first variety is formed by the condensation of a thin layer of protoplasm, the second by the condensation of a thin layer of protoplasm in which granules had been formed, and the third by the condensation of a thin layer of protoplasm in which nuclei had been formed. Certain forms of membrane above described have been called by some basement membranes, because they are the foundation or resting place for the epithelial cells ; by others, 'primary, germinal, or maternal membranes, because they furnish the germs of these cells. They are also called hyaline.membranes, because of their structureless appearance. Basement membrane is found on all the free surfaces 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 lym- phatics. It is also 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 surface. Its office is to limit osmosis of the nutrient fluid, and to modify it in its passage. It also supports the cells, and probably determines the formation of all the cells which are developed on its surface. In all probability, the spots, or nuclei, seen in the basement membrane are the germs of cells, which spring from them as from a centre. TISSUES. CHAPTER III. TISSUES. There are seven distinct tissues in the body viz : white fibrous or connective, yellow elastic, adipose, cartilage, bone (including dentine and enamel), muscle and nerve tissue, to which may be added gelatinous tissue and reticular con- nective tissue of modern histologists. All other tissues are made up of a combination of two or more of these. All, ex- cept muscular and nerve tissues are considered by some to be modified forms of connective tissue, and are described as the connective tissue group. WHITE FIBROUS, OR CONNECTIVE TISSUE. This tissue enters into the formation of ligaments, tendons aponeuroses and membranes. 1st. As ligaments, it connects the bones together and pre- serves the integrity of the joints in their various move- ments. The ligaments assume three different forms : Fu- nicular, which consists of rounded cords of fibrous tissue, as the ligamentum teres. Fascicular, which consists of flattened bands, as the ligaments of the ankle, knee, and elbow ; and Capsular, which forms 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 round—Funicular, as the ten- don of the semi-tendinosus ; others flattened—Fascicular, as the semi-membranosus. The tendons, at their insertion in- tto 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. CONNECTIVE TISSUE. 61 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, perichon- drium, fascia lata, &c. In all the above, a few elastic fibres are found associated with the white fibres. Physical Appearance and Properties.—It presents a beautiful, silvery-white appearance, when freed from extra- neous 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 slo of an inch (50 mmm) in diameter (Fig 20, a.) They are formed of numer- ous fibrillse, varying in size from TFinrcr to joki of an inch Fig. 20. Connective and elastic fibres, (a) Connective fibres, having some embryonic globules, (b) Elastic fibres, (c) Curly elastic fibres, like horse hair. (d) Nuclei of cells, with nu- cleoli, x 320. (Todd and Bowman.) (1.6 to 1.2 mmm.) The bands are capable of being sepa- rated into fibrillse, and have a tendency to split up in a 62 TISSUES. longitudinal direction. When a portion is exposed to the action of acetic acid, it swells out and becomes semi-trans- parent, the fibrillae are entirely obliterated, and a number of connective tissue corpuscles 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 or outline of the cells from which the tissue was originally formed. A number of wandering cells (white corpuscles) and connective tissue corpuscles, are always found in connection with fibrous tissue. This tissue is somewhat elastic, and allows of a slight degree of exten- sion from long-continued force. It possesses no contractility, and its force of cohesion is very great. It is said that the tendo-achillis 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 demon- strated, and its sensibility is very low. The division of a tendon is attended with very little pain. It yields gelatine,on boiling. It is found in the ligamenta subflava, ligamentum nuchge of quadrupeds, internal lateral ligament of the lower jaw, stylo-hyoid and pterygo-maxillary ligaments, chordae vo- cales, crico-thyroid and thyro-hyoid membranes, posterior wall of the trachea, arteries, veins, thoracic duct, and in areolar tissue. YELLOW FIBROUS, OR ELASTIC TISSUE. Physical Appearance and Properties.—This tissue, un- like the preceding, is of a yellowish color, highly elastic and consists of long, single, brittle fibres, with sharply defined dark borders, which show a disposition to curl upon themsel- ves when broken (Fig. 20, b). They vary in size from to TzroTytf of an inch (5. to 2.5 mmm.) the average diameter being about °f an inch (3.5 mmm.) and are round or flattened—depending on their situation or pressure. They ELASTIC TISSUE. anastomose with each other, and are mingled in various pro- portions with the white, to form areolar or connective tis- sue. It yields a modified form of gelatine on prolonged boil- ing; is not acted on by acetic acid, and is not readily dissolved by the gastric juice. The fibres are stained red, with Millon’s re-agent (a solution of proto, and pernitrate of mercury). It resists the approach of disease longer than any other tis- sue 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 honey- combed appearance, on account of the destruction of the white fibrous and muscular tissues with which it is associated. When dried it becomes dark colored, hard and loses its elasticity. 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 now believed to be the same in both connective and elastic tissue. They were sup- posed 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 at first round, and possess a nucleus, nucleolus and granular matter. They then become fusiform, or stellate, surrounded by intercellular substance, and being applied or spliced in a linear manner, coalescence takes place,and fibrillse are formed (Fig.21Y At the same time the nuclei become elongated, and finally disappear, until brought into view by means of acetic acid. According to late observers a certain amount oi material is formed by the cells, called tissue cement or intercellular sub- stance, in which the cells become im- bedded, and which serves to unite them together. This substance is blackened by nitrate of silver (Frey.) Fig. 21. Cells of human connective tis- sue. (a), flat stellate or shovel- shaped cells, (b), coarse granular cells. 64 TISSUES. Areolar Tissue, (Syn., cellular, connective or filamen- tous.) This tissue is found in all parts of the body except the brain, compact tissue of bone, teeth, cartilage, hair, nails, epidermis, etc. It consists of a network formed by a combination of white fibrous or connective tissue and yellow elastic tissue, together with a number of connective tissue cor- puscles. Where great strength is required, the connective tissue predominates, and where motion is necessary, the elastic, as in the tissue of the lungs. The proportion of each may be easily demonstrated b}r acting on it with acetic acid, which dissolves out the white, while it produces no change on the yellow. The interstices or meshes (impro- perly called cells) of areolar tissue communicate with each other. This tissue, therefore, may be inflated with air (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 partially filled with fat cells, and contain a small quantity of serous fluid of an alkaline reaction, composed of water, albumen (.36 in 100) and sodium chloride. When the fat is absorbed by the demands of the system, its place is filled with serous fluid, as in phthisis. Function.—Its function is to surround and connect various organs, and retain them at certain distances; at 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, etc. 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 re- ceives the name of sub-mucous,sub-cutaneous,sub-serous and sub-synovial areolar tissue, respectively. ADIPOSE TISSUE. 65 ADIPOSE TISSUE. This was formerly described as areolar tissue, with fat cells imbedded in its meshes. It exists however, in parts in which not the slightest trace of areolar tissue can be found, as, for example, in the cancellous tissue and marrow of 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 cranial cavity, eyelids, epicranial apon- eurosis, scrotum, penis, etc, but in other parts of the body they are associated together. Adipose tissue is found in abundance in the subcutaneous areolar tissue, called panni- culus adiposus. It is entirely absent in embryonic life. Physical Appearance and Properties.—It is composed of cells or vesicles containing fat, which vary in size from 300 t° wo' °f au inch (83 to 31 mmm) (Fig. 22.). They are usually deposited in clusters, being held together by a mesh of capillaries, which surrounds them, and from which they derive their nutriment This constitutes a lobule. When the adipose tissue ex- ists in considerable quan- tity, the lobules are held to- gether by areolar tissue, con- stituting a mass of fatty tis- sue. It is abundantly sup- plied with blood-vessels, but no nerves or lymphatics have been traced into its substanee. At an early period of its formation, the cell or vesicle possesses a nucleus and nu- cleolus, the nucleus being imbedded in the cell-wall; but they disappear at maturity, being obscured by the oily con- tents of the cells. The cells or vesicles are round, when isolated, but become polyhedral from the flattening of their walls against each other. They are believed by some to ori- Fig. 22. Fat cells of adipose tissue. TISSUES. ginate from connective tissue corpuscles by their transforma- tion into fat cells. They are long-lived, and exosmosis of the fat is prevented by the constant moistening of their walls, by a thin serous fluid which surrounds them, on the same principle that a moist bladder will retain fatty matter, while a dry one allows it to exude. The cell wall in fat ceils can be distinctly seen in a collapsed condition, after dissolving out the fat by means of ether ; the nucleus is then also readily seen by tinging with carmine. Origin and Function.—This tissue is formed partly from the fat used as food, and also by a chemical transfor- mation from the starch and sugar present in the different articles of diet. This process is accelerated by an imperfect supply of oxygen, as is seen in the fattening of animals which are closely penned up. It is also formed in the interior of most cells of the body, when undergoing retro- grade changes, as in fatty degeneration. It fills up spaces otherwise unoccupied, gives rotundity to the body, forms a delicate pad or cushion to facilitate the action of movable parts, as at the base of the heart, behind the eye-ball etc., and from being a bad conductor of heat, it prevents its too rapid escape from the animal body. This is exemplified in those animals possessing little hair on their skin, in which there is a large quantity of adipose tissue beneath the integument. In other instances it gives ease to the gliding movements of parts, and protects them from the ill effects of sudden changes of temperature, as the adipose tissue of the omentum. As fat, it supplies combustible material for the maintenance of the animal heat of the body. It is stored away in the body, to be used, when necessary, to maintain animal heat, and as a source of nourishment, as in the hyberuating animals, the process of absorption of fat being facilitated by the alkaline condition of the serous fluid by which the cells are surrounded. (See oils and fats). CARTILAGE. 67 CARTILAGE. This is a very simple form of tissue, and is found in many parts of the body. In some of the lower animals, as fishes, the skeleton is formed entirely of this tissue, as the skate, sturgeon, etc. PHYSICAL APPEARANCE AND PROPERTIES.—its Color va- ries from pearly white to light yellow, and it is possessed of a considerable degree of elasticity, flexibility and cohesive power. It yields chondrine, when boiled. Cartilage con- sists of cells imbedded in a hvaline or inter-cellular sub- stance, or matrix. The cells are contained in cavities or lacunse in the intercellular substance. Some of these cavities are lined by a thin membrane, the cartilage cap- sule ; in other instances the cells appear to blend with the intercellular substance (Fig. 23). The cells are round or oblong, and vary in size from to °f an inch, (55.5 to 12.5 mmm). Each cell contains a nucleus and one or more nucleoli. The nucleus varies in size from to ¥oVtt °f an inch, (10 to 6.2 mmm.) a'nd sometimes contains fat globules, as a result of some peculiar metamorphosis of the contents. Cell growth takes place by the process of multiplication by subdivision, and parent cells are frequently seen containing two or more young cells. The intercellular substance is either homogeneous, granu- lar, or fibrous. Cartilage is divided into two great classes : Temporary and Permanent; the former constitutes the original frame work of the body, except portions of the vault of the cra- nium and bones of the face ; and is supplanted by bone during development and growth ; the latter is found in Fig. 23. Hyaline (temporary) cartilage becoming transformed into bone substance. Hy- aline substance with cartilage cells imbed- ded in it. 68 TISSUES. different parts of the body and is not transformed into bone. It is also divided into three classes according to the character of the intercellular substance, viz. : Hyaline, elastic or reticular, and connective tissue or fibro-cartilage. Hyaline Cartilage.—This variety of cartilage embraces temporary, articular and costal cartilage, also the cartilages of the nose, larynx, trachea and bronchi, except the epiglottis and cornicula laryngis. In all these situations the in- tercellular substance is homogeneous or finely granular, but occasionally in old costal cartilage a few indistinct fibres may be seen. In temporary cartilage the intercellular sub- stance is not very abundant; but the cells are numerous, and placed at nearly equal distances apart. They are rounded or oval, and vary in size from to °f an inch, (16 to 12.5 mmm.) the nuclei being finely granular. Near the seat of ossification the cells are arranged in rows, run ning towards the ossifying part, and become hardened by intersti- tial or secondary deposit of cal- careous salts (Fig. 24). In the cartilage of the ear in rats, mice, and other small animals, and also in the human chorda dorsalis in early foetal life, the intercellular substance is very small in quan- tity and the cells are closely packed together. This constitutes the so-called cellular cartilage. In articular cartilage which is found in joints, covering the articular surfaces of bones, the intercellular substance is more abundant than in temporary cartilage, and presents a finely granular appearance. The cells are rounded or oval, varying in size from t-jqt to tot °f an to 27.8 mmm). Near the surface of the cartilage, the cells are Fig-. 24. Cartilage cells in rows at the seat of ossification. CARTILAGE. 69 numerous, and arranged in flattened groups, lying with their planes parallel to the surface. This appearance has been mistaken by some physiologists for a layer of epithelium. In the interior of the cartilage, the cells assume a linear direction pointing'towards the surface. This serves to ex- explain the disposition this form of cartilage has, to split up in a direction perpendicular to the surface. In costal car- tilage, the intercellular substance is very abundant, finely mottled and sometimes indistinctly fibrous. The cells are larger than in any other cartilage of the body, being from to zh; °f an inch (38 to 55.5 mmm) in diameter. Some contain two or more nuclei, which are transparent, and others contain nuclei and fat globules. The cells often assume a linear arrangement, the rows being turned in different directions—probably the result of the growth of the cells by subdivision from the parent cell, and their sub- sequent separation from each other in a linear manner. Calcification of cartilage sometimes occurs. It consists in a deposition of lime salts around the cells or cell groups, until the whole intercellular substance presents a dark granular appearance (Fig. 29.) This calcified cartilage, however, d not become bone. Elastic or Rlticular Cartilage.—This is of a yellow- ish color, arranged in the form of plates or lamellae of various thickness, and enters into the formation of the external ear, epiglottis, cornicula laryngis, Eusta- chian tubes etc. These plates serve to maintain the shape of tubes or pass- ages, which require to be kept open, without the expenditure of vital force. It approaches in character to the fibro-cartilage. The intercellular substance is permeated by a clear net- work of fine elastic fibres. The cells are numerous and vary in size from tsW f° soo of an inch (19 to 27.8 mmm.) in diameter (Fig. 25). Fig. 25. Elastic Cartilage; (a) cells; (b) intercellular substance; (c, d,) elastic fibres of the latter. Frey. 70 TISSUES. Connective Tissue—or Fibro-Cartilage.—Fibro car- tilage consists of a mixture of connective tissue and cartilage cells in various proportions. It exists in four forms, Inter- articular, Connecting, Circumferential and Stratiform. The interarticular fibro-cartilages are flattened lamel- lae of different shapes, placed between the cartilages of the temporo-maxillary, sterno-clavicular, acroinio-clavicular, wrist and knee-joints. They are free on both surfaces; thinner at the centre than at the circumference, and are held in position by the surrounding ligaments. Their use is to increase the depth of the articular surfaces ; to moderate the effects of great pressure; as a cushion, to deaden the intensity of shocks; to give ease to the gliding movements of these joints ; and to increase the extent of the synovial membrane for secretion. The connecting fibro-cartilages are placed between the bony surfaces of those joints which possess very little mo- bility ; as between the bodies of the vertebrae, and the sym- physis of the pubes, and serve to connect them together. They are in the form of discs, composed of concentric rings of fibrous tissue and cartilaginous laminae placed alter- nately ; the former predominating towards the circumfer- ence ; the latter, towards the centre. The circumferential variety consists of a rim of fibro-car- tilage which surrounds the margin of some of the articular surfaces, and serves to deepen the cavity ; as, e.g., the glenoid and cotyloid cavities. The stratiform fibro-cartilage lines the grooves through which the tendons of certain muscles pass; as e.g., the bici- pital groove. Vascular Supply.—Cartilage is chiefly supplied by im- bition. It is covered by a layer of white fibrous tissue, containing vessels, called the perichondrium, which corres- ponds to the periosteum of bones. From this covering the cartilage leceives its nutriment. When the cartilage is thin no vessels penetrate it; but when it is more than of an GELATINOUS AND RETICULAR TISSUES. 71 inch in thickness as in costal cartilage it contains canals for their transmission. Articular cartilage is not covered by perichondrium. It derives its nutrition by imbibition from the vessels of the synovial membrane which skirt the circumference of the cartilage, and also from those of the cancelli of the adjacent bone, which are separated from the cartilage by the articu- lar lamella. The vessels of the synovial membrane pass forward to the ftiargin of the cartilage, and then return in loops, and those of the cancellous tissue pass to the internal surface of the articular lamella, form arches, and return to the substance of the bone. Fibro-cartilage is supplied by the vessels of the synovial membrane and perichondrium, with which it is invested. GELATINOUS AND RETICULAR CONNECTIVE TISSUES. Gelatinous tissue constitutes the semi-solid substance which forms the vitreous humor of the eye,and the jelly-like substance which covers the umbilical cord (Whartonian jelly). It consists of a soft homogeneous intercellular sub- stance in which are imbedded a number of rounded trans- parent cells. A higher development of the gelatinous tissue is found in the so-called enamel organ of the growing tooth. The cells in this case are stellate in form. Reticular connective tissue is found in the lymph glands, and lymphoid organs, as the tonsils, thymus gland, Peyers glands, Malpighian corpuscles of the spleen, etc. It con- sists of a delicate areolar tissue in the meshes of which lie innumerable lymphoid cells (white corpuscles). It is some- times called adenoid tissue, and is believed to be a modified form of connective tissue. It is built up of stellate nucleated cells, the arms of which are united like threads, and form meshes in which the lymphoid cells are situated. The meshes are usually rounded, but may assume an elongated form. 72 TISSUES. BONE. This constitutes the solid frame-work of the body. It forms organs of support, levers for motion, or it encloses cavities, and protects delicate organs, as the brain, heart, lungs, &c. Physical Appearance and Properties.—It is a hard, dense, opaque substance, of a whitish color, and possesses a considerable degree of elasticity. It consists of an organic or animal, and an inorganic or earthy material, intimately blended together; the animal matter giving to the bone its elasticity and toughness; the earthy part its hardness and density. The animal matter may be separated from the earthy, by steeping the bone in dilute nitric or muriatic acid. In this way the earthy matter is dissolved out, and the bone becomes quite pliable—so much so, that the fibula, if so treated, can be drawn into a knot. The earthy constitu- ents may be obtained by burning the bone in an open fire. By this means the animal matter is entirely consumed, and the earthy part remains as a white brittle substance. The relative proportion of these two substances varies in differ- ent persons, and in the same person at different periods of life. In the child, the animal matter forms about half the weight of the bone ; in the adult about 333- per cent., and in old age about 25 per cent. In certain diseases of the bones, as rachitis or “rickets” and mollities ossium, there is a deficiency of earthy matter, and in fragilitas ossium, a deficiency of animal matter. Bone, when boiled, yields gela- tine, and from the earthy matter may be obtained granules, from -g-oW 1° T¥000 of an inch, (4. to 1.7 mmm) in diameter. Chemical Constituents.—In 100 parts :— Organic matter-—Areolar tissue, Blood-vessels, Nerves and Fat 33-30 Inorganic or Earthy matter. Lime Phosphate. 51.04 Lime Carbonate 11.30 Calcium Fluoride 2.00 Magnesium Phosphate 1.16 < Soda and Sodium Chloride 1.20 100.00 BONE. 73 Structure of Bone.—Bone presents two varieties of osseous tissue. The one is dense, firm and compact, and always situated on the exterior of the bone, called the com- pact tissue ; the other, loose and spongy, enclosing cells or cancelli, and situated internally, is called the cancellous tissue. In the extremities of the long bones, the cancellous tissue is most abundant, while in the shaft the compact tis- sue predominates. In short and flat bones, the two varie- ties are more evenly distributed. The external surface of the compact tissue (except the articular lamella) is covered by a dense fibrous membrane, the periosteum. The interior of the long bones in adult life, presents a cavity called the medullary canal. This is filled with the so called marrow, which is of a reddish or yellow color, and consists of vessels, nerves, delicate areolar tissue, fat cells, and a number of lymphoid cells. The latter are believed, by some, to be transformed into red blood corpuscles. There are also near the surface of the bone marrow, a number of myeloplaxes or giant cells (Fig. 14 e.) The cancellous tissue also contains marrow. The periosteum is abundantly supplied with blood vessels, and is intimately attached to the bone ; and if separated to any great extent, the bone perishes. It also sends prolongations, accompanied with vessels, through numerous foramina in the bone into the canals of the compact tissue for its supply. It is now settled that the medullary cavity is not lined by a membrane corres- ponding to the periosteum (endosteum), the marrow being applied directly to the bone. If a transverse section from the shaft of a long bone be examined under the microscope, a number of apertures, sur- rounded by a series of concentric rings, may be seen. These apertures are sections of the medullary or Haversian canals (named after the discoverer, Clopton Havers), and the rings are sections of the lamellae which surround the canals. Sur- rounding the Haversian or medullary canals, in a concentric manner, may be seen a series of dark spots or centres, called lacunae. These communicate with each other, and with the TISSUES. Haversian canals, by minute tubes, called canaliculi or pores. The whole constitutes a Haversian system, and is a provision made for the supply of the compact tissue. Fig. 26. Transverse section of the shaft of the humerus x 150. Three Haversian canals are seen with concentric rings ; also the corpuscles or lacunae with the canaliculi extending in all directions. The Haversian canals in the long bones run nearly parallel to each other and to the long axis of the bone; but in the irregular and flat bones, they are irregular in their direction. They vary in size Irom to of an inch (125 to 12.5 mmm) and communicate freely with each other and with the outer and inner surfaces of the compact tissue, by means of transverse and oblique canals, (Fig. 27). They give passage to small arteries and nerves for the supply of the bone. The small arteries are derived from the nutrient artery, the vessels of the periosteum and marrow. The laminae which surround the Haver- sian canals vary in number from 8 to 15, and are called the Haversian lamellae. Besides these, some ap- pear to be arranged concentrically, around the medullary canal or mar- row of the shaft; these are called circumferential, and others Fig. 27. Longitudinal section of bone, showing the Haversian canals and their branches. BONE 75 are situated between the Haversian systems, called inter- stitial lamellm. Lacunae —The lacunae, or bone cells are arranged in con- centric circles around the Haversian canals. They are small cavities of a seiui-lunar shape, the concavity being turned towards the Haversian canals, and vary in size from rsVo to joVtr of an inch, (16.5 to 12.5 mmm). They are reservoirs for the plasma of the blood, previous to its ab- sorption by the tissue, and each contains a nucleated membraneless cell,or bone corpuscle, which is homologous with the connective tis- sue corpuscle, and which in all probability sends prolongations into the canaliculi. Oanaliculi.—These are small tubes or pores, which issue from all parts of the circumfer- ence of the lacunae. They communicate with those from adjacent lacunae, and some open on the free surface of the bone. By this ar- rangement, the plasma of the blood is carried into every part. They vary in size from TTruinr to toom of an inch (1.65 to 1.25 mmm.) in diameter. In cancellous tissue, and in the articular lamella which supports the articular cartilage, there are no Haversian canals, and the lacunae are larger than ordinary. Development.—Bone is not directly formed from temporary cartilage, as was formerly sup- posed. Ossification commences in the cartilage at certain points, called points or centres of ossification, but the calcified cartilage (Fig 29) does not become bone. It dissolves away, and in the sys- tem of cavities thus formed the bone substance is developed from the periosteum. Fig. 28. A lacuna from the ethmoid bone of the mouse; a, basis substance ; b, the bone cell. Fig. 29. Section of diaphysis of cartilage; c, calcified cartilage ; p, perichondrium. 76 7 ISSUES. In long bones there is usually a central point for the shaft, and one for each extremity. The central point is called the diaphysis, the extremity the epiphysis. The point of ossification of a process, as, e. p., the olecranon, is also called the epiphysis, and when finally joined to the shaft, an apophysis. The period at which ossification begins,, varies in different bones. The earliest is the clavicle, which begins about the fourth week of foetal life ; next, the lower jaw, then the ribs, vertebrae, femur, humerus, tibia, upper jaw, etc., in order of succession. Fig. 30. Section of epiphysis showing- the process of ossification. 1.—Cartilage cells imbedded in hyaline substance. 2.— Cavernous tissue, the calcified cartilage having become liquefied. 3.—Ossifying portion, (a)—Cavernous or medullary spaces shown empty, (b)—The same filled with cells, (c)—Remains of the calcified cartilage, (d)—Medullary spaces in which lamelke of bone tissue have been formed from the osteoblasts, (e)—Developing bone cell, (f, g, h)—Imbedded bone cells or lacunse. In the transformation of temporary cartilage into bone preparatory changes take place which consist in its becom- BONE. ing soft and vascular, the vessels growing in from the peri- chondrium. The cartilage cells multiply and form cylindri- cal piles or columns, (become ranked), separated from each other by trabeculae of intercellular substance which is be- coming calcified ('Fig’s. 24 and 30). The calcified substance soon after liquefies in places so as to form cavernous spaces or areolae, which contain groups of cartilage cells, and basis- substance. The cells next the periphery of these cavernous or medullary spaces and which resemble a layer of epithe- lium, become altered in shape and are called osteoblasts. These coalesce with each other and with the intercellular substance to form the first lamella of bone tissue; while here and there one of the osteoblasts is pushed out of line or in- dented, and forms a lacuna or bone corpuscle. This process is again and again repeated by the production of cells from the basis substance until the formation is com- pleted. Each lacuna throws out arms or projections in diff- erent directions, which meet others from adjacent lacunae and in this way canaliculi or pores are formed. This endo- chondral bone which is so irregular and cavernous, is very different however from the beautiful regularity of perma- nent bone tissue. It undergoes a change. According to some the endochondral bone becomes liquified and absorbed in order to permit of the formation of medullary canals, and a new formation of bone takes place from the periosteum,, into which the perichondrium has been changed. Others deny the liquefaction theory, and maintain that the change is due to interstitial growth alone ; we rather incline to the= absorption theory. It is now a well known fact, that living periosteum has the power of generating bone tissue, from the osteoblasts of its deepest layer. According to the absorption, theory, while the liquefying process is going on in the endochondral bone, the osteoblasts of the periosteum grow downwards in cones (osteoblast cones.) These osteo- blast-cones producethe Haversian lamellae, while the flat os teoblast layer immediately beneath the periosteum forms the general or circumferential lamellae. This also explains- 78 TISSUES. the increase in thickness of the bone during growth and development. During ordinary repair, absorption from within and deposition from without are continually going on. The ossification in the vault of the cranium and bones of the face, in which there is no temporary cartilage, is called intra-membranous or ectosteal,in contradistinction to intra- cartilaginous or endosteal. These bones are formed from asoft, foetal connective tissue in which are found nuclei and osteo- blasts, the process of origin of bone being the same as when formed from periosteum. Some modern investigators also favor the view that bone may be formed by the direct transformation of cartilage into bone tissue, or by the de- position of calcareous matter in connective tissue. The latter may be the explanation of the formation of the so-called callus in the repair of bone. Growth.—The growth of bone takes place by layers formed in succession on its external surface—exogenous— and also in an interstitial manner. Bones increase in length by additions between the points of ossification, and by accessions of osseous tissue to the extremeties. This may be shown by inserting metallic pegs in the shaft at certain distances apart, when it will be seen that, notwithstanding the increase in length of the bone, the distance between them remains the same. Bones increase in diameter, by additions of osseous tissue on their exterior. The osseous tissue thus added is not a mere lamina of bone, but consists of complete Haversian systems, the earlier systems being covered over by the more recent ones. This may be demonstrated by feeding animals with madder. The coloring principle is precipitated with the lime phosphate, and on examination, beautiful crimson rings are seen encircling the Haversian canals. This ap- pearance is confined chiefly, to the external or vascular sur- face. When the madder has been given at intervals, colored and colorless portions alternate witli each other. The color remains a long time, indicating a slow change of this tissue. TEETH. In early life there is no medullary canal in the shaft of the long bones, its place being filled with cancellous tissue. This tissue, however, becomes gradually absorbed as age ad- vances, until about the twenty-fourth year, when the canal is completely formed and filled with marrow. Teeth.—There are two sets of teeth with which the hu- man subject is provided. The first set appear in childhood and are called temporary or deciduous teeth. They are twenty in number,—four incisors, two canine, and four molars in each jaw. The second set are called permanent, and are thirty-two in number,—four incisors or front teeth two cuspids (one on each side of the incisors), four bicuspids two on each side), and six molars (three on each side), in each jaw. Each tooth consists of the crown or exposed part, the neck, the constricted part beneath the gum, and a single or multiple fang or root imbedded in the jaw, and contains within it a pulp cavity. The bicuspids, and the molar teeth of the lower jaw, have each two fangs; the molars of the upper jaw, three. The pulp consists of vessels, highly sensitive nerve fila- ments and areolar tissue, which enter by an opening at the extremity of the fang. It also contains dentinal cells or odontoblasts, from which the dentine is formed. These odontoblasts are oval in shape, to ols of an inch (2 to 3 mmm) in diameter, and send some of their fine thread-like processes into the dentinal tubuli. The pulp cavity may be compared to the Haversian canals of bone. The solid structure of the tooth is composed chiefly of dentine, covered with a thin layer of enamel on the crown, and bone tissue (crusta petrosa) on the fang. Dentine consists of minute, wavy tubes, dentinal tubuli, which lie parallel to each other and open into the pulp cavity, being arranged vertically on the summit, and horizontally on the sides. The tubuli are about xriro¥ t*0, of an inch (1 to 2 mmm.) in diameter, and are imbed- ded in a dense, homogeneous substance—the intertubular tissue or matrix. They divide and subdivide dichotomously 80 TISSUES. •as they pass towards the surface, sometimes terminating in inter-globular spaces resembling lacunae,and convey nourishment for the supply of the enamel. The chemical composition of dentine is similar to bone, with a predominance of the earthy matter, in the proportion of seventy-two earthy, to twenty- eight per cent, animal matter. Sometimes the matrix pre- sents lamellae arranged concen- trically with the pulp cavity. Enamel is the hardest tissue of the body, and forms a cov- ering to the dentine of the crown of the tooth. It con- sists of a congeries of minute, solid, hexagonal rods, which are parallel to one another, rest- ing by one extremity, on the dentine, the other being covered by a tough membrane Tsihnr to 30000' (1.6 to .8 mmm.) of an inch in thickness, called the cuticle of the enamel. They are arranged verti- cally on the summit, and horizontally on the sides, like the dentinal tubuli, and are about ?3Yo to ?555 of an inch (4.5 to 3.6 mmm.) in diameter. Small spaces are left be- tween the rods at the dentinal surface to allow of the permeation of fluids from the dentinal tubuli, for the supply of the enamel. It consists of 96.5 parts earthy, and 3.5 parts animal matter. The hone covering the fangs is called crusta 'petrosa, or cement covering. In structure and chemical composition it resembles true bone, but without any lamellar arrange- ment or Haversian canals. Fig. 31. Section of tooth fang, a, Crusta pe- trosa, or cement covering; b, granular or Tomes’ layer with interglobular spaces; c, dentine ; d, dentinal tubuli. Development of the Teeth.—The teeth are essen- tially dermal structures which have become calcified, the TEETH. 81 epithelium forming the enamel, and the subjacent tissue, the dentine and cement. About the sixth week of foetal life, a rounded thickening or projection of the superficial layers of the epithelium of the jaw, appears all around the free border. At the same time the deep layerdips down into the subjacent tissue in the form of a wedge, and forms the ‘primary’ enamel germ (Fig. 32). Here and there in the mucous tissue of the jaw, corresponding to the number of teeth, a convex papillary structure, the tooth germ, grows upwards towards the en- amel germ, and pushes in or indents its under surface, so as to give it the form of a cap or bell. This is the enamel organ. The germs of the teeth continue to grow and are soon enclosed in sac- culi, (Fig. 33). Development of Enamel.—The enamel is developed from petrified or calcified epitheli- um. The enamel organ becomes sep- arated from the point of origin in the epithelium of the jaw. It is lined throughout with cjdindrical and hexagonal epi- thelial cells, cov- ering the surface of the tooth germ, and reflected at its base upon the inner surface of the sac- culus. The space between these two layers is filled with a Fig. 32. a, Epithelium; b, younger layer; c, inferior layer ; e, enamel organ ; f, dentine germ or papilla; g andh, inner and outer layers of the forming sacculus. Fig. 33. a, Dental groove ; h, remains of the enamel germ; c, enamel organ lined with epithelium on its outer (saccular) and inner (papillary) surfaces; d, enamel germ of the permanent tooth; e, dentine germ ; f, section of inferior maxilla; g, Meckel’s car- tilage. 82 TISSUES. gelatinous tissue, which is the pabulum of the columnar en- amel cells, and contains a few stellate cells. These columnar cells upon the surface of the tooth germ become calcified, and form the enamel rods which are completed by the super- position of cells, and their subsequent calcification. Development of the Dentine.—The dentine is devel- oped from the odontoblasts of the tooth germ, by a process of calcification. It commences as a dark area, at the base of the enamel germ. As development proceeds, the cells or odontoblasts become elongated and arranged in a linear manner vertically to the surface of the tooth germ; the outer portions of the cells become calcified and form the intertubular tissue or matrix, while the central part remains unchanged, and forms the dentinal canals. This process gradually extends inwards while the vessels, nerves, and areolar tissue recede until they come to occupy the central part, which is called the pulp cavity. About the fifth month, and prior to the calcification of the temporary teeth, a “ secondary ” enamel germ begins to form on the inner side of the original one for the production of the “perman- ent ” teeth. These pass through the same phases of devel- opment as those already described as the temporary set. Eruption.—When the tooth is sufficiently hard to enable it to pass through the gum, the eruption takes place. The gum is absorbed by the pressure of the tooth against it, which is itself pressed up by the increasing size of the fang. The septa between the dental sacs, at first fibrous, soon ossify, and constitute the septa of the alveoli in which the fangs are lodged. Periods of eruption of the temporary teeth.—The teeth of the lower jaw precede those of the upper. Central Incisors 7th month. Lateral “ 7th to 10th “ Anterior Molars 12th to 14th “ Canines 14th to 20th “ Posterior Molars 18th to 36th “ MUSCLE. 83 Periods of eruption of the permanent teeth : First Molars 6£ years. Middle Incisors 7 “ Lateral “ 8 “ First Bicuspids 9 “ Second “ io “ Canines n to 12 “ Second Molars 12 to 14 “ Wisdom Teeth (Dentes Sapientiae) 17 to 21 “ The teeth of the lower jaw, also precede those of the upper in the permanent set. Many cells of the body, and certain tissues possess the power of changing their form, from time to time, as the white corpuscles, cartilage cells, cilia, spermatozoa, connec- tive tissue, etc., but the muscles are alone those organs by which the various movements of the body are effected. They possess the property of contractility and are the active organs of locomotion. Muscular tissue is divided into two varieties, Striated and Non-striated. They may be dis- tinguished from each other—1st. By their color; the striated are reddish in color, while the nonstriated are pale. 2nd. By the aid of a microscope; the striated muscular fibres are characterized by being marked with transverse lines or striae; other striae pass longitudinally, indicating the direction of the fibrillae. The nonstriated muscular tis- sue consists of pale-colored fusiform fibre cells. 3rd. By galvanism. The striated respond to galvanism instantly, by a clonic spasm, while the nonstriated respond slowly by a tonic spasm. Muscular tissue is also divided into volun- tary and involuntary, according as it is under the control of the will, or independent of it. MUSCLE. Striated.—This variety of muscular tissue comprises the whole of the voluntary muscles, the diaphragm, muscles of the ear, tongue, pharynx, upper part of the oesophagus, heart, and the veins, at their entrance to the heart. When TISSUES. a transverse section of a muscle, as the sartorius, is examined by the microscope, it appears to be formed of a number of large bundles of muscular tissue, enclosed in a coat of areo- lar tissue, which constitutes the sheath or perimysium ex- ternum of the muscle. Each larger bundle consists of nu- merous smaller ones, enclosed in a similar covering of con- nective tissue, called the perimysium internum. Each .smaller bundle contains the primitive fasciculi or fibres, and each primitive fibre contains the primitive fibrillce. In the spaces between the bundles may be seen the ves- sels and nerves for the supply of the tissue. The Primitive Fasciculi or Fibres.—Each primitive fibre contains a number of primitive fibrilke, and is sur- rounded by a sheath of transparent homogeneous membrane, the myolemma or sarcolemma. Resting upon, and sometimes beneath this membrane may be found here and there, oval nuclei surrounded by a small quantity of protoplasm. The primitive fibres are cylindrical or prismatic in shape, and vary in thickness from to of an inch (125 to 50 mmm): their length does not exceed on an average one inch and a half. They are marked by fine, dark, wavy, or curved parallel lines or striae, from Troco Tzhw an inch apart(2.5to 2.12mmm),which pass transversely around them; this is characteristic of this variety of muscular tissue. Other lines, less distinct, run longitudinally, indicating the direction of the fibrillae of which the fibre is composed. They have a tendency to split both in a transverse and longitudinal direction, but cohesion is greatest in the former direction. Fig. 34. Muscular fibre torn across; the sarcolemma still connecting the two parts of the fibres. The Primitive Fibrillas.—These constitute the proper ■contractile tissue of the muscle. They are cylindrical or prismatic, sometimes flattened—depending on pressure— MUSCLE. 85 vary in thickness from T0iM to TW °f an inch (2.5 to 1.4 mmm,), and are marked by transverse strim with which those on the surface of the fasciculi correspond. Each fibrilla consists of a single row of minute par- ticles, named “ sarcous elements,” connected together like a string of beads. When ex- amined by the microscope the sarcous elements present a rectangular outline, and the fibrilke appear to consist of light and dark particles or zones placed alternately ; hence their stri- ated appearance. The dark particles corres- pond with the sarcous elements, and the light ones with the junction of the pairs. They some- what resemble a Volta’s pile. The transverse strise, vary from t° thoo °f an inch apart in the human subject; in birds Toioo> in reptiles —i—, in fish —-—, and in insects —- of an inch, (2 to 3 mmm.) When examined with a high magnifying power, a dark line, with granules above and below, is seen to cross the middle of each light particle, known as Krause’s transverse lines or intermediate discs. The granu- lar appearances above and below, are called secondary discs. A white line has also been observed to cross the middle of the dark zones, known as Hensen’s median disc. Late re- searches have also shown that each fibrilla is surrounded by an extremely thin membrane. This is an argument in favor of the view, that the fibrilla is the anatomical element of muscular tissue. The striated muscle of the tongue and heart of the mammalia and man, is somewhat different from that generally met with. The fibres are not arranged in bundles, and surrounded by connective tissue, but weave or interlace among each other. They also anastomose with each other, so as to form a narrow-meshed net work, and there is no appearance of sarcolemma. Fig. 35. Fibrillse magni' fled 800 diameters • a, a, larger, and b, b, smaller bundles; e," still smaller; d. d, the smallest re- presenting a single series of sarcous elements(Sharpey). Nonstriated.—This variety consists of flattened bands, 86 TISSUES. or elongated fusiform fibre-cells, of a pale color, from to to of an inch (5.5 to 7.5 mmm) broad, finely granular and containing a rod-shaped nucleus, which sometimes appears as a streak (Fig. 36). These fibre-cells may assume differ- ent shapes ; they are generally fusiform, but some are club- shaped, and others of a rectangular shape, with fringed ex- tremities. The length of these fibre-cells is from — to —i— of an inch (500 to 2.5 mmm.) 501000 v # ' They are held together by connective tissue, and the bands are applied to each other in such a way, as to encircle the organ into the form- ation of which they enter. This kind of tis- sue is found in all hollow organs (except the heart and veins attached), as the ducts of the salivary glands, trachea and bronchi, alimen- tary canal, from the lower part of the oesoph- agus to the internal sphincter, gall bladder and ducts, calyces and pelvis of the kidney, ureters and bladder, and in the urethra. In the female; in the vagina, uterus, Fallopian tubes and round ligaments. In the male ; in the scrotum,epididymus,vas deferens, vesiculae seminales, prostate and cavernous bodies, in the coats of arteries, veins and lymphatics ; in the iris and ciliary muscle, and in the integu- ment called the arrectores pilorum. Mode of Development.—There is no differ- ence in the early stage of development between the striated and nonstriated varieties of muscular tissue, both being developed from cells;but whilst the striated variety goes on to complete development into fibrillse,the nonstriated retains permanently its cellular condition. The cellular ele- ments are elongated andappliedend to end,being held together by connective tissue, and in this way they encircle the organ into the formation of which they enter, or are arranged longi- tudinally or obliquely. The striated fibre is not formed as Fig. 36. Nonstriated mus- cular fibre cells, a, Developing cell from the embryo of the hog; b, a more advanced cell, c, to g, various forms of human muscular fibre. MUSCLE. 87 'ormerly supposed by Schwann, directly from the arrange- ment and fusion of the cells in a linear manner (except probabty the fibres of the heart), but by the arrangement md fibrillation of the protoplasm or intercellular substance under the influence of the cells. The cells appear to increase greatly in length, the nuclei increase in number, and the protoplasm and intercellular substance become transformed into the sarcous elements, etc. The fibre becomes trans- versely and longitudially striated, and increases in size by fresh additions of protoplasm upon the outside. The re- mains of the nuclei, surrounded by granular protoplasm (the muscle corpuscle) may be seen on the outside and with- in the sarcolemma, on the addition of a little acetic acid, Attachment of Tendons.—Every muscle is attached at its extremity by means of connective tissue, which consti- tutes the tendon. The extremity of each muscular fibre, whether rounded, pointed, or irregular, is covered by sarcolemma, and is re- ceived into a corresponding cavity in the tendinous bundle to which it is firmly connected, by means of a cement substance. This union is so firm, that rupture of the tendon or muscle will take place before separation at this point. It may be separated for microscopical examination, by means of a solution of potash. Fig. 37. Extremity of muscular fibre, showing the attachment of the ten- don. Chemical Constituents.—Muscular tissue consists as follows in 100 parts : Water 7^-5°- Myosine, Albuminous substances and Hemoglobine.. 18.20. Lactic acid 1 1.00. Gelatine i-N5°- Creatine, Extractive, and Fatty Matter and Salts 2.80. 100.00. It swells out on the addition of acetic acid, and is par- tially dissolved. It is soluble in hydrochloric acid, and is 88 TISSUES. precipitated by ferrocyanide of iron. Muscular tissues is sometimes changed into a substance called adipocere. (See oils and fats.) Vascular Supply.—The arteries intended for the supply of the muscle pierce the sheath, and divide and subdivide, giving oft' small branches which pass between the bundles of which it is composed, until the ultimate twigs insinuate themselves between the primitive fasciculi or fibres, and terminate in the capillaries. Some of these, the longitudinal, course along the fibres, lying in the intervals between them, and others pass transversely across them. The length of the longitudinal capillaries is about -gV of an inch (1.2 mm) the transverse vary according to the size of the fibres. The fibrillse are, therefore, supplied by imbibition through the sarcolemma. Nervous Supply.—The nerve fibres are distributed sim- ilarly to the arteries, until the filaments reach the fasciculi or fibres. They then form a series of loops, which either return to the same trunk, or join an adjacent one. It is stated by some observers, that the nerve fibres pierce the sarcolemma. As they pierce the fibre, their covering be- comes continuous with the sarcolemma, and the axis cylin- der or essential portion of the nerves pass into the interior and are dis- tributed among the fibrillse, and ter- minate either in free extremities, loops, or nerve buds (as they are called). According to other observers the nerve fibres as they approach the sarcolemma form expansions, called terminal, or motor end plates. The sheath of the nerve spreads out and blends with the sar- colemma, the white substance of Schwann terminates ab- ruptly, and the axis cylinder spreads out beneath-the sar- colemma on the surface of the fibrillse, forming an oval Fig-. 33. Termination of a nerve fibre by a motor end plate in museu- ar fibre, (Longet). MUSCLE. nlate, from -J- to —*— of an inch (50 to 25 mmm) in diam- L > 5001000 V 7 eter. (Fig. 38). Properties of Muscular Tissue.—The distinguishing characteristic of muscular tissue is its property of contrac- tility, irritability or tonicity. Some have endeavoured to draw a distinction between these terms ; but, after all, it is a distinction without a difference. The term tonicity how- ever, may be understood to express that insensible and almost constant contraction by which opposing muscles balance each other in a state of rest—a state of passive con- traction. The primitive fibrilla is the proper contractile tissue of the muscle. Still, it is a disputed point as to whether or not it possesses this property in itself, some maintaining that nerve is necessary to charge it with con- tractility ; others that nerve is only necessary to call it into- action, and that this property is inherent in the tissue itself. Contraction is caused by a change in the shape of the sar- cous elements; they become shorter and thicker. This change travels rapidly from one end of the fibrilla to the other, and the muscle is thus very much shortened. Some vegetable structures possess an analogous property, as e. g.. the mimosa or sensitive plant, and venus’ fly-trap (Dioncea). If touched ever so slightly, the irritation causes a change in the shape of the cells, followed by a change in the shape or position of the whole leaf, in consequence of the change travelling from one cell to another. The property, there- fore, of contractility is inherent in the muscular fibrilla itself, and may be called into action by various kinds of stimuli, as by nervous influence, by pinching or pricking the tissue, by the action of an acid or an alkali, or by gal- vanism. The effect of the application of any of these stimuli,, varies according to the kind of muscular tissue to which it is applied. If a portion of striated muscle be irritated, those fibres/ which are touched will contract, and those only,, the motion not being communicated to any other, and the contracted part soon becomes relaxed—the spasm is clonic.. 90 TISSUES. If, on the other hand, a portion of nonstriated muscle be irritated, as the alimentary canal, the contraction takes place more slowly, the spasm is long continued, or tonic, and the movement is communicated to other fibre-cells, until a considerable part of the canal is affected. The muscular fibre is shortened and thickened during contrac- tion, and sometimes thrown into a zigzag shape, and some observers, mistaking the effect for the cause, concluded that the zigzags occasioned the shortening. Coutractility con- tinues for a short time after death, This may be demon- strated, by applying to the muscular tissue any of the above- mentioned stimuli which are known to affect it during life. The duration of this property after death, varies in different animals. In birds, only a few minutes after death; in quadrupeds much longer; while in reptiles it remains for many hours, owing to the nutritive changes being more sluggish in these than in warm-bloods, and the sarcous ele- ments being slowly formed and sluggish in their action, are long-lived. If irritation be continued, the contractility or irritability of the muscle is soon exhausted. The circulation of arterial or oxygenated blood is not only necessary for the purposes of nutrition, but also to the continuance of contractility. The muscles will therefore preserve their contractility after death, and the action of the heart itself will continue for a long time, if oxygenated blood be injected into the veins or if the circulation be kept up by artificial respiration. If the blood be charged with carbonic acid, or chloroform, ether, sulphocyanide of potassium, or a narcotic poison, as opium, etc., the contractility of the muscles is speedily destroyed. Every act of contraction involves the death of a certain amount of muscular tissue, and prolonged exertion causes fatigue, which is an evidence of an impaired condition. Rest is necessary to recovery, and recovery is due to the nutritive process; hence the more a muscle is used, pro- vided it receives a sufficient amount of rest and nutrition, MUSCLE. 91 the more vigorous and bulky does it become ; as e. g., the arm of the smith, and the legs of the rope-walker. On the other hand, disease, as paralysis, or sedentary habits, cause them to become flabby and atrophied, but this may be re- medied by exercise, and the use of friction and galvanism. In some constitutions they are liable to fatty degeneration. Muscular contraction produces a sound resembling the distant rumbling of carriage wheels. This is caused by the movements of the fibres upon each other. For example, the sound caused by the contraction of the masseter and tem- poral muscles may be distinctly heard in the stillness of the night, by placing the side of the face and ear on the pillow, and clenching the teeth firmly together. There is also an elevation of temperature of from 1° to 2° F. This depends partly on the chemical changes which take place in the muscle, as a result of its action, and partly upon the friction consequent on the movements of the fibres upon each other. Muscular tissue is also said to possess a certain amount of elasticity. This is exceedingly small, and is due in great measure to the elasticity of the sarcolemma and the elastic tissue associated with muscle. It is shown by suspend- ing vertically a small weight to a portion of fresh muscle ; it elongates with the weight and recovers itself when it is removed. Rigor Mortis.—This is the stiffening of the muscles which takes place after death, and is due to the coagulation of myosin. This condition is rarely absent ; but it may be very slight, and continue only a short time. Sometimes it comes on within 15 or 20 minutes after death, as in typhus fever. It commonly takes place within 7 or 8 hours after death; but in some cases it may be deferred for 20 or 30 hours. It continues for 21 or 3G hours ; but it may pass off much more rapidly, or be continued for several days. This rigor mortis is a sort of tonic contraction of the mus- cles, and in some cases it may be very violent—as after TISSUES. death from cholera and yellow fever—and has given rise to many absurd superstitions among the uninitiated. It begins in the neck and lower jaw first, next the upper extremi- ties, and extends from above downwards until it reaches the lower limbs. It is most remarkably manifested in the nonstriated muscular tissue, as in the arteries and alimen- tary canal. In consequence of this contraction, the bowels are not unfrequently moved after death ; the arteries are found empty, and so contracted that they cannot be injected until the rigidity passes off. When the rigor mortis sub- sides, decomposition of the muscular tissue begins; hence we may regard it as the last act of life, and in this respect it corresponds to the coagulation of the blood, when drawn from the body. The same causes that interfere with the coagulation of the blood after death, interfere, ako, with the rigor mortis of the muscles, as in animals hunted to death, or killed by lightning, in which both coagulation and rigor mortis are imperfect. Action of Muscles.—In the action of most muscles, and especially those of the extremities, examples of the three orders of levers are afforded. In the first order of levers the power is at one end, the weight at the other, and the fulcrum between the two. In the second order, the power is at one end, the fulcrum at the other, and the weight between the two. In the third order, the fulcrum is at one end, the weight at the other, and the power between the two. The first order of levers, although the most powerful, is that least used in the animal economy, as its use is less pro- ductive of extensive motion. The action of the gastrocne- mius muscle affords an example of this order, as when the foot is raised from the ground, and extended to raise the os calcis and depress the toes : here the moving power is the gastrocnemius attached to the os calcis, the weight is the anterior part of the foot, and the fulcrum is the ankle joint. The same muscle affords an example of the second order MUSCLE. 93 of levers, as when the foot is placed on the ground and the body raised by the action of the muscle ; here the moving power is the gastrocnemius, the fulcrum the anterior part of the foot resting on the ground, and the weight or resistance the body resting on the ankle joint. Fig. 39. Fig. 40. Fig. 41. The upper three figures represent the three kinds of levers; the first illustrating the mode of action in two directions. The lower figures represent the foot when it takes the character of each kind of lever. F, fulcrum ; P, power; W, weight or resistance; M, muscle, affording the power. The ankle joint also affords an example of the third order of levers, as when the foot is raised from the ground and flexed on the ankle joint; here the moving power is the tibialis anticus and peroneus tertius, the fulcrum is the ankle joint, and the weight the anterior part of the foot. The biceps of the arm also affords a good example of the third order, as when a ball or weight is placed in the hand; here the moving power is the biceps inserted into the tuber- osity of the radius, the fulcrum is the elbow joint, and the weight is in the hand In this position, power is sacrificed to extent of motion, as in raising the hand and weight these pass through the arc of a circle of considerable dimensions, while the extent of motion at the insertion of the power is extremely limited. This is still more obvious when we hold a rod in the hand, as a fishing-rod or whip, the ex- treme end of which is made to pass through a space of con siderable magnitude compared with that of the part where 94 TISSUES the power is applied. The great advantage derived from this disposition of levers in the human body, whereby motion is gained at the expense of power, is seen in the various acts of walking, running, leaping, etc. Locomotion.—In the act of walking nearly every muscle in the body is called into action, either in the movement of the limbs or in the maintenance of the body in the erect position. Two main kinds of leverage are employed in walking, one kind chiefly produced by the muscles of the calf which raise the heel, and with it the weight of the body which is pushed forward, and would fall prostrate, but for the other kind of leverage by which the opposite leg is pulled or planted in front of the body to support it. The advance of the opposite leg is effected partly by swinging, but chiefly by muscular action. The muscles concerned are those of the thigh, the rectus, psoas and iliacus, which act in front; the hamstring muscles which slightly bend the knee, and those on the front of the leg, as the tibialis anticus, extensor longus digitorum, extensor longus pollicis and per- orieus tertius which raise the foot and toes, and prevent them catching on the ground. When this foot, which we will suppose to be the right, has reached the ground, the action of the muscles of the left leg has not ceased, but con- tinues to raise the heel and throw the body still more for- ward, until the weight is supported by the right leg, when the left in its turn swings around and is planted in front of the body. The two actions it will be seen, therefore, are taking place at the same time, and are assisting each other. At the same time that the above movements are in pro- gress, the body is being supported in the erect posture and balanced on each leg alternately. This is done by a slight rotation of the pelvis on the head of each femur alternately, so that the centre of gravity of the body shall fall over the foot of that side. This occasions a slight “ rocking move- ment ” which is more noticeable in females than males owing to the greater width of pelvis of the former. This rocking MUSCLE. 95 movement may, however, be lessened, and made more grace- ful by a compensatory outward movement at the hip, and hence some may become more graceful in their walk than others. Running, and leaping or jumping are modifications of the act of walking. In regard to the source of muscular force, it has long been observed that in active muscular exercise, there is an increase in the urea excreted by the kidneys, and it was supposed that this increase of urea was in exact proportion to the amount of muscular exercise. The latter has been found not to be the case; the increase in urea is only very slight, and the waste of muscle cannot be expressed by its increased excretion; neither is the substance of muscle wasted in proportion to the work it performs. There is also no evidence that nitrogenous are superior to non-nitrogenous foods as a source of muscular power ; both may afford the requisite conditions for muscular action. 96 MEMBRANOUS EXPANSIONS. CHAPTER IV. MEMBRANOUS expansions. These are the serous and synovial, mucous and integu- ment. The serous and synovial membranes, anatomically speaking, form shut sacs, with the exception of the periton- eum in the female, which communicates with the uterus through the Fallopian tubes. The mucous membrane lines cavities which communicate with the external surface, and is continuous with the integument. The integument covers the exterior of the body, and serves not only as a means of protection, but also as an organ of sensation. The mucous membrane and integument are convertible membranes. Structure.—The structure of these membranes is very nearly the same in each instance. It consists of a base- ment membrane, lined by epithelial cells on the free sur- face, and presents vessels, nerves, and lymphatics, imbed- ded in areolar tissue which connects it with the subjacent parts (Fig. 42). They there- fore consist of three varts— basement membrane, with epithelial cells on one side, and blood-vessels, nerves and lymphatics, imbedded in ar- eolar tissue, on the other. 1st. Basement Membrane.—The different varieties of basement membrane have been already described in Chap- ter II. Its function is to support the cells, and probably influence their development; to limit osmosis of the nutri- ent fluid from the subjacent capillaries, and modify it in its passage. 2nd. Epithelium.—The layer of cells which line the free Fig. 42. Plan of a membranous expansion ; a, epithe- lium , b, basement membrane ; c, vessels, nerves and lymphatics imbedded in areolar tissue. EPITHELIUM. 97 surface of the membranous expansions, is called epithelium. Those which line the serous and synovial membranes and the vascular system are sometimes called endothelium, and the stratified epithelium of the skin is called epidermis. The epithelial cells can be brought beautifully into view by staining with nitrate of silver. There are two principal varieties of epithelium, viz : 1st. Tesselated, pavement, squamous, laminated or scaly. 2nd. Columnar or cylindrical. In the serous, synovial, and mucous membranes there is generally a single layer of cells, with a quantity of granular matter and a layer of partially developed cells lying on the basement membrane ; but in the integument there are several; the outer being flattened, scaly, and hardened by secondary deposit. The cells which line the serous, synovial and mucous membranes, secrete a fluid which is intended to lubricate the surface, to prevent the ill effects of friction, and to give ease to the gliding movements of the parts over each other. This fluid is formed as a result of the growth, maturity, and decay of the cells. 1st. Tesselated, Pavement, Squamous, or Scaly Epi- thelium.—The cells of this variety are flattened and poly- gonal in shape, and vary in size from T to of an inch (50 to 10 mmm) in diameter. Each cell contains a nucleus, nucleolus, and granular matter. They are, in general, not very active, and are therefore long-lived. In health, they secrete only a limited quantity of fluid. Those which line the synovial membranes, mucous membrane of the mouth, and parts of the body in which a greater sup- ply of fluid is requisite, are some- what rounded in shape and much more active. Tesselated or pave- ment epithelium lines all the serous and synovial membranes, the mu- cous membrane of the mouth, lower part of the pharynx, oesophagus, upper part of the larynx, Fig-. 43. Tesselated epithelium ; a, epith- elium of the peritoneum x 400 ; b, epithelial cell of the mouth x 260 (Henle). 98 MEMBRANOUS EXPANSIONS. intercellular passages (so called), and air cells, lining mem- brane of the ventricles of the brain, tympanum, anterior and posterior chambers of the eye, conjunctiva and canali- culi, arteries, veins, and lymphatics, lower part of the vagina, bladder, and urinary passages, vesiculae seminales, and vas deferens. Those cells which line the bladder and urinary passages are somewhat spheroidal in shape, and would seem to be an intermediate variety. 2nd. Columnar or Cylindrical Epithelium.— This variety is cylindrical in shape, as the name indicates, and placed side by side, one extremity of the cell resting on the basement membrane, and the other forming the free surface. They vary in size from Woo to mjVo of an inch (10 to 7.1 mmm.) in thick- ness, and from to of an inch (42 to 28 mmm.) in length. Each cell contains a nucleus and nucleolus. In some parts, as in the gastrointes- tinal canal, there appears to be a double layer of cells; this depends on their rapid development in these parts, the lower layer being the new cells which are rising up to take the place of the old. These cells not only line the free surface of the membrane, but also dip into the follicles, at the bottom of which they be- come rounded or glandular. This is owing to their greater activity in the latter situation. In some instances their free extremities are club-shaped, in order to comport with their position, as when they stand on the angles formed by the dipping of the follicles. This form of epithelium is found in the alimentary canal, commencing at the cardiac orifice of the stomach, in the ducts which communicate with it, the gall bladder, nose, nasal ducts and lachrymal sacs, frontal sinuses and antra, posterior surface of the palate, upper part of the pharynx, Fig. 44. Columnar epithelium; c, col- umnar epithelium of intestine ; d, columnar ciliated epithelium of the nose. CILIA. Eustachian tubes, larynx—below the superior vocal cords— trachea and bronchi, upper part of the vagina, uterus, and Fallopian tubes. Placed here and there at vari- able distances among the ordinary columnar cells are peculiar oval cells known as Becher or goblet- cells (Fig. 45, a.) These are re- garded by some as the commence- ment of the absorbent system; by others as mere shells of epith- elial cells which have become emptied of their contents by manipulation, or as mucous secreting cells. Fig. 45. Columnar epithelium of small intes- tine ; a, Becher or goblet cells; b, or- dinary cells. Cilia.—Both varieties of epithelial cells occasionally pre- sent a number of minute, conical-shaped filaments or prolon- gations attached to their free extremities or surfaces, termed cilia (Fig. 44, d). They are attached by their bases to the cells, their free extremities being tapered, and they vary in length from nVo to of an inch, (5 to 6 mmm.) From five to thirteen may be seen attached to each cell. The cilia may be considered as prolongations of the cell itself. They are not seen in the early stage of development of the cell, but make their appearance as it arrives at maturity. They are in continual motion; each filament appears to bend from its root to its point and return to its original state, so as to- resemble the waving of a wheat field in a gentle breeze. This motion is independent both of the will and the life of the animal, as it is seen to continue after death. Epithelial cells of the nose may be seen to float about in water by the agency of their cilia, several hours after they have been re- moved from the mucous surface ; and the motion of the cilia has also been observed in the body of the tortoise fif- teen days after death. Ciliary motion continues in animals killed by prussic acid, narcotic or other poisons, and electri- city ; but is destroyed by chloroform, carbonic acid, mineral acids and strong alkalies. 100 MEMBRANOUS EXPANSIONS. The object of the ciliary motion is to propel fluids over the surface, in the direction which the secretion is destined to take, whether external or internal, the movement being generally towards the outlets. In fishes, the external sur- face of the gills is covered with cilia, which serve to propel the water, and bring fresh portions in contact, for the pur- pose of aerating the blood. In many of the lower animals, they serve not only to produce currents for respiration, but also to draw into the mouth minute particles which serve as food. The motion of the cilia is due to the vitality of the cells from which they grow, or the vital contractility of the tis- sue of the cilia themselves, and not to the presence of a kind of delicate muscular tissue, or to nervous force, as some have suggested. It has already been shown, in the preced- ing chapter, that the motion of muscular tissue is due to a change in the shape of the sarcous elements. Now, in the same way, the motion of the cilia may be produced by a change in the shape of the cells to which they belong, so that by an alternate contraction and relaxation of the cell the cilia would be made to wave as they are seen to do. The epithelial cells are developed from the protoplasm supplied by the vascular layer, beneath the basement mem- brane. Ciliated epithelium of the tesselated or squamous variety is found in the lining membrane of the ventricles of the brain, tympanum, intercellular passages (so called), and in the air cells. Ciliated epithelium of the columnar variety is found in the cavity of the nose (except the roof), nasal ducts, lach- rymal sacs, frontal sinuses, maxillary antra, Eustachian tubes, posterior surface of the palate, upper part of the pharynx, (extending as low down as the floor of the nares), larynx below the superior vocal cords, and the anterior part above, trachea and bronchi, upper part of tbe vagina, in the uterus, and Fallopian tubes. SEROUS MEMBRANES. 101 SEROUS MEMBRANES. The serous membranes are the arachnoid, pleura, pericar- dium, peritoneum, tunica vaginalis, and the lining membrane of arteries, veins, and lymphatics. Each membrane, respec- tively, lines the cavity to which it belongs, being attached to the wall by means of areolar tissue. This is called the 'parietal layer. It is then reflected upon the contained organ forming the visceral layer. The free surface is lined by tesselated or squamous epithelium, sometimes called endothelium, which in health secretes a limited quantity of fluid for the purpose of moistening the surface, the process of secretion and absorption being exactly counterbalanced. The normal quantity of serous fluid in the various cavities is as follows ; in the pericardium one to two fluid drachms; in the peritoneum one to three ounces; in the pleural sac two to four fluid drachms. If the secretion be morbidly in- creased, or the process of absorption diminished it is retained in the cavity, and gives rise to dropsies which receive differ- ent names in different parts of the body; in the cavity of the arachnoid, hydrocephalus ; in the pleura, hydrothorax ; in the pericardium, hydro-pericardium; in the peritoneum ascites ; in the tunica vaginalis, hydrocele. The secretion is called serous fluid, and is similar to the serum of the blood. It has an alkaline reaction, and consists of water, albumen and salts. The quantity of albumen varies in different parts, depending on the activity of the part, the degree of motion and the amount of friction to be overcome. In the serous fluid of the pleura there are 2.85 parts in a hundred ; in the peritoneum, 1.13 parts ; in the arachnoid, .6 to .8; in the subcutaneous areolar tissue, .36. The serous membranes are looked upon by some, as large sacs or cavities, which communicate by stomata or pores, with the lymphatic vessels (Klein.) These apertures, which are about of an inch (10 mmm) in diameter, may be seen between the epithelium. Milk and colored fluids have 102 MEMBRANOUS EXPANSIONS. been observed to pass through them into the lymphatic sys- tem. Short lateral passages of the lymphatics are also found to open into these apertures. There is also a considerable quantity of adenoid tissue imbedded in, or forming the walls of the serous membranes. SYNOVIAL MEMBRANES. The synovial membranes are placed between the articular surfaces of the bones. In the foetus they are prolonged over the articular cartilage ; but in the adult they cover merely the margin to the extent of a line or two, and are then reflected on the inner surface of the ligaments, to which they are attached by areolar tissue. In some in- stances they send fringe-like prolongations into the interior of the joints, as for example, the (so called) alar ligaments of the knee joint. They also form sheaths for the tendons of muscles. The free surface of the synovial membrane is smooth and moist, being lined by a layer of tesselated or squamous epithelium, which secretes the synovia, for the purpose of lubricating the joint, and preventing the ill effects of friction. If the secretion be morbidly excessive, the result would be hydrops articuli. Synovia is a transparent, viscid, oily-looking fluid, and resembles the white of an egg, hence its name ( (5-7 " ) Fox *Ttm(6.i ir ) Wolf .... 3W0 (7-o 11 ) Elephant. 1 Woo (9-2 » ) Red Deer. Woo (S-° " > MuskDeer -j-g-Wr (2-° " ) Sloth '2 8J0 o' (9*° " ) In all of the above, the form and appearance of the corpus- cles are the same, although they vary much in size. The 172 BLOOD. elephant, and sloth (Bradypus didactylus) are the only species in which the corpuscles are known to be larger than in man. In the camel tribe (camel dromedary lama) they are oval in shape, but do not possess a nucleus. In all the ovipa- rous vertebrata, as birds, reptiles, and fishes, the corpuscles are of a large size, oval in shape, and contain granular nuclei. The nuclei may be distinctly seen on the addition of acetic acid, which clears up the outer portion. The cor- puscle of the frog is from -1— to —— of an inch (25 to 21 r ° 10001200 v mmm) in diameter,* Mammals. Fig. 61. Birds. Typical characters of the red-blood corpuscles in the main divisions of the Vertebrata {modified from Gulliver.) The average diameter in the longest axis is given in each case. Reptiles. Fishes, Color.—In a single stratum of red corpuscles no color is observed, but when two or three are superimposed upon one another, a reddish tint becomes apparent. The color depends partly on the shape of the corpuscles, but chiefly on WHITE CORPUSCLES. 173 the hemoglobine they contain. They also have a tendency to adhere by their concave surfaces in the form of rouleaux. (Fig. 60, c). This is peculiar to the red corpuscles, and is very much increased in inflammation. If any of the salines be added to the blood, this peculiar tendency is in a measure neutralized. White Corpuscles.—These are so named on account of their white, or colorless appearance. They have a circular outline, appear granular within, and are tolerably uniform in size, theird iameter being about of an inch (8. mmm.) in warm-bloods, and (10 mmm.) in reptiles. In some of them a nucleus may be distinctly seen on the addi- tion of acetic acid; in others the nucleus appears to be broken up, so as to give the cell a granular appearance, (Fig. 60, d). They are more highly refractive than the red under the microscope, and are generally observed in or near the margin of the field, while the red are grouped together in the central part. When examined in the circulating blood of a frog’s foot, they are seen to occupy the exterior of the current, and adhere more or less to the walls of the vessels, or appear to pass from the centre to the walls and back again. The proportion of white to red corpuscles in man, is about one to 400 or 500; but in inflammation it may be one to ten. In certain diseases as anemia, leucocy- thsemia, etc., the white corpuscles are relatively increased. In the oviparous vertebrata the proportion is higher than in man, being about one to sixteen; while in one of the vertebrata (amphioxus) the red corpuscles are entirely absent. In the invertebrate series, on the other hand, the corpuscles are almost invariably white, and hence the so- called white blood of this class of animals. The white corpuscles have the power of spontaneously changing their shape, and of moving in certain directions, closely resembling those of the amoeba, (Fig. 12), and hence termed amoeboid movements, (Fig. 60, e.) This is due to the contractile property of protoplasm. The amoeboid movements are 174 BLOOD. arrested by the addition of water or acetic acid. The white corpuscles are reproduced by the process of fission. The blood also contains granules or molecules, of an inch, (3. mmm.) in diameter, similar to those found in lymph and chyle, some of them fatty, and others probably al- buminous. Origin of the Corpuscles.—The earliest blood cor- puscles are formed from the primordial cells in the vascular tract. The embryonic heart and aorta are formed by the arrangement of masses of the primitive cells, or germinal vesicles, of the mucous or vegetative layer, in the position, form, and thickness of the developing vessels respectively. The external layer of cells is converted into the walls of the vessels, while those in the interior form the first blood corpuscles. The primordial, or primitive vesicles, are large, colorless, spherical cells, each containing a nucleus, nucleolus, granular matter, and fat globules. These cells, gradually clear up, so as to bring into view the nucleus, become reduced in size, and develope the coloring matter (hemoglobine) as they pass into the form of red corpuscles. The blood corpuscles of the human embryo thus formed are circular, disc-shaped, full colored, and, on an average, about 2tVo °f an inch (10 mmm.) in diameter. They each contain a nucleus (and in some cases two), about of an inch (5 mmm.) in diameter, and slightly granular. They are re- produced by the process of multiplication by subdivision, or fission. When the liver begins to be formed this multiplication of blood corpuscles in the mass of blood ceases, according to Kolliker, and a new production of colorless nucleated cells takes place in the vessels of the liver. These nucleated cells undergo a gradual change into red corpuscles, similar to those of the first brood. After birth, when the lymph and chyle corpuscles are thrown into the current of blood, they are developed into red blood corpuscles, so as to supersede those formed as DEVELOPMENT OF THE CORPUSCLES. 175 above described. This is evidenced—First by the formation of color, while the chyle and lymph are passing through the thoracic duct, due to the development of hemoglobine# Secondly, by the presence of corpuscles, which appear to be intermediate stages of development between the lymph corpuscles, and the nucleated red corpuscles in the blood of oviparous vertebrata. Thirdly, by the progressive transi- tion from lymph or white blood, to red blood, which may be observed in the ascending scale of animal life. Development from Chyle and Lymph Corpuscles.— Kolliker and Paget regard the red blood corpuscles as being formed from the smaller of the lymph and chyle corpuscles by a gradual progressive metamorphosis; while Wharton Jones and Huxley maintain that they are formed from the nuclei alone, the outer portion of the cells disappearing in the change. The weight of authority, however, appears to favor the former opinion. The change from chyle and lymph corpuscles to red blood corpuscles, takes place as follows :— The chyle and lymph corpuscles are at first nucleated cells, the nuclei of which are generally more or less obscured by the granular matter which surrounds them, (Fig. 59.) They vary in size from —L- - to —L- of an inch, (10 to 8.1 mmm.) in diameter. The granular matter clears up, and the nuclei disappear. They then become flattened or biconcave, contraction and consolidation of the cells take place, which reduce their size to a certain extent, and hemoglobine is developed. The white corpuscles are also developed from chyle and lymph corpuscles. Lymph corpuscles are formed in the lymphatic glands, spleen, adenoid tissue, and medulla of bone. The red and white corpuscles are regarded by some as two distinct and complete forms, neither being capable of metamorphosis into the other, and each having its own specific purpose to subserve in the animal economy; the greater number of chyle and lymph corpuscles proceeding to the formation of red corpuscles, while a few of them are 176 BLOOD. developed into the white corpuscles of the blood. The argument in favor of this theory is, that the white cor- puscles have been found in the blood in a state of decay, thus showing that they were not destined to proceed to a higher development. By others they are regarded as an early or embryonic condition of the red corpuscles, or an intermediate stage of metamorphosis between the chyle and lymph corpuscles, and the red corpuscles. The latter view is supported by the following arguments : 1st, The colorless corpuscles are intermediate in shape and general appearance. 2nd. They are increased under circumstances un- favorable to normal changes, as in inflammation, or in persons of weak health, as in anemia, leucocythsemia, and in the tubercular diathesis. The red and white corpuscles are supposed by some to be developed directly from the plasma of the blood in which they float, by the ordinary process of cytogenesis. Blood corpuscles, like other cells, have their period of growth, maturity and decay, and while some are undergoing the process of disintegration, others are rising up to take their places. They are, no doubt, formed very rapidly, as is evidenced in their rapid formation after great hemorrhage, and their growth and development may be facilitated by the administration of iron, and a liberal diet. When the corpuscles are beginning to decay, they generally present at first a granular appearance; after a little they break down, and the contents disappear. Many of them may be observed in a granular state in phthisis, albuminuria, and septic poisoning. CHEMICAL AND STRUCTURAL CHARACTERS OF THE BLOOD. Chemical Composition of the Blood.—The average proportion of the constituents of the blood in 1000 parts is as follows:— CHEMICAL COMPOSITION OF BLOOD. 177 Water 784.0 Albumen (of serum) ..... 70.0 Fibrin . . . . . . . . .2.2 Red corpuscles (dry) 130.0 Fatty matters . . . . . . . .1.4 Inorganic Salts : Sodium and Potassium Chlorides . 3.95 Sodium Phosphate, Carbonate and Sulphate . . . . . 1.30 Calcium and Magnesium Phosphates 0.25 Iron Oxide and Phosphate . . 0.5 Odoriferous and coloring matter, glucose, gases, creatine, urea, and other extractive matters . . . 6.40 IOOO. These proportions are subject to considerable variation, even in health, depending on diet, mode of living, etc. The proportion of the various ingredients may be determined as follows:—The blood, as it flows from the vein, is received into two vessels of equal size, the first and last portions of the whole amount into the first, and the second and third portions into the second vessel, in order that the two quantities may be nearly alike, and then weighed. The blood in the first vessel is allowed to coagulate; that in the second is whipped with a bundle of twigs, to separate the fibrin, which is then washed with water—to remove the salts, with alcohol—to remove any coloring matter, and with ether—to remove any fats. It is then weighed. The clot which has formed in the first vessel is then taken out, and after the serum has drained away, it should be weighed. From the weight of the clot subtract the weight of the fibrin obtained from the second vessel, and this will give the weight of the corpuscles. The amount of albumen may be obtained by precipitating it from the serum, filtering and weighing. In this way it may be ascertained that in 100 parts blocd, about 78 parts are fluid,fand 22 parts solid material. In the latter, there are 13 parts corpuscles, 7 parts albumen, \ part fibrin, the salts, etc., making up the balance. In ordinary analysis, the corpuscles are estimated at about 13 per cent, by weight, of the entire blood. This refers, of course, to the dry corpuscles, from which the water has been removed. But it is easily seen, by a 178 BLOOD. microscopic examination, that the corpuscles, in their natural moist condition in the blood, constitute fully one-half of the entire mass ; hence the discrepancy in the analysis of different observers. Lehmann and Schmidt put the moist corpuscles at 512 parts in 1000, or about four times the weight as given above. Three fourths of their weight, consist of water. The red blood corpuscles are composed of a transparent homogenous substance called the stroma, in which the hemoglobins is infiltrated. The stroma is tough and elastic, and consists of globuline,protagon,fatty matters, cholesterine, and salts. The most important of these is the globuline. It is a semi-fluid substance, belongs to the albuminous compounds, and is formed from albumen. It is soluble in water, but not in the liquor sanguinis or fluid plasma of the blood, and is readily acted on by acetic acid, causing the corpuscles to swell out and finally burst..1 It coagulates completely at 200° F. Hemoglobine is a kind of pigment matter which is found in the red blood corpuscles, mingled with the stroma. It is more abundant than any other ingredient of the cor- puscles. It belongs to the albuminous compounds, being developed from albumen or fibrin, and consists of C54 H 7 Nie O21 S.6 Fe.4 the latter of which is an essential ingredient. It is soluble in water, dilute alcohol and alkalies, but is insoluble in ether, strong alcohol and oils. It crys- talizes in rhombic, or hexagonal plates or prisms, form- ing the so-called blood crystals. Although a crystalloid, and soluble in water, it is not diffusible, i.e., it does not pass through the pores of an animal membrane. When heated, it is decomposed into globuline and hematine. The distinguishing characteristic of hemoglobine is its strong affinity for oxj'gen, forming oxy-hemoglobine, which has a scarlet color; this readily parts with its oxygen again in the presence of reducing agents, and assumes a purple hue. On these qualities depend its most important physiological HEMOGLOBINE. 179 properties, viz., as a carrier of oxygen. This also explains the scarlet color of arterial blood, and the purple tint of venous. It was formerly supposed that the scarlet color of the blood was produced by the oxygen rendering the cor- puscles biconcave, and the venous condition by carbonic acid which made them biconvex or rounded. Fig’s. 62 and 63. a. Spectrum of oxidized hemoglobine. b. Spectrum of deoxidized hemoglobine. The two varieties of hemoglobine may be readily dis- tinguished by the spectroscope. A solution of oxy-hemo- globine or diluted arterial blood, presents two absorption bands in the spectrum, between the lines d and E, one in the yellow and the other at the commencement of the green, (Fig. 62, a). The former is narrow and well defined, the latter is broader and not so well marked. The spectrum of deoxidized hemoglobine on the other hand, presents a single absorption band intermediate in position between the other two, (Fig. 63, b). When from any cause the red corpuscles are broken down, the hemoglobine is set free, and stains the coats of the vessels, so as to give rise to an appearance re- sembling arteritis. Rupture of the corpuscles may take place from drinking too much water, or in low forms of disease, as in typhoid fever, purpura hemorrhagica, etc. 180 BLOOD. Distinction between Human and Animal Blood.— It is sometimes of the utmost importance in medical in- vestigations to distinguish between human blood and the blood of animals. In a fluid, or blood stain, when the cor- puscles have been dissolved or destroyed, the presence of blood may still be determined by the spectrum of hemoglo- bine, but the distinction between human and animal blood cannot thus be made. It is only by the use of the micros- cope that this can be determined. If the blood stain be found to contain oval nucleated corpuscles, it cannot be human blood, but that of a fowl, reptile or fish. If, on the other hand, the corpuscles are circular and without nuclei, then it will be impossible to say whether it is human blood, or the blood of some animal, as the cow, sheep, ape, dog, etc., whose corpuscles are nearly of the same size as the human. DIFFERENCE BETWEEN ARTERIAL AND VENOUS BLOOD. Arterial and venous blood differ from each other in general composition and color. The analysis which has already been given is of venous blood. In arterial blood the quantity of solid constituents of the corpuscles is less, but relatively they contain more hemoglobine and salts, and less fat. It also contains more oxygen and less carbonic acid. The liquor sanguinis is richer in fibrin, contains more water, and less albumen. The fatty matters of the serum are dimin- ished, and the extractive matters increased. The phosphorus which exists in the venous blood, is converted at the lungs into phosphoric acid, which then unites with the alkalies of the serum, as lime, potassa, soda, magnesia, etc., forming phosphates. Phosphorus is used in the building up of nerve and bone tissue. Blood of the Portal, Kenal and Hepatic Veins.— Blood drawn from different parts of the arterial system of the same animal is nearly always the same; but great vari- ations exist in the composition of the blood in the different parts of the venous system. The portal vein contains blood GASES. 181 derived from the gastric, mesenteric and splenic veins. During digestion, the blood of the gastric and mesenteric veins is much diluted, and contains the soluble alimentary substances taken up from the stomach and small intestine, as sugar (glucose), albuminose, etc. The fibrin also found in these vessels is less perfectly elaborated than in the blood in general, and liquifies soon after coagulation. On the other hand, the blood of the splenic vein shows a diminution of the red corpuscles, an increase of the white corpuscles, and an increase of the albumen. The fibrin is also increased, but like that of the gastric and mesenteric veins it is not fully elaborated, coagulates imperfectly, and liquifies soon afterwards. The blood of the renal veins is the purest in the body, having, subsequently to its purification in the lungs, been deprived of other impurities by the kidneys, such as urea, creatine, salts, etc. It contains less water, the albumen is neutral in reaction, and the fibrin is scanty and will not coagulate, (Brown Sequard.) The blood of the hepatic veins contains an increased amount of sugar and fat, which are formed during the passage of the blood through the liver. It also contains less water, albumen and salts, and more corpuscles and extractive matter, than that of the portal vein. Gases.—There is a remarkable difference in the amount of gases which arterial and venous blood respectively con- tain. The former contains from 16 to 20 per cent., by volume, of oxygen, while the latter contains about 12. The quantity of carbonic acid, on the other hand, is from 30 to 35 per cent, in arterial, and from 40 to 50 per cent, in venous blood. The quantity of nitrogen varies from 1 to 2 in arterial and venous blood respectively. There are also traces of ammonia. The difference between the amount of oxygen and carbonic acid respectively in arterial and venous blood, confirms the idea that an exchange of oxygen for carbonic acid takes place in the system, and an ex- change of carbonic acid for oxygen in the lungs. The red 182 BLOOD. corpuscles carry oxygen from the lungs to the tissues, and return carbonic acid for elimination. The serum also possesses the property of absorbing or dissolving carbonic acid. A certain part of the oxygen is used directly in the formation of fibrin, from albumen. The proper develop- ment of fibrin does not take place when the due aeration of the blood is interfered with, as in double pneumonia, in which case it is very much diminished. The presence of oxygen seems to be essential to the production of fibrin, and it has been shown by experiments on rabbits, that when pure oxygen is breathed the quantity of fibrin is very much increased. Dr. Gairdner examined the blood of six healthy rabbits, and found it to consist as follows, in 1,000 parts : Fibrin 1.65 Corpuscles 82.35 Albumen 46,30 He also examined the blood of three of these, which had been exposed to an atmosphere of pure oxygen for half an hour, and found it to contain as follows : Fibrin 2.40 Corpuscles 69.56 Albumen 40.23 Another of these animals was exposed to the action of an electro-magnetic current passed between the chest and spine, which produced a great acceleration of the respiratory move- ments, and the blood was found to contain 2.9 parts of fibrin in a thousand. Although the corpuscles appear to be very different in the two tables, yet their relative amount in pro- portion to the albumen is almost exactly the same in both cases. Color.—The difference in color between arterial and venous blood, is due to the hemoglobine which the red cor- puscles contain and the change of color produced in it by the influence of oxygen. It is also partly due to the change of shape of the corpuscles. They are biconcave in arterial blood, and rounded in venous. The former is produced by the in- INFLUENCE OF VENESECTION fluence of oxygen; but it may also be occasioned by con- tact with some of the salts in solution, without any direct exposure to oxygen. The blood is darkened in color by whatever tends to expand the corpuscles, so as to render them rounded, whilst it is brightened by whatever tends to render them biconcave. For example, arterial blood is darkened by the addition of water, which swells out the corpuscles and deprives them of some of their coloring- matter. CONDITIONS WHICH INFLUENCE THE CHARACTER OF THE BLOOD. Influence of Venesection.—It has been found by ex- periment that, in bleeding, the corpuscles suffer most; the fibrin is increased, and the water taken away is soon re- placed by transudation from the tissues, so that the specific gravity is diminished, as will be seen from the following table, the result of the analysis of the blood of ten patients, by Becquerel and Rodier : 1st Bleeding1. 2nd Bleeding. 3rd Bleeding. Specific gravity of defibrinated blood.. 1056.0 I053.O IO49.6 Specific gravity of Serum.... 1026.3 IO25.6 Water 793-o 807.7 823.1 Corpuscles 116.3 99-4 Albumen 63-7 64.6 Fibrin 3-5 3.8 3-4 Extractive and Salts 7-7 6.9 8.0 Fatty Matters 1.6 i-5 1000.0 1000.0 1000.0 From the above it will be seen that the corpuscles are notably diminished, and has no effect what- ever in diminishing the amount of fibrin. Fibrin is in- creased in all inflammatory diseases, and the most copious venesection is unable to check it, but rather increases it. The following table gives the result of bleeding, in a case of rheumatism, from Christison: Water 844 Solids of Serum 93 Corpuscles 57 Fibrin 4 184 BLOOD. Influence of Starvation on the Blood.—This is somewhat similar to prolonged venesection. The following tables show the result of bleeeding upon a well-fed dog; and also the same, in a state of starvation. (Todd and Bowman): 1st. 2nd. 3rd. 4th. f Water 783.79 810.89 815.18 813.04 While being ) Corpuscles 142.85 H3-54 1x0.58 106.95 fed. 1 Solids of Serum. 70.94 70.85 69.92 76.01 ( Fibrin 2.42 4.72 4-34 3-99 Number of Bleedings. After these bleedings, the animal was allowed to recover, and was well fed for about three weeks. He was then starved for about four days, being allowed nothing but water, and bled each day, with the following result: ISt. 2nd. 3rd. 4th. 1 Water 804.40 S05.44 838.30 849.84 While being 1 Corpuscles 121.08 II9-I5 87.98 74.21 Starved. i Solids of Serum. 72.61 71.46 68.46 71.62 ( Fibrin 1.91 3-95 5.26 5-i3 Number of Bleedings. In the latter case, the diminution of the corpuscles is more marked than in the former; and it will be observed that the corpuscles had not entirely recovered from the effects of the first bleeding. It will also be observed that, in both cases, there is at first an increase in the fibrin, and after- wards a diminution-—the latter being caused by the diminu- tion of the red corpuscles, and consequent non-development of the fibrin. Influence of Iron and Flesh Diet on the Blood — The quantity of blood corpuscles may be increased by the administration of iron and flesh diet. Fresh beef is the best diet for this purpose. It contains the most appropriate materials for nutrition, and is comparatively easy of diges- tion. The essence of beef, or beef tea, is still better, especially when the patient is very feeble, and the stomach unable to digest solid food. In anemia, the corpuscles have been increased from forty to sixty, and even ninety in a thousand, in a few weeks, by this mode of treatment. INFLUENCE OF AGE ON THE BLOOD. 185 Influence of Age on the Blood.—During the latter part of foetal life, the solids of the blood, especially the red and white corpuscles, are increased, and remain high for a short time after birth. They then gradually diminish until puberty, when they are again increased, and remain so dur- ing the most vigorous period of adult life, after which they begin to decline, as old age advances. The object of these changes in the increase of solids, is to fit the blood more fully for the nourishment and growth of the body at these important periods, viz ; immediately after birth, at puberty, and during the period of ovulation in the female, and the corresponding period in the male. Influence of Sex on the Blood.—The solid elements of the blood, especially the red corpuscles, are increased in the male. In pregnancy, the blood has a lower sp. gr. than the average, owing to the deficiency of red corpuscles. On the other hand, the white corpuscles and fibrin are increased, the latter especially during the last three months. This may be considered a wise provision of nature to favor the formation of clots in the mouths of the open vessels after parturition and the separation of the placenta, and to prevent post-partum haemorrhage. Influence of Disease on the Blood.—It will be seen from the following table that the principal constituents of the blood may vary much, in health, in different persons; and in the same person, at different times. This may be due to various causes, as the kind or quality of the food, habits, amount of exercise, etc. According to Andral, the variations may be as follows : Fibrin from 2 to parts per thousand. Corpuscles “ no to 152 “ “ Solids of Serum “ 72 to 88 “ “ Water “ 760 to 815 “ “ etc., etc. In estimating the quantity of fibrin in the blood in dis- eased conditions, it should always be borne in mind that it may contain a number of white corpuscles. These are very 186 BLOOD. difficult to separate, and although not very numerous in a state of health, yet in many diseases, as inflammation, anemia, leucocythsemia, etc., they are so much increased as to add materially to the amount of fibrin. There is found to be an invariable increase of fibrin in all acute inflammatory affections of a sthenic kind. This augmenta- tion is so constant, that if more than five parts of fibrin in a thousand be found in the course of any disease, it may be positively affirmed that some local inflammation is present. The maximum proportion of fibrin in inflammation may be stated at about 13.3 (acute rheumatism), the minimum 5r and the average about 7 parts in a thousand. Even in anemia and chlorosis it rises to 6 or 7 in inflammation. In phthisis also, there is an increase, notwithstanding the deterioration of the blood. It is, no doubt, due to the local inflammation going on around the tubercles. In single pneumonia the fibrin has been found as high as 10.7; in acute rheumatism, 13.3. It is slightly increased in all the exanthemata. It is also increased in leucocythsemia. The increase in the quantity of fibrin does not depend upon the febrile condition present in inflammation, but upon the inflammation itself. For example, in continued fever it is lower than in health, but if local inflammation arise in the course of the disease, the fibrin is at once increased. In simple continued fever it has been found as low as 1.6. In typhoid fever it may varj" from 3.7 to 0.9, and in some cases the blood shows no disposition to coagulate, the fibrin either being entirely deficient, or very much lowered in vitality. In double pneumonia it is as low as 0.9, due to the imper- fect aeration of the blood. In scurvy it is sometimes in- creased, and sometimes diminished. In cholera the serum is first diminished next the albumen, and afterwards the fibrin. The vomited matters, and substances passed by the bowels are coagulable by heat and nitric acid. The fibrin is diminished in apoplexy, due probably to the arrest of nerve force. In purpura hemorrhagica it is 0.9, and INFLUENCE OF DISEASES ON THE BLOOD. 187 sometimes entirely deficient. One of the effects of a diminu- tion in the proportion of fibrin is a tendency to the occur- rence of hemorrhage from slight causes, which is difficult to arrest. The amount of red corpuscles is subject to greater varia- tion within the limits of health than the fibrin. In plethora they may be increased to 180 or 190. Plethoric persons are not on that account more liable to inflammation; but they are very prone to congestion, especially of the brain, and apoplexy. This condition may be easily remedied by venesection. The number of corpuscles may be reduced from 180 to 144, or from 60 to 48 in one bleeding. In anemia, on the other hand, the corpuscles are diminished, in some cases as low as 27 in a thousand, but they may be rapidly increased by appropriate treatment. They have been increased in some instances from 40 to 60, and even 90, in three or four weeks. In diabetes mellitus, Bright’s disease, disease of the heart, lead poisoning, tuberculosis, cancer, scurvy, leucocythsemia, etc., they are materially diminished, and often assume a granular appearance. The colorless corpuscles are said to be increased in inflam- mation, but it is by no means constant. In the disease first pointed out by Dr. John Hughes Bennett, of Edinburgh, and termed by him leucocythsemia, they are largely increased. In this disease the specific gravity of the blood is low, and the fibrin is invariably increased. The quantity of albumen seems to vary very little. It is reduced in cholera, albuminuria, etc., so that the entire solids of the serum have been found in some cases as low as 52 in a thousand. The diminution in the amount of the albumen in the serum, in albuminuria, is exactly proportioned to the quantity found in the urine. The fatty matters are very much increased in some in- stances, so as to give the serum a milky appearance, as for example in tuberculosis, Bright’s disease, hepatitis, dropsy, 188 BLOOD. etc., and also during lactation in the female. Very little is known regarding the variations of the alkaline salts in disease. The proportion of water varies according to the amount of solids, being increased when the solids are diminished, and vice versa. In cholera, however, the drain is very great, and the reduction of the watery portion is most marked. Blood Poisons.—Substances which should be excreted from the body, as carbonic acid, urea, bile, etc., may be retained in the circulating current, and be attended with serious and sometimes fatal results. The most serious cases of blood poisoning, however, are those in which the poison is introduced from without, producing fermentation of the mass of blood, and destroying its vitality, as the poison of malignant pustule, typhoid, glanders, venom of serpents, etc. COAGULATION AND VITAL PROPERTIES OF THE BLOOD. The blood is the pabulum of all the tissues of the body. It is a living fluid, which possesses the power of reproduc- ing and maintaining itself, and contains all the elements necessary for the supply of the tissues, and nothing dele- terious or poisonous; for the presence of pus, urea, venom of serpents, or septic poisons, would be alike destructive to the vitality of the blood, and also the tissues. It has a certain amount of viscidity, which seems necessary to its free circulation through the capillaries. Besides, it is observed that, when from any cause the albumen and fibrin are diminished, there is a strong tendency to transu- dation of the watery portions of the blood, resulting in dropsies in different parts of the body. The corpuscles are the vital elements of the blood, and they endow certain other elements, such as fibrin and albumen, with vital properties. The coagulation of the blood consists in a new arrange- ment of its constituents, which occurs when the blood is removed from the vessels, or when the body itself dies. It COAGULATION. 189 depends upon the spontaneous coagulability of the fibrin, (or its constituent elements), during which it forms a net- work of fibres, in the meshes of which are included the corpuscles, in groups, like small piles of money. These are somewhat more numerous near the bottom of the clot. This crassamentum, or clot, then contracts, and squeezes out the serum, which contains the water, albumen and salts. The corpuscles exercise a certain influence in the coagula- tion of the blood, but their immediate presence is not abso- lutely necessary to its performance. This may be shown by filtering frog’s blood, diluted with thin syrup, on a fine paper filter, by which the corpuscles are kept back, and the liquor sanguinis which passes through, will afterwards coagulate. This is due to the vitality which it carries with it from the blood corpuscles. When coagulation is observed under the microscope, there are first seen minute granules which aggregate to form star-shaped spots; these send out arms or projections Fig. 64. Clot of fibrin containing bloocTcorpuseles entangled in its meshes. in different directions, which are formed by the addition of granules in a linear manner. In this way the whole mass is converted into a fibrous net-work, enclosing the corpus- cles in its meshes (Fig. 64). The period required for coagulation varies much. It commences about two minutes after the blood is drawn, and 190 BLOOD. is completed in from half an hour to two hours afterwards; but continues to contract for many hours. The degree of regularity, and the completeness of the coagulation, depends on the previous elaboration of the fibrin, and the character of the surface on which it takes place, whether dead or living, warm or cold, moist or dry, etc. It is not generally supposed to become organized. When it coagulates in the open mouths of vessels, as in the arrest of hemorrhage from wounded arteries, the coagulum is absorbed and carried away, after the vessels have been closed, by the effusion and organization of lymph. Fibrin does not exist as such in the blood, but is supposed to be formed in the process of coagulation, by the union of two previously existing albuminous substances, fibrin- oplastin (or paraglobulin), and fibrinogen, united under the influence of a “ ferment ” formed in the blood after its removal from the body. This is the theory of Schmidt. As the basis of this theory it has been observed that if blood-serum, or the fluid of hydrocele, or any serous effus- ion, be added to any other similarly constituted fluid, as the fluid of ascites, or from the pleural cavity, coagulation takes place, resulting in the production of fibrin. Another theory is that of Denis, according to which a substance exists in the blood, termed plasmine, in the proportion of 25 parts per thousand, which separates into two sub- stances when removed from the body. One of these is fibrin, which coagulates, and the other is metalbumen, which remains in solution. Plasmine however, is regarded by some as a mixture of fibrinoplastin and fibrinogen. Cupped and Buffed Condition of the Blood.—This condition of the blood generally occurs in inflammation, but is not exclusively confined to it, for it has been found to occur in anemia and in the blood of pregnant women during the last three months of gestation. It is occasioned by the increased tendency of the red corpuscles in these cases to run together and sink to the bottom of the vessel, and COAGULATION. 191 thus leave the fibrin in the upper part. The fibrin then contracts very firmly—a circumstance which is favored by the comparative absence of the corpuscles—and in conse- quence of this contraction taking place, first on the surface and sides of the clot, and thence extending internally, it causes it to assume a concave, or cupped appearance, both on the surface and sides. The “ buffed ” appearance is due to the predominance of the fibrin in the upper part of the clot, the characteristic color of which is light yellow or buff. The clot also contains some white corpuscles in its meshes, and these are said to be increased in inflammation. The formation of the cupped and buffed coat, though favored by slow coagulation, is often observed in cases where the coagulation is more rapid than usual. This condition of the blood is due, either to an absolute increase of fibrin, the corpuscles remaining the same ; or to a diminution of the corpuscles, the quantity of fibrin remain- ing the same as in health. It has also been observed that, although the clot is firmer in inflammation, each single fibre is weaker and more easily broken down than that of a healthy clot. This is supposed to be due to the comparative absence of the corpuscles, from their having sunk to the bottom of the vessel during the process of coagulation 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 coagula- tion. Rest 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 considerable time. Exposure to air accelerates the process of coagulation; it takes place more readily in shallow vessels than in deep narrow ones. Also, the multiplicity of points ; as in a lacerated, ragged wound, coagula are more readily formed than in clean, in- cised wounds. The addition of less than twice its bulk of water will promote the coagulation of the blood. 192 BLOOD. A low state of vitality of the vessels, from whatever cause, favors the formation of clots, or embolia, as they are called. These are, no doubt, frequently formed during life, as grooves, marked out by the current of blood, may be observed in clots found in the heart after death. The contact of foreign matter 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 coagula- tion in a remarkable degree, either within or without the living vessels. The presence of pus will produce coagula- tion 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 surrounds it. Circumstances Which Retard Coagulation.—In some instances it would appear that the blood does not coagulate after death; for example, it was stated by Hunter, that in animals hunted to death, killed by lightning, electric shocks, or blows on the epigastrium, the blood did not coagulate ; but it is probable that, even in these cases, it is only retarded, and ultimately coagulates, though imperfectly. It is further stated, by Polli, that the blood invariably coagulates before putrefaction sets in. Nevertheless, in cases of poisoning by hydrocyanic acid, and in death from asphyxia, coagulation may not take place, in consequence of the complete paralysis of the corpuscles and fibrin. In inflammatory conditions the blood drawn is usually slow in coagulating, in consequence of the sinking of the eor- COAGULATION. 193 puscles; but the clot is preternaturally firm, especially at the upper part, where the buffy coat contracts, and produces the “ cupped condition,” which generally indicates a high state of inflammation. The coagulation of the blood is retarded, or altogether destroyed, by keeping it at a tem- perature of 120°F., 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. The addition of more than twice its bulk of ivater retards the coagulation of the blood. Continued agitation also retards 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 remarkable 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 fifteen 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 addition of alkaline or earthy salts, added to fresh blood, have a tendency to retard, and sometimes to prevent coagulation; and the same effect is produced by many vegetable substances, especially those of the narcotic and sedative class, as opium, hyoscyamus, bella- donna, aconite, digitalis, etc. Gulliver mentions that he has kept horses’ blood in a fluid state for fifty-seven weeks, with solution of potassium nitrate, and that it still coagulated, when diluted with water. The presence of bile retards the coagulation of the blood; and septic or animal poisons as the virus of serpents may retard or entirely destroy its coagulating power. It is also retarded by imperfect aera- tion of the blood during life, as in asphyxia. 194 BLOOD. FUNCTION OF THE CONSTITUENTS OF THE BLOOD. Function of Fibrin.—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 Liebeg, that, so far from this being the case, the evidence is precisely the other way. There is no evidence whatever that fibrin (or its constituent elements) is used in the formation of any of the tissues, while, on the other hand, there are negative evidences that their for- mation 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, the small amount of fibrin found in the chyle is simply the result of elaboration in the lym- phatics. Thirdly, the vegetable cell, which is essentially the same as the animal cell, is formed from an albuminous fluid, there being no fibrin in the juices of the plant. As a component of the blood, fibrin is of importance in giving it its proper degree of plasticity, and in this way facilitat- ing its flow along the vessels. It also prevents the blood from exuding through the coats of the vessels, and arrests hemorrhage by plugging up the mouths of the open ves- sels. 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 sur- round abscesses, and prevent the infiltration of pus in the tissues. The same thing may be seen in the hemorrhagic diathesis, in which there is almost an entire absence of coagulable material. Fibrin was formerly supposed to be the material thrown out in the healing of wounds, and in the formation of adhesive bands in inflammation. Some physiologists and pathologists, among whom are Zimmerman, Simon, Jones and Sieveking, etc., have ad- FUNCTION OF 1HE RED CORPUSCLES. 195 vanced the idea that fibrin should be regarded 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 argu- ments. First, ihat fibrin is increased in bleeding, starva- tion, 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 corpus- cles are increased, and the fibrin diminished. Secondly, there is only a small quantity of fibrin in foetal blood, and in the renal veins; 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. Function of the Ked Corpuscles.—One great function of the red corpuscles is to elaborate the materials 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 converting the albumen into fibrin, and in forming globuline and hemoglobine from the albumen and fibrin of the blood. They are also carriers of oxygen to the tissues, and deporters of carbonic acid from the tissues to the lungs, where it is eliminated. The former is due to the affinity of hemoglobine for oxygen. In anemia, when the corpuscles are very much diminished, the strength of the individual is correspondingly reduced. The number 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 herbivora. The want of red corpus- cles in the invertebrata is compensated by the introduction of air through their tracheal apparatus, directly to the tissues themselves. 196 BLOOD, 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 in- vertebrate classes of animals. These corpuscles, which are oat-shaped in the larvie 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 diminished. 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 colorless corpuscles is an evidence of un- healthy 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 leu- cocythsemia, in anemia, and also in inflammation according to some, although, in all probability, this only occurs in sickly, scrofulous, or tuberculous patients. When the cir- culation of the blood is examined in a bat’s wing, or frog’s foot, under the microscope, the white corpuscles may be ob- served running from the centre of the current' to the circumference, and back again, and occasionally adhering to the sides of the vessels. They may also be occasionally seen passing through the coats of the vessels by virtue of their amoeboid movements, or diapedesis. In this process they throw out arms or projections which enter the pores of the vessels and gradually force their way through. They thus pass out in large numbers in the healing process, and in in- flammation, and are supposed to form the lymph. In this they are supplemented by the proliferation of connective tissue cells in the inflamed or wounded parts. Function of Albumen.—This substance is the pabulum, from which the tissues of the body are formed. It is also used in the formation of the fibrin, globuline, and hemoglo- bine*of the blood itself. Albumen by itself, however, is in- capable of organization, and its conversion into the various FUNCTION OF FATS IN THE BLOOD. 197 tissues must depend on their own power of appropriation. It also assists in holding in solution in the blood 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 retrograde 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, scarla- tina, etc. Its presence in the urine may be detected by heat and nitric acid, which cause a precipitate 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 in- tended in part, for the supply of the adipose and nerve tissue ; but their chief use, however, is to afford material for that combustive process which is necessary for the main- tenance of animal heat. It also contributes to the formation of milk. That which is stored up in the body may be looked upon as the surplus. Fat 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 acids, creatine, creatinine, fatty acids and odorous substances, but which do not properly form a part of it, are the result of a retrograde metamorphosis, either of the alimentary sub- stances or of the tissues themselves, and are rapidly elimi- nated by the lungs, kidneys, liver, skin, etc. The uses of the 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 sodium and potassium carbonates and phosphates are necessary to give the blood its alkalinity, to hold in solution the albumen, and to facilitate the passage of the blood through the capillaries, The salts are necessary also for the proper nutrition of the muscular tissue. Lime 198 BLOOD. phosphate, lime carbonate, calcium fluoride, etc., are re- quired to build up the solid tissues, as bone, teeth, etc. The lime phosphate, in particular, may be regarded almost as a histogenetic 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 hemoglobine. Water exists in large quantities, and is liable to consider- able 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 bj’ means of the excretory apparatus, which removes the surplus materials. Each part of the body takes from the blood the peculiar substance which it requires for its nutrition, and 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 phos- phates and carbonates 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 rudimentary organs, as the hair in the foetus, the mammae in the male, etc., 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 composition 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 RELATION TO THE LIVING ORGANISM. 199 through the successive phases of growth, maturity, and de- cay, 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 exan- themata, typhus, typhoid, etc. In all these cases the “ mor- bid poison ” would be eliminated by nature, if time were allowed 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 all the toxic diseases of the zymotic class, there is a natural tendency to self-elimination of the poison, and of the pro- ducts 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 with certainty when the changes may be ex- pected to take place. From the very nature of the action of these poisons on the blood, it is evident that no reliance whatever can be placed on the action of antidotes in check- ing their course. The object of treatment lies wholly in pro- moting the elimination of the morbid poison, in subduing local action, and supporting the vital powers of the patient during the continuance of the disease. 200 CIRCULATION. 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 necessary for its vital actions; and also to carry away the effete sub- stances 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 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 inter- space between the cartilages of the fifth and sixth ribs, one inch to the inner side, and two inches below the left nipple. It is a hollow, muscular organ, which, like a forcing pump, drives the blood through the vascular systen. It weighs from 9 to 10 ounces, and is about equal to the size of the closed fist of the individual, 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. Corresponding to the situation of these valves, there are distinct constrictions in the tube, so THE HEART. THE HEART. 201 that it has the appearance of a series, or chain of hearts. As we7ascend 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 1 ig. 65. Right auricle and ventricle opened, to show their interior. 1, superior vena cava; 2, inferior vena cava; 2', hepatic veins ; 3, right auricle ; 3', fossa ovalis, below which is the Eustachian valve ; 3", coronary vein ; +, +, auriculo-ventricular groove ; 4, 4, cavity of the right ventricle, the upper figure is immediately below the semilunar valves ; 4', large columna carnea or musculus papillaris ; 5, 5', 5", tricuspid valve; 6, in pulmonary artery ; 7, aortic arch close to the ductus arteriosus ; 8, ascending part or sinus of the arch covered at its commencement by the auricular appendix and pulmonary artery ; 9, the innominate and left cartoid arteries ; 10, appendix of the left auricle ; 11, 11, the outside of the left ventricle, the lower figure near the apex. 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 202 CIRCULATION. 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 communicating with its corresponding ventricle, and each ventricle communicating with an arterial trunk. The course of the circulation is as follows :—The venous blood is returned from the body by the super- ior and inferior vense cavse, and poured in- to the right auricle ; thence it passes into the right ventricle, being prevented from returning by the clo- sure 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 iungs, is returned to the left auricle through the pulmonary veins ; this constitutes the pulmonic circulation. It next 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 con- Fig. 66. Diagram of the circulation. PROOFS OF THE CIRCULATION. 203 siderable 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. On reference to the diagram there will also be seen a sub- ordinate stream, or offset of the general or systemic circulation which passes through the liver; this is the portal circulation. The variation in the course of the blood during foetal life is called foetal circulation. Proofs of the Circulation.—The circulation of the blood was discovered by Harvey in 1618. The main arguments by which he proved the circulation were as follows :— 1, The heart propels in half an hour, more blood than the whole mass in the body. 2, The blood spurts in a jetting manner from a wounded artery. 3, If true, the normal course of the circulation explains why the arteries were found empty after death. 4, If the veins were tied near the heart, it became pale and bloodless ; if the artery were tied, the heart became distended. 5, If a ligature be drawn tightly around the limb, no blood can enter and it becomes pale and cold ; if slightly relaxed, blood can enter but cannot leave the limb, hence it swells. 6, The existence of valves in the veins, which permit the blood to flow only towards the heart. 7, The constitutional disturbance re- sulting from poisons introduced at a single point. To these may be added proofs accumulated since the time of Harvey, viz.: the effects of wounds of arteries and veins respectively; in the former hemorrhage may be arrested by pressure above; in the latter, by pressure below the seat of injury. The direct passage of blood corpuscles from small arteries, through the capillaries into the veins, seen by the microscope in the web of the frog’s foot, the tail of the tadpole, etc. The injection of certain substances into the veins, which have been detected in the arteries a short time 204 CIRCULATION. atterwards. The valves of the heart are also so arranged as to permit the blood to pass only in one direction. Muscular Structure of the Heart.—The heart con- sists of striated muscular fibres, and fibrous rings which serve for their attachment. The fibres are not arranged in bundles, but 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, and there is no appearance of sarcolemma. The fibres are also smaller than those of other parts of the body, and the striae are less marked. The dispo- sition of the fibres of the heart may be demonstrated by prolonged boiling, which hardens the fibres and facilitates their separation. The fibrous rings are four in number, the right and left auriculo-ventricular, the aortic and 'pulmonary. The former serve for the attachment 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 walls of the left ventricle are 7 lines in thickness, those of the, right about 2J lines ; the walls of the left auricle are about 1£ lines in thickness, the right 1 line. Fig. 67. Fig. 68. Fig. 67. Muscular fibres of the heart, show- itg their striae, divisions and junctions. Fig. 68. Muscular fibres magnified, showing separate cells with their nuclei. 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 auricles, and are most distinct on the anterior surface. The deep fibres con- sist of two sets, looped and annular. The looped fibres commence at the ariculo-ventricular rings in front, pass FIBRES OF THE VENTRICLES. 205 upwards over the auricle, and return to the rings on the posterior part. The annular fibres surround the auricles in a circular manner, and are continuous with the circular fibres of the veins which open into them. The Fibres of the Ventricles.—These consist accord- ing to Pettigrew, of seven layers, of which three are external, the fourth central, and three internal. In the left ventricle the fibres of the first or external layer, run almost vertically downwards, inclining somewhat from left to right, and are continuous at the apex with the seventh or internal layer, which pass upwards reversely from left to right; these two, are the only layers that are inserted into the auriculo- ventricular and aortic rings. Those of the second layer rnn more obliquely downwards from left to right, and are con- tinuous at the apex with the sixth layer, which pass upwards with a corresponding obliquity in the reversed direction. The third layer is similar in course, hut still more oblique in direction, and is continuous at the apex with the sixth layer. The fourth layer is horizontal or transverse (circular), and appears to be single. The internal layers are thicker than the external, so that the fourth layer is nearer the outer, than the inner surface of the ventricular wall. The fibres of the external layer curve around at the apex in a spiral manner, and form the whorl or vortex, constitut- ing the entire thickness of the heart at this point. From the seventh layer are chiefly formed the musculi papillares- and column® carnese. The fibres of the first four layers pass across the septum from one ventricle to the other; this is specialtynoticeable at the back where there are some transverse fibres—the “ hinge-like ” fibres of the back of the heart. The right ventricle is similarly formed, except that the external fibres are continuous with the internal, not only at the apex, but all along the anterior coronary groove. The septum is formed of fibres from both ventricles, and the left half is twice the thickness of the right. 206 CIRCULATION. The heart is covered externally by a layer of 'pericardium and lined internally by a smooth shining membrane, the endocardium, which is continuous with the lining mem- brane of the arteries and veins. Both these membranes are covered with flattened epithelium (endothelium) which gives them a smooth and glistening appearance. The valves of the heart are formed by reduplications of the lining mem- brane, strengthened by connective and elastic fibres, and are attached by their bases to the tendinous rings. The tri- cuspid and mitral valves which guard the right and left auriculo-ventricular openings respectively, are also attached by their ventricular surfaces and borders to the columnar carnece by slender tendinous chords, the chordce tendinece, The semilunar valves which guard the orifices of the aorta and pulmonary artery, three in number for each, are placed side by side around the orifice, so as to form three little pouches, which lie flat when the blood is passing out, but immediately bulge out to prevent any return, the corpora Arantii closing in the space between the three segments in the centre. Vessels and Nerves.—The heart is supplied by the anterior and posterior coronary arteries ; the nerves are de- rived from the superficial and deep cardiac plexuses, which are formed partly by the cranial nerves, and partly by the sympathetic. 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 afterwards the two ventricles ; and in each case the contraction is immediately followed by a relaxation. The contraction is called systole ; the dilatation, diastole. The auricles gradually fill with blood flowing into them from the veins, part of which passes at once into the ventricles. When the auricles are dis- tended, they contract and force the blood into the ventricles, completing their diastole. The latter immediately contract, SOUNDS OF THE HEART. 207 and their contraction, or systole,follows so rapidly, that it ap- pears as if continuous with that of the auricles. The ven- tricles contract more slowly than the auricles, and empty themselves more completely than the latter, which always contain a small quantity of blood. The contraction of the ventricles upon the blood, closes firmly the auriculo-ventri- cular valves and forces open the semilunar, and the blood is forced into the aorta and pulmonary artery. The musculi papillares by their contraction, and attachment through the chordae, tendinece, prevent the auriculo-ventricular valves from being everted into the auricles. The closure of the tricuspid valve is not always complete, especially if the ventricle is too full, and a small quantity of blood flows back into the right auricle. This has been called the safety valve action of this valve. The semilunar valves, as pre- viously mentioned, lie flat to allow the blood to pass out but immediately fill, bulge out and meet, so as to pre-' vent its return. During contraction the heart appears to become longer and narrower, although, in reality, it becomes shorter and narrower. 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 in- serting another at the apex, so as merely to touch it. If the organ is then stimulated to contraction 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 ac- companied 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 equal to that of the pause. Thus, if the whole period be divided into five parts, the first two would 208 CIRCULATION. be occupied by the first sound, the third by the second sound, and the fourth and fifth by the pause, thus : 2 Parts occupied by the first sound 1 Part occupied by the second sound 2 Parts occupied by the pause Rhythm. A very short pause must also exist between the first and second sound, otherwise two distinct sounds could not be heard. This order of succession is called the rhythm of the heart, which, in a state of health, is remarkable for its regu- larity. 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. The first sound is in all probability, a compound sound, chiefly produced by the closure and vibration of the tricus- pid and mitral valves, and the collision of the blood against the walls of the ventricles. It is also partly attributed to the muscular sound produced by 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 and vibration of the aortic and pulmonary semilunar valves. They are forced back by the recoil of the blood, as one un- furls 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 pulmonary arteries respectively, in some animal, as a calf, so as to allow regurgitation to take place, when it will be ob- served that a bellow’s 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 IMPULSE OF THE HEART. 209 gives rise to murmurs which interfere with the distinctness of the sounds. Impulse of the Heart.—The impulse of the heart is most distinctly felt in the space between the fifth and sixth ribs, two inches below and one inch to the inner side of the left nipple, and is sometimes called the apex beat. The force of the impulse varies in different individuals, and in the same individual at different times; it is very distinct in emaciated persons, and especially in hypertrophy of the heart. It is produced by the contraction of the spiral mus- cular fibres of the ventricles, which causes a tilting of the apex against the walls of the chest, and also by its change of shape in contraction, during which it becomes firm and globular, and impinges upon 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 piace even when the apex has been cut off. The impulse of the heart corresponds with the pulse in the arteries, con- sequently the actions of the heart may be counted by the pulse at the wrist, or in any of the arteries. The beat is not a simple shock as it seems when felt by the finger, but may be shown by the cardiograph (a'modified form of the sphygmograph) to be compounded of three or four shocks the strongest of which only, is felt by the finger. Frequency and Force of the Heart’s Action.—In a healthy adult, the pulsations vary from seventy to seventy- five 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 represents the average number of beats in a minute :— 210 CIRCULA TION. In the foetus 150 At birth 130 In infancy ; no In youth 80 Adult age 75 Old age 65 Posture exercises a most remarkable influence on the fre- quency of the heart’s action. It is most frequent in the erect posture, next to that, in the sitting, and least in the recumbent position. The pulse is also most frequent in the morning, becoming slower towards evening, and is very much diminished during the night. It is more frequent in those of a sanguine temperament, than in the phlegmatic, and in females than in males. Its action is accelerated after a meal, and still more so after bodily exertion, or mental ex- citement. In health, there is a nearly uniform relation between the frequency of the heart’s action and the respira- tions, the proportion being about four of the former to one of the latter. 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 sys- tem, while tlje 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 method), or by causing the blood to act on a column of mercury (the method of Poiseuille and Volkmann.) 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 4J lbs., on the square inch. Poiseuille’s experiments were made with a glass tube, bent so as to form a horizontal FORCE OF THE HEART. 211 (6) and two perpendicular portions {a. c.), the latter being shaped like the letter U (Fig. 69), named the hcemadynamo- meter. The horizontal portion is adapted by a tube to the artery, 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 column which the force of the stream is able to maintain. The results corresponded elcsely with Hales’ estimate, being about lbs. Yolkmann passed a solution of sodium carbonate into the hori- zontal branch, to prevent the blood from coagulating on the sides of the vessel. From his experiments, it appears that the force of the stream is capable of supporting 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. A modification of the hsemadynamometer for registering the variations of the force of the heart, or arterial tension is called a kymograph (Fig. 70). The open mercurial column supports a floating rod and pen (a), in contact with a revolving paper cylinder moved at an uniform rate by clock- work. The movements of the pen, caused by the up and down movements of the column of mercury, are inscribed or registered on the paper cylinder. Influence of the Nerves on the Heart.—The heart’s action is governed by two sets of nerves, the excito-motor Fig. 69. 212 CIRCULATION. and inhibitory. The ganglia and communicating nerve fibres which preside over its action, are situated in the walls of the heart. They have been carefully studied in the frog, in which there are three collections of ganglia, two excito- motor—Remacks, near the infer- ior vena cava, and Bidder’s, in the left auriculo-ventricular septum, and one inhibitory—Ludwig’s in the interventricular septum. The heart receives its excito-motor influence through certain fibres of the sympathetic (inferior cer- vical ganglion and cardiac plex- us) from the medulla oblongata, and its inhibitory or restraining influence from certain fibres of the pneumogastric (superior car- diac). Stimulation of the sympa- thetic nerves supplying the heart, by the galvanic current, increases the heart’s action ; while on the other hand, stimulation of the pneumogastric nerve or its in- terior cut end diminishes it, and if the current is sufficiently trong, arrests it altoge ther, in diastole. Voluntary muscle so Fig. 70. Mercurial kymograph; (a) floating rod and pen ; (b) tube connected with an alkaline solution ; (c) tube and can- ula for insertion in an artery. Fig. 71. Before. During. After. Tracing showing the effect of stimulation of the pneumogastric nerve. treated would induce tetanus, but the heart is completely relaxed; it knows no tetanus. The natural stimulus of the heart’s action is the blood in its cavities, which excites reflex ARTERIES. 213 action through the ganglia and nerves. The heart appears to be constantly acting, but it has also its constant pauses or intervals of rest, so that it differs from other muscles only in its shorter intervals of rest. The effects of temperature on the heart’s action are interesting. In cold blooded animals the heart’s action ceases at 25° F. and again at 104° F.; its frequency is increased from the lower until the maxi- mum 72° F. is reached, and then it declines irregularly. In warm-blooded animals, as the rabbit, it ceases at 114° F. the frequency being increased from the lower to the maxi- mum of 105° F. 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, cartilage, cornea, and the ultimate elements of the tis- sues. They were formerly supposed to contain air, because they were found empty after death, hence the name arteries. ARTERIES. Structure.—They consist of three pcrt.prnn.nl vnlJAJr and internal. The external coat (tunica adventitia) is the thickest and consists of areolar and elastic tissue. In arteries of medium size, this coat is composed of two distinctlayers,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 en- tirely absent. The middle coat is thinner than the preceding, and consists of muscular (nonstriated) and elastic tissue, disposed chiefly in the transverse direction. In tne largest arteries the muscular tissue forms only about one-third or one- fourth of the thickness of the middle coat, while in the Fig. 72. An artery in which the three coats are dissected. 214 CIRCULATION. medium-sized arteries it predominates, and in the smaller it is purely muscular. The internal is the thinnest, and consists of two layers, the inner or epithelial, (endothelial) and outer or elastic. The former consists of a single layer of tesselated epithelium, with round or oval nuclei; the latter is a delicate, trans- parent, fenestrated membrane, which in medium-sized arteries is strengthened by several laminae of elastic tissue. The arteries are supplied with blood-vessels like the other organs of the body. They are called the “vasa vasorum.” They are derived fromsomeof the smallerarterial branches,which ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external and middle coats, probably also to the internal. They are also supplied with plexuses of nerves,derivedchieflyfrom the sym- pathetic system, but partly from the cerebro- spinal. It is through these that the calibre of the vessels is regulated. Function of Elastic Tissue in Arteries. —It protects 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 burst- ing 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 pressure 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 aorticvalves; hence they moderate the jetting movements given to the Fig. 73. Nonstriated mus- cular fibre cells; (a) developing cell; (b) more advanced ; (d, e, /,) fibre cells of human arteries. FUNCTION OF MUSCULAR TISSUE. 215 blood by the systole of the ventricles, and also equalize the current of blood by maintaining pressure upon the stream during the diastole. In this we cannot but admire the beau- tiful simplicity and harmony in the laws of nature. There is no loss of the force of the ventricles, for that part of their 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 ar- teries also gives them a capacity 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 different parts of the body. In conse- quence 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 contraction 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 torsion or twisting the cut ends of the ar- tery. Owing to their contraction after death, the vessels cannot be injected until the rigor mortis passes off. The muscular tissue of the arteries can assist only in a very small degree, in propelling the onward current of the blood. The manner in which the arterial trunks taper towards their distal extremities, renders it mechanically impossible that the strong contraction of circular fibres would drive the blood onward ; in fact, the tendency would be in the op- posite direction. The principal use of the muscular tissue is to regulate the supply to different parts of the body, ac- cording to the activity of the function of each part at differ- ent times ; for example, the brain does not require so much 216 CIRCULATION. blood during sleep as during mental labor; the stomach does not require so much blood during fasting, as during di- gestion, etc. 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 its passive dilatation, so as to diminish or increase the supply of blood according to the demand. The muscular tissue also assists the elastic in adapting the vessels to the quantity of blood they may contain, giving uniformity to the amount of pressure exercised on the blood, and maintaining the tone of the blood-vessels. Again, the contraction of the muscular coat of a wounded artery, first limits, and then arrests the escape of the blood when assisted by the formation of fibrin in the mouth of the wounded vessel. This is nature’s mode of arresting hemorrhage (natural hemostasis). The contrac- tion of the arteries is determined chiefly by the influence of the great sympathetic system. Function of the Arteries.— From what has 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 differ- ent parts of the organism according to the demand. Anastomosis of Arteries.—The arteries have a re- markable tendency to communicate with each other in their course, in order more fully to supply the organs to which they are distributed. This is called an anastomosis. One of the simplest modes is the union of two arteries to form one, as the union of the vertebrals to form the basilar. An- other mode is, the union of two branches 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 re- peated until the resulting branches are reduced to a very small size, when they terminate in the capillaries, as for ex- ample, the mesenteric arteries. A third mode, which is the PULSE. 217 most remarkable, is the communication of two adjacent ves- sels 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 communicating, and the carotid on each side is united to the posterior cere- bral 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 channels 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 communicate with each other at various points, especially around the joints. These branches also communicate with others from adja- cent arteries, as for example, the deep femoral with the sciatic, etc. By such an arrangement, the proper nutrition of the limb is secured by collateral circulation in the event of the main trunk being ligatured, 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 consequence of the free anastomoses between the adjacent branches, it is always necessary when a large artery is wounded, to apply a ligature both above and be- low the wound, in order to prevent the occurrence of subse- quent hemorrhage. Pulse.—When the finger is applied to the wrist, or any of the arteries of the body, it is felt to beat or pulsate in correspondence with the systole of the heart. The sensa- tion 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. It is not supposed that the jet of blood from the ventricle im- parts its pressure on the blood contained in the arteries so as to dilate the whole arterial system at once ; but it dis- places or propels the blood, and flows on by what may be called a head-wave. A certain time will be required for the 218 CIRCULA TION. 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-sixth to one-eighth of a second. I he rapidity of the wave is about 284 feet per second, or from 20 to 30 times as great as the velocity of the stream. Fig-. 74. Sphygmograph applied to the Arm. An instrument for delineating the character of the pulse is termed the Sphygmograph. It is made fast to the arm and the movements of a small button, which takes the place of the finger, are communicated by means of a lever, and registered by tracings in ink upon a card moved by clock- work (Fig. 74). In a healthy pulse the up-stroke or per- cussion impulse is nearly vertical, while the down-stroke is very oblique, and presents a slight notch or re-ascent; the more deficient in tone the pulse, the more distinct is the notch in the down stroke, and vice versa. In some instances, the re-ascent is so marked as to be perceptible to the finger, and is called a dicrotic pulse. The character of the pulse will depend—First, upon the force of the heart ; second, upon the integrity of its valves and orifices; third, upon the quantity and quality of the blood in the system; and fourth, upon the condition of the walls of the arteries, whether rigid or yielding, tense or flabby, etc. The qualities of softness or fulness, or wiry- ness, of compressibility or incompressibility, etc., which are familiar to the practical physician, are determined by the yielding or the resisting condition of the arterial walls. VEINS. 219 Influence of the Nerves on the Arteries. — The arteries in all parts of the body receive nerve filaments from the sympathetic, called vasomotor branches. These give tone to the muscular fibres of the arteries, and if stimulated, as e.g., by an electric current, the arteries contract and diminish the supply of blood to the parts ; if divided, the arteries are paralyzed and become dilated. The vasomotor nerves come primarily from the gray matter of the medulla oblongata, but communicate with the various gan- glia of the sympathetic. The medulla is called the “vaso- motor centre,” and the ganglia of the sympathetic, “second- ary centres.” The reflex impressions received by these centres may either result in contraction or dilatation of the vessels. If the impression received through the sensory nerve of a part is sufficiently strong, it leads to contraction of all the blood-vessels of the body, except those in the part from which the impression was received which become dilated, The former action is called excitomotor, the latter inhibitory. The redness which follows the irritation of the skin is a good example. VEINS. The veins return the blood from the various tissues and organs, to the right side of the heart. They are more numerous, and, with the exception of the pulmonic veins, more capacious than the arteries. They commence in the capillaries, and uniting form trunks, some of which are superficial, and others deep, accompanying their correspond- ing arteries. Structure.—In structure they consist of three coats, which resemble the arteries, except that the outer coat is thicker and contains some muscular tissue, and the middle coat is thinner. Muscular tissue is, however, entirely absent in the sinuses of the dura mater, uterus, and corpora caver- nosa, cerebral veins, retinal veins, and the veins of the can- cellous tissue of bones. Most veins have valves which pre- 220 CIRCULATION. vent the reflux of the 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, 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 sometimes only one. In very small veins they are absent; also in the ven?e cavse, pulmonary veins, hepatic veins, portal vein, renal, uterine, ovarian, 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. Circulation in the Veins.—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 is produced by the vis a tergo of the heart, the action of the capillaries, the contraction of the volun- tary muscles, and the inspiratory movements of the thorax. The vis a tergo of the heart may produce, in certain con- ditions of the system, a distinct venous pulse, corresponding with the impulse of the heart, the wave having passed through the capillaries. This may be called the com- municated or systolic venous pulse, and must be carefully distinguished from the regurgitant venous pulse, which is caused by the regurgitation which takes place, in some per- sons, into the venous trunks, during the systole of the right auricle. In health, the regurgitation is very small and in- distinct ; but when the right cavities of the heart are dilated, a large quantity of blood is regurgitated,and a distinct venous pulse is visible in the superficial and deep veins of the neck. The inspiratory movements of the thorax, 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, VEINS. 221 since the closure of the aortic valves would oppose any reflux in the aorta. This may be demonstrated by intro- ducing a bent glass tube into the jugular vein of an animal, the vein being tied above the point where the tube is in- serted, and the other end immersed 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 ma}' be shown by the hcemadynamometer. The effect of inspiration on the veins is only observable in the larger ones. Forced expiratory movements on the other hand, retard venous circulation, as may be seen by holding the breath for a few seconds, or by straining, when the veins about the neck and face swell up and become distended, but immediately return to their former size when breathing is restored. In surgical operations in the region of the neck, the wounding of an enlarged vein which remains patulous, is liable to be followed by the entrance of air into the circulation during a deep inspiration, and sudden death is the result. The contraction of the voluntary muscles has a most marked effect in favouring the circulation of the blood 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 compressed, and as the blood is prevented, by the valves in the veins, from pass- ing 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-compressed by the renewal of the muscular force, and so on. This force is an important agent in maintaining the circulation, 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 contraction of the muscular tissue of the walls of the veins also exerts considerable influence in the circula- tion of the blood in the veins. 222 CIRCULATION. CAPILLARIES. The capillaries are the connecting link between the arteries and veins, and are found in all parts of the body except the uterine placenta, copora cavernosa of the penis, hair, nails, epidermis, etc. In structure they appear under the microscope, to consist of a homogeneous, finely fibrillated membrane, with cell nuclei which adhere to or are embedded in it, at certain dis- tances apart. This is lined inter- nally by a layer of transparent, elongated and flattened nucleated cells (endothelium). At the point of junction of some of the endo- thelial cells, small openings or stomata (Fig. 75, c) may be seen resembling those of serous mem- branes (p.101), through which the white corpuscles make an active exit, and the red ones are some- times passively forced out. These appearances are readily seen after staining with solution of silver nitrate. The capillaries vary in diameter in the dif- ferent tissues, the average being about of an inch, (8.3 mmm) and their length is about of an inch (.8 mm). The smallest are those of the brain and mucous membrane of the intestines; the largest are those of the skin and medulla of bones. They form meshes, which vary in different tissues ; for example, they are rounded in the lungs, elon- gated in the muscles and nerves, aud looped in the papillae of the tongue and skin. The closest network is found in the lungs, and choroid coat of the eye. In the lungs, the interspaces are smaller than the capillaries themselves. The network is also very fine in the iris, ciliary body, and liver. As a rule the more active the function of an organ, Fig. 75. 1. Capillary with a thin wall and nuclei a and b ; 2, one with double contoured walls ; 3, capillary vessel after the action of silver nitrate solution ; a, endothelial cells; b, their nuclei; c, stomata. CIRCULATION IN THE CAPILLARIES. 223 the closer is the capillary network, 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 tubular 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 ol 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 corpuscles moving with considerable rapid- ity; while near the edges of the vesse there is a transpar- ent stratum of cleai plasma, in whicl may be seen some white corpuscles mo- ving very slowly The stream at the circumference is verj sluggish, almost mo- tionless, and is call- ed the still layer. Ii: the smaller vessels the corpuscles pass along in single file and sometimes become bent and other- wise distorted in order to acommodate 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 a ter go of Fig. 76. Capillary plexus in the frog’s foot, x 110; 1, trunk of vein ; 2, its branches; 3, pigment cells. (Wagner.) 224 CIRCULATION. 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 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 nutrition essentially consist. A certain force is generated by this interchange, which promotes the circulation of the blood through the capillaries. It is termed the attractive or selective power of the tissues, or by Carpenter capillary power. It may be explained as follows:—As the blood charged with oxygen and nutritious substances for the sup- ply of the tissues approaches the capillaries, a rapid imbibi- tion takes place with such energy, that it pushes before it into the veins, the blood from which the nutritious ele- ments had been previously removed, and which also con- tains 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 surrounded hy a plexus of nerves, similar to that of the larger vessels. Their contraction during anger and from fear, and their dilatation during blushing, can only 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 coun- tenance becomes deadly pale, as in anger, fear, etc. Under another kind of nervous emotion the vessels dilate, become filled with blood, and the cheek is suffused, as in blushing. The heart’s action alone is sufficient to carry on the cir- culation of the blood, but it is aided by other forces which are supplementary. The combined forces by which the blood is propelled throughout the body, are, first and chiefly, the muscular 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 VELOCITY OF THE CIRCULATION. 225 muscles among which some of the veins lie ; fifth, the action of the muscular tissue in the coats of the veins ; and sixth, the inspiratory movements of the chest. VELOCITY OF THE CIRCULATION. The velocity of the current of blood at any given point in the system, is inversely proportional to the sectional area at that point. The united area of the capillaries is 400 times as great as that of the aorta, and hence the velocity of the blood in the capillaries is about of that in the aorta. Velocity in the Arteries.—The velocity of the circu- lation in the arteries, may be ascertained by an instrument similar to that used for measuring the force of the heart. It is greater than in any other part of the system. Volkmann estimates the velocity with which the blood moves in the carotid artery, at about tvjelve inches per second. It diminishes during the diastole of the ventricles and in arteries remote from the heart, as the metatarsal, in which it is 2.2 inches per second. Velocity in the Veins.—The velocity of the venous current is to that of the arterial as two to three, or about eight inches per second, as nearly as can be ascertained. Velocity 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 of an inch per second. Velocity in the Body.—It is estimated that the ventricles and auricles are each capable 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 226 CIRCULATION. the whole would be minutes. But it has been ascer- tained by experiments on animals, as the horse, that sub- stances in solution, such as potassium ferrocyanide, barium nitrate, etc., may be detected in the blood drawn from the carotid artery within twenty seconds after it has been introduced 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 potas- sium nitrate in the jugular vein; in the rabbit in about four seconds, and in fowls in about six. The introduction of such poisons as hydrocyanic acid and strychnine, are equally rapid in their effects. Hence, it appears that the rapidity of the circulation is underrated in the estimate founded upon the capacity of the heart, and the number of pulsations in a minute. It has been estimated by Volk- rnann, that in man the whole circuit is completed in con- siderably less than one minute. Peculiarities of the Circulation.—These are observed in the lungs, liver, brain, spleen 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 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 circle of Willis. The occurrence of large venous trunks or indistensible sinuses within the cranium, is also peculiar. 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 be 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 FCETAL CIRCULATION. 227 brain. In the spleen, the most striking peculiarity is that each of the larger branches supplies chiefly that part of the organ to which it is distributed, having no anastomosis with the adjoining branches. The erectile tissues are the penis, clitoris, 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 contraction prevent the due return of blood from the parts, or by their relax- ation 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. Foetal 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 performs the office of the lungs and stomach in the foetus. The course of the circulation in the foetus is as follows:—The arterial blood is carried from the placenta to the foetus, along the umbilical cord, by the umbilical vein. It then enters the umbilicus, and passes upwards along the free margin of the longitu- dinal 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 228 CIRCULATION. 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, ta 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 returning from the lungs. From the left auricle it passes into the left ventricle, from the left ventricle into the aorta, to be distributed chiefly to the head and upper extremities—a small quantity passing into the descending aorta. From the head and upper extremities the blood is returned by the superior vena cava to the right auricle, 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, but the lungs of the foetus being almost impervious, only a small quantity is distributed to them by the pul- monary 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 transmitted 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 arteries 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 gradu- FCETAL CIRCULATION. 229 ally closes up, being completed about the tenth day. The ductus arteriosus contracts as soon as respiration is estab- lished, 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. There is also a peculiarity in the circulation of the blood in connection with the Malpighian bodies of the kidney, closely resembling the portal circulation, for which see structure of the kidney. 230 RESPIRATION. CHAPTER IX. RESPIRATION. As the blood circulates through the different parts of the body, it is deprived of a certain amount of its nutritive ele- ments 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 abundant 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 cavities 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. Each bronchus, on entering the hilum of the lung, divides and sub-divides dichotomously through- out the entire organ until the branches terminate in the lobular bronchial tubes. Each lung is surrounded by a serous membrane—the 'pleura. That portion which covers the lung is called the visceral layer, and is connected to the lung tissue by the sub-serous areolar tissue ; it is then reflected around the inner surface of the chest forming the -parietal layer. These two layers are smooth, moist and coveied with epithelium ; they are everywhere in contact, THE LUNGS. 231 and glide readily upon each other. It is only when filled with air or fluid that there may be said to be a cavity between them. The respiratory apparatus consists essentially of a thin, moist membrane, with blood-vessels on one side, and air or aerating fluid on the other, through which osmosis takes place. The lungs of the newt consist of cylindrical sacs running the entire length of the body, into which the air is forced by a sort of swallowing movement, and is after- wards regurgitated to make room for a fresh supply. In the frog end turtle, the cavity is divided into smaller com- partments by thin septa, all of which communicate with the central cavity. The same principle or plan of construc- tion obtains in the higher animals, the walls of the cavity being folded and refolded in order to increase the extent of aerating surface. In fishes and most aquatic animals the respiratory organs are in the form of gills or branchiae, which are foldings of mucous membrane, containing blood-vessels. These are moved by muscles so as to bring them into contact with fresh portions of water, for the pur- pose of aeration. In certain of the lower order of animals unprovided with lung cavities, and in the vegetable king- dom, tracheal openings, or stomata, exist for the interchange of gases. Minute Structure.—Each lung is divided into lobes, three for the right and two for the left, and eacli lobe is sub- divided into lobules, which are held together by areolar tis- sue. They vary in size form fa to fa of an inch (2 to .8 mm) in diameter. They also vary in shape ; those on the surface are large,of a pyramidal form, with their bases turned towards the surface; those in the interior are smaller, and of various forms. Each lobule is a miniature representation of the v/hole organ of which it forms a part, being composed of the terminal divisions of one cf the smaller bronchial tubes and corresponding air cells, blood vessels, nerves and lymphatics, all held together by areolar tissue. 232 RESPIRATION. 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 to of an inch, (.5 to .2 mm). They are then con- tinued onwards, their sides and extremi- ties being closely covered by numer- ous saccular dilatations—the air cells —in consequence of which the tubes lose their identity, as cylindrical tubes, and present the character of irreg- ular canals or passages—the so-called intercellular passages (Fig. 77). The air cells are small alveolar recesses, which vary from t° °f an inch, to .12 mm) in diameter, and are separated from each other bv thin senta. Thev communicate with the termin- al bronchial tubes which thej’surround by large circular openings; but do not communicate with each other except through the tubes. In these small bron- chial tubes and air cells, the cartilagin- ous and muscular tissues are absent, and the mucous membrane is lined by squamous epith- elium, while the trachea and bron- chi are lined by Fig. 77. Lobule of the human lung ; a, bronchial tube with its divisions ; b, in- tercellular passages; c, air cells. Fig. 78 Air cells of lungs, x 350 ; a, epithelium ; b, fibres of elastic tissue ; c, delicate lining membrane of air cells, with elastic fibres attached t it.—(Kolliker.) VESSELS AND NERVES. 233 columnar ciliated epithelium, among which are to be seen some cup or goblet cells (p. 99). Vessels and Nerves.—The 'pulmonary artery con- veys 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 bron- chial tubes and air cells. Some of the capillaries also pass into the septa between the air cells so that both sides are at once exposed to the air. The blood, puri- fied during its passage through the capillaries, is returned by the pulmonary veins to the left auricle of the heart. The bronchial arteries supply 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 upon the walls of the terminal bronchial tubes and air cells, and terminate 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 into the superior intercostal. The lungs are also abun- dantly supplied with lymphatics. They commence in irreg- ular spaces or lacunae in the walls of the air cells, or bronchi, and in the lymph spaces of the pleura pulmonalis. Nerves.—The lungs are supplied by the anterior and posterior pulmonary plexuses of nerves formed chiefly by branches from the pneumogastric and sympathetic nerves. MECHANISM OF RESPIRATION. 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 mechanical 234 RESPIRA TION. 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 enlarged in every direction, but chiefly in the vertical. The latter is effected principally by the contraction of the diaphragm, and its consequent descent towards the abdomen. The in- crease in the lateral and antero-posterior diameters is due to the elevation of the ribs, both in front and at the sides. The ordinary muscles of inspiration are the diaphragm, exter- nal intercostals (and the internal in front), levatores cos- tarum, serratus magnus, and serratus posticus superior. But in extraordinary or forced inspiration, as during a par- oxysm of asthma, etc., the shoulders are fixed by the patient seizing something firmly, and the serratus magnus, pectoralis major and minor, trapezius, subclavian and scaleni muscles are called into action. The scaleni muscles fix the upper ribs, from which the external intercostals act, as from a fixed point, and elevate the lower ribs, by which the cavity of the chest is enlarged laterally and antero-posteriorly. This action is also promoted by the action of the other muscles previously mentioned. Expiration.—Expiration succeeds inspiration, after a brief interval, and is accomplished, in ordinary respiration, by the elastic recoil of the lungs and walls of the chest, after they have been dilated, and partly by muscular action. The ordinary muscles of expiration are the abdominal muscles, internal intercostals except in front, serratus posti- cus inferior, and triangularis sterni. The extraordinary are the quadratus lumborum, latissimus dorsi, sacrolumbalis, and those which assist in fixing the spine and pelvis. In diffi- cult breathing, almost every muscle in the body is made sub- servient to the action of respiration. Tire duration of in- spiration is generally less than expiration, although in some instances they are nearly or quite equal, and there is a slight pause between the end of expiration and the com- FREQUENCY OF RESPIRATION. 235 menceraent of the next inspiration, and also between the acts. The succession of these acts constitutes the respira- tory rhythm. During inspiration and expiration a sound is heard when the ear is applied to the chest, called the respir- atory murmur. It is longer (§) and more distinct in inspir- ation, and is best heard in children, hence the term puerile respiration. The rima glottidis is also opened at each inspiration by the action of small muscles, and is closed some- what at each expiration by the elastic recoil of the parts. The force 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 vary from sixteen to twenty in a minute. The proportion of respira- tory 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 obstruction to the aeration of the blood, or some derangement of the nervous system. Any great disproportion between the number of respirations, and the number of pulsations or the amount of blood sent to the lungs to be aerated, is attended with dyspnoea. When the action of respiration is chiefly confined to the diaphragm and abdominal muscles, as in pleurisy, etc., the breathing is said to be abdominal; but when chiefly con- fined to the muscles of the thorax, as in peritonitis, etc., it is said to be costal or 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 230 cubic inches the excess being called complemental air. 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 supplemental air. A quantity still re- 236 RESPIRA TION. mains, which cannot be forced out; this is called residual air. The respiratory capacity of the chest is called the 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 230 cubic inches ; and for every inch in height above this stand- ard, 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 in- creases 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 exertion, etc. If the same air be rebreathed several times, it becomes loaded with carbonic acid and animal matter, causing head- ache, languor and depression, and if continued, serious results will follow sooner or later. Experience has shown that the minimum quantity of air which ought to be allowed for each person confined in prisons, hospitals, schools, etc., is about 1200 cubic feet. Provision should also be made for a constant supply of fresh air, and the removal of the impure, which is of even greater importance than the mere actual cubic space. The Fig. 79. Spirometer for measuring the quantity of air taken into the lungs. INFL UENCE OF NER VES IN RESPIRA TION. ventilation should be such as will supply, at least from 1200' to 1500 cubic feet of fresh air for each person per hour. Influence uof the Nerves in Respiration.—The- movements of respiration are presided over by the medulla oblongata, into which may be traced the principal excitor nerves, and from which proceed the principal motor nerves. The chief excitor of the movements of respiration is the pneumogastric nerve. When this is divided on both sides in the dog, the number of respirations are diminished about one-half, and irritation of its trunk is followed by an act of inspiration. The respiratory movements are caused by the presence of blood, loaded with carbonic acid, in the capil- laries 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 or body, or a slap on the 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 accompanied by a deep inspira- tion. It is quite probable also, that the sympathetic nerves, which receive filaments from the spinal nerves and com- municate with the pneumogastric, may be excitors of this function. The motor nerves concerned in the function of respiration are the phrenic, intercostals, facial and spinal accessory. The motor power of the respiratory nerves is exercised, however, not only in the muscles of respiration, but also on those which guard the entrance to the wind- pipe. Division or injury of the medulla oblongata is followed by sudden death from arrest of respiration. After division or injury of the spinal cord in the lower part of the cervical region, inspiration is performed by the diaphragm only, and when injured above the origin of the phrenic nerve, death occurs instantly, because of the inter- 238 RESPIRATION. ruption to all communication between the medulla oblongata and the diaphragm. The respiratory movements, though partly voluntary, are in ordinary respiration essentially independent of the will, for example, during sleep, coma or anaesthesia, 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 subservient to the production of those sounds by which individuals communicate their ideas to each other, as in speaking singing, etc. 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 inspiration, the glottis is then closed and a violent expiration takes place, by which a sudden blast of air is forced up the air passages by the diaphragm and abdominal muscles, forcing open the glottis and carrying before it any substance that may be present. In the act of coughing, the abdominal muscles act as forcibly on the abdominal viscera as on the lungs, and tend to the expulsion of their contents, but the voluntary contraction of the sphincters prevents any escape at the openings. The difference between coughing and sneezing is, that in the latter the blast of air is directed more or less completely through the nose, in order to remove any irritating substance there. Sighing is simply a deep inspiration, in which a larger quantity of air than usual is made to enter the lungs. Yawning is a still deeper inspira- tion, and is accompanied by opening the mouth widely, and contraction of the muscles about the jaws. In laugh- ing, 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 CHANGES IN THE RESPIRED AIR. 239 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 sud- denly closing in the midst of it; the sound is produced by the impulse of the column of air against the glottis. In speaking and singing, the vocal chords are made to vibrate as the air passes over them, and produce sounds which are moulded into words or notes by the tongue, teeth, lips, etc. Changes in the Kespired 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 .03 to .06 parts in a thousand, a variable amount of aqueous vapour, and a trace of ammonia. The changes produced on the atmos- pheric air by respiration are—1st, an increase in the tem- perature 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 organic 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.—The presence of an increased amount of carbonic acid in expired air, may be demonstrated by breathing through lime water, which becomes milky by the formation of insoluble calcium carbonate. It has been ascertained that there are about 4.35 parts of carbonic acid in 100 parts expired air, and subtracting the quantity 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 nearly eight ounces of carbon. The elimination of 240 RESPIRATION. ■carbonic acid may be modified by a number of circum- stances. 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 introduced into the system, are followed by a diminution in the quan- tity of carbonic acid exhaled. Exercise increases the exha- lation of carbonic acid to about one-third more than it is ■during rest. During sleep, on the other hand, it is dimin- ished, owing to the quietness of the breathing ; but directly after waking, the amount is increased. Age and sex influence the quantity of carbonic 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 continue to menstruate, but when men- struation 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. Observations made at various temperatures between 38° 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. Moisture of the air also favors the elimination of carbonic acid very materially. The respiratory movements influence the exha- lation 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 have been previously breathed, the quantity of car- bonic acid exhaled is very much diminished. It should also be borne in mind, that the continued respiration of an AMOUNT OF OXYGEN INHALED. 241 atmosphere charged with the exhalations from the lungs and skin, is a most potent predisposing cause of disease, especially of the zymotic class. The presence of an increased amount of aqueous vapour in expired air, may be shown by breathing upon a looking- glass, or polished metallic surface. The amount of aqueous vapour exhaled from the lungs in twenty-four hours may be estimated, in temperate climates, at from ten to twenty ounces. A certain amount of carbonic acid and water is also eliminated by the integument. Ammonia is an accidental constituent of expired air. The amount of organic matter given off from the lungs in twenty-four hours, is about three grains. Amount of Oxygen Inhaled.—There is always less oxygen in expired air, than in the same quantity of 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 sub- stances besides the carbon, as for example, sulphur and phosphorus, which are eliminated in the urine in the form of sulphuric and phosphoric acid. Its absorption depends on the strong chemical affinity of hemoglobine for it. The quantity of oxygen absorbed is about 542 grains per hour, but it 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 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, under pres- sure, and is also separated by a membrane from that into which it is to be diffused. RESPIRATION. The nitrogen of the atmosphere serves only to dilute the oxygen, and moderate its action in the system. Under ordinary circumstances there is very little difference between the quantity of nitrogen inspired and exhaled. The absorp- tion 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 in the Blood in 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 ; 4th, it contains more fibrin, and the temper- ature is increased from 1° to 2° F. The most obvious change is that of color, the dark venous blood being exchanged for the bright scarlet of arterial blood. The causes of this change have been already discussed in the chapter on blood. It is chiefly due to the absorption of oxygen, which is taken up principally by the hemoglobine of the corpus- cles and partly by the plasma, and carried to the tissues; and to the exhalation of carbonic acid which exists in the blood. The corpuscles also assume a biconcave shape, which reflects the light in such a way as to modify the color. Both oxygen and carbonic acid exist in the corpus- cles and plasma of the blood, partly in a state of solution, and partly in a state of chemical combination; but the corpuscles are the chief agents concerned in the absorption of the gases. The exhalation of carbonic acid 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 respiration is obstructed or seriously impeded, it accumulates in the blood, and may cause death EFFECTS OF ARREST OF RESPIRATION. 243 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 glucose and fats, giving rise to a certain amount of animal heat: 2nd, in the capillaries, by the union of oxygen with the carbon produced by the dis- integration of the tissues; 3rd, in the lungs, by the decom- position of the alkaline carbonates. Effects of the Arrest of Respiration.—When res- piration 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 bod}r. 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 retention of blood in the lungs is due to the non-elimination 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 destro}7ed by asphyxia varies from one and one-half, to four minutes. In new-born and young animals, longer time is required than in older ones, because in the former the respiratory changes in the tissues are much less active. Animals will recover after simple deprivation of air for four minutes, but submersion in water for 1| minutes destroys life completely. This is owing, in all probability, to the filling of the lungs with water. In drowning, very few persons recover who have been sub- merged more than three or four minutes. Cases have been RESP IRA TION. recorded in which recovery took place after the lapse of from fifteen minutes to half an hour; 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° F.; birds from 106° to 1110 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, how- ever, there is an internal source of heat, but it is more active in the one than the other. Even in vegetables a cer- tain amount of heat-producing power is occasionally mani- fest, as for example, in the flowering of plants, malting of barley, etc. In disease, the temperature of the body may deviate somewhat from the natural standard, as e.g,, in scar- latina, typhoid fever, etc., 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. Continued high temperature in fever usually indi- cates a fatal issue, The highest temperature yet observed was reported by Dr. Teale, Eng. in a case of spinal injury, in which the temperature reached 122° F. The patient recovered. In some cases of yellow fever, a remarkable rise PRODUCTION OF ANIMAL HEAT. 245 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. The temperature of the new-born child is 1° F. higher than in the adult. Theory of the Production of Animal Heat.—There have been many theories regarding this subject. Lavoisier supposed that the oxygen taken into the lungs combined with the carbon of the blood and formed carbonic 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 car- bonic acid is formed principally in the blood and tissues, and that the oxygen is taken up by the blood corpuscles and carried away in the general circulation. According to Lie- big, the heat of the animal body is produced by the oxida- tion or combustion of certain elements of the food, while circulating in the blood, as sugar, 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, etc. 2nd, The elements of respiration, 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 phenomenon which results partly from the oxidation, or combustion, of certain elements of the food, and partly from the chemico- vital changes which take place in the blood, and the differ- 246 HEAT, LIGHT AND ELECTRICITY. ent organs of the body. Every change in the condition of the organic constituents of the body, in which their ele- ments enter into new combinations with oxygen, must be a source of the developement of heat; and the amount of oxygen consumed 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 quantity of heat generated in the body is, “ coeterispar- ibus,” in direct proportion to the activity of the respiratory process. For example, in birds, whose function of respira- tion 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 reptiles, 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 the Nervous System in the Produc- tion of Animal Heat.—It has been observed that after the division of the nerves of a limb the temperature 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 tem- perature of 92° F. Again, when death is caused by a severe injury, or removal of the nervous centres, or in poisoning by woorara, etc., the temperature of the body rapidly falls, even though artificial respiration be kept up. On the other hand, severe injuries of the nervous system are sometimes followed by the direct opposite 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 nerves in larger quantities ; the nutrition is therefore more active. REGULATION OF THE HEAT OF THE BODY. Certain emotions of the mind may cause a momentary in- crease of temperature, while others cause a diminution. These circumstances, however, do not prove that heat is produced by mere nervous action independent of any chem- ical change. All the functions of the organism, as nutrition, secretion, excretion, etc., are under the influence of the nerves, and when they are divided, or otherwise injured, or paralyzed, chemico-vital action is in great measure sus- pended. Regulation of the Temperature of the Body. — The temperature of the body is rendered uniform partly by loss of heat by radiation, and conduction ; but chiefly by the evaporation which is continually taking place on its sur- face and to a small extent in the air passages. The intro- duction of food and drink at a lower temperature than the body, and the removal of the excreta, also abstract a small amount of heat. Evaporation of the perspiration 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. Per- sons have been known to remain for several minutes in a dry atmosphere, heated to 250°F, without-injury, the evap- oration 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. In such cases great benefit will be derived from sponging the body frequently with cold or tepid water. 248 HEAT, LIGHT AND ELECTRICITY. LIGHT The evolution of light from the living human body, is a phenomenon of rare occurrence. Luminous exhalations have been frequently observed in burial grounds, and a luminous appearance has been sometimes noticed in newly dissected subjects in the dark. This is due to the development of phos- phoretted 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 charg- ed with phosphoretted hydrogen. The urine also, in some instances, has a luminous appearance, depending upon the presence of unoxidized phosphorus which it contains. The breath of an animal may be rendered distinctly luminous by injecting phosphorus dissolved in olive oil, in the propor- tion of two grains to the ounce, into the veins. 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 elec- trical 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 galvano- meter. The direction of the current is constant in each muscle ; but different muscles have different 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 differ- ELECTRICITY. ELECTRICITY. ent currents are so unevenly balanced, that a constant cur- rent 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 to the surface of a muscle is applied one of the electrodes, and the cut end brought in contact with the other, These results may be obtained with small portions of muscle, even with a single fasciculus. Hence, it would appear, that each integral particle or sar- cous element is a centre of electromotive action, and con- tains 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 mus- cular fibrillse 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 con- tracted, the shock is not so readily transmitted as when they are held gently. Since electricity 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, recently ob- tained from the living body, is placed so that its surface rest& on one of the electrodes, and its cut extremity touches the other, a considerable deflection of the needle is produced in 250 HEAT, LIGHT AND ELECTRICITY. a direction which indicates that the current is from the in- terior 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 molecules of the nerve. The term electrotonus is ap- plied to the condition of the nerve which exists during the time of electric stimulation. The irritability of the nerve is increased in the region of the negative pole or kathode, and is known as katelectrotonus, while it is diminished in the region of the positive pole or anode and is known as the condition of anelectrotonus. Electric currents are conveyed by nerves as well in one direction as another. 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 electri- city of man is generally positive; of woman, more frequently negative ; and irritable men, of sanguine temperament, have more free electricity than phlegmatic persons. In some per- sons 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 mentioned in the American Journal of Medical Sciences (1838), in whom the generation of elec- tricity was so great, that whenever she was insulated by a carpet, or any other feebly conducting medium, sparks pass- ed between her body and any object she approached. Asmuny 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 accompanied with a good deal of pain. In some persons, a sufficient amount of electricity may be generated, when insulated by a carpet, to enable them to ignite a recently extinguished gas jet, by means of the sparks which pass from the fingers. ELECTRICITY. 251 Some animals possess organs in which electricity may be generated and accumulated in large quantities, and from which it may be discharged at will. The most remarkable examples are to be found in certain 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 not severe, but sufficient to benumb the hand that touches it. Sparks of electricity'hnay be produced in most animals having a soft fur, by rubbing the surface, especially in hot weather. This may be easily demonstrated by smoothing the back of a cat with the hand, in a darkened room, rub- bing the horse in a dark stable, or by scraping sugar in the loaf in a dark pantry. 252 SECRETING GLANDS AND THEIR SECRETIONS. CHAPTER XI. SECRETING 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 con- sists of five lobes, which are mapped out on its under surface by five fissures. It is mainly divided into two lobes, the right and left, by a longitudinal fissure, the anterior- portion of which is called the umbilical fissure, and the posterior part, the fissure for the ductus venosus. The right lobe is six times as large as the left, and presents on its under surface the lobus quadratus, lobus caudatus,and lobusSpigelii separated from each other by the transverse fissure, the fis- sure for the gall-bladder and the fissure for the vena cava. The transverse fissure is sometimes called the hilum, and is situated, as in the lungs, kidneys, spleen, etc., nearer the posterior than the anterior border. The liver is intended mainly for the secretion of bile, and is also supposed to ef- fect important changes in certain constituents of the blood in its passage through the gland. Minute Structure.—The liver is surrounded by a re- flection of the peritoneum,which constitutes its serous cover- ing. This is attached to the substance of the gland, except at its point of attachment to the diaphragm and in the THE LIVER. 253 bottom of the different fissures, by fine areolar tissue. The substance of the liver consists of lobules held together by delicate areolar tissue, the ramifications of the portal vein, hepatic artery and ducts, hepatic veins, nerves and lymph- atics. The lobules (acini) are small, oval or roundish bodies, about the size of a millet seed measuring from T\j to of an inch (2.5 to 1.2 mm) in diameter. They surround the 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 pre- sent a foliated margin, and on a transverse sec- tion, they have a poly- gonal outline. When one of the sublobular hepatic veins is laid 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 pre- sents 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. Fig. 80. Longitudinal section of a portal canal contain- ing/P) portal vein ; (a) hepatic artery, and (d) he- patic duct. Lobules are to be seen to the right- and left,and also shining through the thin wall of the vein; in the centre of each lobule is seen the intralobular vein ; a, a, portion of the canal from which the vein has been removed ; b, open- ings of the interlobular veins. Structure of the Lobules.—Each lobule is a miniature 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 commencement of the hepatic vein), arteries, nerves, and lymphatics. 254 SECRETING GLANDS AND THEIR SECRETIONS. 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 cir- Fig-. 81. Hepatic lobule. In the centre is seen the intralobular vein ; vp, termination of the por- tal vein around the lobule, from which a capillary plexus proceeds towards the centre in the meshes of which are seen the hepatic cells ; b, b, biliary ducts, arising within the lobule. (Claude Bernard.) cumference of the lobule (Fig. 81). They are generally spheroidal in shape, but may be polygonal from mutual pressure, and vary in size, from to of an inch (25 to 12.5 mmm.) in diameter. Each cell contains a distinct nucleus, sometimes 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 colouring matter, and some oil globules. Biliary Ducts.—These commence within the lobule by a minute plexus of ducts (bile capillaries), with which the cells are in immediate contact. The ducts then form a Fig. 82. Hepatic Cells. (Frey.) HEPATIC VESSELS. 255 plexus between the lobules (interlobular), and the inter- lobular branches unite into vaginal branches, which lie in the portal canals. These branches finally join to form two large trunks, which leave the liver at the transverse fissure, and uniting 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, to- gether with the branches of the hepatic artery and duct, nerves and lymphatics. These vessels are surrounded 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 given off,which pass between the lobules and cover their external surface, called interlobular -r 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 li ver. It gives off in the portal canals the vaginal branches, which supply the coats of the portal vein and hepatic ducts, and also interlobu- lar branches, which pass between the lobules; the latter pierce the lobules, and terminate in the radicles of the intra- lobular 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 in- terior 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 sublobular 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 chap- ter on digestion. 256 SECRETING GLANDS AND THEIR SECRETIONS. THE KIDNEY AND ITS SECRETION. The kidneys are intended for the secretion of urine. They are situated in the back part of the abdominal cavity, one in each lumbar and hypochondriac region, extending from the eleventh rib to within two inches of the crest of the ilium. The right is somewhat shorter and situated a little lower than the left. They are invested by a thin, smooth, tibrous capsule, which is very easily removed from the sur- face of the gland, and weigh from four to six ounces each. Structure.—The kidney consists of two different sub- stances, an external or cortical, and an internal or medul- lary substance. The cortical substance forms about three- fourths of the whole gland, is reddish in color, soft, granular, and friable in texture, and presents numerous red- dish bodies (the Malpighian bodies) in every part of it, excepting towards the free surface. It is composed of the convoluted tubuli uriniferi, blood vessels, nerves and lymphatics, held together by a small quantity of are- olar tissue. The cortical substance is from J to an inch in thickness opposite the base of each pyramid,and is called the cortical arch. It also sends numerous prolongations inward towards the sinus, between the pyra- mids ; these are called the cortical columns or columns of Bertini. 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 of an inch. They are capsular dilatations of the Fig. 83. Longitudinal section of the kidney ; the swellings upon the surface mark the original con- stitution of the organ, as made up of distinct lobules.—1. The supra-renal capsule. 2. The cor- tical portion of the kidney. 3, 3. Its medullary portion, consist- ing of cones. 4, 4. Two of the papilla; projecting in to their cor- responding calyces. 5,5, 5. The three infundibula ; the middle 5 is situated in the mouth of a calyx. 6. The pelvis. 7. The ureter. KIDNEY AND ITS SECRETION 257 commencing tubuli uriniferi, and are scattered irregularly in the columns of Bertini, but regularly arranged in double rows in the cortical arches. Within each body or capsule may be observed a vascular tuft or glomerulus, 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 caspule near the artery and forms a venous plexus with other efferent vessels around the ad- jacenttubuli(Fig84). The capsules are lined by a layer of epithelium, which is believed by some to be prolonged over the tuft of vessels; while others are of the opinion that the tuft is wholly uncovered. The tuft in the frog, and other reptiles is covered by ciliated epithelium. The medullary substance, which forms about one-fourth of the gland, is pale-red in color, dense in texture, and pre- sents 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 directed towards the circumference of the organ, and their apices towards the sinus, in which they terminate by smooth rounded extremi- ties, called the papillae of the kidney. The conical masses consist of the tubuli uriniferi, blood-vessels, nerves and lymphatics, held together by areolar tissue. The tubuli uriniferi commence at the apices of the cones by small openings; as they pass towards the base they divide Fig. 84. Plan of the renal circulation in man and Mammalia, a, Termi- nal branch of the artery, giving the afferent twig 1, to the Mal- pighian tuft m, from which emerges the efferent vessel, 2. Other efferent vessels, 2, are seen entering the plexus of ca- pillaries, surrounding the urini- ferous tube, t. From the plexus the returning vein, v, springs. 258 SECRETING GLANDS AND THEIR SECRETIONS. and sub-divide, and diverge un- til they reach the cortical sub stance, when they become con- voluted and anastomose freely with each other and terminate in the Malpighian capsules. There are also some convoluted tubes in the Malpighian pyramids, the looped tubes of Henle,which de- scend to a certain distance in the medullary pyramid and return in loops to rejoin the convoluted tubes. The diameter of these looped tubes is about XfVo an inch (20 mmm). The number of orifices on a single papilla is about five hundred. The average diameter of the tubes is about of an inch (50 mmm) and they consist of a nearly homogeneous membrane lined with spheroidal ephithelium in some parts,and cubical in others. Each tube as it passes through the cortical sub- stance, from the number of loops which surround and are connected with it, presents a pyramidal appearance; these are called the “pyramids of Ferrein,” or lobules of the kid- ney. The total number of tubes is about two millions. Arteries and Nerves.—The kidney is supplied by the renal artery, which divides into four or five branches as it enters the liilum. These again sub-divide into the arter- ies propriai renales, which enter the kidney in the spaces between the papillae (columns of Bertini). They here give off branches which supply the Malpighian pyramids, and cortical substance. Opposite the bases of these pyramids they make an abrupt bend, and give off branches {arteriolce rectas) which supply the interior of the pyramid, descending to the apex. They are then continued on between the “ lobules,” or pyramids of Ferrein, under the name of inter- lobular branches, until they reach the capsule. In their Fiir. 85. A. Portion of uriniferous tube mag- nified. B. Epithelial cells more high- ly magnified. SECRETION OF URINE. course they supply the Malpighian bodies, giving them tufts as already described (Fig. 84). The afferent vessel after leaving the Malpighian body, joins the capillary plexus sur- rounding the tubuli uriniferi, and from this plexus arise the veins which return the blood. The circulation in the Malpighian bodies is therefore an off-set from the ordinary circulation, and in this respect resembles the portal cir- culation. The nerves of the kidney are derived from the solar plexus, the semilunar ganglia, and the lesser and smallest splanchnic nerves. 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 infundibula, 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 cupr the base of one or more of the papillae. It is lined by spheroidal epithelium. Secretion of Urine.—The secretion of urine from the blood is effected by the agency of cells. Some substances as urea, uric acid, etc., exist ready formed in the blood, and need only to be removed; but other substances, as the acid phosphates and the sulphates are formed by the agency of cells. It is probable, 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 exerement 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 down the- ureters and enters the bladder drop by drop; this may be seen in some cases of ectopia vesicce. Some substances pass- very rapidly from the stomach through the circulation, to be eliminated by the kidney ; e.g, a solution of potassium ferrocyanide passed in one minute, while some vegetable- 260 SECRETING GLANDS AND THEIR SECRETIONS. substances as rhubarb, occupied from sixteen to thirty-five minutes. The transit is slower, when the substances are taken during digestion. 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 has 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 varies from 1015 to 1025, depend- ing on the time at which it is secreted, the kind of food, drink, etc. 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 introduc- tion of solid food ; 3rd, urina sanguinis, or that secreted from the blood when neither food nor drink has been taken. Tor purposes of investigation, a portion of the urine passed during a period of twenty-four hours should be taken. In disease, as albuminuria, the specific gravity is diminished to 1004 ; while in diabetes it may be increased to 1050 or 1060. The quantity of solids in any given specimen of healthy urine may be determined approximately by doubling the last two figures of the sp. gr.; thus 1018, (18 x 2) =36 grains of solids in 1000 grains of the urine. 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 fifty 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 Uiune.—The urine consists of water, holding in solution certain animal matters, CHEMICAL COMPOSITION OF THE URINE. 261 salts, coloring matters, etc. Its composition according to the most recent analyses is as follows, in 1000 parts. Water 950.00 Urea 26.20 Uric and hippuric acids, combined with sodium, potassium and ammonium 2.15 Creatine, creatinine, mucus and coloring matter 1.22 Sodium and potassium chlorides 12.45 Sodium and potassium sulphates 3-3° Sodium, potassium, calcium and magnesium phosphates ... 4.28 Sodium bi-phosphate V .40 1000.00 Water.—The quantity of water varies in different seasons, and according to the drink, exercise, action of the skin, etc. In some diseases it is very much increased, as in hysteria, diabetes, etc. In other diseases, as albuminuria, diarrhoea and dysentery, it is very much dimiuished. In fevers, albuminuria, and in inflammation also, the quantity of water is almost invariably diminished. Urea.—(C Hi N2 0). This constitutes more than half of the solid matter of healthy urine. The quantity is in- creased by a purely animal or highly nitrogenous diet, and slightly by exercise. The increase of urea in active muscular exercise was formerly supposed to be in exact proportion to the amount of muscular exercise, but this has been found by experiment not to be the case ; the waste of muscle cannot be expressed by the increase in urea. Urea exists already formed in the blood, and is simply re- moved 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 of alcohol; then evaporating and crystallizing. It crystallizes in acicular crystals, which appear, under the microscope, as four-sided prisms, (Fig. 86). It is purified by filtering through animal charcoal. It may also be obtained in the form of urea nitrate (C Hi N2 OHNO3 ), by evaporating urine to one-half,and then adding 262 SECRETING GLANDS AND THEIR SECRETIONS. an equal quantity of nitric acid, and crystallizing. Urea is identical in composition with ammonium isocyanate, (N H4 C NO=C H4 N2 0), and may be prepared artificially by the chemist, by double decompo- sition from potassium isocy- anate, and ammonium sulph- ate. 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 ammonium carbonate. It is also decomposed, in some cases, before it leaves the bladder, as in paralysis, and some low forms of disease. An average of 500 grains (32.4 grammes) of urea are excreted from the body in twenty-four hours, when the kidney is in a health}1, con- dition ; 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 uraemic convulsions and coma. Fig’s 86 and 87. Pig. 86. Crystals of urea. Fig. 87. Crystals of uric acid. Uric or Lithic Acid (C5 H4 N4 03 ).—This substance is rarely absent from healthy urine. It is combined with sodium and ammonium in the form cf urates. It predomi- nates in the urinary excrements of birds, serpents, and other reptiles ; while urea predominates in the mammalia, especially the herbivora. In the urine of the feline tribe, uric acid is sometimes entirely replaced by urea. Uric acid and urea are, therefore, closely allied to each other, and each alone may represent the excretion of the two. The quantity of uric acid, like that of urea, is increased by the use of animal or highly nitrogenized food, and decreased by HIPPURIC ACID. 263 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 sodium urate, and constitutes the so- called “chalk-stones.” Uric acid has been detected in the blood of healthy persons, and in considerable quantity in gouty patients. It is supposed to be formed in the sys- tem 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 ser- pents or birds, which consists almost entirely of ammonium urate. 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 frequently rhombic or diamond shaped (Fig. 87). It is insoluble in alcohol and ether. When the urates are in excess in the urine, they appear as a “ brick-dust ” sediment in the vessel. They may be distinguished from other deposits by their not appearing until the urine becomes cold, and by disappearing again entirely on the application of heat. Hippuric Acid (C9 H9 N03.)—' »-«in PYlst.a in oTYioll quantity in human urine, pro- bably in the form of sodium and potassium hippurates, but is very abundant in the urine of cows, horses and other her- bivorous animals. It is closely allied to benzoic acid(C7 H6 02), and this substance when taken into the system, is excreted in the form of hippuric acid. Hip- puric acid is chiefly formed from vegetable articles of food, and Fig’s 88 and 89. Fig. 88. Crystals of hippuric acid. Fig, 89. Large prismatic crystals of triple phosphates, among which are seen some crystals of ammonium urate. 264 SECRETING GLANDS AND THEIR SECRETIONS. may be prepared from the urine of cows b}r precipitation with hydrochloric acid. It has a hitter taste, is slightly soluble in cold, but very soluble in hot water and alcohol. Creatine—(C4 H9 N3 02 ) occurs in very small quantity in the urine. It is a colorless crystalline body, with a pun- gent taste, soluble in water, but almost insoluble 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—(04 H7 N3 0) 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, and is probably formed from creatine in the system. Urochrome or Urosacine, the coloring matter of the urine, has been already described, (see proximate prin- ciples). A substance termed Indican has been found in the urine by several observers; by its decomposition indigo blue, and indigo red are produced. The urine also contains a certain amount of mucus and epithelial debris from the mucous surface of the urinary passages. Salts.—The salts of the urine constitute less than half of the solid ingredients. Sodium and potassium chlorides 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 precipitated by a solution of silver nitrate after the urine has been acidulated by nitric acid. When silver nitrate is added to healthy urine, a whitish precipitate of silver chloride and sodium phosphate is thrown down; the latter may be dissolved by the addition of a little nitric acid. The silver chloride is readily dissolved by a little ammonia. The sulphates are more abundant in the urine, than in the THE PHOSPHATES. fluids and tissues of the body. They are increased by ex- ercise, and in diseases accompanied by muscular exertion,, as in chorea and delirium tremens. They are also increased by the introduction of sulphur or the sulphides into the system. The sulphuric acid is formed by the oxidation of sulphur, which is derived from the decomposing albuminoid substances. The phosphates are more numerous than the sulphates. Phosphorus is derived from the decomposition of nerve sub- stance, albumen and fibrin, and like sulphur, is oxidized at the lungs, and then unites with the bases to form salts. The alkaline phosphates, or potassium and sodium phosphates are- those salts by which most of the phosphoric acid is elimi- nated in the urine. They are readily soluble, and never appear as a precipitate in urine. The quantity of alkaline phosphates is increased by a diet of animal food: also by great mental exertion, and in phrenitis. They are also in- creased by exercise, while the earthy are diminished. The earthy phosphates, or calcium and magnesium phosphates,, are not very abundant in the urine. They are held in solu- tion by the sodium biphosphate, and when this is absent or neutralized they fall as a precipitate. The acid sodium phosphate, or sodium bi phosphate gives- the urine its acid reaction. It is supposed to be formed from the ordinary sodium phosphate of the blood by the action of uric acid, which unites with a part of the sodium forming sodium urate, leaving an acid sodium phosphate. Though freshly voided urine exhibits an acid reaction, yet it has no free acid, but within a few hours after its discharge it undergoes the so-called acid fermentation resulting in the production of free lactic, and sometimes oxalic acid, formed from some of the organic ingredients. The latter when formed is precipitated with calcium, forming a sediment of calcium oxalate (Fig. 90). In a few days these changes- SECRETING GLANDS AND THEIR SECRETIONS. Fig’s. 90 and 91. cease, and are followed by the so-called alkaline feiwientation, during which some of the phos- phates are thrown down. This change is brought about by the decomposition of urea and its transformation into ammonium carbonate. This causes a pre- cipitation of the earthy phos- phates which unite with some of the ammonium, and are de- posited in the form of ammonio-magnesium phosphate (triple phosphate) Fig. 89. The urine at this time has a strongly ammoniacal odor. Cystin (Fig. 91), is occasionally found in unhealthy urine. Fig. 90 Crystals of calcium oxalate- Fig. 91 Crystals of cystin. MAMMARY GLANDS AND THEIR SECRETION. These are the organs which secrete the milk. They are large and hemispherical in the female, but are quite rudi- mentary in the male. They are situated in front of the pectoralis major, between the third and sixth ribs, and ex- tend from the sides of the sternum nearly to the axillae. They are enlarged at puberty, increased during pregnancy and lactation, and diminished in old age. The outer surface of the mamma presents a little below 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 preg- nancy. Its summit 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 substance for the protection of the nipple during suck- ing. The nipple consists of numerous blood-vessels, nerves, lymphatics, ducts, erectile tissue, and nonstriated muscular fibre-cells, and is capable of slight erection during sexual ex- citement or irritation. MILK. 267 Structure.—The mamma consists of numerous lobes, which are made up of small lobules, connected together by areolar tissue, blood-vessels and ducts. There is also some adipose tissue between the lobules. 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 lactiferi. These vary in number from fifteen to twenty, and converge towards the areola, beneath which the}7 form dilatations, or ampullae, which serve as reservoirs for the milk ; they then become contracted, and continue onwards to the summit of the nipple, where they open b}7 separate orifices, which are narrower than the ducts them- selves. The entire surface of the gland is invested by fibrous tissue, from which numerous septa are derived, which pass between the lobes. Milk.—The secretion of milk is usually limited to the period succeeding parturition, yet this is not invariably 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 ex- pressed from the mammary glands of infants. Milk has an alkaline reaction, and the specific gravity varies from 1020 to 1030. The specific gravity alone is of no value as an indication of the richness of the milk. The average chemical composition of human milk is as follows, in 1000 parts : Water 890 Butter 26 Casein andExtractive 40 Lactose 42 Fixed Salts 2 1000 When milk is examined with a microscope, a large number of minute particles may be seen, termed “ milk globules,” 268 SECRETING GLANDS AND THEIR SECRETIONS. which vary in size from 0 to of an inch (8.3 to 2 mmm) in diameter. They are coated with albuminous Fig. 92. Fig. 93. Oil globules of human milk. Oil globules of cow’s milk. matter, and are soluble in ether and alkalies. In the colostrum, or first milk secreted after labor, large, yellow, granulated bodies may be seen, called colostrum corpuscles. Theyare supposed by some to be exudation corpuscles; others regard them as transformations of the epithelial cells of the gland, containing fatty matter. The colostrum has a pur- gative effect on the child, which is useful in clearing 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 substance 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 (rutic.) These are called butter acids. The casein of human milk is not so readily precipitated as cow’s milk. It requires a large amount of acid, and rennet does not seem to take effect upon it, unless an acid be present. The casein of asses’ milk bears a closei resemblance to that of human milk, than does that of the cow. The best substitute for human milk, however, is cow’s milk diluted with water, and a little sugar added. Lactose or milk sugar (C12 H24 Oi2), may be obtained from whey by evaporation and crystallization. It strongly re- sembles glucose, into which it may be converted by the addi tion of dilute sulphuric or hydrochloric acid. The action of a ferment causes lactose to undergo the lactic acid fer- MILK. mentation; and when lactic acid, or calcium lactate is allowed to stand for some time, it is changed into butyric acid, or calcium butyrate, 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 calcium and magnesium phosphates. 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. From 20 to 40 ounces of milk are secreted in 24 hours. Stimulating liquors often used to incre se the quantity of milk, seldom act otherwise than prejudicial. Certain medicinal agents, when administered to the mother, may pass into the milk, and in this way 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. Emotions of the mind, as anger, grief, fear, etc., pro- duce 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 frequently vitiates it. Fear also diminishes the secretion, and that which is secreted under such circumstances is highly irritating. Violent ex- ercise, or great anxiety of mind, has also a bad effect on the secretion of milk. Cases are recorded in which children have had convulsions, and died shortly after sucking milk secreted under the foregoing circumstances. 270 DUCTLESS OR VASCULAR GLANDS. CHAPTER XII. DUCTLESS OR VASCULAR GLANDS. These are so named from having no excretory ducts ; they are the spleen, supra-renal capsules, thymus and thy- roid glands. They contain the same essential structures as the secreting glands, except the ducts. They are highly vascular, and are concerned in the elaboration of the blood. Their function, however, does not seem essential to life. They may become atrophied, or be removed from animals, without any serious consequences. 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 bluish- red 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 form- ing the suspensory ligament, and at the hilum on to'the great end of the stomach, forming the gastro-splenic omen- tum. The fibrous coat consists of white fibrous and yellow elastic tissue. It covers the exterior of the organ, and sends prolongations inwards at the hilum, in the form of vaginse or sheaths, which surround the vessels. From these sheaths, and from the inner surface of the fibrous coat, numerous tra- beculae or bands pass in all directions, and these uniting STRUCTURE OF THE SPLEEN. 271 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 areolse be- tween the bands are filled with a soft pulpy mass, of a dark reddish-brown color, consisting of colorless and colored ele- ments—the proper substance of the spleen, or spleen pulp— and some rounded bodies the Malpighian corpuscles. The colorless elements form about one-half or two-thirds of the entire pulp, especially in well-fed animals, and consist of granular plasma, free nuclei, about the size of red blood corpuscles, and a few nucleated lymphoid cells. 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 coloring matter of the blood. The Malpighian corpuscles are rounded bodies from to pa of an inch (.8 to .4 mm) in diameter, of a semi-opaque whitish color, and are more distinct in early life than in adult age. Each con- sists of a membranous capsule,homogeneous in structure, and formed by a prolongation from the sheath of the small arteries to which it is attached. They are sur- rounded and embraced by the radicles of the arteries, and present a resemblance to the buds of the moss rose. Each capsule contains a soft white substance, consisting of granular plasma, nuclei, and nucleated lymphoil cells similar to the colorless elements Fig. 94. Branch of the splenic artery, showing the Mal- pighian corpuscles. 272 DUCTLESS OR VASCULAR GLANDS. of the pulp. Small capillaries pass into their interior and form a minute plexus. 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 hilum. Each branch runs transversely from within outwards, and divides into smaller branches ; these ultimately terminate in tufts or pencils, which lie in contact with the pulp. The most striking peculiarity is, that each of the larger branches supplies chiefly that part of the organ to which it is dis- tributed, having no anastomosis with the adjoining branches. The capillaries terminate either directly in the veins, or open into caecal or lacunar spaces, from which the veins arise. The veins arise either in the ordinary way from the capillaries or by communicating intercellular spaces, or distinct caecal pouches. They are much larger and more numerous than the arteries, and by their junction form from four to six branches which emerge at the hilum, and uniting form the splenic vein, the largest branch of the portal. From this it will be seen that the blood returning from the spleen passes through the liver before it enters the general circulation. Function of the Spleen.—In consequence of the vas- cular arrangement and the large amount of elastic tissue which this organ contains, it is liable to undergo great changes in volume. Enlargement of the spleen is apt to occur from internal venous congestion, such as occurs in the cold stage of intermittent fever. When intermittent fever is long-continued, the spleen is generally very much enlarged, constituting what is commonly called “ ague cake.” It was formerly supposed to act as a diverticulum of the liver, relieving its vessels from undue turgescence and pre- venting congestion of the liver, stomach and bowels ; and also that it promoted the disintegration of the red blood corpuscles; but these views cannot be accepted in the present state of our knowledge. The spleen is SUPRA-RENAL CAPSULES. 273 larger four or five hours after food is taken, and contains a larger proportion of finely granular albu- minous material, than at any other time, therefore it is supposed that this organ is the receptacle for the increased quantity of albuminous material of the food, and which can- not 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 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 material is elaborated during its withdrawal. It is also supposed to form the germs of future blood corpuscles, as there is found to be a large in- crease of the colorless corpuscles in the blood of the splenic vein. SUPRA-RENAL CAPSULES. The supra-renal capsules are situated one upon the upper extremity of each kidney, somewhat triangular in shape, the base being applied to the kidney, and the apex directed up- wards. 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, io of a deep yel- low color, and consists of narrow, columnar masses, arranged perpendicularly to the surface, and held together by areolar tissue. These columnar masses measure about TJ its palatine branches. The optic nerve is distributed to the eye, in which it ex- pands to form the internal layer of the retina, and is the nerve 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 mus- cular action. The auditory nerve (portio mollis) is the special nerve of the sense of hearing. It conveys to the brain the sensation of sound, and is incapable of transmitting any other, being entirely destitute of ordinary sensibility. The filaments are distributed to the cochlea, semicircular canals and vestibule. The motor-oculi is a nerve of motion, and is distributed to all the muscles of the eyeball, except the superior ob- lique and external rectus. It also supplies motor filaments 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 (ptosis), the pupil is dilated and insens- TRIFACIAL NERVE. 331 ible to light, the movements of the eyeball are nearly sus- pended, and the eye is directed outwards, owing to the action of the external rectus. Owing to the irregularity of the axes of the eyes, double sight is often experienced. 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 stimulus being conveyed by the optic nerve to the brain, and thence reflected through the third nerve to the iris; consequently 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 supplied by filaments from the fifth cranial nerve and 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 spas- modically, and its division causes paralysis and a loss of rotatory 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 convulsion of the muscle, and the eye is turned outwards. 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 (the Gasserian ganglion) developed 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 buccinator), and its lingual branch is one of the nerves of the special sense of taste. This nerve, within the cran- ium, 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 sensory ; THE NERVOUS SYS TEAT. the third division contains filaments of special sense, sensa- tion and motion. It is the most intensely sensitive nerve in the body, and irritation of its sensory filaments 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 neuralgia 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. Division 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; the cornea becomes opaque, and a low destructive inflammation of the conjunctiva, sclerotic, and interior of the eye occurs, which usually goes on to complete and permanent destruction, and sloughing of the organ; the senses of smell, hearing, and taste, are at the same time im- paired or lost. Injury to the fifth nerve, or some of its branches, is sometimes followed by total blindness in the corresponding eye. These phenomena may be due to the trophic influence of the nerve on these organs, and the defective nutrition which follows its injury. Paralysis of the third nerve may also follow neuralgia of the fifth nerve. The facial nerve (portio dura) supplies all the muscles of the face, the platysma, buccinator, the muscles of the ex- ternal ear, digastric and stylo-hyoid, the palate, stapedius and laxator tympani muscles. It also supplies the parotid gland, and through the chorda tympani it gives branches to the submaxillary gland, lingualis, and other muscles of the tongue. It is a nerve of motion, and not of sensation, and therefore its division, which was formerly resorted to in cases of tic douloureux, is incapable of relieving neuralgic pains, but is followed by paralysis of the muscles which it supplies, Division or paralysis of the facial nerve pre- vents the eye from being closed, and its continued exposure to the air, and particles of dust, is apt to produce inflam- mation. The sense of hearing, taste, and smell may also be impaired. In facial paralysis there is an absence of GLOSSO-PHARYNGEAL NERVE. 333 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 paralyzed, it is drawn to the sound side when protruded, 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. It also supplies filaments to the fenestra ovalis and rotunda, the Eustachian tube, car- otid plexus, and spheno-palatine ganglion. The tongue is 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 nerve. The hypoglossal nerve is a nerve of motion. It is dis- tributed to the muscles which belong to the hyoid bone and tongue, and is concerned in articulation. Irritation of this nerve produces contraction in the muscles supplied by it, and is sometimes attended with pain, the sensibility having been borrowed from the nerves with which it communi- cates. Its division or injury is followed by paralysis. The pneumogastric nerve is one of the most remarkable and important in the body. It supplies the pharnyx, epi- glottis, glottis, larynx, trachea, oesophagus, heart, lungs, liver, stomach and spleen. It possesses motor, sensitive and sympathetic or ganglionic nerve fibres, and is therefore regarded as a triple-mixed nerve. The pharyngeal branch is the motor nerve of the muscles of the pharynx ; the superior laryngeal is chiefly sensory, and supplies the mucous mem- brane of the larynx; the inferior or recurrent laryngeal 334 THE NERVOUS SYSTEM. is for the most part motor, and supplies the muscles; the oesophageal branches supply its muscular tissue ; the cardi- ac branches constitute a channel through which the influ- ence of the central organs and the emotions of the mind are transmitted to the heart; the pulmonary branches form a channel through which the impressionsonthelungs are convey- ed to the medulla oblongata; the motor filaments of the pneu- mogastrie nerve supply the motor influence by which the function of deglutition is performed. In the functions of the larynx, the sensitive filaments suppty that acute sensi- bility by which the glottis is guarded against the ingress of foreign bodies or irrespirable gases. These are instances of “ reflex action.” The cardiac branches of the pneumogastric have an in- hibitory or restraining influence upon the heart (p. 212). When divided the heart’s action is increased; while on the other hand when stimulated, as by a galvanic current, the heart’s action is diminished, or if a strong current be used, it is arrested altogether in diastole. Division of the pneumogastric nerve or its inferior laryn- geal branches produces loss of voice, by paralyzing the muscles of the larynx which act upon the vocal chords. Division of the pneumogastric nerves is also followed 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 respira- tory movements, the imperfect aeration of the blood, g,nd the accumulation of carbonic acid in the air cells, and also in part to the paralysis of the blood-vessels themselves. PNEUMOGASTRIC NERVE. 335 Since respiration is still carried on after the division of the pneumogastric nerves, it is evident that though they are the chief agents by which the respiratory stimulus is conveyed to the medulla oblongata, they are not the only ones. The secretion of gastric juice is temporarily suspended after division of the pneumogastric nerve, and the digestive function is more or less disturbed in various ways, but the sensations of hunger and thirst still remain. In many in- stances the food, taken by the animal never reaches the stomach owing to the paralysis of the oesophagus, but is re- gurgitated in a few moments afterwards—this action being excited by the influence of the sympathetic nerves. The muscular coat of the stomach is also paralyzed by section of this nerve. Division of the pneumogastric nerve also interferes with the proper function of the liver, and irritation of the cen- tral extremity of the divided nerve is followed by the rapid development of sugar in this organ, probably by causing paralysis of the hepatic vaso-motor nerves. The spinal accessory nerve arises partly from the medul- la oblongata, and partly from the spinal cord. It is essen- tially a motor nerve; but it also contains sensitive fibres, and is connected with the ganglion of the pneumogastric. From these circumstances it may be regarded as a mixed nerve. It supplies the sterno-mastoid and trapezius mus- cles, and it is also connected with the vocal movements of the glottis. If the spinal accessory nerve be divided on both sides, or its branch of communication with the pneu- mogastric nerve, the voice is instantly lost, the animal be- ing incapable of uttering a single sound. Division of the pneumogastrics or their inferior laryngeal branches, para- lyzes both the movements of respiration and phonation, while section of the spinal accessory paralyzes the move- ments of phonation alone, or those muscles which nar- row the glottis and approximate the vocal chords, the movements of respiration, which open the glottis and sepa- 336 THE NERVOUS SYSTEM. rate the vocal chords remaining intact. 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 purpose of enabling it to perform two different functions. This is exemplified in the muscles of the larynx. These muscles are concerned in the respiratory movements, the nervous stimulus for which is conveyed by the facial, hypo- glossal, and pneumogastric nerves; but they are also con- cerned in the formation of the voice, the nervous influence for which is conveyed by the spinal accessory. SYMPATHETIC NERVOUS SYSTEM. The sympathetic system (or nervous system of organic life), is so named because it was formerly supposed to be the system through which distant organs manifested sym- pathy with each other in morbid action. It consists of a series of ganglia 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 to 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 anter- ior communicating artery—the ganglion of Ribes. They are arranged as follows:—In the cephalic region there are four ganglia on each side (and the ganglion of Ribes); in the cervical region, three; in the dorsal region, twel ve; 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 and to which, branches pass in various directions, as follows —1st, communicating branches between the ganglia ; 2nd, communicating branches to the cerebral or spinal nerves; 3rd, primary branches of distribution to the arteries in the vicinity of the ganglia, to the viscera, or to other ganglia in THE SYMPATHETIC SYSTEM. 337 the thorax, abdomen, and pelvis. The latter consist of two kinds of nerves, the sympathetic and spinal, and have a remarkable tendency to form intricate plexuses which sur- round the blood-vessels, being conducted by them to the viscera. 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. Fibres of the sympathetic are distributed to the nonstriated muscular tissue of the intestines and other hollow organs, and to the blood-vessels (vaso-motor nerves); to the heart—excito-motor; and to the various glands. Centripe- tal fibres also pass to the vaso-motor centre in the medulla oblongata. The difference between the cerebro-spinal and sympathetic nerves has been already stated (p. 282). Both kinds of nerves are distributed to all parts of the body. 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 transient excesses, and furnishing all transient deficiencies. In struc- ture they are essentially similar, containing nerve fibres entering and emerging, nerve cells' or ganglion corpuscles, and other corpuscles that appear free (Fig. 98). Complex as the whole sympathetic system appears, however, each of its parts exhibits a wonderful simplicity; for each ganglion with its afferent and efferent nerves forms a simple nervous system, and might serve for the illustration of all the ner- vous actions with which the mind is unconnected. Function of the Sympathetic System.—The sympa- thetic nervous system is endowed with sensibility and the power of exciting motion exactly similar to the cerebro- spinal system ; but in the exercise of these functions it is less active. 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, irrita- tion of the sympathetic nerve is felt distinctly enough, but is only responded to after somewhat prolonged application. 338 THE NERVOUS SYSTEM. This comports much with what is known of those organs, supplied chiefly by the sympathetic system, e. g., the movements of the stomach and intestines are not felt under ordinary circumstances; but any excessive or pro- longed irritation may cause them to be exceedingly painful. The general processes which the sympathetic system ap- pears to influence are those of involuntary motion, secretion, and nutrition. The ganglia have the power of conducting, transferring and reflecting impressions made on them simi- lar to the cerebro-spinal system, and the sympathetic nerves are conductors of impressions. Parts chiefly suppli- ed with sympathetic nerves are usually capable of only involuntary movements, as, e.g., the heart, stomach and in- testines, and these parts may still continue to move for a short time after the death of the animal. Thus, in the mammalia the heart continues to beat for one or two minutes after it is taken from the body ; in reptiles and amphibia for several hours; and the peristaltic action of the bowels is continued for a prolonged period. Division of the sympathetic nerve produces immediately a vascular congestion in the parts supplied by it. This was first pointed out by Bernard; he divided the sym- pathetic nerve of a rabbit in the middle of the neck, and found that congestion of the corresponding side of the head immediately followed, which was most distinctly marked in the ears ; and the venous blood returning from the part had a ruddy hue. The pupil is also contracted and the eye partially closed, owing to the increased sensibility of the retina from vascular congestion of the parts. The conges- tion 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 contract and the congestion disappears. The vessels therefore appear to be under the influence of the sympathetic nerves, which accompany them in all their varied distributions and minute ramifications. They are THE S YMPA THE TIC S YSTEM. 339 distributed to 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 eleva- tion of temperature in the affected part; this increase of heat has been found as high as 8° to 9°F., and like the vascular congestion, to which it is due, may last a consider* able length of time. The sympathetic system has also some connection with the special senses, especially with the sense of sight. The ophthalmic ganglion £ives off* small branches to the iris, and receives a communicating motor branch from the third nerve. The contraction of the pupil under the influence of light, and its dilatation in the dark, are affected through this ganglion. With 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 portions 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 example, the contact of food in the intestine excites, through the medium of the sympa- thetic nerves, a peristaltic movement in the muscular coat. The irritation produced by undigested food in the ali- mentary 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. 340 THE SPECIAL SENSES. CHAPTER XIV. THE SPECIAL SENSES. The special senses are jive 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 (Fig. 110, p. 330). The nasal cavity is lined by mucous membrane, called also the pituitary or Schneiderian membrane; it is covered with columnar ciliated epithelium, except in the upper part and roof—the olfactory region, in which it is non-ciliated. The filaments of the olfactory nerves pass through the foramina in the cribriform plate of the ethmoid bone, and are distributed beneath the mucous membrane; they convey the sensitive impressions made by odoriferous particles upon the mucous membrane to the sensorium, 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 is completely lost, while sensibility still remains, and their irritation is not followed by any muscular action, either of a direct or reflex character. Division of the fifth nerve, or some of its branches, which supply the nose, is followed by impairment of the sense of smell. It cannot be inferred from this, how- ever, that it is a nerve of the special sense of smell ; the result is to be attributed to the dry and otherwise deranged state of the mucous membrane, occasioned by the altered nutrition of the parts. SENSE OF SMELL. 341 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 particles Fig'111; Nose, mouth and pharynx ; a, cribriform plate ; b, spine ; c, soft palate ; d, lower jaw ; e, hyoid bone ; f, cavity of the larynx; 1, tongue; m, n, o, superior, middle and nferior turbinated bones, beneath which are the meatuses ; q, frontal sinuses ; s, narrow part of the pharynx; t, tonsil; u, anterior pillar of the fauces; v, posterior pillar; y, the epi- glottis ; z, orifice of the Eustachian tube. 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 peculiar characters are more fully impressed on the olfactory nerves. The frorital sinuses are supposed to assist in the extension of the sense of smell; but since they do not receive filaments from the olfactory nerves, and are largely developed in some animals, 342 THE SPECIAL SENSES. as the grey-hound, in which the sense of smell is by no means acute, it is highly improbable. The sense of smell varies much in different individuals, and, like all the senses, may be improved by frequent practice.* It may become blunted by long-continued exposure to •one kind of smell, as, for example, the effluvia of the dis- secting room. Various odors also affect it differently, as musk, asafoetida; and some produce nausea and even fainting. The irritation produced by the contact of substances which act mechanically or chemically on the mucous mem- brane, as ammonia, nitrous acid, etc., 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 a dry state of the mucous membrane ; by the obstruction of the air passages, as in the case of polypi; by chronic in- flammation, as catarrh, ozaena, and by the frequent use of snuff, which tends to blunt its acuteness and cover the sur- face with its particles. Besides the olfactory and fifth nerve, there are some fila- ments 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 sense of smell and taste, they are probably nerves of associate function. All animals have not the same facility for perceiving odors. Carnivorous animals have the faculty of detecting readily, animal odors, and tracking other animals by the scent. Herbivorous animals, on the other hand, possess the power of detecting readily the odor of vegetable matters. The sense of smell in man is not so acute as in most animals, but it is more uniform and extended. The extreme delicacy of the sense of smell is shown by the fact, that 3 o.troV.o 0 o of a grain of musk may be distinctly smelt. Some odors are pleasant, and some are offensive, but the cause of the difference is not known ; many SENSE OF SIGHT. 343 odors also which are agreeable to one individual, are offen- sive to another. Certain sensations also frequently produce a smell, for example, electricity produces a smell like phos- phorus, and the negative pole of the battery applied to the nose a smell of ammonia , while the positive pole produces an acid odor. In disease or derangement of the olfactory nerve, subjective sensations of smell frequently occur. SIGHT. The eye is the organ of the special sense of sight, and is situated in the cavitj7 of the orbit. It is spherical in form, having the segment of a smaller and more prominent sphere engrafted on its anterior surface. It measures about an inch in the antero-posterior diameter, and a little less trans- versely. 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, thicker behind than in front, which covers the posterior five-sixths of the eye. It is continuous 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 dif- ferent individuals, and in the same individual at different periods of life, being generally more prominent in youth than in advanced age. This differencein the curvature in- fluences considerably the refractive power of the eye, and is partly the cause of long and short-sightedness. The cornea in health is perfectly transparent, contains no bloodvessels, and consists of five layers;—the cornea proper, THE SPECIAL SENSES. a central fibrous structure; in front of this, the anterior elastic lamina, covered by the conjunctiva; behind, the posterior elastic la- mina, covered by the lining mem- brane of the an- terior chamber of the eyeball. The conjunctival epithe- 1 ium consists of sev- eral layers of cells, the superficial ones being flattened and scaly,and the deeper ones columnar or cylindrical. The an- terior and posterior elastic laminae, consist of a thin, transparent homo- genous membrane, and have a tendency to curl upon themselves, with the attached surface inwards, when separated from the cornea proper. The cornea pro- per consists of finely fibrillated bundles of transpa- rent connective tissue, in the spaces of which the branched cornea corpuscles lie. The branched cornea cor- puscles are capable of passing from one space to another by their amoeboid movement. When this tissue is injured in any way, it presents an opaque milky appearance. The posterior elastic lamina and the single layer of epithelium which covers it, is known as Descemet’s membrane. The nerves that supply the cornea are derived from the ciliary nerves. 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 at the ciliary ligament, where it bends inwards and forms Pig. 112. Vertical section of the eye ball. 1, sclerotic; 2, choroid; 3, retina; 4, crystalline lens; 5, hyaloid membrane; 6, cornea; 7, iris ; 8, vitreous body. SENSE OF SIGHT. 345 the ciliary processes. It is composed of three layers, the external, which consists of the larger branches of the ciliary arteries, but chiefly the veins and some star-shaped pigment cells; the middle, which consists of a fine capillary plexus (tunica Ruyschiani) ; 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 tesselatea epithelium. The principal use of the choroid coat is to ab- sorb the rays of light which pass through the retina, and prevent them from being thrown back to dazzle the images formed on the retina. In perfect Albinoes the cells contain no pigment, and they can see best in moderate light, or twi- light. The ciliary processes are formed by the folding inwards 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 (ipi$, a rainbow) is a thin, circular-shaped con- tractile curtain which regulates the quantity of light trans- mitted to the retina. It is suspended in the aqueous humor behind the cornea, and in front of the lens, and presents, 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 anterior and posterior chambers. It consists of & fibrous stroma, muscular fibres, and pigment cells. The muscular tissue is involuntary and consists of circular fibres which surround the 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. The circular fibres are sup- plied by the third cranial nerve, and the radiating fibres by the fifth and sympathetic (p. 331). The fibrous tissue forms a delicate net-work in which the pigment cells, vessels and nerves are contained. The pigment cells are found in the 346 THE SPECIAL SENSES. stroma, and also as a distinct layer on the anterior and posterior surfaces, and give rise to the different color of the iris in different individuals. On the posterior surface of the iris there are several layers of round cells filled with pig- ment granules. These are called the uvea, from their resem- blance in color to a ripe grape. The iris is connected to the choroid and to the external coat of the eyeball at the junc- tion of the sclerotic and cornea, by means of a circular band of white fibrous tissue, the ciliary ligament. At its point of junction with the sclerotic a minute canal is seen, the sinus circular is iridis. The middle coat of the eye is also connected to the exter- nal, by means of a circular band of nonstriated muscular Fig:. 113. tissue, the ciliary muscle. It is about one-eighth of an inch broad, thicker in front than behind, and is attached ante- riorly, or arises at the point of junction of the sclerotic and Posterior part of the retina as seen witn me o^umalinosuope. SENSE OF SIGHT. cornea, and passing backwards 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 compresses the lens, increasing the curvature of its anterior surface, and in this way adjusting 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 serrata ; its inner surface is in contact with the hyaloid membrane which sur- rounds the vitreous humor ; externally it is in relation with the choroid. In the centre of the posterior part, correspond- ing to the axis of the eye, is seen a round, yellowish spot 2ls of an inch in diameter (1 mm.) called the limbus luteus, or the yellow spot of Sotnmering. In its centre is a minute depression, the fovea centralis. 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 principal layers, together with blood-vessels and delicate areolar tissue ; the external or columnar; the middle or granular; and the internal or nervous layer; each of these is again subdivided into sub- layers, as shown in Fig. 114. The external or columnar layer is exceedingly thin, and consists of solid columnar rod-like bodies, with cones filled with fluid interspersed at regular intervals (a, b). These are separated from the granular layer by a transparent homo- geneous membrane, the membrana limitans externa. The middle or granular layer is transparent, finely fibrillated and comprises one-third of the thickness of the retina. It consists of two layers of rounded nuclear particles (c, e) separated by an inter-granular layer (d). The external granular layer is the thicker, and its particles are globular, 348 THE SPECIAL SENSES. and connected with the rods and cones by fibres passing through the membrana limitans. The internal granular layer is the thinner, and its particles are flat- tened, looking like pieces of money seen edgeways, hence called the nummular layer. These cells are, however, bipolar sending one process outwards through the inter-granular layer, and another in- wards through the molecular layer, to reach the expansion of the optic nerve. The internal or nervous layer is thin, semi-transparent and consists essentially of the expansion of the terminal fibres of the optic nerve, and nerve cells. It also presents three layers ; the molecular or finely granular layer, resembling the molecular matter found in the gray substance of the brain and spinal cord ; the layer of ganglion cells or cellular layer, which consists of multipolar cells, some of the processes of which pass outward to the molecular layer and others inwards to the fibrous layer; and the fibrous layer or expansion of the optic nerve. The nerve fibres of this layer consist only of the axis cylinder, and some of them become continuous with the prolongations of the ganglion cells. The inner surface of the retina is lined by a trans- parent homogeneous membrane, which separates it from the vitreous body, the membrana limitans interna. Blood- vessels are only found in the internal layer, and extending to the internal granular stratum of the middle layer. In the external or rod-and-cone layer of birds, the cones predomi- nate, while in man the rods are more numerous. In noctur- nal animals, as the owl, bat, mole, etc., the cones are entirely absent. In the fovea centralis, where vision is most acute, Fig. 114. Vertical section of the human retina, a, Rods; b, cones, resting upon the membrana limitans externa; c, external granular layer; d, intergranular layer ; e, internal granular layer; f, molecular layer ; g, layer of ganglion cells ; h, expansion of the optic nerve fibres ; i, membrana limitans interna. SENSE OF SIGHT. 349 all the layers of the retina are thinner except the rods and cones which are increased, from which it would appear that these are more especially concerned in the function of vision. The aqueous humor occupies the anterior part of the globe, and completely fills the anterior and posterior cham- bers 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 communi- cate through the pupil; but in the foetus, before the seventh month, the pupil is closed by the membrana pupillaris. The persistence of this membrane sometimes occasions congeni- tal blindness. The vitreous humor occupies the posterior four-fifths of the globe. It is perfectly transparent, of the consistence of jelly, and consists of numerous layers of simple membrane with the intervening spaces filled with fluid. It is sur- rounded by the hyaloid membrane, and is hollowed out in front for the reception of the crystalline lens. It refracts the rays of light, and fills the globe of the eye so as to keep the retina at a proper distance from the lens. The vitreous humor contains some salts and a little albumen. In the foetus, a minute arteiy passes through the centre to the pos- terior part of the capsule of the lens* the arteria centralis retinae ; but it disappears in the adult. The crystalline lens, enclosed in its capsule, is situated in front of the vitreous humor and behind the pupil. The cap- sule 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 transparent membrane. This liga- 350 THE SPECIAL SENSES. ment forms part of the boundary of the posterior chamber of the eye ; its posterior surface is separated from the hya- loid membrane by a triangular interval—the canal of Petit. This canal is about one-tenth 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 back- wards. It appears to consist of concentric laminae, like the coats of an onion, the central ones forming a hardened nu- cleus. It also appears to consist of three triangular seg- ments ; this is readily demonstrated by boiling, or immersing it in alcohol. The laminae consist of minute parallel fibres, hexagonal in shape, the edges being dentated and fitting into each other, and are about of an inch (5 mmm.), in diameter. The refracting media of the eye are the cornea, aqueous humor, crystalline lens,and the vitreous humor. There are 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, appear to be : 1st, a dark coat to absorb the rays of light—the choroid ; 2nd, a nervous expansion to re- ceive 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 collect the rays of light and bring them to a focus, so as to form a correct image on the retina —the cornea and the lens; 4th, a contractile curtain with a central opening, to regulate the quantity of light enter- ing the eye—the iris. The eye is thus a simple optical in- strument, endowed with vitality, and acting as required without assistance. It is abundantly supplied with blood-vessels. In addition to the conjunctival vessels, there PHENOMENA OF VISION. 351 are the vessels of the sclerotic, choroid, iris and retina. The latter are derived from the short, long, and anterior ciliary arteries, and the arteria centralis retime. Phenomena of Vision.—In order fully to understand 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 medium of uniform density. 2nd,—When the rays meet with a medium of increased density, they become refracted, or changed in direction, to- wards 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 perpendicu- lar 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, de- pending on the degree of 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. 5th,—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. 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 sensation, 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 (a. b.), and im- pinge on the outer convex surface of the cornea (c. c.), through which they pass, becoming refracted towards the perpendicular. Those which fall on the circumference of 352 THE SPECIAL SENSES. the cornea impinge upon the iris, and are reflected, show- ing the color of this structure; those which pass nearer its Fisr. 115 centre, converge and enter the pupil. They now penetrate the crystalline lens (e. e.), 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 (a. and b.). If the retina be not at F., but at G. or H., certain luminous spots, e and o, or c and f, will be seen ; for at H the rays have not yet met, and at G thejr have crossed and are again diverging. Since rays of light come from all points of the object, and are refracted in their passage, they must cross each other, and thus the image of the object on the retina (f), will be inverted, but this is corrected by the sensorium. The angle of crossing is called the visual angle. Accommodation of the Eye to Vision.—It is quite evi- dent 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 both to an alteration in the position and shape 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 ACCOMMODATION OF THE EYE TO VISION. 353 active accommodation of the eye for the vision of near ob- jects is caused by the advance of the crystalline lens towards the cornea, and also by the increased convexity of its ante- rior surface. It is advanced towards the cornea chiefly by the action of the ciliary muscle, and partly by the compres- sion exercised upon the posterior three-fourths of the eye- ball 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 tine adjuster, which regulates the eye for the vision of near or very small objects. The rays of light which pass through the margin of a lens are more refracted than those which pass through the centre, and owing to this unequal refraction the rays do not all meet at the same point. This defect is called spherical aberration. The formation of distinct and correct images on the retina is favoured by the action of the pupil, which prevents the rays of light from passing through any part of the lens but its centre, and thus preventing any tendency to spherical aberration. In optical instruments, as the micro- scope, telescope, etc., spherical aberration is prevented by the use of a diaphragm with a circular aperture, which shuts out all the marginal rays. Distinctness of vision is 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 from being thrown back again upon the retina, so as -to produce dazzling of the image there formed. When a ray of light passes through an ordinary lens it is partly decomposed into its elementary colors, and a colored margin appears around the image owing to the unequal re- fraction of the elementary colors. This is called chromatic aberration, and is corrected in optical instruments by the combination of two or more lenses, differing in shape and density. The combination usually consists of two lenses of unequal refraction, a convex lens made of crown glass and 354 THE SPECIAL SENSES. and a concave one of flint glass, but the number ma)' be varied to suit the circumstances. Such combinations of lenses are called achromatic. The unequal refractive powers* of the different media of the eye prevent chromatic aber- ration. If a ray of white light be passsed through a prism the different colors are refracted in different degrees, and a colored band appears, called the spectrum, arranged as fol- lows : violet, indigo, blue, green, yellow, orange and red. The violet rays are most refrangible ; the red the least; hence the image of a small white object appears as if sur- rounded with a yellowish or bluish fringe, because it cannot be accurately focused on the retina, This is called irra- diation. For this reason a white figure on a black ground appears larger than a black one of the same size on a white ground. The inverted image of any bright object, as the windows of the room may be distinctly seen in the eye of any albino animal, as a white rabbit; or if an opening be made at the superior surface of the eye so that the retina can be seen through the vitreous humor, a reversed image of any bright object may be seen on the posterior wall of the eye. Impressions once produced on the retina remain for a short their duration depending on the intensity of the impression they have left. A moment- ary impression of moderate intensity continues about one- eighth of a second. This is the reason why the act of wink- ing does not interfere with the continuous vision of surround- ing objects. The spectra which remain on the retina after viewing colored objects are always of the opposite or com- plemental color; e. g, the spectrum of a red object is green, that of violet, yellow, etc. This is because the retina be- comes fatigued by the color looked at; but remains sensitive to the other rays. There is in front of the eye a certain space within which objects are perceived, and beyond which nothing can be distinctly seen ; this is called the circle or field of vision THE BLIND SPOT. 355 and varies in extent in different circumstances. For ex- ample, 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. It is largest when the view is not confined to any near object. The distinctness with which an object may be seen, appears to depend largely upon the number of rods and cones covered by the retinal image, hence, the nearer an object is to the vision of the eye, the more distinctly are its details seen. The images of two points require to be at least T5500 of an inch (2 mmm) apart, in order to be distinguished separately. That portion of the retina which corresponds to the entrance of the optic nerve is insensible to light, and is called the blind spot. It we close the left eye, and direct the right steadily upon the circular spot here shown, while the page is about six inches from the eye, both marks are visible. If the distance be gradually increased, the cross disappears from view, and if the book be still further re- moved, it comes in sight again. The eye, in the uneducated state, cannot comprehend the properties of the objects seen, as color, form, etc., or the distance of the object; this is acquired by experience. Simultaneous Action of the two Eyes.—Although an imageofthe object is formed on each retina, yet theimpression 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 anterior 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. THE SPECIAL SENSES. 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; two images of the object are seen as in diplopia from strabismus. This is owing to the formation of images of the objects on different parts of the two retinae. The power of combining the two images is subservient to the faculty of obtaining a proper conception of bodies raised in relief. When a solid object as a cube is viewed, a different perspective of it is seen by each eye, and more of the surface of the body is seen than if viewed with one eye; in other words a stereo- scopic effect is produced. Defects of Vision.—The normal, or emmetropic eye brings parallel rays of light exactly to a focus on the retina (Fig. 116, 1) and all objects except near ones (within 20 feet), are seen without any effort of accommodation. In looking at near objects the eye is accommodated by the action of the ciliary muscle, and the rays which would otherwise meet behind the retina are correctly focused upon it, (Fig. 116, 2, dotted lines). The defects of vision are myopia, hyperme- tropia, presbyopia and astigmatism. Myopia is due to an abnormal elongation of the eye ball, and too great a degree of convexity of the lens. The rays of light are brought to a focus in front of the retina, and the images are indistinct and blurred (Fig. 116, 4). The eye is naturally accommodated for a near point, and objects near the eye are exactly focused, while those beyond the far point cannot be distinctly seen. This defect is remedied by wear- ing concave glasses. On the other hand, when the eye is short, and the lens flat, parallel rays are focused behind the retina; the eye is naturally accommodated for distant objects (Fig. 116, 3). This is called hypermetropia, and may be remedied by wearing convex glasses which converge the rays of light Presbyopia is an error of refraction, and must not be con- founded with hypermetropia. It is the gradual loss of the power of accommodation which occurs with advanced age, DEFECTS OF VISION. 357 and is likewise remedied by the use of convex glasses. -4s- tigmatism, first discovered by Airy, is due to a greater cur- vature of the eye in one plane than in another, so that vertical and horizontal lines crossing each other cannot be Fig. 116. focused at the same point, and the images are blurred and indistinct. It may be remedied by using glasses curved only in one direction—cylindrical glasses. Daltonism, or color blindness, is also a defect of frequent cocurrence ; many persons are wholly unable to distinguish between red, green and yellow. This would appear to arise from some defect in those elements of the retina which re- ceive the impressions of these colors. 358 THE SPECIAL SENSES. HEARING. 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, the meatus auditorius externus, and auditory canal. Its use is to collect the vibrations of the air, and conduct them to the membrana tympani, or drum, which separates the external from the middle ear. The canal contains some fine hairs at its outer part, and also a number of sebaceous glands throughout its whole extent, which secrete a waxy substance termed cerumen. Fig. 117. a, Pinna ; ft, external auditory passage ; c, membrana tympani (section); d, insertion of membrana tympani in bony canal ;e, insertion of malleus in membrana tympani;/,basejof stapes, inserted in tlie fenestra ovalis ; g, incus, joining stapes and malleus, and complet- ing the chain of ossicles; h, cavity of the tympanum ; i, Eustachian opening of tym- panum ; j, opening of Eustachian tube in the pharynx ; k, posterior part of pharynx; l, semicircular canals ; in, n, cochlea; o, trunk of auditory nerve. The middle ear or tympanum is situated in the petrous portion of the temporal bone, between the membrana tym- pani externally, and the internal ear or labyrinth in- ternally. It is filled with air, and communicates with the SENSE OF HEARING. pharynx through the Eustachian tube, which opens at the back part of the inferior meatus, (Fig 111). It also com- municates posteriorly with air cavities in the mastoid process of the temporal bone, the mastoid cells. It is crossed by a chain of movable bones, which receive the impressions from the membrana tympani, and serve to Fig. 118. Interior of the osseous labyrinth. V. Vestibule, av. Aqueduct of the vestibule, o. Fovea hemielliptica. r. Fovea hemispherica. S. Semicircular canals, s. Superior, p. Posterior, i. Inferior, a, a, a. The ampullar extremity of each. C. Cochlea, ac. Aqueduct of the cochlea, sv. Osseous zone of the lamina spiralis, above which is the scala vestibuli, communicating’ with the vestibule, st. Scala tympani below the spiral lamina. transmit them to the internal ear, upon which the auditory 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 cavity of the tympanum and its chain of bones are lined with mucous membrane, continuous with the pharynx through the Eustachian tube, and covered with ciliated epithelium. The internal ear or labyrinth, is the essential part of the organ of hearing, and consists of the vestibule, semi- 360 THE SPECIAL SENSES. circular canals, and cochlea. 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. The vestibule, is the central organ and middle cavity of the labyrinth. In its inner wall are several openings for the entrance of the branches of the auditory nerve ; in its outer wall is the opening of the fenestra ovalis which re- ceives the stapes ; in its posterior and superior walls are the openings, five in number, of the semicircular canals ; and in its anterior wall the opening into the cochlea. The semicir- cular canals are three arched bony canals which open at both ends into the vestibule, two of them first coalescing. One end of each, more dilated than the other, is called the ampulla. The cochlea is situated in front of the vestibule, and is shaped like a snail shell. Its axis presents a conical column, the modiolus, around which winds a spiral canal, making about two and a half turns from the base to the apex. At the base there are three openings, the vestibular opening, the fenestra rotunda and the aquceductus cochlea. The spiral canal is divided into passages or scalae, by the lamina spiralis ossea which consists of two laminae of bone between which are canals for the entrance of the nervus cochlearis. One of these passages communicates with the vestibule, the scala vestibuli; the other with the tympanum, the scala tympani. Between these is a third space called the scala media,or canalis cochleae (Fig. 119, cc) The lamina spiralis ends at the apex of the cochlea in a small hamulus, the inner and concave surface of which, when separated from the modiolus leaves a small aperture, the helicotrema through which the scalae, separated in the rest of their ex- tent, communicate. The lamina spiralis ossea extends only SENSE OF HEARING. 361 >art of the distance between the modiolus and the outer vail of the cochlea, and swells up at the outer end, forming he limbus lamince spiralis, the border of which is orooved.. he sulcus spiralis from the inferior mar- jin of this groove i membrane stretches icross to the bony wall >f the cochlea eomplet- ng the lamina spiralis jailed the membrana tasilaris, the outei ittachment of which brms a thick triangu- O ar structure the liga- nentum spirale. From )he upper margin ol ihe sulcus spiralis stretches across anothei nembrane which covers over tne organ ot Uorti, he membrana tectoria, or membrane of Corti. Fur- her inwards is another thin membrane, the mem- brane of Reissner, which stretches across and forms he scala media, or canalis cochleae. The organ of Corti s situated upon the membrana basilaris. It consists ol die rods of Corti, arranged in a series of arches formed by he internal and external rods roofing over the zona arcu- ata (Fig. 119. i, 2.). They incline inwards towards each ither, and each ends in a swelling termed the head, the con- vexity of one fitting into the concavity of the other like an articulation. It lias been estimated that there are about 3000 of these pairs of rods or pillars from the base to the apex of the cochlea. On both sides of these rods are cylin- drical epithelial cells, some of which are provided with cilia (cells of Corti.) Within the osseous labyrinth is contained the membran- Fig. 119. Section through one of the coils of the cochlea st, scala tympani; sv, scala vestibuli; cc, scala media or canalis cochleae ; r, membrane of Reissner, with its single layer of nucleated flattened cells ; lls, limbus laminae spiralis; ss, sulcus spiralis ; gs, ganglion spirale seated on nc, the nervus cochlearis, indicated by the black line; Iso, lamina spiralis ossea ; t, membrana tectoria of Corti; b, membrana basilaris ; Co, organ of Corti; Up, ligame itum spirale; 1, internal rod of Corti; 2, external rod of Corti. 362 7HE SPECIAL SENSES. ous labyrinth, upon which is distributed the filaments of the auditory nerve. The membranous labyrinth is filled with a transparent fluid, called endolymph ; while between it and the osseous covering is a fluid called perilymph, so that the sonorous vibrations which reach the auditory nerve in these parts are conducted through fluid, to a membrane con- taining fluid. In the vestibular portion of the membranous labyrinth are two cavities; the upper and larger is named he utriculus, and the lower the sacculus. They are situ- ated respectively in the fovea hemielliptica and the fovea hemispherica and contain small masses of calcareous matter, the otoliths (Fig. 118). The utricle communicates with the membranous semicircular canals and the saccule with the canalis cochleae. The Mechanism of Hearing.—The auditory nerve as it enters the ear divides into two branches, one to the vestibule and the ampullae of the semicircular canals, and the other to the cochlea. The branches of the cochlear nerve enter through openings at the base of the modiolus, and pass into canals between the plates of the lamina spiralis, in which they form a plexus containing ganglion cells (Fig. 119, gs), and terminate in the organ of Corti. The external ear favors the propagation of sound by collecting the sonorous undulations, and conducting them to the membrana tym- pani, and also by the resonance of the column of air con- tained in the auditory canal. The elevations and depressions of the pinna serve a useful purpose, for sonorous undulations from whatever direction they come, must fall perpendicularly upon the tangent of some one of them. Sonorous vibra- tions are conducted to the ear by three different media, the air, the ossicles of the ear, and the fluid of the labyrinth. The propagation of the sounds to the fluid, is made more perfect by reason of the ossicles being fixed in thfe middle of a tense vibrating membrane, with air on both sides, as the tympanum. Sounds are collected by the external ear and are transmitted to the membrana tympani. They THE MECHANISM OF HEARING. 363 are here modified by the tense or lax state of this mem- brane, produced by the action of the laxator and tensor tympani muscles. The modified vibrations from the mem- brana tympani are thence conducted along the chain of bones to the fluid of the labyrinth, and through it trans- mitted to the auditory nerve, which receives the impressions* and conveys them to the sensorium. From various experi- ments 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 expir- ation 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 inspiration exhausts the air from the cavity of the tym- panum, 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 en- hanced by the presence of air in the cavity of the tympa- num. It serves to isolate the bones so as to propagate the vibrations with concentrated intensity, and prevent the dispersion of sound. The air is supplied through the Eusta- chian tube, which communicates with the pharynx just be- hind 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 semicircular canals collect the sonorous undulations from the bon es of the cranium and conduct them to the ampullae and utriculus, where the auditory nerve is distributed. The cochlea is intended for the spreading out of the nerve fibres over a wide extent of surface, and for the perception of sounds by the solid parts and the walls of the labyrinth. The membranous labyrinth of the vestibule and semicircu- 364 THE SPECIAL SENSES. lar canals is suspended free in the perilymph and receives the sounds through the medium of that fluid, while on the other hand the lamina spiralis upon which the cochlear nerve is expanded is continuous with the solid walls of the cochlea from which it receives impressions directly. The function of the rods of Corti is probably to receive impres- sions of various notes and tones, and communicate them to the brain through the filaments with which the rods are connected. The intensity of a sound is due to the length of the vibrations, the 'pitch to the number in a second, and the quality to the number of secondary notes. The power of determining the direction and distance of sounds is ac- quired by experience. Any irritation or excitement of the auditory nerve, as congestion, cerebral disease, etc., may give rise to ringing or buzzing sounds in the ears. These are called subjective sounds, because they are produced by internal causes. The sense of hearing varies much in different individuals, 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 im- pressions. Hearing may be impaired by a preternaturally dry state of the membrana tympani, or the partial closure of the external meatus by collections of wax, particles of dust, etc. In some of the lower animals, the sense of hear- ing is very acute. SENSE OF TASTE. The principal organs of the sense of taste, are the tongue and fauces. The conditions necessary are the presence of special nerves to convey the impressions received, and the excitation of these nerves by sapid matters in a state of solution. The nerves are the lingual branch of the fifth, and the glosso-pharyngeal (p. 333). The tongue is a muscular organ, covered with mucous membrane and presents numerous papillae. These have been already described (p. 107). The muscles are divided into intrinsic, or those that form the SENSE OF TASTE. 365 greater part of the substance of the tongue, as the linguales * and extrinsic or those which attach it to surrounding parts, as the hyo-glossus, genio-hyoglossus, stylo-glossus, etc. The epithelium of the tongue is of the squamous variety, Fig. 120. The tongue with its papillae and nerves. 1, Hypoglossal nerve. 2, Lingual branch of the trifacial. 3, Lingual branch of the glosso-pharyngeal nerve. 4, Chorda tympani. 8, Sub-maxillary ganglion. 11, Anastomoses of the lingual with the hypoglossal uerve. 12, Facial nerve. 13 Mucous membrane detached and thrown upwards; the circumvallate papillae aie seen behind. (Hirschfeld.) and covers every part of the surface, but is thinner in some parts than others, as on the fungiform papillae. Peculiar structures,known as taste buds or taste goblets,have been dis- covered in the circumvallate papillae and on the posterior surface of the epiglottis. They are oval in shape,and con- sist of narrow fusiform gustatory cells surrounded by a layer of broader fusiform or encasing cells (Fig. 121). A depress- ion exists in the epithelium over the goblet, and the gusta- tory cells present hair like processes which resemble cilia. These bodies are found side by side in considerable num- bers,and are believed to be gustatory in function, but as yet no nerves have been traced into them. The fauces, uvula, tonsils, and upper part of the pharynx, all of which are supplied with branches of the glosso- THE SPECIAL SENSES. 366 pharyngeal nerve,are endowed with the sense of taste. In most persons the sense of taste is most acute in the tip and edges of the tongue; while in the middle of the dorsum it is feeble. The tongue also possesses an accurate sense of touch, and is capable of receiving im- pressions of heat or cold, pain, mechanical pressure, and the form of surfaces. Its common sensibility may be impaired or lost, and the sense of taste still continue. The nerve fibres for these two sensations, although found in the same papillae, are distinct, just as the olfactory nerves and the nerves of common sensation in the nose are dis- tinct. The senses of smell and taste are closely associated, for if the former be impaired or lost as in disease, the latter is rendered less acute. Taste appears to be governed to some extent by the same principles as that of sight; viz. that those tastes which are opposite or comple- mentary, render each other more distinct, as sweet and bitter acid and alkaline, etc. The sense of taste is very though not to be compared with the sense of smell. It may be rendered less distinct in regard to any substance by constant contact with it, in the same way as the eye becomes fatigued with the constant perception of a single color Subjective sensations of taste frequently occur in diseased conditions of the nerves of taste, or their associate nerves. Fig. 121. Taste goblet; a, depression in the epithelium over the goblet; b, nuclei of encasing cells ; c, two nuclei of the gustatory cells. SENSE OF TOUCH. The sense of touch has a wider range than the other senses, and varies greatly in the different parts of the body. It is greatest at the extremities of the fingers, lips and SENSE OF TOUCH. 367 ongue, and least in the integument of the trunk, arms and highs (p. 124). There are no special nerves of the sense of ouch; they are simply the nerves of common sensation upplied to all parts of the body, and hence it is that all >arts are endowed with this sense. Touch is simply an ex- .ltation of common sensation. Some are of the opinion, hat common sensation and tactile sensation are communi- ated to the sensorium through different sets of nerves. Chose parts of the body in which the sense of touch is most icute are abundantly provided with papillae, which increase he extent of surface for nerve distribution. These papillae tary in size from T£o to of an inch (.25 to .1 mm). The lerves distributed to them are destitute of the white sub- itance of Schwann, and ap- pear to terminate in oval- shaped bodies, formed of ionnective tissue named tactile corpuscles (Fig. 122, f). In some of the pa- pillae, as those of the lips, ;ongue, palate and integu- nent of the glans penis, the nerves terminate in small round bodies, of an inch (42 mmm,) in diam- eter, the end bulbs ol Krause (Fig. 122,b). In the palms of the hands, points of the lingers and soles of the feet, the papillae are arranged in rows, and form ridges and furrows which may be seen with the naked eye (p. 116). The sense of touch is peculiar from being widely distributed; even the eyelashes, hair (near the root), nails and teeth ex- hibit this sense in a manner peculiar to themselves. The integument is endowed not only with the sense of touch, per se,but also with the sense of pressure, temperature and pain; the latter being a highly exalted sensation of the three former. Fig. 122. A. Tactile corpuscle; B, end-bulbs of Krause (see page 287). 368 THE SPECIAL SENSES. Some parts of the body are sensitive to tickling as the axilla? and soles of the feet, but are comparatively blunt in regard to the special sense of touch. The sense of touch enables the mind to become acquainted with the condition of bodies, whether hot or cold, rough or smooth, hard or soft, wet or dry, and their size, form, etc. The organs by which touch is chiefly exercised, are the hands, and especially the points of the fingers, which are abundantly provided with papillae for that purpose. The variation in sensibility in different parts may be determined by the aid of a pair of compasses. Thus the two points of a pair of compasses may be separately distinguished by the point of the finger when only about one-third to one-half a line apart, while they require to be twenty to thirty lines apart, to be separately felt on the integument of the spine, arm, thigh, sacral or gluteal region. The two points are felt separately on the tip of the tongue when of an inch apart, on the middle of the dorsum of the tongue, of an inch, on the lip of an inch, and on the tip of the nose, when \ of an inch apart. The cesthesiometer, an instrument for determining the relative sensibility of the arms or legs in paralysis, is constructed on this principle. The sense of touch may be very much increased by constant practice, as is seen in the case of the blind, who acquire a remarkable facility for reading raised letters, by the aid of the fingers. The sense of 'pressure is produced by weight or tension, and is intensified according to the increase of the weight or tension. In lifting a body we judge of its weight partly by the pressure on the hands, and partly by the amount of muscular force used in raising it. The latter is called the muscular sense (p. 309). These two faculties give us the power of discerning the relative weight of bodies. We have also the power of estimating beforehand, and regulating the amount of muscular force required in lifting heavy bodies. If we attempt to lift an object which we have conceived to be heavier than it really is, we are liable to be SENSE OF TEMPERATURE. 369 overturned by the muscular effort unnecessarily put forth to overcome the supposed resistance. The sense of temperature is distinct from that of touchy and may remain unimpaired when the latter is for the time in abeyance, as when a nerve is pressed upon or partly in- jured. The sensations of temperature, however, are very deceptive, and cannot be relied upon ; as e.g. in the cold stage of disease, the patient feels excessively cold, while the ther- mometer shows that the temperature is over 100raF. Again, if one hand be put in cold water, and the other in water at a temperature of 110°F., and both are then immersed in water at 80°F., it will feel warm to the hand previously in the cold water, and cold to the other. In examining patients in cases of fever or inflammation, in regard to the heat of the skin, no reliance can be placed on the sensation of heat communicated to the hand, and therefore the ther- mometer should always be used. Some parts of the body will bear a higher degree of temperature than others, e.g., the hand will resist a temperature which would be intoler- able to the body. Only ordinary temperatures can be dis- criminated, viz., from 50° to 120°F.; very high or very low temperatures produce a burning sensation. Subjective sen- sations of touch, arising from some internal causes, are of frequent occurrence, as heat, cold, rigor, neuralgic pains, itching, formication, etc. 370 THE VOICE. CHAPTER XV. The Larynx is the organ of voice, and is situated at the upper part of the air passage, 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, which are held together by ligaments, and acted upon by numerous muscles. It is lined by mucous membrane, covered with columnar ciliated epithelium below the super- ior vocal cords and the upper part in front; the rest of its extent is covered with squamous epithelium. 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 open- ing 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 (Fig. Ill f) p. 341. Of the two vocal cords, the inferior consists of a band of yellow elastic tissue, covered by mucous mem- brane, and is called the true vocal cord; while the superior, which is formed entirely by a folding of the mucous mem- brane, is called the false vocal cord, because it is not con- cerned in the production of the voice. It is in the larynx that the sounds are originally produced; but they may be modified during and after their production by the tongue, palate, VOICE. teeth, lips, etc., constituting, in man, the faculty of speech The interval between the true vocal cords in the mediae line is called the rima glottidis, or chink of the glottis, the narrow- ing or widening of which, and the tension 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, cceteris 'paribus, the higher the pitch of the note. The tension of the vocal cords and the size of the aperture, are regulated by mus- cles which are situated in the larynx. It has b een proved by observation 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 structures above the vocal cords are removed. The essential parts of the larynx are the thyroid carti- lage, the cricoid cartilage, the two arytenoid cartilages and the true vocal chords. The latter are attached behind to the front portion of the base of the arytenoid cartilages, and in front to the depression between the two alse of the thyroid cartilage, so that all movements of the arytenoid cartilages produce an effect on the vocal cords. Movements of the cricoid cartilage also produce an effect on the vocal cords indirectly, since the arytenoid cartilages rest upon its poste- GLOTTIS AND VOCAL CORDS. 371 Fig. 123. Glottis seen with the laryngoscope during the emission of high-pitched sounds.—X, 2, base of the tongue; 3, 4, epiglottis ; 5, 6, pharynx ; 7, ary- tenoid cartilages; 8, opening between the true vocal cords; 9, aryteno-epi- glottidean folds; 10, cartilage of San- torini; 11, cuneiform cartilage; 12, superior vocal cords; 13, inferior vocal cords.—(Le Bon.) 372 THE VOICE. rior part. Those muscles which act upon the arytenoid car- tilages either directly or indirectly, nine in number, are called the intrinsic muscles of the larynx, viz.: two crico- thyroid muscles, two thyro-arytenoid, two 'posterior crico- arytenoid,, two lateral crico-arytenoid, and one arytenoid muscle. The crico-thyroid, produce tension and elongation of the vocal cords by drawing downwards and forwards the thyroid cartilage over the cricoid. The thyro-arytenoid draw the arytenoid cartilages forwards towards the thyroid and relax the vocal cords. The posterior crico-arytenoid rotate the base of the arytenoid cartilages outwards and backwards, separate the vocal cords and open the glottis. The lateral crico-arytenoid rotate the arytenoid cartilages inwards and close the glottis. The arytenoid mus- cle approximates the arytenoid cartilages and closes the glottis, especially at its posterior post. The nerves which govern these actions are the branches of the pneumogastric and spinal accessory (p. 333). The combined action of the muscles places the vocal cords in the various positions necessary for breathing and the production of sounds, as in singing, speaking, etc. In ordinary tranquil breathing the opening of the glottis is wide and triangular, and becomes a little narrower at each expiration. In the production of sound it is narrowed,and the tension of the vocal cords increased. In the production of higher notes the vocal cords are more closely approxi- mated and rendered more tense (Fig. 123). In the space between the arytenoid cartilages at the posterior part of the glottis, no regular vocal sound is produced, nothing more than a mere rustling or gurgling sound. The tone of the voice is somewhat lowered by the action of the epiglottis when it partially covers the cavity of the larynx. The ven- tricles of the larynx are for the purpose of affording free space for the vibrations of the vocal cords. The modes of sequence of the notes of the voice are three in number; 1st. The monotonous, as in ordinary speaking, COMPASS OF THE VOICE. 373 with occasional intonation for the sake of accent; 2nd, the transitional, from high to low notes and vice versa with- out intervals; such as in crying in man, and the howling of animals, and 3rd, the musical, in which each note has a determinate number of vibrations. The compass of the voice varies in different individuals from one to three octaves, and some singers may even ex- ceed three octaves. Before pubertj*, the pitch of the male and female voice is nearly the same, the male voice being a little louder; but at this period the larynx of the male undergoes 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 the voice. The different pitch of the male and female voice depends on the different length of the vocal cords in the two sexes, viz. : as three to two respectively. The lowest note of the female voice is an octave higher than the lowest note of the male voice, and the compass of the two is about four octaves. 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 dis- tinction between the different voices, however, consists 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 chest notes or the notes of the natural voice, and the falsetto notes. The former are produced by the ordinary vibrations of the vocal cords and are much stronger ; the latter, in all probability, by the vibration of only the inner border of the vocal cords, and are of a flute- like character. The voice is principally used in man in the formation of speech. The tone of the speech depends much upon the 374 THE VOICE. 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. Articulate sounds, or the sounds produced in speech, are com- monly 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. During the production of the vowel sounds the posterior nares are closed, and no air issues through the nose. The consonants cannot be sounded except conso- nantly with a vowel, hence the name. They are divided into labial, dental or guttural, according to the interruption to the current of air required in their formation, as by the lips, teeth, palate or pharynx. They may also be classified ac- cording to the character of the movements which give rise to them, as explosives, as p, b, t, d, etc., aspirates, as/, v, s, l. z, etc., resonants, as m, n, ng, etc., and vibratory as r. Ventriloquism appears to consist in the varied modifica- tion of the sounds produced in the larynx, so as to imitate the voice as heard from a distance. It is accomplished 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 generally directed to that part of the room from which the sound is expected, a circum- stance which adds materially to the success of the perform- ance. Stammering, in most instances, is an affection of the nervous system, and not of the articulating organs. It con- sists in an imperfect power of co-ordinating the muscles of speech, associated with a spasmodic action of certain mus- cles concerned in the formation of the voice. Some stam- mer only on attempting to articulate certain letters ; others REPRODUCTION. 375 do so at every attempt to speak. It is much increased by any mental excitement, surprise, etc. Females seldom stam- mer, 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. The process of reproduction comprises the several provi- sions 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,fand so on. This is multiplication by subdivision ; or fissiparous multiplication (Fig. 124). It is seen in the lowest plants, as in the cells of fungi and lichens, and also in carti- ageand other cells of the human body. The amoeba also furnishes a good example of this mode of reproduction. It throws out a large process in a certain direction, becomes contracted at or near the middle, and divides into two or more parts, each containing a portion of the original nucleus. Some organizations, as the polyp, when divided artificially 376 REPRODUCTION. into segments, have the power of developing into a perfect form from each segment. The second mode takes place by a process of gemmation, or budding from the parent stalk. These buds, which con- sist of a mass of cells, are at first entirely nourished by the parent stalk, but gradually become less dependent, and at Fig. 124. Fig. 125. A cell undergoing the process of multiplica- tion by subdivision ; a, original cell; b, cell be- coming oval; c, undergoing hour-glass contrac- tion ; d, division of the cell into two. Amoeba ; in the centre is seen the nucleus and surrounding- it a number of vacuoles and granules last detach themselves and maintain a separate existence. This is termed multiplication by gemmation or gemmipar- ous multiplication. The hydra affords a good example of this variety. The first change which is observed is a slight ele- vation on the surface, which assumes a globular form ; a cavity is then formed in the interior, which communicates with the parent. After a time this channel of communica- tion closes, the newly-formed polyp drops off, and a new creature is formed. The joints of the common tape-worm multiply in this manner. This process is also common among the Bryozoa, and leads to the formation of colonies. 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 Algse 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, and the contents of the two cells become mixed and form a new body termed a spore or sporangium, from which the new plant is formed. ACTION OF THE MALE. 377 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 con- tents of the sperm cell the ovum becomes impregnated, and an embryo is formed from which the adult animal is gradu- ally 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, chrysalis, 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 production of ova. This is called by Prof. Owen metagenesis. Action of the Male.—The male furnishes the sperma- tic fluid or sperm, which is fluid contains the sperm cells in which are developed the sperma- tozoa; also an albuminous substance; various salts and an animal substance resembling fibrin termed sperma- tine. The sperm cells are large spherical vesicles, in which are con- tained from two to nine smaller cells or nuclei, in each of which is found a spermatozoon. The spermatozoa are the essential elements of the sper- matic fluid, and are set free by the breaking down of the sperm cells (Fig. 126 ,a). They are transparent filamentous bodies, about &oxy of an inch (42 mmm.) in length, and from to to otf °f an inch (5 to 25 mmm.) in thickness, being thicker at the anterior ex- tremity or head than the posterior or tail. Their move- ment is accomplished by the constant vibration of the tail; Fig. 126. a, Human spermatozoa magnified 350 diameters; b, sperm cell con- taining the spermatozoon coiled up within it; c, cell elongated by the partial uncoiling of the sper- matozoon. REPRODUCTION. they are said to move at the rate of one inch in seven and one-half minutes. Their movements may be sus- pended, and their power of impregnation destroyed by profuse leucorrhoeal discharges or acrid secretions of the vagina, and by the action of solutions which act chemically upon them, as solution of silver nitrate, zinc sulphate, zinc chloride, etc. In the female organs of generation the move- ments 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 discharge from the ovary. One or more are supposed to pierce the vitelline membrane and pass into the interior of the ovum or germ cell, and unite with it, after which they disappear. It is also supposed by some that they enter through a small opening or micropyle, and by others that they perforate the vitelline membrane. 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 corresponding 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. Each ovary is about an inch and a half long, three-fourths of an inch wide, and half an inch in thickness, and is attached to the uterus by the ligament of the ovary, and to the Fallo- pian tube by one of the fimbriae, the rest of the surface being covered with columnar epithelium, beneath which is the proper covering of the organ—the tunica albuginea— ACTION OF THE FEMALE. 379 which is a dense, firm membrane, enclosing the parenchyma or stroma. The stroma consists of two parts, an external or cortical portion, whitish in color, and an internal medullary or vascular zone, reddish in color, and consisting of vessels elastic fibres and connective tissue among which are a number of non-striated muscular fibres. The external por- tion consists of a network of connective tissue in which the Graafian vesicles are formed. There are also a large num- ber of nuclei in the interstices. The Graafian vesicles or ovisacs, exist in very large numbers from the earliest periods of life, and in all stages of development. They vary in size from a pin’s head to a pea, and contain the ova. Each Graafian vesicle consists of an ex- ternal vascular, and an internal serous coat, named the ovicapsule. The internal 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 num- bers around the ovum, forming a granular zone, the cumulus, discus proligerus, retinacula or chalaza. The cavity of the Graafian vesicle is filled with an albuminous fluid in which granules float. The ovum is a small spherical body, about of an inch (.2 mm) in diameter. It con- sists externally of a transparent envelope, the zona pellucida or vitelline membrane, and within this is the yolk or vitellus. Imbedded in the substance of the yolk is a small vesi- cular body, the germinal vesicle, and within the germinal vesicle is the germinal spot. The latter is about of an inch (8mmm.) in diameter. The vitelline membrane is a colorless transparent membrane, which appears as a bright Fig. 127. Graafian vesicle: 1, stroma; 2, peritoneum; 3 and 4, coats of the Graafian vesicle; 5, membrana granulosa; 6, fluid of the Graa- fian vesicle ; 7, discus proligerus ; 8, ovum. Fig. 128. Ovum: 1, germinal spot; 2, germinal ves- icle ; 3, yolk ; 4, zona pellucida; 5, discus proligerus; 6, adhe- rent granules or cells. 380 REPRODUCTION. ring with a dark border externally and internally, and is about g-sW of an inch (10 mmm.) in thickness. The yolk consists of granular protoplasm, the smaller granules resembling pigment, and the larger, more numerous at the periphery, fat globules. The germinal vesicle contains a watery fluid in which are found a few granules. At the approach of the menstrual period, one (or probably more) of the Graafian vesicles enlarges, approaches the sur- face of the ovary, and when mature, forms a small projec- tion on the surface. It finally bursts, the ovum escapes, and is caught by the fimbriated extremity of the Fallopian tube, and by it conducted to the uterus. Coepus Luteum.—When the Graafian vesicle has ma- tured, and is about to burst and expel the ovum, it becomes highly vascular and opaque, and its coats are thickened by a glutinous looking substance. As the ovum escapes, it leaves behind it the external vascular and the internal serous coats of the Graafian vesicle, the cavity of which is immediately filled with a bloody fluid which soon coagulates, and the cicatrix presents a yellowish appearance ; hence it has been called the corpus luteum (Fig. 129). After a short time the coagulum contracts, and the mem- branes become convoluted and hyper- trophied, so that when the corpus luteum is divided transversely, about three weeks after its formation, it is seen to consist of a central firm coa- gulum surrounded by a convoluted wall of a reddish yellow color. Corpora lutea are divided into true and 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 dis- tinction between them ; but the true corpus luteum becomes Fig. 129. Corpus luteum, natural size, eight days after conception : a, external' coat of the ovary ; b, stroma of the ovary; c, convo- luted wall of the Graafian folli- cle ; d, clot of blood. ACTION OF THE OVIDUCTS. 381 larger and remains longer than the false, in consequence of the increased vascularity of the parts after imm-ee-nation. 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 disappears in the course of about two months, while the true increases in size, until about the fourth or fifth month, and then gradually declines until after parturition, 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 impreg- nated 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 ovi- duct, and in passing the first portion, which is about twc 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 glan- dular. In the upper part, it secretes a viscid fluid which surrounds the yolk 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 chalazse, is called the cha- laziferous membrane. In the rest of this portion, an albumin- ous secretion is poured out to form the albumen or white ol 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 Fig. 130. Corpus luteum, natural size, at the filth month of pregnancy ; 6, stroma of the ovary ; c, convo- luted wall of the Graafian folli- cle ; e, decolorized clot; f, fibr- ous envelope of the corpus lute- um. 382 REPRODUCTION. external. The egg then passes into the fourth division, which is about two inches long. This pours out a secretion 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 middle membranes, at the large end of the egg. The vitellus is the essential part of the egg, the white simply contributing to the nourishment of the chick until it leaves the shell, and the membranes and shell affording the protective coverings. Development of the Ovum.—After the ovum is im- pregnated 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 Fig’s. 131-4. lias divided into two portions. Each of these portions is again subdivided into two, and the four segments thus pro- duced are divided into sixteen, and sixteen into sixty-four, and so on, until the whole mass has assumed a mulberry ap- pearance, and is finally converted into “ vitelline spheres ” or “ true animal cells,” which adhering together, form the blastodermic membrane. These cells are also 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 blastodermic membrane then divides into two layers, the external blastodermic, serous or DEVELOPMENT OF THE OVUM. 383 animal layer, and the internal blastodermic, mucous or vegetative layer, both of which are composed of cells. The former produces the spinal column 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, surrounded 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 thicken- ing and condensation of the external blastodermic mem- brane in one part, forming an elongated oval spot with opaque edges. This is called the embryonic spot. Enclosed Fig. 135. Fiir-136. The impregnated ovum showing the embryonic spot, area pellucida and primitive trace. Commencing formation of the embryo; a, external blastoder- mic layer; b, vitellus; c, embryo. within this is a narrow transparent space, the area pellucida, in the centre 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 de- posited 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 blasto- dermic membrane and the fluid in its cavity. Beneath 384 RE PROD UCPION. the spinal canal is formed a cartilaginous cord, which is called the chorda dorsalis, from which the vertebrae 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 blastodermic layer forms the alimentary canal, the mouth and anus being developed by atrophy and perforation of the external layer of the blasto- dermic 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 atro- phies and disappears. The animal at first breathes by gills ; but these are subsequently replaced by the lungs. In the development of the chick which has been studied very carefully by various observers, the blastodermic mem- brane, or blastoderm divides into three layers, the two lay- ers already referred to in the frog, and an “ intermediate layer ” or mesoblast. These three layers are designated by some, the epiblast, mesoblast or middle layer, and the hypo- blast. The epiblast forms the epidermis and appendages, cere- bro-spinal nerve centres, sensorial epithelium of the nose,eye, ear etc., and the epithelium of the mouth and salivary glands. From the mesoblast is formed the tissues of the body, con- nective, muscular and nervous tissues, vascular and genito- urinary systems, and digestive canal except its epithelium ; and from the hypoblast is developed the epithelium of the alimentary canal and the ducts that open into it, and also the parenchyma of the glands, as the liver and pancreas. In the egg of the fowl, a whitish circular spot is seen, about of an inch (5 mm) in diameter, immediately beneath the vitelline membrane, the cicatricula, in the centre of which Fig. 137. Diagram of a section of the embryo showing the formation of the spine; a, epiblast : b, hypoblast; c, mesoblast; d, margin of the lamina dorsalis; e, medullary groove; f, chorda dorsalis or notochord; g, primitive or protovertebra. DEVELOPMENT OF THE OVUM. 385 is the germinal vesicle. When the egg is fecundated, seg- mentation begins in the cicatricula in the manner already de- scribed, until the blastoderm comes to occupy the place of the cicatricula. It then separates into the three layers above mentioned, in which certain prominences and foldings take place which mark out the commencing development of the different parts of the embryo, as the “ headfold,” “ tailfold,” etc., (Fig. 138.) On each side of the primitive trace (Fig. 135), the epiblast rises up to form the dorsal plates (laminae dorsales), which soon meet and close in the spinal or medul- lary groove, and form a canal for the reception of the spinal cord and brain (Fig. 137, d). Beneath this canal in the mesoblast is formed the chorda dorsalis or notochord, which ultimately becomes the spinal column ; on each side of the chorda dorsalis, a longitudinal thickening of the mesoblast takes place from which is formed the primitive vertebrae (protovertebrae). These structures form the bases out of which the spinal column and muscles are afterwards de- veloped. On the outer side of the primitive, or protover- tebrae, the mesoblast splits into two laminae, one joins the epiblast (somatopleure) and forms the parietes of the trunk, and the other joins the hypoblast (splanchnopleure) and forms the alimentary canal and other parts. The general cavity of the body is formed by downward foldings of the blastoderm, somewhat resembling the formation of the nervous canal (Fig. 138). These downward foldings are called the visceral plates. In the frog these plates close in the whole of the vitellus. In the chick, fish, etc., 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 atro- phied as development proceeds. In the human embryo the umbilical vesicle becomes more completely separated, and forms a cord by its constriction, 386 REPRODUCTION. at the distal extremity of which is situated the vesicle, which contains a clear transparent fluid (Fig. 139, g). 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 (Fig. 141). Formation of the amnion and Allantois.—These are two accessory organs which belong to the higher order of animals, and their development has been carefully studied in the chick. The amnion is formed from the external layer of the blastodermic membrane, and the allantois from the internal; the former encloses a cavity or sac containing fluid in which the foetus floats ; the latter is a vascular structure destined to bring the blood of the embryo to the Fig. 138 Fig. 139. Diagram of the formation of the amnion and allantois a, vitelline membrane covered with the villi of the chorion ; b, folds of the amnion surrounding the embryo ; c, point; of meeting of amniotic folds ; d, outer layer of the amniotic fold ; e, inner do.; /, amniotic cavity; g, umbilical vesicle; h, allantois ; i, cavity of the intestine ; J>', space between the two layers of the amnion ; o, situation of the heart and vessels. external sources of nutrition and atmospheric influence. These are not necessary to the development 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 surrounded. The amnion is first formed; this takes place by foldings of the external blastodermic membrane, which pass upwards from the abdominal surface on all sides of the embryo, until they meet and fuse at a point over the back which is called THE AMNION AND ALLANTOIS. 387 the amniotic umbilicus (I ]g. 138,c). Atrophy and separation then take place at this point, the inner layer of the fold form- ing the amnion; the outer, blending with the vitelline mem- brane, and forming the external investing membrane of the ovum. A shut sac is thus formed between the amnion and the foetus called the amniotic cavity, which is filled with a cleai fluid—the liquor amnii (Fig. 139,/). About this time the allantois commences as a prolonga- tion 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 lavers (Tier. 139, h). It gradually increases in size until it covers the body of the embryo, to- gether with the amnion; it then meets and fuses over the back as did the amniotic folds (Fig. 140). It therefore lines the whole internal surface of the investing membrane of the ovum with a flattened vascu- lar sac, the vessels of which come from the interior of the body of the embryo. The cavity of the allantois is continuous with the cavity of the intestines. The umbilical vesicle is situated between the amnion and allantois. In the chick the allantois comes immediately in contact 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 takes place, oxygen being absorbed from the air, and carbonic acid exhaled from the blood-ves- sels of the allantois. It will be seen, therefore, that a true respiration 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. Fig. 140. Formation of the allantois :-a, in- ner layer of amnion ; 6, outer layer of amnion ; c, amniotie cavity ; d, vessels of the allantois; e, umbili- cal vesicle. 388 REPRODUCTION. 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 between the two. The chorion in the human subject is identical 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 number of minute villi or “villosities” which are found on its surface (Fig. 139). 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 fila- ment terminating in a rounded extremity. 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 villii of the small intestine. The villi of the chorion therefore bear a slight resemblance to those of the small intestine; but are unlike any other structure of the body, and their presence in the uterus or its dis- charges may be considered as a proof of pregnancy. 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 (Fig. 141). Those villi which Fig. 141. The human ovum at about the third month, showing the enlarge- ment of the cavity of the amnion, the formation of the placental por- tion of the chorion, the commencing formation of the umbilical cord, and the atrophy of the umbilical vesicle. PREPARATION OF THE UTERUS. 389 remain, continue to grow, and ultimately form the placenta, which attaches itself to the uterus (Fig. 142). 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 becomes greatly Fig. 142. Vertical section of the womb, containing a developed ovum ; a, neck, filled with a gel- atinous plug ; bb, orifice of the Fallopian tubes ; cc, decidua vera ; d, uterine cavity, almost entirely filled with the ovum ; ee, decidua vera continuous with the decidua reflexa ; /, placenta; g, allantois; h, umbilical vesicle and its pedicle in the umbilical cord; i, am- nion ; k, decidua reflexa and chorion. hypertrophied, tumefied,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 decidua vera. When the ovum reaches the uterus it insinuates itself between the opposite surfaces of the mucous membrane, and becomes lodged in 390 REPRODUCTION. 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 reflexa. 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 exudation of croup, etc., which surrounded the whole internal surface of the uterus, and was called the decidua vera. 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 reflexa. The closure of this folding behind the ovum, was called the decidua serotina. This was the theory of William Hunter. It is now known to be no other than the mucous membrane itself, very much thickened and hypertrophied. Fokmation 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 penetrate or are pushed into the follicles of the mucous membrane, (like the fingers into a glove), which are enlarged for their reception. The growth of the villi and that of the follicles go on sim- ultaneously. and keep pace with each other. The capillaries of the villi are enlarged and become tortuous, and those on the exterior of the follicles enlarge excessively and become dilated into wide sinuses, which are filled with blood derived from the arteries of the uterus, so that two membranes inter- vene between the capillaries of the villi and the sinuses of the uterus, viz., the covering of the villi and the lining mem- brane of the follicles. These afterwards fuse together 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 PLACENTA AND UMBILICAL CORD. 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 commencement of the fourth month, and consti- tutes 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 interven- ing membrane by osmosis, and enters the blood of the foetus. Besides, the placenta is an organ of exhalation as well as of absorption. The impurities circulating in the blood of the foetus are here discharged into the maternal vessels, 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, etc., which disturb the circulation, may occasion deformities and deficiencies of various kinds, nsevi, warts, etc., in the latter. The circula- tion in the foetus has been already described (p. 227). Umbilical Cord and Amniotic Fluid.—The umbilical 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 cho- rion, 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 con- stitute what is commonly called the “ membranes.” As the 392 REPRODUCTION. 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 (Whartonian jelly) and surrounded by a folding of the amnion. The cord at full term varies in length from one to three feet. Parturition.—The discharge of the foetus is termed par- turition. 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 amount of hemorrhage 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 under- goes the process of involution. This consists of a diminution in the size of the uterus, and a change in the appear- ance 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. Fig. 143. Muscular fibre cells of the uterus two weeks after par- turition. GENERAL DEVELOPMENT OF THE EMBRYO. The development of certain parts of the body from the blastoderm, has been already casually referred to. The several organs, and systems of organs will now be considered in their order of succession. DEVELOPMENT OF LHE EMBRYO. 393 Development of the Spine, Cranium and Nervous Jystem.—The epiblast as has been already stated, rises up n the form of plates, and encloses the medullary or spinal anal (Fig. 137). Beneath this in the mesoblast is formed he chorda dorsalis, or notochord, and at each side the proto- rertebrse which increase in size and grow up around the Lotochord and form the spine. The spinal canal becomes nlarged anteriorly, corresponding to the brain, and termi- Lates by a pointed extremity. The cranium is developed rom the protovertebrse, surrounding the upper extremity >f the chorda dorsalis. At the same time a growth of ner- vous matter takes place in the interior of the canal. At first he canal has an oval shape on section, and presents an slongated slit, but presently the opposite sides unite in the :entre, forming the gray commissure and lividing it into an anterior and posterior por- tion ; the former becomes the central canal, and die latter forms the posterior fissure. The an- berior fissure is formed by an inward folding of the anterior part. At this stage the cord con- sists chiefly of gray matter. White matter is now developed from the cells of the mesoblast, and covers the outer surface dipping into the bottoms of the fissures to form the com- missures. The anterior bulbous enlargement, or brain, separates into three portions, the cerebral vesicles, anterior, middle and pos- terior, from which the different portions of the encephalon are developed. The anterior, forms the hemispheres and optic thalami, the middle, the corpora quadrigemina, and the pos- terior, the cerebellum and medulla oblongata. At this period the size of the different parts of the encephalon is different from the same organs in tfte adult; e. g. the hemispheres are only slightly larger than the corpora quadrigemina, and the cerebellum is smaller Fig. 144. The spine at an early age showing the anterior dila- tation and proto- vertebrae ; 1, 2, 3, anterior, middle, and posterior ce- rebral vesicles; a, slight flattening of the anterior vesicle; b, proto- vertebrae ; c, lum- bar enlargement; o, optic vesicle (Longet). 394 DEVELOPMENT OF THE EMBRYO. than the medulla oblongata. As development proceeds, however, the relative size of the different parts soon changes, convolutions begin to make their appearance, and the hemispheres are divided by the longitudinal fissure. Development of the Face.—As the cerebral ex- tremity of the foetus becomes developed, it bends forwards upon its axis and forms the cerebral and frontal prominences and four depressions, the cervical fis- sures. Between the fissures are four foldings or arches,called the visceral or 'pharyngeal arches, in which are developed the bones of the face. Between the first pharyngeal arch and the frontal prominences, is the opening of the mouth. The first pharyngeal arch divides into a superior and an inferior protuberance on each side; the latter unites very soon with its fellow of the opposite side to form the lower jaw. The superior protuberances which form the upper jaw unite in the median line, with the fronto-nasal or intermaxillary process. The growth of these parts diminishes the size of the oral cavity; a lamella grows inwards from the superior maxillary tuberosity, joins the one from the opposite side and forms the palatine arch. If from any cause, the superior maxillary and intermaxillary pro- cesses fail to unite with each other, hare-lip or cleft palate, or both, are the result. This serves also to explain why hare-lip is always on either side of the median line, single or double; in the latter case the intermaxillary process which contains the incisor teeth is frequently detached from the superior max- illa, and is adherent to the nose. Cleft palate is caused by a deficiency in the union of the the lamellae which form the palatine arch. The soft palate may be cleft also. The second pharyngeal arch forms the stapes, stapedius muscle, pyramid, styloid process, styloid ligaments and the lesser cornu of the hyoid bone; from the Fig-. 145. Head of a human foetus at the 5th week; 1, frontal prominen- ces ; 2, cerebral pro- minences ; 3, fronto- nasal process; 4 lateral frontal process; 5, eye; 6, superior maxillary process ; 7, lower jaw; 8, ear; (Ecker). DE VELOPMENT OF THE E YE, EAR AND NOSE. third is formed the greater cornu and body of the hyoid bone ; and from the fourth, the soft parts of_the neck. The cervical fissures all disappear in a short time except the first, which forms the meatus auditorius, Eustachian tube and tympanic cavity. Development of the Eye, Ear and Nose.—The eye is formed from the primary optic vesicle, an outgrowth from the first cerebral vesicle (Fig. 145.) It is at first an open cavity communicating by a hollow stalk with the general cerebral cavity, but as development proceeds it is filled up and becomes the optic nerve. The lens is formed by a thickening of the epidermic layer, and is received into a de- pression in the primary optic vesicle. After a time a secondary cavity is formed behind the one for the lens, in which the vitreous humor is secreted. The lens is at first surrounded by a vascular capsule, connected with the arteria centralis retime, and forms the membrana pupillaris. Ves- sels pass into the ball and form the choroid coat. The epi- thelium of the cornea is developed from the epiblast, and the cornea and the sclerotic are developed from the meso- biast. The iris is formed from a projection of the choroid. The pupil is at first closed by the membrana pupillaris, but it disappears in the human foetus about the seventh month. The ear is developed in the form of a vesicle, the primitive auditory vesicle, on the outside of the third cerebral vesicle over the second pharyngeal arch (Fig. 14G, 8). The cavity of the vesicle forms the internal ear, and the auditory nerve is formed from the mesoblast which unites the cerebral with the auditory vesicle. The middle ear and Eustachian tube are formed from the first pharyn- geal fissure, and the tympanum from a membrane stretched across the fissure. The pinna is formed from the soft parts of the first pharyngeal arch, and the ossicles from the second pharyngeal arch. The nose arises from a depression in the epiblast at each side of the fronto-nasal process, the olfactory fossce. These deepen except at the lower part where they 396 REPRODUCTION. lead by the olfactory groove into the cavity of the mouth. After the formation of the palatine arches, this cavity is divided into two parts ; the lower forms the mouth; the upper, divided by a septum, the nose. The olfactory nerve is derived from a prolongation of the anterior cerebral vesicle. Fig. 146. Area vaseulosa of an embryo, ventral surface. 1, Terminal sinus. 2, Omphalo-mesen- fceric vein. 3, Its posterior branch. 4, Heart in the form of an S. 5, Primitive aorta, or posterior vertebral arteries. 6, Omphalo-mesenteric arteries.—Bischoff. Development of the Extremities. — The upper and lower limbs are formed as buds from the anterior and pos- terior part of the embryo, by a projection of the somato- pleure covered by the epiblast. The division of the extremity of these buds into fingers and toes, which have a webbed appearance, takes place at an early period, and soon after, a constriction or groove marks the situation of the wrist-joint. As growth proceeds another groove shows itself,at the elbows DEVELOPMENT OF THE VASCULAR SYSTEM. 397 and knees. In all animals, the anterior extremities precede the formation of the posterior. Development of the Vascular System.—The vascular system assumes three different forms during different periods of life, viz., the vitelline, placental, and complete. The vitel- line circulation commences at a very early period in the chick, and consists of a number of vessels which ramify over the surface external to the embryo, and form a plexus, the “ area vasculosa.” The vessels are formed from the cells of the mesoblast, which become elongated, or branched, unite with each other and become hollowed out to form the capil- lary walls (p. 222). The blood corpuscles are formed from the nuclei of these cells. The function of this structure is to absorb the nutrient material from the vitellus. About this time the heart begins to make its appearance. This organ and the larger blood-vessels are formed on the same plan. Masses of embryonic cells of the splanchnopleure are arranged in the position, form and size of the developing structures; the external layers of cells are converted into the walls of the organs and the internal form the first blood corpuscles (p. 174). The heart may now be seen as a minute red pulsating point, even before the muscular fibres have been formed ; this is the “ punctum saliens" of Harvey. The heart is at first tubular in form, and receives posteriorly the two omphalo-mesenteric veins, and opens anteriorlv into the primitive aorta, which divides into two vesselsj the vertebral arteries. These form a series of arches and give off the two omphalo-mesenteric arteries to the area vasculosa. It then becomes curved or bent upon itself like the letter S or a horse shoe, and partly divided by constrictions into three cavities. The one corresponding with the arterial end, is the bulbus arteriosus; the one at the venous end, the auricle; and the one in the middle is the ventricle, which becomes more rapidly developed than the others. In some animals, Fig. 147. Heart of the chick at the third day of incubation —1, the veins ; 2, the auricle; 3, the ventricle; 4, the bulhus arte- riosus. —Thomp- son. REPRODUCTION. as the Amphibia, this form remains, no other division by septa taking place ; but in the higher animals and man, both auricle and ventricle are subdivided by septa, and the bul- bus arteriosus disappears in the ventricles. In man and the higher animals in which the vitellus is small, the vitelline form of circulation soon disappears, and is replaced by the placental or allantoic circulation. The two omphalo-mesenteric arteries become blended into one artery, and the corresponding veins into one vein. They are called omphalo-mesenteric arteries because they supply in part the “ omphalos” or umbilical vesicle, and partly the mesentery and intestine. After a time the umbilical vesi- cle and its vessels diminish, the mesenteric vessels increase, and the allantois grows out from the posterior part of the intestinal cavity, carrying with it the allantoic or placental vessels. There are two umbilical arteries and at first two corresponding veins, but after a time one of the veins dis- appears, and the whole of the blood is returned from the placenta by one vein. The complete circulation takes the place of the placental circulation, which is abruptly terminated the separation of the placenta at birth. This transition is more abrupt than the preceding; but has been duly provided for by the gradual development of the necessary organs. The blood vessels first commence to form, as previously stated, in the area vasculosa external to the body of the embryo. The first aortic arch is formed by the division of the primitive aorta into two branches, which arch backwards, and, after descending, unite into one vessel in front of the vertebral column (Fig. 148). Other pairs of arches are formed in succession behind the first, to the number of five. These are not all to be seen at the same time, for as some develope, others disappear. In fishes they all persist through life and form the distribution as seen in the gills. In man and the higher animals, the anterior ones disappear and the posterior ones become transformed into the carotids (5 ), DEVELOPMENT OF THE VASCULAR SYSTEM. subclavian (4 ), arch of the aorta, pulmonary artery, ductus arteriosus, and descending aorta (Fig. 148). The veins that first appear are, as already stated, the omphalo-mesenteric which soon unite to form one. Next is formed the two umbilical veins, which return the blood from the placenta, the left enlarging, while the right disappears. When the liver begins to be formed branches pass into that organ* and give origin to the hepatic veins. This organ receives blood from two sources, the portal, and the umbilical veins. The systemic veins are formed from four trunk veins, two above, and two below, which unite into a canal (sinus of Fig. 148. Fig 149. Aortic arches; five pairs are shown, the upper ones disappear, the three lower remain, and represent the carotids (5), the subclavian (4) and arch of the aorta (3). 1, Trunks which spring from the ventricles ; 2, descending aorta, the left (2) is finally obliterated; the ductus arteriosus is seen at the junction of the arch with the descending portion (6). Diagram of the develop- ment of the veins: c, c, cardinal veins ; j, j, jugu- lar veins ; h, hepatic veins; dc, ducts of Cuvier; sv, sinus venosus. Cuvier) on each side, and open into the rudimentary auricle. (Fig. 149). The two above are called the anterior cardinal, or jugular veins, and the two below are called the posterior or inferior cardinal veins. When the umbilical vein is formed, it at first communicates with the sinus of Cuvier, but after the inferior vena cava is developed, it empties into the latter. The auricle now receives blood from the inferior vena cava, and the sinuses of Cuvier which now become the right and left superior vena cava respectively. The left vena cava finally disappears and its 400 REPRODUCTION. orifice is converted into the coronary sinus ; the right, forms the superior vena cava. An anastomosing branch between the anterior jugular veins becomes the left innominate, and the termination of the right jugular the right innominate vein. The inferior cardinal veins return the blood from the Wolffian bodies, vertebral column, and parietes of the trunk. The inferior vena cava is formed about the fifth week, and finally receives the blood from the inferior cardinal, and the crural veins. The upper part of the cardinal veins remains, the right one as the vena azygos major, and the left as the vena azygos minor and superior intercostal. The middle portion disappears, and the lower becomes the hypogastric. Development of the Alimentary Canal and Glands. —The alimentary canal is formed at a very early stage. It is at first closed at each end, by the blastodermic layers, and communicates with the umbilical vesicle. It consists of three parts ; the anterior, which forms the pharynx and oesophagus ; the middle which forms the stomach, intestines, and upper third of the rectum ; and the posterior which forms the middle third of the rectum. The lower end of the rectum and buccal cavity are formed by a depression in the middle and external layers of the blastoderm, and do not communicate with the common cavity till a later date, hence the occasional occurrence of imperforate anus and im- perforate oesophagus. The middle portion of the intestine, is at first a wide groove, which becomes converted into a straight tube, and is gradually separated from the umbilical vesicle. It now becomes divided into the different parts, as the stomach, small intestine, and large intestine, and is sus- pended in the abdomen by the mesentery which attaches it to the spine. The principal glands are the liver, 'pancreas, spleen and salivary glands. The liver is developed from two promi- nences of the blastoderm in the form of hollow cones, which involve the omphalo-mesenteric vein, from Svhich they re- DEVELOPMENT OF RESPIRATORY ORGANS. 401 ceive branches. These prominences are developed into the right and left lobes. This organ is of large size in propor- tion to the body, and secretes a substance which is poured into the intestine, termed the meconium. The gall bladder is developed as a pouch from the hepatic duct. The salivary glands are developed from the epiblast lining the mouth, in the form of simple canals with bud-like processes, sur- rounded with protoplasm and communicating with the mouth. The canal becomes more ramified as development proceeds. The pancreas is developed from the hypoblast lining the intestine, in a similar way, and the spleen is developed from the mesoblast, proceeding from a segment of the peritoneum. Development of the Respiratory Organs. — The lungs first appear as small tubercles in front of the oesoph- agus. They are formed from the hyyoblast of the alimen- tary canal. They at first open into the oesophagus, but, soon a separate tube is formed at their poiut of junction ; this is the trachea. The primary tubercles thus formed next send off secondary branches into the surrounding meso- blast, and these again tertiary ones on which the air cells are formed. The diaphragm appears early, in the ±urm ui a uue mem- brane separating the lungs from the Wolffian bodies, stomach and liver. Fig. 150. a, b, development of the lungs; c, tertiary branches and air cells. Development of the Urino-sexual Organs.—These organs are formed from the mesoblast. The Wolffian body or primitive kidney may be seen as early as the third week. It has a glandular structure, in many respects similar to the kidney, is provided with an excretory duct, and secretes a fluid containing urea which is con- veyed to the bladder. It attains its highest development, about the sixth week ; it then diminishes, to be replaced by 402 REPRODUCTION. the kidney, iby ppdad sanears the end of the third month The duct of the Wolffian body is formed in the mesoblast behind the pleuro-] ericoneal cavity. The duct is first hollowed out, and then the tubes of the Wolffian body begin to form as branches of the duct which terminate in Malpighian bodies. Next a thickening occurs between the Wolffian body and the mesentery, termed the Wolffian ridge or “germ epithelium” from which the testis or the ovary is developed, as the case may be. A groove is now formed internal to the Wolffian duct, called the duct of Muller. These ducts, together wdth the ureter, when formed, open into the urogenital sinus, or termination of the intestinal cavity. The Wolffian ducts re- main in the male, and form the epididymus, vas deferens and ejaculatory duct on each side. A small portion of the Wolffian body remains in the female term- ed the parovarium, while the re- mains of the Wolffian duct which descends to the vagina forms the “ duct of Gsertner.” The ureter is formed in the mesoblast in which the kidney commences to develope, and leads down to the urachus. The kidney is developed from a series of club-shaped mases, in which are formed the calices. It has therefore a lobulated appearance which continues for some time. The supra-renal capsules are developed from the same mass as the kidney, ‘ and are at first much larger. ° Fig. 151. a, kidney; n, ureter ; c, Bladder ; d, urachus ; e, constriction which becomes the urethra; f, Wolffian body; o. Wolffian duct, with its opening below , a’; h, duet of Miiller, united below, from the two sides, into a single tube, j', which presents a single opening, between the openings of the Wolffian ducts; k, ovary or testicle ; n, gubernaculum testis or round ligan ent of the uterus; m, genito-urinary sinus ; n, 0, external genitalia. DEVELOPMENT OF UTERUS AND VAGINA. The bladder is next developed from the urachus; this is a hollow tube which connects the posterior part of the intes- tines 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 upper part becomes obliterated and forms a fibrous cord which extends from the summit of the bladder to the umbilicus. Sometimes, though very rarely, this part remains pervious and permits of the escape of urine at the umbilicus. The testes or ovaries which are formed on the inner side of the Wolffian bodies, soon begin to descend, the former to the scrotum and the latter to the pelvis. This was formerly supposed to be caused by the action of a muscular organ, the gubernaculum testis, but this is not now g nerally supposed to be the case. The means by which it is effected are not known. The testicle in its descent pushes before it a pouch of peritoneum, be- hind which it lies, which ultimately forms the tunica vagi- nalis or serous covering of the testicle. The uterus, Fallopian tubes, and vagina are developed from the ducts of Muller, already described. The union of the two ducts below form the vagina, cervix, and lower portion of the uterus, while the upper portions form the upper part of the uterus and Fallopian tubes. This explains the occurrence of an occasional bicornute condition of the uterus. The external organs of generation are, at an early stage, the same in botli sexes. The urino-genital opening, or sinus, is formed at the same time as the anal cavity, by a reflection of the epiblast inwards. There is first seen a tubercle in front of the sinus, the genital tubercle, which is soon surrounded by twro folds of integument, the genital folds. The tubercle is surmounted by a glans, and is grooved upon the under surface (Fig. 151), yet no distinction of sex can be made out. As development proceeds, the urino- genital sinus in the female remains and communicates with 404 REPRODUCTION. the vagina; the genital tubercle retracts and forms the clitoris, and the foldings of integument are converted into the nymphse and labia majora. In the male, the genital tubercle elongates, the glans is developed, and the margins of the sinus meet on the under surface to enclose the ure- thra. The large cutaneous folds form the scrotum, which receives the testicles about the eighth month. When the urethra fails to close, hypospadias results, and an appear- ance of hermaphroditism is present, which is increased by the retention of the testicles in the abdomen. APPENDIX. METRIC SYSTEM OF WEIGHTS AND MEASURES. Equivalents. Metre 39-37 or 39f inches. Decimetre 3.93 or 11 Centimetre 39 or f n Millimetre (mm) 039 or u Micromillimetre (mmm) 000039 or 11 Gramme 15.43 or 15J- grains. Decigramme 1.54 or h Centigramme 154 or 11 Milligramme 015 or 11 THE METRIC SYSTEM IN MEDICINE. Old Style. Metric. Mi or gr.i equals 06 gms fr6i or 31 II 4 !• f& or %\ II 32 h The decimal line instead of points makes errors impossible. A teaspoon contains 4 gms. ; a tablespoon 20 gms. Fractions of an inch. Metric. Air Cells TV to 3 to .12 mm Blood Corpuscles, Red, 7-i mmm 11 ti White go'oo 8 mmm Canaliculi of Bone i-4 mmm Capillaries, -g-gVir 8 mmm Cartilage Cells, Tlo to 2 55 to 12 mmm Chyle Corpuscles, -j-gV 0 • • 8 tnmm Cilia TT5Vrr to joW 6 to 5 mmm Cones of Retina, xiroso 2 mmm End-bulbs of Krause, 41 mmm AVERAGE SIZES OF VARIOUS HISTOLOGICAL ELEMENTS. 406 APPENDIX. Epithelium, Columnar, 23 132 Structure of 79 Development of 80 Eruption of ” 82 Temperature of the body 244 in disease 244 of animals 244 how produced ” 245 Regulation of 247 Influence of nerves 246 Sense of . ’.. .369 Tendons g0 Attachment of 87 Tesselated epithelium 97 Tests— Xrommers’ 27 Fehling’s liquor test 27 Fermentation 28 Torulse 28 Moore’s 28 Iodine test 25 Gmelin’s bile test 453 Pettenkofer’s 453 Thalaini optici 324 Thirst 131 Thymus gland . 274 Structure of .......!! 274 Function of 275 Thyroid gland ” 275 Structure of 275 Page, Thyroid gland, Function of 276 Tissues ... go Attractive or selective power of.... 224 Tissue cement g3 Tobacco ’ 130 Tongue '.'.'.’.'.’.'.‘.'.'133, 365 Papillae of joe Touch, sense of 366 Transference of nervous impressions... 294 Trifacial nerve 331 Division of 332 Irritation of 332 Trochlear or pathetic nerve 331 True generation 376 Tuber annulare ..... 306 Tubes of Henle 258 Tympanum 353 m Airi.n ..'363 Tympanites 157 U Umbilicus, amniotic 337 Umbilical vesicle 335 rT core •• ••; 260 Secretion of 259 Specific gravity of !.!.!!!" 260 Chemical composition of 261 Urea 261 Uric or lithic acid 2g2 Hippuric acid ’ ’ , 2g3 Creatine 264 Creatinine 264 Salts of 264 Urosacine or urochrome 45, 264 Acid fermentation of ’ 2g5 Alkaline fermentation of . . . . . . 266 Uterus, preparation for ovum 389 Involution of 32 393 Muscular fibre cells of 32’ 392 V Yalvulse Conniventes 109 Vasomotor nerves 219 „ eentre 306 Vasa vasorum 214 Vasa deferentia ''' 492 Veins ’’’ 219 Structure of 219 Valves of ” 220 Circulation in ’ ’ ’ 220 Velocity of circulation in 225 Ventricles of the larynx 341 370 Ventriloquism ’ 374 Vernix Caseosa 421 Vestibule " 339 Vice, solitary ’ ’ 373 Villi of intestine no 158 Structure of ’ 444 Absorption by ''' 435 of chorion ’ 333 Vis ii tergo ” 220 Vis nervosa !!!!.'” 295 Visceral plates ’' 335 Vision, phenomena of ' 354 Circle or field of Angle of 339 Defects of ' . grg Vital elements of the blood ' 433 Vital capacity of the chest 276- 416 INDEX. Page. Vitelline membrane 379 Vitelline spheres 382 Vitreous humor 349 Vocal cords 370 Voice 370 Tones of voice 372 Compass of 373 Modifications 374 Voluntary attention 322 Vomiting, mechanism of 138 Vowels and Consonants 374 W Warm-blooded animals 244 Water 16 Function of 16 Whartonian Jelly 71, 392 White fibrous tissue 60 Appearance and properties of 61 Page. White fibrous tissue, Development of.. 63 White blood corpuscles 173 Amoeboid movements of 58, 173 Function of 196 White substanee of Schwann 281 Will, power of ' 278, 322 Willis, circle of , . 217, 317 Wolffian bodies 401 Y Yawning 238 Yolk 279 Yellow elastic tissue 62 Appearance and properties of 62 Development of 63 Z Zona pelludida 379