UNIVERSITY OF CALIFORNIA MEDICAL CENTER LIBRARY SAN FRANCISCO Gift of Or. Howard L. Mawdsley ANATOMY AND PHYSIOLOGY FOR NURSES THE MACMILLAN COMPANY NEW YORK BOSTON CHICAGO DALLAS ATLANTA SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON BOMBAY CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO TEXT-BOOK OF ANATOMY AND PHYSIOLOGY FOR NURSES BY DIANA CLIFFORD fKIMBER GRADUATE OF BELLEVUE TRAINING SCHOOL^ FORMERLY ASSISTANT SUPERINTENDENT NEW YORK CITY TRAINING SCHOOL FOR NURSES, BLACKWELLS ISLAND, N.Y. ; FORMERLY ASSISTANT SUPERINTENDENT ILLINOIS TRAINING SCHOOL, CHICAGO, ILL. AND CAROLYN E. GRAY, B.Sc.(u c n tS a y ), R.N. FIFTH EDITION, REVISED gorfc THE MACMILLAN COMPANY 1919 f- Q, 1C Att rights 1 ri 1 Q c r -' JL SLf ^ ^ ^ ^ COPYRIGHT, 1893, BY MACMILLAN AND CO. COPYRIGHT, 1902, 1909, 1914, 1918, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published September, 1894, Nortoooti J. S. Cushing Co. Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE TO THE FIFTH EDITION IT is now a quarter of a century since the appearance of the first edition of this text-book which grew out of Miss Kimber's own experience in the classroom and which has always repre- sented the work of a nurse for nurses. Only one who has worked in nurse-training schools can appreciate the peculiar disadvantages under which the nurse instructor works, because of the varying standards of admission, hours of duty, inadequate equipment, meagre libraries, etc. We believe that in nursing, as in medicine, our most helpful books must be produced within the profession because one who has travelled each step of the way, as pupil, instructor, and administrator, has a more complete understanding of the needs of nurses than can possibly be gained in a less intimate participation in the work. In this revision the basic importance of physiology, in the train- ing and education of the nurse, has been constantly borne in mind. This subject must form the groundwork for the study of hygiene, dietetics, materia medica, and all pathological conditions, as well as for the intelligent practice of nursing methods. Enough anatomy is given to make the physiology intelligible, for we must understand the plan or organization of the body before we can appreciate its functioning. The study of physics and chemistry should precede that of anatomy and physiology. When this is not possible, the best compromise is to have chemistry a parallel course. Physiology, being a constantly growing subject, we cannot expect to teach final truth. If this book raises many more questions than it answers, it will have served its purpose, because to arouse interest, stimu- late curiosity and inquiry are the main objects of teaching. In a cultivation of the scientific habit of thought, the laboratory method is invaluable. We do not expect the student to make vi PREFACE TO THE FIFTH EDITION new discoveries, but she can be shown how the discoveries of others have been brought about. Free use should be made of the reference library and this should be adequate and up-to-date. Blackboard drawings are invaluable. Models and charts are useful, but nothing takes the place of the actual specimen which can be handled and dissected. The aim of this book is to describe in as simple a manner as possible the phenomena of life, and the principal conclusions which have been reached as to their interdependence and causes. The gratifying approval which previous editions have received has made it seem unwise to attempt any change in the order of the chapters. This seems of minor importance since every teacher will wish to follow her own method in teaching, taking the systems in such order as seems to her most reasonable. I have had the advantage, as formerly, of the help and advice of many fellow-workers in the training schools, and to them I extend my thanks. I am specially indebted to Caroline E. Stack- pole, M.A., Instructor in Biology, Teachers College, for reading and criticising my manuscript ; to Robert M. Lovett, M.D., of Boston, for valuable assistance with the chapter on muscles ; to Helen L. Redfern, R.N., for assistance with the illustrations, and to Mabelle S. Welsh, R.N., for assistance in proof-reading and for making the index. I am also indebted to the authors whose works I have con- sulted, and to the various publishers who have granted me per- mission to use illustrations from their books. C. E. G. TABLE OF CONTENTS CHAPTER PAGE I. Explanations and Definitions of Some Chemical and Physical Terms 3 II. Definitions. Cavities of the Human Body .... 13 III. Cells, Tissues, Organs, and Systems. Epithelial Tissue. Nerve Tissue 20 IV. Connective Tissues : Areolar, Fibrous, Elastic, Adipose, Reticular, Neuroglia, Cartilage, Bone 44 V. The Skeleton. Classification of Bones ; Divisions of the Skeleton ; Bones of the Cranium ; Bones of the Face ; Bones of the Trunk ; Bones of the Upper Extremities ; Bones of the Lower Extremities 60 VI. Joints or Articulations . .90 VII. Muscular Tissue : Classification ; Functionally Important Skeletal Muscles 97 VIII. Special Membranes and Glands 140 IX. Vascular System : The Blood; The Clotting of Blood ; Lymph 154 X. The Blood Vascular System, and the Lymph Vascular System 173 XI. The Vascular System Continued : Arteries ; Pulmonary Sys- tem; General System; Veins; Supplementary Channel, and Portal System 197 XII. The Vascular System Continued: The General Circulation; Blood Pressure; The Pulse; Lymph; Foetal Circulation 228 XIII. Respiratory System : Nose ; Larynx ; Trachea ; Bronchi ; Lungs. Respiration ; Abnormal Types of Respiration. Modified Respiratory Movements 247 XIV. The Digestive System : Alimentary Canal and Accessory Organs 271 XV. Food. Digestive Processes ; Changes the Food Undergoes in the Mouth, Stomach, Small and Large Intestines; Absorption 304 XVI. General Metabolism ; Metabolism of Carbohydrates ; Metab- olism of Fats ; Metabolism of Proteins. Ductless Glands 334 XVII. Waste Products; Excretory Organs; Description of the Organs Constituting the Urinary System ; Urine . 355 XVIII. The Skin ; Appendages of the Skin. Body Heat ; Regulation of Heat. Variations in Temperature ..... 376 XIX. The Nervous System ... .... 395 XX. Internal and External Senses : Taste, Smell, Hearing, and Sight 429 XXI. The Organs of Generation : Physiology of Reproduction . 463 GLOSSARY 491 INDEX 509 yii ANATOMY AND PHYSIOLOGY FOR NURSES CHAPTER I EXPLANATIONS AND DEFINITIONS OF SOME CHEMICAL AND PHYSICAL TERMS AN intelligent discussion of the various functions of the human body cannot be given without some elementary considerations in the field of chemistry and its intimately related science of physics. Probably the briefest method for presenting the essential points is in the way of definitions with accompanying illustrations, and explanations where necessary. THE PHYSICAL SCIENCES 1. Physics deals with mechanics, heat, light, sound, and elec- tricity, and their relations to matter. 2. Chemistry deals with change in the composition of matter, the energy change involved therein, and the principles controlling chemical change. MATTER 1. Defined. Matter is usually defined as anything that oc- cupies space, and possesses weight, as wood, air, water. 2. Forms in which matter exists. Elements. An element is a substance which cannot be sepa- rated into more simple substances by any means known to science at present. Elements are supposed to be made up of atoms which are alike for the same element and cannot be divided. There are about eighty of these elements, less than half of which are well known. Some of the most common are carbon, iron, sulphur, mercury, and oxygen. Compounds. A compound is a substance which can be sepa- rated into simpler substances. Compounds are supposed to be made up of molecules which are composed of groups of atoms. Molecules are alike for the same compound and can be divided, 3 4 ANATOMY AND PHYSIOLOGY [CHAP. I giving elements or simpler compounds. For example, water is composed of hydrogen and oxygen, each molecule having in it two hydrogen atoms and one oxygen atom (H 2 O) ; when sepa- rated, water gives the two elements hydrogen and oxygen. Again, sugar is composed of hydrogen, carbon, and oxygen, each mole- cule having in it twelve atoms of carbon, twenty-two atoms of hydrogen, and eleven atoms of oxygen (C^H^On) ; when sepa- rated it gives several compounds with simpler molecules, as car- bon dioxide (CO 2 ), water (H 2 O), methane (CH 4 ), etc. Mixtures. A mixture can be made up of either or both ele- ments and compounds. These can often be separated by simple physical means, as filtration or evaporation. Milk is a mixture of several compounds, water, cream, proteins, sugar, and salts. The cream can be separated by allowing the milk to stand, when it will rise to the top, and can be skimmed off. Salt solution is a mixture of the compounds, salt and water. They can be sepa- rated by evaporating the water. Air is a mixture of compounds and elements, carbon dioxide (compound), nitrogen and oxygen (elements). They cannot be separated by any simple means. 3. Matter undergoes changes. Physical change. When matter has been subjected to a change which does not affect the composition of the matter, the change is said to be a physical one only. The following are given by way of illustration : Water can solidify (freeze) or it can vaporize ; whether it exists in the state of a solid, a liquid, or a gas, depends upon the tempera- ture, but the composition in all these states is identical. Sugar melts, but the solid sugar and the liquid sugar are exactly the same in composition ; the change is only one in physical state. Other physical changes besides change in physical state are, change in size, position, magnetic or electric condition, and change in temperature. Chemical change. When matter undergoes a change in com- position, it is said to have undergone a chemical change. The following are illustrations : when an electric current is passed through water, the water is separated into two distinct substances, hydrogen and oxygen. In this case we start with a single com- pound (water) of definite composition, and as a result of the change, obtain two different substances (oxygen and hydrogen). CHAP. I] EXPLANATIONS AND DEFINITIONS 5 Again, in a bar of iron there is nothing but the element iron, but if it is left exposed to the air, it is converted into a red solid which has iron and oxygen in it, the iron having combined with some of the oxygen from the air. The iron and the iron rust are evidently different in composition. ELEMENTS FOUND IN THE BODY The elements found in the body are : Carbon, 13.5 (C) form 97 per cent of total weight of body. Hydrogen, 9.1 (H) Nitrogen, 2.5 (N) Oxygen, 72.0 (0) "Sulphur, (S) Phosphorus, (P) ^Fluorine, (F) Chlorine, (Cl) Iodine, (I) Silicon, (Si) Sodium, (Na) Potassium, (K) Calcium, (Ca) Magnesium, (Mg) Lithium, . (Li) Iron, (Fe) Manganese, (Mn) Copper, (Cu) Lead, (Pb) These elements are not, of course, found uncombined in the body, but rather combined, usually in the form of rather complex- compounds. Protoplasm, for instance, is a compound of carbon, hydrogen, nitrogen, oxygen, and phosphorus. ORGANIC AND INORGANIC COMPOUNDS The distinction between organic and inorganic compounds dates back to an early period, when there was a belief that certain compounds of carbon found in living organisms could only be built up through the agency of a vital force possessed by the organism, which prevented their being synthesized in the chemical laboratory. In distinguishing such they were spoken of as organic compounds. However, when urea, one of these substances, was prepared in 6 ANATOMY AND PHYSIOLOGY [CHAP. I the laboratory, this theory was abandoned, but the distinctive terms organic and inorganic persisted. Under the present classi- fication organic compounds are compounds that contain carbon. Because of the fact that there are numerous carbon compounds and also because many of these can be grouped into classes with well-defined characteristics, the study of the carbon compounds has become a separate phase of the general study of chemistry and is called organ's- chemistry. SOME CHEMICAL TERMS Atom. An atom is the smallest part into which an element can be divided. Atoms are alike for the same element, but different for different elements. Molecule. A molecule is a group of atoms in chemical com- bination. Compounds are made up of multitudes of molecules, all of which are alike for the same compound. Chemical formula. A chemical formula is a simple means for representing the composition of the molecule. Symbols are made use of to represent the elements and small subscript figures to represent the number of atoms of the respective elements. For example, the formula for the sulphuric acid molecule (H 2 SO 4 ) shows it to be made up of two atoms of hydrogen, one atom of sulphur, and four atoms of oxygen; the formula for the sodium chloride molecule (NaCl) shows it to be made up of one atom of sodium and one of chlorine. Chemical equation. A chemical equation is a simple means for representing the matter change that takes place in a chemical action. When carbon burns it combine* w?th oxygen to form carbon dioxide. The equation that expresses this, C tells that during the process of combination, one atom of carbon combines with one molecule of oxygen (composed of two atoms) to give one molecule of carbon dioxide. In the action of sodium hydroxide with hydrochloric acid, water and sodium chloride are formed. The equation to represent this, NaOH -f HCl-*-H 2 O + NaCl, shows that one molecule of sodium hydroxide reacts with one mole- cule of hydrochloric acid to give one molecule of water and nna molecule of sodium chloride. CHAP. I] EXPLANATIONS AND DEFINITIONS 7 Oxide. An oxide is a compound in which another element is in combination with oxygen, as water (H 2 O), carbon dioxide (02), sulphur dioxide (802), and iron oxide (Fe 2 O 3 ). Acid oxide. An acid oxide (or acid anhydride) is an oxide of a non-metal which in combination with water will form an acid, as carbon dioxide and sulphur dioxide, shown in the follow- in S : ~ C0 2 + H 2 0->-H 2 C0 3 (carbonic acid), SO 3 + H 2 O-^H 2 SO 4 (sulphuric acid). Basic oxide. A basic oxide (or basic anhydride) is an oxide of a metal which in combination with water will give a base, as calcium oxide (CaO) and sodium oxide (Na^O), shown in the following : CaO + H 2 O->-Ca(OH) 2 (calcium hydroxide), Na^O + H 2 O>-2 NaOH (sodium hydroxide). Ion. An ion is an atom or group of atoms charged with elec- tricity. Acid. An acid is a substance, containing hydrogen and an acid radical, which dissolved in water or other dissociating liquid produces hydrogen ions. The acid radical must contain a non- metal and may contain oxygen. Examples are hydrochloric acid (HC1), sulphuric acid (H 2 SO 4 ), carbonic acid (H 2 CO 3 ), hydro- bromic acid (HBr), nitric acid (HNO 3 ). Base. A base is a substance which contains a metal and the hydroxyl (OH) radical. Examples are sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH) 2 ). One exception 'to this is ammonium hydroxide (NH 4 OH), which contains the ammonium radical (NH 4 ) instead of a metal. The alkalies are the bases of sodium, potassium, and ammonium ; they give very strong basic action. Both acids and bases give distinctive characteristic actions. Salt. A salt is a substance containing the metal from a base and the acid radical from an acid. Salts may be obtained by the neutralization of an acid by a base, the characteristic hydrogen of the acid combining with the characteristic hydroxyl of the base to form water, leaving the salt as shown in the following : Base + Acid WVater + Salt NaOH + HC1 ->-H 2 + NaCl (sodium chloride), Ca(OH) 2 + H 2 SO 4 -^2H 2 O + CaSO 4 (calcium sulphate). 8 ANATOMY AND PHYSIOLOGY [CHAP. I SOME GENERAL CHEMICAL ACTIONS Oxidation. Oxidation is the process in which the element oxygen combines chemically with another substance, heat being evolved in the process. The heat evolved may not be perceptible unless the oxidation takes place rapidly, as in the burning of gas, wood, coal, etc. If the substance combines slowly with oxygen, heat may be imperceptible; for example, iron allowed to lie in moist air is covered with rust due to the union of the iron and oxygen. Also in our bodies some of the carbon in the cells unites with oxygen, and thus the temperature of the body is kept up. It is for this reason that oxygen must be taken into the body, which is accomplished by the act of breathing. (See page 258.) Neutralization. Neutralization is the process that takes place in the action of an acid with a base. Water and a salt are the products of the reaction. (See Salt.) Hydrolysis. Hydrolysis can be defined as the chemical change that takes place when a compound in its action with water splits into two other compounds, fixing the elements of water in the process. The action of water with some salts, also the formation of glucose and fructose from cane sugar, may be given as ex- amples, as represented in the following reaction equations : - (Sodium carbonate) (Sodium hydroxide) (Carbonic acid) Na 2 C0 3 + 2H 2 O-^2NaOH + H 2 CO 3 , (Cane sugar) (Fructose) (Glucose) C 12 H 22 O n + H 2 -> C 6 H 12 O 6 + C 6 H 12 6 . Hydration. Hydration is the process by which water enters into direct combination with another compound to form a single compound which is called a hydrate. As examples might be given, sulphuric acid (H 2 SO 4 ) as a hydrate of sulphur trioxide (SO 3 ), calcium hydroxide (Ca(OH) 2 ) as a hydrate of calcium oxide (CaO), and crystalline copper sulphate (CuSO 4 . 5 H 2 O) as a hy- drate of anhydrous copper sulphate (CuSO 4 ). The formation of these hydrates in the process of hydration is represented in the following:-- Anhydrous substances Hydrates SO, + II 2 + H 2 S0 4 CaO + II 2 O : Ca(OH) 2 CuSO 4 + 5 H 2 O CuSO 4 . 5 H 2 O. CHAP. I] EXPLANATIONS AND DEFINITIONS 9 The reverse process by which a compound is split up into water and an anhydrous compound is called dehydration. This process is represented in the equations by the reverse arrows. Catalysis. Catalysis is the process by means of which the time reaction of chemical changes can be varied by substances known as catalyzers. Manganese dioxide is a classical example of a catalyzer. For example, to make potassium chlorate yield up its oxygen it is necessary to raise its temperature to about 360 degrees. If, however, a little manganese dioxide is added, the oxygen is released at a much lower temperature, vice 200 degrees. There are many catalyzers that control chemical reactions in the body. ENERGY Energy is ordinarily defined as the power of doing work. Ex- amples of various types of energy are : mechanical energy, heat energy, electrical energy, and chemical energy. These can be transformed from one form to another. To illustrate : (1) elec- trical energy can be converted into energy of motion, as evi- denced in the motor ; (2) electrical energy can be converted into heat energy, as in the electric stove ; (3) mechanical energy of motion can be converted into electrical energy, as in the dynamo ; also, (4) chemical energy can be transformed into heat energy, as is true in the oxidation of food in our bodies. SOME PHYSICAL TERMS Specific gravity. By specific gravity is meant the comparison between the weight of a substance and the weight of an equal volume of some other substance taken as a standard. The stand- ards usually referred to are air for gases, and water for liquids and solids. For instance, the specific gravity (sp. gr.) of carbon dioxide (air standard) is 1.5, meaning that it is 1.5 times as heavy as an equal volume of air. Again the specific gravity of mercury (water standard) is 13.6, meaning that mercury is 13.6 times as heavy as an equal volume of water. The specific gravity of solutions, as a salt solution, will necessarily vary with the concentration. Diffusion. This term in its ordinary use has to do with the tendency of two liquids or two gases of different densities to mix uniformly. Diffusion can take place either when the substances 10 ANATOMY AND PHYSIOLOGY [CHAP. I are simply superimposed, or when they are separated by a mem- brane. The following illustrations may help to make this clear : 1 . When the gases or liquids are not separated by a membrane, (a) If a bottle of hydrogen is inverted over a bottle of chlorine gas, the lighter hydrogen molecules will move down among the chlorine molecules, while the heavier chlorine molecules will move up to mix with the hydrogen molecules, so that the two will even- tually be mixed uniformly. (6) If a layer of water is placed carefully over a layer of sulphuric acid, in such a way that the two do not mix, two distinct layers will be formed with the heavier sulphuric acid at the bottom. The acid molecules will begin to move up and mix with the water molecules, while the water molecules will move down to mix with the sulphuric acid molecules. The action is much slower than with the gases. 2. When the gases or liquids are separated by certain membranes. (c) In the illustration given in (a) if a membrane, permeable to gases/ be stretched over the mouth of the bottle, the gases will mix evenly through it. Also, if a membranous sac of carbon dioxide is placed in a vessel containing oxygen, the two gases will diffuse through the membrane, until the mixture of gases inside and outside is uniform. (d) When a bladder of alcohol is immersed in water, the two liquids will diffuse through the membrane; the water diffusing more rapidly than the alcohol, the bladder will become distended. This subject of diffusion is an important one as the activities which make life possible for each cell are dependent upon it. (See Respiration, Circulation, Metabolism, and Excretion. Pages 258, 184, 334, 362.) The explanation of the process is found in the suppositions of the kinetic theory that : 1. There are spaces between the molecules making up all fluid bodies. 2. Molecules are in rapid motion in straight lines, the motion of molecules of gases being much more rapid and unrestrained than in the case of molecules of liquids. For an understanding of the two forms of diffusion through membranes called osmosis and dialysis, a few definitions are necessary. CHAP. I] EXPLANATIONS AND DEFINITIONS 11 1. Permeable membranes. Permeable membranes allow the passage not only of water molecules but of substances in solution, i.e., salt molecules. If a tumbler be completely divided vertically by a permeable membrane, and two ounces of salt solution placed on one side and four ounces of water placed on the other, it will be found that the water first passes over to the side containing salt solution ; later the salt molecules will pass over to the water, so that eventually the quantity of water and salt will be equal on both sides of the membrane. In other words there will be three ounces of salt solution on each side of the membrane instead of two ounces of salt solution on one side and four ounces of water on the other, which was the condition we started with. 2. Semipermeable membranes. Semipermeable membranes allow the passage of water molecules but not substances in solu- tion. If our glass had been divided by a Semipermeable mem- brane, the water molecules could have passed through, but not the salt. Most of the membranes we have in the body are approxi- mately Semipermeable, i.e., they allow water molecules to pass through readily, and molecules of substances in solution less readily. In such cases the stream of water is to the side of the dissolved substance, but at the same time the molecules of this substance pass to some extent to the other side. 3. Osmotic pressure. In the experiment just described (under Permeable Membranes) it was said that the water passed over to the side of the glass containing salt solution. The old expression was that the salt attracted the water, but in the newer theories the same fact is expressed by saying that the salt in solution exerts a certain osmotic pressure, in consequence of which more water 'flows from the water side to the side of the salt solution than in the reverse direction. As a matter of experi- ment it is found that the osmotic pressure varies with the amount of the substance in solution, or in other words, depends upon the concentration of the solution. 4. Isotonic, Hypertonic, and Hypotonic. These terms are used to express degrees of osmotic pressure or differences in con- centration. For instance, normal salt solution is used to replace blood lost by hemorrhage, because the osmotic pressure of normal salt solution is equal to that of blood, hence it is isotonic or isomotic to the blood, i.e., contains the same amount of salt as the blood. 12 ANATOMY AND PHYSIOLOGY [CHAP. I If the solution contained a higher percentage of salt than the blood, it would be hypertonic, if lower hypotonic. 5. Solution. When a substance disappears in a liquid in such a way as to thoroughly mix with it and be lost to sight as an individual body, the resulting liquid is called a solution. It there- fore requires two substances to make a solution, one the liquid or solvent, and the other the substance dissolved or solute. 6. Osmosis. Osmosis is the passage of solvent molecules through a membrane. 7. Dialysis. Dialysis is the passage of solute molecules through a membrane. 8. Emulsion. An emulsion is a mixture of two immiscible fluids, where one is scattered through the other in the form of finely divided globules. UNIT FOR MEASURING HEAT Inasmuch as heat is a form of energy, it is not as simple an un- dertaking to speak of it in comparative terms as in the case of matter. It is easy for one to visualize five quarts of milk as five times a certain volume that has been taken as a standard and called one quart. So it is also with weights and distances, and the meas- urement of weights, distances, and volumes is a necessary part of our experience. It is quite as urgent that there should be a basis for the comparison of energy values as well as for matter values, else the coal dealer could not place the value of his coal on a basis of its heat-producing qualities, nor could the dietitian plan meals on a basis of the ultimate energy-producing qualities to the individual. We are only conscious of energy as a result of the ef- fect it produces, consequently, if it is to be measured, it must be on this basis. In physiology the unit used for measuring heat is the calorie. Calorie. The calorie (Cal.) is the amount of heat that is neces- sary to raise 1000 grams of water through 1 C. Occasionally a small calorie is used. This small calorie is the amount of heat that is necessary to raise one gram of water through 1 C. It is, there- fore, only jinny a $ large as the calorie. CHAPTER II DEFINITIONS. CAVITIES OF THE HUMAN BODY DEFINITIONS BEFORE taking up the study of anatomy and physiology in de- tail, it is well to consider the definitions of these terms as follows : Anatomy refers to the structure of an organism. Physiology refers to the functions of an organism. Anatomy teaches us what organs a plant or animal has, and how they are arranged with reference to one another. Physiology teaches us the uses to which these organs are put. Anatomy shows what an organ is ; physiology shows what an organ does. Anatomy may be, and usually is, studied upon the dead creature ; physiology can be studied only upon the living creature. The anatomical position. In describing the body, anatomists always consider it as being in the erect position, with the face toward the observer, the arms hanging at the sides, and the palms of the hands turned forward. Surfaces of the body. When the body is in the anatomical position, the front, or surface facing the observer, is named the ventral surface. (See Fig. 1.) The back, or surface directed away from the observer, is named the dorsal surface. (See Fig. 2.) The median line. This refers to an imaginary line drawn through the middle of the body, from the top of the head to the middle of the floor between the feet. The parts nearest this line are described as medial, the parts farthest from this line are de- scribed as lateral. Internal and external. These terms are used to designate within and without the body itself, also within and without the body cavities. Proximal and distal. Proximal is used to describe a position near the head or source of any part. Distal is used to describe a 13 rtrrH wait on irrrtE TOE FOURTH DIGIT OK fOO THIRD DIGIT OR THIRD ._ WCOND DIGIT OR MCOND T FIRST DIGIT OR GREAT DIOITUS DIG1TUS OUARTQft DIGITU8 Tf RTIUS TUSSECUNOU* PRIMUS, HAUUX. POltrx H0t FIG. 1. FRONT VIEW OF A MAN IN THE ANATOMICAL POSITION. On the right lateral half the parts are labelled in English, on the left in Latin. The right upper limb is drawn away from the trunk in order to show the arm more fully than is possible when it hangs perpendicularly. (Gerrish.) 14 MALLEOLU8 EXTERNU9 FIG 2 - BACK VIEW OF A MAN. On the left lateral half the names of the part* are given in English, on the right in Latin. (Gerrisn.) 15 16 ANATOMY AND PHYSIOLOGY [CHAP. II position distant, or farthest away from the head or source of any part. Periphery. This term is used to describe the circumference of a circle, hence in anatomy it means the outside or surface of a body or an organ. THE HUMAN BODY It is necessary to have the clearest possible conception of the main divisions and the positions of the different parts of the body, NASAL CAVITY BUCCAL CAVITY CRANIAL ENLARGEMENT OF THE DORSAL CAVITY DORSAL CAVITY (SPINAL PORTION) BODIES OF VERTE6R/E THORACIC CAVITY DJAPHRAGM ALIMENTARY CANAL ABDOMINAL CAVITY PELVIC CAVITY FIG. 3. DIAGRAMMATIC LONGITUDINAL SECTION OF THE TRUNK ANF> HEAD. The alimentary canal is represented running through the whole length of the ventral cavity. and we shall therefore outline the structure of the body as a whole. It is readily seen that the human body is separable into trunk, head, and limbs ; the trunk and head are cavities, 1 and contain 1 In this connection it is important to emphasize that so-called body cavities are only potential cavities which do not become real ones unless their contents are CHAP. II] CAVITIES 17 the internal organs or viscera, 1 while the limbs are solid, contain no viscera, and are merely appendages of the trunk. Cavities of the body. The trunk and head contain two main cavities, and looking at the body from the outside we should naturally imagine that these two cavities were the cavity of the head and the cavity of the trunk, respectively. If, however, we divide the trunk and head length- wise into two halves, by cutting them through the middle line from before backwards, we find the trunk and head are divided by the bones of the spine into dorsal and ventral cav- ities, and not into upper and lower. (See Fig. 3.) 1. Dorsal cavity. - The dorsal or back cavity is a complete bony cavity, and is formed by the bones of the skull, and the vertebrae (bones of the spine) . It may be sub- divided into : a. The cranial cavity. This cavity contains the brain. b. The spinal canal. This canal contains the spinal cord, which is continuous with the brain. 2. Ventral cavities. The ventral or front cavities are not corn- removed. In life they are completely filled by the organs plus a small quantity of fluid. 1 Viscera is the plural of the Latin word viscus, which means an organ ; hence viscera are organs contained within the body cavities. Example : heart, stomach, etc. Each of these may be called a viscus, C FIG. 4. POSITION OF THE THORACIC AND AB- DOMINAL ORGANS (FRONT VIEW). (Morrow.) 18 ANATOMY AND PHYSIOLOGY [CHAP. II plete bony cavities, part of their walls being formed of muscular and other tissue. a. Orbital cavity. The orbital cavity contains the eye, the optic nerve, the muscles of the eyeball, and the lacrimal apparatus. b. Nasal cavity. The nasal cavity is filled in with the struc- tures forming the nose. c. Buccal cavity. The buccal cavity or mouth contains the tongue, teeth, and salivary glands. d. Thoracic cavity. - The thoracic cavity, or chest, contains the trachea or windpipe, the lungs, oesophagus or gullet, heart, and the great vessels springing from, and entering into, the heart. Diaphragm. - - The diaphragm is a dome- shaped membranous and muscular partition between the thoracic and abdominal cavi- ties. e. Abdominal cavity. -The abdominal cavity contains the stomach, liver, gall-bladder, pancreas, spleen, small and large intestines. /. Pelvic cavity. The pelvic cavity is that portion of the ab- domen lying below an imaginary line drawn across the prominent crests of the hip bones. It is more completely bounded by bony walls than the rest of the abdominal cavity. It is divided by a narrowed bony ring into the large (false), and small (true) pelvis. FIG. 5. POSITION OF THE THORACIC AND AB- DOMINAL ORGANS (REAR VIEW). (Morrow.) CHAP. II] SUMMARY 19 (See Fig. 59.) The small or true pelvis contains the bladder, rectum, and some of the generative organs. The limbs, or extremities, upper and lower, are in pairs, and bear a rough resemblance to one another, the shape of the bones, and the disposition of the muscles in the thigh and arm, leg and forearm, ankle and wrist, foot and hand, being very similar. There is, however, a marked difference between the mobility of the upper and the lower limbs. The shoulder is freely movable, not so the hip. HUMAN BODY Dorsal Cavity Ventral Cavities a. Orbital cavity b. Nasal cavity d. Thoracic cavity SUMMARY a. Cranial cavity Brain. b. Spinal canal Spinal cord. Eye. Optic nerve. Muscles of the eyeball. Lacrimal apparatus, f Structures forming the 1 nose. f Tongue. c. Buccal cavity < Teeth. I Salivary glands. f (Esophagus Trachea. { Lungs Heart. I Blood-vessels. the thoracic Abdominal cavity The Diaphragm separates and abdominal cavities. Stomach Spleen Pancreas. Liver Gall-bladder. Large and small in- testines - - Kidneys (behind the peri- toneum) . 1. Large (false) pelvis. 2. Small (true) pelvis. Bladder Rectum. Some of the genera- tive organs. /. Pelvic cavity CHAPTER III CELLS, TISSUES, ORGANS, AND SYSTEMS. EPITHELIAL TISSUE -NERVE TISSUE FROM the standpoint of the chemist the body is composed of elements. (See page 3.) From the standpoint of the anatomist the body is composed of cells, and they are regarded as the struc- tural units out of which either directly or indirectly it is built. If the substance of any part of the body, i.e., skin, muscle, or blood, is examined with the unaided eye, it appears homogeneous, but if examined with the microscope it is found to be composed of an innumerable number of minute cells. It is helpful to recall that low down in the scale of life we find animals so simple that they are described as consisting of just one cell. These unicellular animals are alive because they are capable of carrying on the biological functions which are essential to life. As we ascend in the scale of life, we find animals that consist of a greater number of cells. The human animal may be properly described as a multicellular animal consisting of an enormous aggregate of cells. It is important to remember that each individual cell that enters into the structure of a multicellular animal is capable of carrying on the biological functions just as the one cell that forms the uni- cellular animal. Hence, all the varied activities of the body are the result of the activities of the cells which compose it, and it is very desirable that we early acquire some definite conception of these tiny ele- mentary bodies. CELLS A cell 1 is a minute portion of living substance called proto- plasm which is sometimes enclosed in a cell- wall. Within the pro- 1 The word cell is from the Latin cella a cavity and was first used by bot- anists to describe plant cells, like those of cork and elder pith, which have cavities in their substance. It is now known that most animal cells, and many plant cells, do not have cavities, so that the name is not especially appropriate, but it is too firmly fixed in our language to be abandoned. 20 CHAP. Ill] CELLS 21 Protoplasm (living) toplasm lies a body of definite rounded form, called the nucleus, and this in turn often contains one or more smaller bodies or nucleoli. Cytoplasm. f Chromatin. Nucleus < . , I Achromatm. Cell { Centrosome. [ Food. Metaplasm (not living) | Wastes. [ Storage Products. Protoplasm. Protoplasm is a general term for living substance. Cytoplasm. That portion of the protoplasm which surrounds the nucleus is given the name cytoplasm. Cytoplasm is therefore a regional name for a portion of the protoplasm. ATTRACTION-SPHERE ENCLOSING TWO CENTROSOMES NUCLEOLUS NUCLEUS VACUOLE PASSIVE BODIES (METAPLASM SUSPENDED IN THE CYTOPLASMIC MESHWORK) FIG. 6. DIAGRAM OF A CELL. (Modified from Wilson.) Nucleus. That portion of the protoplasm inside the nuclear membrane is called the nucleus. It is more solid, differs in chemi- cal composition, and may or may not contain the minute spherical bodies termed nucleoli. In red blood cells no nucleus can be found. It is known, however, that when first formed each has a nucleus though it is lost in the course of development. If an attempt 22 ANATOMY AND PHYSIOLOGY [CHAP. Ill is made to dye the nucleus with chromatin dyes, certain portions will take the dye, other portions will not. The material which can be dyed is called chromatin, the matter which cannot be dyed is called achromatin. Centrosome. An actively multiplying cell contains a minute structure called the centrosome which is associated with the reproductive function. It is found in or near the nucleus, and is usually surrounded by a mass of slightly differentiated cytoplasm called the attraction sphere. Metaplasm. In the mesh work of protoplasm are often sus- pended various passive bodies, such as food granules, pigment bodies, drops of oil, etc. These may represent reserve food mat- ters, or waste matters, and are collectively designated as meta- plasm, or non-living substances. Life activities in cells. Since the body is composed of cells, it follows that all the activities of the body are the result of the activities of the cells. These activities are designated as the biological functions which are essential to life. They may be enumerated as follows : (1) Support. Each cell is afforded support by the cohesiveness of its own structure; by the cell-wall if one exists; if not, then the outer circumference of the protoplasm approximates the function of a membranous support. (2) Respiration. Each cell coming in contact with oxygen absorbs it. Whenever this absorption takes place a certain amount of the cell-contents is burned or oxidized, and as a result of this oxidation heat and other kinds of energy are produced, and car- bon dioxide, which is a waste product, is formed. Thus it will be seen that the real purpose of respiration is to furnish oxygen to each individual cell, and to take from the cell the carbon dioxide which it does not need. (3) Metabolism. Each cell is able to take to itself, and even- tually convert into its own substance, certain materials (foods) that are non-living ; in this way the protoplasm may increase in amount, or, in other words, the cell may grow. The amount of protoplasm is not permanently increased, because only enough protoplasm is added by the process of assimilation to replace that incidentally oxidized. Chemical changes which involve the building up of living material within the cell have received the CHAP. Ill] CELLS 23 general name of anabolic changes, or andbolism; on the other hand, those which involve the breaking down of such material into other and simpler products are known as katabolic changes, or katabolism, while the sum of all the anabolic and katabolic changes which are proceeding within the cell is spoken of as the metabolism of the cell. These chemical changes are always more marked as FOOD ANABOLISM ENERGY (GIVEN OFF BY CARBOHYDRATES FATS EXCESS PROTEINS) EXCRETIONS CARBON DIOXIDE WATER NITROGEN OXYGEN KATABOLISM FIG. 7. DIAGRAM SHOWING PROCESS OF METABOLISM IN A CELL. the activity of the cell is promoted by warmth, electrical or other stimulation, the action of certain drugs, etc. (4) Motion. This is exhibited in two different forms : - (a) Amoeboid movement. This term is derived from the amoeba, a single-celled organism. It consists in the pushing out- ward by the cell of processes, called pseudopodia. These may be retracted or the contents of the cell may flow into them. In this way the cell may change both its shape and position. By a repe- tition of this process the cell may move slowly away from its original situation, so that an actual locomotion takes place. (b) Ciliary movement. --This is the whipping motion pos- sessed by little hair-like processes called cilia, which project from the surface of some epithelial cells. (5) Circulation. This consists in a " streaming " of the proto- plasm, which occurs within the limits of the cell. By this means nutritive material or waste substances may be carried from one portion of the cell to another. 24 ANATOMY AND PHYSIOLOGY [CHAP. Ill FIG. 8. DIAGRAMS TO SHOW THE SEQUENCE OF EVENTS IN MITOSIS. A, resting cell with nucleus (ri) and centrosome (c). B, preparing to divide, two asters (a) near nucleus, each with a centrosome, chromatin being massed into chromosomes. C, centrosomes separating form- ing a spindle between them, nuclear membrane disappearing, chromosomes formed. D, chro- mosomes (ch) lying.in the equator of the spindle. E, chromosomes divided lengthwise into halves. F, chromosomes separating and moving toward the centrosomes. G, chromosomes forming the two nuclei, arid cell body, beginning to divide. H, division complete, two-cell stage ; each cell has the same structure as the one-cell in A. (Modified from Wilson.) (0) Excretion. - Kndi cell is able to discharge and thus get rid of waste substances. (7) Irritability. - - Ir- ritability is that property which enables a cell to respond to external stimuli. Cells vary in regard to their irrita- bility, the most markedly irritable cells in higher animals being those of the nervous system. (8) Cell division. - Like all living organisms, each cell grows, produces other cells, and dies, so that each cell has a life cycle comparable to, but much shorter than, the body itself. As the cells are constantly dying, the need for constant repro- duction is apparent. This reproduction is accom- plished in two ways, (a) simple direct division and (b) indirect division or mitosis which is the almost universal method. (a) In direct division the cell elongates, the nucleus and cytoplasm become constricted in the centre, and the cell divides and forms two cells which soon grow to the size of the original cell. CHAP. Ill] CELLS . 25 (6) In indirect division, or mitosis, the nucleus passes through a series of remarkable changes which are rather complicated. A careful study of Fig. 8 will give the student some idea of these changes. 1 Differences in cells. Cells differ in (1) size, (2) form, (3) chemical composition, and (4) function. (1) As an example of variation in size 2 a voluntary muscle cell is about an inch (25 mm.) long and 3-^ of an inch (0.05 mm.) in diameter. The o processes of a nerve C~~ ^ A Cell may be 3 feet FIG. 9. SIZES OF CELLS. A, voluntary muscle cell a\ magnified in width 200 times and represented as cut metrej Or more off at 6 I Stapes 2 J Hyoid I \ 206 The spine, or vertebral column (sacrum and coccyx included) 26 Sternum and ribs 25 Upper extremities 64 Lower extremities 62 In this enumeration the sesamoid 1 bones, which are found em- bedded in tendons covering the bones of the knee, hand, and foot, are not included. CLASSIFICATION The bones may be divided, according to their shape, into four classes: 1. Long, 2. Short, 3. Flat, and 4. Irregular. Long bones. A long bone consists of a shaft and two extrem- ities. The shaft is formed mainly of compact tissue, this compact 1 Ses'amoid [from the Greek sesamon, a "seed of the sesamum," and eidos, " form," "resemblance "], resembling a grain of sesamum. 60 CHAP. V] THE SKELETON 61 tissue being thickest in the middle, where the bone is most slender and the strain greatest, and it is hollowed out in the interior to form the medullary canal. (See Fig. 27.) The extremities are made up of cancellated tissue with only a thin coating of compact -PARIETAL -TEMPORAL CARPUS METACARPUS FIG. 30. THE HUMAN SKELETON. (Morrow.) substance, and are more or less expanded for greater convenience of mutual connection, and to afford a broad surface for muscular attachment. All long bones are more or less curved, which gives them greater strength. The long bones are as follows : 62 ANATOMY AND PHYSIOLOGY [CHAP. V 2 Clavicle 2 Tibia 2 Humerus 2 Fibula 2 Radius 10 Metacarpals 2 Ulria 10 Metatarsals 2 Femur 56 Phalanges Short bones. The short bones are small pieces of bone ir- regularly shaped. Their texture is spongy throughout, excepting at their surface, where there is a thin crust of compact substance. The short bones are the sixteen bones of the carpus, the fourteen bones of the tarsus, and the two patellae. Flat bones. Where the principal requirement is either exten- sive protection or the provision of broad surfaces for muscular attachment, the bony tissue expands into broad or elongated flat plates which are composed of two thin layers of compact tissue, enclosing between them a variable quantity of cancellous tissue. The flat bones are as follows : - 1 Occipital 2 Lacrimal 2 Parietal 2 Scapula 1 Frontal 1 Sternum 2 Nasal 24 Ribs 1 Vomer 2 Hip bones Irregular bones. The irregular bones are those which, on account of their peculiar shape, cannot be grouped under either of the preceding heads. The irregular bones are as follows : - 24 Vertebrae 2 Malar 1 Sacrum 2 Maxillae 1 Coccyx 1 Mandible 2 Temporal 2 Palate 1 Sphenoid 2 Inferior turbinated 1 Ethmoid 1 Hyoid The bones of the ear are so small that they are described as ossicles and do not fit in any of these groups. Processes and depressions. If the surface of any bone is examined, certain projections and depressions are seen. The pro- jections are called processes. The depressions are called fosses or cavities , and either a qualifying adjective is used to describe them, or a special name given to them. Processes and depressions are classified as : 1. Articular, 2. Non-articular. The articular are provided for the mutual connection of bones to form joints. The CHAP. V] THE SKELETON 63 non-articular serve for the attachment of ligaments and muscles. The following terms are used : Process. Any marked bony prominence. Tuberosity. A large process. Tubercle. A small process. Spinous. A sharp, slender process. Crest. A narrow ridge of bone. Condyle. A rounded or knuckle-like process. Head. A portion supported on a constricted part or neck. Fossa. A depression in or upon a bone. Cavities. The terms sinus l and antrum are applied to cavities within certain bones. Meatus or Canal. A long tube-like passageway. Fissure. A narrow slit. Foramen. A hole or orifice through which blood-vessels, nerves, and ligaments are transmitted. DIVISIONS OF THE SKELETON In taking up the various divisions of the skeleton, we will con- sider it as consisting of f Cranium. 1. Head or skull .... { -, 1 Face. 2. Hyoid. Vertebrae. 3. Trunk Sternum. fc Ribs. 4. Upper extremities. 5. Lower extremities. The head or skull. The head or skull rests upon the spinal column, and is formed by the union of the cranial and facial bones. It is divisible into 1. Cranium, or brain case, and 2. Anterior region, or face. BONES OF THE CRANIUM Occipital 1 Parietal 2 Frontal 1 Temporal 2 Ethmoid 1 Sphenoid 1 1 The term "sinus" is also used in surgery to denote a narrow tract leading from the surface down to a cavity. 8 64 ANATOMY AND PHYSIOLOGY [CHAP. V Occipital bone. It is situated at the back and base of the skull. At birth the bone consists of four parts, which do not FRONTAL WINGOFSPHENOID NASAL LACRIMAL MALAR MAXILLA MANDIBLE PARIETAL TEMPORAL OCCIPITAL MASTOID PROCESS FIG. 31. SIDE VIEW OP THE SKULL. unite into a single bone until the sixth year. The internal sur- face is deeply concave, and presents many eminences and depres- sions for the reception of parts of the brain. There is a large FRONTAL-* LEFT PARIETAL INFERIOR TU RBI NATE MANDIBLE FIG. 32. FRONT VIKW OK THE SKULL. CHAP. V] THE SKELETON 65 hole the foramen magnum in the inferior portion of the bone, for the transmission of the medulla oblongata (the constricted portion of the brain) where it narrows down to join the spinal Cerebral Fossa FIG. 33. OCCIPITAL, BONE. Inner surface. cord. At the sides of the foramen magnum it presents two processes called condyles, which articulate with the first vertebra. Parietal bones. The right and left form by their union the greater part of the sides and roof of the skull. The external sur- face is convex and smooth ; the internal surface is concave, and presents eminences and depressions for lodging the convolutions of the brain, and numerous furrows for the ramifications of arteries which supply the dura mater (membrane which covers the brain) with blood. Frontal bone. It resembles a cockle shell, and not only forms the forehead, but also enters into the formation of the roof of the orbits, and of the nasal cavity. The arch formed by part of the frontal bone over the eye is sharp and prominent, and is known as the supraorbital margin. Just above the supraorbital margins are hollow spaces called the frontal sinuses (see Fig. 40) which are F 66 ANATOMY AND PHYSIOLOGY [CHAP. V filled with air and open into the nose. In the upper and outer angle of each orbit are two depressions called lacrimal fossae for the reception of the glands of the same name, which secrete the tears. At birth the bone consists of two pieces, which afterwards become united along the middle line, by a suture * which runs from Supraorbital Margin Roof of Orbital Cavity Frontal Sinuses FIG. 34. FRONTAL BONE. the vertex of the bone to the root of the nose. This suture usually becomes obliterated within a few years after birth, but it occasion- ally remains throughout life. Temporal bones. The right and left are situated at the sides and base of the skull. They are named temporal from the Latin word tempus, time, as it is on the temples the hair first becomes gray and thin, and thus shows the ravages of time. The temporal bones are divided into three parts the hard, dense portion, called petrous; a thin and expanded scale-like portion, called squamous; and a mastoid portion, which is prolonged down- ward and forms the mastoid process. This process is filled with a number of connected cancellous spaces, containing air, and called mastoid cells. 2 They communicate with the cavity of the middle ear. The condition known as mastoiditis means inflam- mation of the lining of these cells. The internal ear, the essential part of the organ of hearing, is contained in a series of cavities, channelled out of the substance 1 See Figs. 66 and 67. 2 Cells. The student must bear in mind that the word cell is used with two different meanings in anatomy. Histologically speaking, the word "cell" refers to one of the component units of the body, such as an "epithelial cell " or "nerve cell." In connection with the use of the words "mastoid cells" in the text, the word "cells" refers to tiny enclosed hollow chambers. CHAP. V] Till] SKELETON 67 of the petrous portion. Between the squamous and petrous por- tions is a socket, called the glenoid fossa, for the reception of the condyle of the lower jaw. FIG. 35. THE RIGHT TEMPORAL BONE. Outer surface. The dotted lines indicate the lines of suture between squamous, mastoid, and petrous portions. (Gerrish.) Ethmoid bone. It is an exceedingly light cancellous bone that forms part of the orbits, nasal fossae, and base of the cranium. It consists of a horizontal plate, a vertical plate (see Fig. 36), and HORIZONTAL PLATE SHOWING FORAM/NA VERTICAL PLATE LATERAL MASS FIG. 36. ETHMOID BONE. Seen from under surface. two lateral masses. The horizontal plate forms the roof of the nasal fossae, and also closes the anterior part of the base of the 68 ANATOMY AND PHYSIOLOGY [CHAP. V cranium. It is pierced by numerous foramina or holes, 'through which the nerves conveying the sense of smell pass. Descending from the horizontal plate is the vertical plate which helps to form the nasal septum, and on either side the lateral masses help to form the side walls of the nasal fossae. The lateral masses contain a number of thin-walled cavities called the ethmoidal sinuses, which communicate with the nasal fossae. Descend- ing from the horizontal plate on either side of the septum are two processes of very thin, cancellous, bony tissue, named the superior and middle turbinated pro- cesses. (See Fig. 153.) Sphenoid bone. It is situated at the an- terior part of the base of the skull and binds the other cranial bones together. It helps to form the cavities of the cranium, orbits, and nasal fossae. In form it somewhat resembles a bat with extended wings, and is described as consisting of a body, two pairs of wings, and two pterygoid processes. The body is joined to the ethmoid in front and the occipital behind. It contains cavities which are called sphenoidal sinuses. (See Fig. 40.) They communicate with the nasal fossae. THE SKULL AS A WHOLE The cranium is a firm case or covering for the brain. Four of the eight bones which form this bony covering are classed as flat bones. They consist of two layers of compact tissue, the outer one thick and tough, the inner one thinner and more brittle. The cancellated tissue lying between these two layers, or " tables of the skull," is called the diploe. The base of the skull is much thicker FIG. 37. PARIETAL, TEMPORAL, AND SPHENOID BONES. Posterior aspect. 1, body of sphenoid bone; 2, 2, greater wings of sphenoid bone; 3, 3, parietal bones ; 4, 4, mastoid process of temporal bones ; 5, 5, external pterygoid plate ; 6, 6, internal pterygoid plate. (Gould's Dictionary.) CHAP. V] THE SKELETON 69 >. and stronger than the walls and roof; it presents a number of openings for the passage of the cranial nerves, blood-vessels, etc. The bones of the cranium begin to develop at a very early period of foetal life. Thus, before birth the bones at the top and sides of the skull are separated from each other by membranous tissue in which bone is not yet formed, and being then imper- fectly ossified, they are readily moulded, and overlap one an- other more or less during par- turition. The spaces at the angles of the bone occupied by the membranous tissue are termed the fontanelles, so named from the pulsations of the brain, FlG - J 8 - -7 SKULL ?* NEW -*f N CHILD. To show moulding. (Edgar.) which can be seen in some of them and which the early anatomists likened to the rise and fall of water in a fountain. There are six of these fontanelles. Anterior fontanelle. The anterior fontanelle is the largest, and is a lozenge-shaped space between the angles of the two parietal bones and the two seg- ments of the frontal bone. It remains open until the second year, and occasionally persists throughout life. (See Fig. 66.) Posterior fontanelle. - - The posterior fontanelle is much smaller in size, and is a triangu- lar space between the occipital and two parietal bones. This is closed by an extension of the FIG. 39. SKULL OF NEW-BORN CHILD. Ossifying process a few months To show moulding. (Edgar.) after birth. (See Fig. 67.) The other four fontanelles, two on each side of the skull, are placed at the inferior angles of the parietal bones; they are un- important. Small, irregular ossicles called sutural bones (Wor- mian bones) are found in the sutures of the head, chiefly near the fontanelles, and often assist in the closure of the fontanelles. 70 ANATOMY AND PHYSIOLOGY [CHAP. V Sinuses of the head. Four sinuses communicate with each nasal cavity : the frontal, ethmoidal, sphenoidal, and maxillary or antrum of Highmore. The mucous membrane which lines the nose also lines all of these sinuses, and inflammation of this membrane may extend into any of them and cause sinusitis. (See Fig. 97.) BONES OF THE FACE Nasal 2 Vomer 1 Inf. Turbinated 2 Lacrimal 2 Malar 2 Palate 2 Maxillae 2 Mandible . 1 14 Nasal bones. They are two small oblong bones placed side by side at the middle and upper part of the face, forming by their junction " the bridge " of the nose. (See Fig. 31.) Vomer. It is a single bone placed at the lower and back part of the nasal cavity, and forms part of the central septum of the ANTERIOR PALA T.NE GROOVE HARD PALATE FIG. 40. SAGITTAL SECTION OF FACE, A LITTLE TO THE LEFT OF THE MIDDLE LINE, SHOWING THE VOMEK AND ITS RELATIONS. (Gerrish.) nasal fossse. It is thin, and shaped somewhat like a ploughshare, but varies in different individuals, being frequently bent to one or the other side, thus making the nasal chambers of unequal size. CHAP. V] THE SKELETON 71 FIG. 41. LACRIMAL BONE. Inferior turbinated bones. They are situated in the nostril, on the outer wall of each side. Each consists of a layer of thin, cancellous bone, curled upon itself like a scroll; hence its name, " turbinated." They are below the superior and middle turbi- nated processes of the ethmoid bone. Abnormal con- ditions of these bones and the membranes covering them cause some of the more common nasal diseases. (See Fig. 153.) Lacrimal bones. Are the smallest and most fragile bones of the face. They are situated at the front part of the inner wall of the orbit, and somewhat resemble a finger-nail in form, thinness, and size. They are named lacrimal because they contain part of the canal through which the tear duct runs. Malar, or yoke bone. Forms the prominence of the cheek, and part of the outer wall and floor of the orbit. (See Figs. 31 and 32.) A prominent spine of bone projects backward from the body of the malar, and articulates by its free extremity with the cor- responding spine projecting forward from the temporal bone, thus making the two mem- bers of the true arch known as the zygomatic arch. (See Fig. 35.) Palate bones. They are shaped like an " L," and form (1) the back part of the roof of the mouth ; (2) part of the floor and outer wall of the nasal fossa? ; (3) a very small portion of the floor of the orbit. Maxillae, or upper jaw-bones, also known as superior maxillary. The maxillae are two in number (right and left) and are the principal bones of the face. Before birth these bones usually unite to form one bone. When they fail to do so we have the condition known as deft palate. Each bone assists in form- ing (1) part of the floor of the orbit, (2) the floor and outer wall RiOSlTY PTERYGOID FOSSA FIG. 42. THE Two PALATE BONES IN THEIR NATURAL POSITION. Dorsal view. (Gerrisb.) 72 ANATOMY AND PHYSIOLOGY [CHAP. V NASAL PROCESS FIG. 43. THE RIGHT MAXILLA. Outer surface. (Gerrish.) of the nasal fossae, (3) the greater part of the roof of the mouth. That part of the bone which contains the teeth is called the al- veolar process, and is excavated into cavities, varying in depth and size according to the size of the teeth they contain. The body of the bone is hollowed out into a large cavity known as the antrum of Highmore, which opens into the nose. Abnormal conditions of either the nose or teeth may cause an infection of these an tr urns. Mandible, or lower jaw-bone, also known as inferior maxillary. It is the largest and strongest bone of the face. At birth, it consists of two lat- eral halves, which join and form one bone during the first or second year. It serves for the recep- tion of the lower teeth, and undergoes several changes in shape during life, owing mainly (1) to the first and second dentition, (2) to the loss of teeth in the aged, and (3) the subsequent absorption of that part of the bone which contained them. It articulates, by its condyles, with the sockets in the temporal bones, which allows for free movement in mastica- tion. Hyoid bone (os hyoid- m FIG. 45. -THE HYOID BONE. Viewed from eum ) ~ ' ^ an isolated the left and in front. (Gerrish.) U-shaped bone lying in FIG. 44. THE MANDIBLE. Viewed from the right and a little in front. (Gerrish.) CHAP. V] THE SKELETON 73 front of the throat, just above the laryngeal prominence (Adam's apple) . It supports the tongue, and gives attachment to some of its numerous muscles. TRUNK The bones which enter into the formation of the trunk consist of the vertebrae, sternum, and ribs. FIG. 46. THE VERTEBRAL COLUMN. Right lateral view and dorsal view. (Gerrish.) i The vertebral column as a whole. It is formed of a series of bones called vertebrae, and in a man of average height is about twenty-eight inches long. In youth the vertebrae are thirty- 74 ANATOMY AND PHYSIOLOGY [CHAP. V three in number, and according to the position they occupy are named : Cervical, in the neck 7 Thoracic, in the thorax 12 Lumbar, in the loins 5 Sacral, in the pelvis 5 Coccygeal, in the pelvis .... 4 True vertebrae. False vertebrae. Spinons Troccss FIG. 47. A CERVICAL VERTEBRA. The vertebrae in the three upper portions of the spine are separate and movable throughout the whole of life, and are known as true vertebrae. Those found in the sacral and coccygeal regions are, in the adult, firmly united, so as to form two bones, five entering into the upper bone, or sacrum, and four into the terminal bone of the spine, or coccyx. They are known as false ver- tebrae, and on account of their union the number of vertebrae in the adult is twenty-six. The vertebrae. Each vertebra consists of two essential parts, an anterior solid portion or body, and a posterior portion or arch. Each arch has seven processes : four articular, two to con- nect with bone above, two to connect with bone below ; two trans- verse, one at each side, and one spinous process, projecting back- ward. Cervical vertebra. In the cervical region of the vertebral col- umn the bodies of the vertebrae are smaller than in the thoracic, but the arches are larger. The spinous processes are short, and are often cleft in two, or bifid. The transverse processes are pierced by a foramen for the passage of blood-vessels and nerves. The first and second cervical vertebrae differ considerably from the rest. The first, or atlas, so named from supporting the head has practically no body, and may be described as a bony ring divided into two sections by a transverse ligament. The dorsal CHAP. V] THE SKELETON 75 section of this ring contains the spinal cord, and the ventral or front section contains the bony projection which arises from the upper surface of the body of the second cervical vertebra, the axis (epistropheus) . This bony projection, called the odontoid process, forms a pivot, and around this pivot the atlas rotates when the COSTO-TRANS VERSE FORAMEN TRANSVERSE PROCESS. DORSAL SECTION FIG. 48. THE ATLAS. Viewed from above. (Gerrish.) head is turned from side to side, carrying the skull, to which it is firmly articulated, with it. Thoracic vertebra. The bodies of the thoracic vertebrae are larger and stronger than those of the cervical ; and have a facet or demi-facet for articulation with the vertebral end of a rib. Lumbar vertebra . The bodies of the . ODOID p.octss. lumbar vertebra, are the largest and heaviest in the whole Structure of ver- "" 6PINOUS PROCESS. T PROCESS. tebral Column. The FIG. 49. THE Axis (EPISTROPHEUS). j. f ^ Its right side. (Gerrish.) bodies or the ver- tebrae are piled one upon another, forming a strong, solid pillar, for the support of the cranium and trunk, the arches forming a hollow cylinder behind for the protection of the spinal cord. Viewed from the side, it presents four curves which are alternately convex and concave. The two concave ones are called primary curves because they exist in foetal life and are designed for the accom- modation of viscera. The other two are called secondary or compensatory curves because they enable the child to assume the erect attitude. 76 ANATOMY AND PHYSIOLOGY [CHAP. V The different vertebrae are connected (1) by means of the articular processes, (2) by disks of intervertebral fibro-cartilage placed between the vertebral bodies, and (3) by broad thin liga- ments called the ligamenta flava which connect the transverse processes. The spinal curves confer a considerable amount of TRUE RIBS FALSE RIBS FLOATING RIBS FIG. 50. THORAX. springiness and strength upon the spinal column, which would be lacking were it straight, and the elasticity is further increased by the ligamenta flava, and the discs of fibro-cartilage. These discs or pads also mitigate the effects of concussion arising from falls or blows, and allow of a certain amount of motion between CHAP. V] THE SKELETON 77 the vertebrae. The amount of motion permitted is greatest in the cervical region. Abnormal conditions. As a result of injury or disease the normal curves may become exaggerated and are then spoken of as curvatures. Curvatures may be lateral, dorsal, or ventral. It occasionally happens that the arch of one of the vertebras does not develop properly, and as a result the membranes and fluid of the spinal cord will protrude, forming a tumor upon the child's back. This condition is called spina bifida. Sacrum (os sacrum) . The sacrum is formed by the union of the five sacral vertebrae. It is a large triangular bone situated like a wedge between the coxal bones, and is curved upon itself in such a way as to give increased capacity to the pelvic cavity. Coccyx (os coccygis). The coccyx is usually formed of four small segments of bone, and is the most rudimentary part of the vertebral column. INTERCLAVlCULAR NOTCH THORAX FOR THIRD COSTAL CARTILAGE FOR FOURTH COSTAL CARTILAGE FIFTH COSTAL CARTILAGE FOR SIXTH COSTAL CARTILAGE FOR SEVENTH COSTAL CARTILAGE The thorax is an elongated bony cage formed by the ster- num and costal cartilages in front, the twelve ribs on each side, and the bodies of the twelve thoracic vertebras behind. It contains and protects the prin- cipal organs of respiration and circulation. Sternum, or breast bone. It is a flat, narroAv bone about six inches long, situated in the median line in the front of the chest, and may be likened to a short, flat sword. It consists of three portions. The upper part is termed the handle, or manubrium ; the middle and largest piece is termed the body, or gladiolus ; the in- ferior portion is termed the ensiform, or the xiphoid process. On both sides of the upper and middle pieces are notches for the recep- FOR ARTICULATION OF CLAVICLE fOR FIRST COSTAL CARTILAGE FOR SECOND COSTAL CARTILAGE FIG. 51. THE STERNUM. Ventral aspect. (Gerrish.) 78 ANATOMY AND PHYSIOLOGY [CHAP. V tion of the sternal ends of the costal cartilages. The ensiform or xiphoid process is cartilaginous in structure in early life, but is more or less ossified at the upper part in the adult ; it has no ribs attached to it, but affords attachment for some of the abdominal muscles. Ribs (costse). The ribs, twenty-four in number, are situated twelve on each side of the thoracic cavity. They are all con- nected with the thoracic vertebrae at the back, and the first seven pairs are connected with the sternum in front through the intervention of the costal cartilages. These first seven pairs are called, from their attachment, the true ribs. The remaining five pairs are termed false ribs. Of these, the upper three, FIG. 52. THE EIGHTH RIB OF THE RIGHT SIDE. Viewed from behind. (Gerrish.) eighth, ninth, and tenth, are attached in front to the costal cartilages of the next rib above. The two lowest being unattached in front, are termed floating ribs. The convexity of the ribs is turned outward so as to give roundness to the sides of the chest and increase the size of its cavity; each rib slopes downward from its vertebral attach- ment, so that its sternal end is considerably lower than its dorsal, and the lower border is grooved for the accommodation of the intercostal nerves and blood-vessels. The spaces left between the ribs are called the intercostal spaces. BONES OF THE UPPER EXTREMITIES Clavicle (clavicula, or collar bone) ... 2 Scapula (shoulder blade) 2 Humerus (arm) 2 Ulna 2 1 (torearm) 4/64 Radius 2 Carpus (wrist) 16 Metacarpus (palm of hand) 10 Phalanges (fingers) 28, CHAP. V] THE SKELETON 79 Clavicle, or collar bone. It is a long bone, placed horizontally above the thorax. It articulates with the sternum by its inner extremity, which is called the sternal extremity. Its outer or acromial extremity articulates with the scapula. In the female, the clavicle is generally less curved, smoother, shorter, and more FIG. 53. THE RIGHT CLAVICLE. Upper surface. (Gerrish.) slender than in the male. In those persons who perform consider- able manual labor, which brings into constant action the muscles connected with this bone, it acquires considerable bulk. Scapula, or shoulder blade. It is a large, flat bone, triangular in shape, placed between the second and eighth ribs on the back part of the thorax. It is unevenly divided on its dorsal surface Spine Coracoid process Acromion process Glenoid cavity FIG. 54. THE RIGHT SCAPULA, OR SHOULDER BLADE. (Morrow.) 80 ANATOMY AND PHYSIOLOGY [CHAP. V by a very prominent ridge, the spine of the scapula, which termi- nates in a large triangular projection called the acromion process or summit of the shoulder. Below the acromion process, at the head of the shoulder blade, is a shallow socket, the glenoid cavity, which receives the head of the humerus. Humerus, or arm bone. The humerus is the longest bone of the upper limb. The upper extremity of the bone consists of a Anatomical nee Greater tuberosity Condyles FIG. 55. THE LEFT HUMERUS, OR ARM BONE. (Morrow.) tyloid process FIG. 56. THE BONES OF THE RIGHT FOREARM. Anterior view. (Morrow.) rounded head joined to the shaft by a constricted neck, and of two eminences called the larger and smaller tubercles, also known as tuberosities. The head articulates with the glenoid cavity of the scapula. The constricted neck above the tubercles is called the anatomical neck, and that below the tubercles, the surgical neck, because it is so often fractured. The lower extremity of CHAP. V] THE SKELETON 81 the bone is flattened from before backward into a broad articular surface called the trochlea which is divided by a slight ridge so that it ends in two condyles by means of which it articulates with the radius and ulna. Ulna, or elbow bone. It is placed at the inner side (little ringer side) of the forearm, parallel with the radius. Its upper extremity presents for examination two large curved processes and two concave cavities; the larger process forms the head of the elbow, and is called the olecranon process. The smaller process on the front sur- face is termed the coronoid, and the trochlea of the humerus fits into the cavity the great sigmoid cav- ity between these two processes. The lesser sigmoid cav- ity is on the outer side of the coronoid, and receives the head of the radius. The lower extremity of the ulna is of small size and ends in two prominences; the outer one, called the head, articulates with the radius ; the inner one, named the styloid process, serves for the attachment of ligaments from the wrist; but the ulna is excluded from the wrist by a piece of fibro-cartilage. Radius. It is situated on the outer side of the forearm. The upper end is small and rounded, with a shallow depression on its upper surface for articulation with the humerus, and a promi- nent ridge about it, like the head of a nail, by means of which it G THIRD PHALANX FIG. 57. THE BONES OF THE RIGHT HAND. Palmar aspect. (Gerrish.) 82 ANATOMY AND PHYSIOLOGY [CHAP. V rotates within the lesser sigmoid cavity of the ulna. The lower end of the radius is large, and forms the chief part of the wrist. Carpus, or wrist. The wrist joint is composed of eight small bones (ossa carpi) united by ligaments ; they are arranged in two rows, and are closely welded together, yet by the arrangement of their ligaments allow of a certain amount of motion. They afford origin by their palmar surface to most of the short muscles of the thumb and little finger, and are named as follows : 1st row. Scaphoid ... 1 2d row. Trapezium ... 1 Semilunar ... 1 Trapezoid ... 1 Cuneiform ... 1 Os Magnum . . 1 Pisiform ... 1 Unciform ... 1 Metacarpus, or body of hand. Each metacarpus is formed by five bones (ossa metacarpalia) . The bones are curved longi- tudinally, being convex behind, and concave in front. They articulate at their bases with the second row of carpal bones and with each other. The heads of the bones articulate with the bases of the first row of the phalanges. Phalanges, or digits. They are the bones of the fingers, and are fourteen in number in each hand, three for each finger and two for the thumb. The first row articulates with the meta- carpal bones and the second row of phalanges ; the second row, with the first and third ; and the third, with the second row. BONES OF THE LOWER EXTREMITIES Hip bones (ossa coxae or ossa innominata) ... 2 Femur (thigh bone) 2 Patella (knee-cap) 2 Tibia (shin bone) 2 Fibula (calf bone) 2 j leg '. ' Tarsus (ankle, or root of foot) 14 Metatarsus (sole and instep) . 10 Phalanges (toes) 28 , The bones of the lower extremities correspond to a great extent with those of the upper extremities, and bear a rough resemblance to them, but are heavier and more firmly knit together. Hip bone, or os coxa. It is a large, irregularly shaped bone which, with its fellow of the opposite side, forms the sides and CHAP. V] THE SKELETON 83 front wall of the pelvic cavity. In young subjects it consists of three separate parts, and although in the adult these have become united, it is usual to describe the bone as divisible into three por- tions : (1) the ilium (plural ilia), (2) the ischium (plural ischii), (3) the pubis (plural pubes). The ilium is the upper broad and expanded portion which forms the prominence of the hip. The ischium is the lower and strongest portion of the bone, while the pubis is that portion which helps to form the front of the pelvis. Where these three portions of the bone meet and finally anky- lose, is a deep socket, called the acetabulum, into which the head of the femur fits. Other points of special interest to note in the hip bones are : (1) The spinous process formed by the projection of the crest of the ilium in front, which is called the anterior superior spinous process, and which is a well- known and convenient land- . . , . -ii FIG. 58. DEVELOPMENT OF THE HIP mark in making anatomical and BONE. Showing the union of the three Surgical measurements. portions in the acetabulum. (Gerrish.) (2) The largest foramen in the skeleton, known as the thyroid foramen, situated between the ischium and pubis. (3) The symphysis pubis, or pubic articulation, which also serves for a convenient landmark in making measurements. The pelvis. The pelvis, so called from its resemblance to a basin, is stronger and more massively constructed than either the cranial or the thoracic cavity. It is composed of four bones, the two hip bones forming the sides and front, the sacrum and coccyx completing it behind. It is divided by a narrowed bony ring into the large (false), and small (true) pelvis. The narrowed bony ring which is the dividing line is spoken of as the brim of the pelvis, the ilio-pectineal line, and the strait. The large pelvis is all that expanded portion of the pelvis situated above the brim ; it forms an incomplete or false basin. The small pelvis is all that portion situated below the brim. Its cavity is a little wider in every 84 ANATOMY AND PHYSIOLOGY [CHAP. V FIG. 59. FEMALE PELVIS. direction than the brim itself, while the large pelvis is a great deal wider. The small bony pelvis is a basin with incomplete walls of bone, the bottom of which is composed of the softer tissues, muscles, and ligaments. The opening of the small pelvis, i.e., the FIG. 60. MALE PELVIS. CHAP. V] THE SKELETON 85 space just above the brim, is called the inlet, and the opening below is called the inferior strait, or outlet. The female pelvis differs from that of the male in those particu- lars which render it better adapted to pregnancy and parturition. It is more shallow than the male pelvis, but wider in every direc- tion. The inlet and outlet are larger, the bones are lighter and smoother, and the coccyx is more movable. As can be ^&* ^^ ^~~ Head seen by looking at Fig. 59 and Fig. 60 a distinctive anatomical difference is that the sub-pubic angle in a male is less than a right angle, and in the female it is greater than a right angle. Femur, or thigh bone. - It is the longest, and strong- est bone in the skeleton. The upper extremity of the femur, like that of the humerus, consists of a rounded head joined to the shaft by a constricted neck, and of two eminences, called the greater and lesser tro- chanters. The head articu- lates with the cavity in the hip bone, called the acetabulum. The lower extremity of the femur is larger than the upper, is flattened from before back- wards, and divided into two large eminences or condyles by an intervening notch. It articu- lates with the tibia and the patella, or knee-cap. In the erect position it is not vertical, being separated from its fellow by a considerable interval, which corresponds to the entire breadth of the pelvis, but the bone inclines gradually downward and inward, so as to approach its fellow towards its lower part, Condyles FIG. 61. THE RIGHT FEMUR, OR THIGH BONE. Anterior view. (Morrow.) 86 ANATOMY AND PHYSIOLOGY [CHAP. V BASE in order to bring the knee-joint near the line of gravity of the body. The degree of inclination varies in different persons, and is greater in the female than the male, on account of the greater breadth of the pelvis. Patella, or knee-cap. It is the largest sesamoid bone in the body. It is small, flat, triangular in shape, and AP ! EX placed in front of the knee- FIG. 62. THE RIGHT PATELLA. Ventral joint, which it serves to protect. (See Fig. 30.) It articulates with the two condyles of the femur, and is separated from the skin by a bursa. (See page 143.) Tibia, or shin bone. It is situated at the front and inner side of the leg. The upper ex- tremity is large, and expanded into two lateral eminences with concave surfaces, which re- ceive the condyles of the femur. The lower extremity is much smaller than the upper; it is prolonged down- ward on its inner side into a strong process, the inner, or medial, malleolus. It articu- lates with the fibula and one of the bones of the ankle. (In the male, its direction is verti- cal and parallel with the bone of the opposite side; but in the female it has a slightly oblique direction outward, to compensate for the oblique di- rection of the femur inward.) Fibula, or calf bone. It is situated at the outer side of the leg. It is the smaller of Outer malleolus I Extension of leg, flexes the thigh medius Of Tibialis anterior Peroneus tertius Front of leg 1 Flexes the ankle Moving the Foot Tibialis posterior Gastrocnemius Back of leg f Extensor of ankle 1 Flexes knee and extends ankle Soleus [ Extensor of ankle Peroneus. longus Peroneus brevis Outer part of leg | Extensors Psoas magnus. The great loin muscle arises from the last thoracic and all the lumbar vertebrae with the included inter- 126 ANATOMY AND PHYSIOLOGY [CHAP. VII vertebral cartilages. It extends downward and forward, then downward and backward, to its insertion in the small trochanter of the femur. FIG. 90. PSOAS, ILIACUS, AND OBTURATOR EXTERNUS MUSCLES. (Gerrish.) Iliacus. This muscle and its relation to the psoas magnus is well shown in Fig. 90. It arises from the iliac fossa and is inserted partly into the tendon of the psoas and partly into the small trochanter of the femur. Action. The psoas magnus and iliacus act as one muscle to flex the thigh on the pelvis, and rotate the femur outward or ac- cording to some authors, inward. CHAP. VII] SKELETAL MUSCLES 127 FIG. 91. GLUTEUS MAXIMUS OF RIGHT SIDE. (Gerrish.) Glutei muscles. The three gluteal muscles are coarse in tex- ture, and form the chief prominence of the buttocks. Glutens maximus arises from the ilium, sacrum, and coccyx, and is inserted into the great trochanter of the femur. Action. It is a powerful extensor of the hip-joint. It also rotates the femur out- ward, and adducts the thigh. Glutens medius and glutens minimus are under the gluteus maximus and almost entirely covered by it. They arise from the outer surface of the ilium and are inserted into the great trochanter. Action. Abduction of the thigh, and inward rotation. Adductors. The four ad- ductor muscles are called respectively magnus (great), longus (long) , brevis (short) , and gracilis (slender) . They are situated on the inner side of the thigh. They arise from different portions of the pubic bone, and the first three are inserted into the inner side of the femur. The gracilis is inserted into the shaft of the tibia. Action. The magnus adducts and extends the thigh ; the longus and brevis adduct and flex the thigh. The gracilis adducts the thigh and flexes the leg. Sartorius. The sartorius, or tailor's muscle, is a long, ribbon- like muscle situated on the front of the thigh. It crosses the thigh obliquely from its origin in the ilium to its insertion in the tibia. It was formerly supposed to be the muscle principally concerned in producing the posture assumed by the tailor in sitting cross- legged, hence its name. Action. It flexes the hip and knee joints, everts the thigh, and assists in rotation of the tibia. Biceps. The biceps arises by two heads, one from the ischium, and the other from the posterior surface of the femur. It is in- 128 ANATOMY AND PHYSIOLOGY [CHAP. VII serted into the head of the fibula and the outer tubercle of the tibia. Semitendinosu? and Semimembranosus. They arise from the ischium, and are inserted into the upper and inner part of FIG. 92. MUSCLES IN THE DORSUM OF THE RlGHT THIGH. (Gerrish.) FIG. 93. SUPERFICIAL FRONT PART OF THE RIGHT THIGH. (Gerrish.) the tibia. These three muscles, the biceps, semitendinosus, and semimembranosus, cover the back of the thigh, hence are named posterior femoral, or hamstring muscles. CHAP. VII] SKELETAL MUSCLES 129 Action. They flex the knee, rotate the leg, and extend the thigh. Quadriceps. The quadriceps is a four-headed muscle that covers the front of the thigh, and is analogous to the triceps cover- ing the back of the arm. Each head is described as a separate muscle : (1) rectus femoris, (2) vastus externus, (3) vastus in- ternus, (4) vastus intermedius. I GA< FIG. 94. VASTUS INTERMEDIUS OF RIGHT SIDE. (Gerrish.) The rectus femoris arises from the ilium, the other three arise from the femur. They pass downward, and are inserted by one tendon into the tubercle of the tibia. The tendon passes in front of the knee-joint, and the patella is a sesamoid bone developed in it. Action. The quadriceps is the great extensor of the leg ; it FIG. 95. GASTROC- NEMIUS OF RIGHT SIDE. (Gerrish.) 130 ANATOMY AND PHYSIOLOGY [CHAP. VII also flexes the thigh, and antagonizes the action of the hamstring muscles. Gastrocnemius and soleus. The gastrocnemius and soleus form the calf of the leg. The gastrocnemius arises by two heads from the two condyles of the femur. The soleus is in front of the gastrocnemius. It arises from the tibia and fibula. The direc- tion of both is downward, and they are inserted into a common tendon, the tendon of the heel (tendo Achillis), which is the thick- est and strongest tendon in the body, and is inserted into the cal- caneum, or heel bone. Action. The gastrocnemius flexes the knee, extends the ankle, and is responsible for the spring in the gait at the end of a step. The muscle is a powerful one and should be capable of rais- ing about twice the weight of the body. The soleus is a powerful extensor of the ankle. 1 1 Additional muscles included in Summary. CHAP. VII] SUMMARY 131 Muscular tissue Classification Striated f Voluntary Skeletal Non- f Involuntary striated i Visceral Cardiac Striated Involuntary Visceral Characteristics of muscular tissue Function . . . SUMMARY Cells become elongated. Intercellular substance which is at a minimum. Connective tissue supporting framework. Well supplied with nerves and blood-vessels. 1. Striated, voluntary, skeletal. 2. Non-striated, involuntary, visceral. 3. Cardiac. 1. Marked with transverse striae. 2. Under control of will. 3. Attached to skeleton. 4. Composed of bundles of multinuclear elon- gated cells. 5. Reticular tissue framework. 6. Attached to bones, cartilage, ligaments, skin by means of tendons. 7. One muscle connects with another by means of an aponeurosis. 8. Muscles closely covered by sheets of fascia. 9. Deep fascise form annular ligaments in vicin- ity of wrist and ankle. 10. Origin more fixed attachment. 11. Insertion more movable attachment. 1. Not marked with transverse striae. 2. Not under control of will. 3. Found in walls of blood-vessels and viscera. 4. Composed of bundles of elongated cells that contain just one nucleus. 5. Reticular tissue framework. 1. Striated but not distinctly. 2. Not under control of will. 3. Made up of short cells, that contain one nucleus, no sarcolemma. 4. Cells grouped in square bundles. 5. Fine fibrils from cells form a supporting net- work. 6. Reticular tissue framework. 1. Irritability response to a stimulus. 2. Contractility muscle becomes shorter and thicker. 3. Extensibility muscle can be stretched. 4. Elasticity muscle readily returns to original shape. 5. Tonicity mild, sustained contraction. Contraction. On this muscular activity depends. 132 ANATOMY AND PHYSIOLOGY [CHAP. VII Stimuli Varieties of Muscular Movements Nerves Conditions of Con- traction Source of Energy . Varieties Involuntary automatic Cardiac automatic Term used to describe influences which irritate or stimulate. 1. Chemical. 2. Mechanical. 3. Thermal. 4. Electrical. 5. Nervous important one. Voluntary stimuli from central nervous system. Stimuli from nervous system increase or decrease activity. Afferent Carry impulses from periphery to brain, spinal cord, or ganglia. Afferent nerves connected with mus- cles are spoken of as sensory. Efferent Carry impulses to the periphery from brain, spinal cord, or ganglia. Efferent nerves that end in muscles are spoken of as motor. Skeletal muscle contracts quickly, relaxes promptly. Visceral muscle contracts slowly, maintained for some time, fades out slowly. Heart muscle contracts and relaxes unceas- ingly during life. ' Result of series of rhythmic stimuli. Contrac- Latent period . .01 sec. tions Consist of Contraction period .04 sec. Relaxation period .05 sec. Tetanus compound contraction, due to stimuli being received too rapidly to allow for periods of relaxation. Well supplied with blood from which glycogen is obtained and stored. Glycogen represents potential energy. Stimuli transform potential energy to mechanical energy. Oxidation of glycogen and perhaps fat. Carbon dioxide Chemical Change Waste sub- stances Water Lactic acid Fatigue . . Loss of nutritive materials. Accumulation of waste substances, CHAP. VII] SUMMARY 133 eyebrows, wrinkles of * - l-s O _ ^ ,a5 8.3 5 8.3 a 'O O r O o3 r q c3C|F O O Pn PH PH PH PH H 08 ?3 > ^ -o > PH H H i a a -1 J| ||-S -S ^'-5 & : 03*0 03*0 >>' II III I I s 3-3 CQ g S O S ~ ^ Q} j jj-g o3 1 * 3 S b I I ^ I-S t'l' .^ S ^-g^ & o P S S- I' S d & s ^ O o O M cj c^ -J-3 -j_? -1-3 -4-3 ^J 1=3 O 1 *s 1 1 o !. 1 oS -4^> '& 1 X a j-i o a IM O X a 1 1 1 1 ! o p 1 f .2 1 f "| 1 fc | 1 33 1 hH 1 I-H t< ?^ W OQ 1 I-H > O H S (A |l 134 ANATOMY AND PHYSIOLOGY [CHAP. VII O -3.3 C ^ * s 2 I 2 2 ^ Q 1 ,aj LslS s s 5= a -1 s 1111 o - Ijliiifll +a'T3Oc+-OC tf 0^0 ll ^ *s 02 '3 03 02 o^ t g cS 1 id s CD CD 3 3 '-3 3 c 3 o ^ o o5 fee o '55 ' 'o 02 CD It ^^ S fl ^ r-^ 1 ^ W ^ -^ Q K ^J go^"S-J S 6 a 03*3 > .s'l -1 Hf ~ S fH SI rj p^ fl O CD S ?3 c5 ^ a s W Q CQ CO CO CO 1*1 sl s I O PQ og ^'co w r ^ 02 ^C _c' o o CO o 1> . SSI-Si^ -J fe ' oo 3 ' a> T3 a> .-2 8 s .-s Q i a fr si- 03 1 i 1 1 as 1 -la 9 11 . ss 136 ANATOMY AND PHYSIOLOGY [CHAP. VII of ^o t _ i=H 02 LO s' t-i o S o S a a o a o a 1-1- O o O O e * H o **" o 1^1" < <1 02 ^, ^S'g P 1 IsS ^ O .2* 1 S c 3 H hH CHAP. VII] SUMMARY 137 II |l| il sl'fcla g ^ Si's rr> ^ >-^ rrt 03 O .S'53 ., PH fi flj f-^( QJ e-g H a bC 'S^ S 02 O) ^ 02 33 Is I "B,rfi >< O/DSJ Q H S ^ s B.S ^ 'i 03 P fi fl It 11- - ^ ^ J a 03 02 o CO N O >^ fi o fi w f o o a I ^^ l^o^Sg, ^ o w ^^ g p. 4J *o 2 fi -M '-(-= S|1&2 O5 vS ^3 g 02 tS t+_ SUOI.VN.OHJ 8HOX31J saoivxwag 138 ANATOMY AND PHYSIOLOGY [CHAP. VII "x 8 e B.S .S-g -2 ""-^ c3 -a bJQ g -a III ^.^ "5 2 e 2 s exion rotat H Pn 8 IS S^t.i^. *!75 c3 r< +-* fe -*- > li^lll, ^^33.33.5 H < >-. g 03 5 ^> 5 l&iJiJ PL, 2 ^ 02 02 02 02 mill = G fl S C I f t I HH I I O O Hume O> O) ^ i P o3 I 3 O ll O> o "S^ C3 1 um, cyx a 2 2 --111 o "o -S o- a eg c3 g *t *^ o3 -j ^ J3 p ^ Q} J-H t-i " l& a a J3 ri fl ^^ 1J1J.J .still lalalllsii P H H ! lll s s : r 02 ^H 02 fn iff :i- ll -5? -Sl'S-l-a's! ll. f-q pq H OH S 02 I O VH S Did L CHAP. VII] SUMMARY 139 5 -a P t-< o> "9 ^| " s . 11111 ^T3 Q;^ ^ ^.-S^I TEAR DUCTsX UPPER UP OIOAL SINUSES AXILLARY NUSES DDLE EARS MASTOIO CAVITIES EUSTACHIAW TUBES COLON FIG. 97. DIA- GRAM OF THE GASTRO- PULMONARY MUCOUS MEMBRANE, SHOW- ING THE CONTINUITY OF ALL ITS PARTS. (Gerrish.) tends on each side, along the passage to the ear, Eustachian tube, 1 and offsets in the alimentary canal go to line the sal- ivary, pancreatic, and bili- ary ducts, and the gall- bladder. (2) Genito-urinary. - The genito-urinary mu- cous membrane lines the inside of the bladder, and the whole urinary tract from the interior of the kidneys to the meatus urinarius, or orifice of the urethra; in the female it also lines the vagina, uterus, and Fallopian (uterine) tubes. A study of. Figs. 98 and 99 will make this plain. Structure. A mucous membrane is composed of four layers of tissue which occur in the following order : (1) Epithelium. (2) Basement membrane. (3) Corium. (4) Muscularis mucosse. (1) The epithelium is the most constant part of a mucous membrane, being continued over certain re- gions to which the other parts of the membrane 1 Named after Eustachius, a famous anatomist. CHAP. VIII] SPECIAL MEMBRANES AND GLANDS 145 cannot be traced. It may be. scaly and stratified, as in the throat; columnar, as in the intestine; or ciliated, as in the respiratory tract. (2) The basement membrane consists of a layer of flattened cells, and is really part of the corium. (3) The corium of a mucous membrane is composed of either areolar or lymphoid connective tissue. It is generally much thicker than in serous or synovial membranes, and varies much in structure in different parts. FIG. 98. DIAGRAM OF THE FEMALE GENITO-URINARY Mucous MEMBRANE, SHOWING CONTINUITY OF ALL ITS PARTS. (Gerrish.) (4) The muscularis mucosce consists of a thin layer of muscular tissue. The mucous membranes are attached to the parts beneath them by areolar tissue, here named submucous. This differs greatly in quantity as well as in consistency in different parts. The con- nection is in some cases close and firm, as in the cavity of the nose. In other instances, especially in cavities subject to frequent vari- ations in capacity, like the oesophagus and the stomach, it is lax; and when the cavity is narrowed by contraction of its outer coats, the mucous membrane is thrown into folds, or rugce, which dis- appear again when the cavity is distended. In certain parts the mucous membrane forms permanent folds that cannot be effaced, and these project conspicuously into the cavity which it lines. The best-marked example of these folds is seen in the small in- testine, where they are called vahulce conniwntes l (circular folds), i See page 285, 146 ANATOMY AND PHYSIOLOGY [CHAP. VIII which are doubtless provided for increasing the amount of absorbing surface for the products of digestion. In some lo- cations the free surface of mucous membrane contains minute glands, or is covered with papillae, villi, or cilia. Papillae. The papillae are best seen on the tongue ; they are small processes of the corium, mostly of a conical shape, containing blood-vessels and nerves, and covered with epithelium. Villi. The villi are most fully developed on the mucous coat of the small intestine. They are little projections of the mucous membrane, covered with epithelium, containing blood-vessels and lacteals, and are favor- *ljp*** ably arranged for ab- ' sorbing nutritive matters from the intestines. Cilia. For descrip- tion of cilia see page 29. Function of mucous membranes. The func- tion of mucous mem- branes is (1) protection, (2) support of blood- vessels and lymphatics, (3) to furnish a large amount of surface for absorption. FIG. 99. -DIAGRAM OF THE MALE GENITO- (l) . Tt P rotects V URINARY Mucous MEMBRANE SHOWING CoNTi- forming a lining or inside NUITY OF ALL ITS PARTS. (Gerrish.) i ' n ,-, skin for all the passages that communicate with the exterior. These passages are sub- ject to the contact of foreign substances, which are introduced into the body; and waste materials, which are expelled from the body. The mucus which it secretes is a thicker and more sticky fluid than either serum or synovia, and by coating the surface lessens the possibility of irritation from food, waste ma- terials, or secreted substances. The cilia of the respiratory tract also assist in the function of protection. They keep up an inces- sant motion, and thus carry mucus toward the outlet of these passages. Dust and foreign materials usually become entangled in the mucus and are forced out with it. CHAP. VIII] SPECIAL MEMBRANES AND GLANDS 147 (2) The redness of mucous membranes is due to their abun- dant supply of blood. The small blood-vessels which convey blood to the mucous mem- branes divide in the submucous tissue, and send smaller branches into the corium, where they form a network of capillaries just under the basement mem- brane. The lymphatics also form networks in the corium, and com- municate with larger vessels in the sub- mucous tissue below. (3) The modifica- tions of mucous mem- brane, such as the CAPILLARY- COLUMNAR EPITHELIUM CAPILLARY NETWORK LACTEAL VESSEL FIG. 100. AN INTESTINAL VILLUS. nified.) NETWORK (Highly mag- nifiprM valvulse conniventes, 1 and villi, are largely for the purpose of increasing the surface for absorption, and also to enable it to carry more blood-vessels and lymphatics. CUTANEOUS MEMBRANE By this term is indicated the membrane which covers the body and ,is commonly spoken of as skin. It is a complex structure, and has several functions in addition to serving as a protective covering for the deeper tissues lying beneath it. It will be more fully considered in Chapter XVIII. GLANDS A gland is a secreting organ, or an organ which abstracts cer- tain materials from the blood and makes of them a new substance. The simplest form of a gland may consist of just one cell, such as the goblet cells, 2 or may be a mere depression on the surface of a membrane, or may consist of a vast number of secreting recesses. The liver and pancreas are examples of the latter. No matter See Fig. 168. 2 See page 274. 148 ANATOMY AND PHYSIOLOGY [CHAP. VIII what the size or shape may be, all glands have three essential characteristics : (1) epithelial cells which are the active secreting agents, (2) a liberal blood supply from which the material for the secretion is drawn, (3) they are under the direct control of the ner- vous system and secretion is their response to stimulation, just as contraction is the response of a muscle. The usual arrangement is A D c D FIG. 101. DIAGRAM SHOWING DEVELOPMENT OF GLANDS: A, a mere dimple in the surface or a simple tubular gland ; B, enlargement by division or a branched tubular gland ; C, enlargement by dilatation or a saccular gland ; D, a combination of B and C or a branched saccular gland ; E, a compound saccular or a racemose gland ; F, development of method of E ; G, a single tube intricately coiled or a convoluted tubular gland. for the cells to cover the free surface of a basement membrane, a dense network of capillaries to be spread upon its under surface, and nerve fibrils to form a network in contact with the cells. In order to economize space and to provide a more extensive secreting surface, the membrane is generally increased by dipping down and forming variously shaped recesses. (See Fig. 101.) Classification. The secreting glands are of three kinds : 1. Simple. 2. Compound. 3. Ductless. 1. Simple glands. The simple glands are generally tubular or saccular cavities, which open upon the surface by a single duct. Sometimes the tube is so long that it coils upon itself, as in the sweat glands of the skin. 2. Compound glands. In the compound glands the cavities are subdivided into smaller tubular or saccular cavities, opening by small ducts into the main duct, which pours the secretion upon the surface. If composed of many tubes, either straight or convoluted, they are called compound tubular glands ; if com- posed of groups of small sacs, they are called racemose glands. CHAP. VIII] SPECIAL MEMBRANES AND GLANDS 149 3. Ductless glands. This term is applied to a collection of glandular structures that possess no ducts. Whatever secretion or excretion they produce is discharged into the blood, either directly or indirectly by way of the lymphatics. SECRETION A new substance, the product of a gland, elaborated from the blood by cell action, and intended for use in the body, is called a secretion. For purposes of study we may divide the secretions into two groups : (1) External secretions. (2) Internal secretions. External secretions. This term is used to designate those secretions of glandular tissues which are carried to their destina- tion by a duct. All of the digestive fluids saliva, gastric fluid, pancreatic fluid, bile, and intestinal fluid are examples of ex- ternal secretions, because they are carried off from the respective glands in which they are formed by means of ducts. Function. The function of the external secretions is dealt with in connection with the organs which produce them. Internal secretions. This term is used to designate those secretions of glandular tissues which are not carried off to the exterior by a duct, but instead are discharged into the blood or lymph. The conception is that probably all the ductless glands form secretions which are called internal secretions. It has also been shown that not only the ductless glands, but some at least of the typical glands provided with ducts, may give rise to internal secretions. For example, the pancreas forms the pancreatic fluid and discharges it by means of a duct into the small intestine. In addition, it is believed that the pancreas forms an internal se- cretion which passes into the blood. Function. The quick adaptive reactions by which emergencies are met and by which the various bodily activities are coordinated, are functions of the nervous system, but the internal secretions have a great deal to do with internal adjustments. They contain chemical substances called hormones, which are carried from place to place by the blood. A hormone is a substance produced in a 150 ANATOMY AND PHYSIOLOGY [CHAP. VIII definite locality but having its effect elsewhere, perhaps at a great distance. 1 Excretion. An excretion is a secretion, except that the excre- tion is generally formed to be thrown out of the body, whereas the secretion is intended for use in the body. It therefore follows that all excretions are first secretions, and some substances are made use of before they are eliminated. For instance, bile serves several purposes before it is eliminated, so that it is first a secretion and then an excretion. Urine, on the other hand, is a secretion, but is formed only to be eliminated. SUMMARY f Any thin expansion of tissue. Definition { ' , . [ An enveloping or lining tissue. 1. Serous membranes. 2. Sy no vial membranes. 3. Mucous membranes. 4. Cutaneous membranes. Varieties f 1. Endothelium a single layer of flat cells. 12. Serous membranes proper Corium a thin layer of fibrous tissue. Found lining closed cavities or passages that do not communicate with the exterior. They are moistened by serum. Pleurae cover the lungs and line the chest. Pericardium covers the heart and lines the outer fibrous pericar- dium. Peritoneum covers the abdominal and the top of some of the pel- vic organs, lines the abdominal cavity. Heart: Blood-vessels. Lymphatics. Back of eye capsule of Tenon. Lining membrane of the cavity of the central nervous system. Three Classes Lining membrane of the vascular system Lining membrane of cer- tain cavities 1 See Secretin, page 322. CHAP. VIII] SUMMARY 151 en fe D <; o2 cd PQ 2 W y Function Protection < 1. Furnishes a cover or lining Viscera. Vascular system. Certain cavities. 2. Furnishes a secretion serum which acts as a lubricant. Consist of Three Classes Function Protection f 1. Imperfect layer of irregularly shaped cells. 2. Layer of fibrous tissue. f Surround cavities of Articular sy no vial membranes { .. . . [ movable joints. f Form sheaths for Vaginal synovial membranes , Sacs interposed be- tween two sur- faces which move upon each other. Joints. Tendons. Sacs between muscles and bones. Furnishes a secretion synovia which acts as a lubricant. Bursal synovial membranes Furnishes a cover or lining Gastropulmonary Found Lining passages that communicate with the exterior and are protected by mucus. Alimentary canal. Air-passages. Cavities communicating with Two Divisions both alimentary canal and air-passages. f Urinary tract. 1 Generative organs. Stratified. Columnar. Ciliated. 2. Basement membrane, a layer of flat cells. Areolar tissue, or Lymphoid tissue. 4. Muscularis mucosse thin layer of muscular tissue. Genito-urinary Consist of 1. Epithelium 3. Corium 152 ANATOMY AND PHYSIOLOGY [CHAP. VIII Modifications Function / (Esophagus. Rug* - temporary folds ( Stomach Valvulae conniventes permanent folds of mucous membrane found in small intestine. Papillae conical processes of mucous membrane best seen on tongue. Contain blood- vessels and nerves. Villi tiny thread-like projections of the mucous membrane of small intestine. Cilia hair-like processes. Inside skin. Protection Secretion of mucus. Action of cilia. Support for network of blood-vessels. Absorption Various modifications increase the surface. Definition Glands are organs that form secretions. A single cell, or many cells arranged in various ways. Epithelial cells. Structure Classification Essentials A liberal blood-supply. Intimate connection with nervous system. 1. Simple one duct. 2. Compound many ducts. 3. Ductless no duct. Definition Secretions are substances elaborated from the blood by the glands. They are intended to perform some office in the body. External secretions are substances formed by the simple and compound glands and discharged by means of a duct. Internal secretions are substances formed by any kind of gland and discharged into the blood or lymph. External secretions studied later. Essential to many internal ad- Classification Internal secretions Function justments. Stimulate by means of hormones. Excretion A secretion which is eliminated. CHAP. VIII] SUMMARY 153 TABLE OF SECRETIONS AND EXCRETIONS SECRETION SECRETING ORGANS REACTION MAIN PURPOSE Mucus Mucous cells of Alkaline Lubricant and diluent. mucous mem- brane Serum Serous mem- Alkaline Lubricant and diluent. branes Tears Lacrimal glands Alkaline To moisten the conjunctiva. Saliva Salivary glands Alkaline To moisten food and begin the digestion of carbohydrates. Gastric Stomach Acid To begin the digestion of pro- fluid teins. Pancreatic Pancreas Alkaline To digest proteins, fats, and fluid carbohydrates. Succus Intestines Alkaline To stimulate the secretion of entericus pancreatic fluid, also digest proteins, fats, and carbo- hydrates. Bile Liver Alkaline Part of the bile is used in diges- tion and reabsorbed. Part is a true excretion (bile pig- ments) . Milk Mammary glands Alkaline Food. Sebum Sebaceous glands Alkaline To lubricate the skin. of the skin Sweat Sweat-glands of Alkaline Helps to regulate body tem- skin perature. Eliminates water and carbon dioxide. Vaginal Vagina Acid Lubricant, moistens and pro- tects. Urine Kidneys Acid Eliminates water and urea. CHAPTER IX VASCULAR SYSTEM: THE BLOOD; THE CLOTTING OF BLOOD; LYMPH IT is helpful to recall that the body consists of an enormous number of individual cells, and that each cell must be supplied with materials to enable it to carry on its activities, and at the same time it must have the waste materials that are the result of its activities removed. Many cells are far from the source of supplies and the organs of elimination; hence the need of a medium to distribute supplies and collect waste, and the need of a system so that the distribution will be orderly and systematic. These two needs are met by the vascular system, the divisions of which may be outlined as follows : Vascular System . .. ' f Blood. Circulating fluids Lymph [ Blood vascular. S ^ stems 1 Lymph vascular. THE BLOOD Characteristics. The most striking external feature of the blood is its well-known color, which is blood red, approaching to scarlet in the arteries, but of a dark red or crimson tint in the veins. It is a somewhat sticky liquid, a little heavier than water; its specific gravity is about 1.055. It has a peculiar odor, a saltish taste, a slightly alkaline reaction when tested with litmus, and a temperature of about 100 F. (37.8 C.). Quantity of blood. The quantity of blood contained in the body of an adult is estimated to be about -fa of the body weight. This proportion was formerly said to be about -fs, but later ex- periments seem to place the figure at -fa. This, in an individual weighing 160 pounds (80 kilos), would weigh about 8 pounds (4 kilos), or measure 4 quarts (4 litres). 154 CHAP. IX] THE BLOOD 155 Functions of the blood. Blood is commonly spoken of as the nutritive fluid of the body. This is correct, but it is more than a nutritive fluid, as will be seen from the following list of its functions : (1) It serves as a medium for the interchange of gases, e.g., carries oxygen to the cells and carbon dioxide from the cells. (2) It serves as a medium for the interchange of nutritive and waste materials. It carries food to the cells and waste materials from the cells. (3) It serves as a medium for the transmission of internal se- cretions. The presence of these secretions controls the chemical activities of cells. (4) It aids in equalizing the temperature of the body. Blood passing through a tissue which is undergoing lively metabolism will have a higher temperature when it leaves than it had when it entered. This extra temperature will be lost in passing through a tissue that is not so active. In this way an average temperature is maintained. (5) It aids in protecting the body from toxic substances. Composition of the blood. Seen with the naked eye, the blood appears opaque and homogeneous; but when examined with a microscope it is seen to consist of minute, solid particles called cells or corpuscles, floating in a transparent, slightly yellowish fluid called plasma. Red or erythrocytes. Cells or Corpuscles White or leucocytes. d Blood-plates. Plasma Red cells. The red cells are usually described as being cir- cular biconcave discs, with rounded edges. The average size is 3 2*0 o of an inch (0.008 mm.) in diameter. Because of their extremely small size, the red cells do not appear red when viewed singly with a microscope, but merely of a yellowish red tinge, or yellowish green in venous blood. It is only when great numbers of them are gathered together that a distinctly red color is pro- duced. Authorities differ regarding the structure of the red cells. Some describe them as consisting of a colorless, filmy, elastic framework infiltrated in all parts by a red coloring matter termed haemoglobin. 156 ANATOMY AND PHYSIOLOGY [CHAP. IX Others describe them as consisting of a colorless elastic envelope enclosing a solution of haemoglobin. In either case it is correct to consider them as packets of haemoglobin moving passively at the mercy of the blood current. They have no nuclei, are soft, flexible, and elastic, so that they readily squeeze through aper- tures and passages narrower than their own diameters, and im- mediately resume their proper shape. Hcemoglobin. Haemoglobin is a substance which is formed of an iron salt and a protein. In the presence of oxygen it has the power to combine with it to form an unstable compound called oxyhsemoglobin, and in an environment where oxygen is scarce, it gives up this oxygen, and is then known as reduced haemoglobin. Hemolysis or " Laking." - Under certain circumstances haemo- globin may pass out of the red cells into the surrounding fluid. This process is known as hemolysis or " laking " and a few of the ways in which it may be brought about are (1) by adding water to the blood, (2) by adding to it the blood of certain other ani- mals, 1 and (3) by adding to it various toxins such as snake venom or certain products of bacterial activity. Number of red cells. The average number of red cells in a cubic millimetre of healthy blood is given as 5,000,000 for men, and 4,500,000 for women. Pathological conditions may cause a marked diminution in number, and differences have been observed even in health. The number varies with altitude ; temperature ; the constitution, nutrition, and manner of life; with age, being greatest in the foetus and new-born child ; with the time of day, showing a diminution after meals ; in the female menstruation is accompanied by an increase and pregnancy by a decrease. The condition known as anemia may be due to a diminished number of red cells w T hich means a diminished supply of oxygen, and a consequent interference with the processes of metabolism. Function of the red cells. The red cells, or erythrocytes, by virtue of the haemoglobin which they contain, are emphati- cally oxygen carriers. Exposed to the air in the lungs the haemo- globin becomes fully charged with detachable oxygen and is known as oxyhaemoglobin. The red cells carry this oxyhaemoglobin to 1 Before transfusing blood from one human being to another, the blood of the donor is always tested in several ways. The purpose of one test is to make sure that it will not hemolyze the red cells of the recipient. CHAP. IX] THE BLOOD 157 the tissues, where it gives up the loosely engaged oxygen. It is then known as reduced haemoglobin and is ready to be carried to the lungs for a fresh supply. The color of the blood is dependent upon the combination of the haemoglobin with oxygen ; when the haemoglobin has its full complement of oxygen, the blood has a bright red hue; when the amount is decreased, it changes to a dark crimson hue. The scarlet blood is usually found in the ar- teries, and is called arterial ; the dark crimson in the veins, and is called venous blood. Life cycle of the red cells. The red cells like all the cells of the body have a definite tefm of existence. There is every reason to believe that this term of existence is very short, possibly not more than a few days. They originate in the red marrow of the bones. Before entering the blood stream they lose their nuclei, and this of itself suggests that they do not live a great while in the circu- lation. It has been suggested that their destruction takes place in the liver, spleen, or lymph nodes. 1 White cells. The white cells are typical cells containing a nucleus, sometimes even two or three nuclei. They are variable in size, but are somewhat larger than the red cells. Number of white cells. The average number of white cells in a cubic millimetre of healthy blood is from 5000 to 7000. A marked increase in number is designated as leucocytosis , a marked decrease as leucopenia. Leucocytosis 2 occurs under normal conditions, such as digestion, exercise, or cold baths. It also occurs under abnormal conditions, and a knowledge of the variations under pathological conditions is an important aid in diagnosis. 1 Some authors give the weight of man as 70 K., and as 1 K. equals 2.28 Ib. or 1000 gm., this reduced to grams would give 70,000 gm. as the weight of man. We are taught that the blood in the body equals ^ of the body weight. ^V of 70,000 gm. is 3500 gm. In every 100 gm. of blood there are 14 gm. of hematin so that 3500 gm. of blood would contain 3500 divided by 100, multiplied by 14, which equals 490 gm. This means that the body contains 490 gm. of hematin. The destruction products of 48 gm. of hematin are eliminated by the liver daily. Hence, it would take as many days to eliminate 490 gm. as 48 gm. is contained in it. This equals ten days plus, and gives us the approximate life of a red blood cell. According to some authors, the daily loss of pigment is much less, hence the life of the red cells would be much longer. 2 Leucocytosis is found in practically all infectious processes except typhoid and tuberculosis. A leucocytosis is demonstrated by a "blood count," i.e., counting the white blood cells in a given volume of a known dilution of blood, using special pipettes and ruled slides, under the microscope. Any considerable increase, i.e., over 8000, is evidence of a leucocytosis. 158 ANATOMY AND PHYSIOLOGY [CHAP. IX Varieties of white cells. At least five varieties have been studied and described. They are classified under two main groups : (1) Lymphocytes. (2) Leucocytes. The most marked difference is in the" nuclei and in the amount of amoeboid movement exhibited. FIG. 102. VARIETIES OF WHITE CELLS FOUND IN HUMAN BLOOD. When stained with blood stains various kinds of white cells can be distinguished. Five varieties are shown above. A, lymphocyte; B, C, mononuclear leucocytes; D, polynuclear leucocyte ; E, eosinophile leucocyte ; F, mast cell. Each of these groups may be subdivided into two or more sub- groups, and some authorities hold that each variety has some special function, but this has not been proven. Amoeboid movements of white cells. One distinctive property of white cells is their power of making amoeboid movements, which enables them to change their form and escape through the walls of the blood capillaries into the surrounding tissues. This property has earned for them the title of wandering cells and the process is spoken of as migration. It occurs under normal con- ditions, but is vastly accelerated under pathological conditions. Function of the white cells. Many functions are ascribed to the white cells, and many theories are advanced in support of CHAP. IX] THE BLOOD 159 these functions. A few of the most important are (1) they act as protective agents, (2) they aid in the absorption of digested fats and proteins from the intestines, 1 (3) they assist in clotting of the blood. 2 Their function of protection is very important and it has been suggested that it may be accomplished in two ways : (a) By contributing to the formation of antibodies; 3 (b) by virtue of their amoeboid movement they can project irregular pro- cesses which are very sticky, so that the bacteria stick to them, and are ingested by them. This process is called phagocytosis and has earned for them the name of phagocytes. According to some authorities this property depends upon the presence in the plasma of a certain class of antibodies called opsonins 4 which in some way prepares bacteria for ingest ion by the leucocytes. Inflammation. When any of the tissues become inflamed either as the result of injury or infection, the first effect is irritation, followed by an increased supply of blood to the part. If the irri- tation continues or is severe, the flow of blood begins to slacken, and a condition of stasis or engorgement results. The white cells become particularly active and migrate into the infected tissues in large numbers. Some of the blood plasma exudes, and a small number of red cells are forced through the capillary walls. 5 This general condition is described as inflammation, and the symptoms of pain, heat, redness, and swelling are due, (1) to the increased supply of blood, (2) to the engorgement of the blood- vessels, and (3) to the collection of fluid in the tissues, which is spoken of as inflammatory exudate. Under these conditions a death struggle between the leucocytes and bacteria takes place. If the leucocytes are victorious, they not only kill the bacteria but remove every vestige of the struggle, and find their way back to the blood. If the bacteria are victorious, and suppuration en- sues, the leucocytes become pus cells. Also, in the case of a wound, the leucocytes, by virtue of their amoeboid movements, escape from the blood-vessels, accumulate in the region of the wound, and act as barriers against infection. 1 See page 325. a gee page 163. 8 See page 162. 4 From opso'no, I prepare food for. 6 This passive ability of red corpuscles to pass through the capillary walls is called diapedesis. 160 ANATOMY AND PHYSIOLOGY [CHAP. IX Life cycle of the white cells. The white cells like all other cells have a definite term of existence. We do not know the length of this term, or where they are destroyed, except that large num- bers are lost in the battle waged against bacteria, others by hem- orrhage, and others may be converted into granulation tissue. These lost leucocytes are replaced by new leucocytes which re- sult from the division of former leucocytes. This division usually takes place in the lymph nodes and the spleen. Differences between white and red cells. - (1) White cells are larger than red cells, but normally are present in smaller numbers. (2) They have no pigment or haemoglobin, hence are colorless. (3) On account of the property of amoeboid movement their shape varies. (4) They always have a nucleus, sometimes two or three nuclei. (5) There are five varieties that differ in microscopical structure and possibly in function. (6) During circulation they keep close to and even seem to adhere to the walls of the vessels, while the red cells keep in the middle of the stream. (7) By virtue of their amoeboid movement they escape through the walls of the capillaries and are found in the tissue spaces. They are also found in lymph, chyle, and pus. (8) The functions of the white cells are quite different from the function of the red cells. Blood-plates. They are disc-shaped bodies, which vary in size but are always smaller than the red cells. Their origin, fate, and function are still open questions. It is not decided whether they are to be considered as independent cells or as fragments of disintegrated cells. There is considerable evidence to show that they take part in the process of clotting. (See page 163.) Plasma. The ulasma of the blood is of a clear, slightly yel- lowish color. It is a very complex fluid and contains a great variety of substances as might be inferred from its double relation to the cells, serving as a source of nutrition and as a means of re- moving the waste products that result from their functional ac- tivity. It consists of water holding in solution or suspension : CHAP. IX] THE BLOOD 161 Extractives Represent waste products. f Fibrinogen. Proteins | Paraglobulin or serum-globulin. [ Serum-albumin. Sugars. Fats. Urea Uric acid Hippuric acid Creatin Creatinin f Chlorides I Sulphates I Phosphates [ Carbonates f Oxygen. Gases . . . . . . I Nitrogen. [ Carbon dioxide. Internal Secretions Enzymes Inorganic Salts of f Sodium. | Calcium. [ Magnesium. Special Substances Antithrombin. Prothrombin. Epinephrin. Antigens and Antibodies. Proteins of the blood-plasma. Three proteins are usually described as existing in the plasma of circulating blood, i.e., fibrino- gen, paraglobulin, and serum-albumin. The first two of these proteins belong to the group of globulins and hence have many properties in common. Serum-albumin belongs to the group of albumins 2 of which white of egg constitutes another member. Many experiments seem to indicate that fibrinogen may be formed in the liver. When blood is shed fibrinogen is changed to an insoluble protein known as fibrin. 3 The significance of paraglobulin and serum-albumin is obscure. Not long ago they were thought to be formed continually in the cells lining the intestine, and consumed as food by the tissues, but this does not seem so probable since the presence of amino-acids 4 in the blood has been shown. They are now looked upon as 1 This list is by no means complete. For more detailed analysis the student is referred to the standard books on Physiology and Physiological Chemistry. 2 Albumins and globulins give the same general tests ; they are both coagulated by heat, and the chief difference is in their solubilities. ' See page 163. < See page 308. M 162 ANATOMY AND PHYSIOLOGY [CHAP. IX a rather stable and permanent mass, little subject to depletion and hence requiring little renewal. Extractives. Extractives are substances other than proteins that may be extracted from dried blood by special methods. Sugar in the form of glucose is present under normal conditions in the amount of 0.1 to 0.15 per cent. A temporary increase in the amount of sugar may follow the ingestion of a large quantity. Fat is found in the plasma in about the same proportion as sugar. It is much more subject to variation, rising notably after a meal in which there was much fat. Waste products found in the plasma represent the end products resulting from the oxidation of our food. Due to the efficiency of the kidneys, they occur in very small quantities. Salts. The salts found in the blood are derived from the food and from the chemical reactions going on in the body. The most abundant is sodium chloride. Gases. Oxygen, nitrogen, and carbon dioxide gas are found in the blood. Carbon dioxide is the result of oxidation in the tissues, and is found in both arterial and venous blood, but the quantity is greater in venous blood. Internal secretions. The blood serves as a medium to carry internal secretions. (See page 149.) Enzymes. See page 311. Special substances. Antithrombin and prothrombin are con- sidered in connection with the clotting of blood. Epinephrin. It is generally believed that the blood receives a constant supply of epinephrin from the adrenal glands. (See page 345.) Antigens and Antibodies. The term antigen is applied to substances which stimulate the formation of antibodies. The term antibodies includes all defensive substances found in the blood, e.g., agglutinins, opsonins, 'antitoxins, immune bodies, etc. When the body is invaded by pathogenic bacteria, the toxic sub- stances produced by these organisms (antigens) stimulate the tissues to form specific antitoxins (antibodies) which are capable of neutralizing the action of the bacterial toxins. CHAP. IX] THE BLOOD 163 FIG. 103. BOWL OF RECENTLY CLOTTED BLOOD, SHOWING THE WHOLE MASS UNI- FORMLY SOLIDIFIED. (Dalton.) THE CLOTTING OF BLOOD Blood when drawn from the blood-vessels of a living body is perfectly fluid. In a short time it becomes viscid, and this vis- cidity increases rapidly until the whole mass of blood becomes a complete jelly. If the blood in this jelly stage be left untouched in a glass vessel, a few drops of an almost colorless fluid soon make their appearance on the surface of the jelly. Increasing in number and running together, the drops after a while form a superficial layer of pale straw- colored fluid. Later on, similar layers of the same fluid are seen at the sides, and finally at the bottom of the jelly, which, shrunk to a smaller size and of firmer con- sistency, now form a clot, floating in a fluid which is called serum. If a portion of the clot is examined under the microscope, it is seen to consist of a network of fine fibrils, in the meshes of which are entangled the red and some of the white cells of the blood. The fibrils are composed of fibrin, which is essential to the formation of a clot. The formation of insoluble fibrin from soluble fibrinogen is an instance of enzyme action and is comparable to the clotting of milk under the influence of ren- nin. The enzyme which causes the fibrin to form is called thrombin, and exists in the blood in an inactive form called pro- thrombin. Prothrombin may be converted to active thrombin by the action of calcium, but in circulating blood this is prevented by another enzyme called antithrombin. This antithrombin must be neutralized to permit the calcium to react with pro- thrombin to form thrombin, which in turn reacts with the fibrino- gen to form fibrin. One theory is that this neutralizing or thromboplastic 1 substance is furnished by the blood-plates, leu- FIG. 104. BOWL OF CLOTTED BLOOD AFTER TWELVE HOURS, SHOW- ING THE CLOT CON- TRACTED AND FLOATING IN THE FLUID SERUM. (Dalton.) 1 Various preparations of thromboplastic material are obtainable, and are in use to check hemorrhage. Some are applied externally to a bleeding surface such 164 ANATOMY AND PHYSIOLOGY [CHAP. IX cocytes, and cells of the tissues over which the blood flows when it escapes from the blood-vessels. This may be represented in diagrammatic form as follows : Cellular elements of blood and tissues >thromboplastic substance. Thromboplastic substance neutralizes antithrombin. Prothrombin + calcium >thrombin. Thrombin + fibrinogen = clot. Value of clotting. This property is of very great importance in the arrest of hemorrhage. The clot formed closes the openings of wounded vessels, and the procedures used to check hemorrhage are directed toward hastening the formation of a clot, and stimu- lating the blood-vessels to contract so that a smaller-sized clot will be sufficient. The clotting power of the blood differs in different individuals and in rare cases is so slight that the most trivial operation involv- ing hemorrhage is attended with great danger. This condition is known as hemorrhagic diathesis or hemophilia. Conditions affecting clotting. Clotting is hastened by : - (1) A relatively high temperature, e.g., the use of hot towels to check bleeding from the stump of an amputated limb ; the use of hot douches to check postpartum hemorrhage. (2) Contact with any foreign substance, or rough surface such as gauze. (3) Injury to the walls of the blood-vessels. (4) Rest. If blood is contained in a dish agitation hastens the process of clotting, because like the first three conditions it favors the formation of thromboplastic substance. Clotting is hindered by : (1) A very low temperature. Cold hinders the formation of a clot but is often used to check hemorrhage, because it stimulates the blood-vessels to contract. (2) Contact with the lining of the heart and blood-vessels. (3) The addition of strong acids or alkalies, neutral salts, oil or other viscid substances, certain organic ferments, or a large quantity of water. (4) Absence of calcium salts. as is left after an operation for removal of tonsils ; or injected into the tissues, and one, i.e., cephalin-protein, is introduced directly into the blood-vessels. CHAP. IX] THE BLOOD 165 (5) Absence of fibrinogen. (6) Removal of fibrin. If fresh blood, before it has time to clot, be whipped with a bundle of twigs, the fibrin will form on the twigs, and if the whipping of the blood be continued until after the fibrin has been deposited on the twigs, the blood left in the vessel will be found to have lost the power of clotting. Such blood is called defibrinated. Why blood does not clot within the blood-vessels. In ac- cordance with the theory of clotting which we have considered, blood does not clot within the blood-vessels because of the presence of antithrombin. Intravascular clotting. It is well known that clots occasionally form within the blood-vessels. The most frequent causes are : (1) When the internal coat of a blood-vessel is injured, as for instance by a ligature, the endothelial cells are altered and may act as a foreign substance. If in addition there is a stasis of blood at this point, disintegration of the blood-plates and white cells may result in the formation of thrombin and a clot. (2) Any foreign material, even air, that is introduced into the blood and not absorbed, may stimulate the formation of thrombin and a clot. Thrombus and embolus. A clot which forms inside a blood- vessel is called a thrombus. A thrombus may be broken up and disappear, but the danger is that it' may be carried to some point in an important vessel where it acts as a wedge, blocks circulation, and may cause instant death. A thrombus that becomes dis- lodged from its place of formation is called an embolus. Regeneration of the blood after hemorrhage. A large portion of the total amount of blood in the body may be lost suddenly by hemorrhage without producing a fatal result. It is probable that a healthy individual may recover from the loss of as much as three per cent of the body weight, provided the lost blood is at once replaced by a solution having the same degree of concentra- tion (i.e., isotonic) and containing one or more of the important salts of the blood. Physiological saline solution, i.e., sodium chloride 0.7 to 0.9 per cent, fulfills these conditions, and is usually introduced directly into a vein. This operation is called intra- venous infusion, and the benefits derived from it are : 166 ANATOMY AND PHYSIOLOGY [CHAP. IX (1) The heart-beat is increased, because it must make stronger contractions to propel the extra fluid. (2) The volume of the circulating fluid is sufficiently increased to maintain normal conditions of pressure and velocity. (3) The red cells are kept in rapid circulation and thus loss of oxygen to the tissues is prevented. (4) The tissue cells are provided with water and thus protected from the bad effects that would follow the withdrawal of water. Plasma is regenerated with some rapidity (probably within a few hours) but it may take days or even weeks before the number of red cells and the quantity of -haemoglobin is replaced. LYMPH Lymph is a colorless liquid found in the lymph-vessels and in all the tissue-spaces of the body. It is slightly alkaline, has a salty taste, and no odor. When examined with the microscope, it is seen to consist of a clear liquid with white cells floating in it. In composition it resembles the blood-plasma, as indicated in the following table : - BLOOD LYMPH Specific gravity about 1.055 Contains red cells Contains white cells Contains blood-plates A high content of proteins A low content of waste products Normally clots quickly and firmly Specific gravity about 1.015 Does not contain red cells (normally) Contains white cells Does not contain blood-plates A low content of proteins A higher content of waste products Clots slowly and does not form a firm clot Sources of lymph. By the action of physical and chemical pro- cesses, the details of which are not entirely understood, the plasma of the blood makes its way through the thin walls of the capil- laries into such spaces as exist between the cells forming the tissues. Some physiologists claim that the combined action of the physical processes of filtration, diffusion and osmosis, is sufficient to account for the formation of lymph. Others claim that in ad- dition it is necessary to assume an active secretory process on the CHAP. IX] THE LYMPH 167 part of the endothelial cells composing the capillary walls. This plasma plus the leucocytes that have left the vessels by migration make up the lymph. Besides this the lymph that fills the lacteals of the intestinal villi absorbs some of the products of digestion, especially the fats. The portion of the lymph that has absorbed the fats is milky in appearance, and is called chyle. The lymph, broadly speak- ing, is dilute blood-plasma minus its red cells. The chyle is lymph plus a very large quantity of minutely divided fat. Functions of the lymph. The lymph bathes all portions of the body not reached by the blood. It delivers to the cells the material each cell needs to maintain its functional activity, and picks up and returns to the blood the products of this activity, which products may be simple waste, or matters capable of being made use of by some other tissue. There is thus a continual in- terchange going on between the blood and the lymph. This interchange is effected by means of osmosis and dialysis. Osmosis and dialysis. The lymph becomes altered by the metabolic changes of the tissues which it bathes, and we have two different fluids, separated by the moist membrane which forms the walls of the blood-vessels, the lymph in the tissues outside the walls of the capillaries and the blood inside the capillary walls. Some of the constituents of the lymph pass into the blood, while some of the constituents of the blood pass into the lymph, by the processes of osmosis and dialysis. 1 In consequence of the different wants and wastes of different tissues at different times, both the lymph and blood must vary in composition in different parts of the body. But the loss and gain is so fairly balanced that the average composition is pretty con- stantly maintained. The chyle, or lymph of digestion, absorbs nutrient materials (mostly fat) from the intestines and pours this food into the blood current, to be distributed to all parts of the body. 1 See page 12. 168 ANATOMY AND PHYSIOLOGY [CHAP. IX Vascular System Circulating Fluids Systems Blood Description Functions Composition with SUMMARY r Blood. I Lymph. f Blood vascular. I Lymph vascular. ~ , f Bright red in arteries. Color [ Dark red in veins. Sticky fluid. Specific gravity, about 1.055. Alkaline reaction when tested litmus. Temperature, 100 F. Peculiar odor. Salty taste. ^ of the body weight. Serves as a medium for the interchange of gases. Serves as a medium for the interchange of nutritive and waste materials. Serves as a medium for the transmission of internal secretions. Aids in equalizing the temperature of the body. Aids in protecting the body from toxic substances. Cells f Red, or erythrocytes. (minute, solid < White, or leucocytes. particles) Plasma, transparent, slightly yellowish fluid. [ Blood-plates. Water, 90%. Proteins. Extractives. Inorganic salts. Gases. Internal secretions. Enzymes. Special substances. Red Cells Description Number Biconcave discs in. in diameter. Packets of hemoglobin { Have no nuclei. Soft, flexible, and elastic. Cubic milli- metre of blood [ Protein. 5,000,000 for men. 4,500,000 for women. Number varies, even in health. Pathological conditions may cause decrease. CHAP. IX] SUMMARY 169 Red Cells Function Life Cycle Description Number Varieties Functions Life Cycle Oxygen carriers. Color due to oxygen in combination with haemo- globin. Originate in red marrow of bones. Lose their nuclei before being forced into the circulation, which suggests that their term of existence is short. f Liver. Disintegrate probably in | Spleen. [ Lymph nodes. Typical cells Masses of protoplasm. Nucleus (sometimes two or three nuclei) . No cell-wall. Variable in size, but larger than red cells. 5000 to 7000. Marked increase = leucocytosis. Marked decrease = leucopenia. Cubic milli- metre of blood 1. Lymphocytes. 2. Mononuclear leucocytes. 3. Polynuclear leucocytes. 4. Eosinophile leucocytes. 5. Mast cells. 1 Protective f ( By contributin g to the J- . JT1 Ul/cL- 1/1 V t/ I / , p j i i j formation of antibodies. [ (6) By process of phagocytosis. 2. Aid in absorption of fats and proteins. 3. Assist in clotting of blood. New leucocytes formed in lymph nodes and spleen. (1) Battles against bacteria. (2) Hemorrhage. (3) Formation of granula- tion tissue. Numbers lost in f Irritation resulting from injury or infection. Engorgement of blood-vessels. Migration of .white blood-cells. Diapedesis of red blood-cells. Exudation of plasma. f Pain. Heat. I Redness. I Swelling. Symptoms 170 ANATOMY AND PHYSIOLOGY [CHAP. IX Inflam- mation Result (a) Resolution White blood-cells eat up bacteria, clear up debris, and return to blood. (6) Suppuration -- Bacteria destroy white blood-cells and tissue cells, and form pus. Plasma. Red cells. White cells. Tissue cells. (c) Pus consists of - . f dead. Bacteria \ r . ( living. Toxins produced bacteria. by Dif- ferences between white and red cells Blood- plates 1. Size and number. 2. Color. 3. Property of amoeboid movement and shape. 4. Nucleus or nuclei. 5. Varieties. 6. Location during circulation. 7. Migration. Found in other fluids. 8. Functions. Description Plasma Disc-shaped bodies, vary in size, always smaller than red cells. Origin, fate, and function are open questions. May assist in clotting of blood. j obscure. )duces the fibrin of clotted Normally present, .1% to 0.15%. May be increased after inges-- tion of large amount. Derived from food. Amount subject to wide varia- tions. Represent waste products, re- sult of oxidation of food. Normally present in small quantities. Water, 90%. Serum-albumin Proteins Paraglobulin Fibrinogen pr blood. Sugar Fats Extractives Urea Uric acid Hippuric acid Creatin Creatinin CHAP. IX] SUMMARY 171 Inorganic Salts Chlorides Sulphates Phosphates Carbonates j Sodium Calcium < Magnesium De c a f r Oxygen. c Gases Nitrogen. Carbon dioxide. Found in both venous blood. Plasma arterial and Enzymes Special Substances with Clotting from our food, and also result from chemical reactions in our bodies. Oxygen. Nitrogen. Carbon dioxide. Found in botl venous blood. Internal Secretions See page 149. Substances produced by living cells which act by catalysis. Antithrombin j function in connection Prothrombin 1 clotting of blood. Epinephrin active principle of internal secf e- tion of adrenal glands. Antigens substances which stimulate the tissues to form antibodies. Antibodies defensive substances found in the blood. Water. Mineral salts. White cells. Albumin. Fibrin formed from fibrinogen. Cells, red and white. Cellular elements of blood and tissues > thromboplastic sub- stance. Thromboplastic substance neu- tralizes antithrombin. Prothrombin + calcium > throm- bin. Thrombin+ fibrinogen > clot. Checks hemorrhage. Condition of blood that lacks clotting power. ( A temperature higher than that of body. Contact with any rough surfaces. Contact with foreign substances. Injury to the walls of the vessels. . Rest. {A very low temperature. Contact with lining of the heart and blood- vessels. Description Serum Clot Process < Value . Hemophilia Hastened by 172 ANATOMY AND PHYSIOLOGY [CHAP. IX Clotting . . \ Hindered by Regeneration of blood after hemorrhage Intravenous Infusion Addition of strong acids, alkalies, neutral salts, oils, certain ferments, water. Absence of calcium salts. Absence of fibrinogen. Removal of fibrin. (Defibrinated blood.) Circulating blood contains antithrombin. Injury to internal coat of blood-vessels. Any foreign material that will stimulate clotting. Name given to clot which forms inside vessel. A thrombus that has become dislodged from place of formation. [ If immediate ill effects are counteracted by intravenous infusion, plasma is regenerated rapidly, red cells within a few days or weeks. Theory to account for rare occur- rence Intravascular Clotting Causes . . Thrombus Embolus Lymph Definition Benefits Description Sources . Function . Chyle . . . Injection of physiological saline solution directly into vein. 1. Heart stimulant. 2. Increases volume of circulating fluid. 3. Red cells kept circulating, and oxygen supply kept up as far as possible. 4. Tissue cells provided with water. Colorless liquid. Alkaline reaction when tested with lit- mus. Salty taste. No odor. Consists of blood plasma plus leucocytes. Specific gravity about 1.015. Contains a low content of proteins. Contains a high content of waste products. Clots slowly, does not form a firm clot. Filtration. Physical processes of Diffusion. Osmosis. Active secretory process on part of en- dothelial cells. Lymph acts as middleman between the blood and the tissues. Carries nourishment from blood to tissues. Carries waste from tissues to blood. Dependent upon osmosis and dialysis. Lymph plus nutrient material, mostly fats. CHAPTER X THE BLOOD VASCULAR SYSTEM, AND THE LYMPH VASCULAR SYSTEM BLOOD VASCULAR SYSTEM THE blood is the internal medium on which the cells live. It is contained in branched tubes named blood-vessels. It is driven along these tubes by the action of the heart, which is a hollow mus- cular organ placed in the centre of the vascular system. One set of vessels the arteries conducts the blood out from the heart and distributes it to the different parts of the body, whilst other vessels the wins bring it back to the heart again. The blood from the arteries gets into the veins by passing through a network of fine tubes which connect the two, and which are named, on account of their small size, the capillary (i.e., hair-like) vessels. f Heart. Blood Vascular I Arteries small arteries are named arterioles. System | Capillaries. Veins small veins are named venules. HEART The heart is a hollow, muscular organ, situated in the thorax between the lungs, and above the central depression of the dia- phragm. It is about the size of the closed fist, shaped like a blunt cone, and so suspended by the great vessels that the broader end or base is directed upward, backward, and to the right. The pointed end or apex points downward, forward, and to the left. As placed in the body, it has a very oblique position, and the right side is almost in front of the left. The impulse of the heart against the chest wall is felt in the space between the fifth and sixth ribs, a little below and to the inner side of the left nipple. 173 174 ANATOMY AND PHYSIOLOGY [CHAP. X FIG. 105. HEART in situ (Dalton, in Flint, "On the Heart"). 1, 2, 3, 4, 5, intercostal spaces ; vertical line, median line ; triangle, superficial cardiac region ; X on the fourth rib, nipple. Myocardium. The main substance of the heart is composed of muscular tissue and is called myocardium. (See page 100.) The arrangement of the muscles is very intricate ; they run transversely, lon- gitudinally, obliquely, and in the apex take a spiral turn or twist. Between the muscles is a certain amount of reticular tissue, with numerous blood-ves- sels and lymphatics, and, in some parts, nerves and ganglia. There is also a considerable amount of atj co u ecte( i chiefly at ^ base of the heart, FIG. 106. - ANTERIOR VIEW OF HEART, DISSECTED, AFTER LONG BOILING, TO SHOW THE SUPERFICIAL MUSCLES. (Quain.) beneath the pericardium. CHAP. X] THE HEART 175 Pericardium. The heart is covered by a membranous sac called the pericardium (around the heart). It consists of two parts : (1) an external fibrous portion, and (2) an internal serous portion. (1) The external fibrous pericardium is composed of white fibrous tissue, and is attached by its upper surface to the large BRONCHIAL TUBES FIG. 107. THE PULMONARY ARTERY AND AORTA. The front part of the right lung has been removed, and the pulmonary vessels and the bronchial tubes are thus exposed. Note the artery marked "brach.-ceph." It is also named the innominate. (See page 203.) (Gerrish.) blood-vessels which emerge from the heart. It covers these vessels for about an inch and a half (3.8 cm.) and blends with their sheaths. The lower border is firmly adherent to the diaphragm, and the front surface is attached to the sternum by means of fibrous bands. (2) The internal or serous portion of the pericardium is a completely closed sac ; it envelops the heart and lines the fibrous 176 ANATOMY AND PHYSIOLOGY [CHAP. X pericardium. The heart, however, is not within the cavity of the closed sac. (See Fig. 108.) That portion of the serous peri- cardium which lines and is closely adherent to the heart is called the visceral portion (viscus, organ) ; the remaining part of the serous pericardium, namely, that which lines the fibrous pericardium, is known as the parietal por- tion (paries, a wall) . The cavity of the serous peri- FIG. 108. DIAGRAM OF THE HEART AND ,. . .. SEROUS PERICARDIUM. A shows heart and CardlUHl Contains a Small pericardium lying separately B shows the q uant ity of SCrOUS liquid, pericardium invagmated by the heart. V. P. ^ shows visceral layer that clings close to the heart Its Opposed SUrf aCCS are muscle. P. P. shows parietal layer that lines > i > IJ.IT i the fibrous pericardium. P. C, pericardial &*** by endothelmm and cavity which in actual conditions is a very nar- are very smooth and row space filled with pericardial fluid. polished. As the opposing surfaces, owing to the constant contractions of the heart, are continually sliding one upon the other, they are admirably constructed to protect the heart from any loss of power by friction. Endocardium. The interior of the heart is lined by a smooth, delicate membrane, called the endocardium. This pavement membrane (endothelium) lines all the cavities of the heart, and is continued into the blood-vessels, forming their innermost coat. The cavities of the heart. The heart is divided from the base to the apex, by a fixed partition, into a right and left half, fre- quently called right and left heart. The two sides of the heart have no communication with each other after birth. The right side always contains venous, and the left side arterial, blood. Each half is subdivided into two cavities, the upper, called auricle (atrium) ; the lower, ventricle (ventriculum) . If we examine these cavities, we notice that the muscular walls of the auricles are much thinner than those of the ventricles, and the wall of the left ventricle is thicker than that of the right (the proportion being as 3 to 1). This difference in bulk is to be accounted for, as we shall see later on, by the greater amount of work the ventricles, as compared with the auricles, have to do. These cavities com- municate with one another by means of constricted openings, the CHAP. X] THE HEART 177 auriculo-ventricular orifices, which are strengthened by fibrous rings and protected by valves. Important orifices of the heart. Eight large blood-vessels are connected with the heart. These eight orifices plus the two between the auricles and ventricles, make a total of ten. RIGHT PULMO NARY VEINS 1 Left pulmonary veins Left auricular appendix Anterior coro- nary vessels Dart pointing to aortic opening Cavity of left ventricle Base of anterior columna? carnese (Anterior columnse carnese cut in two and lifted up and back External flap of mitral valve FIG. 109. LEFT AURICLE AND VENTRICLE, THE HIND WALL OF EACH HAVING BEEN REMOVED. The columnae carneae are muscle columns which project from nearly the whole of the inner surface of the ventricles. Some of them give origin to the papillary muscles. (Gerrish.) On the right side of the heart, the superior and inferior vena cava empty into the auricle, and the pulmonary artery leaves the ventricle. On the left side of the heart, four pulmonary veins empty into the auricle, and the aorta leaves the ventricle. There are some smaller openings to receive blood directly from the heart sub- stance, and before birth there is an opening between the right and 178 ANATOMY AND PHYSIOLOGY [CHAP. X left auricle called the foramen ovale. Normally this closes as soon as the infant breathes. Valves of the heart. The auriculo-ventricular orifices and the openings into the aorta and pulmonary artery are guarded by valves. The tricuspid valve. The valve guarding the right auriculo-ventricular opening is composed of three irregular-shaped flaps, or cusps, and hence is named tricuspid. The flaps are mainly formed of fibrous tissue covered by endocardium. At their bases they are continuous with one another, and form a ring-shaped membrane around the margin of the auricular opening : their pointed ends are directed downward, and are attached by cords, the chordce tendinece, to FIG. 110. CROSS-SECTION THROUGH BOTH VENTRICLES, SHOWING THE SHAPE or THEIR CAVITIES AND THE RELATIVE THICKNESS OF THEIR WALLS. (Gerrish.) FIG. 111. VALVES OP THE HEART AND GREAT ARTERIES, VIEWED FROM ABOVE, THE AURICLES HAVING BEEN REMOVED. (Gerrish.) little muscular pillars, the papillary muscles, provided in the in- terior of the ventricles for this purpose. The bicuspid valve. The valve guarding the left auricular opening consists of only two flaps or cusps, and is named the bi- CHAP. X] . THE HEART 179 cuspid, or mitral valve. It is attached in the same manner as the tricuspid valve, which it closely resembles in structure, except that it is much stronger and thicker in all its parts. Function. These valves oppose no obstacle to the passage of the blood from the auricles into the ventricles because the free edges of the flaps are pointed in the direction of the blood cur- rent ; but any flow forced backward gets between the flaps and the wall of the ventricle, and drives the flaps upward, until, meeting at their edges, they unite and form a complete transverse partition between the ventricle and auricle. Being retained by the chordse tendinese, the expanded flaps of the valve resist any pressure of the blood which might otherwise force them to open into the auricle ; at the same time the papillary muscles, to which the chordae tendinese are attached, contract and shorten and thus keep them taut. Semilunar valves. The valves between the ventricles and arteries are called the semilunar valves (aortic and pulmonary). OPENING OF RIGHT SINUS OF 1 OPENING OF LEFT CORONARY ARTERY VALSALVA /|\ CORONARY ARTERY = _ (LEFT POSTERIOR ANTERIOR: < "^W^ \ SEGME NT SEGMENT CORPUS/ R|QHT FIBROUS THICKEN- 1 POSTERIOR ING OF EDGE SEGMENT FIG. 112. AORTIC VALVE. The artery has been cut open between the anterior and left posterior segments, and spread out. (Gerrish.) These valves consist of three half-moon-shaped pockets, each pocket being attached by its convex border to the inside of the artery where it joins the ventricle, while its other border projects into the interior of the vessel. Small nodular bodies, called the corpora Arantii, are attached to the centre of the free edge of each pocket. Function. These valves offer no resistance to the passage of 180 ANATOMY AND PHYSIOLOGY [CHAP. X blood from the heart into the arteries, as the free borders project into the arteries, but they form a complete barrier to the passage of blood in the opposite direction. In this case each pocket becomes filled with blood, and the free borders are floated out and distended so that they meet in the centre of the vessel. The corpora Arantii assist in the closure of these valves and help to make the barrier perfect. The orifices of the heart which open into veins are not pro- tected by valves, with the possible exception of the opening into the inferior vena cava which is partly covered by a mem- brane known as the Eustachian valve. Auriculo- ventricular bundle of His. The muscular tissue of the auricles is not continuous with that of the ventricles. They SUPERIOR VENA CAVA SINO-AURICULAR NODE AURICULO- VENTRICULAR NODE .PULMONARr VEINS LEFT AURICLE BUNDLE OF HIS MITRAL VALVE LEFT VENTRICLE RIGHT VENTRICLE FIG. 113. DIAGRAM OF THE AURICULO-VENTRICULAR NODE AND BUNDLE OF His. are connected by fibrous tissue and the auriculo-ventricular bundle of His, which consists of muscular and nervous tissue. This bundle arises in a collection of cells known as the auriculo- ventricular node, located in the septum between the auricles. It is connected with the muscles of the auricles and also with the remnant of sinus tissue the sino-auricular node which is located at the mouth of the superior vena cava. 1 It passes down 1 See page 217. CHAP. X] ARTERIES 181 the septum between the auricles to the septum between the ventricles, where it divides into right and left bundles, one for each ventricle. In the lower part of the ventricles each bundle sepa- rates into numerous strands which spread over the entire internal surface. The terminal strands are called Purkinje fibres. The significance of these structures is discussed on page 230. Blood supply. Just after the aorta leaves the left ventricle it gives off two small branches, called the right and left coronary arteries. They encircle the heart like a crown, hence their name. They supply the substance of the heart with blood, as the blood contained within the cavities of the heart only nourishes the endocardium. Nerve supply. The heart is supplied (1) by the vagi nerves from the central nervous system and (2) by nerves from the sympathetic system. Stimulation of the vagi fibres slows the action of the heart. They are therefore known as cardiac in- hibitors. Stimulation of the sympathetic nerves increases the force of the heart beat, therefore they are known as cardiac accelerators. ARTERIES The arteries are tubes that carry blood from the heart and are composed of three coats : 1 . An inner endothelial lining which is continuous with the endothelium lining the heart. It furnishes a smooth, slippery surface over which the blood can flow without friction. 2. A middle coat of fibrous elastic tissue with muscles interlaced and circularly disposed around the vessel. By virtue of the structure of the middle coat, the arteries are both ex- tensile and elastic.* J t FIG. 114.- DIAGRAM OF A CROSS-SECTION OF AN ARTERY, SHOWING THE COMPOSITION OF ITS is thicker and contains TUNICS. (Gerrish.) 1 It is well to bear in mind the difference between extensile and elastic. By extensile we mean that an object can be stretched ; by elastic that it returns to its former shape as soon as the stretching force is removed. 182 ANATOMY AND PHYSIOLOGY [CHAP. X a larger proportion of elastic tissue in the larger arteries. In the smaller arteries it is thinner and contains a larger proportion of muscular tissue. The proper functioning of the arteries depends upon their extensibility and elasticity and may be demonstrated by the following example : If we tie a piece of a large artery at one end and inject fluid into the other end, the artery swells out to a very great extent, but will return at once to its former size when the fluid is let out. The great extensibility and elasticity of the arteries adapts them for receiving the additional amount of blood thrown into them at each contraction of the heart. 3. An outer, dense fibrous coat with fibres arranged longi- tudinally. The strength of an artery depends largely upon the outer fibrous coat ; it is far less easily cut or torn than the other coats, and serves to resist undue expansion of the vessel. The arteries do not collapse when empty, and when an artery is severed the orifice remains open. The muscular coat, however, contracts somewhat in the neighborhood of the opening, and the elastic fibres cause the artery to retract a little within its sheath, so as to diminish its caliber and permit a blood-clot to plug the orifice. This property of the severed artery is an important factor in the arrest of hemorrhage. Blood and nerve supply of the arteries. The blood which flows through the arteries nourishes only the inner coat. The middle and outer coats are supplied with arteries, capillaries, and veins, called vasa vasorum, or blood-vessels of the blood-vessels. The muscular tissue found in the walls of the arteries is supplied with nerves chiefly from the sympathetic system. These nerves are called vasomotor, and are divided into two sets, (1) vaso- constrictor, and (2) vaso-dilator. Stimulation of one set of these nerves (vaso-constrictor) causes contraction of the muscles and constriction of the arteries ; stimu- lation of a second set (vaso-dilator) causes a relaxation of the muscles, and dilatation of the arteries. The widening and nar- rowing of the arteries not only affects the local circulation in different parts of the body, but the amount of resistance they oppose to the arterial impulse also influences in some degree the character of the heart-beat. The term " tone of the arteries " is used to express the normal degree of contracture of the arterial CHAP. X] CAPILLARIES 183 walls. This is an inherent property which is independent of the nervous system. Sheaths of the arteries. The greater number of the arteries are accompanied by a nerve and one or two veins and surrounded by a sheath of connective tissue, which helps to support and hold these structures in position. Size of the arteries. The largest arteries in the body, the aorta and pulmonary artery, measure about one inch (2.8 cm.) in diameter, at their connection with the heart. These arteries give off branches, which divide and subdivide into smaller branches. A branch of an artery is always less than the trunk from which it springs, hence the arteries grow smaller as they subdivide, and gradually lose their characteristic structure. The smallest arte- ries are called arterioles, and at their distal ends, where only the internal coat remains, the capillaries begin. CAPILLARIES The capillaries are exceedingly minute vessels which average about 2Too" f an mcn (-0125 mm.) in diameter. They connect the arterioles (smallest arteries) with the venules (smallest veins), thus receiving the blood from the ar- terioles and carrying it to the venules. Structure. The walls of the capil- laries are formed entirely of one layer of simple endothelium composed of flattened cells joined edge to edge by cement substance, and continuous with the layer which lines the arteries and veins. Distribution. The capillaries com- municate freely with one another and form interlacing networks of variable form and size in the different tissues. All the tissues, with the exception of the cartilages, hair, nails, cuticle, and cornea of the eye, 1 are traversed by these networks of capillary vessels. Their diameter is so small that the blood cells must pass FIG. 115. FINE CAPIL- LARIES FROM THE MESENTERY. (Collins.) 1 These parts not penetrated by the blood-vessels imbibe nutritive matter from adjacent tissues, and are just as dependent on the blood as all the other tissues. 184 ANATOMY AND PHYSIOLOGY [CHAP. X through them in single file and very frequently the cell is larger than the caliber of the vessel, and has to be squeezed to enable it to pass through. In many parts they lie so closely together that a pin's point cannot be inserted between them. They are most abundant, and form the finest networks, in those organs where the blood is needed for purposes other than local nutrition, as, for example, secretion or absorption. Function. In the glandular organs the capillaries supply the substances requisite for secretion; in the alimentary canal they take up some of the elements of digested food ; in the lungs they absorb oxygen and give up carbon dioxide ; in the kidneys they discharge the waste products collected from other parts; all the time, everywhere through their walls, that interchange is going on which is essential to the renovation and life of the whole body. It is in the capil- laries, then, that the chief work of the blood is done ; and the object of the vascular mechanism is to cause the blood to flow through these ves- sels in the manner best adapted for accomplishing this work. VEINS The veins are tubes that carry blood to the heart. They have three coats and on the whole resemble the arteries in structure. They differ from them in having : (1) much thin- ner walls (see Fig. 116) ; (2) they contain less elastic tissue, more white fibrous tissue, and because of this are not so elastic or contractile as the arteries; (3) many of the veins are provided with valves. Valves. The valves are semilunar folds of the internal coat of the veins ; and usually consist of two flaps, rarely one or three. The convex border is attached to the side of the vein, and the free edge points toward the heart. Their function is to prevent FIG. 116. TRANSVERSE SEC- TION THROUGH A SMALL ARTERY AND VEIN, SHOWING THE RELA- TIVE DIFFERENCE IN THE THICK- NESS OF THEIR WALLS. In the vein (V} the outer coat is thickest, in the artery (A) the extensile and elastic middle coat is thickest. (Klein and Noble Smith.) CHAP. X] LYMPH VASCULAR SYSTEM 185 regurgitation and keep the blood flowing in the right direction, i.e., toward the heart. If for any reason the blood on its onward course toward the heart is driven backward, the refluent blood, getting between the wall of the vein and the flaps of the valve, will press them inward until their edges meet in the middle of the channel and close it. The valves are most numerous in the veins where regurgitation is most likely to occur, i.e., the veins of the extremities. For the same reason a greater number are found in the lower than in the upper limbs. They are absent in many of the small veins, in the large veins of the trunk, and in veins not subjected to muscular pressure. The veins, like the arteries, are supplied with both blood-vessels and nerves ; the supply, however, is far less abundant. It must be remembered that although the arteries, capillaries, and veins have each the distinctive structure above described, it is at the same time diffi- cult to draw the line between the arteriole and large capillary ; and between the large capillary and venule. The veins on leaving the capillary networks only gradually assume their several coats, while the arteries dispense with their coats in the same imperceptible way as they approach the capillaries. LYMPH VASCULAR SYSTEM As the process of lymph formation is continual, 1 it follows that oedema would result from the accumulation of lymph if some system of drainage were not provided to return the lymph to the blood. This drainage system is called the lymph vascular system. Lymph spaces Lymph capillaries. Lymphatics. Thoracic duct. Right lymphatic duct. FIG. 117. DIAGRAM SHOWING VALVES OF VEINS. A, part of a vein, laid open, with two pairs of valves ; B, longitudi- nal section of vein, show- ing valves closed. (Shar- pey.) Lymph Vascular System Lymph vessels Lacteals. Serous cavities. Lymph nodes 1 See page 166. FIG. 118. THE REGIONS WHOSE LYMPH FLOWS INTO THE RIGHT LYMPHATIC DUCT ARE SUGGESTED BY THE RED AREA ; THOSE WHICH ARE TRIBUTARY TO THE THORACIC DUCT BY THE BLUE AREA. (Gerrish.) 186 CHAP. X] LYMPH VASCULAR SYSTEM 187 Lymph spaces. The microscopic spaces which exist between the cells are always filled with lymph and are called lymph spaces. In them the lymphatics begin. Lymph vessels. The plan upon which the lymphatic system is constructed is similar to that of the blood vascular system, if we omit the heart and the arteries. In the lymph spaces we find the closed ends of minute microscopic vessels, called lymph capillaries, which are comparable to, and often larger than, the blood capillaries. These lymph capillaries unite to form larger vessels called lymphatics, which are comparable to the veins. The lymphatics continue to unite and form larger and larger vessels until finally they con- verge into two main channels, (1) the thoracic duct, and (2) the right lymphatic duct. The thoracic duct. The thoracic duct begins at the second lumbar vertebra and ascends upward to the seventh cervical. It lies in front of the bodies of the vertebrse, gradually inclining towards the left, until, on a level with the seventh cervical vertebra, it turns outward and arches downward and forward to terminate in the innominate vein at the point of junction of the left internal jugular and left subclavian. It is from fifteen to eighteen inches (38-45 cm.) long in the adult, and is about the size of a goose quill. It receives the lymph from the left side of the head, neck, and chest, all of the abdomen and both lower limbs, also the chyle from the lacteals. It is dilated below, where it receives the lymph from the lower limbs and the chyle from the lac- teals, the dilatation being known as the chyle cistern (recep- taculum chyli). (See Fig. 145.) The right lymphatic duct. The right lymphatic duct is a short vessel, usually from one-half to one inch (1.3 to 2.5 cm.) in length. It pours its contents into the innominate vein at the junction of the right internal jugular and subclavian veins. The lymphatics from the right side of the head, neck, the right arm, and the upper part of the trunk enter the right lymphatic duct. The parts drained by each are suggested by Fig. 118. FIG. 119. VALVES OF THE LYMPHATICS. 188 ANATOMY AND PHYSIOLOGY [CHAP. X Structure of the lymph vessels. The lymphatics resemble the veins in their structure as well as in their arrangement. The smallest have but a single coat of endothelioid cells, having a peculiar dentated outline. The larger vessels have three coats, similar to veins, except that they are so thin as to be trans- parent, and are more abun- dantly supplied with valves. The valves are constructed and arranged in the same fashion as those of the veins, but fol- low one another at such short intervals that, when distended, they give the vessel a beaded or jointed appearance. They are usually wanting in the smaller networks. The valves allow the passage of material from the smaller to the larger lymphatics, and from these into the veins, but obstruct the flow in the opposite direction. Classification of lymphatics. -The lymph, like the blood in the veins, 'is returned from the limbs and viscera by a superficial and a deep set of vessels. The superficial lym- phatic vessels are placed im- mediately beneath the skin, and accompany the superficial veins. In the interior of the body the lymphatics lie in the submucous tissue throughout the whole length of the gastro pulmonary and genito-urinary tracts, and in the subserous tissue of the thoracic and abdominal cavities. The deep lymphatics, fewer in number and larger than the superficial, accompany the deep blood-vessels. Lacteals. The lymphatics that have their origin in the villi FIG. 120. LACTEALS AND LYMPHATICS, DURING DIGESTION. (Dalton.) CHAP. X] LYMPH VASCULAR SYSTEM 189 of the small intestine are called lacteals. During the period of intestinal digestion they are filled with chyle, which has a white aspect, due to fat absorbed from the food, and suspended in it like oil in milk. After fasting, the lacteals contain lymph which differs very little from the lymph found in the ordinary lymphatics. Serous cavities. A close relationship exists between the lym- phatics and the serous cavities of the body, i.e., pleural, pericardial, and peritoneal ; also the synovial bursae. These cavities are lined by endothelium through which the lymph transudes by osmosis. Function of the lymphatics. The function of the lymphatics is to carry from the tissues to the veins all the materials which the tissues do not need. Functionally they may be considered between the capillaries and the veins, as they gather up the lymph which exudes through the thin capillary walls, and return it to the innominate veins. Here it becomes mixed with the blood, enters the superior vena cava, and then the right auricle of the heart. The function of the lacteals is to help in the absorption of digested food, especially fats. Lymph nodes. The lymph nodes are numerous round or ovoid bodies placed in the course of the lym- phatics. They vary in size from a pinhead to an almond. A lymph node is covered by an envelope, or capsule, of connective and muscular tissue. This capsule sends fibrous bands called trabeculse (little beams) into the substance of the node, and di- vides it into irregular spaces, which communicate freely with each other. The irregular spaces are occupied by a mass of cellular pulp substance, which, however, does not quite fill them as it never touches the capsule or trabeculse, but leaves a narrow in- terval between itself and them. It looks as if the pulp had originally filled the framework and then shrunk away slightly on FIG. 121. A LYMPH NODE WITH ITS AFFERENT AND EFFER- ENT VESSELS. (Gerrish.) 190 ANATOMY AND PHYSIOLOGY [CHAP. X DEEP CERVICAL NODE .PROPER AXILLARY NODES EPICONDYLAR NODE 'ALMAR PLEXUS FIG. 122. THE LYMPH NODES AND VESSELS OF THE UPPER LIMB. (Gerrish.) CHAP. X] LYMPH VASCULAR SYSTEM 191 all sides. The spaces thus left form channels for the passage of the lymph, which enters by afferent vessels, and, after circulating through the node, is- sues by efferent vessels. The substance of a lymph node is reticular adenoid tissue. They are well supplied with blood. Location of nodes. There is a super- ficial and a deep set of nodes, just as there is a superficial and a deep set of lymphatics and veins. Occasionally a node exists alone, but they are usually in groups or chains, and arranged around blood-vessels. They are found in great numbers in the neck, thorax, axilla, groin, mesentery, and alongside of the aorta, inferior vena cava, and the iliac vessels. A few are found in the poplit- eal space and in the arm as far as the elbow, but none farther down the leg or forearm. They are usually named from the position in which they are found in the body, viz. cervical in the neck, thoracic in the thorax, axillary in the axilla, inguinal in the groin, mesenteric in the mesentery. Function of the lymph nodes. The lymph nodes serve two important pur- poses : (1) As filters for the lymph. In this way they act as safety-valves and serve to retard the spread of infection through the body. If any portion of the body is infected, the poison may be carried by the lymphatics to their special nodes. There its course is stopped and the node may suffer enlargement or even break down and be destroyed. If the FIG. 123. THE LYMPH NODES AND VESSELS OF THE LOWER LIMB. (Gerrish.) 192 ANATOMY AND PHYSIOLOGY [CHAP. X infection is not arrested, the node next in line will suffer, then the next, and so on. FIG. 124. THE LYMPH NODES OF THE NECK AND UPPER PART OF THE THORAX. (Gerrish.) (2) Multiplication of leucocytes. In its passage through the node the lymph takes up fresh leucocytes, which are continually multiplying by cell division in the substance of the node. CHAP. X] SUMMARY 193 Blood Vascular System Location Structure Cavities Orifices Right heart Left heart Right heart Left heart Right auricle Right ven- tricle SUMMARY Heart. Arteries small arteries are named arterioles. Capillaries. Veins small veins are named venules. Between lungs. Above diaphragm. Smooth lining on inside Endocardium. Muscle substance Myocardium. f Fibrous portion. Outside covering Pericardium { a f Visceral. Serous { . . [ [ Parietal. ( Receives blood. [ Thin walls. Expels blood into pulmonary artery. Thick walls. Left f Receives blood. auricle ( Thin walls. Left ven- f Expels blood into aorta, tricle [ Very thick walls. f Superior vena cava re- turns blood from upper Right portion of body, auricle Inferior vena cava returns blood from lower portion I of body. Auriculo-ventricular orifice between au- ricle and ventricle. Right ven- f Pulmonary artery carries tricle [ blood from heart to lungs, f Two right pulmo- j Return Left nary veins blood auricle Two left pulmo- from nary veins J lungs. Auriculo-ventricular orifice between auri- cle and ventricle. Left ven- f Aorta distributes blood to tricle [ all parts of body. 194 ANATOMY AND PHYSIOLOGY [CHAP. X Valves branches from aorta. Tricuspid valve composed of three cusps situated in the right ventricle. Bicuspid or mitral valve composed of two strong, thick cusps situated in the left ventricle. Function Prevent flow of blood from ventricles into auricles. Aortic composed of three half-moon- shaped pockets between aorta and left ventricle. Semilunar J Pulmonary composed of three half- valves 1 moon-shaped pockets between pulmo- nary artery and right ventricle. Function. Prevent flow of blood from arteries into ventricles. Auriculo-ventricular bundle. Bundle of muscular and nervous tissue located in septum between right and left heart, which con- nects the musculature of auricles and ventricles. Central nervous system. Vagi nerves, inhibitory fibres, slow the heart. Sympathetic system. Accelerator fibres increase rapidity and force of heart. Right coronary artery 1 Left coronary artery J Hollow tubes Carry blood from heart. 1. Endothelial lining. Coats 2. Muscular and elastic tissue. 3. Fibrous tissue. Sheaths outside covering of connective tissue which surrounds the arteries. Size Aorta about one inch in diameter. Arteries grow smaller as they subdivide. Smallest ones are microscopic and are called arterioles. Tiny tubes about T1 fo T of an inch in diameter. Con- nect arterioles and venules. One coat of simple endothelium. Communicate freely form networks. Collapsible tubes smallest ones, called venules, begin where capillaries end. Carry blood to heart. Three coats, same as arteries but thinner. Valves semilunar pockets. Vaso vasorum Term applied to blood-vessels that are supplied to coats of other blood-vessels. Vasomotor. Term applied to nerves supplied to J Vaso-constrictor. blood-vessels 1 Vaso-dilator. Nerve Supply Blood Supply Arteries . . . Characterized by elasticity Capillaries . . Characterized by multiplic- ity Veins . . . . Characterized by valves CHAP. X] SUMMARY 195 Lymph Vascular System Lymph spaces Microscopic spaces which exist between cells of which tissues are composed. Lymph capillaries. Lymphatics. Thoracic duct. Right lymphatic duct. Lacteals. Serous cavities. Lymph vessels Lymph nodes Lymph Capillaries Lymphatics Lymph Vessels Thoracic Duct Right Lym- phatic Duct Classification Lacteals Origin in lymph spaces. One coat of endothelium dentated. Start as microscopic lymph capillaries, unite to form lymphatics. Compa- rable to formation of veins. three coats numerous valves. 15 to 18 in. long. Size of goose-quill. In front of vertebra from 2d lumbar to 7th cervical. Has three coats numerous valves. Dilatation at lower portion called chyle cistern. Receives lymph from left side of head, neck, and chest, left arm, all of abdo- men, and both lower limbs. Re- ceives chyle from lacteals. Pours lymph and chyle into left in- nominate vein. | to 1 in. long. Receives lymph from right side of head, neck, and chest, also right arm. Pours lymph into right innominate vein. Superficial beneath skin, accompany superficial veins. Deep accompany deep blood-vessels. Lymphatics of the intestines. Many originate in villi of small in- testine. During digestion chyle. Contain During period of fasting lymph. Absorb fatty substances. Expanded lymph spaces. Lymph transudes by osmosis. Function Drain off lymph from all parts of the body and return it to the innominate veins. Serous Cavities 196 ANATOMY AND PHYSIOLOGY [CHAP. X Lymph Nodes Description Location . Function . f Round. Shape < r I Ovoid. Size varies from pinhead to almond. f Connective and mus- Outer capsule \ , I cular tissue. Interior divided into irregular spaces like sponge. Spaces partially filled with reticular adenoid tissue. Communicating channels for lymph, which enters by afferent, leaves by efferent vessels. Are well supplied with blood. Superficial and deep set. Usually arranged around blood- vessels. Neck, thorax, axilla, groin, mesentery. In the arms as far as elbows. In the legs as far as popliteal space. Usually name indicates location. 1 . Filters preventive and protec- tive. 2. Multiplication of leucocytes. CHAPTER XI THE VASCULAR SYSTEM CONTINUED : ARTERIES ; PULMONARY SYSTEM; GENERAL SYSTEM; VEINS; SUPPLEMENTARY CHANNEL, AND PORTAL SYSTEM ARTERIES THE arteries, which carry and regulate the supply of blood from the heart to the capillaries, are distributed throughout the body in a systematic manner, and before attempting the study of the CAPILLARY NETWORK TERMINAL BRANCHES CALLED ARTERIOLES END IN CAPILLARIES ANASTOMOSIS RECURRENT BRANCH FIG. 125. DIAGRAM SHOWING THE BRANCHINGS, ANASTOMOSES, AND CONFLU- ENCE OF ARTERIES. (Gerrish.) circulation, we must try to gain a general idea of this system of distribution, in order that we may be able to locate the position of these important vessels. The arteries usually occupy protected 197 198 ANATOMY AND PHYSIOLOGY [CHAP. XI situations, that they may be exposed as little as possible to acci- dental injury, or to the effects of local pressure. Division. As they proceed in their course they divide into branches, the division taking place in different ways. (1) An artery may at once resolve itself into two branches of nearly equal size (dichotomous division, or splitting in two). (2) It may give off several branches in succession and still main- tain its character as a trunk. (3) It may give off one branch that divides into three equal branches. In this case the parent branch is called an axis. Ex- ample coeliac axis. Anastomosis or inosculation. The distal ends of arteries unite at frequent intervals, when they are said to anastomose, or inoscu- late. Such inosculations admit of free communication between the currents of the blood, tend to obviate the effects of local in- terruption, and to promote equality of distribution and of pres- sure. This arrangement makes it possible to tie veins and arteries during operations, or after injuries, without serious interference with the circulation. Plexus. A plexus or network is formed by the inosculations of a number of arteries in a limited area. Arteries usually pursue a tolerably straight course, but in some parts of the body they are tortuous. The facial artery, in its course over the face, and the arteries of the lips are extremely tortuous, so that they may accommodate themselves to the movements of the parts. Divisions of the vascular system. The blood-vessels of the body are arranged in two main systems, namely, the pulmonary and the general or systemic. THE PULMONARY SYSTEM The pulmonary system is the lesser system and provides for the circulation of the blood from the right ventricle to the lungs, and then back to the left auricle. This is called the pul- monary circulation. Blood-vessels of the pulmonary system. The blood-vessels of the pulmonary system are (1) the pulmonary artery and all its branches, (2) the capillaries which connect these branches with the veins, and (3) the pulmonary veins. CHAP. XI] THE PULMONARY SYSTEM 199 The pulmonary artery. The pulmonary artery conveys the venous blood from the right side of the heart to the lungs. The Facial Temporal External carotid Common carotid Suhclavian Aorta Axillary Brachial Radial Ulnar Palmar arch. Femoral Popliteal Anterior tibial Posterior tibial Dorsalis pedis FIG. 126. THE PRINCIPAL ARTERIES OF THE BODY. (Morrow.) main trunk is a short, wide vessel about two inches (5 cm.) in length and a little more than one inch (about 3 cm.) in diameter. It arises from the right ventricle, in front of the aorta, and runs for a distance of two inches (5 cm.) upward, backward, and to 200 ANATOMY AND PHYSIOLOGY [CHAP. XI the left. (See Fig. 107.) On a level with the intervertebral disc, between the fifth and sixth thoracic vertebrae, it divides into two branches, the right and left pulmonary arteries which pass to the right and left lungs. From these main branches, arteries arise which divide and subdivide, grow smaller in size, and finally merge Branch of pul- .... monary artery Entrance of vena azygos FIG. 127. PULMONARY VEINS, SEEN IN A DORSAL VIEW OF THE HEART AND LUNGS. The left lung is pulled to the left, and the right lung has been partly cut away to show the ramifications of the air-tubes and blood-vessels. (Gerrish.) into capillaries which form a network upon the walls of the air- cells. 1 These capillaries unite, grow larger in size, and gradually assume the characteristics of veins. The veins unite to form the pulmonary veins. The pulmonary veins. - The pulmonary veins are four short trunks which convey the blood from the lungs to the left auricle, and are found, two on each side, in the root of the corresponding lung. The pulmonary veins have no valves. 1 See page 257. CHAP. XI] THE VASCULAR SYSTEM 201 THE GENERAL SYSTEM The general system is the larger system and provides for the circulation of blood from the left ventricle to all parts of the body by means of the aorta and its branches, and the return to the right auricle by means of the venae cavse. This is called the systemic circu- lation. The blood-vessels of the general system. - The blood-vessels of the general system consist of (1) the aorta, and all the arteries that originate from it, including the terminal branches called arterioles ; (2) the capil- laries which connect the arterioles and venules ; (3) all the venules and veins of the body which empty either directly into the heart, or indirectly by means of the superior and inferior venae cavae. The aorta. The aorta is the main trunk of the arterial system. Spring- ing from the left ventricle of the heart, it arches over the root of the left lung, descends along the vertebral column, and after passing through the diaphragm into the abdominal cavity, ends opposite the fourth lumbar vertebra by dividing into the right and left common iliac arteries. In this course the aorta forms a continuous trunk, which gradually diminishes in size from its commencement to its termination (from one and one-eighth FIG. 128. THORACIC AORTA. (Gerrish.) 202 ANATOMY AND PHYSIOLOGY [CHAP. XI inches or 2.8 cm. to seven-tenths of an inch or 1.75 cm.). It gives off large and small branches at various points. Adrenal or Supra-renal gland A lumbar vein FIG. 129. THE ABDOMINAL AORTA AND INFEKIOH VENA CAVA. (Gerrish.) It may be divided as follows : (1) the ascending aorta is the short part which is contained within the pericardium. (2) The arch is about two inches (5 cm.) in length and extends CHAP. XI] THE GENERAL SYSTEM 203 from the ascending aorta to the border of the fourth thoracic vertebra. It forms a well-marked curve in front of the trachea and around the root of the left lung. (3) The descending thoracic aorta is the comparatively straight part that extends from the lower border of the fourth thoracic vertebra on the left side, to the aortic opening in the diaphragm in front of the lower border of the last thoracic vertebra. It has a length of from seven to eight inches (17.5 to 20 cm.). (4) The abdominal aorta commences at the aortic opening of the diaphragm, in front of the lower border of the last thoracic vertebra, and terminates below by dividing into the two common iliac arteries. The bifurcation usually takes place about halfway down the body of the fourth lumbar vertebra, which corresponds to a spot on the front of the abdomen, slightly below and to the left of the umbilicus. Its length is about five inches (12.5 cm.). Branches of the ascending aorta. The only branches of the ascending aorta are the right and left coronary arteries. They arise immediately above the semilunar valves and encircle the heart, giving off numerous branches that supply the heart muscle. (See Fig. 112.) Branches of the arch of the aorta. The branches given off from the arch of the aorta are three in number the innominate, the left common carotid, and the left subclavian arteries. (See Fig. 107.) The innominate (brachio-cephalic) artery arises from the right upper surface of the arch, ascends obliquely toward the right, until, arriving on a level with the upper margin of the clavicle, it divides into the right common carotid and right subclavian arteries. Its usual length is from one to two inches (2.5 to 5 cm.). (See Fig. 107.) The left common carotid arises from the middle of the upper surface of the arch of the aorta, and the right common carotid arises at the division of the innominate, consequently the left carotid is an inch or two longer than the right. They ascend obliquely on either side of the neck until, on a level with the upper border of the laryngeal prominence (Adam's apple), they divide into two great branches : (1) the external carotid, (2) the internal carotid. At the root of the neck the common carotids are separated from each other by only a narrow interval, corre- sponding with the width of the trachea; but as they ascend 204 ANATOMY AND PHYSIOLOGY [CHAP. XI they are separated by a much larger interval, corresponding with the breadth of the larynx and pharynx. Each external carotid has eight branches, which are distributed to the throat, tongue, face, ears, and walls of the cranium. FIG. 130. SUBCLAVIAN AND AXILLARY ARTERIES. (Gerrish.) Each internal carotid has many branches which are distributed to the brain and eyes. The chief ones are the cerebral and ophthalmic. Circle of Willis. The circle of Willis is a remarkable anastomo- sis formed by the blood-vessels of the brain. It is situated at the base of the brain and is formed by the union of (1) the anterior and posterior cerebral arteries, which are branches of the internal carotid, and (2) branches of the basilar artery, which is formed by the union of the two vertebrals. 1 These arteries are joined in such 1 The vertebral arteries are branches given off from the subclavian. They ascend on either side of the vertebral column, pass through the foramen magnum, and at the base of the brain unite to form the basilar artery. CHAP. XI] THE GENERAL SYSTEM 205 a manner as to form a ' complete circle, and this arrangement (1) equalizes the circulation of the blood in the brain, and (2) in case of destruction of one of the arteries, provides for the blood reaching the brain through .other vessels. The subclavian arteries. The right subclavian arises at the division of the innominate, and the left subclavian from the arch of the aorta. The subclavian arteries are the first portions of a long trunk which forms the main artery of the upper limb, and ANTERIOR CEREBRAL INTERNAL CAROTID POSTERIOR CEREBRAL BASILAR VERTEBRAL FIG. 131. DIAGRAM OF THE CIRCLE OF WILLIS. which is artificially divided for purposes of description into three parts; viz.: (1) Subclavian, (2) Axillary, and (3) Brachial. The subclavian artery passes a short way up the thorax into the neck, and then turns downward to rest on the first rib. At the lower border of the first rib it ceases to be called subclavian, and is continued as the axillary. It gives off large branches to the brain, back, chest, and neck. The axillary artery passes through the axilla, lying to the inner side of the shoulder joint and upper part of the arm. It gives off branches to the chest, shoulder, and arm. The brachial artery (continuation of the axillary) extends from the axillary space to just below the bend of the elbow, where it divides into the ulnar and radial arteries. It may be readily lo- 206 ANATOMY AND PHYSIOLOGY [CHAP. XI Radial cated, lying in the depression along the inner border of the biceps muscle. Pressure made at this point from within outward against the humerus will control the blood supply to the arm. The ulnar, the larger of the two vessels into which the brachial divides, extends along the inner side of the forearm into the palm of the hand, where it terminates in the superficial palmar arch. The radial artery appears, by its direction, to be a continuation of the brachial, although it does not equal the ulnar in size. It extends along the outer side of the front of the fore- arm as far as the lower end of the radius, below which it turns around the outer border of the wrist, and passes forward into the palm of the hand. It terminates in the deep palmar arch. The superficial and deep palmar arches anastomose and supply the hand with blood. Branches of the thoracic aorta. - The branches derived from the tho- racic aorta are numerous but small, and the consequent decrease in size is not marked. The principal branches are (1) the bronchial, (2) the cesopha- geal, (3) the mediastinal, (4) the peri- cardial, and (5) the intercostal. (1) The bronchial arteries are the nutrient vessels of the lungs, and vary in number, size, and origin. As a rule, there are two left bronchial arteries and one right. The left arise from the thoracic aorta, and the right arises from the first aortic intercostal or from the left bronchial. Each vessel runs along the back part of the corresponding bronchus, dividing and subdivid- FIG. 132. DEEP ANTERIOR VIEW OF THE ARTERIES OF THE ARM, FOREARM, AND HAND. CHAP. XI] THE GENERAL SYSTEM 207 ing along the bronchial tubes, supplying them, and the cellular tissue of the lungs. (2) The oesophageal arteries are four or five in number and form a chain of anastomoses along the oesophagus. They anasto- mose with branches of the thyroid arteries above, and with ascend- ing branches from the gastric and phrenic arteries below. (3) The mediastinal arteries are numerous small arteries which supply the nodes and areolar tissue in the posterior mediastinum. (See page 257.) (4) The pericardial arteries are small and are distributed to the pericardium. (5) The intercostal arteries are ten or eleven on each side. They are subdivided into the superior and aortic intercostals. The su- perior intercostal artery which is a branch of the subclavian sup- plies the two superior intercostal spaces on each side. The aortic intercostals are usually nine in number on each side and arise from the back of the aorta. Each intercostal artery is accompanied by a vein and nerve ; and each one gives off numerous branches to the muscles and skin. (See Fig. 128.) Branches of the abdominal aorta. Branches of the abdominal aorta may be divided into two sets : 1. Visceral, or those which supply the viscera. 2. Parietal, or those which are distributed to the walls of the abdomen. Visceral group. The visceral group includes (a) the coeliac axis; (b) the right and left supra-renal; (c) the superior mesenteric ; (d) the right and left renal ; (e) the right and left sper- matic or right and left ovarian ; and (/) the inferior mesenteric. (a) The coeliac axis is a short, wide vessel, usually not more than half an inch (1.25 cm.) in length, which arises from the front of the aorta, just below the opening in the diaphragm. It divides into three branches ; viz. (1) the gastric, which supplies the stomach ; (2) the hepatic, which supplies the liver and the duodenum, or portion of the intestine nearest to the stomach ; and (3) the splenic, which supplies the spleen, and also takes part in the blood supply of the stomach and pancreas. (See Fig. 129.) (6) The supra-renal arteries are of small size. They arise from the side of the aorta and supply the supra-renal or adrenal bodies. (See page 345 and Fig. 129.) 208 ANATOMY AND PHYSIOLOGY [CHAP. XI (c) The superior mesenteric artery arises from the fore part of the aorta, a little below the supra-renals. It supplies the small intestine beyond the first portion, and half of the large intestine. (See Fig. 129.) FIG. 133. SUPERIOR MESENTERIC ARTERY. (Gerrish.) (d) The renal arteries are of large size, in proportion to the bulk of the organs (kidneys) which they supply. They arise from the sides of the aorta, below the superior mesenteric artery, that of the right side being generally a little lower down than that of the left. Each is directed outward, so as to form nearly a right angle with the aorta. (See Fig. 129.) (e) The spermatic arteries in the male arise close together from CHAP. XI] THE GENERAL SYSTEM 209 They the front of the aorta, a little below the renal arteries. are distributed to the testes. (/) The ovarian arteries in the female arise from the same por- tion of the aorta as the spermatic arteries in the male. They supply the ovaries, and, joined to the uterine artery, a branch EScNTER O INFERIOR HEMORRHOIDAL FIG. 134. INFERIOR MESENTERIC ARTERY. (Gerrish.) of the internal iliac, also assist in supplying the uterus. During pregnancy the ovarian arteries become considerably enlarged. (g) The inferior mesenteric artery arises from the front of the aorta, about an inch and a half (3.8 cm.) above its bifurcation, and supplies the lower half of the large intestine. Continued 210 ANATOMY AND PHYSIOLOGY [CHAP. XI under the name of the superior hemorrhoidal artery, it also takes part in the blood supply of the rectum. (See Fig. 129.) Parietal group. The parietal group includes (a) the right and left phrenic arteries; (6) the first, second, third, and fourth pairs of lumbar arteries ; and (c) the middle sacral. (a) The phrenic arteries arise from the aorta above the coeliac axis and are distributed to the diaphragm. (See Fig. 129.) (b) The lumbar arteries supply the muscles and walls of the respective regions that their names suggest. (c) The middle sacral artery arises from the lower end of the abdominal aorta and passes down to the sacrum and coccyx. Common iliac. The common iliac arteries, commencing at the bifurcation of the aorta, pass downward and outward about two inches (5 cm.), and then each divides into the internal (or hypo- gastric) and the external iliac arteries. The internal iliac artery (or hypogastric) supplies branches to the pelvic walls, pelvic viscera, the external genitals, and the buttocks. The uterine artery in the female, which supplies the tissues of the uterus with blood, is a very important branch .of the internal iliac. The external iliac is placed within the abdomen, and extends from the bifurcation of the common iliac to the lower border of the inguinal ligament. It forms a large, continuous trunk, which extends downward in the lower limb, and is named in successive parts of its course, femoral, popliteal, and posterior tibial. The femoral artery lies in the upper three-fourths of the thigh, its limits being marked above by the inguinal (Poupart's) liga- ment and below by the opening in the great adductor muscle. After passing through this opening the artery receives the name of popliteal. In the first part of its course the artery lies along the middle of the depression on the inner aspect of the thigh, known as Scarpa's triangle. 1 In this situation the beating of the artery may be felt, and the circulation through the vessel may be most easily controlled by pressure. 1 Scarpa's triangle is a name given to a triangular space situated on the upper, anterior, and inner surface of the thigh. It is bounded above by Poupart's liga- ment, on the outer side by the sartorius muscle, and on the inner side by the ad- ductor. CHAP. XI] THE GENERAL SYSTEM 211 The popliteal artery, continuous with the femoral, is placed at the back of the knee ; just below the knee-joint it divides into the posterior tibial and anterior tibial arteries. The posterior tibial artery lies along the back of the leg, and extends from the bifurcation of the popliteal to the ankle, where it divides into the internal and external plantar arteries. ANTERIOR CRURA NERVE EXTERNAL C/RCUMFLEX SUPERFICIAL EPIGASTRIO SUPERFICIAL EXTERNAL PUDIC EEP EXTERNAL PUDIC SUPERIOR EXTERNA ARTICULAR INFERIOR EXTERNA ARTICULAR ANASTOMOTICA MAGNA INFERIOR INTERNAl ARTICULAR FIG. 135. FEMORAL, ARTERY. (Gerrish.) 212 ANATOMY AND PHYSIOLOGY [CHAP. XI ANTERIOR TIBIAL RECURRENT i ANTERIOR TIBIAL NERVE ANTERIOR PERONEAL EXTERNAL MALi-EOLAR INTERNAL MALLEOLAR FIG. 136. ARTERIES uv THE DORSAL PART OF THE LEG. (Gerrish.) FIG. 137. ANTERIOR TIBIAL ARTERY. (Gerrish.) CHAP. XI] VEINS 213 The peroneal artery is a large branch given off by the posterior tibial just about an inch (25 mm.) below the bifurcation of the popliteal. The anterior tibial artery, the smaller of the two divisions of the popliteal trunk, extends along the front of the leg to the bend of the ankle, whence it is prolonged into the foot under the name of the dor- salis pedis artery. This unites with the external and internal plantar ar- teries to form the plantar arch which supplies blood to the foot. 1 VEINS The arteries begin as large trunks, which gradu- ally become smaller and smaller until they end in arterioles, which merge into capillaries, while the veins begin as small branches called venules which at first are scarcely distinguishable from the capillaries, and unite to form larger and larger vessels. They differ from the arteries in their larger capacity, greater number, thinner walls, and in the presence of valves which prevent backward circulation. The veins may be divided into two sets a superficial and a deep set. The superficial set are found immediately beneath the skin. The deep set accompany the arteries and are usually called by the same names. FIG. 138. ARTERIES OF THE DORSUM OF THE FOOT. Of the dorsal interosseous only the second is labelled. (Gerrish.) 1 Drawing the outline of the aorta with its branches as an arterial tree will greatly aid the student in mastering the arterial distribution. 214 ANATOMY AND PHYSIOLOGY [CHAP. XI Sometimes two deep veins accompany an artery, and are then called venae comites, or companion veins, or one vein may accompany an artery, and then be known as the vena comes of that artery. The superficial and the deep veins have very frequent communications with each other, and the anastomoses of veins are always more numerous than those of arteries. The systemic veins. The systemic veins are naturally divided into two groups : - 1. Those from which the blood is carried to the heart by the superior vena cava, viz. the veins of the head, neck, upper extremi- ties, and the walls of the thorax. In this group we include the veins of the heart, which, however, pass directly into the right auricle without entering the superior vena cava. 2. Those from which the blood is carried to the heart by the inferior vena cava, viz. the veins of the lower limbs, the lower part of the trunk, and the abdominal viscera. (1) Superior vena cava group. Veins of the head and neck. The blood returning from the head and neck flows on each side into two principal veins, the external and internal jugular. External jugular veins. The right and left external jugular veins are formed in the substance of the parotid glands by the union of two of the veins of the face. This union takes place on a level with the angle of the lower jaw, and each vein descends al- most vertically in the neck to its termination in the subclavian. These two veins receive the blood from the face and the exterior of the cranium. Internal jugular veins. These veins begin at the base of the skull and descend on either side of the neck, first with the external carotid, then with the common carotid, and join at a right angle with the subclavian to form the innominate (brachio-cephalic) vein. They receive the blood from the veins and sinuses of the cranial cavity. (See Fig. 141.) Sinuses. The blood from the interior of the skull is returned to the large veins by venous channels that are called sinuses. They are formed by a separation of the layers of the dura mater, the fibrous membrane which covers the brain. Their outer wall consists of the dura mater, and their inner lining of endothelium CHAP. XI] VEINS 215 is continuous with the lining membrane of the vessels that com- municate with them. (See Fig. 202.) Veins of the upper extremities. The blood from the upper limbs is returned by a deep and a superficial set of veins. The deep veins are the venae comites of the forearm and arm and are CEPHALIC MEDIAN CEPHALIC' RADIAL MEDIAN -BASILIC MEDIAN BASILIC COMMON ULNAR BRANCH FROM DEEP SET POSTERIOR ULNAR FIG. 139. SUPERFICIAL VEINS OF FRONT OF FOREARM AND LOWER PART OF ARM. (Gerrish.) called by the same names as the arteries. They communicate with the superficial veins at the hand and elbow, and the vena comes of the brachial artery unites with a superficial vein, i.e., the basilic, to form the axillary vein. The superficial veins. The superficial veins are much larger than the deep, and take a greater share in returning the blood, 216 ANATOMY AND PHYSIOLOGY [CHAP. XI especially from the distal portion of the limb. They commence in two plexuses, one on the back of the hand and one on the front . of the wrist. They comprise the following : (1) The radial vein begins in the dorsal plexus and runs up the radial side of the forearm to a little above the bend of the elbow, where it joins the median cephalic vein to form the cephalic. * (2) The posterior ulnar begins in the dorsal plexus and extends upward along the back part of the ulnar side of the forearm. Near the bend of the elbow it usually receives the anterior ulnar vein. (3) The anterior ulnar vein ascends from the wrist along the ulnar side of the front of the forearm. (4) The common ulnar is formed by the union of the anterior and posterior ulnar veins just below the elbow, and after a short course it joins the median basilic. (5) The median vein begins in the plexus on the wrist and ascends along the front of the forearm to the bend of the elbow where it bifurcates into the median basilic and median cephalic veins. (6) The median basilic is directed upward and joins the com- mon ulnar to form the basilic vein. The median basilic is the vein usually chosen for the operation of phlebotomy or intravenous in- fusion. (7) The median cephalic vein is directed upward and joins the radial vein to form the cephalic. (8) The basilic vein ascends in the groove on the inner side of the biceps. It unites with the inner vena comes of the brachial artery to form the axillary vein. (9) The cephalic vein ascends in the groove external to the biceps and ends in the axillary vein. The axillary vein. The axillary vein begins at the junction of the inner brachial and the basilic, and ends at the outer border of the first rib, in the subclavian. This vein accompanies the axillary artery and collects all the blood of the upper ex- tremities. The subclavian vein. This vein continues the axillary from the first rib to the joint between the sternum and clavicle, where it unites with the internal jugular to form the innominate vein. CHAP. XI] VEINS 217 The innominate veins. The innominate (brachio-cephalic) veins, commencing on each side by the union of the subclavian and internal jugular, transmit the blood returning from the head and neck, the upper limbs, and a part of the thoracic wall ; they end below by uniting to form the superior vena cava. Both in- nominate veins are joined by many side tributaries ; they also CEPHALIC VEIN) ENTERING f AXILLARY ) SUBCLAVIAN VEIN AXILLARY (BASILIC VEIN "\ PERFORATING (DEEP FASCIA ..-B AS I Lid VEIN FIG. 140. SUPERFICIAL VEINS OF FRONT OF ARM AND SHOULDER. (Gerrish.) receive, at the junction of the subclavian and internal jugular, the lymph ; on the left side from the thoracic duct, and on the right from the right lymphatic duct. The superior vena cava. The superior, or descending, vena cava, is formed by the union of the right and left innominate veins, just behind the junction of the first right costal cartilage with the sternum. It is about three inches (7.5 cm.) long, and opens into the right auricle, opposite the third rib. Thoracic veins. The great majority of the thoracic veins follow the same course as the arteries, and bear the same names. 218 ANATOMY AND PHYSIOLOGY [CHAP. XI Two exceptions are the inferior vena cava and the azygos veins which w y ill be described later. FACIAL INTERNAL MAMMARY FIG. 141. VEINS OF THE NECK AND UPPER PART OF THORAX. Front View. (Gerrish.) (2) The inferior vena cava group. Veins of the lower extremities. The blood from the lower limbs is also returned by a deep and a superficial set of veins. They are more abundantly supplied with valves than the veins of the upper limbs. The deep veins. Below the knee the deep veins accompany the arteries in pairs, as vense comites, and as in the upper limbs are called by the same names. The veins from the foot empty into anterior tibial and posterior tibial veins. They unite to form the CHAP. XI] VEINS 219 single popliteal vein, which is continued as the femoral and becomes the external iliac. The superficial veins. The internal or long saphenous and the external or short saphenous are the two largest superficial veins. I FIG. 142. SUPERFICIAL VEINS OF THE FRONT OF THE LEG AND FOOT. (Gerrish.) FIG. 143. SUPERFICIAL VEINS OF THE FRONT OF THE RIGHT THIGH. (Gerrish.) 220 ANATOMY AND PHYSIOLOGY [CHAP. XI The internal saphenous extends from the ankle to within an inch and a half (3.8 cm.) of the inguinal ligament. It lies along the inner side of the leg and thigh and ter- minates in the femoral vein. The external saphenous arises from the sole of the foot, and, passing up the back of the leg, ends in the deep popliteal. The femoral veins. These vessels are a continuation of the popliteal veins and extend from the opening in the adductor magnus to the level of the inguinal liga- ment. The external iliacs. These vessels are a continuation of the femoral veins, and extend from the level of the inguinal (Poupart's) ligament, on either side, to the joint between the sacrum and the ilium. They receive the blood from the deep and superficial veins of the lower limbs. (See Fig. 129.) The internal iliacs. They are formed by the union of veins corresponding to the branches of the internal iliac arteries. They accompany the internal iliac arteries and unite with the external iliac veins to form the common iliacs. (See Fig. 129.) The common iliacs. The common iliacs extend from the base of the sacrum to the fourth lumbar vertebra, and then the two common iliacs unite to form the inferior vena cava. (See Fig. 129.) The inferior vena cava. The inferior, or ascending, vena cava, returns the blood from the lower limbs, pelvis, and abdomen. It begins at the junction of the two com- mon iliacs, and thence ascends along the right side of the aorta, perforates the diaphragm, and terminates by entering the right auricle of the heart. The inferior vena cava receives many tributaries, the chief of which are the lumbar, ovarian, renal, and hepatic veins. (See Fig. 129.) FIG. 144. SUPER- FICIAL, VEINS OF THE DORSUM OF THE LEG. (Gerrish.) CHAP. XI] VEINS 221 Supplementary channel. A supplementary channel between the inferior and superior vena cava is formed by the azygos veins. They are three in number and lie on the sides of the front of the vertebral bodies. INTERNAL JUGULAR SUBCLAVIAN RIGHT-^ INNOMINATE INTERNAL JUGULAR EXTERNAL JUGULAR UPPER END OF THORACIC DUCT SUBCLAVIAN LEFT INNOMINATE ASCENDING LUMBAR FIG. 145. AZYGOS AND INTERCOSTAL VEINS. (Gerrish.) The right or major azygos vein is an upward continuation of the lumbar vein which communicates with the common iliac vein, and often with the inferior vena cava and renal vein. It ascends 222 ANATOMY AND PHYSIOLOGY [CHAP. XI FIG. 146. PORTAL SYSTEM OF VEINS. The liver is turned upward and back- ward, and the transverse colon and most of the small intestines are removed. (Gerrish.) CHAP. XI] THE PORTAL SYSTEM 223 on the right side of the vertebral column to the level of the fourth thoracic vertebra, where it empties into the superior vena cava. The left lower azygos (minor) vein commences on the left side of the abdomen in a manner similar to the right. It ascends on the left side of the vertebral column, and at about the level of the eighth thoracic vertebra it connects with the right azygos vein. The left upper azygos vein connects above with the superior intercostal vein, and opens below into either the left lower azygos, or the major azygos vein. These veins receive many tributaries from the thoracic walls and so are often grouped with the thoracic veins. It is important to remember that in case of obstruction in the inferior vena cava these veins form a supplementary channel by which blood can be conveyed from the lower part of the body to the heart. The portal system. The gastric, splenic, inferior, and superior mesenteric veins which bring back the blood from the intestinal tract do not take it directly to the inferior vena cava. Just back of the pancreas, the splenic and superior mesenteric unite to form the portal vein, and the gastric and inferior mesenteric empty into it. The portal vein runs upward and to the right for about three inches (7.5 cm.), then enters the liver, where it divides into many small veins, and these finally form plexuses of capillaries. These capillaries unite with another set of capillaries which arise from the hepatic artery, and form the hepatic vein, which carries the blood from the liver to the inferior vena cava. Thus it will be seen that the liver receives blood from two sources (1) the portal vein which carries blood to the liver in order that certain chemical changes may take place, and (2) the hepatic artery which carries blood to the liver for nutritive purposes. The blood from both sources of supply is carried from the liver by the hepatic vein. The portal vein and all its branches constitute the portal system, which is often described as a third or accessory system. 224 ANATOMY AND PHYSIOLOGY [CHAP. XI Arteries , SUMMARY Begin as large trunks, grow smaller. Usually deep seated for protection. Two branches of nearly equal size. Division Trunk gives off several branches. One branch that serves as an axis. Anastomosis or inosculation distal ends unite. Plexus many inosculations within limited area. Usually straight (facial and uterine are tortuous). Provides' for pulmonary circulation. Right pulmonary Pulmonary Divisions System of the Vascular ] System General System 1. Pulmonary artery artery right lung. Left pulmonary artery left lung. 2. Capillaries connect arterioles and venules. 3. Four pulmonary veins two from each lung. Provides for systemic circulation. 1. Aorta and all its branches. 2. Capillaries connect arterioles and venules. 3. Veins empty into heart either directly or by means of inferior and superior vena cava. Aorta Ascending Aorta Right and left coronary supply the heart. Int. carotid brain Right com- and eye. mon caro- Ext. carotid throat, tid tongue, face, ears, Innominate 12. _ O " walls of cranium. Superficial I. Arrh of to 2 in. Right sub- Ulnar palmar f\l \*1 V/l clavian, arch. Aorta axil- 2 in. lary - brachial . J Deep palmar Radial i , I arch. Left common carotid same branches as right common carotid. Left subclavian same branches as right sub- clavian. Bronchial to the lung tissue. II. (Esophageal to the oesophagus. Thoracic Mediastinal to the nodes and areolar tissue in Aorta the mediastinum. 7 to 8 in. Pericardial to the pericardium. [ Intercostal to the intercostal spaces. CHAP. XI] SUMMARY 225 f Diaphragm muscle is dividing line between thoracic and ab- dominal aorta. Gastric stomach, and Aorta III. Abdominal Aorta Sin. Visceral Group Parietal Group Cceliac axis Sup. mesenteric Common Iliac Arteries 2 in. Hepatic liver duodenum. Splenic spleen, stomach, and pan- creas. Supra-renal supra-renal bodies. Small intestine, ex- cept duodenum. Half of large intes- tine. Renal kidneys. Spermatic testes. Ovarian ovaries and uterus. Inf. I Lower half of large mesenteric intestine and rec- l turn. Phrenic diaphragm. Lumbar dorsal, spinal, and ab- dominal walls. Middle sacral sacrum and coccyx. Internal iliac walls and viscera of pelvis. Veins External iliac femoral popliteal Differ from arteries Sets Posterior tibial Ext. plantar 1 Plantar Int. plantar j arch. . Peroneal. Anterior 1 tibial I Dorsalls pedis ' Begin small, grow larger. Larger capacity. Greater number. Thinner walls. Valves. More frequent anastomosis. Superficial. f Venae comites companion veins. Deep . ( Vena comes companion vein. Receive blood from the face and the exterior of the cranium. Formed in parotid gland, terminate in the sub- clavian. Receive blood from the veins and sinuses of the cranial cavity. Begin at base of skull, unite with subclavian. External r * Jugular > 2 VH f^ Veins O ^^ ' CX rt Internal 5 Jugular I Veins Q 226 ANATOMY AND PHYSIOLOGY [CHAP. XI [ r Axillary Veins I o S iuperior Ve Sub- clavian m Veins Innominate Veins Superior Vena Cava Thoracic Veins (2) Receive blood from ficial veins super- Femoral Veins External Iliacs Internal Iliacs Common Iliacs Inferior Vena Cava (1) Receive blood from the deep veins of the forearm and arm. They accompany the arteries and are called by the same names. Radial. Posterior ulnar. Anterior ulnar. Common ulnar. Median. Median basilic. Median cephalic. Basilic. Cephalic. Formed by union of the inner brachial and basilic, end in the subclavian. Continuation of axillary from first rib to the joint be- tween the sternum and clavicle. Unite with internal jugular to form innominate. Transmit blood from head, neck, upper limbs, and part of thoracic wall. Receive lymph. Formed by union of internal jugular and subclavian. One on each side of body. Formed by union of right and left innominate veins. Three inches long. I Opens into right auricle. Majority follow same course and bear same name as arteries. Continuation of the popliteal and extend from opening in adductor magnus muscle to the inguinal ligament. (1) Receive blood from deep veins of foot, leg, and thigh. They accompany the arteries and are called by the same names. (2) Receive blood from the [ superficial veins, two j Intend saphenoiis. are important External saphenous. Continuation of femoral veins. Extend from inguinal ligament to the joint between sacrum and ilium. J Formed by union of veins corresponding to branches ( of internal iliac artery. f Formed by union of external and internal iliacs. Extend I from base of sacrum to the fourth lumbar vertebra. Formed by union of the common iliacs. Extends from fourth lumbar vertebra to the right auricle of the heart. Receives many tributaries corresponding to arteries given off from the aorta. CHAP. XT] SUMMARY 227 Supplement- ary Channel Portal Cir- culation 1. Right azygos vein 2. Left lower azygos vein 3. Left upper azygos vein Connect with superior vena cava above, and inferior vena cava below. Portal Vein Splenic vein and superior mesenteric vein Gastric vein and inferior mesenteric vein Unite to form portal vein. Empty into the portal vein be- fore it enters the' liver. Carries blood to liver, breaks up into capil- laries, then unites with capillaries from hepatic artery to form hepatic vein. Hepatic Vein empties into inferior vena cava. CHAPTER XII THE VASCULAR SYSTEM CONTINUED: THE GENERAL CIRCULA- TION; BLOOD PRESSURE; THE PULSE; LYMPH; FCETAL CIRCULATION THE GENERAL CIRCULATION OF THE BLOOD THE blood is contained in a closed set of tubes which it com- pletely fills. Interposed in this set of tubes is the heart which fills with blood from the veins and then contracts, thereby forcing a part of this blood into the lungs and a part to all the rest of the body. To trace the general circulation, we will begin with the venous blood which is returned to the right auricle by the superior and inferior venae cavse. It enters and fills the right auricle, and the right ventricle which for the time being may be thought of as f a single chamber, with the tricuspid valve open. 1 Then the auricle contracts and forces the blood over the open valve into the ven- tricle, which has already been passively filled, and now becomes well distended by the extra supply. The blood gets behind the cusps of the tricuspid valve and closes them. After a brief pause, (possibly T^tr of a second) the ventricle contracts and forces the blood over the open semilunar valves into the pulmonary artery. The pulmonary artery divides into two branches and carries the blood to the lungs, where it passes through the innumerable capil- laries that surround the alveoli or air sacs of the lungs. These capillaries unite to form veins, and these unite to form larger veins, until finally two pulmonary veins return the blood from each lung to the left auricle and ventricle. The left auricle now contracts and forces the blood over the open bicuspid valve into the left ven- tricle, just as described for the right side of the heart. The bicuspid valve is closed in the same way as the tricuspid and after 1 It is a mistake to think that the blood all accumulates in the auricle before any is forwarded to the ventricle. 228 CHAP. XII] THE GENERAL CIRCULATION 229 a brief pause the left ventricle contracts, forcing the blood over the open semilunar valve, into the aorta. From the aorta and its branches the blood travels in the capillaries to every part of the body. The capillaries unite to form veins, and finally the blood is returned by means of the vense cavse to the right auricle, which completes the circuit. The pulmonary circulation. The lesser circulation, from the right ventricle to the left auricle, is called the pulmonary circula- Pulmbnary artery. Superior cava or vein from head and neck. Right auricle. Inferior vena cava- Right ventricle. Portal circulation. Second renal circu- lation. Pulmonary capillaries. Pulmonary veins. Aorta. Arteries to head and neck. Left auricle. Left ventricle. Gastric and intestinal vessels. m First renal circulation. ..Systemic capillaries. FIG. 147. : DIAGRAM OF THE CIRCULATION. (Halliburton.) tion. The purpose of the pulmonary circulation is to carry the blood which has been through the system, giving up oxygen and collecting carbon dioxide, to the air sacs of the lungs, where the red cells are recharged with oxygen, and the carbon dioxide is reduced to the standard amount. (See page 261.) The systemic circulation. The more extensive circulation, from the left ventricle to all parts of the body, and the return to the right auricle, is known as the systemic circulation. The pur- pose of the systemic circulation is to carry oxygen and nutritive material to all parts of the body, and gather up waste products. This double circulation, pulmonary and systemic, is constantly 230 ANATOMY AND PHYSIOLOGY [CHAP. XII and simultaneously going on, as each half of the heart is in a lit- eral sense a force pump. The heart as a pump. The muscles 1 of the auricles and ven- tricles are so arranged that when they contract, they lessen the capacity of the chambers which they enclose. When this happens the blood from the contracting chamber is expelled in the direc- tion of the arrows, since the valves prevent its passage in the op- posite direction. The first sign of contraction is noted in the sinus tissue of the right auricle the sino-auricular node which is sometimes designated as the pace-maker of the heart. From this spot the wave of contraction spreads over the muscles of both auricles. These contract simultaneously, driving the blood into the ventricles. Meanwhile the wave of contraction has passed from the auricles to the ventricles, and now spreads over the ventricles, which contract simultaneously. The wave of contraction. If a stimulus be applied to one end of a muscle, a wave of contraction sweeps on over the entire tissue. It is therefore easy to conceive how a wave of contraction can sweep over the muscular tissue of the auricles which is practically continuous. The question is how is this wave transmitted to the muscular tissue of the ventricles which is not continuous with that of the auricles? The connecting pathway is furnished by the auriculo-ventricular bundle of His which transmits the im- pulses and causes the wave of contraction to spread over the ven- tricles. (See page 180.) The heart-beat. By a heart-beat we mean a coordinated contraction of the cardiac muscle resulting in the expulsion of blood from both ventricles. It consists of (1) an active phase or period of contraction called the systole, and (2) a passive phase or period of dilatation and rest 2 called the diastole. The com- bination of the systole and diastole constitutes a cardiac cycle and corresponds to the heart-beat. The heart of a man at rest may beat seventy-two times a minute. Some individuals have a lower and others a higher average. This rate may be doubled by ex- ercise. If we assume that the heart beats 75 times a minute, the time required for a cardiac cycle is about 0.8 of a second, and half 1 See page 174 and Fig. 106. 2 The period of rest is now often considered separately as the diastasis or pause CHAP. XII] THE GENERAL CIRCULATION 231 of this, or Q.4 of a second, represents the diastole or passive phase. Heart sounds and murmurs. If the ear be applied over the heart, certain sounds are heard, which recur with great regularity. The first sound is a comparatively long, booming sound ; the second, a short, sharp, sudden one. The sounds resemble the syllables ' lubb dup. The first sound is thought to be due to vi- brations caused by the closure of the auriculo-ventricular valves and the contraction of the ventricles ; the second is attributed to vibrations set up by the sudden closure of the semilunar valves. In certain diseases of the heart these sounds become changed and obscure, and are called murmurs. These are often due to failure of the valves to close properly, thus allowing regurgitation of the blood. Cause of the heart-beat. The cause of the heart-beat is still an unsettled question. We do not know whether the rhythmic con- tractions are due to the nerve tissue which the heart contains, or whether they are due to a power inherent in the muscle itself. The results of many experiments support the theory that the func- tion of the nerve tissue is regulatory; that the contractions are due to the inherent power of automaticity, and that the stimulus which excites the contractions is a chemical one dependent upon the presence of definite proportions of certain salts in the blood. It has been shown that all the constituents of the blood can be dispensed with except water and these essential salts, i.e., sodium chloride 0.9 per cent, calcium chloride 0.024 per cent, and potassium chloride 0.042 per cent. 1 Under normal con- ditions these salts are always present, and as the blood is con- stantly passing through the heart, it follows that the heart is subjected to a continuous stimulus. It is natural to question why the heart is not in a state of continuous contraction? In other words, how is relaxation possible? In answer it may be stated that as soon as the heart has contracted it loses its irri- tability to every sort of stimulus and relaxes. After a time its irritability returns and it reaches a condition in which it is again able to respond to a stimulus and contracts again. Each con- traction is followed by a period of relaxation known as the refractory period. Thus the rhythmic action of the heart is due to the refractory period. 1 A solution of this composition is known as Ringers' solution. 232 ANATOMY AND PHYSIOLOGY [CHAP. XII Automaticity . The most remarkable power of cardiac muscle is its automaticity. Skeletal muscle rarely contracts except in response to the arrival of stimuli by way of the motor nerves. Visceral muscle shows an automatic tendency, but this power is most highly developed in the heart. This may be demonstrated by removing the heart of a frog from the body of the animal. The heart will continue to beat for hours provided it is kept moist with Ringers' solution. The degree of automatic power pos- sessed by different regions of the heart varies. Some parts beat faster than others. The most rapidly contracting part is the sino- auricular node of the right auricle. It is from this particular spot that the wave of contraction radiates, and from here it is trans- mitted over the bundle of His to the ventricles. Ordinarily, the ventricles beat at the rate set by the right auricle, but if for any reason the auricle ceases to beat, the ventricles will beat inde- pendently but at a slower rate. 1 Thus the normal sequence of the contraction depends upon the fact that the automaticity of the right auricle is more highly developed than that of the ven- tricles. Nervous control of the heart. Although the heart contracts automatically and rhythmically, it is under normal conditions controlled by two sets of nerves. These consist of inhibitory nerves coming to the heart from the pneumogastric or vagus nerve, and accelerator nerves from the sympathetic system. The inhibitory nerves have their cell-bodies situated in the medulla where they form a cardio-inhibitory centre. The location of the cardio-accel- erator centre has not been determined. Both the inhibitory and accelerator nerves are in a state of constant, though slight, ac- tivity. This means that the heart-beat is controlled by two antagonistic influences, one tending to slow the heart action, and the other to quicken it. If the inhibitory centre is stimulated to greater activity, the heart is slowed still further. If this center is inhibited, the heart-rate is increased, because the inhibitory action is removed. Stimulation of the accelerator nerves results in a quickened heart-beat, and section of these nerves slows the heart. 1 Experimentally the bundle of His may be damaged, with the result that the auricles beat as before, but the ventricles adopt a slower rate, thus creating a condi- tion known as heart-block. CHAP. XII] THE GENERAL CIRCULATION 233 Factors maintaining arterial circulation. The most important factors maintaining arterial circulation are (1) the pumping action of the heart, 1 (2) the extensibility and elasticity of the arterial walls, and (3) the peripheral resistance. The extensibility and elasticity of the arterial walls. Each time the ventricles contract they force a certain amount of blood into arteries that are already full. 2 The extensibility of the ar- teries enables them to distend and receive this extra supply of blood. This period of distention corresponds to the contraction period of the heart. Just as soon as the force is removed, the elas- ticity of the arteries causes them to contract, and exerts such a pressure on the contained blood, that this blood is forced into the capillaries just rapidly enough to allow the arteries time to reach their usual size by the beginning of the next contraction period of the heart. They thus serve not only as conducting tubes but exert a force that assists the heart in driving the blood into the capillaries. The extensibility and elasticity of the arteries change with the health and age of the individual. Sometimes as the result of dis- ease, and always as we grow older, the arterial walls grow stiffer and more rigid, and become less well adapted for the unceasing work they are called upon to perform. This condition is known as arteriosclerosis. Peripheral resistance. This term is used to designate the re- sistance offered by the innumerable arterioles and capillaries into which the large arteries empty. It is easy to realize that a large tube like the aorta offers less resistance to the flow of blood, than an enormous number of microscopic tubes like the capil- laries. Factors maintaining venous circulation. The effect of the pumping action of the heart is not entirely spent in forcing the blood through the arteries and capillaries. A little force still remains to propel the blood back to the heart again, and the pres- ence of valves keeps it flowing in the right direction, i.e., toward the heart. The return flow is also favored by (1) the suction action of the heart caused by the emptying of the auricles, (2) the heart and respiratory movements which cause continual changes of pressure in the thorax and abdomen, (3) the contractions of the 1 See page 230. J Estimated all the way from 2 to 6 ounces. 234 ANATOMY AND PHYSIOLOGY [CHAP. XII skeletal muscles which exercise a massaging action upon the veins, and aided by the valves, propel the blood toward the heart. The velocity of the blood-flow. In all the large arteries the blood moves rapidly; in the capillaries very slowly; and in the veins the velocity is augumented as they increase in size, but never equals that in the aorta. The underlying principle is that in any CAPILLARIES FIG. 148. DIAGRAM TO ILLUSTRATE VARIATIONS IN VELOCITY OF BLOOD FLOW. If a vessel divides into two branches, these will be individually of less cross- section than the main trunk, but united they will exceed it. Linear velocity will be lower in the branches than in the parent stock. The sum of the cross-sectional areas of the capillaries is greater than that of the artery or vein. stream the velocity is greatest where the cross-section of the channel is least, and lowest where the cross-section is greatest.. The application of this principle requires that we regard the aorta as the narrowest and the capillaries as the widest part of the vascular system. This is readily admitted if we remember that it is the combined channels of millions of capillaries which we have to com- pare with the aorta. It is a generally accepted truth that when a vessel divides, the sum of the cross-sections of the two branches is greater than that of the main trunk. Consequently the velocity will be reduced when an artery divides, and increased when two veins unite to make one. The reason why the velocity in the veins never equals that in the aorta is because the cross-section of the two venae cavse is greater than the cross-section of the single aorta. The actual service of the blood to the tissues is rendered in the capillaries (since the walls of the arteries and veins are too thick to permit of diffusion), hence the value of the slow passage. CHAP. XII] BLOOD PRESSURE 235 Distribution of blood to different parts of the body. The quantity of blood contained in the body is always about the same, but the distribution varies, and is determined by the needs of the different parts. When the digestive organs are active, they need an extra supply of blood, which is furnished by depleting the quantity in less active organs, i.e., the muscles or skin. On the other hand, active muscular work requires that an increased supply of blood be sent to the muscles and lungs and less to the digestive organs. BLOOD PRESSURE By blood pressure is meant the pressure the blood exerts against the walls of the vessels in which it is contained. The term includes arterial, capillary, and venous pressure. A vein is easily flattened under the finger ; an artery offers a stronger resistance. This is an indication of a great difference between arterial and venous pres- sure. This difference is also shown when an artery and a vein are cut ; the blood springs from the artery in a pulsating spurt, while the flow from the vein is continuous and even when copious " wells up " rather than " spurts out." Various experiments have put us in possession of the following facts. Pressure in the arteries is high and fluctuating, slightly higher in the large trunks than in their branches ; pressure in the veins is low and relatively constant. It must be higher in the small veins than in the large ones they unite to form, because the direction of the blood-flow is from the smaller to the larger ones. When the blood leaves the left ventricle the high pressure which it exerts against the wall of the aorta may be regarded as a measure of energy. This energy is transformed into heat in overcoming the friction encountered in the vessels. When the blood reaches the capillaries, the surface is multiplied and the friction increased, This offers an impediment to the flow, and the result is a decided drop in the pressure. Arterial pressure is not uniform, but varies (1) with the systole and diastole of the heart, being greater during the systole ; (2) it is less in youth, and increases as we grow older,, because the arteries are less elastic ; (3) conditions of health may affect the normal muscular tone of the arteries and heart. When the arteries lose their tone, or the heart-beat loses its force, the blood pressure is 236 ANATOMY AND PHYSIOLOGY [CHAP. XII low. When the arteries are overconstricted, or the heart over- stimulated, the blood pressure is high. Method of determining blood pressure. It is customary to try the pulse at the wrist to determine whether the patient has B FIG. 149. SPHYGMOMANOMETERS. A, the mercury instrument is accurate, although a trifle more bulky than the spring type. B, the spring type of instrument. CHAP. XII] BLOOD PRESSURE 237 high blood pressure. If the radial artery is hard and incom- pressible it may indicate either that some change has occurred in the vessel, or that the pressure is high. If, however, the pulse is easy to obliterate with the fingers it is usual to find a low pressure. Of late years many forms of apparatus have been devised by which a more accurate knowledge of this condition can be ob- tained. This apparatus is called a sphygmomandtneter, and con- sists of a scaled column of mercury which is connected with an air bag by rubber tubing. The air bag is in turn connected with a small hand pump and is contained in a cuff of either leather or cloth. Some instruments are constructed with a spring scale instead of a column of mercury but the principle is the same. The air bag contained in the cuff is buckled snugly about the arm just above the elbow so as to compress the brachial artery. By placing the finger upon the pulse at the wrist (as we inflate the bag) , we finally reach a point where the pulse disappears, or in other words, the pressure in the bag as indicated on the instrument is equal to the pressure, which is necessary to overcome the pressure of the artery wall, plus the force of the heart-beat. This is known as systolic pressure. Another method is to place a stethoscope over the brachial artery (instead of the hand on the pulse) , and note the point at which the pulse disappears. After the systolic pres- sure has been ascertained by releasing the air slightly in the cuff and allowing the scale to drop, the pulse first becomes more posi- tive and then fainter until it is lost to the stethoscope. The point lowest on the scale where it disappears is known as the diastolic pressure. The diastolic pressure cannot be taken by the finger- pulse method. It is necessary to use a stethoscope. Normal degree of blood pressure. The normal degree of blood pressure necessary to obliterate the pulse in the brachial artery is about 11 to 13.5 cm. (centimetres of mercury column) for systolic, and 5.5 to 7 cm. diastolic. Pressure varies with age, and even in health is not constantly the same. Increase in the force and frequency of the heart increases the pressure. Cold, drugs, etc. which constrict the arterial pulse may raise the blood pres- sure. Heat, and the drugs of the vaso-dilator group like nitro- glycerin, may lower it. 238 ANATOMY AND PHYSIOLOGY [CHAP. XII THE PULSE When the finger is placed on an artery, a sense of resistance is felt, and this resistance seems to be increased at intervals, corre- sponding to the heart-beat, the wall of the artery at each heart- beat being felt to rise up or dilate under the finger. This alternate dilatation and contraction of the artery constitutes the pulse; and in certain arteries which lie near the surface this pulse may be seen with the eye. When the finger is placed on a vein, very little resistance is felt; and, under ordinary circumstances, no pulse can be perceived by the touch or by the eye. As each expansion of an artery is produced by a contraction of the heart, the pulse, as felt in any superficial artery, is a con- venient guide for ascertaining the character of the heart's action. Locations where the pulse may be felt. The pulse may be counted wherever an artery approaches the surface of the body. These locations are : (1) The facial artery, where it passes over the lower jawbone. (2) The temporal artery, above and to the outer side of the outer canthus of the eye. (3) The brachial artery, along the inner side of the biceps muscle. (4) The radial artery, on the thumb side of the wrist. On ac- count of its accessible situation the radial artery is usually em- ployed for this purpose. (5) The femoral artery, where it passes over the pelvic bone. (6) The* dor sails pedis, on the dor sum of the foot. Points to note in feeling a pulse. In feeling a pulse the follow- ing points should be noted. (1) Frequency, or the number of pulse-beats per minute. (2) Strength, or the force of the heart-beat. (3) Regularity, or the same number of beats per minute. (4) Equality. Each beat should have the same force, not some strong and some weak. It sometimes happens that a beat is missed because the heart-beat is too weak to distend the artery. This is called an intermittent pulse. Occasionally there is a lack of tone in the arterial walls and a dicrotic pulse is felt. This means that the pulsations are divided and the second part of the beat is weaker than the first. CHAP. XII] THE LYMPH 239 (5) Blood pressure. This is suggested by the amount of force that is required to obliterate the pulse. Average frequency of the pulse. The average frequency of the pulse in man is seventy-two beats per minute. This rate may be increased after eating or by muscular action. Even the varia- tion of the muscular effort entailed between the standing, sitting, and recumbent positions will make a difference in the frequency of the pulse of from eight to ten beats per minute. Mental excite- ment may also produce a temporary acceleration, varying in degree with the peculiarities of the individual. Age has a marked influence. At birth the pulse rate is about 130 per minute; at three years, 100; in adult life, 72; in old age, 65. It is some- what more rapid in women than in men and is lowered during sleep. Idiosyncrasies are frequently met with. A person in perfect health may have a much higher or a much lower rate than 72. The relative frequency of the pulse and respirations is about four heart-beats to one respiration. As a rule, the rapidity of the heart's action is in inverse ratio to its force. An infrequent pulse, within physiological limits, is usually a strong one, and a frequent pulse comparatively feeble ; the pulse in fever or debilitating affections becoming weaker as it grows more rapid. LYMPH Formation of lymph. The lymph is derived from the blood in the capillaries, but the exact process is still an open question. It is considered probable that it is partly a process of filtration which depends on the permeable nature of the walls of the capil- laries, and partly the result of a secretory process on the part of the endothelial cells lining the capillaries. The filtration theory is supported by the fact that the blood in the capillaries is under greater pressure than in the arteries or veins. The secretory pro- cess is supported by the chemical differences between the blood and the lymph. Factors controlling the flow of lymph. The onward progress of the lymph from the tissues to the veins is maintained chiefly by three things. (1) Differences in pressure. The lymph in the tissue spaces is under greater pressure than the lymph in the lymph capillaries, 240 ANATOMY AND PHYSIOLOGY [CHAP. XII and the pressure in the larger lymphatics near the ducts is much less than in the smaller vessels. Consequently we may consider that the lymphatics form a system of vessels leading from a region of high pressure, viz. the lymph spaces of the tissues, to a region of low pressure, viz. the interior of the large veins of the neck. (2) Muscular movements and valves. The muscular move- ments of the body compress the lymphatics and force the lymph on in the proper direction. The numerous valves prevent a return flow in the wrong direction. (3) Respiration. During each inspiration the pressure on the thoracic duct is less than on the lymphatics outside the thorax, and the lymph is accordingly " sucked " into the duct. During the succeeding expiration the pressure on the thoracic duct is in- creased, and some of its contents, prevented by the valve from escaping bejow, are pressed out into the innominate veins. (Edema. The lymph in the various lymph spaces of the body varies in amount from time to time, but under normal circum- stances never exceeds certain limits. Under abnormal condi- tions, these limits may be exceeded, and the result is known as oedema, or dropsy. Similar excessive accumulations may also occur in the larger lymph spaces, the serous cavities. Among the possible causes of oedema are : (1) An excessive formation, the lymph gathering in the lymph spaces faster than it can be carried away by a normal flow. (2) Any obstruction to the flow of lymph from the lymph spaces. FCETAL CIRCULATION Certain structures are necessary to the performance of fcetal circulation, but are of no use after birth. They are as follows : - (1) Foramen ovale. An opening between the two auricles. It furnishes direct communication between them. (2) Ductus arteriosus. A blood-vessel connecting the aorta and pulmonary artery. (3) Ductus venosus. A blood-vessel connecting the umbilical vein and the inferior vena cava. (4) The placenta and umbilical cord. The placenta is a ir.ass of tissue rich in blood-vessels which is in close contact CHAP. XII] THE FCETAL CIRCULATION 241 with the lining of placenta with the of two arteries and one large vein pro- tected by Wharton's jelly. The arteries are branches of the arterial system of the foetus, and carry blood from the foetus to the placenta where it is sepa- rated by the thin- nest of walls from the maternal blood in the blood-vessels of the uterus. The usual distinctions between arterial and venous blood cannot be recognized, as the blood of the foetus is never up to the arterial standard of the mother. The best blood is that which has been im- proved by effecting exchanges with the blood in the uterine vessels, and is car- ried from the pla- centa to the foetus by the vein. By means of the pla- centa the foetus ob- tains oxygen, but it is more than a lung; it is the seat the uterus. The umbilical cord unites the navel of the child. The cord is made up A* | "] ARTERIAL BLOOD $M VENOUS BLOOD FIG. 150. DIAGRAM OF CIRCULATION BEFORE BIRTH. Foetal type. The arrows indicate the course of the blood. (Cooke.) 242 ANATOMY AND PHYSIOLOGY [CHAP. XII of the absorption of food, and serves for the unloading of wastes. Course of the blood. The blood is carried from the placenta along the umbilical cord by the umbilical vein. Entering the foetus it is conveyed into the ascending vena cava partly through the liver but chiefly through the ductus venosus, which con- nects these two vessels. From the ascending vena cava it enters the right auricle, passes through the foramen ovale into the left auricle, thence into the left ventricle, and out through the aorta, which distributes it principally to the upper extremities. The blood from the head and upper extremities returns by the descend- ing vena cava to the right auricle, then, passes into the right ven- tricle, and out through the pulmonary artery to the lungs. As the lungs in the fcetus are solid, they require very little blood (only for nutrition), and the greater part of the blood passes through the ductus arteriosus into the descending aorta, where, mixing with the blood delivered to the aorta by the left ventricle, it descends to supply the lower extremities of the foetus. The chief portion of this blood is carried to the placenta by the two umbilical arteries, but a small amount passes back into the as- cending vena cava and mixes with the blood from the placenta. From this description of the foetal -circulation, it follows : 1. That the placenta serves the purpose of a respiratory, nu- tritive, and excretory organ. 2. That the liver receives blood directly from the placenta; hence the large size of this organ at birth. 3. That the blood from the placenta passes almost directly into the arch of the aorta, and is distributed by its branches to the head and upper extremities ; hence the large size and perfect development of these parts at birth. 4. That the blood in the descending aorta is chiefly derived from that which has already circulated in the upper extremities, and, mixed with only a small quantity from the left ventricle, is distributed to the lower extremities ; hence the small size and imperfect development of these parts at birth. Changes in the vascular system at birth. From the foregoing description it is obvious that at birth very important changes must take place : 1. The blood clots in the umbilical vein, between the usual CHAP. XII] THE FCETAL CIRCULATION 243 ligature and the liver, also in the ductus venosus. The blood clot becomes organized and these two vessels become obliterated. 2. As respiration commences, the blood traverses the pul- monary arteries, and then returns to the heart by the pulmonary veins ; this raises the blood pressure in the left auricle, and causes the valve over the foramen ovale to close. 3. The blood in the ductus arteriosus clots, the clot organizes, and the ductus arteriosus becomes a fibrous cord. 4. The blood in the hypogastric arteries also clots, the clots organize, and these vessels become obliterated. Occasionally some of the embryonic by-passes fail to close, and so much venous blood enters the arterial system that a blue baby is the result. In such instances the child suffers from malnutrition and the chances for survival are slight. 244 ANATOMY AND PHYSIOLOGY [CHAP. XII Pulmonary Circulation General Circulation < Systemic Circulation Heart Pumping Action Wave of Contrac- tion Heart Beat Heart Sounds SUMMARY Right auricle to right ventricle, then pulmonary arteries to lungs. Capillary system. Re- turn by pulmonary veins to left auricle. Purpose To increase oxygen and decrease carbon dioxide to standard amount. Left auricle to left ventricle, then by means of aorta and its branches to all parts of the body. Capillary system. Return by veins which empty into superior and inferior venae cavae. Carry, and Oxygen. give up to Nutritive ma- Purpose ^ the cells terials. Take from f Carbon dioxide, the cells [ Waste products. f Muscles contract and lessen capacity of auricles < and ventricles, thus forcing blood into I arteries. {Starts at sino-auricular node, transmitted to bundle of His, which in turn transmits it to the ventricles. Coordinated contraction of cardiac muscle. Cardiac cycle, 72 Systole Active stage Diastole Passive stage per minute. Occupies about 0.8 of a second, inherent in heart Automaticity muscle. f Sodium. Stimulated by chlorides I Potassium. Cause [ [ Calcium. Vagus nerve inhibi- tory. Sympathetic system accelerator. {Vibrations caused by closure of auric- ulo-ventricular valves and the con- traction of ventricles. Dup Vibrations caused by closure of semi- lunar valves. Innervation is regu- latory. Factors Maintaining Arterial Circulation 1. Pumping action of the heart. 2. The extensibility and elasticity of the arterial walls. 3. Peripheral resistance. CHAP. XII] SUMMARY 245 Factors Maintaining Venous Circulation Velocity of Blood-flow Blood Pressure Pulse 1. Some force due to pumping action of the heart. 2. Suction action of the heart. 3. Changes of pressure in thorax and abdomen due to heart and respiratory movements. 4. Contractions of the skeletal muscles. Arteries blood moves rapidly in large arteries, more slowly in smaller ones. Capillaries blood moves very slowly. Veins blood moves slowly in small veins, more rapidly in larger veins, but never as rapidly as in arteries. Pressure blood exerts against walls of vessels. High and fluctuating. 1. Higher during systole. 2. Lower during diastole. 3. Increases with age. Arterial 4. Not uniform Decreases if heart or arteries lose their tone. Venous Low and constant. 1 . Scaled column of mercury with Determined by use of sphyg- momanometer connected air Normal 2. An air bag contained in a cuff of leather or cloth. 3. Air bag also connected with hand pump. f Systolic or maximum 11.0 to 13.5 cm. 1 Diastolic or minimum 5.5 to 7.0 cm. Alternate contraction and expansion of artery. Locations where Pulse may be Counted Points to Note Pulse Rate Facial artery. Temporal artery. Brachial artery. Radial artery. Femoral artery. Dorsalis pedis. Frequency. Strength. Regularity. Equality. Blood pressure. Infant, 130 Three years, 100 Adult, 72 Old age, 65 Higher in women than in men. 246 ANATOMY AND PHYSIOLOGY [CHAP. XII Pulse Lymph . . (Edema Foetal Circulation Changes in Vascular System at Birth Changes in Pulse Rate may be Due to Formation Eating. Muscular activity. Mental excitement. Age. Sleep. Condition of health. Idiosyncrasies. Process of filtration. Process of secretion. Factors Con- [ Differences in pressure. trolling Flow < Muscular movements and valves. [ Respiration. Accumulation of lymph in tissues. f 1. Excessive formation. May be d 2 Obgtmction to flow of lymph from tissue. 1. Direct communication between right and left auricle by means of foramen ovale. 2. Direct communication between umbilical vein and inferior vena cava. Ductus venosus. 3. Direct communication between pulmonary artery and aorta. Ductus arteriosus. 4. Oxygen and nutritive substances obtained from placenta. 1. Umbilical vein and ductus venosus become obliter- ated. 2. Respiration stimulates pulmonary circulation ; this raises the blood pressure in left auricle, and closes foramen ovale. 3. Ductus arteriosus becomes a fibrous cord. 4. Hypogastric arteries become obliterated. CHAPTER XIII RESPIRATORY SYSTEM: NOSE; LARYNX; TRACHEA; BRONCHI; LUNGS. RESPIRATION ; ABNORMAL TYPES OF RESPIRA- TION. MODIFIED RESPIRATORY MOVEMENTS THE process of respiration is dependent upon the proper func- tioning of certain organs, which we group together and call a res- piratory system. The essentials of a respiratory system consist of a moist and permeable membrane, with a moving stream of AIR THfN MUCOSA I - I I 1 I ^~ CAPILLARY BLOOD VESSEL FIG. 151. DIAGRAM OF THE ESSENTIALS OF A RESPIRATORY SYSTEM. (Gerrish.) blood containing a high percentage of carbon dioxide on one side, and air or fluid containing a high percentage of oxygen on the other. In most aquatic animals the respiratory organs are external in the form of gills ; in terrestrial, or air-breathing animals, the respira- tory organs are situated internally in the form of lungs, and are placed in communication with the nose and mouth by means of the bronchi, trachea, and larynx. NOSE The nose is the special organ of the sense of smell, but it also serves as a passageway for the entrance of air to the respiratory organs. It consists of two parts, the external feature, the nose, and the internal cavities, the nasal fossae. The external nose is composed of a triangular framework of bone and cartilage, covered by skin and lined by mucous membrane. On its under surface are two oval-shaped openings the nostrils, which are the external openings of the nasal fossae. The margins of the nostrils are provided with a number of stiff hairs, which ar- 247 248 ANATOMY AND PHYSIOLOGY [CHAP. XIII rest the passage of dust and other foreign substances which might otherwise be carried in with the inspired air. The nasal fossae are two irregularly wedge-shaped cavities, separated from one another by a partition, or septum. The septum is formed partly by the vertical plate of the ethmoid, partly by the vomer, and partly by cartilage. Figure 152 shows the portions formed by the ethmoid, vomer, and cartilage. The turbinated bones "and turbinated processes of the ethmoid, which are exceedingly light and spongy, project into the nasal FRONTAL SINUSES NASAL- VERTICAL PLATE OF ETHMOID CARTILAGE OF SEPTUM MAXILLA SPHENOIDAL SINUSES VOMER FIG. 152. BONKS AND CARTILAGE FORMING SEPTUM OF NOSE. cavities, and divide them into three incomplete passages from be- fore backwards, the superior, middle, and inferior meatus. The palate and maxillae separate the nasal and mouth cavities, and the horizontal plate of the ethmoid forms the partition between the cranial and nasal cavities. These cavities 1 communicate with the air in front by the anterior nares, or nostrils, while behind they open into the back of the pharynx by the two posterior nares. They are lined with mucous membrane 2 which is continuous externally with the skin, and internally with the mucous membrane lining the passages and 1 Eleven bones enter into the formation of the nasal cavities : the floor is formed by the palate (2) and part of the maxilla? bones (2) ; the roof is chiefly formed by the horizontal plate of the ethmoid bone (1), the sphenoid (1), and by the (2) small nasal bones ; in the outer walls we find, in addition to processes from other bones, the two scroll-like turbinated bones (2). The vomer (1) forms part of the septum. 2 It is known as the pituitary or Schneiderian membrane. CHAP. XIII] RESPIRATORY SYSTEM 249 sinuses shown in Fig. 97. Inflammatory conditions of the nasal mucous membrane may extend into the sinuses. Advantages of nasal breathing. Under normal conditions breathing should take place through the nose only (1) because the arrangement of the turbinated bones makes the upper part of the SPHENOIDAI SIN US VESTIBULE FIG. 153. SAGITTAL, SECTION OP THE FACE AND NECK, SHOWING THE FIRST PORTIONS OF THE ALIMENTARY AND RESPIRATORY TRACTS. (Gerrish.) nasal passages very narrow ; (2) these passages are thickly lined, and freely supplied with blood-vessels, so that they can, even in the very coldest weather, moisten and warm the air before it reaches the lungs ; and (3) the presence of hairs at the entrance to the nostrils serves as filters. Mouth and pharynx. The mouth serves as a passageway for the entrance of air, and the pharynx transmits the air from the nose or mouth to the larynx, but both are more closely associated with digestion than respiration, and will be described with the digestive organs. 250 ANATOMY AND PHYSIOLOGY [CHAP. XIII RESPIRATORY SYSTEM Under this heading we group the organs which are concerned in the process of respiration. In man they are as follows : 1. Larynx. 3. Bronchi. 2. Trachea. 4. Lungs. THE LARYNX The larynx, or organ of voice, is placed in the upper and front part of the neck, between the base of the tongue and the top of the trachea. Above and behind lies the pharynx, which opens into the oesophagus, or gullet, and on either side of it lie the great ves- sels of the neck. The larynx is broad above and shaped somewhat like a triangular box, with flat sides and prominent ridge in front. Be- low it is narrow and rounded where it blends with the trachea. It is made up of nine pieces of fibro-cartilage, united by elastic ligaments, and moved by numer- ous muscles. The three principal cartilages are the cricoid, thyroid, and epiglottis. The cricoid resembles a seal ring with the hoop part in front and the signet part in the back. The thyroid resembles FIG. 154. DIAGRAM OF THE RESPIRATORY SYSTEM. CHAP. XIII] RESPIRATORY SYSTEM 251 a shield and is the largest. It rests upon the cricoid and con- sists of two square plates, or alse (right and left), which are joined in front and form by their union the laryngeal prominence, called Adam's apple. The epiglottis is shaped like a leaf. The stem is inserted in the notch between the two plates of the INFERIOR VOCAL FOLD FIG. 155. LARYNX. Viewed from above. (Gerrish.) thyroid. The larynx is lined throughout by mucous membrane, which is continuous above with that lining the pharynx, and below with that lining the trachea. The glottis. Across the middle of the larynx is a transverse partition, formed by two folds of the lining mucous membrane, stretching from side to side, but not quite meeting in the middle line. They thus leave in the middle line a chink, or slit, running from front to back, called the glottis, which is the narrowest seg- ment of the air passages. The glottis is protected by the leaf- shaped lid of fibro-cartilage, called the epiglottis, which shuts down upon the opening during the passage of food or other matter into the oesophagus. The vocal cords. Embedded in the mucous membrane at the edges of the slit are fibrous and elastic ligaments, which strengthen the edges of the glottis and give them elasticity. These ligamen- tous bands, covered with mucous membrane, are firmly attached at either end to the cartilages of the larynx, and are called the true vocal cords, because they function in the production of the 252 ANATOMY AND PHYSIOLOGY [CHAP. XIII voice. Above the true vocal cords are two false weal cords, so called because they do not function in the production of the voice. Variations in size of glottis. The glottis varies in shape and size, according to the action of the muscles upon the laryngeal walls. When the larynx is at rest during quiet breathing, the glottis is V-shaped ; during a deep inspiration it be- comes almost round, while during the pro- duction of a high note the edges of the folds approximate so closely as to leave scarcely any opening at all. Voice. The vocal cords produce the voice. A blast of air, driven by an expira- tory movement out of the lungs, throws the two elastic cords into vibrations. These im- part their vibrations to the column of air above them, and so give rise to the sound which we call the voice. The pharynx, mouth, and nasal cavities above the glottis act as resonating cavities, and by alterations in their shape and size, they are able to pick out and emphasize certain parts of the tones produced in the larynx. Differences between male and female voice. At puberty in the male, the larynx enlarges, giving rise to what is commonly called Adam's apple. The increase in the size of the larynx causes an increase in the length of the vocal cords. To this is due the lower pitch of the voice in the male. FIG. 156. THE LARYNX AS SEEN BY MEANS or THE LARYNGOSCOPE IN DIFFERENT CONDITIONS OF THE GLOTTIS. A, while singing a high note; B, in quiet breathing ; C, during a deep inspiration. I, base of tongue ; e, upper free edge of epiglottis ; e', cushion of the epiglottis ; ph, part of anterior wall of pharynx ; cv, the true vocal folds ; cvs, the false vocal folds ; tr, the trachea with its rings. CHAP. XIII] RESPIRATORY SYSTEM 253 THE TRACHEA The trachea, or windpipe, is a fibrous and muscular tube, about four and a half inches (11.2 cm.) in length, and three-quar- Superior Horn Inferior Horn FIG. 157. FRONT VIEW OF CARTILAGES OF LARYNX. Trachea and Bronchi. ters of an inch (1.9 cm.) from side to side. It lies in front of the oesophagus and extends from the larynx on the level of the sixth cervical vertebra, to opposite the fourth or fifth thoracic vertebra, 254 ANATOMY AND PHYSIOLOGY [CHAP. XIII where it divides into two tubes, the two bronchi, one for each lung. The walls are strengthened and rendered more rigid by hoops of cartilage embedded in the fibrous tissue. These hoops are C-shaped and incomplete behind, the cartilaginous rings being completed by bands of plain muscular tissue where the trachea comes in contact with the oesophagus. Like the larynx, it is lined by mucous membrane, and has a ciliated epithelium upon its inner surface. The mucous membrane, which also extends into the bronchial tubes, keeps the internal surface of the air- passages free from impurities; the sticky mucus entangles par- ticles of dust and other matters breathed in with the air, and the incessant movements of the cilia continually sweep this dirt- laden mucus upward and outward. THE BRONCHI The two bronchi, into which the trachea divides, differ slightly; the right bronchus is shorter, wider, and more nearly horizontal, the left bronchus is longer, narrower, and more nearly vertical. They enter the right and left lung, respectively, and then break up into a great number of smaller branches which are called the bron- chial tubes, or bronchioles. The two bronchi resemble the trachea in structure; but as the bronchial tubes divide and subdivide their walls become thinner, the small plates of cartilage cease, the fibrous tissue disappears, and the finer tubes are composed of only a thin layer of muscular and elastic tissue lined by mucous membrane. LUNGS The lungs are cone-shaped organs which occupy almost all of the cavity of the thorax that is not taken up by the heart, the large blood-vessels, the lymphatics, and the oesophagus. Each lung presents an outer surface which is convex, a base which is concave to fit over the convex portion of the diaphragm, and a summit or apex which rises half an inch above the clavicle. On the inner surface is a vertical notch called the hilum, which gives passage to the bronchi, blood-vessels, lymph-vessels, and nerves. The right lung is the larger and heavier ; it is broader than the left, owing to the inclination of the heart to the left side; it is CHAP. XIII] RESPIRATORY SYSTEM 255 also shorter by one inch, in consequence of the diaphragm rising higher on the right side to accommodate the liver. The right lung is divided by fissures into three lobes, upper, middle, and lower. The left lung is smaller, narrower, and longer than the right. It is divided into two lobes, upper and lower. The front border is deeply notched to accommodate the heart. RIGHT LUNG LEFT LUNG FlG. 158. BRONCHI AND BRONCHIOLES. The lungs have been widely sepa- rated and tissue cut away to expose the air-tubes. (Gerrish.) Anatomy of the lungs. The lungs are hollow, rather spongy organs, and consist of the bronchial tubes and their terminal dilatations, numerous blood-vessels, lymphatics, nerves, and an abundance of fine, elastic connective tissue, binding all together. (See Fig. 107.) Each lobe of the lung is composed of many lobules, and into each lobule a bronchiole enters and terminates in an en- largement having more or less the shape of a funnel, and called an infundibulum. From each infundibulum there is a series of small sac-like projections known as alveoli, the walls of which are honey- combed with cavities called the air-cells. In this way the amount FIG. 159. DIAGRAM OF A LOBULE OF THE LUNG. A bronchiole is seen divid- ing into two branches, one of which runs upward and ends in the lobule. In the lobule are four groups of infundibula. At the left are two infundibula, the alveoli of which present their outer surfaces. Next are three infundibula in vertical section, the alveoli of each opening into the common passageway. In the next group the first infundibulum shows a pulmonary arteriole surrounding the opening of each alveolus, and the second gives the same with the addition of the close capillary network in the wall of each alveolus. Around the fourth group is a deep deposit of pigment, such as occurs in old age, and in the lungs of those who inhale coal dust and the like. On the bronchiole lies a 1 (ranch of the pulmonary artery (blue), bringing blood to the infundibula for aeration. Beginning between the infundibula are the radicles of the pulmonary vein (red), a root of which lies upon the bronchiole. The bronchial artery is shown as a small vessel bringing nutrient blood to the bronchiole. (Gerrish.) 256 CHAP. XIII] RESPIRATORY SYSTEM 257 of surface exposed to the air and covered by the capillaries is so immensely increased that it is estimated the entire inner surface of the lungs is one hundred times greater than the skin surface of the body. 1 Blood-vessels of the lungs. Two sets of vessels are distrib- uted to the lungs : (1) the branches of the pulmonary artery, and (2) the branches of the bronchial arteries. (1) The branches of the pulmonary artery accompany the bronchial tubes and form a plexus of capillaries around the al- veoli. The walls of the bronchioles consist of a single layer of flattened epithelioid cells, surrounded by a fine, elastic connec- tive tissue, and are exceedingly thin and delicate. Immediately beneath the layer of flat cells, and lodged in the elastic connective tissue, is this very close plexus of capillary blood-vessels ; and the air reaching the alveoli by the bronchial tubes is separated from the blood in the capillaries only by the thin membranes forming their respective walls. The pulmonary veins begin at the margin of the alveoli and return the blood distributed by the pulmonary artery. (2) The branches of the bronchial arteries supply blood to the lung substance, the bronchial tubes, coats of the blood-vessels, the lymph nodes, and the pleura. The bronchial veins return the blood distributed by the bronchial arteries. Pleura. Each lung is enclosed in a serous sac, the pleura, one. layer of which is closely adherent to the walls of the chest and diaphragm (parietal) ; the other closely covers the lung (visceral). The two layers of the pleural sacs, moistened by serum, are nor- mally in close contact ; they move easily upon one another, and prevent the friction that would otherwise occur between the lungs and the walls of the chest with every respiration. Inflam- mation of the pleura is called pleurisy. Mediastinum. The mediastinum is the space left in the median portion of the thorax between the pleural sacs. It extends from the sternum to the spinal column, and contains a portion of many organs, i.e., the trachea, oesophagus, great vessels connected with the heart, lymph-nodes, thoracic duct, and various nerves. 1 It is estimated that the amount of lung surface which is exposed to the air is 90 square metres and the average skin surface is estimated to be & of one square metre. 258 ANATOMY AND PHYSIOLOGY [CHAP. XIII RESPIRATION The main purpose of respiration is to supply all the cells of the body with oxygen and rid them of the excess carbon dioxide which results from oxidation. It also helps to equalize the temperature of the body and get rid of excess water. To accomplish these purposes three processes are necessary : (1) Breathing. The process of breathing may be subdivided into inspiration or breathing in, and expiration or breathing out. Inspiration is a preliminary process whereby air is introduced into the lungs. Expiration is the process by which air is expelled from the lungs. This air has given up about one-fourth of its oxygen and increased the quantity of carbon dioxide one hundred times. (See page 263.) (2) External respiration. This includes two processes : (a) external oxygen supply or the passage of oxygen from the alveoli of the lungs to the blood ; and (6) external carbon dioxide elimi- nation or the passage of carbon dioxide from the blood into the alveoli of the lungs. (3) Internal respiration. This also includes two processes : (a) internal oxygen supply or the passage of oxygen from the blood to the cells of the tissues ; and (6) internal carbon dioxide elimination or the passage of carbon dioxide from the cells of the tissues to the blood. It is evident that external respiration is a process that takes place in the lungs and that internal respiration is a process that takes place in all the cells that make up the tissues of the body. Mechanism of inspiration and expiration. During inspiration the cavity of the chest is enlarged in all three diameters: (1) antero-posterior, (2) lateral, and (3) vertical. This is brought about by the action of the intercostal and other muscles, which elevate the ribs and thereby increase the antero-posterior and lateral diameters. The descent of the diaphragm increases the vertical diameter. The lungs are expanded exactly in proportion as the cavity enlarges. The expansion affects chiefly the elastic sacs or alveoli, and air presses into them as into a widening bellows. The atmospheric pressure outside the body is greater than the pressure within the alveoli, and this forces the air in. Upon the relaxation of the inspiratory muscles, the elasticity of the lungs, CHAP. XIII] RESPIRATORY SYSTEM 259 and the weight and elasticity of the chest walls, cause the chest to return to its original size, in consequence of which the air is ex- pelled from the lungs. As in the heart, the auricular systole, the ventricular systole, and then a pause, follow in regular order ; so in the lungs the inspiration, the expiration, and then a pause, succeed one another. Control of respiration. Respiration is both a voluntary and an involuntary act. It is possible for a short time to increase or decrease the rate of respiration within certain limits by voluntary effort, but this cannot be done continuously. If we intentionally arrest the breathing or diminish its frequency, after a short time the nervous impulse becomes too strong to be controlled, and the movements will recommence, as usual. If, on the other hand, we purposely accelerate respiration to any great degree, the exertion soon becomes too fatiguing for continuance, and the movements return to their normal standard. Cause of respiration. Unlike the beat of the heart the con- tractions of the respiratory muscles are entirely dependent on the nervous system, especially that part known as the respiratory centre, which is located in the medulla oblongata. 1 Efferent nerves from the respiratory centre travel down the spinal cord and end at different levels, where they connect with the fibres of the vagi and sympathetic nerves that are distributed in the lung tissue. Afferent nerves lead from these different levels to the respiratory centre. The consensus of opinion at the present time seems to be that the action of the respiratory centre is automatic, but that the rate and rhythm of the respiratory movements are controlled (1) by the vagi nerves, and (2) by the chemical condition of the blood. (1) The fibres from the vagi are of two kinds : (a) inspiratory fibres which tend to increase the rate of respiration, and (6) ex- piratory fibres which check the action of the inspiratory set. The inspiratory fibres are stimulated to action when the lung collapses ; the expiratory when the lung expands. (2) The respiratory centre shows a specific irritability for carbon 1 It is important to remember the difference between the heart action and respiration : the heart beats of itself, and the respiratory muscles are thrown into contraction by the brain. 260 ANATOMY AND PHYSIOLOGY [CHAP. XIII dioxide, and an increased amount of carbon dioxide in the blood acts as a stimulus, increasing the rate and depth of the respirations, so that the lungs are more thoroughly ventilated. Increased activ- ity, or any abnormal condition that increases the oxf Nation of the tissues, naturally results in an increased production of carbon dioxide, and an increase in the rate and depth of the respirations. On the other hand, an excess of oxygen in the blood may cause a condition known as physiological apnoea, i.e., where the blood is so rich in oxygen and poor in carbon dioxide that a respiratory act is unnecessary. Reflex stimulation of the respiratory centre. Every one must have noticed that the respiratory movements are affected by stimulation of the sensory nerves. Strong emotion, sudden pain, or a dash of cold water on the skin produce changes in the rate of the respirations. It is assumed, therefore, that the respiratory centre is in connection with the sensory fibres of all the cranial and spinal nerves. Cause of the first respiration. The immediate cause of the first respiratory effort is closely connected with the cause of the activity of the respiratory centre during life. The stimulus is supposed to come from (1) the increased amount of carbon dioxide in the blood, due to the cutting of the umbilical cord ; and (2) stimulation of the sensory nerves of the skin, due to cooler air, handling, etc. During intrauterine life the foetus receives its supply of oxygen, and gives off carbon dioxide by means of the blood-vessels of the cord, which connect with the placenta. The lungs are in a collapsed condition and contain no air. The walls of the air-sacs are in close contact, and the walls of the smaller bronchial tubes, or bronchioles, touch one another. When the chest expands with the first breath, the inspired air has to overcome the adhesions existing between the walls of the bron- chioles and air-sacs. The force of this first inspiratory effort, spent in opening out and unfolding, as it were, the inner recesses of the lungs, is considerable. In the succeeding expiration, most of the air introduced by the first inspiration remains in the lungs, succeeding breaths unfold the lungs more and more, until finally the air-sacs and bronchioles are all opened up and filled with air. The lungs thus once filled with air are never completely emptied again until after death. CHAP. XIII] RESPIRATORY SYSTEM 261 Frequency of respiration. The average rate of respiration for an adult is about eighteen per minute. Even in health this rate may be increased by muscular exercise, emotion, etc. Anything that affects the heart-beat will have a similar effect on the respira- tions and except in diseased conditions the ratio of the respirations and heart-beat (1 to 4) remains the same. Age has a marked in- fluence. The average rate in the newly born infant has been found to be forty-four per minute, and at the age of five years, twenty- six per minute. It is reduced between the ages of fifteen and twenty to the normal standard. Respiratory sounds. The entry and exit of the air are ac- companied by respiratory sounds or murmurs. These murmurs differ as the air passes through the trachea, the larger bronchial tubes, and the bronchioles. They are variously modified in lung disease, and are then often spoken of under the name of rales. In labored breathing the contraction of the respiratory muscles not usually brought into play, such as the muscles of the throat and nostrils, becomes very marked. Effects of respiration upon the blood. Once or twice each minute all the blood in the body passes through the capillaries of the lungs. This means that the time during which any portion of blood is in a position for respiratory exchange is only a second or two. Yet during this time, the following changes take place : (1) it loses carbon dioxide; (2) it gains oxygen, which combines with the reduced haemoglobin of the red cells and turns it into oxyhsemoglobin, and as a result of this the crimson color shifts to scarlet ; and (3) the temperature is slightly reduced. It is helpful to compare the amounts of oxygen and carbon dioxide found in the venous blood brought to the lungs, and the amounts found in the arterial blood carried from the lungs. OXYGEN CARBON DIOXIDE NITROGEN Venous blood contains .... Arterial blood contains .... 8-12% 20% 45-50% 38% 1-2% 1-2% From these figures it is evident that the cells do not remove all the oxygen nor do the lungs remove all the carbon dioxide from the circulating blood. There is always a considerable amount of 262 ANATOMY AND PHYSIOLOGY [CHAP. XIII oxygen in venous blood, also a considerable amount of carbon dioxide in arterial blood. Consequently, the main result of the respiratory exchange is to keep the gas content of the arterial blood nearly constant at the figures given. Under normal conditions it is not possible to increase appreciably the amount of oxygen absorbed by the blood flowing through the lungs. 1 Capacity of the lungs. As the lungs are not emptied at each expiration, neither are they filled. If filled to their utmost, they can hold a little more than one gallon (4500 c.c.) of air. This total is divided as follows : (1) Tidal. (3) Reserve. (2) Complemental. (4) Residual. Tidal air is the air introduced with every ordinary inspiration (30 cu. in. or about 500 c.c.). Complemental air is the excess over the tidal air which may be introduced during a forced inspiration. Reserve air is the amount of air in addition to the tidal air one can expel from the lungs in a forced expiration. Residual air is the air remaining in the lungs after the most powerful expiration. The vital capacity is the sum of the tidal, Complemental, and reserve air added together. It equals about 225 cubic inches (3700 c.c.). It is not correct to think of the residual air in the lungs as stationary, for the air is being constantly moved and renewed. This movement is maintained by : (1) the alternate expansion and collapse of the lungs in respiration, (2) the convection 2 currents due to the differences in temperature between the inspired air and the residual air, (3) the pulsation of the arteries, and (4) the difference in the proportion of carbon dioxide and oxygen in the inspired air and residual air. This fourth factor is also responsible for the interchange of gases between the air in the air-sacs and the 1 Student nurses sometimes find it difficult to reconcile this fact with the practice of using pure oxygen in critical cases of pulmonary disease. The relief of the pneumonia patient who inhales pure oxygen is usually marked because the blood absorbs an increased amount of oxygen. The reason for this seeming contradiction is that normal blood cannot absorb an increased amount of oxygen, but in the case of the pneumonia patient the composition of the blood as regards oxygen is below normal, and the inhalation of pure oxygen brings it up to the standard, hence the marked relief. 2 See Glossary, p. 494. CHAP. XIII] RESPIRATORY SYSTEM 263 blood in the capillaries. The reason is that the blood contains more carbon dioxide and less oxygen than the air in the alveoli, and the tendency of gases is always to mix in uniform proportions. The effects of respiration upon the air outside the body. With every inspiration a well-grown man takes into his lungs about 30 cubic inches (500 c.c.) of air. The air he takes in differs from the air he gives out mainly in three particulars : 1. Whatever the temperature of the external air, the expired air is nearly as hot as the blood ; namely, of a temperature between 98 and 100 F. (36.7 and 37.8 C.). 2. However dry the external air may be, the expired air is quite, or nearly, saturated with moisture. 3. When breathed the air loses 4.94 per cent of oxygen and gains 4.38 per cent of carbon dioxide. Thus : - OXYGEN CARBON DIOXIDE NITROGEN Inspired air 2096% 004% 79% Expired air 1602% 438% 79% 4.94 loss 4.34 gain Ventilation. Since at every breath the external air gains carbon dioxide and loses oxygen, it was formerly taught that the general discomfort, headache, and languor that result from sitting in a badly ventilated room were due to the increase in carbon di- oxide and the loss of oxygen. The results of many experiments seem to prove that people can become so accustomed to a high percentage of carbon dioxide and a low percentage of oxygen that they suffer little discomfort ; though odors given off from the body and its clothing when present in any amount may affect the nervous system disagreeably. It is now thought that the injurious effects of remaining in a badly ventilated room are due to inter- ference with the heat-regulating mechanism of the body. Under favorable conditions the surface of the human body is kept com- fortably cool by the air currents which pass over it and by the evaporation of perspiration. The former are an aid to the latter. In a confined space there is a lack of movement in the air and it tends to become warm and humid. Moisture is not taken from the skin promptly and the temperature rises. This results in a 264 ANATOMY AND PHYSIOLOGY [CHAP. XIII dilatation of the blood-vessels of the skin and an increased amount of blood is sent to the surface of the body, thereby increasing the unpleasant warmth. There is likely to be some reduction of the general blood-pressure leading to drowsiness or at least a feeling of inertia. In accordance with these views, the most effective precautions that can be taken to secure comfort in a room are to keep it cool and to have some circulation of the air. It has been shown that starting an electric fan in a close room may relieve an almost intolerable condition. It does not improve the air chemically but it favors the removal of heat from the bodies of the inmates and braces up their vasomotor systems. One writer suggests that the real difficulty with a stuffy room is that there is a lack of stimulation for the nervous system. One becomes re- laxed and indolent because the nerve-endings in the skin are not being played upon as they would be by a constant change in en- vironmental conditions. Because of these facts we are now taught that proper ventilation requires (1) there must be continuous move- ment of the air ; (2) the temperature and degree of humidity must favor the evaporation of perspiration from the skin; (3) odors from skin, clothing, light, and other sources must be eliminated. Dyspnoea. The word dyspnoea means difficult breathing. It is caused by (1) an increase in the percentage of carbon dioxide in the blood, (2) a decrease in the oxygen, and (3) any con- dition that stimulates the sensory nerves and causes pain in the lungs. Hyperpncea. The word hyperpncea means excessive breath- ing and is applied to the initial stages of dyspnoea, when the res- pirations are simply increased. Apncea. The word apnoea means a lack of breathing. Cheyne-Stokes respirations. This is a type of respirations which was first described by the two physicians whose names it bears. It appears in two forms : (1) the respirations increase in force and frequency up to a certain point, and then gradually de- crease until they cease altogether, and there is a short period of apncea, then the respirations recommence and the cycle is repeated. (2) The respirations increase in force and frequency up to a certain point, then cease, and the period of apncea intervenes, without the gradual cessation of the respirations. This condition is asso- ciated with disease of the kidney, brain, or heart. The cause is CHAP. XIII] RESPIRATORY SYSTEM 265 not settled, but it is of bad prognosis and generally indicates a fatal termination. (Edematous respiration. When the air cells become infil- trated with fluid from the blood, the breathing becomes oedema- tous and is recognized by the moist, rattling sounds, called rales, that accompany each inspiration. It is a serious condition be- FIG. 160. STETHOGRAPH TRACING OF CHEYNE-STOKES RESPIRATIONS IN A MAN. The time is marked in seconds. (Halliburton.) cause it interferes with aeration of the blood and often results in asphyxia. Asphyxia. This condition is usually the sequel to severe dysp- noea and cedematous respiration. It is produced by any condition that causes prolonged interference with the aeration of the blood. After death from asphyxia it will be found that the right side of the heart, the pulmonary arteries, and the systemic veins are over- loaded, and the left side of the heart, the pulmonary veins, and the systemic arteries are empty. MODIFIED RESPIRATORY MOVEMENTS Various emotions may be expressed by means of the respiratory apparatus. Sighing is a deep and long-drawn inspiration, followed by a sudden expiration. Yawning is an inspiration, deeper and longer continued than a sigh, drawn through the widely open mouth, and accompanied by a peculiar depression of the lower jaw. Hiccough is caused by a sudden inspiratory contraction of the diaphragm ; the glottis suddenly closes and cuts off the column of air just entering, which, striking upon the closed glottis, gives rise to the characteristic sound. 266 ANATOMY AND PHYSIOLOGY [CHAP. XIII Sobbing is a series of convulsive inspirations during which the glottis is closed, so that little or no air enters the chest. Coughing consists, in the first place, of a deep and long-drawn inspiration by which the lungs are well filled with air. This is followed by a complete closure of the glottis, and then comes a forcible and sudden expiration, in the midst of which the glottis suddenly opens, and thus a blast of air is driven through the upper respiratory passages. Sneezing consists of a deep inspiration, followed by a sudden and forced expiration, which directs the air through the nasal passages. Laughing consists essentially in an inspiration, followed by a whole series of short, spasmodic expirations, the glottis being freely open during the whole time, and the vocal cords being thrown into characteristic vibrations. Crying consists of the same respiratory movements as laugh- ing; the rhythm and the accompanying facial expressions are, however, different, though laughing and crying often become indistinguishable. Speaking consists of a voluntary expiration and the vibration of the vocal cords as the air passes over them. CHAP. XIII] SUMMARY 267 SUMMARY Respiration is dependent upon the proper functioning of organs that com- prise the respiratory system. Air passes through the nose or mouth to these organs. Special organ of the sense of smell. Function j Passageway for entrance of air to the respiratory organs. Framework of bone (nasal) and cartilage. Covered with skin, lined with mucous External I membrane known as pituitary, or nose Schneiderian. Nostrils are oval-shaped openings on under surface, separated by a partition. Extend from nostrils to the pharynx. Two wedge-shaped cavities. 2 palate. 2 maxillae. 1 ethmoid. 1 sphenoid. 2 nasal. 2 turbinated, and pro- cesses of the eth- moid Nose Respiratory System Larynx Internal cavities, or nasal fossae Formed by Superior meatus. Middle meatus. Inferior meatus. J_ vomer. % 11 bones. Advantages Warmed, of nasal Air Moistened breathing Filtered. 1. Frontal. Communicat- 2. Ethmoidal. ing sinuses 3. Maxillary or antrums of Highmore. ( 4. Sphenoidal. 1. Larynx. 3. Bronchi. 2. Trachea. 4. Lungs. Special organ of voice. Triangular box made up of nine pieces of cartilage. Situated between the tongue and trachea. Contains vocal cords. Slit or opening between cords called glottis, which is pro- tected by leaf -shaped lid called epiglottis. Connected with external i Mouth, air by \ Nose. 268 ANATOMY AND PHYSIOLOGY [CHAP. XIH Voice Trachea Bronchi Lungs Right Left Produced by vibrations of vocal cords. Pharynx. Resonating cavities Mouth. Nasal cavities. Lower pitch of male voice is due to greater length of vocal cords. Fibrous and muscular tube, 4| in. long. Strengthened by C-shaped J Complete in front. hoops of cartilage 1 Incomplete behind. In front of oesophagus. Extends from larynx to fifth thoracic vertebra, where it divides into two bronchi. Right and left structure similar to trachea. 1 in. long. Almost horizontal. 2 in. long. Almost vertical. Divide into innumerable bronchial tubes or bronchioles. Location Occupy all of the cavity of the thorax that is not taken up by the heart, blood-vessels, lymphatics, oesophagus, and lymph nodes. Outer surface convex to fit in concave cavity. Base concave to fit over convex dia- phragm. Apex rises half an inch above the clavicle. Hilum or depression on inner surface gives passage to bronchi, blood-vessels, lymphatics, and nerves. Larger, heavier, broader, shorter three lobes. Smaller, narrower, longer, front border deeply indented two lobes. Hollow, spongy organs. Consist of bron- chial tubes infundibula alveoli, also blood-vessels, lymphatics, and nerves held together by connective tissues. Blood for aeration. Accompanies bronchial tubes. Pulmonary Plexus of capillaries around artery alveoli. Returned by pulmonary veins, arteries supply lung sub- Cone-shaped organs Right Left Anatomy Blood-vessels Nerves Bronchial stance. 1 . Branches from the sympathetic system, 2. Branches from the vagi. CHAP. XIII] SUMMARY 269 Moistened by serum. Function Respiration Closed sac. Envelops lungs, but they are not in it. Visceral next to lung Pleura . . { Two layers Parietal outside of vis- ceral Function To lessen friction. Mediastinum Space between pleural sacs. Extends from sternum to spinal column. f Increase the amount of oxygen. J Decrease the amount of carbon dioxide. ] Help to maintain temperature. [ Help to eliminate waste. Inspiration Process of taking air into lungs. Expiration Process of expelling air from lungs. External oxygen f supply Takes P lace External carbon di- ] oxide elimination [ lun g s - Internal oxygen supply Internal carbon di- oxide elimination Elevation ribs. Descent of diaphragm. Lungs expand. Mechanism Air rushes in through trachea and bronchi, of Inspira- f Inspiratory tion and muscles re- Expiration lax. Chest cavity made smaller Processes < Breathing External Respiration Internal Respiration Inspiration Cause of Respiration Expiration Chest cavity enlarged Takes place in the cells. of Recoil of elas- tic thorax. Recoil of elas- tic lungs. Air forced out through trachea. Respiratory centre Action is automatic. Assumed to be in connection with all the cranial and spinal nerves. Inspiratory tend to increase rate. Expiratory check Rate and rhythm controlled by Vagi nerves the action of the inspira- tory set. Carbon dioxide content of blood. 270 ANATOMY AND PHYSIOLOGY [CHAP. XIII Cause of First Respi- ration Respiratory Rate Effect of Respiration upon the Blood Capacity of Lungs Movement of Residual Air Maintained by Effect of Respiration upon the Air outside the Body Proper Ven- tilation Abnormal Types of Respiration ' 1. Increased amount of carbon dioxide due to cutting of the umbilical cord. 2. Reflex, due to stimulation of the sensory nerves of the skin. Muscular exercise. Emotion. Influenced by 18 times per minute. Ratio to pulse 1 to 4. A little more than 1 gallon of -air (4500 c.c.) Vital capacity 3700 c.c. Heart-beat. Age. 1. Loses about 10% of carbon dioxide. 2. Gains about 10% j Oxyhaemoglobin. of oxygen 1 Scarlet color. 3. Temperature is slightly reduced. Tidal Complemental Reserve Residual 1. Alternate expansion and collapse of lungs. 2. Convection currents. 3. Pulsation of the arteries. 4. Diffusion of gases. 1 . Temperature increased. Expired air is as hot as blood. 2. Moisture increased. Expired air is saturated with moisture. 3. Oxygen decreased by 4.94%. 4. Carbon dioxide increased by 4.34%. 1. Continuous movement of the air. 2. The temperature and degree of humidity must favor the evaporation of perspiration from the skin. 3. Disagreeable odors must be eliminated. Dyspncea difficult breathing. Hyperpncea excessive breathing. Apnoea lack of breathing. Cheyne-Stokes (Edematous air rattling sounds. Asphyxia oxygen starvation. 1 . Respirations increase in force and frequency, then gradually de- crease and stop. Cycle re- peated. 2. Respirations increase in force and frequency up to a certain point, then stop. Cycle repeated, cells filled with fluid, hence moist, -. CHAPTER XIV THE DIGESTIVE SYSTEM: ALIMENTARY CANAL AND ACCESSORY ORGANS IN complex multicellular bodies, the cells where food is needed are so far removed from the points of entrance of food material, that it is necessary that these foods should be changed physically and chemically into such standard substances as can diffuse into the blood system and be carried by the blood to all the cells of the body and diffuse into them. Chemical and physical changes necessary to reduce our varied foods to such standard substances as the tissues can use are effected in certain organs that are grouped together and called the digestive system. THE DIGESTIVE SYSTEM The digestive system consists of the alimentary canal and the accessory organs : (1) the salivary glands, (2) the tongue, (3) the teeth, (4) the pancreas, and (5) the liver. ALIMENTARY CANAL The alimentary canal is a continuous tube which extends from the mouth to the anus. It measures about 30 feet (9 m.) in length, the greater part being coiled up in the cavity of the abdomen. The portion above the diaphragm is composed of three coats; and the portion below the diaphragm is composed of four coats. Beginning at the inner lining these coats are : (1) The mucous. f Both described in (2) The areolar or sub-mucous. { Chapter VIII (3) The muscular coat consists almost entirely of non-striated muscular tissue, usually arranged in two layers. The internal cells are circular in direction, and the external cells run longi- tudinally. By the alternate contraction and relaxation of cells arranged in this fashion (the contractions starting from above), the contents of the tube are propelled from above downward. (4) The serous coat is derived from the peritoneum. 271 272 ANATOMY AND PHYSIOLOGY [CHAP. XIV The peritoneum. This is the largest serous membrane in the body and in the male consists of a closed sac, 1 the parietal layer of which lines the walls of the abdominal cavity ; the inner or vis- ceral layer is reflected over the abdominal organs, and the upper surface of some of the pelvic organs. The arrangement of the peri- toneum is very complex, for several elongated sacs and double folds extend from it, to pass in between and either wholly or partially surround the viscera of the abdomen and pelvis. One important fold is the omentum, which hangs like a curtain in front of the stomach and the intestines ; another is the mesentery, which is a continuation of the serous coat and attaches the small and much of the large intestine to the spine. When the abdominal cavity is opened, the intestines appear to lie within the cavity like a loose coil of rope. If, however, an attempt is made to lift a coil from its place a clear, glistening sheet of tissue is found attached to it. This is the mesentery. The posterior portion is gathered into folds which are attached to the spine along a short line of insertion which results in a struc- ture that has the appearance of a ruffle or flounce. Functions of the peritoneum. Like all serous membranes the peritoneum serves to prevent friction between contiguous organs by secreting serum which acts as a lubricant. To a limited ex- tent it serves to hold the abdominal and pelvic organs in position, also unites and separates these organs. In addition to these func- tions, the omentum usually contains fat, and serves to keep the organs it covers warm. Divisions of the alimentary canal. For convenience of descrip- tion, the alimentary canal may be divided into : - Mouth, containing tonsils, tongue, salivary glands, and teeth. Pharynx. (Esophagus. Stomach. f Duodenum. Small or thin intestine j Jejunum. I Ileum. Caecum. Large or thick intestine j Colon. - [ Rectum. Ascending. Transverse. Descending. 1 In the female the peritoneum is not a closed sac, because the Fallopian tubes open into it at their extremities. CHAP. XIV] THE DIGESTIVE SYSTEM 273 MOUTH, OR BUCCAL CAVITY The mouth cavity is a nearly oval-shaped cavity with a fixed roof anteriorly, a flexible roof posteriorly, and a movable floor. It is bounded in front by the lips, on the sides by the cheeks, below by the tongue, and above by the palate. The palate. The palate consists of a hard portion in front formed by bone 1 covered by mucous membrane, and of a soft portion behind containing no bone. The hard palate forms the partition between the mouth and nose; the soft palate arches backward and hangs like a curtain between the mouth and the pharynx. Hanging from the middle of its lower border is a pointed portion of the soft palate called the uvula (little grape). Fauces. The fauces is the name given to the aper- ture leading from the mouth into the pharynx, or throat cavity. Pillars of the fauces. From the base of the uvula on either side there passes a curved fold of muscular tissue covered by mucous membrane, which shortly after leaving the uvula is, as it were, split into two pil- lars, the one going outward, downward, and forward, passing to the side of the tongue, the other outward, downward, and backward to the side of the pharynx. These pillars are known respectively as the anterior and the posterior pillars of the fauces. Tonsils. In the lower part of the triangular space between the anterior and posterior pillars, on either side, lie the small masses FIG. 161. THE SOFT PALATE AND TON- SILLAR REGIONS. (Gerrish.) Processes of the maxillae and palate bones. 274 ANATOMY AND PHYSIOLOGY [CHAP. XIV of lymphoid tissue called tonsils. They consist of a collection of lymph nodules held together by a distinct capsule and covered on their exposed surface by mucous membrane. Function. The function of the tonsils is imperfectly under- stood. They may be a source of lymphocytes and leucocytes, or they may act as filters and prevent the entrance of microorgan- isms. Inflammation of the tonsils is called tonsillitis. The palate, uvula, pillars of the fauces, and tonsils are plainly seen if the mouth is widely opened and the tongue depressed. The tongue. The tongue 1 is the special organ of the sense of taste and assists in speech. It has also to be considered with ref- erence to digestion, (1) because stimulation of the nerves of the sense of taste starts the secretion of digestive fluids, (2) it assists in swallowing, and (3) the follicles at the back of the tongue secrete mucus, which lubricates the food and makes swallowing easier. The salivary glands. - The mucous mem- brane lining the mouth contains many minute glands consisting of just one cell. These are called goblet cells and pour their secretion upon its surface, but the chief secretion of the mouth is supplied by the salivary glands, which are three pairs of compound saccular glands called the parotid, submaxillary, and sublingual, respectively. Each parotid gland is placed just under and in front of the ear; its duct (Stenson's) passes forward along the cheek, until it opens into the interior of the mouth opposite the second molar tooth of the upper jaw. The submaxillary and sublingual glands are situ- ated below the jaw and under the tongue, the submaxillary being 1 A. detailed description of the tongue will be found in Chapter XX. FIG. 162. THE SALIVARY GLANDS. CHAP. XIV] THE DIGESTIVE SYSTEM 275 placed farther back than the sublingual. One duct from each sub- maxillary and a number of small ducts from each sublingual open in the floor of the mouth beneath the tongue. The secretion of these salivary glands, mixed with that of the small glands of the mouth, is called saliva. Secretory nerves. The salivary glands receive a double nerve supply, in part from the cranial nerves and in part from the sympathetic system. These nerves are called secretory because they control the activity of the cells which form the secretion. Not only are secretory nerves distributed to these glands, but vasomotor fibres are contained in the same nerves. The cranial nerves contain vaso-dilator fibres. Stimulation of these causes a dilatation of the small arteries and an increased blood-flow; while the sympathetic carries vaso-constrictor fibres that constrict the arteries and diminish the blood-flow. The teeth. The semicircular borders of the upper and lower jaw-bones (the alveolar processes) contain sockets for the recep- tion of the teeth. A dense, insensitive, fibrous membrane covered by smooth mucous membrane the gums covers these pro- cesses and extends a little way into each socket. These sockets are lined by periosteum, which connects with the gums and serves (1) to attach the teeth to their sockets, and (2) as a source of nourishment. Each tooth consists of three portions : (1) the root, consisting of one or more fangs contained in the socket ; (2) the crown, which projects beyond the level of the gums; and (3) the neck or constricted portion between the root and the crown, which is enveloped by the gum. Each tooth is composed principally of dentine, which gives it shape and encloses a cavity, the pulp cavity. The dentine of the crown is capped with a dense layer of enamel. The dentine of the CROWN NECK ROOT ENAMEL PULP CAVITY DENTINE CEMENT CANAL IN ROOT FIG. 163. SECTION OF HUMAN MOLAR TOOTH. (Adapted from Dalton.) 276 ANATOMY AND PHYSIOLOGY [CHAP. XIV root is covered by cement. These three substances, enamel, dentine, and cement, are all harder than bone, enamel being the hardest substance found in the body. They are developed from epithelial tissue. The pulp cavity is just under the crown and is continuous with a canal that traverses the centre of each root, and opens by a small aperture at its extremity. It is filled with dental pulp, which consists of loose connective tissue holding a number of blood-vessels and nerves which enter by means of the canal from the root. There are two sets of teeth developed during life : the first, temporary or deciduous ; and the second, permanent. Temporary teeth. In the first set are twenty teeth, ten in each jaw : four incisors, two canines, and four molars. The cut- ting of the temporary teeth usually begins at six months and ends at about the age of two years. 1 In nearly all cases the teeth of the lower jaw appear before the corresponding ones of the upper jaw. TEMPORARY TEETH MOLARS Upper Lower Permanent teeth. During childhood the temporary teeth are replaced by the permanent. In the second set are thirty-two permanent teeth, sixteen in each jaw. The first molar usually appears between five and seven years of age. 2 PERMANENT TEETH MOLAR BICUSPIE Upper Lower 1 The temporary teeth are usually cut in the following order: Lower central incisors 6 to 9 months Upper incisors 8 to 10 months Lower lateral incisors and first molars . . . . 15 to 21 months Canines . 16 to 20 months Second molars 20 to 24 months 2 The permanent teeth appear at the following periods: First molars 6^ years Two middle incisors 7th year Two lateral incisors 8th year First bicuspid . . . . ' 9th year Second bicuspid 10th year Canine llth to 12th year Second molars 12th to 13th year Third molars . . .. , ,,,.,,, 17th to 21st year MOLARS CANINE INCISORS CANINE MOLARS 2 1 4 1 2 2 1 4 1 2 MOLAR BICUSPID CANINE INCISOR CANINE BICUSPID MOLAR 3 2 1 4 1 2 3 3 2 1 4 1 2 3 CHAP. XIV] THE DIGESTIVE SYSTEM 277 According to their shape and use the teeth are divided into incisors, canines, bicuspids, and molars. Incisors are eight in number and form the four front teeth of each jaw. They have wide, sharp edges, and are specially adapted for cutting food. Canines are four in number, two in each jaw. The upper canines are commonly called eye-teeth ; the lower, stomach teeth. They have sharp, pointed edges and are longer than the incisors. In the human being they serve the same purpose as the incisors. Bicuspids are eight in number in the permanent set. There are none in the temporary set. There are four in each jaw, two being placed just behind each of the canine teeth. They are broad, with two points or cusps on each crown ; these teeth have only one root ; the root, however, being more or less completely divided into two. Their function is to cut and grind food. Molars are twelve in number in the permanent set, and only eight in the temporary set. The molars, or true grinders, have broad crowns with small, pointed projections, which make them well fitted for crushing and bruising the food : they each have two or three roots. The twelve molars do not replace the temporary teeth, but are gradually added with the growth of the jaws ; the last or hindmost molars may not appear until twenty-one years of age; hence called late teeth or wisdom teeth." Function. The teeth assist in the process of mastication by cutting and grinding the food. It might be thought that the vigorous employment of the teeth for this purpose would only hasten their wear and tear. This may be true at a time when their life is nearly extinct, but at an earlier period mastication is good for the teeth because they are made to sink and rise in their sockets with a massaging effect upon the gums which tends to promote circulation in the pulp. THE PHARYNX The pharynx, or throat cavity, is that part of the alimentary canal which is behind the nose, mouth, and larynx. It is a mus- culo-membranous tube shaped somewhat like a cone, with its broad end turned upward and its constricted end downward 278 ANATOMY AND PHYSIOLOGY [CHAP. XIV to end in the oesophagus. It is about five inches (12.5 cm.) in length. Above, it is attached to the base of the skull, and behind, to the cervical vertebrae ; in front and on each side are apertures which communicate with the nose, ears, mouth, and larynx. Of these apertures there are seven : Two in front above, leading into the back of the nose, the posterior nares. Two, one on either side above, leading into the Eustachian tubes, which communicate with the ears. One midway in front, the fauces. Two below, one opening into the larynx and the other into the oesophagus. The mucous membrane lining the pharynx is well supplied with glands, and at the back of the cavity there is a considerable mass of lymphoid tissue. During infancy and childhood this may increase to such an extent that it interferes with nasal breathing. The child is then said to have adenoids and is obliged to breathe through the mouth ; hence the term " mouth breathers." Function. The muscular tissue in the walls of the pharynx is of the striped variety, and when the act of swallowing is about to be performed, the muscles draw the pharynx upward and dilate it to receive the food ; they then relax, the pharynx sinks, and the other muscles contracting upon the food, it is pressed down- ward and onward into the oesophagus. THE (ESOPHAGUS, OR GULLET The oesophagus is a comparatively straight tube, about nine inches (22. cm.) long, which commences at the lower end of the pharynx, behind the trachea. It descends in front of the spine, passes through the diaphragm, and terminates in the upper or cardiac end of the stomach. Structure. The walls of the oesophagus are composed of three coats : (1) an external or muscular, (2) a middle or areolar, and (3) an internal or mucous, coat. The muscular coat is arranged in an external longitudinal and an internal circular layer. Con- traction of the outer layer produces dilatation of the tube ; con- traction of the inner, constriction. Consequently this arrange- CHAP. XIV] THE DIGESTIVE SYSTEM 279 ment is of importance in the movements which carry the food from the pharynx to the stomach. These movements are called peri- staltic, and consist of contractions of the longitudinal layer, fol- lowed by contractions of the circular layer. The areolar coat serves to connect the muscular and mucous coats. The mucous mem- RIGHT HYPOCHON- DRIAC REGION RIGHT LUMBAR REGION RIGHT ILIAC EGION LEFT HYPOCHON- DRIAC REG.ON ._ jCARTrtAGE OF TENTH RIB UMBILICAL REGION HIGHEST LEVEt F ILIAC CREST ANT. SUP. ILIAC SPINE HYPOGASTRIC REGION FIG. 164. REGIONS OF THE ABDOMEN. (Gerrish.) The following structures are found within the cavity : 1. The greater part of the alimentary canal, viz., stomach, small intestine, and large intestine. 2. Digestive glands : the liver and pancreas. 3. Ductless glands : the spleen and the two supra-renal glands. 4. Urinary apparatus : the kidneys, ureters, bladder and part of urethra. 5. The internal generative organs, according to the sex. 6. Blood-vessels and lymph vessels, and lymph nodes. 7. The abdominal portion of the central and sympa- thetic nervous systems. 8. The peritoneum the serous membrane which lines the cavity, and is reflected over most of its contained viscera. brane is disposed in longitudinal folds which disappear upon dis- tent ion of the tube. Function. The oesophagus serves (1) to connect the pharynx with the stomach, and (2) to* receive the food from the pharynx and by a series of peristaltic contractions pass it on to the stomach. Regions of the abdomen. That portion of the alimentary canal which is below the thorax is contained in the abdomen. For convenience of description, the abdomen may be artificially 280 ANATOMY AND PHYSIOLOGY [CHAP. XIV divided into nine regions by drawing the following arbitrary lines : 1. Draw a circular line around the body at the level of the tenth costal cartilages. 2. Draw another circular line at the level of the anterior superior spines of the ilia. 3. Draw a vertical line on each side from the centre of Poupart's ligament upward. These lines are to be considered as edges of planes which divide the abdomen into the nine regions illustrated in Fig. 164. THE STOMACH After the ossophagus perforates the diaphragm it ends in the stomach (gaster), which is the most dilated portion of the alimen- tary canal and serves as a temporary receptacle for food. It lies obliquely or horizontally in the epigastric and left hypochondriac PYLOR FUNGUS INTERMEDIATE REGION FIG. 165. FORM AND OUTLINE OF THE STOMACH AT DIFFERENT STAGES OF DIGESTION. A, when empty and contracted. B, at an early stage of gastric digestion. regions of the abdomen, directly under the diaphragm. The shape and position of the stomach are modified by changes within itself, and in the surrounding organs. These modifications are deter- mined by (1) the amount of the stomach contents, (2) the stage of digestion which has been reached, (3) the degree of development and power of the muscular walls, and (4) the condition of the ad- jacent intestines. When empty or contracted the shape of the stomach is comparable to a sickle or sausage. At an early stage of gastric digestion, the stomach usually consists of two segments, CHAP. XIV] THE DIGESTIVE SYSTEM 281 a large globular portion on the left, and a narrow tubular portion on the right. When distended with food it has the shape shown in Fig. 166. FIG. 166. THE STOMACH AND INTESTINES, FRONT VIEW, THE GREAT OMEN- TUM HAVING BEEN REMOVED, AND THE LIVER TURNED UP AND TO THE RIGHT. The dotted line shows the normal position of the anterior border of the liver. (Gerrish.) The stomach presents two openings and two borders or curva- tures. Openings. The opening by which the oesophagus communi- cates with the stomach is known as the cardiac or oesophageal orifice, and the orifice which communicates with the duodenum is known as the pyloric. Both the cardiac and pyloric apertures are guarded by strong bands of muscle which are in a state of qqntrac- 282 ANATOMY AND PHYSIOLOGY [CHAP. XIV tion during digestion. By this arrangement, the food is kept in the stomach until it is ready for intestinal digestion, when the circular fibres guarding the pyloric aperture relax. The acidity of the stomach contents seems to produce this relaxation. Curvatures. In all positions the stomach is more or less curved upon itself. A line drawn from the cardiac orifice along the con- cave border to the pyloric orifice is said to follow the lesser curva- ture. A much longer line connecting the same points, but follow- ing the convex border, defines the greater curvature. Component parts. The fund us is the blind rounded end of the stomach to the left of the heart. The opposite or smaller end is called the pyloric extremity and lies under the liver. The central portion between the fundus and pyloric extremity is called the intermediate region. Structure. The wall of the stomach consists of four coats : (1) serous, (2) muscular, (3) submucous or areolar, and (4) mucous. (1) The serous coat is formed by a fold of the peritoneum. This fold is thrown over the stomach and covers it before and behind. The anterior and posterior folds unite at the lower border and form an apron-like appendage, the omentum, which is sus- pended in front of the intestines. (2) The muscular coat of the stomach is beneath the serous coat and closely connected with it. It consists of three layers of unstriped muscular tissue : an outer, longitudinal layer ; a middle or circular layer; and an inner, less well-developed, oblique layer. (3) The submucous coat consists of loose areolar tissue con- necting the muscular and mucous coats. It carries nerves and vessels. (4) The mucous coat is very soft and thick, the thickness being mainly due to the fact that it is densely packed with small glands. It is covered with columnar epithelium, and in its undistended condition is thrown into folds or rugae. The surface is honey- combed by tiny, shallow pits, into which the ducts or mouths of the glands open. Gastric glands. The gastric glands are of three varieties, (1) cardiac ; (2) true gastric or peptic ; and (3) pyloric. (1) Cardiac glands are simple tubular glands found about the cardiac or cesophageal orifice. They secrete mucus. CHAP. XIV] THE DIGESTIVE SYSTEM 283 PARIETAL CELLS (2) True gastric or peptic glands are simple tubular glands distributed throughout the fundus and intermediate region of the stomach and may even be found at the pylorus. These glands are lined by epithelial cells of which there are two varieties, (a) One variety of cell is found lining the lumen of the tube. These are called chief cells and se- crete pepsinogen. (6) A sec- ond variety called parietal cells are found behind the chief cells, where they do not come in contact with the lumen. These cells secrete acid, and pepsinogen in the presence of acid is converted into B8^BB8S^CHIEF CELLS pepsin. (3) Pyloric glands are branched tubular glands found most plentifully about the pylorus. They secrete pep- sinogen and mucus. The combined secretion of these glands forms the gastric fluid. Nerves and blood-vessels. The stomach is supplied with nerves from the sympathetic system, and also with branches from the vagus nerve, which comes from the central nervous system. The blood-vessels are derived from the three divisions of the coeliac axis, i.e., gastric, and branches of the hepatic and splenic. Functions. The functions of the stomach are (1) to connect the oesophagus with the intestine, (2) to receive the food and hold it while it undergoes certain mechanical processes which reduce it to the consistency of thick soup, and also while it undergoes certain chemical changes brought about by secretion of the gastric glands, (3) to secrete mucus and gastric fluid. THE SMALL, OR THIN, INTESTINE The small intestine extends from the stomach (pyloric valve) above to the large intestine (valve of the colon) below. It is a convoluted tube about twenty feet (6 m.) in length, and fills LUMEN FIG. 167. PORTION or TRUE GASTRIC OR PEPTIC GLAND. 284 ANATOMY AND PHYSIOLOGY [CHAP. XIV the greater part of the front abdominal cavity. Its diameter at the beginning is about two inches (5 cm.), but it gradually dimin- ishes in size and is hardly an inch (2.5 cm.) in diameter at its lower end. The small intestine is divided by anatomists into three portions : the duodenum, jejunum, and ileum. The duodenum. The duodenum is twelve fingers' breadth in length (ten inches or 25 cm.), and is the widest part of the small intestine. It extends from the pyloric end of the stomach to the jejunum. Beginning at the pylorus, the duodenum at first passes up- ward and backward to the under surface of the liver ; it then makes a complete bend and passes downward in front of the kidney ; it again turns in a right angle direction to the left and passes horizontally across the front of the vertebral column. This third portion of the duodenum lies retroperitoneally, so that only its anterior aspect is covered by peritoneum. The small intestine now passes forward so as to leave the posterior abdominal wall, and becomes completely invested by peritoneum and has a true mesentery. The point at which it becomes completely invested by peritoneum marks the termination of the duodenum and the beginning of the jejunum. The jejunum. The jejunum or empty intestine, so called because it is always found empty after death, constitutes about two-fifths of the remainder, or seven and a half feet (2.2 m.), of the small intestine, and extends from the duodenum to the ileum. The ileum. The ileum, or twisted intestine, so called from its numerous coils, constitutes the remainder of the small intestine, and extends from the jejunum to the large intestine, which it joins at a right angle. There is no definite landmark to determine the point at which the jejunum ceases and the ileum begins, although the mucous membrane of the one differs somewhat from the mucous mem- brane of the other; the change is a gradual transition, and one structure shades off into the other. The lengths in feet as given are arbitrary, but those usually accepted. Coats of the small intestine. The small intestine has four coats, which correspond in character and arrangement with those of the stomach. (1) The serous coat furnished by the peritoneum forms an al- CHAP. XIV] THE DIGESTIVE SYSTEM 285 FIG. 168. PORTION OF SMALL INTES- TINE LAID OPEN TO SHOW VALVUL^E CON- NIVENTES. Not highly enough magnified to show villi on valvulse conniventes. (Col- lins.) most complete covering for the whole tube except for part of the duodenum. (2) The muscular coat of the small intestine has only two layers : an outer, thinner and longitudinal ; and an inner, thicker and cir- cular. This arrangement is necessary for the peristaltic action of the intestine. (3) The submucous, or areolar coat, carries blood- vessels, lymphatics, and nerves. (4) The mucous coat is thick and very vascular. Valvulce conniventes. About one or two inches beyond the pylorus the mucous and submucous coats of the small intestine are arranged in circular folds called valvulse conni- ventes. Some of these folds extend all the way around the cir- cumference of the in- testine ; others extend only one-half or one- third of the way. Un- like the rugse of the stomach, the valvulse conniventes do not dis- appear when the intes- tine is distended. About the middle of the jejunum they be- gin to decrease in size, and in the lower part of the ileum they almost entirely disap- pear. The purpose of the valvulse conniventes is : (1) to prevent the food from passing through the intestines too quickly, and (2) to present a greater surface for the absorption of digested food. Villi. Throughout the whole length of the small intestine the COLUMNAR EPITHELIUM CAPILLARY"" / 'CAPILLARV NETWORK LACTEAL' VESSEL NETWORK FIG. 169. AN INTESTINAL VILLUS. magnified.) (Highly 286 ANATOMY AND PHYSIOLOGY [CHAP. XIV mucous membrane presents a velvety appearance due to minute finger-like projections called villi. Each villus consists of a cen- tral lymph channel called a lacteal, surrounded by a network of blood capillaries, held together by lymphoid tissue. This in turn is surrounded by a layer of columnar cells. After the food has been digested it passes into the capillaries and lacteals of the villi, so that this arrangement increases the surface for absorption. Glands and nodes of the small intestine. Besides these projections formed for absorption the mucous membrane is thickly studded with secretory glands and nodes. These are known as 1. Simple follicles or crypts of Lieberkuhn. 2. Duodenal or Brunner's glands. , , J (a) Solitary lymph nodules. 3. Lymph nodules | (6) Aggregated lymph nodules . (1) Simple follicles. These glands are found over every part of the surface of the small intestine. They are simply tubular FIG. 170. PORTION OF THE Mucous MEMBRANE, FROM THE ILEUM. Moderately magnified, exhibiting the villi on its free surface, and between them the orifices of the tubular glands. 1, portion of an aggregated lymph nodule; 2, a solitary lymph nodule ; 3, fibrous tissue. (Dalton.) depressions in the mucous membrane, lined with columnar epithe- lium. (2) Duodenal glands. These glands are better known as Brunner's glands. They are compound glands found in the submucous tissue of the duodenum. The simple follicles and the duodenal glands secrete the intestinal digestive fluid which is named the succus entericus. (3) Lymph nodules. These are of two varieties, (a) solitary lymph nodules, (b) aggregated lymph nodules of Peyer. (a) Solitary lymph nodules. Closely connected with the lym- phatic vessels in the walls of the intestines are small, rounded bodies of the size of a small pin's head, called solitary lymph nodules. These bodies consist of a rounded mass of fine lym- CHAP. XIV] THE DIGESTIVE SYSTEM 287 phoid tissue, the meshes of which are crowded with leucocytes. Into this mass of tissue one or more small arteries enter and form PLANE OF f MUCOUS SURFACE -LAYER OF CIRCULAR FIBRES / ||| 'LAYER OF .LONGITUDINAL FIBRES' .JFiG. 171. MUCOSA OF SMALL INTESTINE IN IDEAL VERTICAL CROSS-SECTION. (Gerrish.) a capillary network, from which the blood is carried away by one or more small veins. Surrounding the mass are lymph channels which are continu- ous with the lymphatic ves- sels in the tissue below. Aggregated lymph nodules. They are simply collec- tions of lymph nodules, commonly called Peyer's patches. A well-formed Peyer's patch consists of fifty or more of these soli- tary lymph nodules, ar- Fm 172 . _ AGGREGATED LYMPH NODULE ranged in a single layer (Peyer's Patch). (Gerrish.) close under the epithelium of the intestinal mucous membrane, and stretching well down into the tissue beneath. These patches are circular or oval in 288 ANATOMY AND PHYSIOLOGY [CHAP. XIV shape, from ten to sixty in number and vary in length from one- half inch to four inches (1.25 to 10 cm.). They are largest and most numerous in the ileum. In the lower part of the jejunum they are small and few in number. They are occasionally seen in the duodenum. These Peyer's patches are the seat of local inflammation and ulceration in typhoid fever. Function. It is in the small intestine that the greatest amount of digestion and absorption takes place. The valvulae conniventes delay the food so that it is more thoroughly subjected to the action of the digestive fluids ; and being covered with villi they increase the surface for absorption. The glands of the small intestine secrete the succus entericus which aids in the digestion of food. THE LARGE, OR THICK, INTESTINE The largeness of the next division of the alimentary canal is in its width, not in its length; for it is only about five feet (1.5 m.) long, but is wider than the small intestine, being two and one- half inches (6.3 cm.) in its broadest part. It extends from the ileum 'to the anus. Like the small intestine, it is divided into three parts : the caecum with the vermiform appendix, colon, and rectum. The caecum. The caecum (ccecus, blind) is a large blind pouch at the commencement of the large intestine. The small intestine opens into the side wall of the large intestine about two and a half inches (6.3 cm.) aboye the commencement of the large intestine. This two and one-half inches of large in- testine form a cul-de-sac below the opening, and this cul-de-sac is called the caecum. The open- ing from the ileum into the large intestine is provided with two large projecting lips of mucous membrane which allow the passage of material into the large intestine, but effectually prevent FIG. 173. CAVITY OF THE C/ECUM, ITS FRONT WALL, HAVING BEEN CUT AWAY. The valve of the colon (ileo- caecal) and the opening of the appendix are shown. (Gerrish.) CHAP. XIV] THE DIGESTIVE SYSTEM 289 the passage of material in the opposite direction. These mucous folds form what is known as the valve of the colon, or the ileo- csecal valve. The vermiform appendix is a narrow, wormlike tube about the diameter of an ordinary lead pencil, and from three t^ seven inches (7.5 to 17.5 cm.) long. It is attached to the lower end of the caecum, but its directions and relations are very variable. In a general way it may be said to be located in the right iliac region. The colon. The colon, though one continuous tube, is sub- divided into the ascending, transverse, and descending colon, with the sigmoid flexure. The ascending portion ascends on the right side of the abdomen until it reaches the under surface of the liver, where it bends abruptly to the left (right colic or hepatic flexure), and is continued across the abdomen as the transverse colon until, reaching the left side, it curves beneath the lower end of the spleen (left colic or splenic flexure), and passes down- ward as the descending colon. Reaching the left iliac region on a level with the margin of the crest of the ileum, it makes a curve like the letter S, hence its name of sigmoid flexure, and finally ends in the rectum. (See Fig. 166.) The rectum. The rectum is from six to eight inches (15 to 20 cm.) long; it passes obliquely from the left until it reaches the middle of the sacrum, then it follows the cui-ve of the sacrum and the coccyx, and finally arches slightly backward to its ter- mination at the anus. The anus is the aperture leading from the rectum to the exterior of the body. It is guarded, and except during defecation is kept closed by the contraction of two involuntary circular muscles called, respectively, the internal and external sphincters. Coats of the large intestine. The large intestine has the usual four coats except in some parts where the serous coat only par- tially covers it, and the rectum, where the serous coat is lacking. The muscular coat consists of two layers of fibres, one arranged longitudinally and the other circularly. Beginning at the appen- dix, the longitudinal fibres are arranged in three ribbon-like bands, which extend the whole length of the colon to the rectum, and these bands being shorter than the rest of the tube, the walls are puckered between them. The third coat consists of submucous areolar tissue, and the fourth or inner coat consists of mucous u 290 ANATOMY AND PHYSIOLOGY [CHAP. XIV membrane. The mucous coat possesses no villi and no circular folds. It contains numerous tubular glands and solitary lymph nodules which closely resemble those of the small intestine. Functions. The functions of the large intestine are three. (1) The process of digestion is continued. This is due to the pres- ence of bacteria, and to the digestive fluids with which the food becomes mixed in the small intestine. (2) The process of absorp- tion is continued, and (3) the waste products are removed from the body. ACCESSORY ORGANS OF DIGESTION The accessory organs of digestion are : (1) the salivary glands, (2) the tongue, (3) the teeth, (4) the pancreas, and (5) the liver. The first three have been described. -* PANCREAS The pancreas is an elongated organ, of a pinkish color, which lies in front of the first and second lumbar vertebrae and behind the stomach. It weighs between two and three ounces (60 to 90 grams), is about six inches (15 cm.) long, two inches (5 cm.) wide, and one-half inch (1.25 cm.) thick. In shape it somewhat resembles a hammer, and is divided into head, body, and tail. The right end, or head, is thicker and fills the curve of the duode- num, to which it is firmly attached. The left, free end is the tail, and reaches to the spleen. The intervening portion is the body. Structure of the pancreas. It is a compound racemose gland composed of lobules. Each lobule consists of one of the branches of the main duct which terminates in a cluster of saccules that are grape-like in appearance. The lobules are joined together by connective tissue to form lobes, and the lobes, united in the same manner, form the gland. The small ducts from each lobule open into one main duct about the size of a goose-quill, which runs lengthwise through the gland, from the tail to the head. The pancreatic and common bile duct usually enter by means of a common opening into the duodenum about three inches (7.5 cm.) below the pylorus. Sometimes the pancreatic duct and the com- mon bile duct open separately into the duodenum, and there is frequently an accessory duct which opens into the duodenum about an inch above the orifice of the main duct. (See Fig. 174.) CHAP. XIV] THE DIGESTIVE SYSTEM 291 Islands of Langerhans . Scattered throughout the pancreas are round or ovoid bodies known as the islands of Langerhans, Each island is about one twenty-fifth inch (1 mm.) in diameter and consists of a group of many-sided cells. They are surrounded by COMMON BILE DUCT ORIFICE OF ACCESSORY - PANCREATIC DUCT ORIFICE! OF BILB AND PANCREATIC DU.CTS SUP. MSEtJTERIC A.RTERY FIG. 174. DUCTS OF THE PANCREAS. Part of the front wall of the duodenum is cut away. (Gerrish.) a rich capillary network. Their function is to furnish the internal secretion of the pancreas. Function. Two secretions are formed in the pancreas. (1) The pancreatic fluid, which is one of the most important of the digestive fluids, is an external secretion and is poured into the duodenum during intestinal digestion. (2) The secretion formed by the islands of Langerhans is an internal secretion that is ab- sorbed by the blood and carried to the tissues. This internal secretion aids in the oxidation of glucose. Diabetes mellitus. This is a disease characterized by a lack of oxidation of glucose and its consequent loss to the body as it is excreted in the urine. ,The cause is not settled, but it is be- 292 ANATOMY AND PHYSIOLOGY [CHAP. XIV lieved that disease of the pancreas involving the islands of Langer- hans may produce this condition. (See page 337.) THE LIVER The liver (hepar) is the largest gland in the body, weighing ordinarily from fifty to sixty ounces (1500 to 1800 grams). It measures eight to nine inches (20 to 22 cm.) from side to side, six to seven inches (15 to 17.5 cm.) from front to back, and four to FIG. 175. THE LIVER. Front view. (Gerrish.) five inches (10 to 12 cm.) from above downward in its thickest part. It is a reddish brown organ, placed directly below the diaphragm, in front of the right kidney, the pyloric end of the stomach, and the upper part of the ascending colon. The upper convex sur- face fits closely into the under surface of the diaphragm. The under concave surface of the organ fits over the right kidney, the upper portion of the ascending colon, and the pyloric end of the stomach. The number five prevails in the parts and appendages of the liver. Ligaments. The liver is connected to the under surface of the diaphragm, and the anterior walls of the abdomen by five ligaments, four of which are formed by folds of peritoneum, and CHAP. XIV] THE DIGESTIVE SYSTEM 293 the fifth, or round ligament, is a fibrous cord resulting from the atrophy of the umbilical vein of intra-uterine life. Fissures. The liver is divided by five fissures into five lobes. The important fissures are (1) the portal, or transverse, which is the gateway for vessels, ducts, and nerves to enter and leave LOBg FIG. 176. THE LIVER. Lower surface. (Gerrish.) the liver, and (2) the gall-bladder fissure, which supports the gall- bladder. Both these fissures are in the under surface of the liver. Lobes. The liver is divided into five' lobes : 1. Right (largest lobe). 2. Left (smaller and wedge-shaped). 3. Quadrate (square). 4. Caudate (tail-like). 5. Spigelian. Vessels. The liver has five sets of vessels : 1. Branches of portal vein. 2. Hepatic veins. 3. Bile ducts. 4. Branches of hepatic artery. 5. Lymphatics. Minute anatomy of liver. The liver may be regarded as made up of many minute livers called lobules. Each lobule is an irregular body from one-twentieth to one-tenth of an inch (1-2 294 ANATOMY AND PHYSIOLOGY [CHAP. XIV mm.) in diameter, composed of a multitude of hepatic cells packed so closely together that only enough room is left between them for the passage of blood-vessels, ducts, and nerves. Thus each lobule has all the essentials of a gland ; (1) blood-vessels in close connec- tion with secretory cells, (2) cells which are capable of forming a secretion, and (3) ducts by which the secretion is carried away. The portal vein. The portal vein brings to the liver venous blood from the stomach, spleen, pancreas,' and intestines. After entering the liver, it divides into a vast number of branches INTERLOBULAR VEIN INTERLOBULAR DUCT HEPATIC CELLS 1NTRALOBULAR VEIN A FIG. 177. DIAGRAMMATIC REPRESENTATION OF Two HEPATIC LOBULES. A shows the interlobular veins running around the outside of the lobule and sending their capillaries into the lobule to join the central vein. In B, the bile capillaries are seen with the hepatic cells between them, the bile capillaries radiating to the periphery of the lobule, where they join the interlobular bile ducts. which form a network surrounding each lobule, and hence are known as interlobular (between the lobules) veins. From this network minute capillaries enter the lobule, penetrate between each cell and thus surround them, so that each cell is generously supplied with blood containing the raw material for the manufacture of bile. These capillary branches which enter the lobule and surround the cells are called intralobular (within the lobule). These vessels converge toward the centre of the lobule like the spokes of a wheel and empty into a vein (central) which carries the blood away from the lobule. The central veins from a number of lobules empty into a much larger vein upon whose surface a vast number of lobules rest, CHAP. XIV] THE DIGESTIVE SYSTEM 295 and therefore the name sublobular (under the lobule) is given to these veins. They empty into stili larger veins, the hepatic, which converge to form three large trunks and empty into the inferior vena cava, which is embedded in the posterior surface of the gland. The bile ducts. The surfaces of the hepatic cells are grooved, and the grooves on two adjacent cells fit together and form a channel into which the bile is poured as soon as it is formed by the cells. These channels form a network between and around the cells as intricate as the network of blood-vessels. They are called intralobular ducts, and empty into larger ducts called interlobular. These unite and form larger and larger ducts until two main ducts, one from the right and one from the left side of the liver, unite in the portal fissure and form the hepatic duct. The hepatic duct runs down- ward and to the right for about two inches (5 cm.) and then joins at an acute angle the duct from the gall-bladder, termed the cystic duct. The hepatic and cystic ducts together form the common bile duct (ductus communis choledochus) , which runs down- ward for about three inches (7.5 cm.) and enters the duodenum about three inches (7.5 cm.) below the pylorus. This orifice usually serves as a common opening for both the common bile and the pancreatic duct. It is very small and is guarded by a sphincter muscle which keeps it closed except during digestion. (See Fig. 174.) Hepatic artery. We must remember that the blood brought to the liver by the portal vein is venous blood and is not intended for purposes of nourishment of the liver itself, hence arterial blood is furnished by the hepatic artery. It enters the liver with the portal vein, divides and subdivides in the same manner as the FIG. 178. LOBULE OF RABBIT'S LIVER, VESSELS AND BILE DUCTS IN- JECTED, a, central or intralobular vein ; 6, 6, interlobular veins ; c, interlobular bile duct. 296 ANATOMY AND PHYSIOLOGY [CHAP. XIV portal veins, thus forming another network between the lobules, and in the lobules between' the cells. The capillaries from the portal vein and the hepatic artery are separate and distinct until, near the centre of each lobule, they unite, and all the blood sup- plied to the liver by the portal vein and hepatic artery is carried away from it by the hepatic veins which empty into the inferior vena cava. Lymphatics. There is a superficial and a deep set. They begin in irregular spaces in the lobules, form networks around the lobules, and run always from the centre outward. They drain off waste products and unconsumed nutritious substances. Glisson's capsule. The whole liver is invested in an outer capsule of areolar connective tissue, which is reflected inward at the portal fissure and encloses the vessels and ducts passing through this opening. Serous membrane. With the exception of a few small areas, the liver is enclosed in a serous tunic derived from the peritoneum. Nerves. Nerves are derived from the left vagus and the solar plexus. 1 Functions. The liver may be compared to a wonderful laboratory, the most wonderful in the body. It has three im- portant functions : 1 . Bile secreting. The cells of the liver manufacture bile from the blood brought to them by the portal vein. The function of bile is considered in the next chapter. 2. Glycogenic. The cells of the liver take from the blood brought to them by the portal vein a substance called glucose, which is derived from the carbohydrates of our food. This is stored in the liver in the form of glycogen until such time as the body needs more glucose than the food furnishes. When such demand is made, the liver cells reconvert the glycogen into glucose and pour it into the circulation. 3. Higher chemical activities. Many of the end-products of protein digestion cannot be eliminated until they are acted upon by the liver, and changed into other substances which the kid- neys can eliminate, e.g., urea is made from some of these end- products brought to the liver by the blood. It is probable that the liver possesses other important metabolic functions which at pres- 1 See page 401. CHAP. XIV] SUMMARY 297 ent are not fully understood. Some physiologists are of the opinion that fibrinogen and antithrombin are formed in the liver. The gall-bladder. The gall-bladder is a pear-shaped sac lodged in the gall-bladder fissure on the under surface of the liver, where it is held in place by connective tissue. It is about four inches (10 cm.) long, one inch (2.5 cm.) wide, and holds about ten drachms (40 cc.). It is composed of three coats : (1) the inner one is mucous membrane, (2) the middle one is muscular and fibrous tissue, and (3) the outer one is serous membrane derived from the peritoneum. It is only occasionally that the peritoneum covers more than the under surface of the organ. Function. The gall-bladder serves as a reservoir for the bile. During digestion the bile is constantly poured into the intestine ; in the intervals it is stored in the gall-bladder. SUMMARY Digestion. Digestion is dependent on the proper functioning of certain organs that are grouped together and called the digestive system. Mouth. Pharynx. (Esophagus, or gullet. Stomach. Duodenum. Jejunum. Digestive System Alimentary Canal Alimentary canal Accessory organs Small or thin in- testine Large or thick in- testine Ileum. Caecum. Colon Rectum. Ascending. Transverse. Descending. Salivary glands. Tongue. Teeth. Pancreas. Liver. Continuous tube from mouth to anus. About 30 ft. long. From mouth to diaphragm 3 coats From diaphragm to rectum 4 coats Mucous. Areolar. Muscular. Mucous. Areolar. Muscular. Serous derived peritoneum. from 298 Mouth, or Buccal Cavity Tonsils Tongue Salivary Glands Teeth ANATOMY AND PHYSIOLOGY [CHAP. XIV 1. Hard palate. Above palate Below tongue. Front lips. Sides cheeks. - Tonsils. 2. Soft palate uvula, pillars of the fauces, and tonsils. Contains Tongue. Salivary glands. Teeth. Collections of lymph nodules occupy triangular space between pillars of the fauces on either side of throat. 1. May be a source of lymphocytes and leu- cocytes. 2. May act as a filter and prevent entrance of microorganisms . Function Special organ of sense of taste. 1. Stimulates secretion of digestive fluids. 2. Assists in swallowing. 3. Secretes mucus. Assists in digestion Parotid just under and in front of ear. Submaxil- "| lary \ Below the jaw and under the tongue. Sublingual J Function Form a secretion, that mixed with the secre- tion of the glandular cells of the mouth is called saliva. Contained in sockets of alveolar processes of maxillae and mandible. Gums cover processes and extend into sockets. Sockets lined with perios- f Attaches teeth to sockets. teum 1 Source of nourishment. f Root one or more fangs contained in J socket. 1 Crown projects beyond level of gums. [ Neck portion between root and crown. Gives shape. Encloses pulp cavity which con- tains nerves and blood-vessels, that enter by canal from root. Enamel Caps the crown. Cement Covers the root. 3 portions Composed of three substances developed from epi- thelium Dentine CHAP. XIV] SUMMARY 299 Teeth 2 sets 1 . Temporary f Incisors 8 } < Canines 4 I Molars 8 Incisors 8 Canines 4 Bicuspids 8 Molars 12 Function To assist in the process of mastication. Temporary 6 months to 2 yrs. Permanent 6| yrs. to 21 yrs. of age ^20. J 32. Pharynx 'Cone-shaped tube, 5 inches long, between mouth and oesophagus. Muscular, lined with mucous membrane. 2 posterior nares. 2 Eustachian tubes. 7 apertures 1 fauces. 1 larynx. . 1 oesophagus. (Esophagus, or Gullet Tube 9 in. long. Extends from pharynx to stomach. Inner mucous disposed in folds. Middle submucous. 3 coats ( Internal circular layer. Outer muscular j External longitudinal I layer. 1. Connects the pharynx with the stomach. Function ^ 2. Receives the food and passes it on to stomach. Stomach, or Gaster Dilated portion of canal, size and shape vary. Oblique position in epigastric and left hypochondriac regions under the diaphragm. Openings j Cardiac orifice connects with oesophagus. 1 Pyloric orifice connects with duodenum. Curvatures Parts 4 coats Lesser curvature concave border. Greater curvature convex border. Fundus blind end to the left of the heart. Intermediate region between fundus and pyloric extremity. Pyloric extremity under the liver. 1. Outer serous peritoneum. [ 1. Longitudinal layer. 2. Muscular j 2. Circular layer. [ 3. Oblique layer. 3. Submucous vascular. 300 ANATOMY AND PHYSIOLOGY [CHAP. XIV Stomach, or Gaster 4 coats Small, or Thin, Intestine 4. Mucous < Glands Cardiac Peptic Rugae j secrete I mucus, chief cells secrete pep- sinogen ; parieta 1 cells secrete acid. f secrete Pyloric Pepsino- I gen and ( mucus. j Sympathetic system. 1 Vagi nerves Blood-vessels from coeliac axis. 1. Connects the oesophagus with the intes- tine. 2. To hold the food while it undergoes gastric digestion. I 3. To secrete mucus and gastric fluid. Convoluted tube extends from stomach to valve of colon. Twenty feet, coiled up in abdominal cavity. f Duodenum. 3 divisions < Jejunum. I Ileum. 1 . Serous from peritoneum, called mesentery. 2. Muscular { Longitudinal layer. I Circular layer. {Blood-vessels. Lymphatics. Nerves. 4. Mucous 1 V *lvula3 conniventes. i Villi contain lacteals. Simple follicles ] Nerves Functions 4 coats Glands and nodes Duodenal or Brunner's Lymph nodules ? Secrete intestinal fluid. Solitary. Aggregated lymph nod- ules of Peyer fifty or more solitary lymph nodules form so-called patches in small in- testine. Function {Digestion. Absorption. Secretion of succus entericus. CHAP. XIV] SUMMARY 301 Large, or Thick, Intestine Pancreas Largeness in width, not in length. Length, 5 ft. ; width, 2^ in. to \\ in. Extends from ileum to anus. CaBCum, with vermiform appendix. Ascending. Transverse. Descending with sigmoid flexure. Internal sphincter. External sphincter. 1. Serous, except that in some parts it is only a partial covering, and at rectum it is wanting. 3 divisions 4 coats Colon Rectum anus 2. Muscular - f Arranged in three Longitu- I ribbon-like bands that be- gin at appen- dix, and extend to rectum. dinal layer Circular layer 3. Submucous. No villi. No valvulae conniventes. 4. Mucous { i Tubular glands. Numerous j Solitary lymph [ nodules. f Continuance of digestion and absorption. I Elimination of waste. In front of first and second lumbar vertebrae, behind stomach. Head attached to duodenum. Body in front of vertebra. Tail reaches to spleen. Six inchss long. Two inches wide. One-half inch thick. Weight two to three ounces. Compound gland sacculated ends of tubules form lobules. Lobules held together by connective tissue Structure { form lobes. Lobes form gland. Duct from each lobule empties into pan- creatic duct. Function Hammer shape Size Function 1. Secretes pancreatic fluid. 2. Forms an internal secretion. 302 ANATOMY AND PHYSIOLOGY [CHAP. XI? Liver Five fis- sures Formed by folds of peri- toneum. Results from atrophy of umbilical vein. Under surface. Dorsal surface. Largest gland in body. Right hypochondriac. Location Epigastric. Left hypochondriac. Convex above fits under diaphragm. Concave below fits over right kidney, ascending colon, and pyloric end of stomach. 1. Suspensory, broad, or falciform Five liga- I 2. Coronary ments | 3. Right lateral 4. Left lateral 5. Round liga- ment 1. Umbilical fis- sure 2. Gall-bladder fissure 3. Portal or trans- verse fissure 4. Ductus venous fissure 5. Vena cava 1. Right (largest lobe). 2. Left (smaller and wedge-shaped). 3. Quadrate (square). 4. Caudate (tail-like). 5. Spigelian. f 1. Branches of portal vein. 2. Bile ducts. 3. Hepatic veins. 4. Branches of hepatic artery. 5. Lymphatics. Hepatic cells jsW in. in diameter grouped in lobules. Lobules is in. in diameter. Interlobular veins (be- tween lobules). Intralobular capillaries (within lobules). Branches of por- Central veins. tal vein I Sublobular veins (under lobules) . Hepatic veins exit at portal fissure, empty into inferior vena cava. Five lobes Five sets of vessels Anatomy of liver CHAP. XIV] SUMMARY 303 Liver Gall-bladder Anatomy of liver Functions Bile ducts Branches of he- patic artery Lymphatics { Channels between cells (within lobules). Intralobular -ducts. Interlobular ducts. Hepatic duct exit at portal fissure. Interlobular arteries (between lobules). Intralobular capillaries (within lobules). Course beyond the in- tralobular capillaries same as that pursued by blood from portal vein. Start in lobules, form network, and run from centre to periphery. Act as drain-pipes. Glisson's capsule encloses the whole of the liver. Serous membrane from the peritoneum almost completely covers it. 1. Bile secreting. 2. Glycogenic. Changes toxic substances so that they are less harmful and more easily eliminated, e.g., urea. Pear-shaped sac lodged in gall-bladder fissure on under surface of liver. f Four inches long. \ One inch wide. [ Capacity about ten drachms. !1. Mucous membrane. 2. Fibrous and muscular tissue. 3. Serous membrane from peritoneum. Function Serves as a reservoir for bile. Higher chem- ical activities Size 3 coats CHAPTER XV FOOD. DIGESTIVE PROCESSES; CHANGES THE FOOD UNDER- GOES IN THE MOUTH, STOMACH, SMALL AND LARGE INTES- TINES ; ABSORPTION THE process of digestion takes place in the alimentary canal and the purpose of it is to prepare food for absorption and utilization by the tissues of the body. It includes not only the physical process of changing the food to a solution or emul- sion, but also the chemical process of cleavage, i.e., the splitting of large and complex molecules into smaller and simpler ones. Both these processes favor diffusion. Of equal significance is the standardization of food. Digestion obliterates many of the char- acteristics which differentiate foods and gives us at last much the same set of products, whatever the meal may have been. From the large number of complex compounds taken into the stomach, only a small number of simple substances are contributed by the intestines to the blood. It is also a process of refining as it sepa- rates the useful from the useless residue of our food. FOOD Definition. Food is any substance taken into the body, (1) to provide material for the growth of body tissues, (2) to repair tissue waste, and (3) to supply heat and other kinds of energy. After birth the material for the growth of the body is derived from our food ; also the material to make good the loss resulting from the daily wear and tear of body tissues. All the body ac- tivities require a certain amount of energy ; this and all the heat dissipated from the body must be supplied by food. The energy in our food is present in the form of potential or latent energy, binding the atoms into molecules, and the molecules into larger masses. The splitting of these complex molecules into smaller and simpler ones releases energy. Food material, over and above 304 CHAP. XV] FOOD 305 what is needed for this purpose, is stored in the body either in the form of fat, or as glycogen in the liver and muscles. This may be regarded as so much reserve fuel which is oxidized when needed to furnish energy. Classification of food. Chemical analysis shows that the elements l found in the body are also found in food. Various combinations of these elements give us a great variety of com- pound substances which are divided into two great classes of nutrients. This division is based on the presence or absence of carbon. Those which contain carbon are organic, those which do not are inorganic. These are further subdivided as follows : Nutrients or Food Principles 1. Inorganic 2. Organic f Water. Mineral matter or salts. Carbohydrates. Fats. Proteins. Water. Water (H 2 O) is a very stable compound of hydrogen and oxygen. It enters into the composition of all the tissues, supplies fluid for the body, acts as a solvent for food, and aids in the elimination of waste. Next to air it is the most necessary prin- ciple of life and constitutes about two-thirds of the body weight (66 per cent). Salts. The principal inorganic salts are : Chloride Phosphate Sulphate Carbonate of sodium and potassium. Phosphate ] , . \ of calcium and magnesium. Carbonate J The inorganic salts are an essential part of all the tissues, and take part in the functions of the body in six ways : (1) they maintain the alkaline or neutral reaction of the fluids of the body ; (2) they furnish the material for the acidity or alkalinity of the digestive fluids and other secretions ; (3) they help in regulating the flow of fluids to and from the tissues, because they maintain the normal osmotic pressure; (4) they enter largely into the composition of the bones, teeth, and cartilage ; (5) they are necessary for the 1 See page 5. 306 ANATOMY AND PHYSIOLOGY [CHAP. XV clotting of blood ; and (6) they give the fluids of the body their influence upon the elasticity and irritability of nerve and muscle. Carbohydrates. All sugars and starches are grouped under the name of carbohydrates. They contain but three ele- ments, carbon, hydrogen, and oxygen, the two latter in the pro- portion to form water. The varieties of carbohydrates are as follows : Glucose or dextrose, found in fruits, es- pecially the grape, and in the blood. Simple or Mono- saccharids Fructose or levulose, found with glucose in fruits. C 6 Hi 2 6 . Invert sugar. Simple sugars. Simple sugars are one of the standard sub- stances which the tissues can use, and as they are freely soluble and of small molecule they are readily absorbed. Complex or Disaccharids f Sucrose or cane sugar. Ci 2 H 22 Oii. | Lactose or milk sugar. Ci 2 H 22 Oii. [ Maltose or malt sugar. Ci 2 H 22 On. Complex sugars. A study of the formulas of the complex sugars will show that the composition is the same but they are differently named because they give different reactions. Before any of the complex sugars can be utilized in the body they must first be changed either into glucose, or into invert sugar, which consists of a molecule each of glucose and fructose. Only one splitting is necessary as one molecule of a complex sugar plus one molecule of water will form one molecule of glucose and fructose. COMPLEX SUGAR WATER GLUCOSE FRUCTOSE + H 2 = C 6 H 12 6 . C 6 H 12 6 Poly saccharids Invert Sugar Starch found in grain, tubers, roots, etc. Cellulose outside covering of starch grains, and basis of all woody fibres. Glycogen form in which sugar is stored in the liver and muscles. Dextrin formed from starch by partial hydrolysis. (C 6 H 10 5 )n (C 6 H 10 5 )n (C 6 H 10 6 )n (C 6 H 10 5 )n Poly saccharids. In all of these compounds the composition of the molecule is supposed to be rather complex, although the CHAP. XV] FOOD 307 elements are present in the same relative proportion, as shown in the formulae. The value of n, however, may be very small or very large and is probably different for each polysaccha- rid, which makes the actual composition of each member of the group different. For instance, n for the starch molecule is large, while for the dextrin molecule it is smaller, so that a single starch molecule in digestion may split into several molecules of dextrin of the same relative composition. In the disaccharids only one splitting is necessary, as each molecule of a complex sugar plus one molecule of water will give two molecules of a simple sugar. As poly sacchar ids are so complex, they must pass through several stages before they are changed by hydrolytic cleavage to a simple sugar. Each splitting of the molecule gives substances with simpler composition, though with the same relative proportion of the constituents, and to each is given a special name. Thus as the result of the first splitting we have dextrin, of which there are three varieties, i.e., erythrodextrin, achroodextrin, and maltodextrin, each one being produced as a result of the further splitting of the molecules; then maltose, a disaccharid, is yielded, and finally glucose, a monosaccharid or simple sugar. The number of molecules of simple sugar resulting from the hydrolysis of any polysaccharid would depend upon the value of n. Fats. Fats are composed of carbon, hydrogen, and oxygen, but the hydrogen content is relatively high. The ordinary fats of animal and vegetable food are not simple substances, but are mixtures of simple fats named palmitin, stearin, and olein, which are derived from the fatty acids, palmitic, stearic, and oleic. Each molecule of a simple fat is made from one molecule of glycerine and three molecules of a fatty acid. This reaction is comparable to the neutralization of an acid by a base resulting in a salt and water. (See page 8.) !.<- -^ %V Acid -f Base -> Salt + Water HC1 + NaOH -> NaCl + H 2 O Acid + Base -- Salt + Water (STEARIC ACID) (GLYCERINE) (STEARIN) (WATER) 3 H Ci 8 H 3 502 + C 3 H 5 (OH)3 * C 3 H 5 (C 18 H35O 2 )3 + 3 H 2 O 308 ANATOMY AND PHYSIOLOGY [CHAP. XV In general, fats and oils are practically the same, and the mixture of fats found in the body is liquid at the body temperature. They are soluble in ether, chloroform, and hot alcohol, but are insoluble in water. Under the influence of steam, mineral acids, and cer- tain enzymes found in the body, fats split up into the substances of which they are built, i.e., glycerine and fatty acids. Accord- ingly, the digestion of fats is a reaction in exactly the opposite di- rection from the one above. Salt + Water ->- Base + Acid (STEARIN) (WATER) (GLYCERINE) (STEARIC ACID) 2 )3 + 3 H 2 ->- C 3 H 5 (OH) 3 + 3 H.Ci 8 H 35 O 2 The process of saponification is similar to the above, only that instead of water a base is used and the final products are glycerine and soap. Salt + Base -> Base + Soap (POTASSIUM (STEARIN) HYDROXIDE) (GLYCERINE) (SOAP) C 3 H 6 (Ci 8 H 35 2 ) 3 + 3 KOH -> C 3 H 5 (OH) 3 + 3 K(C 18 H 35 O 2 ). Proteins. Proteins consist of carbon, hydrogen, nitrogen, oxygen ; sulphur, phosphorus, and other elements may be present. They are more complex than either carbohydrates or fats and dif- fer from them in having nitrogen, hence they are described as nitrog- enous compounds. Proteins are difficult to analyze but modern chemists have shown that they are built up of simpler substances called amino-acids. Accordingly, the digestion of proteins which is a process of hydrolysis means reducing them to amino-acids, and the number of stages through which they pass depends upon the size 1 and the complexity of the molecule. Each splitting of the molecule gives substances with simpler composition and to each such substance is given a special name, i.e., -> Protein --Metaprotein->-Proteo3es->- Peptones -> Peptids -> Amino-acids. The number of molecules of amino-acids resulting from the hy- drolysis of any protein would depend upon the size of the molecule. About twenty amino-acids have been described, and are some- times compared to the letters of the alphabet. Various com- binations of letters result in an enormous number of words. In a similar way various combinations of amino-acids result in many 1 The large size of the protein molecule can be judged by the empirical formula assigned to globin, one of the simplest forms: CHAP. XV] FOOD 309 Simple Conjugated Proteins different kinds of proteins which give different reactions and are represented by different formulae. Classification of proteins. For experimental purposes proteins have been classified as shown below; the classification being based on their solubility in various reagents and on other reactions. Albumins. Globulins. Glutelins. Alcohol-soluble proteins (prolamines). Albuminoids. Histons. Protamins. Nucleoproteins. Glycoproteins. Phosphoproteins. Haemoglobins. Lecithoproteins. Primary derivatives 1 (formed through hy- drolytic changes which cause only slight al- terations of the protein molecule) Secondary derivatives (products of further hydrolytic cleavage of the protein molecule) In this classification the group called simple proteins hydrolyze to amino-acids, conjugated proteins yield amino-acids and some other body. This latter substance is nuclein in the nucleoproteins, a carbohydrate in the glycoproteins, a phospho body in the phos- phoproteins, hsematin in haemoglobins, and a fatty substance in lecithoproteins. The derived proteins are changed forms produced by the action of heat, acids, alkalies, or enzymes. Accessory articles of diet. In addition to the foodstuffs proper, our foods contain numerous other substances which in one way or another are useful in nutrition, although not absolutely necessary. These substances, differing in nature and importance, may be classified under the three heads of : Flavors : The various oils or esters that give odor and taste to foods. Condiments : Salt, pepper, mustard, etc. Stimulants : Tea, coffee, cocoa, meat extracts, etc. Derived Proteans. Metaproteins. Coagulated proteins. Proteoses. Peptones. Peptids. 310 ANATOMY AND PHYSIOLOGY [CHAP. XV DIGESTIVE PROCESSES In a broad sense all the processes by which foods are rendered available to an organism are digestive processes. The word alimentation is often used to include the preparatory processes together with the digestive processes. In this sense, many indus- trial and domestic processes are in line with digestion and often initiate the task which the digestive organs complete. This is particularly true of cooking, for by it various chemical changes are brought to pass ; such, for example, as changing starches into dex- trins, partially splitting fats into glycerine and fatty acids, and changing some proteins to the first stages of their decomposition products. A second reason for classifying cooking as a digestive process is that the appearance, odor, and taste of food are im- proved, and these facts stimulate the end organs of the special senses, causing a reflex stimulation of the digestive mechanisms. In a third way cooking may profoundly aid digestion by killing parasites or bacteria which otherwise would gain a foothold in the alimentary canal and thus modify or change digestive processes. It is usual to describe digestion within the body as consisting of two processes, i.e., mechanical and chemical. Both the mechanical and chemical processes of digestion are controlled by the nervous system. Any severe strain or strong emotion which 'affects the nervous system unpleasantly, inhibits the secretion of the digestive fluids and interferes with digestion, often checking the appetite and even preventing the taking of food. On the other hand, pleasurable sensations aid digestion, hence the value of attractively served food, pleasant surroundings, and cheerful conversation. Mechanical digestion. Mechanical digestion is effected by various physical processes that occur in the alimentary canal. It is to be considered as preliminary to the more important chemical digestion. It serves four important purposes : (1) in taking food in and moving it along through the alimentary canal just rapidly enough to allow the required chemical changes to take place in each part; (2) in lubricating the food by adding the mucin and water secreted by the glands of the alimentary canal ; (3) in lique- fying the food by mixing it with the various digestive fluids ; and (4) in separating the food into small particles, thereby increasing CHAP. XV] DIGESTIVE PROCESSES 311 the amount of surface to come in contact with the digestive fluids. The mechanical processes consist of : 1. Mastication. 2. Deglutition or swallowing. 3. Peristaltic action of oesophagus. 4. Movements of the stomach. 5. Movements of the intestines. 6. Defecation. Chemical digestion. The most essential part of digestion is chemical and is a process of hydrolytic cleavage which is de- pendent upon the presence of enzymes. The term hydrolysis means the breaking down of complex, molecules into simpler ones with the absorption of water. An example of hydrolysis is the conversion of any of the complex sugars into simpler sugars. (See page 306.) Necessity for chemical digestion. Chemical digestion is neces- sary because organic foods, with the exception of simple sugars, cannot diffuse through animal membranes, and even if diffusion were possible, the tissues could not use them, hence they must be reduced to smaller molecules and to such standard substances as the tissues can use, i.e., (1) simple sugars, resulting from the digestion of all carbohydrate foods ; (2) glycerine and fatty acids, resulting from the digestion of fats ; and (3) amino-acids, result- ing from the digestion of proteins. Cause of chemical digestion. It is possible to make carbo- hydrates, fats, and proteins undergo the same changes outside the body as occur during digestion. Carbohydrates, fats, and pro- teins, if boiled with a mineral acid or subjected to the action of enzymes, will hydrolyze and split up into simpler substances. Within the body these changes take place at body temperature, and are due to the enzymes present in all of the digestive fluids. Enzymes. The exact composition of enzymes is not known. One author suggests the following definition : " An enzyme is a substance produced by living cells which acts by catalysis." In other words, they are organic substances which vary (hasten or retard) the speed of reactions, but do not initiate them. Their efficacy is destroyed by boiling. The following characteristics may be noted : 312 ANATOMY AND PHYSIOLOGY [CHAP. XV Optimum temperature. The body enzymes act best at the temperature of the body. They are destroyed by a high tem- perature and their effect is retarded wholly or in part by a low temperature. Medium. Each enzyme requires a medium of definite reaction either acid, alkaline, or neutral. The enzyme of saliva requires an alkaline or neutral medium, while the enzymes of the gastric fluid require an acid medium. Active and inactive form. It has been demonstrated that an enzyme may exist within the cell producing it in an antecedent or inactive form which is designated as a zymogen. The zymogen may be stored in the cell in the form of granules which are con- verted into active enzyme at the moment of secretion, or it may be secreted in inactive form and require the cooperation of some other substance before it is capable of effecting its normal reaction. In such cases the second substance is said to activate the enzyme. An example is found in the case of the enterokinase which acti- vates the trypsinogen of the pancreatic secretion. (See page 321.) Coenzymes. There are some cases where the action of an enzyme is helped by, or even dependent upon the presence of some other substance. A good example of this activity is furnished by the influence of bile-salts upon lipase. 1 These cases of coactivity are to be distinguished from activation, by the fact that the combination may be made or unmade. For example, in a mixture of bile salts and lipase, the bile salts may be removed by dialysis. In activation, on the contrary, the active enzyme cannot be changed back to the inactive zymogen. Classification of enzymes. There is no consensus of opinion among physiologists or chemists as to the system to be followed in naming or classifying enzymes. Recently it has been suggested that an enzyme be designated by the name of the substance on which it acts, and that all of them be given the termination ase. According to this system the enzyme acting on starch would be amylase ; that on maltose, maltase ; that on fat, lipase. This suggestion has been followed in part only, as the older enzymes are still most frequently referred to under their original names. The following classification is a modification from a standard physiol- ogy : 2 - 1 See page 322. 2 Howell's " Text-book of Physiology," sixth edition. CHAP. XV] DIGESTIVE PROCESSES 313 1. The sugar-splitting enzymes. These fall into two subgroups: (a) The inverting enzymes, which convert the double sugars or disac- charids into the monosaccharids. Examples: Maltase, which splits maltose to dextrose; invertase, which splits cane-sugar to dextrose and levulose; and lactase, which splits milk-sugar (lactose) to dextrose and galactose. (6) The enzymes, which split the monosaccharids. There is evidence of the presence in the tissues of an enzyme capable of splitting the sugar of the blood and tissues (glucose) into lactic acid. 2. The amylolytic or starch-splitting enzymes. Examples: Ptyalin or salivary diastase, amylase, or pancreatic diastase. They cause a hydrolytic cleavage of the starch molecule. 3. The lipolytic, or fat-splitting enzymes. Example: The lipase found in the pancreatic secretion, in the liver, connective tissues, blood, etc. They cause a hydrolytic cleavage of the fat molecule. 4. The proteolytic or protein-splitting enzymes. Examples : Pepsin of gastric fluid, trypsin of pancreatic fluid. They cause a hydrolytic cleavage of the protein molecule. 5. The clotting enzymes, which convert soluble to insoluble proteins. Example : The clotting of the casein of milk by rennin. 6. The oxidizing enzymes, or oxidases. A group of enzymes which set up oxidation processes. Opinions differ in regard to the manner" in which these enzymes act. 7. The deaminizing enzymes. All amino-acids contain an NH 2 group which is split off by hydrolytic cleavage and is converted to ammonia > NH 3 , and then probably to urea ->- NH 2 CO NH 2 . See page 339. CHANGES THE FOOD UNDERGOES IN THE MOUTH Mastication. When solid food is taken -into the mouth it is cut and ground by the teeth, being pushed between them again and again by the muscular contractions of the cheeks, and the movements of the tongue, until the whole is thoroughly crushed and ground down, thus exposing a larger surface to the action of the digestive fluids. Insalivation. During the process of mastication saliva is poured in large quantities into the mouth, and mixing with the food, lubricates, moistens, and reduces it to a soft, pulpy condi- tion. A certain amount of air caught in the bubbles of the saliva also becomes entangled in the food, and this facilitates the pene- tration of the gastric fluid. Secretion of saliva. The secretion of saliva is the result of reflex stimulation of the nerves connected with the salivary glands. This is a psychical reflex which is initiated by the sight, thought, or 314 ANATOMY AND PHYSIOLOGY [CHAP. XV smell of food, acting as stimulants to the sensory or afferent nerves which carry these impulses to a nerve centre in the brain (prob- ably in the medulla oblongata), and from thence motor impulses are transmitted through efferent nerves to the gland. The move- ments of mastication and the taste of food continue this stimu- lation, so that the secretion is continued till the end of the meal. Saliva. Saliva is a mixture of the secretions of all three pairs of salivary glands, as well as of the small glands of the mucous membrane of the mouth. It consists of water, some mucin, and an enzyme called ptyalin or salivary diastase. It has a specific gravity of 1 .004 to 1 .008 and an alkaline reaction when tested with litmus paper. The amount secreted in twenty-four hours is estimated to be from one to two quarts (1-2 litres). The functions of saliva. Saliva has four distinct functions : (1) by softening and moistening the food it assists in mastication and deglutition ; (2) by coating the food with mucin it lubricates it and insures a smooth passage along the oesophagus ; (3) by dis- solving dry and solid food it provides a necessary step in the pro- cess of stimulating the taste nerves, and taste sensations play an important part in the secretion of gastric fluid ; (4) by virtue of the enzyme which it contains it changes starch to simpler sub- stances, i.e., dextrin and maltose. Ptyalin or salivary diastase. By the action of the enzyme ptyalin which is present in saliva, starch is partially changed to dextrin and maltose. This process is a complicated one con- sisting of a series of hydrolytic changes which take place in suc- cessive stages, and result in a number of intermediate compounds. The change is best effected at the temperature of the body, 1 in a slightly alkaline solution, saliva that is distinctly acid hindering or arresting the process. Boiled starch is changed more rapidly and completely than raw, but food is rarely retained in the mouth long enough for the saliva to more than begin the transformation of starch. Deglutition or swallowing. The softened and moistened food is brought together on the upper surface of the tongue and pressed backward through the fauces into the pharynx. Then the muscu- lar bands in the wall of the pharynx contract and force the food into 1 A temperature of 100 F. in the alimentary canal is necessary for digestion, hence iced drinks or iced foods that lower this temperature delay digestion. CHAP. XV] DIGESTIVE PROCESSES 315 the oesophagus. At this moment breathing has to be suspended and the passages closed against the possible entrance of food. The soft palate is drawn back, thus protecting the nasal passages, and the larynx is shielded by being pulled forward under the root of the tongue, and has an additional safeguard through the folding down upon it of the epiglottis. When food is once within the oesophagus; breathing may be resumed and the downward passage of the food is assisted by the peristaltic action of the oesophagus. When liquids are swallowed they are shot down the oesophagus by the initial act of swallowing, and may find the cardiac orifice closed. In this case, the liquid is held until the peristaltic wave reaches the cardiac orifice, when the tissues relax and allow the liquid to pass. Peristalsis. Peristalsis occurs in such tubular viscera as the oesophagus, stomach, intestines, etc., which possess muscular coats. Peristalsis consists of a series of wave-like contractions of the circular fibres which affect successive portions of the tube from above downward. The constricted portion is always pre- ceded by an area of relaxation, which renders the contraction more effective in forcing the contents onward. The direction is always the same, and the action is under the control of the nervous system. Summary. During the process of mastication, insalivation, and deglutition the food is first reduced to a soft, pulpy condition ; second, any starch it may contain begins to be changed into sugar ; third, it acquires a more or less alkaline reaction. Vomiting. Under ordinary circumstances the contractions of the cardiac sphincter muscle prevent the regurgitation of food, but strong contractions of the stomach or spasmodic contractions of the abdominal muscles may, if the diaphragm is fixed, force the contents of the stomach through the oesophagus and mouth to the exterior. This is called vomiting. \CHANGES THE FOOD UNDERGOES IN THE STOMACH, OR STOMACH DIGESTION The food which enters the stomach is delayed there by the contraction of the sphincter muscles at the cardiac and pyloric openings. The cavity of the stomach is always the size of its contents, which means that when it is empty it is contracted, but when food enters, it expands just enough to hold it. Within a 316 ANATOMY AND PHYSIOLOGY [CHAP. XV few minutes after the entrance of food small contractions start in the middle region of the stomach and run toward the pylorus. These contractions are regular and become more and more forcible as digestion progresses. As a result of these movements the food is macerated, mixed with the acid gastric fluid, and reduced to a thin liquid mass called chyme. At certain intervals the pyloric sphincter relaxes and the wave of contraction forces some of the chyme into the duodenum. The fundal end of the stomach does not take part in these movements, but serves as a reservoir for food which is under slight pressure, as the muscles are in a state of continual contraction or tone. Due to the lack of movement and the muscular tone, the gastric fluid cannot penetrate the bolus of food, and the ptyalin with which it became mixed in the mouth continues its action, and the digestion of starch continues for about half an hour. As the chyme is gradually forced into the duodenum, the pressure of the fundus forces the food into the pyloric end. The stomach is admirably adapted to receive a large amount of food within a short period of time. It reduces this food to chyme, and at intervals charges the intestine with small amounts of this chyme in such condition as to admit of rapid digestion. It seems probable that without the stomach, our mode of eating would have to be changed, as it would not be possible to load the intes- tine with the amount of food ordinarily consumed at a meal. Time required for stomach digestion. It is obvious that the time required for gastric digestion depends upon the nature of the food eaten. An average meal of mixed food requires about five hours for gastric digestion. The ejection of chyme through the pylorus occurs at regular intervals, and is supposed to depend upon the consistency and acidity of the chyme. Solid particles forced against the pylorus tend to keep it closed, but hydrochloric ify/ acid in the stomach seems to favor or produce relaxation of ther/ pyloric sphincter. In the intestines hydrochloric acid has a con- trary effect, as it causes a contraction of the sphincter, which remains closed after each ejection until the acidity has been neutralized. Secretion of gastric fluid. The secretion of gastric fluid seems to begin in advance of the actual arrival of food in the stomach, and to be in proportion to the pleasure of the meal. It continues as long as food remains in the stomach, and is caused CHAP. XV] DIGESTIVE PROCESSES 317 and maintained by two factors : (1) psychical, the sensations of eating ; the taste and odor of food stimulate the sensory nerves situated in the mouth and nose. These afferent impulses are transferred through nerve centres to efferent fibres of the vagus nerve, and thus are carried to the stomach. (2) Chemical, (a) by secretogogues contained in certain foods and (6) by secreto- gogues contained in the products of digestion. Certain foods, such as meat juices and extracts, contain substances called secreto- gogues or hormones which are supposed to act directly upon the nerves of the pyloric mucous membrane and form a substance called gastrin or gastric secretin, which is absorbed into the blood and carried to the gastric glands. This substance stimulates the glands to secretion. Other foods, such as milk, bread, white of egg, etc., do not appear to contain secretogogues. When such foods are eaten, a psychical secretion is started and when this has acted, some products of their digestion in turn become capable of stimulating a further secretion of gastric fluid. Gastric fluid. Gastric fluid is secreted by the gastric glands 1 lining the mucous membrane of the stomach. It is a thin, colorless, or nearly colorless liquid with a strong acid re- action, and a specific gravity of about 1.002-1.003. The quan- tity secreted depends upon the amount of food to be digested. Upon analysis it is found to contain some protein, some mucin, and inorganic salts, but the essential constituents are hydro- chloric acid and two or possibly three enzymes, pepsin, rennin, and lipase. Hydrochloric acid. It is generally believed that the parietal cells of the gastric glands secrete the hydrochloric acid, from chlorides found in the blood. The chief chloride is sodium chloride (NaCl), and by some means this is decomposed ; the chlorine (Cl) combines with hydrogen (H), and is then secreted upon the free surface of the stomach as hydrochloric acid (HC1). In normal gastric fluid it is found in the proportion of 0.2 to 0.4 per cent. It serves (1) to activate pepsinogen and convert it to pepsin ; (2) provides an acid medium which is necessary for the pepsin to carry on its work ; (3) swells the protein fibres, thus giving easier access to pepsin ; (4) it helps in the inversion of sugar, i.e., chang- ing complex sugars to simple ones ; (5) it acts as a disinfectant 1 See page 282. 318 ANATOMY AND PHYSIOLOGY [CHAP. XV and kills many bacteria that enter the stomach, and (6) it helps to regulate the opening and closing of the pyloric valve. Pepsin. Pepsin is supposed to be formed in the pyloric glands and the chief cells of the gastric glands. It is present in these cells in the form of a zymogen, an antecedent inactive sub- stance called pepsinogen which is quickly changed to active pep- sin by the action of hydrochloric acid. Pepsin is a weak proteolytic enzyme requiring an acid medium in which to work. It has the property of converting more or less of the protein of the food into simpler and more soluble proteoses and peptones. This action is preparatory to the more complete hydrolysis that takes place in the intestines under the influence of trypsin and erepsin, for peptones are not absorbed but suffer a further hydrolysis to amino-acids. Rennin. Rennin, like pepsin, is supposed to be formed in the chief cells of the gastric glands in a zymogen form, the prorennin which after secretion is converted to the active enzyme. So far as is known, this enzyme acts only upon the soluble protein of milk, which is called caseinogen. It converts this substance into a clotted mass called curd ; the digestion of which is carried on by the pepsin, and later in the intestine by the trypsin. Various observers have described other enzymes in addition to the pepsin and rennin, but the evidence regarding these is uncer- tain. It is probable that the ptyalin swallowed with the food continues the digestion of starchy material in the fundus for some time. Regarding the fats, it is believed that they undergo no true digestive change in the stomach. They are set free from their mixture with other foodstuffs by the dissolving action of the gas- tric fluid; they are liquefied by the heat of the body, and are scattered through the chyme in a coarse emulsion by the move- ments of the stomach, all of which favors the subsequent action of the pancreatic fluid. Emulsified fats like cream are acted upon to a limited extent by a third enzyme called gastric lipase, and this action may be important in the digestion of milk fat by infants, as the pancreas is inactive. Summary. The stomach serves as a place for storage and maintains a gradual delivery to the intestine. The movements are adapted to promote the mechanical reduction of food. Sali- vary digestion of starch continues until the acidity is everywhere CHAP. XV] DIGESTIVE PROCESSES 319 established. Gastric digestion affects proteins chiefly and is in- complete. There is some digestion of emulsified fat. CHANGES THE FOOD UNDERGOES IN THE SMALL INTESTINE The chyme, entering the duodenum, after an ordinary meal, is a mixture of various matters. It probably contains proteoses and peptones derived from the proteins ; dextrins and sugar from the carbohydrates ; traces of glycerine and fatty acids from the fats ; portions of all the foods not yet digested ; hydrochloric acid from the gastric fluid ; and lactic acid produced by fermentation. It is in the intestines that this mixture undergoes the most profound digestive changes. These changes which constitute intestinal digestion are effected by : (1) the movements of the intestines, (2) the pancreatic fluid, (3) the succus entericus or secretion of the intestinal glands, and (4) the bile. Movements of the small intestine. The movements of the small intestine are of two kinds : (1) peristaltic and (2) pendular or rhythmic segmentation. (1) A peristaltic movement may be defined as a quick succes- sion of waves of contraction and inhibition passing slowly along the intestine. The wave of contraction begins at a certain point, passes downward away from the stomach, and is always pre- ceded by an area of inhibition or relaxation. The purpose of it is to pass the food slowly forward, and it is obvious that the wave of contraction is more effective in forcing the contents forward because just in front of it the intestine is relaxed. (2) The movements of pendular or rhythmic segmentation con- sist of local constrictions of the intestinal wall which occur rhyth- mically at points where masses of food lie. The purpose of these constrictions is to divide the string of food into a number of equal segments. Within a few seconds each of these segments is halved and the corresponding halves of adjoining segments unite. Again constrictions recur and these newly formed segments are divided, and the halves reform in the same position as they had at first. In this way every particle of food is brought into intimate contact with the valvulse conniventes and is thoroughly mixed with the digestive fluids. 320 ANATOMY AND PHYSIOLOGY [CHAP. XV Secretion of pancreatic fluid. Just as the chewing and swallow- ing of food starts the gastric secretion, so the presence of acid chyme in the intestine starts the pancreatic secretion. This effect is due to a special substance called secretin which is formed by the action of the acid upon a substance called prosecretin which is present in the mucous membrane of the intestine. This secretin is absorbed by the blood and carried to the pancreas, which it stimulates to activity. (See page 322.) Pancreatic fluid. Healthy pancreatic fluid is a clear, some- what viscid fluid, with a very decided alkaline reaction. The amount secreted in twenty-four hours is about one to one and two- thirds pints (500 to 800 cc.). It contains few solids and is depen- dent for its remarkable power on three enzymes : (1) trypsin, (2) pancreatic diastase (amylase), and (3) lipase (steapsin). Some authors state that the secretion contains a fourth enzyme, i.e., rennin. Action of pancreatic fluid upon food. Pancreatic fluid has the power of acting on all the foodstuffs, proteins, carbohydrates, and fats. This action is due to its enzymes. (1) Trypsin. Trypsin is secreted in the form of a zymogen called trypsinogen, and is activated by enterokinase, an enzyme which is contained in the mucous membrane of the small intestine. Trypsin, like pepsin, causes hydrolytic cleavage of proteins, but the action is more rapid and powerful, and the protein mole- cule is broken up into simpler substances than peptones, depending on the amount of trypsin and the time that it acts. If complete hydrolysis takes place, the end-products consist chiefly of amino- acids. Trypsin attacks proteins in slightly acid, neutral, or strongly alkaline mediums. The preliminary action of pepsin, on a protein molecule, hastens the action of trypsin, and renders it more complete than if the trypsin acted alone. (2) Diastase (Amylase) . The action of diastase is similar to that of ptyalin. It causes hydrolysis of starch with the production of achroodextrin and maltose. The starchy food that escapes diges- tion in the mouth and stomach becomes mixed with this enzyme and continues under its action until the ileo-caecal valve is reached. Before absorption, achroodextrin and maltose are further acted upon by the maltase of the intestinal secretion and converted to dextrose. CHAP. XV] DIGESTIVE PROCESSES 321 (3) Lipase (Steapsin) . Lipase is an enzyme capable of hy- drolyzing fats to glycerine and fatty acids. The process of hydroly- sis is preceded by the mechanical process of emulsification which results in tiny droplets of fat. This increases the surface of fat ex- posed to the chemical action of the lipase and from a physiological standpoint is regarded as a preparatory process. Glycerine and fatty acids are absorbed by the epithelium of the intestine, and again combine to form fat. It is probable that in this synthesis the fatty acids combine with the glycerine in such proportions as to make the kind of fat characteristic of the animal. The action of lipase is said to be reversible, i.e., it causes both the splitting of the fats and the synthesis of the split products, not only in the intestines, but in the various tissues, during the metabolism or the storage of fat. Lipase is found in blood and in many tis- sues, muscle, liver, mammary glands, etc. There is a possibility that the fat (salt) may combine with an alkali (base) and form soap. This reaction is known as saponifica- tion. It is difficult to say how far it usually goes on. Succus entericus, or intestinal fluid. Succus entericus is the secretion of the intestinal glands. It is a clear, yellowish fluid, having a marked alkaline reaction and containing a certain quan- tity of mucin. There is much disagreement as to the properties and importance of this secretion. It is said to have little or no digestive action except upon starches ; nevertheless, the general tendency is to attribute to it, plus the intracellular enzymes, a larger share in the work of digestion than was formerly granted. These intracellular or endo-enzymes are not secreted into the lumen of the intestine but are held within the cells, and strictly speaking, are not a constituent of the intestinal fluid. However, it is their action on food that is the important contribution of the intestinal glands to digestion. These enzymes and their actions are as follows : Enterokinase. This enzyme activates the trypsinogen of pan- creatic fluid and converts it into trypsin. Erepsin. This enzyme hydrolyzes proteoses and peptones to amino-acids, thus completing the work begun by the pepsin and trypsin. It is claimed that it occurs not only in the intestinal mucosa but also in the liver, kidney, pancreas, and possibly in other tissues. 322 ANATOMY AND PHYSIOLOGY [CHAP. XV Inverting enzymes. These enzymes are three in number and convert disaccharids into monosaccharids. 1. Maltase acts upon the products formed in the digestion of starches, i.e., dextrin and maltose, and converts them to dextrose. 2. Invertase or sucrase acts upon sucrose and changes it to dextrose and levulose. 3. Lactase acts upon lactose and changes it to dextrose and galactose. This inverting action is necessary because double sugars cannot be used by the tissues and would escape in the urine, but in the form of simple sugars they are readily used by the tissues. Secretin. This is not an enzyme, but a hormone, and plays an important part in the control of the secretion of the pancreas. It is secreted or formed in the intestinal mucosa in a preliminary form called prosecretin, and under the influence of acid is changed to secretin. Secretin is absorbed and carried to the pancreas, which it stimulates to activity. Bile. Bile is a fluid of a golden brown or greenish color l with an alkaline reaction. It is secreted continuously by the liver, but only enters the duodenum during the period of digestion. During the intervening period it is prevented from entering the duodenum by the sphincter which closes the' common bile duct, and consequently backs up into the gall-bladder. Apparently the ejection of chyme into the duodenum excites a contraction of the gall-bladder and an inhibition of the sphincter which results in an ejection of bile. The quantity secreted in twenty-four hours varies with the amount of food taken, but is estimated at about one to one and two-thirds pints (500 to 800 cc.). Bile contains no enzymes, but serves as a coenzyme and activates the lipase of the pancreatic fluid. Its physiological effects may be grouped as follows : 1. Digestive secretion. It serves as a digestive secretion by accelerating the action of the lipase of the pancreatic fluid in splitting fats to glycerine and fatty acids, and aids in the absorption of these products. 2. Excretion. Its value as an excretion we know little about, 1 The color of bile is determined by the respective amounts of the bile pigments : (1) biliverdin, and (2) bilirubin, that are present. CHAP. XV] DIGESTIVE PROCESSES 323 but it is thought to serve as a channel by which the products of the disintegration of haemoglobin are carried from the body. 3. Antiseptic. It has a feeble and questioned antiseptic action upon the intestinal contents, and its presence limits putrefaction to some extent. Action of bacteria in small intestine. Numerous bacteria which are able to hydrolyze carbohydrates and proteins are con- stantly present in the small intestine. Fermentation of the car- bohydrates gives rise to organic acids, such as lactic and acetic, but none of the products of this fermentation are considered toxic. On the other hand, the putrefaction of proteins gives rise to a num- ber of end-products that are distinctly toxic. Under normal con- ditions and on a mixed diet, carbohydrate fermentation is the char- acteristic action of the bacteria in the small intestine ; while protein putrefaction occurs in the large intestine. The reason for this seems to be that carbohydrates serve to protect proteins because some of the bacteria of the small intestine, i.e., bacillus coli, will not at- tack proteins as long as carbohydrate material is present. In addition, the organic acids produced by the fermentation of car- bohydrates tend to neutralize the alkalinity of the intestinal secretion, and may even give an acid reaction. An acid reaction is unfavorable to the action of the bacteria that hydrolyze proteins, and in this way putrefaction in the small intestine is prevented. From this it follows that the nature of bacterial activity in the small intestine depends upon the character of the diet, which may be intentionally chosen to favor one or the other kind. CHANGES THE FOOD UNDERGOES IN THE LARGE INTESTINE Movements of the large intestine. After the food passes from the small intestine into the large intestine, its regurgitation is prevented by the closure of the ileo-csecal valve. When the caecum becomes filled, strong contractions of the walls exert pres- sure upon the contained food and force it into the ascending colon. The waves of contraction which pass over the walls of the ascend- ing colon are described as antiperistaltic because they pass in two directions, (1) from the small intestine, and (2) toward the small intestine. This delays the food, keeps it moving backward and forward, and helps absorption. It has been estimated that it 324 ANATOMY AND PHYSIOLOGY [CHAP. XV requires about two hours for the food to pass from the ileo-csecal Valve to the hepatic flexure, and about four and one-half hours to reach the splenic flexure. Secretion of the large intestine. The secretion of the large intestine contains much mucin, shows an alkaline reaction, and is not characterized by the presence of enzymes. When the con- tents of the small intestine pass the ileo-caecal valve, they still contain a certain amount of unabsorbed food material. This re- mains a long time in the intestine, and since it contains the diges- tive enzymes received in the duodenum, the process of digestion and absorption continues. By the abstraction of all the soluble constituents, and especially by the withdrawal of water, the liquid contents become, as they approach the rectum, changed into a firm and solid mass of waste matters, ready for ejection from the body, and called feces. Action of bacteria in large intestine. Protein putrefaction due to the action of bacteria is a constant and normal occurrence in the large intestine. The reaction is alkaline, and whatever pro- tein may have escaped digestion and absorption is acted upon by the bacteria and undergoes putrefactive fermentation. The' split- ting of the protein molecule by this process is very complete, and the end-products differ from those resulting from the hydrolysis caused by acids or enzymes. The list of end-products of putre- faction is a long one. Some are given off in the feces, others are absorbed and later excreted in the urine. The action of bacteria is considered of doubtful value. It is possible that they may act upon the cellulose of vegetable foods and render it useful in nu- trition. A conservative view is that bacteria confer no positive benefit, but under normal conditions the body is able to neutralize their injurious action. The feces. The feces consist of: (1) the undigested and indigestible parts of the food, (2) the products of bacterial de- composition, (3) great quantities of bacteria of different kinds, (4) bile and other secretions, (5) enzymes, and (6) inorganic salts. Some authorities teach that a certain amount of indigestible ma- terial in the diet is wholesome. It stimulates the lining of the intestines, promotes peristalsis, and as it is pushed along the tube takes with it the less bulky but more toxic wastes. The color of feces is due to the presence of pigments derived from the bile. CHAP. XV] ABSORPTION 325 Defecation. The anal canal is guarded by an internal sphincter muscle of the involuntary type, and an external sphincter that is voluntary, but both are supplied with nerves from the central nervous system and consequently defecation is a voluntary act. Normally the rectum is empty until just before defecation. Various stimuli (depending on one's habits) will produce peristaltic action of the colon, so that a small quantity of feces enters the rectum. This irritates the sensory nerve-endings and causes a desire to defecate. The voluntary contraction of the abdominal muscles, the descent of the diaphragm, and powerful peristalsis of the colon all combine to empty the colon and rectum. One of the commonest causes of constipation is the retention of feces in the rectum because of failure to act on the desire for defe- cation. After feces once enter the rectum there is no retroperi- stalsis to carry it back to the colon, and the sense of irritation be- comes blunted. The desire may not recur for twenty-four hours, and during this time the feces continue to lose water, become harder, and more difficult to expel. ABSORPTION This is the process by means of which the digested food is taken from the intestines and carried into the blood. We have now to consider this process, for, properly speaking, though the food may be digested and ready for nutritive purposes, it is practically out- side the body, until it passes through the walls of the alimentary canal. Absorption. Absorption is a very complex process and may be subdivided into a physical and a physiological process. The physical process consists in the passage of the digested food from the intestines into the blood-vessels, and is governed by the laws of diffusion and osmosis. The physiological process consists in the building up of the end-products of digestion into the substances found in the blood. This process of reconstruction is dependent on the living epithelial cells that make up the intestinal walls. Paths of absorption. There are two paths by means of which the products of digestion find their way into the blood : (1) By the capillaries in the walls of the intestines. (2) By the lymphatics in the walls of the small intestine (the lacteals) . 326 ANATOMY AND PHYSIOLOGY [CHAP. XV There is reason to believe that but little absorption occurs in the " stomach. It is now thought that by far the greater part of ab- sorption is a function of the small intestine. Normally, the valu- able part of the digested food has been absorbed before the colon is reached, but it is true that the colon possesses some reserve power of absorption, which may be considered supplementary to the absorption occurring in the small intestine. An interesting fea- ture is the marked absorption of water. In the small intestine the loss of water due to absorption is made good by osmosis or secretion of water into the intestine, since the contents at the ileo- csecal valve are quite as fluid as at the pylorus. In the large in- testine water is absorbed in large quantities and there is no com- pensating secretion to offset this loss, hence the contents as they approach the rectum become more firm and solid. CHAP. XVj SUMMARY 327 Digestion Food Classifica- tion Nutrients Inorganic or Food Principles Organic Water Mineral Matter Carbohy- drates SUMMARY Physical process of changing food to a solution or emulsion. Chemical process of splitting large and complex molecules into smaller and simpler ones. Any substance taken into the body to 1. Provide material for growth of tissues. 2. Provide material for repair of tissue waste. 3. To supply heat and other kinds of energy. Chemical analysis shows that elements found in body are found in food. Classification based on presence or absence of carbon. Water. Mineral matter or salts. Carbohydrates. Fats. Proteins. H 2 0. About 66 per cent of body weight. Found in all tissues. Supplies fluid. Acts as solvent. Aids in elimination of waste. Chloride Phosphate Sulphate Carbonate Phosphate Carbonate of sodium and potassium. of calcium and magnesium. 1. To maintain alkaline or neutral reaction of body fluids. 2. To furnish material for acidity or alkalinity of digestive fluids. Functions \ 3. To maintain osmotic pressure. 4. To enter into bones, teeth, and cartilage. 5. To assist in the clotting of blood. 6. To influence elasticity and irritability of nerves and muscles. Consist of C, H, and 0, the two latter in the proportion to form water. Include sugars and starches. Simple or monosac- charids Complex or disac- charids Polysac- charids Glucose or dextrose C 6 Hi 2 6 Fructose or levulose Invert sugar. Sucrose or cane sugar Ci 2 H 22 Oii. Lactose or milk sugar Ci 2 H 22 On. Maltose or malt sugar Ci 2 H 2 20n. Starch (C 6 H 10 5 )n. Cellulose (C 6 H 10 5 )n. Glycogen (C 6 H 10 5 )n. Dextrin (C 6 Hio0 5 )w. 328 ANATOMY AND PHYSIOLOGY [CHAP. XV Fats Proteins Consist of C, H, and 0, but the H content is relatively high. Made from one molecule of glycerine and three molecules of fatty acid. Reaction comparable to neutralization of an acid by a base. Stearic acid + Glycerine ->- Stearin 4- Water 3 H. C 18 H 3 502+C3H 5 (OH)3 > C3H5(C 18 H350 2 )3+3 H 2 Fats are liquid at body temperature. Soluble in ether, chloroform, and hot alcohol. Under influence of body enzymes split into substances out of which they are built. Reaction reverse of above. Stearin + Water -> Glycerine -f- Stearic acid H 2 -- C 3 H 5 (OH) 3 + 3 H. C 18 H 35 2 Consist of C, H, N, 0; S, P, and other elements may be present. Differ from carbohydrates and fats in having nitrogen, hence called nitrogenous. Built up of simpler substances called amino-acids. About twenty amino-acids have been described, and various combinations result in many different kinds of proteins. Digestion of proteins means hydrolysis of complex molecules into simpler ones, i.e., protein ->- metaprotein -> pro- teoses ->- peptones -> peptids -> amino-acids. Albumins Globulins Glutelins Alcohol-soluble proteins Albuminoids Histons Protamins Nucleoproteins yield acids and nuclein. Glycoproteins yield amino-acids and a carbohydrate. Phosphoproteins - - yield amino- acids and a phospho body. Haemoglobins yield amino-acids and hscmatin. Lecithoproteins -- yield amino- acids and a fatty substance. Classifica- tion Simple Conjugated Yield amino- acids on hydrolysis. ammo- CHAP. XV] SUMMARY 329 Proteins Classifica- tion Derived f Primary deriva- tives (formed through hydro- lytic changes which cause only slight al- terations of the protein mole- cule) Secondary derivatives (products of further hydrolytic cleavage of the protein mole- cule) Proteans. Metaproteins. Coagulated proteins. Proteoses. Peptones. Peptids. Accessory Articles of Diet. Flavors : The various oils and esters that give odor and taste to food. Condiments : Salt, pepper, mustard, etc. Stimulants : Tea, coffee, cocoa, meat extracts. Digestive Processes Enzymes Mechanical Chemical Mastication. Deglutition or swallowing. Peristaltic action of oesophagus. Movements of stomach. Movements of intestines. Defecation. Splitting of complex substances into simpler ones. Process of hydrolysis that is dependent on enzymes. Rendered necessary by variety and com- plexity of foods, which must be reduced to standard and simple substances that the tissues can use, Simple sugars. Glycerine and fatty acids. Amino-acids. Substances produced by living cells which act by catalysis. Efficacy destroyed by boiling. Act best at body temperature. Require medium of definite reaction. Antecedent or inactive form called zymogen. Substances which help or act with an enzyme called co- enzymes. 330 ANATOMY AND PHYSIOLOGY [CHAP. XV Enzymes Classification 1. Sugar-splitting a. Inverting. b. Enzymes which act on simple sugars. 2. Amylolytic or starch-splitting. 3. Lipolytic or fat-splitting. 4. Proteolytic or protein-splitting. 5. Clotting enzymes. 6. Oxidizing enzymes, or oxidases. 7. Deaminizing enzymes. LIST OF DIGESTIVE FLUIDS AND CHIEF ENZYMES DIGESTIVE FLUIDS Saliva Gastric Fluid Pancreatic Fluid Succus Entericus Bile ENZYMES ( Ptyalin or salivary \ diastase Pepsin Rennin Trypsin Diastase or Amylase Lipase (Steapsin) Enterokinase Erepsin Maltase Inverting Invertase Lactase No enzyme FUNCTIONS Hydrolyzes starch to dextrin and sugar (maltose) . In an acid medium hydrolyzes proteins into proteoses and peptones. Curdles the caseinogen of milk. In a slightly acid, neutral, or strongly alkaline medium, splits proteoses into pep- tones and amino-acids. Hydrolyzes starch to dextrin and sugar (maltose). Splits fats to glycerine and fatty acids. Activates the trypsinogen, and converts it into trypsin. Hydrolyzes proteoses and pep- tones to amino-acids. Hydrolyzes dextrin and mal- tose to dextrose. Hydrolyzes sucrose to dex- trose and levulose. Hydrolyzes lactose to dex- trose and galactose. Serves as coenzyme and acti- vates the lipase of the pan- creatic fluid. CHAP. XV] SUMMARY 331 Changes Food under- goes in Mouth Mastication (chewing). Jnsalivation (mixing with saliva). , . Parotid becreted by sali- vary glands and mucous of mouth. glands Result of Submaxillary Sublingual f 1. Reflex stimulation. 12. Psychical. Consists of water, mucin, and enzyme ptyalin. Specific gravity 1.004-1.008. Alkaline reaction. One or two quarts in 24 hours. Saliva f 1. Assists in mastication and de- glutition. 2. Serves as a lubricant. 3. Dissolves or liquefies the food, Functions I thus stimulating the taste nerves, and indirectly the secretion of gastric fluid. 4. Hydrolyzes starch to dextrin and maltose. Deglutition (swallowing) . Stom- ach Diges- tion Movements of stomach. Serves as reservoir. Maintains a gradual delivery to intestine. Time required for stomach digestion about 5 hours. Psychical. Chemical Secretin. Cardiac, becreted by glands of stomach Secretion of gastric fluid Gastric fluid True gastric or peptic. Pyloric. Acid reaction due to free hydrochloric acid, about 0.2 to 0.4 per cent. Pepsin. Enzymes Rennin. Gastric lipase. 332 ANATOMY AND PHYSIOLOGY [CHAP. XV Small Intestine Movements of small ( [ rhyt hmic segmentation. Pancreatic fluid Secretion of pan- / Psychical. creatic fluid \ Chemical secretin. Secreted by pancreas, discharged into small intestine during digestion. Viscid fluid, alkaline reaction. f Trypsin. Enzymes < Diastase. [ Lipase. Secreted by f 1. Intestinal or Lieber- glands found < kuhn's. in intestines [ 2. Duodenal or Brunner's. Yellowish fluid, alkaline reaction, contains mucin. Bile Large Intestine Succus entericus Hormone Secretin. Golden brown or greenish liquid with alka- line reaction. Secreted by liver, stored in gall-bladder, discharged into small intestine during di- gestion. 1. Coenzyme activates lipase of pancreatic fluid. 2. Digestive secretion aids lipase in hydrolysis of fats and aids in Action { absorption of split products. 3. Thought to excrete products of disintegration of haemoglobin. 4. Questioned antiseptic action on intestinal contents. / Decompose carbohydrates. \ Little or no effect on protein. Movements of large intestine { I^staltic. Time required for food to pass from caecum to splenic flexure about 6| hours. f Alkaline reaction. Secretion { Contains a great deal of mucin. [ No enzymes. ( Hydrolysis of proteins constant. Bacteria < Possible action on cellulose. [ Benefit doubtful. Undigested and indigestible portions of food. Products of bacterial decomposition. Feces I Great quantities of bacteria. Bile and other secretions. Enzymes and inorganic salts. Defecation This term is applied to the act of expelling the feces from the rectum. Bacteria CHAP. XV] SUMMARY 333 Absorption Process of taking up digested foodstuffs and carrying them to the blood. Physical Diffusion and osmosis. Two Physiological Reconstruction of end-products processes | of digestion into substances found in the blood. 1. Capillaries in the walls of the intestines. This blood is carried by means of portal vein to liver, from liver by hepatic veins to inferior vena cava, thence to right auricle. 2. Lymphatics in the walls of small intestine (lacteals) absorb digested fats and empty into chyle cistern of thoracic duct, superior vena cava, and right auricle of heart. Paths of absorption CHAPTER XVI GENERAL METABOLISM; METABOLISM OF CARBOHYDRATES; METABOLISM OF FATS ; METABOLISM OF PROTEINS. DUCT- LESS GLANDS THE nutritive processes in the human body include : (1) the reception and digestion of food, followed by absorption of the dif- ferent food products, and the distribution of these products to all the cells by the circulating liquids of the body ; (2) the absorption of oxygen by the circulating liquids in the lungs, its distribution to all the cells of the body, and its union with the constituents of the cells. We have studied digestion and absorption, and our special problem in this chapter is metabolism. METABOLISM General metabolism includes all the changes that occur in digested foodstuffs from the time of their absorption until their elimination in the excretions. Sometimes the term is used more specifically to relate to the chemical activities that take place within cells. Functions of metabolism. Metabolic changes serve two im- portant purposes : (1) the repair and growth of tissue, and (2) the release of chemical energy in the form of heat, nervous activity, and muscular activity. Factors which promote metabolic changes. The factors which promote metabolic changes are : (1) enzymes, (2) oxygen, and (3) internal secretions. It was formerly taught that the oxygen absorbed from the lungs was responsible for all the processes of oxidation that occur in the body. More accurate study has dem- onstrated that while oxygen is an important factor, it is only one, and the enzymes that are present in nearly all the body tissues are capable of splitting complex materials into simpler substances. Moreover, it is generally considered that the action of the tissue 334 CHAP. XVI] GENERAL METABOLISM 335 enzymes comes first and causes splitting by hydrolysis, then other enzymes termed oxidases activate the process of oxidation. Metabolic changes. These chemical changes can be classified under two heads : (1) anabolism, or the building-up processes, and (2) katabolism, or the splitting of complex substances into simpler ones. The most important are as follows : A. The cells take from the blood the substances which they require for repair and growth, and build it up into protoplasm. This involves the conversion of non-living material into the living protoplasm of the cells, and is an example of anabolism. B. Oxidation, or the union of oxygen with the constituents of the cells, resulting in the release of energy and the breaking down of complex substances into simpler products. This is an example of katabolism. Some of the simpler products that result from oxidation are acids. These acids must be eliminated or changed chemically, as all the digestive fluids of the body, with the exception of the gastric fluid, are alkaline or neutral, and this condition is essential to nutrition and even to the immediate continuance of life, (a) Some of the weaker acids are eliminated in the urine ; one, carbonic acid (H 2 CO 3 ), is a very unstable compound and breaks down to form water (H 2 O) and carbon dioxide (02). (6) When proteins are oxidized, sulphur is set free. This sulphur (S) unites with water (H 2 O) and oxygen (O 2 ) to form sulphuric acid (H 2 SO4). Sulphuric acid is promptly neutralized by the alkalies present in the tissues, so that the body never contains sulphuric acid but does contain sulphates and water, which result from the process of neutralization. (See page 8.) C. The conversion of glucose into glycogen, and the reconversion of glycogen into glucose. D. The conversion of glucose into fat. E. The conversion of fat into glucose. F. The conversion of amino-acids to glucose. G. The conversion of amino-acids to fat. METABOLISM OF CARBOHYDRATES It is convenient to consider the history of carbohydrates under three heads : (1) its supply ; (2) its storage ; and (3) its consump- tion. 336 ANATOMY AND PHYSIOLOGY [CHAP. XVI (1) The supply is regulated by the diet. (2) The storage is provided for temporarily by the liver, the muscles, and the cells of all tissues. During the process of digestion all the carbohydrates are changed to simple sugars. It is possible that a small amount of sugar is absorbed in the stomach, but by far the greater part passes into the capillaries of the small intestine. These capillaries pour their contents into the portal vein, which carries the blood rich with glucose to the liver. The liver cells take this glucose from the blood, and by putting together a number of molecules and with- drawing water, 1 the soluble glucose is changed to insoluble glyco- gen, which is stored in the liver cells. In thus storing up glycogen and doling it out as needed, the liver helps to maintain the normal quantity of glucose 0.1 to 0.15 per cent in the blood. From the blood stream glucose is taken up by the muscles and other cells and stored as glycogen until needed, or it may be oxidized at once. The maximum storage of glycogen in the body is about one pound. This means that the formation of glycogen cannot continue indefinitely, and if the carbohydrate intake is in excess of the current consumption, conditions are favorable for the de- velopment of fat from the surplus carbohydrates. This trans- formation is a well-established and frequent occurrence and is probably responsible for much of the obesity which is such a com- mon condition. (3) At the consumption end the amount of sugar oxidized is controlled by the energy needs of the tissues, particularly the muscles. Factors controlling the metabolism of carbohydrates. The metabolism of carbohydrates is under the control of the nervous system, but how this control is maintained is still an open question. One view is that there is a sugar regulating centre which may be influenced by the amount of sugar in the blood, just as the respiratory centre is influenced by the amount of carbon dioxide in the blood. If this is true, the way in which this centre exerts its control is complicated and indirect. There is much evidence to support the view that the internal secretion of the adrenal glands, of the pancreas, and of the hypophysis play a very important part. 1 This is a process of dehydration and is exactly the opposite of hydrolysis. See p.'ure 8. CHAP. XVI] GENERAL METABOLISM 337 Functions of carbohydrates. The oxidation of glucose serves the following purposes : (1) It furnishes the main if not the only source of energy for muscular work, and for all the nutritive processes of the body. (2) It furnishes an important part of the heat needed to maintain the body temperature. (3) It pre- vents oxidation of the body tissues, because it constitutes a re- serve fund that is the first to be drawn upon in time of need. (4) An excess of carbohydrates over and above what can be stored as glycogen in the liver and muscles is converted into adi- pose tissue. Waste products of carbohydrate metabolism. The waste products resulting from the oxidation of glucose are carbon dioxide (CO 2 ) and water (H 2 O). This process is thought to be compar- able to the fermentation of sugar outside the body, and the same substances are formed, viz. alcohol, acids, carbon dioxide, and water. Derangements of carbohydrate metabolism. The storage of glycogen may be deranged by injuries to the central nervous sys- tem or by hypersecretion of the adrenal glands or the hypophysis, in which case hyperglycemia (excessive amount of sugar in blood) and glycosuria (sugar in the urine) result. Or the liver and muscles may be unable to store all the sugar absorbed from the alimentary canal, and in this case there is temporary hypergly- cemia and glycosuria. Inability to oxidize the sugar at the consumption end brings on a hyperglycemia and glycosuria of a serious nature. Diabetes mellitus. Defective sugar metabolism is the central condition in this disease. When the body cannot oxidize sugar, the continual addition of digested sugar to the blood leads to hyperglycemia. When this state is reached, i.e., the concentration of sugar in the blood exceeds the normal limit, the kidneys abstract it, and allow it to escape in the urine. . In severe cases all the sugar entering the blood passes into the urine without having con- tributed to the activities of the tissues. The inability to oxidize sugar is accompanied by inability to make and hold glycogen in the liver and muscles. When diabetes reaches its full intensity, and no sugar can be broken down, there follows a faulty fat metabolism and acidosis of the gravest kind. (See page 338.) 338 ANATOMY AND PHYSIOLOGY [CHAP. XVI METABOLISM OF FATS The tendency of recent work is to favor the view that after fat is split into glycerine and fatty acids, it is absorbed by the epithelial cells of the villi and reconstructed in the very act of passing through them. This reconstruction is not a mere repro- duction of the original fat. The glycerine and fatty acids combine in such proportion as to make the fat characteristic of the human animal. This fat passes into the lacteals of the villi. From these small lacteals it must find its way through the larger lymphatics in the mesentery to the thoracic duct, and then through the thoracic duct to the blood. This fat is carried by the blood to all the different parts of the body, and the tissues slowly take it out as they need it in their metabolic processes. Within the tissues it serves as fuel and is oxidized to supply the energy needs of the cells. If fat is burned outside the body, heat is liberated, and the waste products are carbon dioxide and water. This pro- cess is similar to the one that takes place in the body. Fat that is not required for the production of energy is stored up in certain parts of the body, but not all the adipose tissue found in the body is derived from fats, as excess carbohydrates are also stored as fat. In addition there is a possibility that fat may be formed from proteins. The amino-acids resulting from protein digestion, if in excess of what are needed to reconstruct body proteins, may be converted to sugar and glycogen, also to fat. Functions of fat. The uses of fat are (1) to serve as fuel and yield heat and other forms of energy. (2) To provide a store of reserve food to be drawn upon in time of need. When the supply of food is insufficient, or in diseased conditions, the body oxidizes first the glycogen stored in the muscles and liver, and then the fat stored in adipose tissue. (3) It acts as a protein sparer. In ex- treme conditions, when there is no glycogen or fat available, the body may oxidize the proteins of the tissues. If the supply of fat is large, it follows that the proteins of the tissues will be pro- tected. Derangements of fat metabolism. When fat is fully oxidized the only end-products are carbon dioxide and water. In certain diseased conditions, for instance, severe diabetes, the oxidation of fat is incomplete, and certain compounds of an acid character are CHAP. XVI] GENERAL METABOLISM 339 formed. These may accumulate and be responsible for a condi- tion of severe poisoning called acidosis. The cause of obesity. This condition is usually caused by eating more food than the body needs, especially fat and carbo- hydrates. The excess is stored as glycogen and adipose tissue. The needs of different individuals vary, depending on their mode of life, and on their capacity to oxidize food materials, so 'that a diet which will give an excess to one individual may in the body of another be entirely consumed. A sedentary life and absence of worry lessen the oxidation of food products and increase the ten- dency to take on flesh, while a very active muscular life has the opposite effect. METABOLISM OF PROTEINS As a result of digestion, proteins are hydrolyzed to amino-acids, and are absorbed by the blood capillaries of the villi. From the intestines this blood passes through the liver before it reaches the general circulation. Because of this it is considered possible that one stage in the metabolism of some of these amino-acids may be carried out in the liver. After a meal the amino-acids in the blood are increased in amount and are carried to all the tissues. The fate of these bodies varies. They may be taken up by the tissues, combined to form proteins, and used (1) during the period of growth to build up new tissue, and (2) both in youth, and after growth has ceased, to replace tissue that has been oxidized. Or they may split at once into a nitrogenous and non-nitrogenous part. The nitrog- enous part passes to the liver, and is transformed into urea to be excreted by the kidneys. The non nitrogenous part is used in the formation of sugar and fat, and may be stored as glycogen and adipose tissue. Sooner or later it is oxidized, liberating energy. Functions of proteins. We have seen that the main function of proteins is to build up tissue, and they are the one class of foods capable of doing this. In addition they serve the same purpose as carbohydrates and fats and may even be converted into adipose tissue. Nutritive value of different proteins. Proteins vary in their constituents and in their nutritive value. Because of this they are classed as adequate and inadequate proteins. Adequate proteins contain all the constituents for the growth and maintenance of 340 ANATOMY AND PHYSIOLOGY [CHAP. XVI the body. Inadequate proteins furnish material for energy needs, but not for growth and the repair of tissue waste. The difference between the two kinds seems to lie in the character of the ammo- acids of which they are composed. Gelatine is an example of an inadequate protein. It is easily digested and absorbed, under- goes oxidation, which results in the liberation of energy and the production of urea, carbon dioxide, and water, but it does not supply the material needed for the repair of tissue waste. On the other hand, the casein of milk and the glutenin of wheat contain all the essential amino-acids and not only furnish energy, but can build tissue. Nitrogen equilibrium. The protein molecules are characterized by containing 16 per cent of nitrogen. After the metabolism of protein, nitrogen is eliminated chiefly in the urine, and to a limited extent in the feces. The body is said to be in nitrogen equilibrium when the amount of protein nitrogen taken into the body is equal to the amount eliminated in the excreta. If there is a plus balance in favor of the food, it means that protein is being stored in the body, and this is an ideal condition during the period of growth or convalescence from wasting illness. If the balance is minus, the body must be losing protein, but under normal conditions this does not occur. Nitrogen equilibrium may be maintained at various levels. That is, the amount of food eaten may be in- creased or decreased to a considerable degree without disturbing the equilibrium. This means that the greater the amount of ni- trogen ingested, the greater the amount excreted. If nitrogen equilibrium can be estimated at various levels, the practical ques- tion which arises is : At what level should it be maintained to secure the best results? This question is difficult to answer. The average diets recommended range from 75-130 gms. protein per day, but experiments have shown that for considerable periods the body can be maintained on 35-40 gms. Our present knowledge does not warrant our stating that one is better or worse off for an excessively low protein diet. Flavors and condiments. The most important service rendered by these bodies is that by making the food appetizing they increase the secretion of gastric fluid. Stimulants. Under this heading is included tea, coffee, cocoa, and meat extracts. Tea and coffee owe their stimulating action CHAP. XVI] GENERAL METABOLISM 341 to caffeine. Cocoa, or the chocolate made from it, contains nourishment in the form of carbohydrate, fat, and protein. Its stimulating effects are due to theobromin, and are similar to those of caffeine. Meat extracts contain secretogogues which stimulate the gastric glands to secretion, but aside from this have little nutritive value. Alcohol. Alcohol is rapidly absorbed and quickly oxidized. It yields heat, and gives rise to carbon dioxide and water. It is not transformed into fat or glycogen, hence is not stored. In- directly it may cause obesity in two ways : (1) moderate drinking creates a keen appetite and so favors overeating ; (2) the oxidation of alcohol lessens the need for the oxidation of fats or carbohy- drates. Thus fat is spared to be accumulated, or carbohydrates to be changed into it. Energy value of food. All the energy required for muscular work may be derived from the carbohydrates and fats provided they are supplied in sufficient quantities. If they are not, then protein is used as a source of energy. If there is an abundance of non-nitrogenous food, the amount of nitrogen excreted remains pretty constant. Exercise does not increase it, neither does sleep decrease it. In health the temperature of the body is comparatively constant, 1 despite the changes in outside temperature. The supply of heat needed to maintain this constant temperature is derived from the oxidation of non-protein food. The amount of chemical energy in any substance determines its heat value. This may be as- certained by burning the substances and noting the amount of heat given off. It matters little whether the burning occurs in a test tube or in the living body. The heat produced is measured in terms of calories by means of a calorimeter. A large calorie (cal.) is the amount of heat required to raise one kilogram of water 1 C. The large calorie (Cal.) is the one referred to in physi- ology. As the result of many tests the caloric value of the different foodstuffs has been found to be as follows : 2 Carbohydrate 1 gm. = 4 cal. Fat 1 gm. = 9 cal: Protein 1 gm. = 4 cal. 1 See page 389. 2 These figures are lower than those usually given, e.g., carbohydrate 4.1, fat 9.3, and protein 4.1, which are now known to allow too little for losses in digestion. 342 ANATOMY AND PHYSIOLOGY [CHAP. XVI The amount of food necessary for normal nutrition. In a normal condition the main object of food is : (1) to furnish the material for the growth and maintenance of tissue, and (2) to fur- nish energy for heat, muscular work, etc. The most important factors influencing the amount of food required are age, activity, and in lesser degree, size, shape, body composition, lactation, and climate. The greater the amount of muscular work, the greater the amount of food required. Children need more food in propor- tion to their weight than adults, because they are more active in- ternally and externally, and in addition must provide for the growth of new tissue. Increased age usually means less active life as well as less active metabolism and thus less food is required. Women, as a rule, require less food than men, because they are smaller, have less active tissue in proportion to weight, and tend to more sedentary life. In an extremely cold climate more food is required for heat production in order to make up for the loss of heat from the body. It is ordinarily estimated that the daily diet should yield between 2300 and 2400 calories for an individual weighing 60 kilograms (130 Ib.) ; that is, about 40 calories for each kilogram of body weight. An excellent authority on this subject recommends that the daily diet be arranged about as follows : CALORIES Carbohydrate 275 gm. X 4 = 1100 Fat 100 gm. X 9 = 900 Protein 75 gm. X 4 = 300 Total 2300 Within certain limits the fats and carbohydrates may be sub- stituted for each other. For a healthy person leading a normal life appetite and experience seem safe guides by which to control the diet. They will at least prevent undernutrition, and the con- sequent lessening of the body's natural powers of resistance to disease. The opposite danger of overeating is a real one, because an excess of food puts unnecessary strain upon the organs of nutrition and excretion, and favors the formation of excessive adipose tissue. Excess of proteins may overload the system with the products of intestinal putrefaction. Excess of carbohydrates may cause flatu- lence, due to fermentation of these foods. An excess of fat in- terferes with digestion by retarding the secretion of gastric fluid. CHAP. XVI] DUCTLESS GLANDS 343 Vitamines. Many nutrition experiments have made it evi- dent that for growth and maintenance the human animal requires not only certain amounts of proteins, carbohydrates, and fats, but - certain other essential substances called vitamines. (It has been i suggested that food hormones would be a better name.) They do not serve as a source of energy and probably not as direct building stones, but they are in some (as yet undetermined) way essential to metabolism. Various animals have been fed on special I diets amply covering all the needs in the way of protein, carbohy- drate, and fat, but not foods containing vitamines. Young animals grow for a certain time, then come to a standstill, sicken, and die unless food containing vitamines is added to the diet. Other j experiments have led some observers to suggest that certain dis- eases such as beriberi, scurvy, and pellagra are caused by a de- ficiency of vitamines in the diet. Vitamines are present in cer- tain foods and absent in others. They are found in fresh fruit juices, milk, eggs, and in the bran of wheat, rice, and other cereals. DUCTLESS GLANDS The ductless glands form a group of organs that produce secre- tions, called internal secretions, which leave the gland by the blood or lymph, and not by means of a duct. Many of the glands that possess ducts and form an external secretion form an internal secretion as well, i.e., the liver and pancreas, but these are not classed as ductless, because the external secretion is carried out of the gland by means of a duct, though the internal secretion passes into the blood or lymph just as in the ductless glands. The func- tion of the ductless glands is intimately connected with the pur- pose of the internal secretions, and this is imperfectly understood. 1 However, a diseased condition or removal of these glands pro- duces symptoms which make evident their importance in the nor- mal carrying out of the body functions. The most important ductless glands are : . (1) The Thyroid. (5) The Hypophysis. (2) The Parathyroids. (6) The Epiphysis (Pineal body). (3) The Thymus. (7} The Testes (see page 477). (4) The Adrenals (supra-renal capsules) . (8) The Ovaries (see page 463). 1 See page 149. 344 ANATOMY AND PHYSIOLOGY [CHAP. XVI (1) The thyroid. The thyroid is a small, flat gland lying against the fore part of the trachea, below the thyroid cartilage. It is of a deep red color, weighs about an ounce (30 gms.), and consists of two lateral lobes connected at their lower parts by an isthmus. The lobes are broader below and taper to a point above. Small masses of thyroid tissue are sometimes found along the BIGHT LOBE OF, THYROID BODY . PYRAMID OF THYROID BODY FIG. 179. THE THYROID Bopy AND THE RELATED BLOOD-VESSELS. (Gerrish.) trachea as far down as the heart. They are called accessory thyroids. Comparatively little is known about the action of the thyroid secretion, but much clinical evidence supports the theory that it is necessary for the continuance of normal metabolism. Cretinism is a condition caused by congenital defects of the thyroid or atrophy occurring in early life. The growth of the skeleton ceases and there is complete arrest of mental develop- ment. Children so afflicted are not only dwarfed, but ill-propor- tioned, having heavy heads and abdomens and weak muscles. Myxcedema is a disturbed condition of metabolism that fol- lows the removal or atrophy of the gland. The individual so CHAP. XVI] DUCTLESS GLANDS 345 afflicted presents a peculiar appearance, as the subcutaneous con- nective tissue becomes thickened, the face and hands swollen and puffy. The mental faculties become blunted and idiocy results unless proper treatment is instituted. Cretinism and myxoedema are both supposed to be due to a lack of the internal secretion of the thyroid, and much success has followed the administration of thyroid extract in various ways. Goitre is a condition in which the gland is enlarged, but the se- cretion may not be interfered with. Exophthalmic goitre is a disease characterized by extreme ner- vousness, quickened heart action, protruding eyeballs, and goitre. It is caused by an overabundant production of thyroid secretion, due to enlargement and overactivity of the gland. (2) The parathyroids. Embedded in the surface of each lateral lobe of the thyroid are two little masses, each about one- fourth inch (6.25 mm.) in diameter. They are solid accumula- tions of epithelioid cells, invested with a tunic of areolar tissue and well supplied with blood-vessels. The function of the para- thyroids is supposed to consist in neutralizing toxic substances formed elsewhere in the body. In their absence acute tetanic convulsions develop. (3) The thymus. The thymus is a temporary organ attain- ing its full size at the end of the second year. Then it ceases to grow and remains practically stationary until puberty, at which time it degenerates. At the period of most active growth it con- sists of two lateral lobes situated below the thyroid and in front of the trachea. The function of this gland is not known, but it is thought to have a definite connection with growth and with the development of the reproductive organs. (4) The adrenals or supra-renal capsules. The adrenals are small flattened bodies of a yellowish color which are placed one above each kidney. They secrete a substance called adrenalin, which owes its power to adrenin or epinephrin. This secretion raises the blood-pressure, slows the heart, and increases the amount of sugar in the blood. The rise in blood-pressure is due to the contraction of the blood-vessels, especially those of the abdominal viscera. These glands are supplied with secretory nerves which may be stimulated reflexly. Sensory stimuli and strong emotions 346 ANATOMY AND PHYSIOLOGY [CHAP. XVI increase the activity of the gland. On the strength of these facts it has been suggested that the adrenals are emergency organs; that at times of great emotional stress, fear, anger, etc., their secretion is increased, resulting in an increased blood-supply for the muscles, as well as a rapid transformation of glycogen into FIG. 180. THE THYMUS, THE STERNAL AND COSTAL CARTILAGES HAVING BEEN REMOVED. (Gerrish.) sugar, which at once enters the blood, and is readily available for the production of energy. Another service of adrenin is to postpone fatigue. A very small addition of adrenin to the blood of an animal whose strength is flagging may give a renewed command of the muscles. It is now believed that " the strength of desperation " is due to the timely discharge of adrenin into the blood. Under conditions of rest the adrenals exercise considerable influence, for if they are removed or wasted by disease, several indispensable hormones seem to be lost. In such cases the victim grows weak, suffers from incessant nausea, and dies as though from exhaustion. (5) The hypophysis. The hypophysis, also called the pitui- tary body, is of an ovoid form, a reddish gray color, and consists of two lobes. The anterior lobe is larger and distinctly glandular, CHAP. XVI] DUCTLESS GLANDS 347 the posterior lobe is smaller and composed of nerve-cells and fibres. The pituitary is lodged in a depression of the middle portion of the sphenoid bone, and is firmly held in place by the dura mater. 1 From the results of various experiments it is evident that the pituitary body is essential to normal metabolism, and moreover that the anterior and posterior lobes exercise different functions. This differentiation in function cannot be made complete, but it would seem that the anterior lobe furnishes a secretion which stimulates the growth of the skeleton, possibly of all the connective tissues, and in addition exerts some essential influence on metab- olism. The posterior lobe furnishes several hormones which have a stimulating effect on the tone of plain muscle, the secretory activity of several glands, and the process of glycogenolysis (chang- ing glycogen to glucose). In addition it shares with the thymus and adrenals a regulating influence upon the normal development of the reproductive organs. Gigantism, or excessive growth, and dwarfism, or underdevelop- ment, are thought to be due to abnormal conditions of this gland in early life. In later life abnormal conditions are attended with enlargement of the bones of the extremities and the features of the face, a condition known as acromegaly. (6) The epiphysis. The epiphysis or pineal body is a small reddish gray body located in the third ventricle of the brain. In early life it is glandular and attains its maximum growth about the seventh year. After this period, and particularly after puberty, it decreases in size, and the glandular tissue is replaced by fibrous tissue. It is thought that in early life the gland furnishes a secretion that inhibits growth, and restrains the development of the reproductive glands. SPLEEN Some authorities class the spleen with the ductless glands ; other authorities question this, as it has not been possible to demonstrate that it furnishes an internal secretion. It is directly beneath the diaphragm, behind and to the left of the stomach, and is covered by the peritoneum. It is bean-shaped, convex on the 1 See page 410. 348 ANATOMY AND PHYSIOLOGY [CHAP. XVI outer surface, concave on the inner, and weighs usually from five to eight ounces (150 to 240 gms.). Beneath the serous coat it is covered by a fibrous and muscular capsule which sends fibrous bands (trabecules) to form a network in the interior of the organ. The meshes of this fibrous framework are filled with a substance called spleen pulp. Blood supply. Blood is supplied to the spleen by the splenic artery, which enters the concave side of the spleen at a depression called the hilus. The arrangement of the blood-vessels is peculiar to this organ. The splenic artery divides into several branches be- fore entering the organ, and after entering rapidly divides into smaller vessels. When the minute arteriole stage is reached, the vessels terminate, and the blood escapes into the spleen pulp. The blood is collected from the pulp by thin-walled veins, which unite to form the splenic vein. The splenic vein unites with the superior mesenteric to form the portal vein, and carries the blood to the liver. Functions. The functions of the spleen are imperfectly under- stood, but it is usually credited with the following : (1) The formation of red cells during foetal life and for a short period after birth. (2) The presence of a large amount of iron suggests that it may help in the preparation of new haemoglobin, or in the preservation of the iron set free by the death of the red cells. The presence of iron was formerly considered an evidence that the red cells were de- stroyed in the spleen, but this is not accepted at the present time. FIG. 181. THE SPLEEN, SHOWING THE GASTRIC AND RENAL SURFACES AND THE BLOOD-VESSELS. (Gerrish.) CHAP. XVI] SUMMARY 349 (3) The spleen increases in size during digestion ; after diges- tion is over it returns to its usual size. It is always large in well-fed, and small in starved animals. This supports the belief that it may be concerned in digestion or metabolism. (4) It is probable that the spleen is concerned in the production of uric acid. Various waste products that result from the metab- olism of proteins are found in the spleen, and it is thought that by the action of special enzymes these substances are changed to uric acid. (5) In certain diseases, more especially typhoid and malaria, a temporary enlargement takes place. Some physiologists inter- pret this as an evidence that the spleen has an important protec- tive function. Metabolism Functions Dependent upon Equals the sum of the SUMMARY Refers to changes that occur in foodstuffs from time of absorption to elimination. Sometimes applied specifi- cally to the chemical activities that take place within cells. 1. Repair and growth of tissue. 2. Release of chemical energy in the form of heat, nervous, and muscular ac- tivity. Enzymes. Oxygen. Internal secretions. Anabolic or constructive changes. Katabolic or destructive changes. A. Conversion of non-living material into protoplasm. B. Oxidation, including neutralization or elimination of acids. C. Conversion of glucose into glycogen and Consists of { the reconversion of glycogen into glucose. D. Conversion of glucose into fat. E. Conversion of fat into glucose. F. Conversion of amino-acids to glucose. . G. Conversion of amino-acids to fat. 350 ANATOMY AND PHYSIOLOGY [CHAP. XVI History Dependent upon Metabolism of Carbohydrates Functions Waste j Products I Derange- j ments of 1 1. Supply regulated by diet. 2. Storage provided for temporarily by liver, muscles, and cells of tissues. Simple sugars stored as glycogen. 3. Consumption controlled by the energy needs of the tissues. Control of nervous system, and the internal secretions of the adrenals, pancreas, and hypophysis. Furnish main source of energy for muscular work and all the nutritive processes. Help to maintain the body temperature. Form reserve fund for time of need (glyco- gen). Protect the body tissues. Excess carbohydrates are converted into adipose tissue. Carbon dioxide. Water. 1. Interference with storage of glycogen. 2. Inability to oxidize at consumption end. Metabolism of Fats Reconstruction In act of passing through epithelial cells of villi, glycerine and fatty acids combine to form fat peculiar to animal. Serve as fuel, yield heat and other forms of energy. Functions { Form reserve fund for time of need (adipose tissue) . Act as protein sparers. Waste j Carbon dioxide. Products 1 Water. Derange- j Results in formation of compounds of an ments of I acid character acidosis. Due to excessive amounts of carbohydrates and fats. Obesity Sedentary life and absence of worry are contributing factors. CHAP. XVI] SUMMARY 351 Absorbed as amino-acids, carried by blood to all the cells of the body. 1. Build up tissue. Functions 2. Serve same purpose as carbohydrates and fats. Metabolism Adequate proteins contain all the materials of Nutritive for maintenance and growth of tissue. Proteins Value Inadequate proteins serve same purpose as carbohydrates and fats. Nitrogen Equilib- Condition when the amount of protein nitrogen taken into the body in food is equal to the amount eliminated in the rium excreta. Flavors Have no nutritive value, but increase the and Con- secretion of eastric fluid. diments Tea stimulating action due to caffeine. Coffee - stimulating action due to caffeine. Contains carbohydrate, fat, and Croons protein. Stimulants V_yU^L/d Stimulating effects due to theo- bromin Accessory IVIeats Contain secretogogues which Articles Extract stimulate the gastric glands to of Food secretion. Oxidized rapidly, yields heat. Waste i Carbon dioxide. Products Water. Moderate drinking creates keen Alcohol appetite, and thus favors Favors overeating. Obesity Lessens need for oxidation of fat or carbohydrates, hence these are spared to accumulate. Oxidation changes latent energy of food into energy of motion, and heat. Constant Temper- ature Supply of heat needed to maintain tem- perature, derived from oxidation. Energy Value Unit of measurement for heat production. of Food Calorie Large calorie = quantity of heat necessary to raise one kilogram of water 1 degree centigrade. Carbohydrates 1 gm. = 4 cal. Fat 1 gm. = 9 cal. Protein 1 gm. = 4 cal. 352 ANATOMY AND PHYSIOLOGY [CHAP. XVI Average Amount of Food Required Recommended Distribution Dependent f 1. Activity 3. Size upon 1 2. Age 4. Sex About 40 calories for each kilogram of body weight. Cal. Carbohydrate 275 gm. X4 = 1100 Fat 100gm.X9= 900 Protein 75gm.X4= 300 Total 2300 Undernutrition lessens natural powers of resistance to disease. 1 . Puts unnecessary strain on the organs of nutrition and excretion. 2. Favors obesity. Overeating ^ 3. Increases amount of waste products, toxic material, and causes flat- ulence. 4. Retards secretion of gastric juice. Vitamines Substances essential to metabolism. Do not serve as source of energy or as direct building stones. Necessary for growth, and probably to prevent such diseases as beriberi, scurvy, and pellagra. Found in fresh fruit juices, milk, eggs, bran of wheat, rice, and other cereals. Ductless Glands Glandular structures that possess no ducts. Produce internal secretions that are carried from the gland by the blood or lymph. Function is imperfectly understood. The Thyroid. The Parathyroids. The Thymus. Most im- The Adrenals, portant | The Hypophysis. The Epiphysis. The Testes. The Ovaries. Thyroid Small gland. Weighs about one ounce. Consists of two lobes connected by an isthmus. Placed in front of trachea, below thyroid cartilage. Function not definitely known, but the internal secretion is thought to be necessary for the continuance of normal metabolism. CHAP. XVI] SUMMARY 353 Parathyroids Thymus . . Adrenals Hypophysis Epiphysis . 2A Four small masses, each about j in. diameter. Two are embedded in each lobe of thyroid. Consist of epithelioid cells, invested with areolar tissue. Function is supposed to consist in neutralizing toxic substances. Consists of two large masses of glandular tissue situated below the thyroid and in front of the trachea. Temporary organ. Attains its full size at end of second year. Then ceases to grow, remains stationary until puberty, at which time it degenerates. Function not definitely known, but it is thought to have a definite connection with growth and with the develop- ment of the reproductive organs. Small glands lying above each kidney. Weigh one drachm. Consist of a fibrous framework, the spaces of which are filled with groups of cells. They are enclosed in a fibrous capsule and are well supplied with blood- vessels, lymphatics, and nerves. Internal secretion adrenalin, which owes its power to adrenin. 1. As emergency organs in times of emo- tional stress. Functions ^ 2. To postpone fatigue. 3. Furnishes seemingly indispensable hormones. Small reddish gray gland. Consists of f d nterior lo , b ?' large a ,? d glandular ' two lobes Functions I Posterior lobe, small and composed of [ nerve tissue. Lodged in depression of the sphenoid bone. Anterior lobe furnishes secretion which stimulates growth of skeleton, possibly all connective tissues, and exerts some essential influence on metabolism. Posterior lobe furnishes several hormones which have a stimulating effect on tone of plain muscle, secretory activity of several glands, glycogenolysis, etc. Small reddish gray body located in the third ventricle of the brain. Glandular organ; attains maximum growth about seventh year. From this period and particularly after puberty it decreases in size and be- comes fibrous. Function not definitely known; it is thought to inhibit growth and restrain the development of the reproduc- tive organs. 354 ANATOMY AND PHYSIOLOGY [CHAP. XVI Spleen Descrip- tion Functions Beneath diaphragm, behind and to the left of the stomach. Consists of a fibrous network filled with a vascular pulp, enclosed in a fibrous and muscular capsule which is covered by serous membrane. Blood supply peculiar arteries veins, no connecting capillaries. Not definitely known. Credited with the following : 1. Formation of red cells during foetal life and for short period after birth. 2. Helps in preparation of new haBmo- globin or preservation of iron set free by death of red cells. 3. May assist in digestion and metabolism. 4. May assist in production of uric acid. 5. May protect body from infections. CHAPTER XVII WASTE PRODUCTS ; EXCRETORY ORGANS ; DESCRIPTION OF THE ORGANS CONSTITUTING THE URINARY SYSTEM; URINE IN the previous chapters we have seen that the blood is con- stantly supplied by means of the respiratory and digestive mecha- nisms with all the chemical substances it requires to maintain the life, growth, and activity of the body. These substances, enter- ing the current of the blood, are carried to all the cells and are in- cessantly combining with the chemical substances of which these cells are composed. One of the results of these chemical com- binations is the formation of waste products, which must be removed from the body, as many of them are toxic. WASTE PRODUCTS The wastes of cell metabolism may be listed as follows : Q i KI G u I Nitrogenous salts, e.g., urea. 1. Soluble halts \ r , ,. , . . , [ Inorganic salts, e.g., sodium chloride. 2. Liquid Water. 3. Gas Carbon dioxide. 4. Solids Waste materials from food. These wastes are classed as excreta and the process by which they are removed from the body as excretion or elimination. EXCRETORY ORGANS The organs that function as excretory organs and the products that they eliminate may be tabulated as follows : - ESSENTIAL INCIDENTAL Lungs .... Kidneys . . . Alimentary canal Carbon dioxide Water and soluble salts, resulting from metabo- lism of proteins, neutral- ization of acids, etc. Solids Water Carbon dioxide and solids. Water, carbon dioxide, and salts. 355 356 ANATOMY AND PHYSIOLOGY [CHAP. XVII KIDNEV In this chapter we devote ourselves to the consideration of the urinary system, which includes the following organs : - Kidneys, which form the urine from mate- rials taken from the blood. Ureters, ducts which convey the urine away from the kidneys. 1 Bladder, a reser- voir for the reception of urine. Urethra, a tube through which the urine passes from the bladder and is finally voided. KIDNEYS The kidneys are two compound tubular glands, placed at the back of the abdominal cavity, one on each side of the spinal column and behind the peritoneal cavity. They correspond in position to the space included between the upper border of the twelfth thoracic and the third lumbar vertebra. The right is a little lower than the left in consequence of the large space occupied by the liver. Capsule and supports. The kidneys are covered by a thin but rather tough envelope of fibrous tissue called the capsule, the inner surface of which is slightly attached to the substance of the kidney by means of fine fibres and blood-vessels. The kidneys are usually embedded in a mass of fatty tissue termed the peri- renal fat, and are not held in place by any distinct ligaments, but rather by the pressure and counter-pressure exerted upon them by neighboring structures. BLADDER URETHRA FIG. 182. THE' URINARY SYSTEM VIEWED FROM BEHIND. CHAP. XVII] URINARY SYSTEM 357 Size and shape. Each kidney is about four and one-half inches (11.2 cm.) long, two and one-half inches (6.2 cm.) broad, one and one-half inches (3.7 cm.) thick, and weighs about four and one-half ounces (135 gm.). They are bean shaped, with the con- cave side turned toward the spine, and the convex side directed outward. Near the centre of the concave side is a depression called the hilum, which serves as a passageway for the ureter, PYRAMIDS CORTEX MEDULLA g COLUMNS OF BERTINI URETER RENAL ARTERr FIG. 183. LONGITUDINAL SECTION OF THE HUMAN KIDNEY. (Modified from Huxley.) and for the blood-vessels, lymph-vessels, and nerves going to and from the kidney. Anatomy of the kidney. If a kidney is cut in two lengthwise, it is seen that the upper end of the ureter expands into a basin- like cavity, called the pelvis of the kidney. This pelvis is irregu- larly subdivided into smaller, cup-like cavities, called calyces, which receive the pointed projections of the kidney substance. The substance of the kidney is readily seen by the naked eye to consist of two distinct parts : (1) an outer, and more solid por- tion, called the cortex (bark) ; and (2) an inner, striated portion, called the medulla (marrow), which is not a solid mass, but more or less distinctly divided into pyramidal-shaped sections. The cortical substance penetrates for a variable distance between the 358 ANATOMY AND PHYSIOLOGY [CHAP. XVII pyramids, separating and supporting them. These inter-pyram- idal extensions are called the columns of Bertini and support the blood-vessels. The pointed projections, or papilla, of the pyramids are received by the cup-like cavities or calyces of the pelvis. The bulk of the kidney substance, both in the cortex and medulla, is composed of little tubes or tubules, closely packed together, having CAPSULE PROXIMAL CONVOLUTED TUBE "CAPSULE AM V PROXIMAL CONVOLUTED TUBE COLLECTING TUBE LOOP OF HENLE EXCRETORY TUBE FIG. 184. DIAGRAM OF THE COURSE OF Two URINIFEROUS TUBULES. only just enough connective tissue to carry a large supply of blood-vessels and a certain number of lymphatics and nerves. Uriniferous tubules. Examined under the microscope, it is seen that the uriniferous tubules begin as little hollow globes, called capsules, in the cortex of the kidney. These capsules are joined to the tubules by a constricted neck, and the tubules, after running a very irregular course, open into straight collecting tubes, which FIG. 185. DIAGRAM OF THE STRUCTURE or A LOBE OF THE KIDNEY. The lobe is seen in vertical section, the cortex being marked off from the medulla. Four medullary rays encroach upon the cortex. At the left is shown the course of a single continuous series of tubes the straight and spiral tubes appearing in the medul- lary ray; the straight, looped, and excretory in the medulla proper; the capsule, neck, convoluted, irregular, and arched in the cortex proper. Next is seen the labyrinth, composed of a mass of tubes in the cortex, with a medullary ray for a centre. Equidistant from the ray on each side is a broken red line, marking the position of an interlobular artery. The parts between these lines constitute a lobule. Farther to the right is an interlobular artery, giving off lateral branches (afferent vessels), each of which ends in a tuft of capillaries, from which the blood is collected by an efferent vessel. The uppermost of the tufts is shown enclosed in a capsule. On the right of the interlobular artery the efferent vessels break up into a capillary network which surrounds the (unrepresented) tubes in the cortex and ray. The lowest efferent sends vertical vessels also into the medulla. On the right the interlobular vein is seen gathering the blood from all the parts supplied by the interlobular artery. A branch of the renal artery courses upward between cortex and medulla, and forms an arch (here broken) over the base of the medulla. From it the interlobular arteries pass upward into the cortex, and straight branches go downward into the medulla, supplying its structure, and ending at the apex in the capillaries. From the last the radicles of the renal vein arise, and accompany the straight arteries to the base of the medulla, where a venous arch is formed, continuous with which is the vena comes of the entering artery. The calyx embraces the apex of the medullary pyramid. It is lined with epithelium, which continues from it over the apex, the latter being perforated with the many apertures of excretory tubes. (Gerrish.) 359 360 ANATOMY AND PHYSIOLOGY [CHAP. XVII pour their contents through their openings in the pointed ends or papillae of the pyramids, into the calyces of the kidney. The tubules are composed of basement membrane, lined through- out by epithelial cells. The cells vary in the different parts of a tubule, those of the capsule and convoluted or irregular parts being more especially adapted to secretory purposes than the straight parts of the tubule. RENAL OR MALPIGHIAN CORPUSCLES URINIFEROUS TUBULE PLEXUS FIG. 186. PLAN OF THE BLOOD-VESSELS CONNECTED WITH THE TUBULES. Pyramid. These collecting tubules en masse, together with interstitial tissue, blood-vessels, and lymphatics, make a pyramid. The number of pyramids varies. Renal or Malpighian corpuscles. In the cortical portion of the kidney are found renal corpuscles which consist of two parts : (1) a minute tuft of capillaries called a glomerulus, surrounded by (2) a closed capsule which is the beginning of a uriniferous tubule. The investment of the glomerulus by the capsule is double and CHAP. XVII] URINARY SYSTEM 361 complete except at one point, where an afferent vessel enters and an efferent vessel leaves. The blood supply of the kidney. For its size, the kidney is abundantly supplied with blood. The renal artery, coming di- rectly from the aorta, divides, before it enters the hilus of the kid- ney, into several branches, which pass into the tissue of the organ. Branches from these arteries have two destinations : (1) into the cortex, and (2) into the pyramids. (1) When the arteries reach the level of the base of the pyra- mid, the branches divide laterally to form more or less complete arches between the cortex and medulla. From the arterial arches, vessels pass upward through the cortex (interlobular), giving off at intervals tiny arteries, each of which enters 1 the dilated commencement or capsule of a uriniferous tubule. These tiny arteries, entering the capsule, are spoken of as afferent vessels. They push the thin walls of the capsule before them, break up into a knot of capillary vessels, called a glomerulus, and finally issue from the capsule as efferent vessels, near the point at which the afferent vessel entered. These efferent vessels are much smaller than the afferent vessels. They do not immediately join to form veins, but break up into a close meshwork or plexus of capillaries around the tubules, before they unite to form the larger vessels and pour their contents into the veins. These veins terminate in venous arches between the cortex and medulla. It is in this way that the cortex is supplied with blood. (2) The pyramids also receive their blood supply from the ar- terial arches. The blood passes downward in straight vessels be- tween the uriniferous tubules, to be returned by more or less straight veins to the venous arches, whence it is conveyed by large branches into the renal vein, which leaves the kidney at the hilus and pours its contents into the inferior vena cava. It is worthy of note that, unlike the lungs and the liver, the kidney receives blood from just one artery, and this blood distrib- uted in different sets of vessels serves the purposes of nourishment for the kidney substance, and the purposes of excretion. It is from the capillaries of the glomeruli and the plexus of capil- 1 The artery does not penetrate the wall of the capsule, but the knot of capillary vessels is contained within the capsule, as the heart is contained within the peri- cardium. 362 ANATOMY AND PHYSIOLOGY [CHAP. XVII laries around the convoluted portion of the tubules, that the passage of waste material from the blood into the tubule takes place. Other capillaries serve to hold the blood that is used for nourishment. Nerves and lymphatics. The kidneys are well supplied with nerves derived from both the sympathetic and central nervous systems. Many of these nerves are vasomotor nerves, and by regu- lating the contraction and dilatation of the blood-vessels, they influence the blood pressure in the kidneys. They are also well supplied with lymphatics. Function of the kidneys. The function of the kidneys is to separate waste matters (urine) from the blood, and thus help to maintain its normal composition. The waste matters are those resulting from metabolism, particularly of proteins; water, salts, and foreign matters such as toxins, whether formed in the body, or taken into the body from outside. The concentration of urine, and not the quantity, is our criterion for judging the amount of work done by the kidneys. It is probable that they are most severely taxed when they have to remove from the blood a maximum of dissolved solids in a minimum of water. The secretion of urine. The exact way in which the kidneys separate the urine from the blood is not known, but it is thought to be a double process, being partially accomplished by a mechani- cal filtration and partially by secretion due to the selective action of the cells lining the tubules. (1) Into each hollow capsule which forms the beginning of a uriniferous tubule an afferent artery enters. This artery breaks up into capillaries which form a bunch of looped and twisted blood-vessels called a glomerulus. The walls of the capsule being double, the glomerulus pushes back the inner wall or visceral layer, until the capsule is entirely filled, leaving only a small space between it and the outer wall or parietal layer. The blood in the glomerulus is only separated from the interior of the tubule by the thin walls of the capillaries and the inverted wall of the cap- sule. The artery (afferent) which enters the capsule is larger than the issuing (efferent) vessel, and during its passage through the glomerulus, the blood is subjected to considerable pressure. As a result of this, a transudation of the watery constituents of the blood, with some dissolved salts, takes place through the CHAP. XVII] URINARY SYSTEM 363 walls of the blood-vessels and the walls of the capsule into the capsular space, then into the tubule. (2) After leaving the capsule, the efferent vessel communicates with other similar vessels, which together form a meshwork or plexus of capillaries closely surrounding the tubules, so that the blood is again brought into close communication with the in- terior of the tubules. The tubules are lined with secreting cells, and these cells appear to have the power of selecting from the blood the more solid waste matters (especially the urea), which fail to filter through the flat cells forming the wall of the capsule. THE URETERS The ureters are the excretory ducts of the kidneys. They consist of a distended portion called the pelvis, which is contained within the kidney, and a duct. Each duct is about the diameter of a goose- quill, and from ten to twelve inches (25 to 30 cm.) long. They consist of three coats : an outer fibrous coat, a middle muscular, and an inner mucous lining which is continuous above with that of the pelvis of the kidney, and below with that of the bladder. FIG. 187. DIAGRAM SHO\\- .., ING METHOD OF ENTRANCE OF Function. The Ureters connect THE URETER INTO THE BLADDER. the kidneys with the bladder and (Gerrish.) serve as a passageway to convey urine from the kidneys to the bladder. BLADDER The bladder is a hollow muscular organ situated in the pelvic cavity behind the pubes, in front of the rectum in the male, and in front of the anterior wall of the vagina, and the neck of the uterus, in the female. It is a freely movable organ, but is held in position by ligaments. During infancy it is conical in shape and projects above the upper border of the pubes into the hypogastric region. In the adult, when quite empty, it is placed deeply in the pelvis ; when slightly distended, it has a round form ; but when greatly distended, it is ovoid in shape and rises to a considerable height hi the abdominal cavity. It is customary to speak of the widest 364 ANATOMY AND PHYSIOLOGY [CHAP. XVII part as the fundus, and the part where the bladder becomes continuous with the urethra as the neck, or cervix. It has four coats : 1. The serous coat is a reflection of the peritoneum, and only covers the upper portion of the fundus. 2. The muscular coat has three layers, an inner longitudinal, middle circular, and outer longitudinal. The circular fibres are collected into a layer of some thickness around the cervix or neck, where the bladder becomes continuous with the urethra. These circular fibres around the neck form a sphincter muscle which is normally in a state of contraction, only relaxing at intervals, when the accumulation of urine within the bladder renders its expulsion necessary. 3. The areolar coat connects the mucous and muscular. 4. The mucous membrane lining the bladder is continuous with that of the ureters and the urethra. Function. The bladder serves as a reservoir for the reception of urine. When moderately distended, it holds about one pint (about one-half litre). THE URETHRA The urethra is a narrow, membranous canal, about an inch and a half (3.8 cm.) in length in the female. Its normal diameter is about one-quarter of an inch (6.3 mm.), but it admits of consid- erable dilatation. It extends from the neck of the bladder to the external orifice, which is named the meatus urinarius. It is placed behind the symphysis pubis, and is embedded in the anterior wall of the vagina. Its direction is obliquely downward and forward, its course being slightly curved, with the concavity directed for- ward and upward. Its external orifice is the narrowest part and is located between the clitoris and the opening of the vagina. (See Fig. 222.) The wall of the urethra consists of three coats, an outer muscular coat, a submucous coat, and an inner mucous coat which is con- tinuous with that of the bladder. MICTURITION Urine is secreted continuously by the kidneys. It is carried to the bladder by the ureters, and at intervals is expelled from the CHAP. XVII] WASTE PRODUCTS 365 bladder through the urethra. The act by which the urine is ex- pelled is called micturition. It occurs normally as the result of irritation due to the accumulation of urine within the bladder. The accumulation stimulates the muscular walls to contract, and the resistance of the sphincter at the neck of the bladder is over- come. The action is involuntary, but it may be controlled by voluntary effort. Involuntary micturition. Involuntary micturition may occur as the result of lack of consciousness, and as the result of spinal injury involving the nerve centres which send nerves of control to the bladder. It may be due to a want of tone in the muscu- lar walls, or it may result from some abnormal irritation. Retention of urine. Retention or failure to void urine may be due to : (1) dulling of the senses so that there is no desire to void, (2) nervous contraction of the urethra, and (3) some ob- struction in the urethra or in the neck of the bladder. In some cases the bladder may become so fully distended that the retention of urine may be accompanied by more or less con- stant voiding of small amounts of urine. Suppression of urine. A far more serious condition than re- tention is the failure of the kidneys to secrete urine. This is spoken of as suppression, and is usually due to extreme conges- tion of the kidneys, as in acute nephritis. THE URINE Normal urine may be described as a transparent, amber-colored liquid, with a characteristic odor, an acid reaction when tested with litmus paper, and a specific gravity of about 1.020. Transparency. The transparency of urine may be diminished in health by the presence of mucus, derived from the genito- urinary tract, or by the deposit of salts. In disease the urine may become clouded by the presence of pus. Color. The color of urine depends upon the quantity voided and the relative amounts of water and coloring matters. If the quantity is abnormally increased, it is usually more dilute and of a paler color ; as, for instance, the copious light-colored urine of hysteria or diabetes insipidus. One exception to this is diabetes mellitus, where the quantity is increased, but the color is dark 366 ANATOMY AND PHYSIOLOGY [CHAP. XVII because of the presence of sugar. When the quantity is diminished as in fevers, it is generally highly colored, because the amount of solids present is large. Other causes of change of color are the presence of abnormal substances, and large doses of certain drugs. Reaction. The reaction of human urine is largely dependent on the kind of food eaten. Many of the waste products that result from a mixed diet are acid, hence the reaction of human urine is usually acid. On a diet of vegetables the urine will be alkaline, as it is with herbivorous animals. If human urine is allowed to stand for any length of time, it will become alkaline, because bacteria will decompose the protein constituents into ammonia and other alkalies. In certain diseased conditions of the urinary organs this same process takes place within the body. Specific gravity. The specific gravity depends upon the amount of solid waste matters present in the urine. In health, it may vary from 1.010 to 1.030. When the solids are dissolved in a large amount of water, the specific gravity will naturally be lower than when the urine is more concentrated. A high specific gravity denotes the presence of abnormal constituents; as, for instance, the specific gravity is notably heightened by the presence of sugar in diabetes mellitus. Quantity. The average quantity of urine secreted in twenty- four hours by a healthy adult is from forty to fifty ounces (1.2 to 1.5 litres). A child voids relatively more urine than an adult, but absolutely it voids less. From 2-5 years, 16-24 ounces (480-720 cc.). From 5-8 years, 24-32 ounces (720-960 cc.). From 9-16 years, 32-40 ounces (960-1200 cc.). The quantity of urine may be increased by (1) the ingestion of a large amount of liquid, (2) the action of diuretics, (3) nervous- ness, (4) certain diseases such as diabetes insipidus, diabetes mellitus, and hysteria. The quantity of urine may be decreased by (1) the ingestion of a small amount of liquid, (2) vomiting, (3) diarrhoea, (4) high fever, (5) disease of the kidneys, and (6) the action of diapho- retics, muscular activity, or any treatment that induces free per- spiration. CHAP. XVII] WASTE PRODUCTS 367 COMPOSITION OF URINE The composition of urine is very complex; even in health it varies, depending on the quantity and kind of food eaten, etc. It is not difficult to understand this complexity when one recalls that the kidneys eliminate some of all the end-products resulting from food metabolism, together with the products of bacterial fermentation in the stomach and intestines. Under pathological conditions the composition may be still further modified. It is not possible to describe all the numerous constituents here. A few are as follows : Urine Water, 95 per cent Urea (2 per cent of total solids). Uric acid. Purin bodies Xanthin. Organic, about 3.7 Creatinin. Hypoxanthin. Hippuric acid. Other substances. Soluble salts < 5 per cent Sodium chloride. Sulphates. Phosphates. Inorganic, Potassium. i about 1.3 Ammonium. Magnesium. Salts of . Calcium. Other substances. Urea. Urea constitutes about one-half of the solid constitu- ents of the urine, and represents the chief end-product resulting from the metabolism of the proteins of the food and tissues. The result of the oxidation of protein material exists in the blood until it reaches the liver. Under the action of the liver cells this material is converted into urea. About 0.028 per cent of urea is present normally in the blood and tissues. The kidneys constantly remove urea as it is formed, and by their activity keep the amount of urea in the blood at the low level given above. If, for any reason, the kidneys fail to eliminate urea, the accumulation in the blood and tissues leads to a condition of poisoning. Normally an adult voids about one ounce (30 gms.) of urea in 368 ANATOMY AND PHYSIOLOGY [CHAP. XVII twenty-four hours, but the quantity is increased by a diet rich in proteins, strenuous exercise, hot baths, fever in its early stages, and some diseases. A small amount of protein food, excessive vomiting, free perspiration, and diseases that interfere with elimination will decrease the amount of urea voided. Purin bodies. In the classification of proteins given on page 309 nucleoproteins are listed. These are compounds of protein with a complex organic acid called nucleic acid, which contains phosphorus. They are found in the nuclei and protoplasm of body cells, also in various protein foods. When nucleoproteins either of the food or tissues are oxidized in the body, they give rise to purin bodies, i.e., uric acid, xanthin, and hypoxanthin. Uric acid is the most important, and next to urea is the medium by which nitrogen is eliminated from the body. Uric acid com- bines with potassium and sodium to form urates, and is found in the form of urates in the urine. In gout the excretion of urates is decreased, and it accumulates in the blood and is deposited in the joints in the form of insoluble salts. In this and similar con- ditions purin-free diets, i.e., diets free from nucleoproteins, are prescribed. Creatinin. Creatinin occurs in the urine constantly. Its physiological history is imperfectly known. Under normal con- ditions the amount of creatinin formed in the body is independent of the proteins eaten. This has led some observers to think that it represents an end-product of the metabolism of protein tissue. Creatin l is found in the muscles, liver, heart, brain, and other organs. Nothing definite is known of the function of creatin, but it is probable that from it the creatinin of the urine is formed. Creatin is absent from normal urine, but is present in the urine during starvation, in acute fevers, and in conditions where there is a rapid loss of muscular tissue. Hippuric acid. Hippuric acid represents one of the chemical methods of defence of the organism against toxic substances. The amount found in the urine varies with the diet. On a diet containing much fruit and vegetables the amount ex- creted is increased. As a result of the digestion, fermentation 1 The formula for creatin is C The formula for creatinin is C4H;NsO. The difference is H2O. Creatinin is the anhydride of creatin. CHAP. XVII] WASTE PRODUCTS 369 by bacteria, or oxidation of fruits and vegetables, certain toxic acids are formed, e.g., benzoic acid. This is rendered less toxic by combining it with glycocoll to form hippuric acid which the kidneys excrete. Salts. The salts found in the blood are derived partly from the food eaten, and partly from the metabolism of proteins, par- ticularly the neutralization of acids. Sodium chloride is the most abundant, and, next to urea, is the chief solid found in urine. In certain inflammatory conditions, coupled with serous exudate, e.g., pneumonia, the amount of sodium chloride excreted is very much diminished. Abnormal constituents. The chief abnormal constituents that are liable to appear in the urine are albumin, glucose, indican, acetone, casts, calculi, pus, and blood. Albumin. Normally the kidney cells do not allow albumin to pass into the tubules, but a condition of temporary albuminuria may follow overeating or severe muscular exercise. In abnormal conditions of the kidneys associated with nephritis and acute fevers, albumin is usually found in the urine. In cases of heart disease, where the blood-vessels of the kidneys are subjected to ab- normal pressure changes, albumin is usually present in the urine. Glucose. Normal urine contains no sugar, or so little that for clinical purposes it may be considered absent. In health the amount of glucose present in the blood varies from 0.1 to 0.15 per cent. A higher per cent is irritating to the tissues, so when the quantity of sugar eaten is greater than the system can promptly change to glycogen and fat, the kidneys secrete and excrete it. When glucose is found in the urine from this cause, it is called temporary glycosuria. Temporary glycosuria frequently follows an injury to the head, or occurs during convalescence from fevers. In these cases it is thought to be due to temporary inability of the system to oxidize sugar. In the disease called diabetes mel- litus, glucose persists in the urine. In mild cases this condition can be controlled by lessening the amount of carbohydrate food, but in severe cases glucose will appear in the urine even when no carbohydrates are eaten. This condition is serious because it means that the body tissues are being oxidized to form glucose. Indican. Indican is a potassium salt that is formed from indol. Indol results from the putrefaction of protein food in the 370 ANATOMY AND PHYSIOLOGY [CHAP. XVII large intestine. It is absorbed by the blood and carried to the liver, which it is thought changes the indol to indican, a less poisonous substance. Traces of indican are found in normal urine, but the presence of it in any amount is abnormal and de- notes : (1) excessive putrefaction of protein food in the intestines, or (2) disease of the stomach. (1) Excessive putrefaction may be due to a diseased condition of the intestine that interferes with absorption, to a diet containing too much protein food, or to con- stipation. (2) In certain diseases of the stomach, food is held until it undergoes fermentative changes. Acetone. Acetone is a volatile substance that is thought to be the result of incomplete oxidation of fats and possibly of pro- teins. It is found in the urine of individuals suffering from de- fective metabolism, and in the urine of normal individuals during periods of fasting. Casts. In some abnormal conditions the kidney tubules be- come lined with substances which harden and form a mould or cast inside the tube. Later these casts are washed out by the urine, and their presence in urine can be detected by the aid of a micro- scope. They are named either from the substances composing them or from their appearance. Thus there are (1) pus casts, (2) blood casts, (3) epithelial casts from the walls of the tubes, (4) granular casts from cells which have decomposed and form masses of granules, (5) fatty casts from cells which have become fatty, and (6) hyaline casts which are formed from coagulable elements of the blood. Calculi. Deposits of solid matter that have been precipitated from the urine are called urinary calculi or stones. These vary in size, shape, and composition ; the size and shape being determined largely by their composition and location. They may be formed in any part of the urinary tract from the tubules to the external orifice of the urethra. The causes which lead to their formation are (1) an increase in the slightly soluble constituents of the urine, (2) a decrease in the amount of water secreted, and (3) abnor- mally acid or abnormally alkaline urine. Pus. In suppurative conditions of any of the urinary organs pus cells are present in the urine. Blood. In cases of acute inflammation of any of the urinary organs, of tuberculosis, of cancer, and of renal stone, blood may CHAP. XVII] SUMMARY 371 be found in the urine. If present in large quantity, the urine is deep red, and this condition is known as hematuria. Toxicity of urine. As urine is the medium by which the body gets, rid of toxic material, it follows that urine itself is toxic, and must be eliminated, else a condition of toxemia will result. This condition is called uremia, because it was thought that the symp- toms of poisoning were due to the retention of urea in the body. It is now believed that while urea is poisonous, it is only one of several substances that renders urine toxic. During illness the kidneys always try to eliminate any poisonous substances that find their way into the blood, whether these substances result from defective metabolism or from bacterial activity. This ac- counts for the fact that after a severe illness the kidneys are often left in a damaged condition. SUMMARY Wastes of Cell Metabolism Excretory Organs Urinary System Location Capsule and supports Size and f Nitrogenous salts, e.g., urea. ]S ( Inorganic salts, e.g., sodium chloride. 2. Liquid water. 3. Gas carbon dioxide. 4. Solids - waste materials from food. Lungs. Kidneys. Alimentary Canal. Kidneys (2) secrete urine. Ureters (2) ducts which convey urine from kidneys to bladder. Bladder (1) reservoir for urine. Urethra (1) tube through which urine is voided. Posterior part of lumbar region, behind peritoneum. Placed on either side of spinal column and extend from upper border of twelfth thoracic to third lumbar vertebra. Covered by tough envelope of fibrous tissue. Supported by pressure and counter-pressure of neigh- boring structures. Four and one-half inches long, two and one-half inches broad, one and one-half inches thick. Weight, four and one-half ounces (130 gms.). Bean-shaped, tubular glands. Concave side toward spine, convex side outward. Hilum depression near centre of concave side serves for vessels to enter and leave. 372 ANATOMY AND PHYSIOLOGY [CHAP. XVII ' Pelvis upper expanded end of ureter. Calyces cup-like cavities of the pelvis that receive papillae of pyramids. Cortex outer, more solid portion. Medulla inner, striated portion. Columns of Bertini interpyramidal extensions of corti- cal substance. Begin as hollow globes or capsules in the Uriniferous cortex of kidney, and after a very ir- regular course open into straight col- tubules lecting tubes which pour their contents into calyces of pelvis. Cone-shaped masses in the medullary por- tion of the kidney. Vary in number. Bases directed toward cortex. Pyramids < Papillae apices of the pyramids, di- rected toward pelvis. ' Consist of uriniferous tubules, blood- vessels, and lymphatics, held together [ by connective tissue. Minute tufts of capillaries glomeruli Renal in the cortical portion of kidneys which Anatomy corpuscles are surrounded by inverted capsule of the < of uriniferous tubule. kidney Renal artery direct from aorta. Enters hilus of kidney, divides into many branches. Lateral branches at the level of .... the base of the pyramids. al 1. Send branches to cortex arches (cortical). 2. Send branches to pyramids. Blood {Lateral branches at level of base supply of pyramids. Receive blood from cortex. Receive blood from pyramids. Veins empty into renal vein, leave kidney at hilus, and empty into inferior vena cava. Note Blood from renal artery serves for purposes of nourishment of kidney and purposes of excretion. Nerves from sympathetic and central ner- Nerves and vous system. lymphat- Many are vasomotor, and by regulating size ics of blood-vessels influence blood pressure. Well supplied with lymphatics. 1. Process of mechanical filtration. Water and saline elements are filtered from the blood during the circulation through the glomeruli. Function < Secretion of urine 2. Secretory action of the cells lining the uriniferous tubules. Urea and other foreign substances are separated from the blood during the circulation through the plexus of capillaries which surrounds the tubules. CHAP. XVII] SUMMARY 373 Ureters Bladder Urethra Micturition Excretory ducts. Extend from kidneys to bladder. Consist of expanded portion called pelvis and duct. Size of goose-quill. 10-12 in. long. 1. Mucous lining. 2. Muscular 1 T > '""ina! layer. Three coats Function . I Outer, circular layer. 3. Fibrous carries blood-vessels and nerves. ( Connect kidneys with bladder. \ Passageway for urine. Hollow muscular organ. Situated in pelvic cavity behind the pubes in front of rectum in male, in front of anterior wall of vagina and neck of uterus in female. Freely movable. Held in position by ligaments. Size, shape, and position depend upon age, sex, and whether bladder is full or empty. Fundus widest part. Cervix where the bladder becomes continuous with the urethra. 1 . Mucous lining. 2. Areolar connects mucous and muscular. Inner layer longitudinal. Middle layer circular. Outer layer longitudinal. 4. Serous partial covering derived from peritoneum. Serves as a reservoir for the reception of urine. When moderately distended, holds about one pint. Four coats Function 3. Muscular Membranous canal, extends from the bladder to the meatus urinarius. 1| in. long and I in. in diameter in female. Behind symphysis pubis, and embedded in the anterior wall of vagina. \ 1. Mucous lining. Three ! 2. Submucous supports network of veins, coats | f Inner longitudinal. I 3 ' Muscular | External -circular. Meatus urinarius external orifice located between cli- toris and vagina. Act of expelling urine from bladder. Occurs as result of irritation due to accumulation of urine in bladder. [ Involuntary act can be controlled by voluntary effort. 374 ANATOMY AND PHYSIOLOGY [CHAP. XVII Due to Failure to void urine. 1. Dulling of the senses. 2. Nervous contraction of urethra. Retention . I 3. Some obstruction in urethra or neck of bladder. May be accompanied by overflow or constant voiding of small amounts. Suppression Failure of the kidneys to secrete urine. Transparency depends on absence or presence of mucus and pus. Color depends on concentration. Relative amounts of water and solids. ' Reaction usually acid. Specific gravity average 1.020. Depends on concentra- tion. f Average 40 to 50 ounces. Ingestion of large amount of liquid. Urine . 1 Action of diuretics. I nrtraaaari Nervousness. ( Diabetes insipidus. Diseases J Diabetes mellitus. [ Hysteria. Ingestion of small amount of liquid. Decreased by Quantity Increased by Vomiting, diarrhoea. High fever. Disease of kidneys. Increased action of skin. Composition , of Urine Water, 95 per cent Soluble Salts 5 per cent Organic about 3.7 Inorganic, about 1.3 f Urea (2 per cent of total solids). Uric acid. Purin bodies Xanthin. Hypoxanthin. Creatinin. Hippuric acid. Other substances. Sodium chloride. Sulphates. Phosphates. Potassium. Ammonium. Magnesium. Calcium. Other substances. Salts of CHAP. XVII] SUMMARY 375 Urea Purin bodies Creatinin Hippuric acid Salts . Abnormal constitu- ents End-product resulting from metabolism of proteins. Average excreted in twenty-four hours 1 ounce. About 0.028 per cent present normally in blood and tissues. Diet rich in proteins. Strenuous exercise hot baths. Some diseases. Small amount of protein food. Excessive vomiting, free perspiration. Diseases that interfere with elimination. Increased by End-products resulting from metabolism of nucleoproteins of food and tissues. Decreased by Uric acid Xanthin Hypoxanthin f It is probably an end-product of the metabolism of protein 1 tissue. Chemical method of defence against toxic substances. Digestion of fruits and vegetables give rise to toxic acids, e.g., benzoic acid. Benzoic acid plus glycocoll > hippuric acid. Derived from food eaten. Derived from neutralization of acids. Sodium chloride is most abundant. Albumin. Casts. Glucose. Calculi. Indican. Pus. Acetone. Blood. CHAPTER XVIII THE SKIN; APPENDAGES OF THE SKIN. BODY HEAT; REGULA- TION OF HEAT. VARIATIONS IN TEMPERATURE THE SKIN Functions. The skin is not, like the kidneys, set apart to perform one special function. It serves : (1) as a protective cov- ering for the deeper tissues lying beneath it, (2) as a sense organ, (3) as an excretory organ, (4) as an important organ in heat regu- lation, and (5) as a respiratory organ. Structure. It consists of two distinct layers : (1) Epidermis; scarf skin, or cuticle. (2) Derma ; cutis vera, or corium. Epidermis. The epidermis is a stratified epithelium, com- posed of a number of layers of cells. It varies in thickness from arc- inch (0.104 mm.) to ^ inch (1.04 mm.), being thickest on the palms of the hands and on the soles of the feet, where the skin is most exposed to friction, and thinnest on the ventral sur- face of the trunk, and the inner surfaces of the limbs. It forms a protective covering over every part of the true skin, upon which it is closely moulded. It is roughly divisible into two layers : (1) Superficial, or Horny. (2) Germinative, or Malpighian. (1) The superficial layer consists of three strata of cells, which are practically dead, and are constantly being shed and renewed from the cells of the germinative layer. (2) The germinative layer consists of soft protoplasmic cells. The growth of the epidermis takes place by the multiplication of these cells. As they multiply they push upward toward the surface those previously formed. In their upward progress 376 CHAP. XVIII] THE SKIN 377 they undergo a chemical transformation, and the soft proto- plasmic cells become converted into the flat scales which are con- stantly being rubbed off the surface of the skin. The pigment in the skin of the negro, as well as that of the nipple in white races, is found in the deepest cells of the germinative layer. stratum lucidum stratum a:? granulosum Gr. or Derma FIG. 188. VERTICAL SECTION THROUGH THE SKIN OF THE PALMAR SIDE OF THE FINGER, SHOWING Two PAPILLA (ONE OF WHICH CONTAINS A TACTILE COR- PUSCLE) AND THE DEEPER LAYER OF THE EPIDERMIS. (Schafer.) No blood-vessels pass into the epidermis; it, however, receives fine nerve-fibrils between the cells of the germinative layer. Derma. The derma is a highly sensitive and vascular layer of connective tissue. It is described as consisting of two layers : (1) Upper, or papillary layer. (2) Deeper, or reticular layer. (1) The surface of the papillary layer is increased by protru- sions in the form of small conical elevations, called papillae, whence this layer derives its name. They project up into the epidermis, 378 ANATOMY AND PHYSIOLOGY [CHAP. XVIII which is moulded over them, and contain for the most part looped blood-vessels, but they also contain the terminations of nerve- fibres in the shape of little bodies called tactile corpuscles. The papilla? seem to exist chiefly for the purpose of giving the skin its sense of touch, being always well developed where the sense of touch is exquisite. They are specially large and numerous on the palm of the hand and the tips of the fingers, and on the cor- responding parts of the foot. (2) The reticular layer of the corium is a continuation of the papillary layer, there being no real division between them. It is made up of bundles of white fibrous and elastic tissue. The derma is attached to the parts beneath it by a layer of areolar tissue, here named subcutaneous, which layer, with very few exceptions, contains fat. The connection in some parts is loose and movable, as on the front of the neck; in others, close and firm, as on the palmar surface of the hand and the sole of the foot. Blood-vessels. The blood-vessels of the skin are found in the derma only. They form a network of capillaries in which the ves- sels are very close to each other, and send branches to the papilla? and glands of the skin. The capillaries of the skin are capable of holding from one-half to two-thirds of the blood contained in the body. The amount of blood they contain is dependent on their caliber, and this is regulated largely by the vasomotor nerves. Nerves. The skin is provided with a great variety of nerves. 1 They are classified as follows : (1) Vasomotor nerves, which are distributed in the walls of the blood-vessels. (2) Two sets of nerves concerned in the temperature sense, which terminate in the hot and cold spots of the skin. (3) The nerves concerned in the sense of touch or pressure. (4) Nerves which are stimulated by pain. (5) Motor nerves, which are derived from the sympathetic sys- tem and distributed to the glands and the arrector muscles. Because of the number of afferent nerves which lead from the skin to centres in the brain and spinal cord, nearly every nerve centre in the body may be affected by sensations arising in the skin. 1 See page 430. CHAP. XVIII] THE SKIN 379 It is for this reason that hydro therapeutic applications, heat, cold, and counter irritants excite so many and such varied reflexes. THE APPENDAGES OF THE SKIN The appendages of the skin are the nails, the hair, the sebaceous glands, the ceruminous glands, and the sudoriferous or sweat glands. The nails. The nails are composed of clear, horny cells of the epidermis, joined so as to form a solid, continuous plate. Each nail is convex on its outer surface, concave on its inner side, and closely adherent to the un- derlying derma, which is modified to form what is called the bed, or matrix, of the nail. At the hinder part of the B0ir bed of the nail the skin forms a deep fold, M LUNULA^ in which is lodged the root of the nail. The growth of the nail is accomplished by constant multiplication of the soft cells in the germinative layer at the root. These cells are transformed into dry, hard scales, which unite into a solid plate, and ., . . 'IT,. FIG. 189. THUMB-NAIL. the nail, constantly receiving additions (Gerrish.) from below, slides forward over its bed and projects beyond the end of the finger. When a nail is thrown off by suppuration or torn off by violence, a new one will grow in its place provided any of the cells of the germinative layer are left. The hair. The hair is a growth of the epidermis, developed in little pits, the hair-follicles, which extend downward into the deeper part of the true skin, or even into the subcutaneous tissue. The hair grows from the bottom of the little pit or follicle. The part which lies within the follicle is known as the root, and that portion which projects beyond the surface of the skin is called the shaft or stem. The substance of the hair is composed of coalesced horny cells, arranged in different layers, and we usually distinguish three parts in the stem or shaft of a hair : (1) Cuticle an outer layer of delicate, scale-like cells. (2) Fibrous substance a middle portion, formed of elongated cells. These cells and the intercellular spaces contain a varying 380 ANATOMY AND PHYSIOLOGY [CHAP. XVIII CUTICLE amount of pigment, and the color of the hair depends upon the quantity. The gray hair of old age is produced by loss of pig- ment. (3) Medulla a central pith formed of round cells. The root of the hair is enlarged at the bottom of the follicle into a bulb or knob. This bulb is composed of soft-growing cells, and fits over a vascular papilla which projects into the bottom of the follicle. Hair has no blood-vessels but receives nourishment from the blood- vessels of the papilla. Growth of hair. Hair grows from the bottom of the follicle by multiplication of the soft cells which cover the papilla. These cells become elongated to form the fibres of the fibrous portion, and as they are pushed to the surface, they become flattened and form the cuticle. If the scalp is thick, pliable, and moves freely over the skull it is favorable to the growth of hair. A thin scalp that is drawn tightly over the skull tends to constrict the blood- vessels, lessen the supply of blood, and cause atrophy of the roots of the hair by pressure. In such cases massage of the head loosens the scalp, improves the circulation of the blood, and usually stimulates the growth of hair. With the exceptions of the palms of the hands, the soles of the feet, and the last phalanges of the fingers and toes, the whole skin is studded with hair. The hair of the scalp is long and coarse, but most of the hair is very fine and extends only a little beyond the hair follicle. Arrector muscles. The follicles containing the hairs are nar- row pits which slant obliquely upward, so that the hairs they con- tain lie slanting on the surface of the body. Connected with each follicle is a small muscle called the arrector muscle. It is com- posed of bundles of plain muscular tissue which pass from the surface of the true skin, on the side to which the hair slopes, obliquely downward, to be attached to the bottom of the follicle. When these muscles contract, as they will under the influence of FIBROUS- SUBSTANCE MEDULLA FIG. 190. PIECE or HUMAN HAIR. (Highly magnified.) CHAP. XVIII] THE SKIN 381 cold or terror, the little hairs are pulled up straight, and stand " on end " ; the follicle also is dragged upward, and in this way the roughened condition of the skin known as " gooseflesh " is pro- duced. Sebaceous glands. The sebaceous glands are small, saccular glands, which lie between the hairs and their arrector muscles. SUBCUTANEOUS AREOLAR TISSUE .OMERULU8 OF SWEAT GLAND BULB OF HAIR PAPILLA OFHAI8 FIG. 191. VERTICAL SECTION OP THE SKIN, SHOWING SEBACEOUS GLANDS, SWEAT-GLANDS, HAIR AND FOLLICLE, ALSO ARRECTOR MUSCLE. (Gerrish.) They occur everywhere over the skin surface, with the exception of the palms of the hands and the soles of the feet. Each gland consists of a collection of small tubes overspread with a network of capillaries. From the gland a small duct as- cends, and opens either upon the surface of the skin, or as is more common, into a hair follicle. Their size is not regulated by the length of the hair. Thus, some of the largest are found on the nostrils and other parts of the face, where they often become en- larged with pent-up secretion. Sebum. The secretion of the sebaceous glands is called sebum. 382 ANATOMY AND PHYSIOLOGY [CHAP. XVIII It contains fat, soaps, epithelial cells, aibuminous matter, and inorganic salts. It serves to remove waste matters and is classed as an excretion, but its more important purposes are to keep the skin and hair soft and pliable, and to form a protective layer on the surface of the skin. An accumulation of this sebaceous matter upon the skin of the foetus furnishes the thick, cheesy, oily sub- stance called the vernix caseosa. Ceruminous glands. The skin lining the external auditory canal contains modified sweat-glands called ceruminous glands. They secrete a yellow, pasty substance resembling wax which is called cerumen. Sweat-glands. The sweat-glands are simple, convoluted, tubu- lar glands with the blind ends coiled into little balls which are lodged in the true skin or subcutaneous tissue ; from the ball the tube is continued as the ex- cretory duct of the gland up through the true skin and epidermis, and finally opens on the surface by a slightly widened orifice called a pore. Each tube is lined by a secreting epithelium continuous with the epidermis. The coiled end is closely invested by a mesh work of capillaries, and the blood in the capillaries is only separated from the cavity of the glandular tube by the thin membranes which form their respective walls. The secretory apparatus in the skin is somewhat similar to that which obtains in the kid- neys; in the latter the blood-vessels are coiled up within the tube, while in the skin the tube is coiled up within the mesh- work of blood-vessels. The sweat-glands are abundant over the whole skin, but they are largest and most numerous in the axillae, the palms of the hands, soles of the feet, and the forehead. Perspiration, or sweat. The sweat is a watery, colorless liquid, FIG. 192. COILED END OF A SWEAT- GLAND, a, the coiled end ; 6, the duct ; c, net- work of capillaries, inside which the sweat- gland lies. CHAP. XVIII] THE SKIN 383 slightly turbid, of a salty taste, with a distinctive odor and an alka- line reaction, although when first secreted it may be acid. It is an excretion, the chief normal constituents of which are water, salts, fatty acids, a small quantity of carbon dioxide, and a slight amount of urea. In various forms of kidney disease urea may be present in considerable quantity, the skin supplementing to a certain extent the deficient work of the kidneys. Quantity of perspiration or sweat. Under ordinary circum- stances, the perspiration that we are continually throwing off evap- orates from the surface of the booly without our becoming sensible of it, and is called insensible perspiration. When more sweat is poured upon the surface of the body than can be removed at once by evaporation, it appears on the skin in the form of drops, and we then speak of it as sensible perspiration. The average amount discharged during twenty-four hours is about one quart (1 litre), but it may be increased to such an extent that even more may be discharged in an hour. The secre- tion of sweat is increased by : (1) a dilute condition of the blood such as results from drinking large quantities of liquids, (2) in- creased temperature or humidity of the atmosphere, (3) exercise, (4) pain, (5) mental excitement or nervousness, (6) dyspnoea, (7) use of diaphoretics, (8) certain diseases, such as tuberculosis, acute rheumatism, and malaria, (9) use of electricity to stimulate the secretory nerves. The secretion of sweat is decreased by : (1) voiding of a large quantity of urine, (2) cold, (3) diarrhoea, (4) certain drugs, and (5) certain diseases, such as fevers, diabetes, and some cases of paralysis. Activity of the sweat-glands. Experimental work with animals has led some observers to believe (1) that there is a definite sweat centre in the brain. The exact location of this centre has not been determined, but reasoning from analogy it seems probable that it may be located in the medulla. (2) That definite secretory nerves from this centre are distributed to the sweat-glands. The activity of these glands may be influenced by external heat, dyspnoea, muscular exercise, and the action of various drugs. In all such cases the effect is supposed to be the result of either direct stimulation of the nerve-endings in the glands, or indirect stimulation through the nerve centres. The common cause of 384 ANATOMY AND PHYSIOLOGY [CHAP. XVIII profuse sweating is a high external temperature or muscular ex- ercise. It is known that the high temperature acts upon the sen- sory cutaneous nerves and stimulates the sweat fibres indirectly through the nerve centres, and possibly directly by increasing the irritability of the nerve-endings. Excretory function of the skin. While sweat is an excretion, its value lies not so much in the elimination of waste matter as in the loss of body heat by the evaporation of water. Each gram of water requires about 0.5 calorie to cause it to evaporate, and this heat is taken from the body. This loss of heat helps to balance the production of heat that is constantly taking place. BODY HEAT From the standpoint of heat production animals. may be divided into two great classes : (1) Constant temperature 1 animals, or those whose temperature remains practically constant whether the surrounding air is hotter or cooler than the body. The term warm-blooded is also applied to this class. It includes human beings. (2) Variable temperature 2 animals, or those whose tempera- ture varies with that of the surrounding medium. This class is also described as cold-blooded. The human foetus is cold-blooded. The great difference between these two classes is in their reac- tions to external temperature. A cold environment reduces the temperature of the cold-blooded creature, reduces the metabolism of all its tissues, and thus reduces its heat production. The warm-blooded animal reacts in precisely the opposite way. Since his temperature remains constant, his heat production must in- crease in order to neutralize the effect of cold surroundings. Production of heat. Heat in the body is produced by such chemical changes going on in the tissues as are associated with oxidation. Friction is a minor source of heat, i.e., that caused by the movements of the muscles, the circulation of the blood, and the ingestion of warm food. Where heat is produced. Wherever metabolic changes are tak- ing place, there heat is set free. These changes take place more rapidly in some tissues than in others, and in the same tissues 1 Homothermous, 2 Poikilothermous. CHAP. XVIII] BODY HEAT 385 at different times. The muscles always manifest a far higher rate of activity than the connective tissues, and consequently the former evolve a larger proportion of the bodily heat than the latter. We might liken the different tissues of the body to so many fire- places stored with fuel, the fuel in some of the fireplaces being more easily ignited and burning more rapidly than in others. The muscles and the secreting glands, especially the liver, are sup- posed to be the main sources of heat, as they are the seats of a very active metabolism. Loss of heat. The heat thus continually produced is as con- tinually leaving the body by the skin and the lungs, and by the urine and feces which are at the temperature of the body when voided. It has been calculated that in every 100 parts, about : 73.0 per cent is lost by conduction and radiation. 14.5 per cent is lost by evaporation. 10.7 per cent is lost by expired air : (a) vaporization of water, 7.2 per cent. (6) warming of air, 3.5 per cent. 1.8 per cent is lost by urine and feces. The temperature and humidity of the atmosphere may cause considerable difference in the per cents given above. A low tem- perature will increase the loss of heat by radiation and decrease that by evaporation. A high temperature will decrease the loss of heat by radiation and increase that by evaporation, owing to the greater production of sweat. From the above figures it is evident that the skin is the important factor in getting rid of body heat. This is due : (1) to the large surface offered for radiation, conduction, and evaporation; and (2) to the large amount of blood which it contains. Distribution of heat. The blood, as we know, permeates all the tissues in a system of tubes or blood-vessels. Wherever oxidation takes place and heat is generated, the temperature of the blood circulating in these tissues is raised. Wherever, on the other hand, the blood-vessels are exposed to evaporation, as in the moist membranes in the lungs, or the more or less moist skin, the temperature of the blood is lowered. The gain and loss of heat balance one another with great nicety, and the blood, circulating rapidly, now through warmer, and again through cooler, tubes, is kept at a uniform temperature of about 100F. (37.8C.). 2c 386 ANATOMY AND PHYSIOLOGY [CHAP. XVIII In this way the whole body is warmed in somewhat the same way as we warm a house, the warm blood in the blood-vessels heating the tissues, as the hot water in the hot-water pipes heats the rooms in water-heated dwellings. THE REGULATION OF BODY HEAT The regulation of body heat is due to the maintenance of a certain balance between heat production and heat dissipation. To many physiologists it has seemed reasonable to suppose that this balance was controlled by a definite set of heat nerves connected with heat centres in the brain. While such an apparatus may exist the evidence in favor of it is not convincing, and the conservative view is that the control of heat production and heat dissipation is effected by the coordinated activities of different centres plus such voluntary means as (1) the regulation of muscular exercise and diet, (2) the use of suitable clothing, and (3) the use of hot and cold baths. The involuntary regulation of the body temperature is effected chiefly through the following centres : 1. The quantity and character of food. 2. The motor nerve centres and the motor fibres to the skeletal muscles. 1. The respiratory centre. Heat 2. The sweat centres and sweat nerves. Dissipation 3. The vaso-constrictor centres and nerves distributed to the skin. Heat production. (1) In a previous chapter we described how the oxidation of different foodstuffs produced varying amounts of heat. (2) The motor nerve-fibres which are distributed to the skeletal muscles are indirectly stimulated by cold. It causes the muscles to contract and speeds up the processes of oxidation. Heat dissipation. (1) The stimulation of the sensory nerves of the skin that are affected by cold influences the respiratory cen- tre, increases the rate of the respirations, and consequently in- ' creases the loss of heat. In man respiration plays only a small part in heat regulation, but in animals that do not perspire, res- piration is an important means of regulating the temperature. (2) When the external temperature is high, the nerve-endings which respond to heat are stimulated, and these impulses are CHAP. XVIII] BODY HEAT 387 transmitted over sensory nerves to the nerve centres controlling the motor nerves of the sweat-glands. The motor nerves stimu- late the activity of the sweat-glands, and an increased amount of sweat is poured out upon the surface of the body. An increased amount of heat is required to vaporize this sweat, and thus heat is lost. Excessive humidity interferes with the evaporation of water, and thus interferes with the loss of heat; hence the dis- comfort experienced on hot, humid days. (3) The sensory nerves which are stimulated by heat not only transmit impulses that stimulate the sweat-glands to activity, but at the same time transmit impulses that result in the depression of the vaso-constrictor nerves of the arterioles of the skin. In con- sequence the arterioles dilate and more blood is sent to the surface to be cooled. When the external temperature is low, the sensory nerve-endings which are stimulated by cold transmit impulses which result in stimulation of the vaso-constrictors, and conse- quent contraction of the arterioles of the skin. This lessens the amount of blood in the skin arterioles, and lessens the amount of heat lost. The voluntary regulation of body temperature is effected by the following means : By muscular exercise and diet. Muscular contractions give rise to heat, therefore muscular activity is used as a means to counteract the effects of external cold. On the other hand, muscular activity does not increase the temperature in hot weather to any marked extent. This is accounted for by the fact that when muscular exertion causes the blood to circulate more quickly than usual, the blood-vessels in the skin dilate, the sweat-glands at the same time are excited to pour out a more abundant secretion, and the heated blood passing in larger quantities through the cu- taneous vessels (which are kept well cooled by the evaporation of the perspiration), the general average temperature of the body is maintained. During digestion heat is produced partly by the peristaltic ac- tion of the intestines, and partly by the activity of the various digestive glands (particularly the liver). The quantity of food eaten, and the relative amount of heat-producing food, influence the temperature of the body. In cold weather an increase in food (usually accompanied by an increase of fats) serves to replace the 388 ANATOMY AND PHYSIOLOGY [CHAP. XVIII greater amount of heat lost. When muscular exercise is impos- sible, as in infants, an increase in fats serves the same purpose as exercise in a healthy adult. By clothing. By clothing we can aid the functions of the skin and the maintenance of heat ; though, of course, clothes are not in themselves sources of heat. Clothing of any kind captures a layer of warm and moist air between it and the skin, and thus diminishes greatly the loss by evaporation and radiation. In considering the heat value of clothing the important properties are : (1) whether it is loosely or tightly woven, (2) its thickness, and (3) its color. (1) Materials that are loosely woven will be warmer than those that are tightly woven, because the meshes in a loosely woven material are capable of holding air, which is a poor conductor of heat, and thus prevents radiation. (2) Thick material does not allow cold air to penetrate to the skin. (3) Dark-colored materials absorb heat to some extent, hence they are warmer than light-colored textiles. Thick, porous ma- terials are used to keep the body warm. Wool has an additional advantage, as evaporation takes place more slowly from it than from linen, cotton, or silk. Thin and very porous materials help to keep the body cool, because they allow the air to penetrate to the skin, and thus assist the evaporation of sweat. Hot baths. The primary effect of a hot bath is to prevent radiation of heat from the surface of the body, and some increase in temperature may result. If the bath is not continued for too long a time, this effect is counteracted by the increased perspira- tion that follows. Cold baths. The primary effect of a cold bath is similar to the effect of cold air. The cold contracts the arterioles of the skin, drives the blood to the interior, and increases oxidation. If the bath is a short one and is followed by friction, the reaction is for the arterioles to dilate, the heated blood is sent to the surface, the circulation is quickened, and there is a consequent loss of heat. In health the gain in heat is usually balanced by the loss of heat, and the purpose of a cold bath is to exercise the arterioles and stimulate the circulation. If the bath is continued for some time, the temperature of the skin, and of the muscles lying beneath, is CHAP. XVIII] TEMPERATURE 389 reduced, and either the heat-producing processes may be checked and a loss of temperature result ; or shivering may intervene. In this case the muscular contractions and constriction of the blood- vessels stimulate metabolism and heat production. When cold baths are given for the purpose of increasing heat elimination, friction is used during the bath to prevent shivering. Friction stimulates the sensory nerves of the skin, causes dilatation of the arterioles, and favors the flow of hot blood to the surface, thus decreasing the sensation of cold and increasing heat elimination. If properly given, cold baths stimulate the nervous system, im- prove the tone of the muscles, including the muscles of the heart and blood-vessels, stimulate the circulation, and favor the elimi- nation of heat. VARIATIONS IN TEMPERATURE Normal variations. The temperature of the human body is usually measured by thermometers placed in the mouth, axilla, or rectum. Such measurements show slight variations, as the temperature in the interior of the body is slightly higher than on the surface of the skin. The average temperature in the rectum 1 is 98.9 F., in the axilla is 98 F., in the mouth is 98.3 F. Other normal variations depend upon the manner of living, time of eating, age, etc. The lowest temperature is usually in the early morning, it rises slowly during the day, reaches its maximum in the evening, and falls again during the night. This corresponds to the usual temperature ranges in fever, when the minimum is in the early morning, and the maximum is in the evening. Mus- cular activity and food may cause a slight increase in tempera- ture during the day. Age has some influence. Infants and young children have a slightly higher temperature than adults. It is also true that the heat-regulating mechanism in infants 2 and young children is not so efficient as in adults, consequently they are more subject to changes of body temperature, and these changes are not as significant as they would be with adults. Aged people show a 1 Rectal temperature is the most reliable ; and that by mouth (if properly taken) is almost equally reliable. Axillary temperature has little value. 2 At birth the heat-regulating mechanism is not " in working order," and during the first few weeks of life infants are not able to regulate their body temperature, hence the importance of keeping them warm. Premature infants are even less able to regulate their body temperature, hence need of special means to keep them warm. 390 ANATOMY AND PHYSIOLOGY [CHAP. XVIII tendency to revert to infantile conditions, and their temperature is usually slightly higher than in middle life. Abnormal variations. Fever. The term fever is applied to an abnormal condition, characterized by increased temperature, increased heart-beat, increased respiration, increased tissue waste, and faulty secretion. Cause. The exact cause of fever is unknown. It is the result of causes which disturb the balance between heat production and heat elimination. One theory is that toxic substances circulating in the blood or abnormal conditions of the various organs of the body may interfere with the proper functioning of various nerve centres. The toxic substances circulating in the blood may result from faulty metabolism, as in diabetes, gout, etc. ; or from the action of bacteria, as in infectious diseases ; or from injury to the tissues of a mechanical, thermal, or chemical nature. Value of fever. When fever is due to infection by bacteria, the body seems better able to fight the infection if the tempera- ture is elevated. For this reason fever is thought to be a protec- tive measure and antipyretics are not used unless the elevation is extreme, or long continued. In such cases measures must be taken to reduce the temperature, or death may ensue from coagu- lation of the body proteins. Subnormal temperature. In some maladies the temperature falls distinctly below normal. This is due chiefly to dimin- ished metabolism. In cases of starvation the fall of tem- perature is very marked, especially during the last days of life. The diminished activity of the tissues first affects the central nervous system ; the patient becomes languid and drowsy, and finally unconscious; the heart beats more and more feebly, the breath comes more and more slowly, and the sleep of unconscious- ness passes insensibly into the sleep of death. CHAP. XVIII] SUMMARY 391 Skin Func- tions Con- sists of SUMMARY 1. Protective covering for deeper tissues. 2. As a sense organ. 3. As an excretory organ. 4. Most important as organ in heat regulation. Small amount oxygen taken in. Small amount carbon dioxide is thrown off. 5. As a respiratory organ Derma is a layer of con- nective tissue Superfi- cial or horny b. a. Stratum corneum Stratum lucidum Stratum granulo- sum Practically dead cells being con- stantly shed and renewed from germi- native layer. Soft protoplasmic cells that are constantly multiplying by cell division. Epidermis is a strat- ified epi- thelium 2. Germina- tive or Mal- pighian 1 . Papillary layer papillae are minute coni- cal elevations of the cutis vera. They contain looped blood-vessels and ter- minations of nerve-fibres called tactile corpuscles. Bundles of fibrous and elastic 2. Reticular tissue, with network of layer blood-vessels, lymphatics, and nerves. Blood-vessels They are found in derma only. Send branches to papilla? and glands of skin. Capable of holding one-half to two-thirds total amount of blood in body. Nerves Appendages Vasomotor. Two sets concerned in temperature sense. Nerves concerned in sense of touch or pressure. Nerves stimulated by pain. Motor nerves from sympathetic system. Nails. Hair. ' Sebaceous glands. Ceruminous glands. Sweat-glands. 392 ANATOMY AND PHYSIOLOGY -[CHAP. XVIII Nails Hair Sebaceous Glands Ceruminous Glands Sweat- glands Sweat Consist of clear, horny cells of epidermis. . True skin forms a bed or matrix for nail. | Root of nail is lodged in a deep fold of the skin. [ Nails grow from soft cells in germinative layer at root. The hair grows from the roots. The roots are bulbs of soft, growing cells contained in the hair follicles. Hair follicles are little pits developed in the derma. Stems of hair extend beyond the surface of the skin, con- sist of three layers of cells : (1) cuticle, (2) fibrous substance, and (3) medulla. { Palms of the hands. Found all over I . f , , , , Soles of the feet. [ Last phalanges of the fingers and toes. Arrector muscles are attached to true skin and to each hair follicle. Saccular glands the ducts of which usually open into a hair follicle, but may discharge separately on the sur- face of the skin. Lie between arrector muscles and hairs. , [ Palms of hands. 1 ound over entire skin surface except i . r ,. I Soles of feet. Secrete sebum, a fatty, oily substance, which keeps the hair glossy, the skin flexible, and forms a protective layer on surface of skin. Modified sweat-glands. Found in skin of external auditory canal. Secrete cerumen, a yellow, pasty substance, like wax. Tubular glands, consist of blind ends coiled in balls, lodged in subcutaneous tissue, and surrounded by a capillary plexus. Secrete sweat and discharge it by means of ducts which open exteriorly. (Pores.) Watery, colorless, turbid liquid, salty taste, distinctive odor, and an alkaline reaction. Consists of water, salts, fatty acids, urea, and carbon dioxide. Average quantity, one quart in twenty-four hours. 1. Dilute condition of blood. 2. Increased temperature or humidity of the atmosphere. Amount increased I 3. Exercise, by 4. Pain. 5. Mental excitement or nervousness. 6. Dyspnoea. 7. Use of diaphoretics. CHAP. XVIII] SUMMARY 393 Sweat Activity of Sweat- glands Excretory Function Body Heat Amount increased by 8. Certain diseases Tuberculosis. Acute rheuma- tism. Malaria. 9. Use of electricity to stimulate secretory nerves. 1. Voiding a large quantity of urine. 2. Cold. 3. Diarrhoea. 4. Certain drugs. Fevers. 5. Certain diseases Animals divided into 2 classes Amount decreased by Diabetes. Some paralyses. Controlled by definite secretory nerves leading to centre in brain. 1 . Direct stimulation of nerve-ending in sweat-glands. 2. Indirect stimulation of nerve centres. Importance not in elimination of waste substances in perspiration, but because of heat needed to cause evap- oration of perspiration. 1. Homothermous or those which have an almost constant tempera- ture. Human beings are in this class. 2. Poikilothermous or those whose temperature varies with that of their environment. The human fcetus is cold-blooded. Chemical changes associated with oxidation. Friction of muscles, blood, etc. Ingestion of warm food. Wherever metabolic . changes are taking place. Offers large surface for radiation, conduction, and evaporation of sweat. Contains large amount of blood. Lungs 10.7 per cent is lost warming the expired air and the evaporation of the water of respiration. Urine and Feces 1.8 per cent is lost warming the urine and feces. Distributed by the blood circulating through the. blood-vessels. Produced by Lost by Skin 87.5 per cent 394 ANATOMY AND PHYSIOLOGY [CHAP. XVIII Due to maintenance of balance between heat production and heat dissipation. Heat 1. The quantity and character of food. Production 2. The motor nerve centres and the motor fibres to the skeletal muscles. 1. The respiratory centre. Heat 2. The sweat centres and sweat nerves. Dissipation 3. The vaso-constrictor centres and Regulation nerves distributed to the skin. of Body Heat 1. The coordinated activities of all the different nerve centres. (a) Regulation of mus- cular exercise and Controlled by diet. 2. Voluntary 4 (6) Use of suitable means clothing. | (c) Use of hot and cold baths. Variations in Temperature Normal 1. Depends on where temperature is taken Abnormal Mouth. Axilla. Rectum. 2. Depends on time j Lowest in early morning. of day 1 Highest in early evening. 3. Slightly increased by muscular activity and the digestive processes. 4. Age. Higher and f Infants, children, and more variable in I the aged. Increased temperature. Increased pulse. Increased respiration. Increased tissue waste. Faulty secretion. Cause not definitely known. Value thought to help the body to I fight infection. Subnormal due to diminished metabolism. Fever Symptoms CHAPTER XIX A.P. THE NERVOUS SYSTEM As brought out in Chapter III in the section on nerve tissue, the structural and functional unit of the nervous system is the neurone. Neurones as there described are large irregular cells with elongated processes, one of which is an axone, and one or more of which are dendrites. (See Figs. 16 and 18.) The reflex concept. In the same way that the nervous system may be reduced to a simple unit designated as the neurone, so may all nervous action be reduced to the so-called reflex action. Just as the neurone forms the building stone of the nervous system, so does the reflex circuit form the functional basis of all nervous activity. At least two neurones enter into the formation of a reflex circuit, a receptor or sensory neurone and an effector or motor neurone. A receptor or sensory neurone is one in which the afferent process ends in a re- ceptor of one kind or another. . An effector or motor neurone is one in which the effer- ent process ends in a muscle or gland cell. Neurones w r hich are interpolated between other neurones are called central or cor- relation neurones. A simple reflex circuit may consist in the functioning of a sensory and a motor neurone. Most reflex circuits consist in the functioning of a sensory neurone, a corre- lation or central neurone, and a motor neurone, or. by complexes of each of these. 395 FIG. 193. A REFLEX CIRCUIT CONSISTING OF A SENSORY AND MOTOR NEURONE. R, receptor ; A. P., afferent process; S, synapse ; E. P., efferent process ; E, effector (mus- cle). (Burton-Opitz.) 396 ANATOMY AND PHYSIOLOGY [CHAP. XIX Synapse. We conceive each neurone to be a separate entity and not directly connected with other neurones. The fine branches of an axone of one neurone interlace or dovetail with the branches of a dendrite of another neurone, forming a synapse. The nerve- impulse travelling through a nerve-cell must cross a microscopic gap at the synapse to enter the next neurone. Figure 193 illustrates a reflex circuit consisting of a sensory and a motor neurone. Figure 194 illustrates a reflex circuit consisting of a sensory, cbrrelation, and motor neurone. M FIG. 194. A REFLEX CIRCUIT CONSISTING OF A SENSORY, CORRELATION, -AND MOTOR NEURONE. S, sensory cell ; C, central or correlation cell ; M, motor cell. On applying an appropriate stimulus to the receptor ending of the sensory neurone, an impulse is generated which passes along the afferent process to the cell-body of the neurone, thence along the efferent process across the synapse through the correlation neurone and across another synapse to an afferent process of the motor neurone, then through the cell-body and an efferent process to the muscle or gland cell where action is produced. (Trace this out in Fig. 194.) Because of its likeness to a telephone system the peripheral end of the sensory nerve is often called the receptor (telephone trans- mitter). The processes are called carriers (telephone wires), the synapses and cell-bodies are called adjusters (telephone operators), and the ending in muscle or gland cell an effector (telephone re- ceiver). The receptor receives the stimulus, transforms it to a nerve-impulse, and passes it on to the afferent process. In the adjusting mechanism the nerve-impulse may be transferred across some synapses rather than others for it must be remembered that each neurone forms synapses not simply with one neurone, as in Fig. 194, but probably with many, as in Fig. 195. CHAP. XIX] THE NERVOUS SYSTEM 397 Reaction circuit. When cells in the volitional centres enter into the reflex circuit the resulting action is due to volition or is voluntary, as we say. This reflex circuit is called a reaction cir- cuit. In Fig. 195 the circuit starting at R and running through CEREBELLUM WHITE MATTER OF SPINAL CORD FIG. 195. DIAGRAM TO ILLUSTRATE SOME REFLEX CIRCUITS OF THE CEREBRO- SPINAL SYSTEM, SHOWING A NUMBER OF CORRELATION AND MOTOR CELLS WITH THEIR SYNAPSES. 1, sensory cell in spinal ganglion; 2, 2', 2", 2'", motor cells; 3, 3', 3", 4,5,6, 7, correlation cells, a, afferent process ; e, efferent process ; s, synapse. R, receptor ; E, effector. (Adapted from Huxley-Lee.) to the cerebral cell may represent a reaction circuit. It will be noted that the difference between a reflex and reaction circuit is found in the fact that in the reflex circuit the voluntary centre is not involved, or the resulting action is involuntary, while in the reaction circuit the voluntary centre is involved and the resulting action is voluntary. Volitional centres lie in the cerebrum. 398 ANATOMY AND PHYSIOLOGY [CHAP. XIX FIG. 196. DIAGRAM TO ILLUSTRATE A SPREADING REFLEX. A, axone divid- ing into terminal branches which connect with cells B, B. These cells send their fibres C, C, C, C, to supply a number of different muscles. Classification of reflexes. In relation to the kind of re- sponse brought about by a stimulus, reflex circuits may be classi- fied as : - (a) Simple reflexes in which a single muscle or gland is involved. As an example of this group may be mentioned the corneal reflex. (6) Complex reflexes, in which several muscles or glands are affected, the response remaining perfectly coordinated in spite of the greater number of muscles or glands affected. The patellar reflex and the ankle- jerk are examples of this type. (c) Spreading reflexes in which a large number of differ- ent muscles are involved. (d) Tonic or continuous re- flexes. The reaction following a stimulus lasts as a rule much longer than the stimulus. In many cases it becomes tonic in character. This result is frequently obtained when the nervous system is extremely irritable as after the administration of strychnine. (e) Clonic or periodic reflexes. In many cases a stimulus may cause a certain reaction to be repeated a number of times at regular intervals. This is frequently true of the acts of sneez- ing, coughing, hiccoughing, swallowing, and trembling. (/) Association or perception reflexes. For some reactions a definite mental picture is the stimulus to produce the reaction. Thus, the flow of saliva or gastric fluid may be started when well- cooked food is seen or smelled, or a person may find himself yawn- ing when another person yawns. Nature and speed of nerve-impulses. The nature of a nerve- impulse is not known. We know that nerve-fibres may be stimu- lated by several means, and the practical result is similar to the result obtained were the nerve stimulated by the natural physio- logical impulse. The nerve-fibre has no power to initiate a nerve-impulse, but serves merely as a conductor of the impulse which has been started either in the end organs or in the nerve- cell. CHAP. XIX] THE NERVOUS SYSTEM 399 There are four means usually applied to the artificial stimu- lation of a nerve-fibre, viz. chemical, thermal, mechanical, and electrical. The latter is the most usual. That the true physio- logical impulse is none of these can be readily proven. (See any standard work of physiology.) The best explanation is that the true nature of a nerve-impulse is a physical molecular vibration set up either in the nerve-cell or the end organs and transmitted along the nerve-fibre. Within the body nerve-impulses travel in two directions : (1) from the cell-body to the periphery, and (2) from the periphery to the cell-body. The speed at which an impulse travels along a nerve-fibre is found to be about 100 to 140 feet (27-33 m.) per second. It may be interesting to note how very slow a nerve-impulse is when compared with light which travels at the rate of about 186,000 miles per second, and sound which travels about 11,000 feet per second. Identity of nerve-impulses. The generally accepted belief is that nerve-impulses are identical in character and vary only in intensity. According to this the impulses carried by a sensory nerve are similar in character to those carried by a motor nerve, and yet the result is different. The result is thought to be deter- mined by the nature of the centre in which a nerve-fibre ends, rather than by the nature of the fibre itself. Reaction of nerve-endings. A study of the previous clas- sification 1 shows that the sensory nerve-endings are not all affected by the same stimulus, nor do they react in the same way. Thus some of the sensory nerve-endings are affected by pressure, and others by temperature. The endings of the auditory nerve in the ear are affected only by sound, and the endings of the optic nerve in the eye are affected by sight, though a similar effect may be produced by a blow on the head, or an accident which jars the spinal column. ANATOMY AND PHYSIOLOGY OF THE NERVOUS SYSTEM Grouping of neurones. The nervous system is said to be com- posed of gray and white matter. The cell-bodies, most of the 1 See page 3, 400 ANATOMY AND PHYSIOLOGY [CHAP. XIX dendrites, and the commencement of the axone processes are not scattered promiscuously throughout the body, but are gathered together in certain definite regions or groups. These form the gray matter of the brain, spinal cord, and ganglia. The medullated nerve-fibres found in the brain, spinal corcl, ganglia, and also in the nerve trunks distributed to all parts of the body form the white matter. It will therefore be seen that the white matter is made up of the carriers of nerve-impulses, and the gray matter contains the cell- bodies and the synapses where the adjusting of sensory to motor neurones takes place. For purpose of study, it is convenient to classify the nervous system as has been done in Chapter III, or more simply still into : 1. Vertebral ganglia. 2. Collateral ganglia. 3. Terminal ganglia and plexuses. 4. Sympathetic ganglia in the brain and cord. 5. Sympathetic nerves. Spinal cord and spinal nerves. Medulla oblongata. Cerebellum. Pons Varolii. Cerebrum. Cranial nerves. Nervous System Sympathetic System Central Nervous System Brain THE SYMPATHETIC SYSTEM The sympathetic system consists of four sets of ganglia and the nerves connected with them : - 1. Vertebral or lateral ganglia. 2. Collateral or prevertebral ganglia, and plexuses. 3. Terminal ganglia and plexuses. 4. Sympathetic ganglia in the brain and cord. The vertebral ganglia. The vertebral ganglia consist of a chain of ganglia situated on each side of the spinal column, extend- ing from the base of the skull to the coccyx. (See Fig. 197.) They are grouped as cervical, thoracic, lumbar, and sacral, and except in the neck they correspond in number to the vertebrae against which they lie : Cervical Thoracic 3 pairs 10-12 pairs Lumbar Sacral 4 pairs 4-5 pairs CHAP. XIX] THE NERVOUS SYSTEM 401 They are connected with each other by nerve-fibres called ganglia cords, and with the spinal nerves by branches which are called rami communicantes. They are also connected with the viscera and blood-vessels by branches which travel different pathways : (a) they pass directly to the viscera ; (6) they converge to form three main nerve-trunks, called the great splanchnic, the small splanchnic, and the least splanchnic, and then send branches from these trunks to the viscera; (c) they join the collateral ganglia and plexuses ; (d) they join the spinal nerves, by way of the gray rami, and in them reach the part of the body for which they are destined. The collateral ganglia. The collateral or outlying ganglia consist of masses of gray matter and their nerves, which are lo- cated principally in the thoracic and abdominal cavities. They are connected with the spinal nerves, with the vertebral ganglia, and send branches to the viscera. These branches form plexuses, the most important of which are : (1) the cardiac plexus, located above the heart and supplying it with sympathetic fibres, (2) the solar plexus, located behind the stomach and supplying most of the abdominal viscera, (3) the hypogastric or pelvic plexus, lo- cated in the lower part of the abdomen and supplying the viscera of the pelvis. The terminal ganglia. The terminal ganglia include all the ganglia situated in the walls of the organs themselves, as for in- stance those in the walls of the heart, and in the walls of the ali- mentary canal. These ganglia are directly connected with the collateral ganglia, and in some instances the nerves derived from the collateral plexuses form a secondary or terminal plexus on the organs. Sympathetic ganglia in the brain and spinal cord. Sympa- thetic ganglia are found in the spinal cord and in the medulla, also in connection with a few of the cranial nerves, such as the third and fifth. (See vasomotor centre, page 412.) Rami communicantes. The nerve-fibres that connect the vertebral ganglia and the spinal nerves are called rami communi- cantes. Each connection consists of two rami, one white and the other gray. The white ramus consists of medullated fibres, and these pass from the spinal cord to the sympathetic ganglion. The gray ramus consists of non-medullated fibres that pass from the 2D 402 ANATOMY AND PHYSIOLOGY [CHAP. XIX sympathetic ganglion to join the spinal nerve, and so reach the part of the body they are to supply. Plexuses. The term plexus has been used to designate a net- work of nerves. It is worthy of special mention because the nerve- fibres arborize with each other, and there is an interchange of fibres between the different nerve-trunks. The advantages of this ar- rangement are : (1) each nerve is less dependent on the unimpaired condition of any single portion of the nerve-trunk or nerve centre, (2) each nerve has a wider communication with the nerve centres, and (3) any given part of the body is not dependent on' one nerve. The various plexuses of the sympathetic system serve all these purposes, and in addition the organs constituting any one system are brought into direct communication with each other. In this way coordination of action is secured. Distribution of sympathetic nerves. Nerve-fibres from the sympathetic system are distributed : (1) to the heart, (2) to the involuntary muscles of the blood-vessels, lymphatics, and viscera, (3) to the secretory glands, and (4) to some of the special senses, such as those that regulate the pupil of the eye. Functions of the sympathetic system. The sympathetic ner- vous system exercises a regulatory control over the visceral ac- tivities of the body. Our awareness of these actions is limited as most of them are performed quite unconsciously. Nevertheless, they are of enormous importance not only in maintaining our physical welfare, but also as the background of our entire conscious life. In addition to the power of automaticity possessed in a pre- eminent degree by the heart and more or less by all visceral mus- cles, and the chemical control exercised by the internal secretions, the viscera are under nervous control of two sorts, i.e., from the sympathetic nervous system and the central nervous system. Moreover, the nerves which carry impulses from the central nervous system to the viscera are distributed to the viscera through the sympathetic system. Autonomic nervous system. The activities controlled by means of the sympathetic ganglia are typically reflex in their character and are relatively independent of the central nervous system. Moreover, they are vegetative or visceral in their nature and are usually described as autonomic. Accordingly, some authorities CHAP. XIX] THE NERVOUS SYSTEM 403 use the term autonomic when speaking of the functional side of the sympathetic system, while others apply it to subdivisions of the sympathetic system. 1 Interdependence of the sympathetic and central nervous system. - From the preceding description it is evident that the sympa- thetic nervous system cannot be sharply separated either anatomi- cally or physiologically from the central nervous system. Ana- tomically the fibres which connect the sympathetic ganglia and the spinal nerves form a direct pathway from all of the viscera to the spinal cord and brain. Moreover, many of the viscera are con- nected with the brain by the cranial nerves. 2 As previously stated the visceral activities are usually performed quite uncon- sciously, but it frequently happens that they attain conscious- ness. As an example might be mentioned the hunger contractions of the stomach, or sensations of pain from the viscera of the abdomen, both of which show the functional connection between the sympathetic and central nervous system. SPINAL CORD A brief sketch of the lower animals characterized as seg- mental, is helpful in understanding the structure and functions of the spinal cord. Segmental animals are made up of a num- ber of smaller units which are capable of leading an inde- pendent existence. This is made possible by the fact that each segment possesses separate circulatory, digestive, excretory, and nervous systems, so that the segments may be separated without endangering or seriously impairing their life processes. As far as the nervous system is concerned, we find that each segment of these animals is equipped with a centrally placed ganglion from which nerve-fibres extend in all directions to the different tissues of this segment. A stimulus applied to its surface is soon followed by movement or some other motor response. It appears, therefore, that the nervous elements allotted to each segment are arranged in the form of reflex circuits, their centres being grouped in the shape of a central ganglion. The life of the animal as a whole, however, requires a certain correlation be- tween the activities of its different segments and a subordination 1 See " Introduction to Neurology " by C. Judson Herrick. 8 See page 421. 404 ANATOMY AND PHYSIOLOGY [CHAP. XIX Sa UE> SB FIG. 197. VENTRAL, VIEW OF BASE OF BRAIN, SPINAL CORD, AND SPINAL NERVES. On the leftr-hand side the sympathetic chain of ganglia is shown. V-IX, cranial nerves. D l -D 12 , L l -L 5 , S*, S 5 , and Cocc., spinal nerves, seen emerging from spinal cord by two roots, with ganglia on the dorsal roots. B.P., brachial plexus. L.P., lumbar plexus. S.P., sacral plexus. ,SV/, S'>, ,Vc, cervi-al sympa- thetic ganglia. of the latter to the functional necessities of the whole. This end is attained first by inter- mediary neurones which unite the successive ganglia with one another and secondly, by a hyper- development of the head-ganglion which thus gains a directing con- trol over the others. A nervous system of this kind is reflex in its nature and forms the basal stem around which the nervous system as it appears in the highest animals is eventually developed. The head-ganglion is comparable to the brain, the segmental ganglia to the spinal cord, and from these parts the afferent and efferent nerves arise. The spinal cord is that portion of the nervous system lodged within the spinal canal of the vertebral column. It consists of a collection of gray and white substance, extending from the foramen magnum of the skull, where it is continuous with the medulla oblongata, to about the second lumbar vertebra, where it tapers off into a fine thread. Be- fore its termination it gives off a number of fibres which form a tail-like expansion, called the cauda equina. (See Fig. 21.) Structure of the cord. The spinal cord does not fit closely into the spinal canal, as the brain does in the cranial cavity, but is, as it were, suspended within CHAP. XIX] THE NERVOUS SYSTEM 405 it. A series of spaces intervene between its surface and the walls of the canal, affording freedom of movement of the vertebral column without exerting undue tension upon the cord. 1 It di- minishes slightly in size from above downward, with the excep- tion of presenting two enlargements in the cervical and lumbar regions, where the nerves are given off to the arms and legs respectively. It varies in length from sixteen to twenty inches (40 to 50 cm.), and has an average diameter of three-fourths of VENTRO-MIDIAH ORSAL BOOTS FIG. 198. TRANSVERSE SECTION OF THE SPINAL CORD AT THE MIDDLE OF THE THORACIC REGION. The neuroglia septum has been removed from between the dorsal columns. (Gerrish.) an inch (19 mm.). The spinal cord is almost completely divided into lateral halves by a ventral and dorsal fissure; the ventral fissure dividing it in the middle line in front, and the dorsal fissure in the middle line behind. In consequence of the pres- ence of these fissures, only a narrow bridge of the substance of the cord connects its two halves. This bridge, also called the isthmus, is traversed throughout its entire length by a minute central canal. On making a transverse section of the spinal cord, the gray matter is seen to be arranged in the form of an H, and presents on each side a ventral and dorsal horn. The former is short and bulky while the latter is long and slender. The transverse bar of gray matter found in the isthmus is called the gray commissure, and connects the two lateral masses of gray matter. The white matter is arranged around and between 1 See Membranes of the Cord. 406 ANATOMY AND PHYSIOLOGY [CHAP. XIX the gray matter, the proportion of gray and white varying in dif- ferent regions of the cord. The white matter is composed of medullated nerves, and the gray matter consists of cell-bodies, dendrites, axones, and collaterals, all held together and supported by neuroglia. The white matter may be said to consist of three portions or funiculi, namely, an anterior, a lateral, and a posterior. Each funiculus is in turn divided into smaller segments or fascic- uli, commonly called columns or tracts. Some of these tracts consist of fasciculi made up of fibres which are ascending or sensory. They begin in the gray matter of the FIG. 199. CONDUCTION IN SPINAL CORD. 1, 2, fasciculi in dorsal funiculus ; 3, 4, 5, fasciculi in lateral funiculus ; 6, 7, fasciculi in ventral funiculus of one side of cord. DF, dorsal fissure ; DR, dorsal root ; GM, gray matter ; SG, spinal gan- glion ; SN, spinal nerve ; VF, ventral fissure ; VR, ventral root. 1, Column of Goll ; 2, column of Burdach ; 3, crossed pyramidal tract ; 4, Flechsig's tract ; 5, Gower's tract ; 6, ventral ground bundle ; 7, direct pyramidal tract. (Burton-Opitz.) cord, ascend and terminate in the gray matter of the brain, e.g., 1, 2, 4, 5 in Fig. 199. Other tracts consist of fasciculi which are descending or motor. They begin in the gray matter of the brain, descend and terminate in the gray matter of the cord, e.g., 3 and 7. Other tracts, e.g., 6, are made up chiefly of short ascending and descending fibres beginning in one region of the spinal cord and ending in another. Membranes of the cord. The spinal cord is protected and nourished by three membranes which are continuous with the membranes covering the brain and are called by the same names, viz. (1) pia mater, (2) arachnoid, and (3) dura mater. Surround- ing these three membranes are three spaces, called respectively (a) subarachnoid, (6) subdural, and (c) epidural. (1) The pia mater closely invests the entire surface of the CHAP. XIX] THE NERVOUS SYSTEM 407 spinal cord. The subarachnoid space between it and the arach- noid membrane contains a sm ill amount of cerebrospinal fluid. (2) The arachnoid is a delicate serous membrane placed between the pia mater and the dura mater. The subdural space between these two membranes is very small and contains just enough cerebrospinal fluid to moisten their contiguous surfaces. (3) The dura mater constitutes the outermost and thickest sheath. It does not serve as a periosteum for the vertebral bones, being separated from them by the epidural space which contains a certain quantity of areolar and adipose tissue and a network of veins. SPINAL NERVES There are thirty-one pairs of spinal nerves, arranged in the following groups, and named for the region of the vertebral column from which they emerge. Cervical 8 pairs Thoracic 12 pairs Lumbar 5 pairs Sacral 5 pairs Coccygeal 1 pair The first cervical nerve arises from the medulla oblongata and leaves the neural canal between the occipital bone and the atlas. With this one exception the spinal nerves spring from both sides of the spinal cord, and all except the coccygeal pass out through the intervertebral foramina. The coccygeal passes from the lower extremity of the canal. Mixed nerves. The spinal nerves consist almost entirely of medullated nerve-fibres, and are called mixed nerves because they contain both sensory and motor fibres. Each spinal nerve has two roots, a ventral root and a dorsal root. The fibres connected with these two roots are collected into one bundle, and form one nerve just before leaving the canal through the intervertebral open- ings. Before joining to form a common trunk, the fibres connected with the dorsal root present an enlargement, this enlargement being due to a ganglion, or small nerve centre, situated in the in- tervertebral foramina. The fibres of the ventral root arise from the gray matter in the ventral horn, and are direct prolongations from the cell-bodies 408 ANATOMY AND PHYSIOLOGY [CHAP. XIX there. Accordingly, all the fibres making up the ventral root are efferent fibres, and convey nerve-impulses from the spinal cord to the periphery. The fibres of the dorsal root arise from the cells composing the enlargement or ganglion of the dorsal root ; each cell of the ganglion, besides sending a nerve-fibre toward the periphery, sends a branch along the dorsal root up into the gray matter of the dorsal horn, there to form a synapse with the dendrites of other neurones. The fibres making up the dorsal root are afferent fibres, and convey nerve-impulses from the periphery to the spinal cord. It should be borne in mind that the ventral roots contain only motor fibres, and these have their origin within the central nervous system ; while the dorsal roots contain only sensory fibres, and these fibres always have their origin outside of the cord, i.e., in the spinal ganglia. The relations of the roots, fibres, and so forth, can be best understood from a study of the accompanying diagrams (Figs. 199 and 200). Degeneration and regeneration of nerves. Since the cell-body is essential for the nutrition of the whole cell, it follows that if A B FIG. 200. DEGENERATION OF SPINAL NERVES AND NERVE-ROOTS AFTER SECTION. A, section of nerve trunk beyond the ganglion; B, section of ventral root ; C, section of dorsal root ; D, excision of ganglion ; a, ventral root ; p, dorsal root ; g, ganglion. the processes of a neurone are cut off, they will suffer from malnu- trition and die. If, for instance, a spinal nerve be cut, all the pe- ripheral part will die, since the fibres composing it have been cut off from their cell-bodies situated in the cord, or in the spinal ganglia. The divided ends of a nerve that has been cut across readily reunite by cicatricial tissue, that is to say, the con- nective tissue framework unites, but the cut ends of the fibres CHAP. XIX] THE NERVOUS SYSTEM 409 themselves do not unite. On the contrary, the peripheral or severed portion of the nerve begins to degenerate, the medullary sheath breaks up into a mass of fatty molecules and is gradually absorbed, and finally the axone also disappears. In regeneration, the new fibres grow afresh from the axone of the central end of the severed nerve-trunk, and penetrating into the peripheral end of the neurilemma, grow along this as the axone of the new nerve, each axone after a time becoming surrounded with a medullary sheath. Restoration of function in the nerve may not occur for several months, during which time it is presumed the new nerve- fibres are slowly finding their way along the course of those which have been destroyed. Distribution of the terminal branches of the spinal nerves. - After leaving the spinal canal each spinal nerve divides into two main trunks known as the ventral and dorsal divisions. Each of these contain sensory and motor fibres. The ventral division supplies the extremities and parts of the body in front of the spine. The dorsal division supplies the muscles and skin of the back of the head, neck, and trunk. Each ventral division connects with the sympathetic system by means of fibres which pass from the nerve to the sympathetic system and vice versa. Previous to their final distribution in the cervical, sacral, and lumbar regions these nerves form plexuses known as the cervical, sacral, and lumbar plexuses. In passing to the viscera, muscles, skin, etc., these terminal nerves follow the same pathway as the blood-vessels. (See Fig. 197.) Names of peripheral nerves. Many of the larger branches given off from the spinal nerves bear the same name as the artery which they accompany, or the part which they supply. Thus the radial nerve passes down the radial side of the forearm, in com- pany with the radial artery ; the intercostal nerves pass between the ribs in company with the intercostal arteries. An exception to this are the two sciatic nerves which pass down from the sacral plexus, one on either side of the body near the centre of each buttock, and the back of each thigh, to the popliteal region where each divides into two large branches which supply the leg and foot. Motor branches from these nerves pass to nearly all the muscles of the legs and feet and they receive sensory branches from nearly all parts of the skin of the lower extremities. 410 ANATOMY AND PHYSIOLOGY [CHAP. XIX Functions of the spinal cord : (a) Conduction, or the conveyance of impulses and sensations between the centres and the periphery. (6) Reflex action, i.e., the origination of an impulse or action in response to stimulation from the periphery, without of neces- sity involving the brain in the act, or even without consciousness of the reflex act, on the part of the individual. (c) Automatic acts, i.e., acts set up primarily in the cells of the cord by the cells themselves, and not as a result of stimula- tion by brain cells (voluntary acts) nor as a result of peripheral stimulation. (d) Inhibition of reflex acts. If every outside stimulation were allowed its full effects in the setting up of reflex acts, the body would be on "the jump " all the time. This overactivity is checked unconsciously by the cells of the spinal cord endowed with this function. (e) Transference, i.e., an apparent transferring of impulses from one set of fibres to another. THE BRAIN The brain is the largest and most complex mass of nervous tissue in the body. It is contained in the cavity formed by the bones of the cranium, and is covered by three membranes (also named meninges), the dura mater, pia mater, and arachnoid. The dura mater is a dense membrane of fibrous connective tis- sue containing a great many blood-vessels. It is arranged in two layers and the layers are attached except in a few places. The external layer is adherent to the bones of the skull, and forms their internal periosteum. The internal layer covers the brain and sends numerous prolongations inward for the support and protec- tion of the different lobes of the brain. These projections also form sinuses that return the blood from the brain, and sheaths for the nerves that pass out of the skull. It may be called the protective membrane. The pia mater is a delicate membrane of connective tissue, containing an exceedingly abundant network of blood and lymph- vessels. It dips down into all the crevices and depressions of the brain, carrying the blood-vessels which go to every part. It may be called the vascular or nutritive membrane. CHAP. XIX] THE NERVOUS SYSTEM 411 The arachnoid is a delicate serous membrane which is placed between the dura mater and the pia mater. With the exception of the longitudinal fissure, it passes over the various eminences and depressions on the surface' of the brain and does not dip down into them like the pia mater. Between the arachnoid and the pia mater is a space called the subarachnoid space in which is a cer- tain amount of cerebro-spinal fluid. Meningeal spaces and cerebro-spinal fluid. The meningeal membranes and the spaces filled with fluid form a pad enclosing the brain and cord on all sides. The fluid within the ventricles and surrounding the brain is in free communication with that within the central canal of the cord, and the spaces surrounding the cord. Experimental work indicates that cerebro-spinal fluid is formed in the ventricles from the blood and may be due to a process of active secretion. The stream of liquid starts within the ventricles, passes out through foramina into the subarachnoidal spaces, from which it is in turn absorbed by the veins. The cerebro-spinal fluid is a thin, watery fluid having a specific gravity of 1.007 to 1.008. It contains traces of proteins and other organic substances. The normal amount is difficult to determine but is usually stated as from 60 to 80 cc. It may be formed very promptly from the blood, and when in excess be absorbed quickly by the blood. Structure of the brain. The whole brain appears to consist of a number of isolated masses of gray matter some large, some small connected together by a multitude of medullated fibres (white matter) arranged in perplexing intricacy. But a general arrangement may be recognized. The numerous masses of gray matter in the interior of the brain may be looked upon as forming a more or less continuous column, and as forming the core of the central nervous system, while around it are built up the great mass of the cerebrum and the smaller mass of the cerebellum. This central core is connected by various bundles of fibres with the spinal cord, besides being, as it were, a continuation of the gray matter in the centre of the cord. It is also connected at its upper end by numberless fibres to the gray matter on the surface of the cerebrum. Weight of the brain. With the exception of the whale and the elephant, the human brain is heavier than that of any of the lower 412 ANATOMY AND PHYSIOLOGY [CHAP. XIX animals. The average weight of the brain in the male is 49.5 ounces avoirdupois (about 1485 gms.) ; in the female, 44 ounces avoirdupois (about 1320 gms.). It appears that the weight of the brain increases rapidly up to the fifth year and ceases to grow generally in the eighteenth or twentieth year. After the sixtieth year the brain loses weight, at first slowly, later more rapidly. Divisions of the brain. The brain is divided into four principal parts : the cerebrum, the cerebellum, the pons Varolii and the medulla oblongata. The medulla oblongata. The medulla oblongata, also known as the spinal bulb, is continuous with the spinal cord, which, on passing into the cranial cavity through the foramen magnum, widens into an oblong-shaped mass. It is directed (from above) backward and downward, its ventral surface resting on a groove in the occipital bone and its dorsal surface forming the floor of a cavity between the two halves, or hemispheres, of the cerebellum. It is hollow, and the cavity, called the fourth ventricle, is an expanded continuation cf the tiny central canal which runs throughout the whole length of the spinal cord. The gray matter is found in the interior, and the white matter on the exterior ; most of the gray matter is found on the floor of the fourth ventricle, and from this gray matter arise most of the cranial nerves. The medulla has a ventral and a dorsal median fissure; at the lower part of the ventral fissure are nerve-fibres which cross from one side to the other or decussate. Functions of the medulla oblongata. The functions of the medulla are similar to the first three listed under the functions of the cord, i.e., conduction, reflex action, and automatic action. As all the impressions passing between the brain and spinal cord must be transmitted through the medulla, the function of con- duction is a very important one. As previously stated, the me- dulla contains important vital and reflex centres. The principal ones are : (1) The respiratory centres for regulating the function of respiration. (2) Accelerator centres for the heart. (3) Vasomotof centre. Subsidiary centres are also found in the spinal cord. The vaso- motor nerves are of two kinds, vaso-oonstrictor and vaso-dilator. These nerves control the caliber of the blood-vessels and thus help CHAP. XIX] THE NERVOUS SYSTEM 413 to control such important processes as the circulation of the blood, metabolism, and heat regulation. While these nerves are always considered as belonging to the sympathetic system, it should be noted that the centre controlling them is located in the medulla. (4) Other centres, e.g., the vomiting centre, etc. V r ^'~.*i, ; , Tli SYLVIAN T ^""FISSURE >^T ^ NTIO* .CEREBELLUM FIG. 201. UNDER SURFACE OF THE BRAIN, SHOWING THE SUPERFICIAL ORIGINS OF THE CRANIAL NERVES. The romaii numerals indicate the nerves. (Gerrish.) The medulla being the seat of such important centres as those controlling respiration and the heart's action, the student will readily appreciate that, if the medulla be seriously injured, death will result. Cerebellum. The cerebellum, or " little brain," occupies the lower and back part of the skull cavity, overhanging the medulla oblongata. It is of a flattened, oblong shape, and measures from three and a half to four inches (8.7 to 10 cm.) trans- versely, and from two to two and a half inches (5 to 6.3 cm.) from before backward. It is arbitrarily divided into a medial segment called the vermis and two lateral lobes or hemispheres ; each lobe being subdivided by fissures into smaller portions. 414 ANATOMY AND PHYSIOLOGY [CHAP. XIX The surface of the cerebellum consists of gray matter and is traversed by numerous curves, or furrows, which vary in depth. The interior consists of white matter. Peduncles of cerebellum. The cerebellum is connected with the rest of the cerebro-spinal system by many white nerve fibres grouped in bundles, called the peduncles. The peduncles are arranged in three pairs The anterior (superior) peduncles pass forward from the cerebellum to enter into the cerebrum. The posterior (inferior) peduncles pass down to the medulla, where they are known as the restiform bodies. The middle pair pass into and make up the larger portion of the pons Varolii, thus serving as a means of intercommunication between the two halves of the cerebellum. Thus it is seen that the cerebellum communicates freely with the entire cerebro- spinal system. Functions of the cerebellum. The principal function of the cerebellum seems to be the coordination of ordinary movements and the maintenance of equilibrium. 1 The reason for this belief is that disease or destruction of the cerebellum apparently exerts no malign influence on sensory nerves nor upon the intellect. The motor system is, however, profoundly deranged. Motion itself is not destroyed, but coordination is so interfered with that movements of one part of the body cannot be adapted to other parts. Pigeons deprived of the cerebellum will fly if thrown from a roof, but the delicacy of the coordination being lost, they turn a series of somersaults in the air and soon fall to the ground. Pons Varolii. The pons Varolii, or bridge of Varolius, lies in front of the upper part of the medulla oblongata. It consists of interlaced transverse and longitudinal white nerve-fibres inter- mixed with gray matter. The transverse fibres are those de- rived from the middle peduncles of the cerebellum and, as already stated, serve to join its two halves. The longitudinal fibres join the medulla with the cerebrum. Functions of pons Varolii. The pons is a bridge of union be- tween the two halves of the cerebellum and a bridge between the medulla and the cerebrum. It is also a place of exit for the fifth, sixth, seventh, and eighth cranial nerves. 1 A portion of the inner ear is also concerned in maintaining equilibrium. CHAP. XIX] THE NERVOUS SYSTEM 415 Cerebrum. The cerebrum is by far the largest part of the brain. It is egg-shaped, or ovoidal, and fills the whole of the upper portion of the skull. The entire surface, both upper and under, is composed of layers of gray matter, and is called the cortex because, like the bark of a tree, it is on the outside. The bulk of the white matter in the interior of the cerebrum consists of very small fibres running in three principal directions : (1) from above down- ward, (2) from the front backward, and (3) from side to side. The fibres link the different parts of the brain together, and con- nect the brain with the spinal cord. Fissures and convolutions. In early life the cortex of the cerebrum is comparatively smooth, but as time passes and the FIG. 202. FALX CEREBRI AND TENTORIUM, LEFT LATERAL VIEW. (Gerrish.) brain develops, the surface becomes covered with depressions which vary in depth. The deeper depressions are called fissures , the more shallow ones sulci, and the ridges between the sulci are called convolutions. The fissures and sulci are infoldings of gray matter, consequently the more numerous and deeper they are, the greater is the amount of gray matter. The number and depth of these fissures and sulci is thought to bear a close relation to intellectual power ; babies and idiots have few and shallow folds, while the brains of men of intellect are always markedly con- 416 ANATOMY AND PHYSIOLOGY [CHAP. XIX voluted. There are five important fissures which are always pres- ent. They are the following : (1) The Great Longitudinal Fissure, which extends from the back to the front of the cerebrum, and almost completely divides it into two hemispheres, the two halves, however, being connected in the centre by a broad, transverse band of white fibres called the corpus callosum. A process of the dura mater extends down into this fissure and separates the two cerebral hemispheres. It is called the falx cerebri, because it is narrow in front, and broader behind, thus resembling a sickle in shape. Blood is returned from the brain in venous channels called sinuses. Two important sinuses are lodged between the layers of the falx cerebri. The superior longitudinal sinus is contained in the upper border, and the inferior longitudinal sinus in the lower border. See Fig. 202. (2) The Transverse Fissure, which is between the cerebrum and the cerebellum. A process of the dura also extends into this fissure, and covers the upper surface of the cerebellum and the under surface of the cerebrum. It is called the tentorium cerebelli. (3) Fissure of Rolando, or 1 , There is one of each in each central fissure. , . , ^ , ,.. . P ^ i - hemisphere, tor location see (4) Fissure of Sylvius. 2Q3 (5) Parieto-occipital fissure. . Lobes of the cerebrum. The longitudinal fissure divides the cerebrum into two hemispheres, and the transverse fissure divides the cerebrum from the cerebellum. The three remaining fissures divide each hemisphere into five lobes. With one exception these lobes were named from the bones of the cranium under which they lie ; hence they are known as : (1) Frontal lobe. (2) Parietal lobe. (3) Temporal lobe. (4) Occipital lobe. (5) Central lobe, or Island of Reil (the exception) . (1) The frontal lobe is that portion of the cerebrum lying in front of the fissure of Rolando, and usually consists of four main convolutions. (2) Parietal lobe is bounded in front by the fissure of Rolando, and behind by the parieto-occipital fissure. CHAP. XIX] THE NERVOUS SYSTEM 417 (3) Temporal lobe lies below the fissure of Sylvius and in front of the occipital lobe. (4) Occipital lobe occupies the posterior extremity of the cerebral hemisphere. When one examines the external surface of the hemisphere, there is no marked separation of the occipital lobe from the parietal and temporal lobes that lie to the front; but -ALSO KNOWN AS FISSURE OF ROLANDO FIG. 203. THE LOBES OF THE CONVEX SURFACE OF THE HEMISPHERE, LEFT SIDE. (Gerrish.) when the surface of the longitudinal cleft is examined, the parieto- occipital fissure serves as a boundary anteriorly for the occipital lobe. (5) Central lobe, or Island of Reil, is not seen when the sur- face of the hemisphere is examined, for it lies within the fissure of Sylvius, and the overlying convolutions of the parietal and frontal lobes must be lifted up before the central lobe comes into view. Ventricles of the brain. In describing the spinal cord, ref- erence was made to the central canal, being a minute canal running through the centre of the cord throughout its entire length, thus converting the cord into a tube with exceedingly thick walls but very small internal caliber. In the brain proper this same central channel persists, and just as the walls or solid portions of the brain are directly continuous with the wall or solid portion of the spinal cord, so is the cavity of the brain directly con- 2E 418 ANATOMY AND PHYSIOLOGY [CHAP. XIX tinuous with the central canal of the cord. The cavity in the brain presents some marked differences to that of the cord ; while the latter is a straight, fairly uniform canal of very small diameter, the former is at some points very narrow, and at others much widened out so as to form quite good-sized chambers, and these chambers are called the ventricles of the brain. These ventricles are filled with cerebro-spinal fluid, just as the canal of the cord is likewise filled with the same fluid. The ventricles are five in number. The most posterior is the enlargement or expansion of the central canal, occupying the sub- stance of the medulla oblongata, and is called the fourth ven- tricle. Leading forward from the anterior end of the fourth ven- tricle, the caliber of the canal again narrows to a very small diameter ; the canal on reaching the brain substance uniting the two halves of the cerebrum, again expands into a somewhat smaller chamber, called the third ventricle. The small canal already mentioned as joining the third and fourth ventricles is known as the aqueduct of Sylvius. Toward the forward end of the third ventricle there are noted two small channels, the foramina of Monro, one on either side leading in a direction forward, upward, and outward, each fora- men leading into a very large ventricle occupying the centre of its corresponding cerebral hemisphere, called the lateral ven- tricle. The fifth ventricle is very small, lies between the two lateral ventricles, and is^not in communication with the other ventricles. The student will thus see that both the brain and spinal cord are hollow. In some portions, however (as the spinal cord), the interior cavity is so minute and the walls so exceedingly thick that the cavity is a negligible quantity, and the mass can practically be considered as solid ; on the other hand, in the case of the ventricles, especially the lateral ventricles, the cavity is large enough to occupy an appreciable space, and may become overdistended with cerebro-spinal fluid in certain conditions of disease. Functions of the cerebrum. The nerve centres which govern all our mental activities and the coordination of movements are centred in the cerebrum. These centres are the seat of reason, intelligence, will, memory, and all the higher emotions and feelings. CHAP. XIX] THE NERVOUS SYSTEM 419 Localization of brain function. As the result of numerous experiments on animals, and close observation of individuals suffering from cerebral diseases or wounds, physiologists have been able to localize certain areas in the brain which control motor and sensory activity. They have also been able to gain some knowl- edge of the areas in the cerebrum which are concerned with the higher mental activities. Names of areas. That portion of the cerebrum which governs muscular movement is known as the motor area, the portions con- trolling sensation as the sensory areas, and those connected with the higher faculties, such as reason and will, as association areas. Motor areas. The surface of the brain assigned to the func- tion of motion is the posterior part of the frontal lobe, i.e., the FISSURE OF ROLANDO OR CENTRAL 'B. FIG. 204. LOCALIZATION OF FUNCTION IN THE CEREBRAL CORTEX. (Adapted from Woolsey's "Surgical Anatomy.") The cortical area marked A is the motor speech centre, damage to which causes loss of the word-forming power (motor aphasia). Damage to the cortical area marked B abolishes the power of writing, a form of sensory aphasia called agraphia. Damage to the centre marked C produces word-deafness (sensory aphasia) . Damage to the cortical area marked D produces word-blindness (sensory aphasia). Stereognosis means the ability to recognize the form of objects by the sense of touch. gray matter immediately in front of the fissure of Rolando. The movements of various parts of the body are controlled by nerves arising in this area, and the special portions of the area in which the nerves supplying the various parts arise can be studied in Fig. 204. 420 ANATOMY AND PHYSIOLOGY [CHAP. XIX Decussation .of nerves. The fibres extending from the brain into the cord, and from the cord into the brain, decussate or cross in the medulla. Because of this it follows that the nerves arising in the cortex of the right side govern the movements of the left side of the body, and vice versa. In many cases of paralysis or convulsions, it is possible to locate the exact portion of the brain that is affected, by close ob- servation of the part of the body involved in the loss of function or convulsion. Sense areas. The term sense areas is used to designate those parts of the brain to which sensation is due, and which control vision, hearing, smell, taste, and to some extent, speech. The visual area is situated in the posterior part of the occipital lobe ; the auditory area in the superior part of the temporal lobe ; and the olfactory and gustatory areas are in the anterior part of the temporal lobe. Location of speech areas. There are four small areas in the cerebral cortex, marked A, B, C, D, in Fig. 204 which are known as the speech centres. They do not develop in both hemispheres. In right-handed persons they become fully developed in the left hemisphere, and in left-handed persons in the right hemi- sphere. Injury to these centres results in some form of in- ability to speak, 1 to write, 2 or to understand, spoken 3 or written 4 words. It is customary, therefore, to distinguish two types of aphasia, i.e., motor and sensory. By motor aphasia is meant the condition of those who are unable to speak, al- though there is no paralysis of the muscles of articulation. By sensory aphasia is meant the condition of those who are unable to understand written, printed, or spoken symbols of words, although the sense of vision and of hearing are unimpaired. These centres are really memory centres and aphasia is due to loss of memory either of words, or the meaning of words seen or heard, or of how to form letters. How these areas control memory is not known. The basis of language is a series of memory pictures : (1) of the sound of words ; (2) of their appearance ; (3) of the effort necessary to enunciate them ; and (4) to write their symbols. These memory pictures are closely related to each other by associ- ation fibres passing between their centres. Aphasia. 2 Agraphia. 3 Word-deaf ness. 4 Word-blindness CHAP. XIX] THE NERVOUS SYSTEM 421 Association areas.. The motor and sense areas previously outlined form, so to speak, small islands which are surrounded on all sides by cerebral tissue in which as yet no definite functions have been localized. These unknown regions are designated as association areas and are supposed to be set aside for the medi- ation of the various mental activities. The different sensory im- pressions are here moulded into complex perceptions and concepts and are then brought into relation with the motor organs. In a general way it may be said that the cerebrum is the seat of associations the sum total of which constitutes our psychic life. In the absence of this organ, any animal must cease to be an as- sociation or reaction animal and must become a reflex animal. In other words, all its actions are then removed from volition, in fact, from consciousness. All responses that depend upon memory of acquired and inherited experience have been destroyed. THE CRANIAL NERVES The cranial nerves consist of twelve pairs. They each have a superficial and a deep origin. The superficial origin is the point where they emerge from the under surface of the cerebrum and the medulla, but they can be traced back to various centres in the higher part of the brain, and these centres constitute their deep origin. Classification. The cranial nerves are of three varieties : (1) sensory nerves, (2) motor nerves, and (3) mixed nerves or those containing both sensory and motor fibres. Many of the cranial nerves arise from several nerve centres, and therefore con- sist of several bundles of nerve-fibres. After these nerves leave the cranium they split up into branches that are widely distributed. Numbers and names. They are named numerically according to the order in which they arise from the brain, and also by names which describe their nature, function, or distribution. The fol- lowing doggerel may assist the beginner in learning the order of the cranial nerves. Each capital letter denotes a cranial nerve. "On Old Manhattan's Peaked Tops, A Finn And German Picked Some Hops/' (1) The olfactory nerve is the special nerve of the sense of smell. Its origin is in the olfactory bulb, and its peripheral fibres are distributed to the upper third of the nasal cavity. 422 ANATOMY AND PHYSIOLOGY [CHAP. XIX (2) The optic nerve is the special nerve of the sense of sight. Its cell-bodies are situated in the retinal coat of the eye. (3) The motor oculi nerve supplies all the muscles of the eye except the superior oblique and the external rectus. It originates in the gray matter of the pons Varolii. (4) The pathetic, or trochlear, nerve supplies only the superior oblique muscle of the eye. It arises close to the preceding nerve. (5) The trifacial has two roots, a dorsal, or sensory, and a ventral, or motor. The fibres from the two roots coalesce into one trunk, and then subdivide into three large branches : (1) the oph- thalmic, (2) the superior maxillary, and (3) the inferior maxillary. The ophthalmic branch is the smallest, and is a sensory nerve. It supplies the eyeball, the lacrimal gland, the mucous lining of the eye and nose, and the skin and muscles of the eyebrow, forehead, and nose. The superior maxillary, the second division of the fifth, is also a sensory nerve, and supplies the skin of the temple and cheek, the upper teeth, and the mucous lining of the mouth and pharynx. The inferior maxillary is the largest of the three di- visions of the fifth, and is both a sensory and a motor nerve. It sends branches to the temple and the external ear ; to the teeth and lower jaw ; to the muscles of mastication ; it also supplies the tongue with the special nerve (lingual) of the sense of taste. The cell-bodies of the motor fibres are situated in the pons ; while those of the sensory fibres, as in the case of the spinal nerves, are situ- ated in a ganglion. This ganglion is called the Gasserian ganglion. (6) The abducens nerve supplies the external rectus muscle of the eye. (7) The facial nerve is the motor nerve of all the muscles of expression in the face ; it also supplies the neck and ear. Its cells of origin, like those of the abducens nerve, are situated in the medulla. (8) The auditory nerve is the special nerve of the sense of hear- ing. It arises from cells which compose the organ of Corti in the internal ear, to which its fibres are exclusively distributed. (9) The glossopharyngeal nerve is distributed, as its name indicates, to the tongue and pharynx, being the special nerve of taste to part of the tongue, the nerve of sensation to the mucous membrane of the pharynx, and of motion to the pharyngeal muscles. CHAP. XIX] SUMMARY 423 (10) The pneumogastric or vagus nerve has a more extensive distribution than any of the other cranial nerves, passing through the neck and thorax to the upper part of the abdomen. It con- tains both motor and sensory fibres. It supplies the organs of voice and respiration with motor and sensory filaments ; and the pharynx, oesophagus, stomach, and heart with motor fibres (car- diac inhibitory). (11) The spinal-accessory nerve consists of two parts : one, the spinal portion, and the other, the accessory portion to the tenth nerve. It is a motor nerve supplying certain muscles of the neck. It differs from the other cranial nerves in arising from the spinal cord, but it leaves the skull by the same aperture as the pneumo- gastric and glossopharyngeal. (12) The hypoglossal nerve is the motor nerve of the tongue. Functions of the nervous system. The various systems of the body function together harmoniously and in such a way that the individual responds properly to his environment. The inter- pretation of environmental conditions and the adaptive responses of the organism as a whole to these conditions, is carried out by the nervous system. It enables us to think and to will, to recog- nize our surroundings and to accommodate ourselves to them; to move, to talk, to hear, to see; and it guarantees equilibrium and muscular coordination. In short, it makes possible all the higher functions of human life. SUMMARY f The nervous system may be reduced to a simple unit called a Neurone * , * I neurone. The neurone may be regarded as the building [ stone of the nervous system. f Nervous activity of all kinds may be reduced to reflex action. { The reflex circuit forms the functional basis of all nervous Concept [ activity. ~ . , f Receptor or sensory. 1. Consists of two neurones i ^^ I Effector or motor. Types of u 1 J Sensory or receptor. 2. Consists of three neurones \ Central or correlation. Circuits LIT i /* [ Motor or effector. 3. Consists of complexes of above. 424 ANATOMY AND PHYSIOLOGY [CHAP. XIX Synapse Interlacing of the fine branches of the axone of one neurone, with the branches of a dendrite of another neurone. Not an anatomical continuation. Nerve-impulses are able to bridge the microscopic gap. Reaction f When cells in the volitional centres in the cerebrum enter into Circuit 1 the reflex circuit, it is spoken of as a reaction circuit. Classifi- cation of Reflexes Nature and Speed of Nerve Impulses Nerve- endings Simple. Complex. Spreading. Tonic or continuous. Clonic or periodic. Association or perception. Nature not positively known. Presumably a physical molecular vibration. Identical in character, vary only in intensity. Speed is about 100 to 140 ft. per second. f Not all affected by the same stimuli. 1 Special end organs to mediate each sense. Gray matter Grouping of Neurones White matter Cell-bodies. Consists of Found in Found in Dendrites. Commencement of axones. Brain. Spinal cord. Ganglia. Consists of medullated nerves. Brain. Spinal cord. Ganglia. Nerve-trunks. Sympathetic System Nervous System Central Nervous System 1. Vertebral ganglia. 2. Collateral ganglia. 3. Terminal ganglia and plexuses. 4. Sympathetic ganglia in the brain and cord. 5. Sympathetic nerves. 1. Spinal cord and spinal nerves. Medulla Oblongata. Cerebellum. Pons Varolii. Cerebrum. 3. Cranial nerves. 2. Brain CHAP. XIX] SUMMARY 425 Distribu- tion of Sympa- thetic Nerves Chain of ganglia situated on either side of spinal Cervical 3 prs. Thoracic 10-12 prs. Lumbar 4 prs. Sacral 4-5 prs. 1. With each other by ganglia cords. 2. With spinal nerves by rami com- municantes. a. Pass directly to viscera. Great splanchnic. 6. Converge , Small 3. With to form | splanchnic, viscera I Least splanchnic. c. Join collaterals and plexuses. d. Join spinal nerves. >rincipally in thoracic and abdominal With spinal nerves. With vertebral ganglia. With viscera. Cardiac plexus. Solar plexus. Hypogastric or pelvic plexus. Terminal f Located on walls of organs themselves. Ganglia { Connected with collateral ganglia. Sympathetic Ganglia are found in the medulla, spinal cord, and in connection with some of the cranial nerves. Sympathetic Nerves. To the heart. To the involuntary muscles of the blood-vessels, lymphatics, and viscera. To the secretory glands. [ To some of the special senses. Chain of { column. Grouped as Vertebral Ganglia Con- nected Sympa- thetic System Located p cavities. Collateral Ganglia Con- nected Form Function and interde- pendence of Sym- pathetic System Regulatory control over visceral activities. The term autonomic applied to functional activities of sym- pathetic system. Sympathetic and central nervous system are interdependent both anatomically and physiologically. 426 ANATOMY AND PHYSIOLOGY [CHAP. XIX Spinal Cord Spinal Nerves Brain Located in spinal canal. Extends from foramen magnum to second lumbar vertebra. Varies in length from 16 to 20 inches. Gray matter in form of H. Anterior. White matter in funiculi Consists of Posterior. Lateral. Fissures I Ventral divides front portion in lateral halves. 1 Dorsal divides back portion in lateral halves. Isthmus connects lateral halves. Canal centre of isthmus. Pia mater inner membrane, closely invests spinal cord. Subarachnoid space. Membranes { Arachnoid middle membrane. Subdural space. Dura mater outer membrane. Epidural space. 1. Conduction. 2. Reflex action. Functions < 3. Automatism. 4. Inhibition. 5. Transference. Number Variety Cervical 8 pairs. Thoracic 12 pairs. Lumbar 5 pairs. Sacral 5 pairs. Coccygeal 1 pair. 31 pairs. Medullated. , T . , f Sensory. Mixed < . , , J I Motor. Origin two roots Distribution two trunks / Ventral in gray matter of cord. \ Dorsal in spinal ganglia. Ventral, supplies extremities, and parts of body in front of spine. Dorsal, supplies muscles and skin of back of head, neck, and trunk. Located in cranial cavity. Covered by meninges same as spinal cord. f Medulla Oblongata. Cerebellum. DiYinon. { pons Varoli . Cerebrum. CHAP. XIX] SUMMARY 427 Cerebro- spinal Fluid Found in meningeal spaces of brain and cord, central canal of cord, and ventricles of the brain. Thin, watery fluid formed from blood. Specific gravity 1.007 to 1,008. Amount is about 60 to 80 cc. Medulla Oblon- gata Description Function Oblong-shaped mass, upward continuation of cord. Gray matter in interior. White matter on exterior. Conduction. Reflex action. Automatism. Respiratory centre. Accelerator centre for heart. Vasomotor centres and others. Cerebellum Pons Varolii Description Function Cerebrum Flat oblong-shaped mass, overhangs medulla. 3-4| in. transversely. 2-2| in. from before backward. Gray matter on exterior. White matter in interior. f Coordination. \ Maintenance of equilibrium. A bridge of nerve-fibres connecting two halves of cerebel- lum and also medulla with cerebrum. Egg-shaped or ovoidal. Fills upper portion of skull. f Fissures. Gray matter \ , . , . , \ Sulci. on outside I ~. , A . I Convolutions. White matter on inside. Great longitudinal fissure. Transverse fissure. Rolandic. Sylvian. Parieto-occipital . Frontal. Parietal. Occipital. Temporal. Central, or Island of Reil. Fourth ventricle. Third ventricle. Lateral ventricles (two). Fifth ventricle. Description Fissures Lobes Ventricles 428 ANATOMY AND PHYSIOLOGY [CHAP. XIX Cerebrum Function Governs all our mental activities Names of Areas Reason. Intelligence. Will. Memory. Higher emotions. Movement and coordination of same- Motor area in front of Fissure of Rolando. Visual occipital lobe. Auditory superior part of the temporal lobe. Sense areas \ anterior part of temporal lobe. Gustatory J Cranial Nerves Association areas cerebral tissue surrounding motor and sense areas, in which as yet no definite functions have been localized. I. Olfactory. II.. Optic. III. Motor oculi. IV. Pathetic. V. Trifacial. VI. Abducens. VII. FaciaL """" VIII. Auditory. IX. Glossopharyngeal. X. Pneumogastric. XI. Spinal accessory. XII. Hypoglossal. Functions of the Nervous System Interpretation of environmental conditions and adap- tive responses of the organism as a whole; makes possible all the higher functions of human life. CHAPTER XX INTERNAL AND EXTERNAL SENSES: TASTE, SMELL, HEARING, AND SIGHT THE sensory nerves which we have discussed in the previous chapter have their peripheral endings in receptors or sensory end organs. These receptors receive stimuli, transform these stimuli to nerve-impulses and pass them on to the nerves which carry them to centres in the central nervous system for interpretation or for linkage with motor nerves. Sense-organ. A typical sense-organ or sensory unit consists of (1) a peripheral end organ or receptor which in most cases is constructed so as to be responsive only to a special form of stimu- lus, (2) connecting neurones whose only function is to conduct the nerve-impulses originating in the end organ, and (3) a centre in the nervous system which interprets and determines the quality of the sensation. In this connection physiologists use the phrase specific nerve energy to designate the fact that each sense- organ arouses its own specific quality of sensation, and no other. For example, the specific energy of the optic apparatus is visual sensation, and of the auditory apparatus is sound sensation. The view generally adopted is that this specificity is not due to the end organs or conducting nerves, but to the centre in the brain. Definition of sensation. Sensation is defined as perception through the sense-organs, and is the result of stimulation of these organs. The sensitiveness of the numerous receptors to stimula- tion varies; some respond to a very mild stimulus, e.g., in some parts of the body the slightest pressure will arouse a sensation while a similar degree of pressure in another part may fail to pro- duce any sensation at all. The minimal stimulus necessary to arouse a sensation in any receptor is described as the threshold stimulus for that organ. 429 430 ANATOMY AND PHYSIOLOGY [CHAP. XX Where sensations are interpreted. Sensations are felt and interpreted in the brain. Our habit of projecting sensations to the part that is stimulated, tends to obscure this fact. In reality we see and hear with our brains, because the eye and ear serve only as end organs to receive the stimulus which must be carried to the brain and interpreted before we do see or hear. CLASSIFICATION OF SENSATIONS Sensations were formerly classified into two groups, i.e., special and common. The special senses were sight, hearing, touch, taste, and smell. All other sensations were grouped as common. A more recent classification is dependent on the part of the body to which the sensation is projected, and the two groups are named : (1) internal or interior senses, and (2) external or exterior senses. These classifications have much in common, but differ slightly. Internal or interior senses. The internal senses are those in which the sensations are projected to the interior of the body. It is by means of these senses that we acquire a knowledge of the condition of our body. Among the interior senses we must include pain, the sensations from the semicircular canals and vestibule of the internal ear, hunger, thirst, sexual sense, muscle sense, fatigue, and various obscure sensations which proceed from the viscera and give us the feeling of well-being or the reverse, also the desire for defecation or urination. External or exterior senses. The external senses are those in which the sensations are projected to the exterior of the body. They form the means by which we become acquainted with the outside world. They include pressure and temperature sense, (heat and cold), taste, smell, hearing, and sight. Even this classi- fication is not absolutely distinctive, as some sensations may be projected either to the interior or exterior of the body. Tem- perature and pain are examples of this class. Cutaneous sensation. Modern physiology teaches that the sensory nerves of the skin mediate four different qualities of sensation, i.e., pressure, cold, heat, and pain. As a result the sur- face of the skin is a mosaic of tiny sensory spots separated by rela- tively wide intervals. Each spot coincides with the location of some special end organ and serves a specific sense. These various CHAP. XX] INTERNAL AND EXTERNAL SENSES 431 spots are placed either singly or in clusters. In some loca- tions one variety predominates, in others another. It is a matter of common knowledge that the sensitiveness of these va- rieties of cutaneous sensation differs in different parts of the body, e.g., the tip of the finger is more sensitive to pressure or contact than to alterations of temperature. The hot and cold spots and FIG. 205. DIAGRAM OF COURSE OF CUTANEOUS FIBRES ON REACHING THE CORD, (Dawson.) the pressure points can be located by passing a metallic point slowly over the skin. At certain points a feeling of contact or pressure will be experienced, and at other points a feeling of cold or heat, depending on whether the temperature of the instrument is higher or lower than that of the skin. Classification of cutaneous sensations. It has recently been suggested that the cutaneous senses be classified on the basis of the loss of sensation after division of the cutaneous nerves and the subsequent, gradual, and separate return of these sensations, after suture of the divided ends. It has been found that the skin 432 ANATOMY AND PHYSIOLOGY [CHAP. XX is supplied with two sets of nerve-fibres which regenerate at dif- ferent times and these are named respectively protopathic and epicritic. The protopathic group comprises three qualities of sensation, i.e., (1) pain, (2) heat above 37 C., and (3) cold below 26 C. This system conveys sensations of pain and of extreme changes of temperature but the sensibility is low and the locali- zation poor. It is found in the viscera and from a functional standpoint may be considered as a defensive agency toward pathologic changes. The epicritic group contains separate fibres for heat, cold, light pressures, and tactile discriminations which give us sensations of (1) light touch and (2) small differences of temperature between 26 C. and 37 C., i.e., the range of tempera- ture to which the temperature nerves of the protopathic system are insensitive. This group constitutes the special characteristic of the skin area and is not found in other organs. In addition to the protopathic fibres the deeper tissues are sup- plied with fibres which give us a sense of pressure, and in the case of the muscles and joints, with fibres which give us a knowledge of the position of the movable parts of the body. The paths which these various fibres take in their journey through the central ner- vous system may be studied in Fig. 205. Pain. It is probable that pain is the most widely distributed sense in the body. It is present throughout the skin and may be aroused by stimulation of the sensory nerves in the various viscera and membranes of. the body. Our knowledge of the physiological properties of the end organs and nerves mediating this sense is limited to the skin. There is much evidence to support the view that for cutaneous pain there exists a special set of fibres which have a specific energy for pain. The pain points in the skin are more numerous than the pressure points and their sensitiveness varies, e.g., the threshold stimulus for the cornea is lower than in the case of the finger tips. Referred pains. Normally we are able to localize pain arising in the skin, accurately. On the contrary, pain arising in the vis- cera is often located very inaccurately and referred to an entirely wrong place. The explanation of this misreference is that the pain is referred to, or appears to come from, the skin region that is supplied with sensory fibres from the same spinal segment that supplies the organ in question, and is due to a diffusion in the nerve centres. CHAP. XX] INTERNAL AND EXTERNAL SENSES 433 Muscle sense. The end organs of the muscle sense are situated in the tendons and between the fibres of the muscles. From these end organs afferent fibres carry impulses to centres in the brain, which send out impulses along efferent fibres to the muscles. There is thus a circle of nerves between the brain and the muscles, one nerve giving the sense of the condition of the muscle to the brain, and another carrying the impulse from the brain to the muscle. This gives us a certain consciousness of the condition of our muscles at all times, and enables us to coordinate the contractions of harmonious groups in order to produce volun- tary movements. Hunger. Hunger occurs normally at a certain time after meals and is usually projected to the region of the stomach. It is presumably due to contractions of the empty stomach, which stimulate the nerves distributed to the mucous membrane. In abnormal conditions, e.g., severe illness and extreme fatigue these periodic contractions may be weaker than usual, or may not occur at all. Thirst. This sensation is projected to the pharynx. We know very little about the nervous mechanism involved, but it is thought that when the water content in the tissues falls below a certain amount, the sensory nerve-fibres in the pharynx are stimu- lated and produce the sensation of thirst. TASTE Necessary conditions. Aside from the conditions which are always necessary for sense-perception, viz. proper organs for receiving, communicating, and perceiving the sensory impulse, there must be present a sapid substance which must be in solu- tion. The solution in the case of dry substances is effected by saliva. It is also necessary that the surface of the organs of taste shall be moist. The substances which excite the special sensa- tion of taste, act by producing a change in the terminal filaments of the fifth, seventh, and ninth nerves and this change furnishes the required stimulant. Organs of taste. The special organs of the sense of taste are end organs of nerve filaments which are derived from the trifacial, facial, and glossopharyngeal nerves. These end organs are called taste buds and are situated chiefly on the surface of the tongue, 2F 434 ANATOMY AND PHYSIOLOGY [CHAP. XX though some are scattered over the soft palate, fauces, epiglottis, and even the vocal cords. The tongue. The tongue is a freely movable muscular organ consisting of two distinct halves united in the centre. The base or root of the tongue is directed backward and is attached to the hyoid bone by numerous muscles. It is connected with the epi- glottis by three folds of mucous membrane, and with the soft palate by means of the anterior pillars of the fauces. MUCOUS GLANDS MUCOUS FILIFORM PAPILLAE FUNGIFORM PAPILLAE FIG. 206. THE UPPER SURFACE OF THE TONGUE. (Sappey.) Papilla of the tongue. The tongue is covered and lined with mucous membrane. The mucous membrane on the under surface is similar to that lining the rest of the mouth, but the mucous membrane on the upper surface is studded with papillae which pro- ject as minute prominences and "give the tongue its characteristic rough appearance. Of these papillae there are three varieties : (1) Circumvallate (walled in) papillae are the largest, are circu- lar in shape, and form a V-shaped row near the root of the tongue, with the open angle of the V turned toward the lips. They serve to secrete mucus and contain taste buds in which the filaments of the glossopharyngeal nerve terminate. CHAP. XX] INTERNAL AND EXTERNAL SENSES 435 (2) Fungiform papillae are the next in size, and are so named because they resemble fungi in shape. They are found principally on the tip and sides of the tongue. Each fungiform papilla? con- tains a loop of capillaries and a nerve-fibre derived from the glosso- pharyngeal nerve. (3) Filiform papillae are the smallest and most numerous. They are found 'all over the tongue, except at the root, and bear on their free surface delicate hair-like processes which seem to be specially connected with the sense of touch, which is very highly developed on the tip of the tongue. Nerve supply of the tongue. The nerve-fibres which terminate in the taste buds are : (1) filaments of the lingual nerve, which is a branch of the fifth or trif acial, (2) filaments of the chorda tympani, a branch of the seventh or facial, and (3) filaments of the ninth or glossopharyngeal nerve. 1 The twelfth or hypoglossal nerve is distributed to the tongue, but is a motor nerve and is not con- cerned in the sense of taste or touch. Other sensations in the tongue. The sense of touch is very highly developed here, and with it the sense of temperature, pain, etc. Upon these tactile and muscular senses to a great extent depend the accuracy of the tongue in many of its important uses speech, mastication, deglutition, sucking. We often confound taste with smell. Substances which have a strong odor, such as onions, are smelled as we hold them in our mouths ; and if our sense of smell is temporarily suspended, as it sometimes is by a bad cold in the head, we may eat garlic and onions and not taste them. Hence the practice of holding the nose when we wish to swallow a nauseous dose. SMELL Necessary conditions. The first essentials are a special nerve and nerve-centre, the changes in whose condition are perceived as sensations of odor. No other nerve structure is capable of such sensations, even when acted on by the same cause. The special organs for this sense must be in their normal condition, and a stimulus (odor) must be present to excite them. Odors are caused either by minute particles of solid matter or 1 This is the generally accepted view, but other statements may be found in the various text-books. 436 ANATOMY AND PHYSIOLOGY [CHAP. XX by gases which are in the atmosphere, and they must be capable of solution in the mucus of the pituitary 1 membrane. Odorous particles in the air, passing through the lower, wider air passages, pass by diffusion into the higher, narrower, nasal chambers, and falling on the membrane which is provided with olfactory nerve-endings, produce sensory impulses which, ascending to the brain, give rise to the sensation of smell. If we wish to smell anything particularly well, we sniff the air up into the higher nasal chambers, and thus bring the odorous particles more closely into contact with the olfactory nerves. OLFACTORY NERVE BRANCH OF FIFTH NERVE MIDDLE TURBINATE INFERIOR TURBINATE HARD PALATE FIG. 207. VERTICAL LONGITUDINAL SECTION OF NASAL CAVITY. Each substance we smell causes its own particular sensation, and we are not only able to recognize a multitude of distinct odors, but also to distinguish individual odors in a mixed smell. The sensation takes some time to develop, after the contact of the odorous stimulus, and may last a long time. When the stim- ulus is repeated, the sensation very soon dies out, the sensory terminal organs quickly becoming exhausted. 2 Olfactory nerves. The olfactory nerves are the special nerves of the sense of smell, and are spread out in a fine network over 1 This name is given to the membrane that lines the nasal passages. 2 This accounts for the fact that one may easily become accustomed to foul odors, and is of special importance to nurses. Foul odors are quickly noticed by any one coming into a sick room from out of doors, but a nurse who is in the sick room constantly may become accustomed to such odors. Hence the importance of act- ing on the first sensation of a disagreeable odor. CHAP. XX] INTERNAL AND EXTERNAL SENSES 43* the surface of the superior turbinated processes of the ethmoid bone and on the upper third of the septum. The nerves end in special organs known as olfactory cells, which lie under the epithe- lium, but send prolongations between the mucous cells to the sur- face. The central portions of the olfactory cells are prolonged as nerve-fibres into a mass of gray matter, called the olfactory bulb, which rests upon the cribriform plate of the ethmoid bone. The nerves which ramify over the lower part of the lining membrane of the nasal cavity are branches of the fifth or tri- geminal nerve. These nerves furnish the tactile sense and enable us to perceive, by the nose, the sensations of cold, heat, tickling, pain, and tension or pressure. It is this nerve which is affected by strong irritants, such as ammonia or pepper. HEARING The auditory apparatus consists of : (1) the external ear ; (2) the middle ear ; (3) the internal ear ; and (4) the auditory nerve. External ear. The external ear consists of an expanded por- tion named pinna, or auricle, and the auditory canal, or meatus. The auricle, except the lower portion, consists of a frame- work of cartilage, containing some fatty tissue and a few muscles. In the lower portion, which is called the lobe, the cartilage is replaced by connective tissue. The auricle is covered with skin, and joined to the surrounding parts by ligaments and a few muscles. It is very irregular in shape, and appears to be an unnecessary appendage to the organ of hearing, except that the central depres- sion, the concha, serves to some extent to collect sound-waves, and to conduct them into the auditory canal. The auditory canal is a tubular passage, about an inch (2.5 cm.) in length, leading from the concha to the drum-membrane. The exterior portion of the wall of the auditory canal consists of carti- lage, which is continuous with that of the auricle; the posterior portion is hollowed out of the temporal bone. This canal is slightly curved upon itself so as to be higher in the middle than at either end, and its direction is forward and inward. Lifting the auricle upward and backward tends to straighten the canal ; except in the case of children it is best straightened by drawing the auricle downward and backward. It is lined by a prolongation of the skin, which in the outer half of the canal is very thick and not at 438 ANATOMY AND PHYSIOLOGY [CHAP. XX all sensitive, and in the inner half is thin and highly sensitive. Near the orifice the skin is furnished with a few hairs, and far- ther inward with modified sweat-glands, the ceruminous glands, which secrete a yellow, pasty substance resembling wax. This wax is thought to be offensive to insects, and consequently a de- fence against their intrusion. FIG. 208. SEMI-DIAGRAMMATIC SECTION THROUGH THE RIGHT EAR. M , concha ; G, the external auditory canal ; T, tympanic, or drum-membrane ; P, tympanum, or middle ear ; o, oval window ; r, round window. Extending from T to o is seen the chain of the tympanic bones ; R, Eustachian tube ; V, B, S, bony labyrinth ; V, vestibule ; B, semicircular canal ; S, cochlea ; b, I, v, membranous labyrinth in semicircular canal and in vestibule. A, auditory nerve dividing into branches for vestibule, semicircular canal, and cochlea, Middle ear. The middle ear, or tympanum, is a small, ir- regular bony cavity, situated in the petrous portion of the tem- poral bone, and lined with mucous membrane. It is separated from the external auditory canal by the drum-membrane (mem- brana tympani), and from the internal ear by a very thin, bony wall in which there are two small openings covered with mem- brane the oval window, or fenestra ovalis, and the round win- dow, or fenestra rotunda. The cavity of the middle ear is so small that probably five or six drops of water would completely fill it. CHAP. XX] INTERNAL AND EXTERNAL SENSES 439 It communicates below with the pharynx by the small passage called the Eustachian tube. 1 The function of the tube is to ventilate this cavity and keep the atmospheric pressure equal on each side of the drum-membrane. The middle ear also communicates with a number of bony cavities in the mastoid portion of the temporal bone. These cavities, called mastoid cells, are lined with mucous membrane, which is continuous with that covering the cavity of the tympa- num. Membrana tympani (membrane of the drum) . It is a tough, fibrous membrane set in the bony opening of the external audi- MALLEUS HORT PROCESS OF INCUS LONG PROCESS OF INCUS TMALLEUS LONG PROCESS HANDLE STAPES STAPES OF MALLEUS OF MALLEUS FIG. 209. OSSICLES OF THE TYMPANUM, X 4. (Flint.) tory canal. The degree of tension of the membrane is regulated by the tensor tympani muscle. This muscle is lodged in a bony canal that is above and parallel with the Eustachian tube. Ossicles.^ Stretching across .the tympanic cavity is a chain of tiny, movable bones, three in number, and named from their shape the malleus, or hammer, the incus, or anvil, and the stapes, or stirrup. The handle of the hammer is attached to the drum- membrane, and the opposite end or head of the hammer is at- tached to the base of the anvil. The long process of the anvil is attached to the stapes, and the footpiece of the stapes is attached to the fibrous membrane that is stretched across the oval window. 1 This direct connection between the ear and the pharynx is one of the important reasons for the frequent cleansing of the mouth necessary in infectious diseases. The Eustachian tube forms a passageway for germs to travel from the mouth to the middle ear and there cause various infections. 440 ANATOMY AND PHYSIOLOGY [CHAP. XX These little bones are held in position, attached to the drum-mem- brane, to each other, and to the membrane of the oval window by minute ligaments and muscles. They are set in motion with every movement of the drum-membrane. Vibrations of the mem- brane are communicated to the hammer, taken up by the anvil, and transmitted to the stirrup, which rocks in the fenestra ovalis, and is therefore capable of transmitting to the fluid in the cavity of the labyrinth the impulses which it receives. Internal ear. The internal ear, or labyrinth, receives the ulti- mate terminations of the auditory nerve, and is, therefore, the essential part of the organ of hearing. It consists of a bony labyrinth, which is composed of a series of peculiarly shaped cavities, hollowed out of the petrous portion of the temporal bone, and named from their shape : (a) The vestibule. (6) The semicircular canals. (c) The cochlea (snail-shell). Within the bony labyrinth is a membranous labyrinth, having the same general form as the cavities in which it is contained though considerably smaller, being separated from the bony walls by a quantity of fluid called the perilymph. It does not float loosely in this liquid because in some places it is attached to the bone by bands of fibrous tissue. The cavity within the membrane is filled with a fluid called endolymph. The vestibule is the central cavity situated between the cochlea in front and the semicircular canals behind. It communicates with the middle ear by means of the oval window in its outer wall. The vestibular membrane does hot conform to the shape of the bony cavity but consists of two small sacs, called respectively the saccule and the utricle. The saccule is in front and nearer the cochlea, and the utricle is back and nearer the semicircular canals. These sacs are connected by a tube called the endolymph duct, which is shaped like a Y. The walls of these sacs contain nu- merous columnar cells provided with stiff hairs which project into the endolymph. These cells are in relation with fibres of the ves- tibular branch of the auditory nerve and serve as end organs. Among these hair-cells rest several small crystals of calcium car- bonate which are called otoliths. CHAP. XX] INTERNAL AND EXTERNAL SENSES 441 The cochlea opens from the front end of the vestibule and sac- cule. It resembles a snail-shell and consists of a spiral tube of two and one-half turns around a central pillar called the modiolus. Projecting from the modiolus is a thin lamina or plate of bone. At its outer margin this lamina connects with a membrane which extends to the outer wall of the cochlea. This lamina and mem- brane divide the spiral canal into two passages or scalse. The lower portion of this membrane is called the basilar membrane FIG. 210. THE LEFT BONY LABYRINTH OF A NEW-BORN CHILD, FORWARD AND OUTWARD VIEW, X 4. 1, the wide canal, the beginning of the spiral canal of the cochlea ; 2, the fenestra rotunda ; 3, the second turn of the cochlea ; 4, the final half-turn of the cochlea ; 5, the border of the bony wall of the vestibule, situated between the cochlea and the semicircular canals ; 6, the superior, or sagittal semicircular canal ; 7, the portion of the semicircular canal bent outward ; 8, the posterior, or transverse semicircular canal ; 9, the portion of the posterior connected with the superior semi- circular canal ; 10, point of junction of the superior and the posterior semicircular canals ; 11, the ampulla ossea externa ; 12, the horizontal, or external semicircular canal. (Flint.) and consists of a network of fibres which forms the foundation for thousands of cells which serve as the end organs of the auditory nerve. These end organs constitute a structure that is known as the organ of Corti. They receive nerve-fibres which arise in the ganglia contained in the cavity of the modiolus. Both the modio- lus and lamina are pierced by numerous openings for the passage of these nerves. The semicircular canals are three bony canals lying above and behind the vestibule, and communicating with it by five openings, in one of which two tubes join. They are known as the posterior, 442 ANATOMY AND PHYSIOLOGY [CHAP. XX vertical, and horizontal canals, and their position is such that each one is at right angles to the other two. One end of each tube is enlarged and forms what is known as the ampulla. The membrane of the ampulla is covered with cells that are similar to those found in the utricle and saccule. These hair-cells serve as end organs for the vestibular branch of the auditory nerve. The auditory nerve. The eighth or auditory nerve is a sensory nerve and contains two distinct sets of fibres, which differ in their function, origin, and destination. One set of fibres is known as the cochlear division and the other as the vestibular. The fibres of the cochlear nerve arise from bipolar cells that are situated in the modiolus of the cochlea. One axone frem each cell passes through the foramina of the modiolus or lamina, and terminates in and around the cells that constitute the organ of Corti. The other axone passes through the internal auditory meatus to a portion of the brain, called the cochlear root of the auditory nerve. This root is located at the lower edge of the pons Varolii. The nerve-fibres which pass from the ear to the pons or from the pons to the ear are not continuous strands, as there are several relays of ganglia in which the axones of one cell inter- lock with the dendrites of another cell. The fibres of the vestibular nerve have their origin in the gray matter of the pons Varolii. Some of these fibres extend to the cerebellum and to motor centres of the spinal nerves. Other fibres extend to the vestibule and are distributed around the hair- cells of the saccule, utricle, and the ampulla of the semicircular canals. Physiology of hearing. All bodies which produce sound are in a state of vibration, and communicate their vibrations to the air with which they are in contact. When these air-waves, set in motion by sonorous bodies, enter the external auditory canal, they set the drum-membrane vibrat- ing ; stretched membranes taking up vibrations from the air with great readiness. These vibrations are communicated to the chain of tiny bones stretched across the middle ear, and their oscilla- tions cause the membrane leading into the internal ear to be alternatively pushed in and drawn out ; the vibrations are in this way transmitted to the perilymph. The movements of the peri- lymph are transmitted to the basilar membrane, and set some of CHAP. XX] INTERNAL AND EXTERNAL SENSES 443 the strings in motion. In some unknown way these movements are transmitted to the hair-cells and through them to the nerve- fibres at their base. By means of the nerve-fibres the stimulus is conveyed to the brain and interpreted there, so that it is with the brain we hear. The sense of equilibrium. Among the various means (such as sight, touch, and muscular sense) whereby we are enabled to maintain our equilibrium, coordinate our movements, and become aware of our position in space, one of the most important is the action of the vestibule and semicircular canals. Though these structures are found in the inner ear and com- municate with the cochlea, it is now thought that they are not connected with the sense of hearing. Just how they perform their function is not known, but it is thought that move- ments of the head set up movements in the endolymph of the canal, and these act as a stimulus to the nerve- endings around the hair-cells. The canals are so arranged (Fig. 211) that any movement of the head causes an increase in the pressure of the endolymph in one ampulla, and a corresponding diminution in the ampulla of the parallel canal on the opposite side. Thus, a nodding of the head to the right would cause a flow of the endolymph from a to b in the right anterior vertical canal, but from &' to a' in the left poste- rior vertical canal. Hence the pressure upon the hairs is de- creased in a, but increased in a'. Such stimulations of the sen- sory hairs are transmitted by the dendrites of the vestibular nerve, through the cell-bodies of the vestibular ganglion and the axones of the auditory nerve, to the pons Varolii and thence to the cere- bellum. It is thought that the cerebellum is the centre in the brain which interprets and adjusts the impulses that arise from stimulation of the sensory nerves concerned with muscular sense. It is also the centre that interprets and adjusts impulses that arise from stimulation of the vestibular nerve-endings. From this it follows that the cerebellum controls equilibrium. FIG. 211. DIAGRAM SHOW- ING RELATIVE POSITION OF THE PLANES IN WHICH THE SEMI- CIRCULAR CANALS LIE. Rt., right ear; Lt., left ear; A.V., anterior vertical canal; P.V., posterior vertical canal; H., horizontal canal ; a, am- pulla of Rt. anterior vertical canal ; a', ampulla of Lt. pos- terior vertical canal. 444 ANATOMY AND PHYSIOLOGY [CHAP. XX SIGHT The visual apparatus consists of the eyeballs, the optic nerves, and the nerve centres in the brain. In addition to these essential organs, there are accessory organs which are necessary for the protection and functioning of the eyeball. Accessory organs of the eye. Under this heading we class : (1) eyebrows, (2) eyelids, (3) lacrimal apparatus, and (4) muscles of the eyeball. Eyebrows. The eyebrows are two thickened ridges of skin, covered with hairs. They are situated on the upper border of the orbits, and protect the eyes from too vivid light. Eyelids. The eyelids are two folds projecting from above and below in front of the eye. They are covered externally by the skin, and internally by a mucous membrane, the conjunctiva, which is reflected from them over the globe of the eye. They are composed for the most part of connective tissue, which is dense and fibrous under the conjunctiva, where it is known as the tar sal cartilage. Arranged in a double or triple row at the margin of the lids are the eyelashes; those of the upper lid more numerous and longer than those of the lower. The upper lid is attached to a small muscle which is called the elevator of the upper lid (levator palpebrce superioris) , and arranged as a sphincter around both lids is the orbicularis palpebrarum muscle, which closes the eye- lids. The slit between the edges of the lids is called the palpebral fissure. It is the size of this fissure which causes the appearance of large and small eyes, as the size of the lobe itself varies but little. The outer angle of this fissure is called the external can- thus; the inner angle, the internal canthus. The eyelids are obviously provided for the protection of the eye; movable shades which by their closure exclude light, par- ticles of dust, and other injurious substances. Tarsal glands (Meibomian glands) . Embedded in the tarsal cartilage of each eyelid is a row of elongated sebaceous glands, the tarsal * glands, the ducts of which open on the edge of 1 By everting the eyelids, these glands may be seen through the conjunctiva lying in parallel rows. CHAP. XX] INTERNAL AND EXTERNAL SENSES 445 the eyelid. The secretion of these glands prevents adhesion of the eyelids. Lacrimal apparatus. This apparatus consists of : (1) the lacrimal gland, (2) canaliculi, (3) lacrimal sac, and (4) nasal duct. The lacrimal gland is a compound gland, and is lodged in a de- pression at the upper and outer angle of the orbit. It consists of two portions, an upper portion about the size and shape of an almond, and a lower portion con- sisting of a group of small glands arranged in a row. These two portions are only partially separated by a fibrous septum. Seven to twelve minute ducts lead from the gland to the surface of the con- junctiva of the upper lid. The secretion (tears) is usually just enough to keep the eye moist, and after passing over the surface of the eyeball is sucked into two tiny canaliculi through the punctce and is conveyed into the lacriihal sac, which is the upper dilated portion of the nasal duct. The nasal duct is a membranous canal, about three-quarters of an inch (1.9 cm.) in length, which extends from the lacrimal sac to the nose, into which it opens, by a slightly expanded orifice. The tears consist of water containing a little salt and albumin. They are ordinarily carried away as fast as formed, but under certain circumstances, as when the conjunctiva is irritated, or when painful emotions arise in the mind, the secretion of the lacrimal gland exceeds the drainage power of the nasal duct, and the fluid, accumulating between the lids, at length overflows and runs down the cheeks. The conjunctiva. The conjunctiva is the mucous membrane which lines the eyelids and is reflected over the front of the eyeball. FIG. 212. THE LACRIMAL APPARATUS. (Note that preference is given to the spelling "lacrimal" as found in text, instead of "lachry- mal" as found on illustration.) 446 ANATOMY AND PHYSIOLOGY [CHAP. XX It is often considered part of the lacrimal apparatus as it secretes a fluid like that of the lacrimal gland. Muscles of the eye. For purposes of description the muscles of the eye are divided into two groups : (1) intrinsic, and (2) extrinsic. The intrinsic muscles are the ciliary muscle, and the muscles of the iris. 1 The extrinsic muscles are those which move the eyeball and include the four straight, or recti, and the two oblique. They have been described in Chapter VII. Nerves of the eye. The nerves which are supplied to the eye are : (1) the optic nerve, concerned with vision only ; (2) the motor oculi nerve which controls the internal rectus, the superior rectus, the inferior rectus, and the inferior oblique muscles ; (3) the pathetic nerve which controls the superior oblique muscle ; (4) the abducens which controls the external rectus ; and (5) the ophthal- mic, which is a branch of the trifacial nerve, supplies general sensation. The orbits. The orbits are the bony cavities in which the eyeballs are contained. Seven bones assist in the formation of each orbit, namely frontal, malar, maxilla, palate, ethmoid, sphenoid, and lacrimal. As three of these bones are mesial (frontal, ethmoid, and sphenoid) there are only eleven bones forming both orbits. The orbit is shaped like a four-sided pyramid ; the apex, directed backward and inward, is pierced by a large opening the optic foramen through which the optic nerve and the ophthalmic artery pass from the 'cranial cavity to the eye. A larger opening to the outer side of the optic foramen the sphenoidal fissure provides a passage for the ophthalmic vein and the nerves which carry impulses to and from the muscles, i.e., the motor oculi, the pathetic, the abducens, and the ophthalmic. The base of the orbit, directed outward and forward, forms a strong, bony edge for protecting the eyeball from injury. Each orbit averages about 2 inches (5 cm.) in depth, is lined with fibrous tissue, and contains a pad of fat, which serves as a support for the eyeball. A condition of emaciation is usually accompanied by sunken eyes, which results from the absorption of this fat, and the consequent sinking of the eyeballs in the orbits. Between the pad of fat and the eyeball is a serous sac the 1 See page 449. CHAP. XX] INTERNAL AND EXTERNAL SENSES 447 capsule of Tenon which envelops the eyeball from the optic nerve to the ciliary region and forms a socket in which the eyeball rotates. This sac secretes a lubricating fluid, the function of which is to prevent friction when the eyeball moves. The eyeball. The eyeball Is spherical in shape, but its trans- verse diameter is less than the antero-posterior, so that it projects SUPERIOR flECTUS CHOR010 OPTIC NERVE ORQIO -INFERIOR RTCTUS FIG. 213. DIAGRAMMATIC SECTION OF THE EYE. (Flint.) anteriorly, and looks as if a section of a smaller sphere had been engrafted on the front of it. The eyeball is composed of three coats, or tunics, and contains three refracting media or humors. They are as follows : Tunics. (1) Protective: (a) sclera; (6) cornea. (2) Vascular : (a) choroid ; (6) ciliary body ; (c) iris. (3) Visual : retina. Refracting media. (1) Aqueous. (2) Crystalline lens and capsule. (3) Vitreous. Protective tunics. (a) The sclera, or white of the eye, covers the posterior five-sixths of the eyeball. It is composed of a firm, unyielding, fibrous membrane, thicker behind than in front, and serves to protect the delicate structures contained within it, and maintain the shape of the eyeball. It is opaque ; white and 448 ANATOMY AND PHYSIOLOGY [CHAP. XX smooth externally, and behind is pierced by the optic nerve. In- ternally it is stained brown where it comes in contact with the choroid coat. It is supplied with very few blood-vessels, and the existence of nerves in it is doubtful. (6) The cornea covers the anterior sixth of the eyeball. It is directly continuous with the sclera, which, however, overlaps it slightly above and below, as a watch crystal is overlapped by the case into which it is fitted. The cornea, like the sclera, is composed of fibrous tissue, which is firm and unyielding, but, unlike the sclera, it has no color, and is perfectly transparent ; it has. been aptly termed the " window of the eye." The cornea is well sup- plied with nerves and lymph-spaces, but is destitute of blood-ves- sels, so that it is dependent on the lymph contained in the lymph- spaces for nutriment. Vascular tunics. (a) The choroid, or vascular coat of the eye, is a thin, dark brown membrane lining the inner surface of the sclera. It is composed of delicate connective tissue, the cells of which are large and filled with pigment, and it contains a close network of blood-vessels. The pigment cells and blood-vessels render this membrane dark and opaque, so that it darkens the chamber of the eye by preventing the reflection of light. It ex- tends to within a short distance of the cornea. (6) The ciliary body is located between the choroid and the iris, and contains the ciliary processes, and the ciliary muscle. Just behind the edge of the cornea, the choroid is folded inward and arranged in radiating folds, like a plaited ruffle, around the lens. There are about seventy of these folds, and they constitute the ciliary processes. They are well supplied with nerves and blood- vessels, and also support a muscle, the ciliary muscle. The fibres of this muscle arise from the sclera near the cornea, and extending backward are inserted into the outer surface of the ciliary pro- cesses and the choroid. The action of this muscle determines the position of the lens. (c) The iris (iris, rainbow) is a colored, fibro-muscular curtain hanging in front of the lens and behind the cornea. It is attached at its circumference to the ciliary processes, with which it is prac- tically continuous, and is also connected to the sclera and cornea at the point where they join one another. Except for this attach- ment at its circumference, it hangs free in the interior of the eye- CHAP. XX] INTERNAL AND EXTERNAL SENSES 449 ball. In the middle of the iris is a circular hole, the pupil, through which light is admitted into the eye chamber. The iris, like the choroid, is composed of connective tissue containing a large num- ber of pigment cells and numerous blood-vessels. It contains, in addition, two sets of muscles. One set is arranged like a sphincter with its fibres en- circling the pupil, and is called the contractor of the pupil. The other set consists of fibres which radiate from the pupil to the outer circumference of the iris, and is called the di- lator of the pupil. The action of these muscles is antagonistic. The posterior surface of the iris is covered by a thick layer of pigment cells designed to darken the curtain and pre- vent the entrance of Ught. The anterior surface of the iris is also covered with pigment cells, and it is chiefly these latter which cause the beautiful colors seen in the iris. The different colors of eyes, how- ever, are mainly due to the amount, and not to the color, of the pigment deposited. Function of the iris. The function of the iris is to regulate the amount of light entering the eye, and thus assist in obtaining clear images. It is enabled to perform this function by the action of the muscles described above, as their contraction or relaxation determines the size of the pupil. When the eye is accommodated 1 for a near object, or stimulated by a bright light, the sphincter muscle contracts and diminishes the size of the pupil. When, on the other hand, the eye is accommodated for a distant object, or the light is dim, the dilator muscle contracts, and the pupil is pulled wider open. 2 G l See page 453. FIG. 214. SEGMENT OF THE IRIS, CILIARY BODY, AND CHOROID. Viewed from the internal surface. (Gerrish.) 450 ANATOMY AND PHYSIOLOGY [CHAP. XX Visual tunic. The retina, the innermost coat of the eyeball, is the most essential part of the organ of sight, since it is the only one directly sensitive to light. It is a transparent membrane of a grayish color that is formed by the spreading out or expansion of the optic nerve. It is situated between the inner surface of the cho- roid and the outer sur- face of the vitreous humor, and extends from the entrance of the optic nerve forward to the margin of the pupil. The retina is usually described as consisting of eight layers and two limiting membranes ; of these layers, three are most important : Eighth layer, or layer of nerve-fibres, is the internal layer. Seventh layer is the layer of nerve-cells. First layer, or layer of rods and cones, is the external layer. (See Summary, page 461.) The fibres of the optic nerve, after piercing the sclera and choroid at the back of the eye, spread out and form the eighth, or innermost, layer of the retina. The fibres then pass, with more or less direct communications, peripherally through the other layers, until they may be said to terminate in the layer of rods and cones. Rays of light produce no effect upon the optic nerve without the intervention of the rods and cones, which act as end organs. Blind spot. The optic nerve pierces the eyeball not exactly at its most posterior point, but a little to the inner side. This point where the optic nerve enters is called the blind spot. There are no rods and cones at this spot, and rays of light falling upon it produce no sensation. FIG. 215. CHOROID MEMBRANE AND IRIS EXPOSED BY THE REMOVAL OF THE SCLERA AND CORNEA. Twice the natural size, d, one of the segments of the sclera thrown back ; I and k, iris ; c, ciliary nerves ; e, one of the veins of the choroid. The ciliary muscle is crossed by the line from k, and should be represented as radiating. (Collins.) CHAP. XX] INTERNAL AND EXTERNAL SENSES 451 Macula lutea. There is one point of the retina that is of great importance, and that is the macula lutea, or yellow spot. It is situated about one-twelfth inch (2.08 mm.) to the outer side of the exit of the optic nerve, and is the exact centre of the retina. In LAYER OF RODS AND CONES LAYER OF NERVE-CELLS LAYER OF NERVE-FIBRES FIG. 216. DIAGRAMMATIC SECTION OF THE HUMAN RETINA. its centre is a tiny pit, fovea centralis, which. is the centre of direct vision ; that is, it is the part of the retina which is al- ways turned towards the object looked at. From this point the sensitiveness of the retina grows less and less in all directions. At this point (fovea centralis) are found none of the fibres of the optic nerve, but a great increase in the number of cones, as well as in their size. Perception of light. It is commonly believed that all space is filled by ether, a medium so transparent and subtle that we are 452 ANATOMY AND PHYSIOLOGY [CHAP. XX not able to perceive it by any of our senses. Transverse vibrations or waves of this ether produce light, which enters the eye, falls upon the retina, and acts as a stimulus. It is supposed that waves of light cause chemical changes in the rods and cones which give rise to impulses that are carried by the optic nerve to the brain, and result in sight. Just how this is accomplished is not known, but the rods con- tain a kind of pigment which is called visual purple, and this as well as the pigment of the retina may function in these changes. The optic chiasm. The fact that the two retinae and the two eyeballs work in unison is largely due to the crossing of the nerve-fibres at the optic chiasm. The optic nerve from each eye passes backward through the optic foramen, and shortly after leaving the orbit the two nerves come together, and the fibres from the inner portion of each nerve cross. This is called the optic chiasm, and is really an incomplete crossing of fibres, as the outer fibres do not cross. (See Fig. 218.) Refracting media. (1) The aqueous humor is a colorless, transparent, watery fluid, which fills the aqueous chamber; the latter is the space bounded by the cornea in front and by the lens, suspensory liga- ment, and ciliary body be- hind. This space is partially divided by the iris into an anterior and posterior chamber. (2) The crystalline lens is a transparent, refractive body, with FIG. 217. THE POSTERIOR HALF OF THE RETINA OF THE LEFT EYE VIEWED FROM BEFORE. Twice its natural s.ize. , cut edge of the sclera ; ch, choroid ; r, retina ; in the interior at the middle, the macula lutea with the depression of the fovea centralis is represented by a slight oval shadow ; toward the left side the light spot indicates the entrance of the optic nerve or blind spot. (Collins.) Retina Optic nerve Optic chiasm Optic tract FIG. 218. DIAGRAM OF OPTIC CHIASM. CHAP. XX] INTERNAL AND EXTERNAL SENSES 453 convex anterior and posterior surfaces placed directly behind the pupil, where it is retained in position by the counterbalancing pres- sure of the aqueous humor in front, and the vitreous body behind, and by its own suspensory ligament from the hyaloid membrane. It is a fibrous body, enclosed in an elastic, non-vascular capsule. The posterior surface is considerably more curved than the an- terior, and the curvature of each varies with the period of life. In infancy, the lens is almost spherical ; in the adult, of medium con- vexity ; and in the aged, considerably flattened. Its refractive power is much greater than that of the aqueous or vitreous humor. (3) The vitreous humor, a semi-fluid, gelatinous substance, fills the posterior four-fifths of the globe of the eyeball. It is enclosed in a thin membrane the hyaloid membrane. This membrane is attached to the retina at the back of the eyeball, and furnishes a suspensory ligament to the lens. Elsewhere it is perfectly separable from its surroundings. The vitreous humor enclosed in this capsule distends the greater part of the sclera, supports the retina, which lies upon its surface, and preserves the spheroidal shape of the eyeball. Its refractive power, though slightly greater than that of the aqueous humor, does not differ much from that of water. Refraction. Refraction is the bending or deviation in the course of rays of light in passing obliquely from one transparent medium into another of different density. (See page 505.) The refractive apparatus. In order that our vision of objects looked at should be clear and distinct it is necessary that the rays of light entering the eye should be focussed on the retina. In the normal eye this is secured by the mechanism of accommoda- tion (see next paragraph). The refractive apparatus consists of the aqueous humor, the crystalline lens, and the vitreous humor, which have just been described. Accommodation. Accommodation is the ability of the eye to adjust itself so that it can see objects at varying distances. The theory most generally accepted is that the ciliary muscle is the active agent in accommodation. When the eye is at rest or fixed upon distant objects the suspensory ligament exerts a tension upon the lens which keeps it flattened, particularly the anterior surface to which it is attached. When the eye becomes fixed on near objects, as in reading, sewing, etc., the ciliary muscle contracts 454 ANATOMY AND PHYSIOLOGY [CHAP. XX and draws forward the choroid coat, which in turn releases the tension of the suspensory ligament upon the lens, and allows the anterior surface to become more convex. The accommodation for near objects is an active condition and is always more or less fatiguing. On the contrary, the accommodation for distant ob- jects is a passive condition, in consequence of which the eye rests for an indefinite time upon remote objects without fatigue. Common conditions that af- fect accommodation. The con- ditions that affect accommoda- tion are : (1) hypermetropia, (2) myopia, (3) presbyopia, and (4) astigmatism. Hypermetropia. Hyper- metropia or far-sightedness is a condition in which rays of light from near objects do not converge soon enough and are brought to a focus behind the retina. This IS Usually caused V a flattened condition of the lens or cornea, or an eyeball that is too shallow, and convex lenses 1 are used to concentrate and focus the rays more quickly. Myopia. Myopia or near-sightedness is a condition in which rays of light converge too soon, and are brought to a focus before reaching the retina. This is the opposite of hypermetropia and is caused by a cornea or lens that is too convex, or an eyeball of too great depth. To remedy this condition concave lenses are worn to disperse the rays and prevent their being focussed too soon. Presbyopia. Presbyopia is a defective condition of accom- modation in which distant objects are seen distinctly, but near objects are indistinct. This is a physiological process which af- fects every eye sooner or later, and is not due to disease. It is said to be caused by a loss of the elasticity of the lens. page 501. FIG. 219. DIAGRAM ILLUSTRATING RAYS or LIGHT CONVERGING IN (A) A CHAP. XX] SUMMARY 455 Astigmatism. Astigmatism is the condition in which the curva- ture of the cornea or lens is defective. An excess of curvature in the long axis of the cornea, as compared with that of its horizontal axis, is the more common defect. Glasses with curvatures the opposite of those of the eyes are used to correct this defect. Inversion of images. Due to refraction, light rays as they enter the eye cross each other and cause the image of external objects on the retina to be inverted. The question then arises, " Why is it that objects do not appear to us to be upside down? " This question is easily answered if we remember that our actual visual sensations take place in the brain, and that the projection of these sensations to the exterior is a secondary act that has been learned from experience. Sense-organ SUMMARY Peripheral end organ or receptor. Connecting neurones for conduction of nerve-impulses. A centre in the nervous system for interpretation or linkage with motor nerves. Sensation Perception through the sense-organs. Interpreted in the brain. Internal or those in which the sensations are projected to the interior of the body.. Classification 2. External or those in which the sensations are projected to the exterior of body. Pain. Sensationsfromsemi- circular canals and vestibule of the internal ear. Hunger. Thirst. Sexual sense. Muscular sense. Fatigue. Visceral sensations. Pressure. Temperature (heat and cold). Taste. Smell. Hearing. Sight. 456 ANATOMY AND PHYSIOLOGY [CHAP. XX Cutaneous Sensations Pain Muscle Sense . Hunger Thirst . Taste . Surface of skin is a mosaic of sensory spots which coincide with location of special end organs for pressure, cold, heat, or pain. 1. Fibres for light pressure. 2. Fibres for small difference of temperature, i.e., between 26 and 37 C. Special characteristic of skin Classification Epicritic Protopathic area. 1. Fibres for pain. 2. Fibres for heat 37 C. above Sensibility low, localization poor. Much evidence to support the theory that for cutaneous pain there exists a special set of fibres with a specific energy for pain. Overstimulation of sensory nerves in viscera and other parts of the body cause pain. Pain arising in viscera and referred to skin Referred area supplied with sensory fibres from Pain the same spinal segment that supplies organ in question. 1. End organs situated in tendons and between fibres of muscles. 2. Afferent fibres carry impulses to centres in brain. 3. Efferent fibres carry impulses from brain to muscle. Presumably due to contractions of empty stomach, acting on nerves distributed to mucous membrane. In abnormal conditions contractions may be weak or fail to occur at all. I Presumably due to stimulation of nerves of pharynx by \ low water content in tissues. 1. Taste-buds are end organs. Sensory ap- 2. Nerve-fibres of trifacial, facial, and glos- paratus sopharyngeal nerves. 3. Centre in brain. Solution of sapid substances must come in contact with taste-buds. Surface of tongue. Taste-buds are distributed over Soft palate and fauces. Tonsils and pharynx. CHAP. XX] SUMMARY 457 Tongue . Smell . Hearing Freely movable muscular organ. Attached to hyoid bone, epiglottis, and pillars of the fauces. Circumvallate. Surface covered by papillae Nerves Sense of Sensory Fungiform. Filiform. Lingual, branch of trifacial. Chorda tympani, branch of the facial. Glossopharyngeal. Motor Hypoglossal. 1. Taste 2. Temperature 3. Pressure 4. Pain Are all well developed. f Olfactory nerve-endings. Sensory ap- | Olfactory nerve-fibres. paratus [ Centre in brain olfactory bulb. f Minute particles of f Must be capable Odors solid matter of solution in [ Gases [ mucus. Olfactory nerve-endings found in lining of upper part of nose (smell). Branches of trigeminal nerve found in lining of lower part of nose (pressure) . Auditory ap- paratus External ear. Middle ear. Internal ear. Auditory nerve. Centre in brain. Air-waves enter external auditory canal and cause vibra- tions of drum-membrane. The vibrations are conveyed to nerve-endings of organ of Corti, and thence by the auditory nerve to the brain. External Ear Pinna, or auricle Auditory canal Structure Cartilaginous framework, some fatty and muscular tissue, covered with skin. Function Collects sound-waves and reflects them into the auditory canal. 1 in. long, partly cartilage, partly bone. Closed internally by the f Membrana drum-membrane 1 tympani. Hairs directed outward. Ceruminous glands secrete a yellow, pasty substance. 458 ANATOMY AND PHYSIOLOGY [CHAP. XX Middle Ear Bones Openings Bony Labyrinth An irregular cavity in the temporal bone. Five or six drops of water will fill it. Malleus (hammer). Incus (anvil). Stapes (stirrup). Fenestra ovalis closed by a mem- brane and the stapes. Fenestra rotunda closed by a mem- brane. Eustachian tube connects with the pharynx ; ventilates cavity. Vestibule antechamber just inside of fenestra ovalis. Semicircular f Three in number. canals 1 Open into vestibule. Vestibular branch ~f auditory nerve distributed to vestibule and semi- circular canals. A spiral tube. 2 1 turns around modiolus. Cochlea \ Fenestra rotunda. Cochlear branch of the au- ditory nerve. Surrounded by perilymph. Internal Ear Contains endolymph. , ., , f Saccule. Lines the vestibule 1 TTJ . , I Utricle. Lines the semicircular canals. Membranous Lines the cochlea, and here it is called Labyrinth the canalis cochlearis, or scala media. Membrana basilaris is name given to membrane at base of canal. Organ of Corti, name given to end organs of auditory nerve lodged on membrana basilaris. Cochlear terminates in and around Auditory the cells of organ of Corti. Nerve Vestibular terminates in hair-cells of saccule, utricle, and ampulla. Function of the vestibule and semicircular canals. Lining membrane supplied with sensory hairs which connect with vestibular nerve. Contains several small otoliths which float in the endolymph. Flowing of the endolymph stimulates the sensory hairs; this is transmitted to the vestibular nerve, thence to auditory nerve, thence to brain. Sense of Equilibrium CHAP. XX] SUMMARY 459 Visual Ap- paratus Accessory Organs Accessory organs Eyebrows Eyelids Eye. Optic nerve. Centre in brain. Eyebrows. Eyelids. Lacrimal apparatus. Muscles. f Thickened ridges of skin furnished with short, thick hairs. Control to a limited extent amount of light admitted to eye. Folds of connective tissue covered with skin, lined with mucous membrane (conjunctiva), which is also reflected over the eyeball. Provided with lashes. Closed by orbicularis palpebrarum muscle. Upper lid raised by levator palpebrae superioris. Slit between lids called palpebral fissure. Inner angle of slit called internal canthus. Outer angle of slit called external canthus. Function is protection. Serve as shades. Tarsal glands are a row of glands embedded in tarsal cartilage of each lid. Lacrimal gland in the upper and outer part of the orbit. Secretes tears. Ducts 7 to 12 lead from gland to con- junctiva. Canaliculi 2 canals i to t in. long, begin at punctse and open into lacrimal sac. Lacrimal sac upper dilated portion of the nasal duct. Nasal duct canal f in. long, extends from lacrimal sac to the nose. Secretion constant. Moisten the eyeball and help to moisten inspired air. _ . f Water. Consist | SalL I Albumin. Carried off by nasal duct. Superior rectus. Inferior rectus. Internal rectus. External rectus. Superior oblique. Inferior oblique. Ciliary / Determines the posi- muscle \ tion of the lens. Muscles / Contractor of pupil. of iris \ Dilator of pupil. Lacrimal apparatus Muscles Tears Extrinsic Intrinsic 460 ANATOMY AND PHYSIOLOGY [CHAP. XX 1. Optic nerve Nerves of Eye . . 2. Motor oculi controls Internal rectus muscle. Superior rectus muscle. Inferior rectus muscle. Inferior oblique muscle. 3. Pathetic controls the superior oblique muscle. 4. Abducens controls the external rectus muscle. 5. Ophthalmic. Orbit . Bony cavity formed by seven bones Frontal. Malar. Maxilla. Palate. Ethmoid. Sphenoid. Lacrimal. Lined by fibrous tissue. Contains pad of fat supports eyeball. Capsule of Tenon prevents friction when eyeball moves. Shaped like four-sided pyra- j Apex directed backward. mid I Base directed forward. Optic foramen opening for passage of optic nerve and ophthalmic artery. Sphenoidal fissure opening for passage of ophthalmic vein and motor oculi, pathetic and abducens nerves. Eyeball Spherical in shape, but it projects anteriorly. 1. Protective sclera and cornea. Tunics . ! 2. Vascular choroid, ciliary body and iris. 3. Visual retina. 1. Aqueous. Media . \ 2. Crystalline lens and capsule. 3. Vitreous. Protective Tunics Sclera Cornea Tough, fibrous, opaque. Covers posterior | of eyeball. Stained brown internally. Fibrous, transparent covers anterior of eyeball. Well supplied with nerves. CHAP. XX] SUMMARY 461 Vascular Tunics Choroid Ciliary Body Iris Vascular coat, lines the sclera. Composed of connective tissue cells filled with pigment. Terminates in front by the ciliary processes. Ciliary processes 70 to 80 parallel folds of the choroid, rising gradually from behind and forming a plaited zone between the choroid and iris. Support ciliary muscle action of this muscle determines the position of the lens. A circular curtain. Central perforation pupil. Pupil contracted by circular muscle-fibres. Pupil dilated by radial muscle-fibres. Contains pigment amount of which deter- mines color of the eyes. Hangs free except for attachment at circum- ference to the ciliary processes and choroid. Function Regulates amount of light enter- ing eye. Visual Tunic or Retina Visual layer transparent membrane of nervous and con- nective tissue situated between the choroid and vitreous humor. Formed by the spreading out of optic nerve. Has eight layers and two membranes. Counting from the choroid inward as follows : Pigment layer, usually described as a membrane. 1. Layer of rods and cones (perceptive layer) external layer. 2. Limitans externa. 3. External granules. 4. External molecular. 5. Internal granules. 6. Internal molecular. 7. Ganglion or nerve-cells. 8. Optic nerve-fibres innermost layer. Membrana limitans interna. Entrance of optic nerve. There are no rods and cones. Totally insensitive to light. T V in. outside the blind spot. Central pit fovea centralis is the centre of [ direct vision. Vibrations of ether enter eye, strike on rods and cones, thence sensation is carried to the visual centre in the brain. Blind Spot Macula Lutea 462 ANATOMY AND PHYSIOLOGY [CHAP. XX Refractive Apparatus Aqueous Crystal- line lens Vitreous Aqueous chamber is between cornea in front, and lens, suspensory ligament, and ciliary body behind. Aqueous humor is a colorless, trans- parent, watery fluid. Fibrous body enclosed in an elastic capsule. Double convex in shape. Situated behind the pupil. Held in position by counterbalancing of the aqueous and vitreous humors and the sus- pensory ligament. Semi-fluid, gelatinous substance. Fills the posterior four-fifths of the globe of the eyeball, and is enclosed in the hyaloid membrane. Distends the sclera and supports the retina. Refraction Bending or deviation in the course of rays of light, in pass- ing obliquely from one transparent medium into another of different density. Accommodation Ability of the eye to adjust itself so that it can see objects at varying distances. f Far-sightedness. Cause Rays of light do not converge soon enough. Near-sightedness . Cause Rays of light converge too soon. Defective condition of accommodation in which distant objects are seen dis- tinctly, but near objects are indistinct. Condition in which the curvature of the cornea or lens is defective. Hypermetropia Conditions that affect Myopia . . Accommo- dation Presbyopia . Astigmatism CHAPTER XXI THE ORGANS OF GENERATION: PHYSIOLOGY OF REPRODUCTION Female generative organs. The female generative organs are divided into an internal and an external group. The internal are contained within the true pelvis, and the external are grouped under the name of vulva or pudendum. INTERNAL GENERATIVE ORGANS The internal generative organs comprise the following struc- tures : (1) Ovaries, two glandular organs in which the ova are formed. (2) Fallopian [uterine] tubes, two canals through which the ova reach the uterine cavity. (3) Uterus, a hollow, pear-shaped organ, which receives the ovum. VAGINA FIG. 220. UTERUS, OVARIES, AND FALLOPIAN TUBES. (4) Vagina, a canal extending from the uterus to the vulva. Ovaries. The ovaries are two almond-shaped, glandular bodies, situated one on each side of the uterus, in the posterior fold 463 464 ANATOMY AND PHYSIOLOGY [CHAP. XXI of the broad ligament, behind and below the Fallopian tubes. Each ovary is attached at its inner end to the uterus by a short ligament, the ligament of the ovary, and at its outer end to the Fallopian tube by one of the fringe-like processes of the fim- briated extremity. The ovaries each measure about one and a half inches (3.8 cm.) in length, three-fourths of an inch (1.9 cm.) in width, and one-third of an inch (8.5 mm.) in thickness, and weigh from one to two drachms (3.7 to 7.5 gms.). Function. The function of the ovaries is to produce, develop and mature the ova, and to discharge them when fully formed. In addition, the ovary furnishes an internal secretion, which is picked up by the blood. Structure. If the substance of an ovary be minutely examined it is found to consist of : (1) a stroma or bed composed of white and yellow fibrous tissue, blood-vessels, lymphatics, and nerves, (2) Graafian follicles, and (3) a covering of columnar epithelial cells, called germinal epithelium, which is continuous with the peritoneum. Graafian (vesicular) follicles. The Graafian follicles are sacs or vesicles which contain the ova and are embedded in the meshes of the stroma. Each follicle consists of : (1) an outer coat of fibrous tissue that is derived from the stroma, and connected with it by a plexus of blood-vessels, and (2) an inner layer of nucleated cells. With the exception of the smallest vesicles each one is filled with fluid, and suspended in this fluid is an ovum surrounded by a mass of cells, called the discus proligerus. At birth the ovaries are said to contain about 36,000 vesicles, each measuring from ^-g- to y^y of an inch in diameter, but only a small number of these ever develop, as the great majority shrink and disappear. At the time of puberty the ovaries enlarge, be- come very vascular, and some of the follicles increase in size. As the follicles increase in size they approach the surface and begin to form small protuberances on the outside of the ovary. When fully matured the wall of the ovary and the wall of the follicle burst at the same point, and the contents of the follicle the fluid, the ovum, and the surrounding cells escape. This pro- cess of development, maturation, and rupture of a follicle is known as ovulation, and continues at regular intervals from puberty to the menopause. CHAP. XXI] THE ORGANS OF GENERATION 465 The corpus luteum. After the rupture of a follicle, and the escape of the ovum, the walls collapse and the cavity becomes filled with blood which forms a clot. Later this clot becomes surrounded by cells containing a yellow pigment, which gives the follicle a yellow color, and hence it is known as the corpus luteum. The size and duration of the corpus luteum is dependent on whether pregnancy occurs or not. If pregnancy does not occur the corpus luteum increases in size for two or three weeks and then is absorbed. If pregnancy does occur the corpus luteum increases in size during the first few months, and does not show retrogressive changes until about the sixth month. Opinions differ regarding the physiological importance of the corpus luteum. Some physi- ologists regard it as a protective mechanism by means of which the cavity resulting from the rupture of the follicle is filled with a tissue which can be easily absorbed. Others attribute to the cor- pus luteum secretory functions of the most important character in connection with menstruation, the implantation of the fertilized ovum and its subsequent growth. Fallopian tubes. The Fallopian tubes or oviducts are two in number, one on each side, and pass from the upper angles of the uterus in a somewhat tortuous course between the folds and along the upper margin of the broad ligament, towards the sides of the pelvis. They are about four inches (10 cm.) long, and at the point of attachment to the uterus are very narrow, but gradually in- crease in size so that the distal end is larger. The margin of the distal end is surrounded by a number of fringe-like processes called fimbrice. One of these fimbrise is attached to the ovary. The uterine opening of the tube is minute, and will only admit a fine bristle ; the abdominal opening is comparatively much larger. The Fallopian tube consists of three coats : (1) The external, or serous, coat is derived from the peritoneum. (2) The middle, or muscular, coat has two layers : one a layer of longitudinal cells and the other of circular cells. (3) The internal, or mucous* coat is arranged in longitudinal folds and covered with ciliated epithelium. It is continuous at the inner end with the mucous lining of the uterus, and at the dis- tal end with the serous lining of the abdominal cavity. This is the only place in the body where a mucous and serous lining are continuous with one another. 2n 466 ANATOMY AND PHYSIOLOGY [CHAP. XXI Function. The function of the Fallopian tubes is to convey the ova from the ovaries to the uterus. Just how the ovum, after its discharge into the abdominal cavity, reaches the Fallopian tube is not known. It is thought that the movement of the cilia on the fimbrise and in the tubes produces a current which draws the ovum into the tube. After the ovum enters the tube it is carried to the uterus by the peristaltic action of the tube and the move- ment of the cilia. It is considered probable that many of the ova discharged from the ovaries remain in the abdominal cavity, because of failure to reach the tubes. These ova disintegrate, are absorbed, and carried away by the blood. Occasionally such an ovum becomes impregnated and ectopic gestation results. The uterus. The uterus is a hollow, pear-shaped organ. In the virgin state it is situated in the pelvic cavity between the blad- der and the rectum. Its length is estimated to be about three inches (7.5 cm.), its width two inches (5 cm.) at the upper part, and its thickness one inch (2.5 cm.). During pregnancy the uterus becomes enormously enlarged, attains the length of a foot (30 cm.) or more, extends into the umbilical region, and measures about eight to ten inches (20 to 25 cm.) in width. After partu- rition the uterus returns to almost its original size, but is al- ways larger than before pregnancy. After the menopause, the uterus becomes smaller and atrophies. Divisions. For purposes of description the uterus is divided into three parts : the fundus, body, and neck. The fundus is the convex part above the entrance of the tubes. The body is the part between the fundus and" the neck. The cervix or neck is the lower constricted part and extends from the body of the uterus into the vagina. The cavity of the uterus is small because of the great thickness of its walls; that part within the body is triangular in shape (v), and has three openings, one at each upper angle, communi- cating with the Fallopian tubes, and one, the internal orifice, open- ing into the cavity of the cervix below. The cavity of the cervix, which is, of .course, continuous with the cavity in the body, is constricted above, where it opens into the body by means of the internal orifice (internal os), and below, where it opens into the vagina by means of the external orifice (external os). Between these two openings the canal of the cervix is somewhat enlarged. CHAP. XXI] THE ORGANS OF GENERATION 467 Structure. The walls of the uterus are thick and consist of three coats : (1) An external serous coat derived from the peritoneum. It covers all of the uterus, and the posterior surface of the cervix, but not the anterior surface. (2) A middle muscular coat which forms the bulk of the uterine walls. It consists of layers of plain muscular tissue intermixed with blood-vessels, lymphatics, and nerves. The arrangement of the muscles is very complex, as they run cir- cularly, longitudinally, spirally, and cross and interlace in every direction. (3) An internal mucous membrane, which is continuous with that lining the vagina and Fallopian tubes. It is highly vascular, provided with numerous mucous glands, and is covered with cili- ated epithelium. Blood supply of uterus. The uterus is abundantly supplied with blood-vessels. The blood reaches the uterus by means of the uterine arteries from the internal iliacs, and the ovarian ar- teries from the aorta. Where the neck joins the body of the uterus, the arteries from both sides are united by a branch vessel, called the circumflex artery. If this branch is cut during a surgi- cal operation, or a tear of the neck during parturition extends so far as to sever it, the hemorrhage is very profuse. The arteries are remarkable for their tortuous course and frequent anastomoses. The veins are of large size, and correspond in their behavior to the arteries. Position of the uterus. The uterus is not firmly attached or ad- herent to any part of the skeleton. It is, as it were, suspended in the pelvic cavity by ligaments. A full bladder pushes it back- ward ; a distended rectum, forward. It alters its position, by gravity, or with change of posture. During gestation it rises into the abdominal cavity. The fundus of the uterus is inclined forward, and the external orifice is directed downward and backward. (See Fig. 221.) Anteversion is the condition where the fundus turns too far forward. Retroversion is the condition where the fundus inclines backward. A bend may exist where the neck joins the body, and if the body is bent forward, it is described as anteflexion; if bent backward, retroflexion. 468 ANATOMY AND PHYSIOLOGY [CHAP. XXI Ligaments. The uterus is suspended by five ligaments. Three are arranged in pairs. 1. The broad, or lateral ligaments, two in number, are folds of peritoneum slung over the front and back of the uterus, and extending laterally to the walls of the pelvis. They are composed of two opposed, serous layers, and between these layers are found the following structures: (a) Fallopian tubes; (6) the ovaries FIG. 221. INTERNAL ORGANS OF GENERATION. (Cooke.) and their ligaments; (c) the round ligaments; (d) blood-vessels and lymphatics ; (e) nerves ; (/) some smooth muscle tissue. The posterior fold covers the back of the uterus, and extends far enough below to also cover the upper one-fifth of the back wall of the vagina, when it turns up and is reflected over the anterior wall of the rectum. Thus the uterus, with and between its two broad ligaments, forms a transverse partition in the pelvic cavity, the bladder, vagina, and urethra being in the front compartment, and the rectum in the back compartment. The smooth muscles of the broad ligaments are derived from the CHAP. XXI] THE ORGANS OF GENERATION 469 superficial muscular layer of the uterus. They pass out between the serous folds and become attached to the pelvic fascia. 2. The round ligaments are two rounded, fibro-muscular cords, situated between the folds of the broad ligament. They are about four and a half inches (11.3 cm.) long, and take their origin from the upper angle of the uterus (on either side), in front and a little below the attachment of the Fallopian tube. They extend for- ward and outward, and finally end in the tissues of the labia majora and mons Veneris. The round ligaments are composed of muscles, areolar tissue, blood-vessels, and nerves. 3. The utero-sacral ligaments extend between the cervix and sides of the rectum. They serve to connect the cervix and vagina with the sacrum, and are partly serous, partly of smooth muscular tissue. 4. Between the bladder and uterus the peritoneum forms a shallow pouch called the utero-vesical pouch. This peritoneum, which forms the floor of the pouch, is described as the anterior ligament of the uterus. 5. Behind the uterus the peritoneum forms a second and deeper pouch called the recto-vaginal, or cul-de-sac, of Douglas. This peritoneum is described as the recto-vaginal ligament. Function. The function of the uterus is to receive the ovum from the Fallopian tubes, and if it becomes fertilized to retain it during its development. Later when the ovum has developed into a mature foetus, it is expelled from the uterus, chiefly by the contractions of the uterine walls. The vagina. The vagina is a musculo-membranous canal which encircles the lower portion of the cervix, and extends downward and forward from the uterus to the vulva. The posterior wall is about three and a half inches (8.75 cm.) long, while the anterior wall is only two and one-half inches (6.25 cm.). The front, or anterior wall, is united by connective tissue with the posterior walls of the bladder and urethra, the partition, or septum, between the bladder and vagina being called the vesico-vaginal, and that between the urethra and vagina the urethro-vaginal, septum. Structure. The vagina is made up of three coats : an outer, fibrous; middle, muscular; and inner, mucous, which in the ordinary contracted state is thrown into folds, its anterior and 470 ANATOMY AND PHYSIOLOGY [CHAP. XXI posterior walls being in contact. The muscular coat increases during pregnancy, and the mucous coat, because of the transverse folds, or rugae, allow of dilatation of the canal during labor and birth. DORSAL VC OF CLITORIS f>ncpucc or CLITORIS CLANS CLI- TORIOIS FIG. 222. SAGITTAL SECTION OF THE VAGINA AND NEIGHBORING PARTS. (Gerrish.) THE EXTERNAL ORGANS The external organs of generation are grouped under the name of vulva or pudendum and include the following : 1. Mons Veneris 4. The Clitoris 2. Labia Majora 5. The Hymen 3. Labia Minora ^, , f Vulvo- vaginal 6. Glands { TT [ Urethral Mons Veneris. The mons Veneris is an eminence situated in front of the pubic bones. It consists of areolar, adipose, and fibrous tissue covered with skin and after puberty with hair. Labia majora. The labia majora are two longitudinal folds of skin containing adipose and connective tissue. They are con- tinuous with the mons Veneris in front, and extend to within an inch (25 mm.) of the anus behind. Labia minora. The labia minora are two longitudinal folds of modified epithelium situated between the labia majora. They are joined anteriorly in the hood or prepuce of the clitoris, and extend downward and backward for about one and one-half inches (3.8 cm.). CHAP. XXI] THE ORGANS OF GENERATION 471 The clitoris. The clitoris is a small body situated at the apex of the triangle formed by the junction of the labia minora. It contains many vessels and nerves and is almost completely cov- ered by the hood or prepuce. The hymen. The hymen is a fold of mucous membrane which surrounds the lower part of the va- gina and renders the orifice smaller. It is quite elastic and may remain intact even after child-birth. Oc- casionally it extends entirely across and closes the orifice al- together. This con- dition is spoken of as imperf orate hymen. Glands. In con- nection with the vulva are found : (1) Vulvo-vaginal glands or glands of Bartholin. (2) Urethral glands. The vulvo-vaginal are two round, or oval, glands, situated on either side of the vagina. Their ducts open into the vulval canal one on either side, in the groove between the hymen and labia minora. Their secretion lubricates the vulval canal. The urethral glands are found chiefly beneath the walls and floor of the urethra. They secrete mucus. Perineum. The perineum bounds the external outlet of the pelvis and constitutes the floor of the genital canal. It consists of bands of muscular tissue strengthened and held together with fascia and covered with skin. An important part of the perineum is the triangular portion between the vagina and rectum. It is distensible and stretches to a remarkable extent during labor. Nevertheless it is frequently torn, and when the tear is of any FIG. 223. VULVA OF A VIRGIN. The labia have been widely separated. Foss. Nav., fossa navicu- laris ; Int. Vag., introitus vaginae; Lab. Min., labium minus ; Vestib., vestibule. (Gerrish.) 472 ANATOMY AND PHYSIOLOGY [CHAP. XXI extent, and is not repaired, the vagina and uterus lose the support afforded by it, and various abnormal conditions follow. PHYSIOLOGY OF THE FEMALE GENERATIVE ORGANS Functions. The functions of the female generative organs are : (1) the formation and development of the ovum, (2) the reten- tion and sustenance of the fecundated ovum until it develops into a mature foetus ready to live outside the body, and (3) the expul- sion of the foetus. Puberty. Puberty is the period at which the sexual organs be- come matured and functional and the girl develops into a woman. The event is not accomplished at once, but extends over con- siderable time. The girl undergoes a gradual change in figure, the hips broaden, the breasts develop, and for the first time a menstrual flow is noticed. At first the menstrual periods are scanty and irregular, but after a few months they settle down to the characteristic rate and duration. In temperate climates the age at which girls usually attain puberty is about fourteen years. In southern countries it is somewhat earlier, and in the arctic regions, a year or two later. However, no fixed rule can be given, as the time of arrival at puberty varies with every individual, depending on race, temperament, hygiene, and general surround- ings. The period of puberty during which the physical changes are occurring, is known as the period of adolescence. Ovulation. Ovulation includes the process of the develop- ment and maturation of the follicle and its ovum, and the rupture of the follicle. The commonly accepted theory is that about or shortly before the age of puberty, the Graafian follicles begin to discharge their ova, and this process continues until the menopause. The fre- quency with which well-developed ova are discharged is the subject of much dispute. The most conservative view is that there is one mature ovum discharged for each menstrual epoch. Menstruation. Menstruation consists of the periodical dis- charge of bloody fluid from the uterine cavity. When once es- tablished it occurs on the average every twenty-eight days from the time of puberty to the menopause, with the exception of the period CHAP. XXI] THE ORGANS OF GENERATION 473 of pregnancy and lactation. The average duration is from four to five days and the amount of blood lost is from four to six ounces (120 to 180 cc.). The menstrual fluid consists of mucus, epithelial cells, and blood. Some authorities are of the opinion that the mucous membrane of the uterus is normally shed during this pro- cess, others do not share this opinion. The menopause or climacteric. By menopause or climacteric is meant the physiological cessation of the menstrual flow, and the end of the period during which the Graafian follicles develop in the ovaries, and consequently the end of the child-bearing period. It is marked by atrophy of the breasts, uterus, tubes, and ovaries. The age of menopause varies as does the age of puberty ; in general, we may say the earlier the puberty the earlier the menopause, and vice versa. In temperate climates the average period for the arrival of the menopause is at the age of forty-five years. - ' -1 , Changes in the generative organs in connection with menstrua- tion. At the beginning of menstruation there is a general con- gestion of the generative organs, including the breasts, accompanied by more or less discomfort and even pain. The mucous membrane of the uterus undergoes the following changes : (1) some days be- fore the process there is marked hypertrophy and congestion of the mucous membrane, (2) during menstruation there is capillary hemorrhage and the epithelium of the mucous membrane may be cast off, (3) during the week following menstruation a new epithe- lium is formed and the mucous membrane returns to its normal size, (4) a period of rest extends to the next period of congestion. Connection between ovulation and menstruation. Whether ovulation depends upon menstruation or menstruation upon ovulation, or whether either has any connection with the other, is a matter of lengthy controversy. At the present time the generally accepted view is that menstruation is dependent upon the ovaries, and that their influence is exerted through the medium of the blood. It is thought that an internal secretion is formed in the ovaries ; some physiologists think by the cells of the corpus luteum. This secretion is carried to the uterus by the blood and is responsible for the hypertrophy and congestion that precedes menstruation. So far it has not been possible to decide whether the internal secretion is entirely responsible for menstruation, or whether it is partly due to a power inherent in the uterine muscle. 474 ANATOMY AND PHYSIOLOGY [CHAP. XXI The fact that operations for the removal of the ovaries are fol- lowed by atrophy of the uterus and cessation of menstruation, supports the theory that the ovaries are in some way responsible for menstruation. Purpose of menstruation. The purpose of the hypertrophy and congestion of the uterus is thought to be nature's way of preparing the uterine walls for the reception of the ovum should it become fertilized. Mammary glands. The two mammary glands, or breasts, may be considered as accessory organs of generation. Function. The function of the mammary glands is to secrete the milk which is needed for the nourishment of the young infant. Location. Each breast covers a nearly circular space in front of the pectoral muscles, extending from the second to the sixth rib, and from the sternum to the border of the arm-pit. Structure. The breasts are convex in shape, are covered ex- ternally by skin, and about the centre of the convexity a papilla projects, which is called the nipple. The nipple contains the openings of the milk ducts, and is surrounded by a small circular area of pink or dark colored skin, which is called the areola. They are compound glands, and are divided by connective tissue parti- tions into about twenty lobes, each of which possesses its own ex- cretory duct, which as it approaches the top of the breast dilates and forms a small reservoir in which milk can be stored during the period when the gland is active. Each duct opens by a sepa- rate orifice upon the surface of the nipple. The lobes are subdi- vided, and the small lobes, or lobules, are made up of the terminal tubules of the duct, which lie in a mesh of fibrous areolar tissue containing considerable fat. Blood-vessels and nerves. The mammary glands are well supplied with blood brought to them by branches of the axillary, internal mammary, and intercostal arteries. The nerves are chiefly intercostal nerves. Development of the mammary glands. The increase in the size of the mammary glands at the time of puberty is due to an increased development of the connective tissue and fat. The glandular tissue remains undeveloped and does not function unless conception takes place. When conception occurs the glandular CHAP. XXI] THE ORGANS OF GENERATION 475 tissue undergoes a process of gradual development that produces marked changes. The breasts become larger and harder, the veins on the surface become more noticeable, the areola becomes enlarged and darkened, the nipple becomes more prominent, and toward the end of pregnancy a fluid called colostrum can be CLAVICLE PCCTORALIS MAJOR SKIN FIBROUS SEPTUM GLAND SUBSTANCE A'DIPOSC TISSUE IRO RIB REOLAR TISSUE FIRST RIB SECOND RIB PECTORALIS MINOR INTERCOSTALE9 SHEATH OF PEC- TORALIS MAJOR SUPERFICIAL FASCIA FOURTH RIB LUNG ADIPOSE TISSUE HORIZONTAL PLANE OF NIPPLE FIFTH RIB FIG. 224. RIGHT BREAST IN SAGITTAL SECTION, INNER SURFACE OF OUTER SEGMENT. (Gerrish.) squeezed from the orifice of the ducts. After delivery the amount of colostrum increases for a day or two, and then its composition changes to that of milk. The primary development and later functioning of the mam- mary glands suggests an intimate connection between these glands and the uterus and ovaries. The present theory is that the in- crease in the size of the breasts at the time of puberty is influenced 476 ANATOMY AND PHYSIOLOGY [CHAP. XXI by the internal secretion of the ovaries, for if the ovaries are re- moved before puberty, the breasts do not develop, or if the ovaries are removed after puberty, the breasts are apt to atrophy. The development of the glandular tissue that follows conception is thought to be due to some chemical substance, e.g., a hormone, that results from the metabolism of the foetus. The chemical nature of this substance is not known, but presumably it stimulates the development of the gland, and also prevents secretion, as active secretion does not commence until after delivery, and if conception occurs during the months of lactation, the character of the milk is changed and its secretion checked. The stimulus which causes the active secretion of milk is thought to result from the emptying of the milk ducts, because of the fact that when a woman does not nurse her infant, the secretion of milk is checked, and the breasts return to their usual size. The active secretion of milk is also influenced by the nervous system, and this influence is probably exerted through the vasomotor nerves which control the size of the blood-vessels, and consequently the amount of blood sent to the gland. The secretion of milk. The secretory portion of the mammary glands is the milk ducts, and these are lined with secreting cells. Some of the constituents of the milk, i.e., water, salts, and sugar, are secreted by these cells from the blood, but it is thought that the cells themselves disintegrate and form the proteins and fat. The sugar contained in the milk is lactose, and the sugar of the blood is glucose, so if the first is derived from the second, some chemical change must take place either during or after secretion. Colostrum and milk. The secretion of the mammary glands during the first few days of lactation is called colostrum. It is a thin, yellowish fluid, composed of proteins, fat, sugar, salts, and water, but not in the same proportion as in milk. It also contains numerous cells containing large masses of fat. These are called colostrum corpuscles, and are secreting cells that are not completely broken down. Human milk is specially adapted to the requirements of the infant and so differs in some respects from that of all other animals. Cow's milk is most frequently substituted for human milk and the relative composition of the two can be seen in the following table : CHAP. XXI] THE ORGANS OF GENERATION 477 HUMAN (average) Cow's (average) Water 87-88% 87.00% 2-3% 4.00% Fat 3-4% 4.00% Lactose .... 6-7% 4.30% Salts 2-3% 070% In substituting cow's milk for human milk the differences that must be taken into consideration are not only the different relative proportions, but also the following : (1) the difference in the pro- teins ; the protein of human milk is one-third caseinogen, and two- thirds lactalbumin, and that of cow's milk is five-sixths caseinogen and one-sixth lactalbumin ; (2) the difference in the curds formed in the stomach ; human milk curdles in small flocculi, and cow's milk curdles in large heavy curds; and (3) the reaction of both human and cow's milk is amphoteric, but cow's milk is more nearly acid than human milk. Male generative organs. The male generative organs con- sist of the following structures : Testes, two glandular organs which produce the sper- matozoa. Vas Deferens. Seminal Vesicles. Ejaculatory Ducts. The Spermatic Cords. The Penis. The Prostate Gland. Cowper's Glands. Testes. The testes are two glandular organs which are sus- pended from the inguinal region by the spermatic cords, and are surrounded and supported by the scrotum. Each gland weighs from six to eight drachms (22 to 30 gms.) and consists of two portions : (1) the testicle proper, and (2) the epididymis. (1) The testicle proper is ovoid in shape and covered exteriorly by fibrous tissue which sends incomplete partitions into the cen- tral portion of the gland, dividing it into communicating cavities. In these cavities are winding tubules which are surrounded by blood-vessels and held together by interstitial tissue. These 478 ANATOMY AND PHYSIOLOGY [CHAP. XXI tubules inosculate in a sort of mesh (rete testis) and finally all unite in the epididymis. (2) The epididymis is a long, narrow body which lies along the posterior portion of the testicle and consists of a tortuous tubule, which is lined with mucous membrane, and contains some muscular tissue in its walls. If unravelled it is found to be about twenty feet (5 metres) long. It con- nects the testicle proper with the vas deferens. Function. The func- tion of the testes is the production of sperma- tozoa. These sperma- tozoa are the essential part of the seminal fluid. The spermatozoa origi- nate in the cells of the testes lining the tubules which compose the bulk of the testes. An in- ternal secretion is also supposed to be formed here. "Prepuce FIG. 225. MALE SEXUAL APPARATUS. (Hall.) Descent of the testes. In early foetal life the testes are abdom- inal organs lying in front of and below the kidneys. During the process of growth they are drawn downward through the inguinal canal and shortly before birth are normally found in the scrotum. Sometimes, particularly in premature infants, a testis is found in the inguinal canal or even in the abdominal cavity; as a rule it soon descends and occupies its proper position ; but occasionally it does not descend and an operation is necessary. The Vas Deferens. The vas deferens is a continuation of the epididymis, and is the excretory duct of the testicle. After a very devious course it joins the duct of the seminal vesicle at the base of the bladder. It consists of three coats, an external areolar, a middle muscular, and an internal mucous coat. CHAP. XXI] THE ORGANS OF GENERATION 479 The Seminal Vesicles. The seminal vesicles are two pouches which are placed each one on the outer side of each vas deferens, between the bladder and the rectum. They are pyramidal in form, with the broad ends directed backward and widely separated. The anterior portions converge, become narrowed, and unite on either side with the corresponding vas deferens to form the ejacu- latory duct. Function. The seminal vesicles serve as a reservoir for the semen, to which they add a secretion of their own. The Ejaculatory Ducts. The ejaculatory ducts are two in num- ber, one right and the other left. They are formed by the union of the seminal vesicle and vas deferens of each side. They run downward and converge as they descend, enter and pass between the lobes of the prostate gland and open into the floor of the pros- tat ic portion of the urethra. Each has an external areolar, middle muscular, and internal mucous coat. The scrotum. The scrotum is a pouch which contains the testes and a part of each spermatic cord. It consists of a layer of skin, and the dartos. The skin is thick and dark, presents folds or rugae, is furnished with sebaceous glands, and covered with short hairs. The dartos is a thin tunic of a reddish color consisting of muscular fibres and elastic tissue and containing numerous blood- vessels. It is continuous with the superficial fascia of the groin and perineum. It sends in a partition, which separates the two testes. The Spermatic Cord. The spermatic cord forms the pedicle of each testis and extends from the internal abdominal ring to the back of the testis. Each cord consists of the vas deferens, arteries, veins, lymphatics, nerves, the layers of fascia which cover the testis, and the remains of the peritoneal testicular process. These parts are connected together by areolar tissue. The Penis. The penis consists of three more or less cylindrical bodies of erectile l tissue enclosed in fibrous sheaths. The two corpora cavernosa lie above the corpus spongiosum, in which the urethra is contained. The glans penis is continuous with 1 Erectile tissue is found in the clitoris, penis, and the nipples. The form, size, and consistency of this tissue changes according to the amount of blood contained in it. An increased amount of arterial blood causes swelling, and consequent press- ure on, and occlusion of, the veins. 480 ANATOMY AND PHYSIOLOGY [CHAP. XXI the corpus spongiosum. The covering of the penis is of loose skin, but over the glans penis, and lining the prepuce, it re- sembles mucous membrane. In this region there is an abundant subcutaneous nerve plexus and numerous Pacinian 1 corpuscles, so that it is possessed of acute sensibility. The urethra extends from the bladder through the corpus spongiosum to the end of the penis. It is usually divided into three parts : (1) the prostatic urethra, (2) the membranous urethra, and (3) the penile or spongy portion. The length is usually given as eight inches (20 cm.), a large part of which lies inside the pelvis. It is lined with mucous membrane and furnished with numerous muscular fibres. The Prostate. The prostate gland is situated in front of the neck of the bladder and around the commencement of the urethra. It resembles a chestnut in form and consists of a dense fibrous capsule containing glandular and muscular tissue. The glandular tissue consists of tubules which communicate with the urethra by minute orifices. Function. The function of the prostate gland is to secrete the prostatic fluid, which is an essential element of the seminal fluid. Cowper's glands. These are two small bodies about the size of a pea situated one on each side, adjacent to, and opening into the membranous urethra. They secrete a fluid which goes to form part of the seminal fluid. Puberty. Puberty is the period at which the sexual organs become matured and functional, and the boy develops into a man. This occurs in the male about a year later than in the female, about fifteen years of age. At this time the " Adam's apple " develops, producing a marked change in the voice, the external genitals grow somewhat rapidly, hair grows on the face, pubes, axillae, and other parts of the body, and seminal fluid begins to be secreted. At the same time sexual desires unknown before are experienced. Semen. The semen is a fluid derived from the various sexual glands in the male. The main elements in this fluid are the sper- matozoa ; the other constituents are derived from the seminal vesicles, prostate gland, and Cowper's glands. 1 Pacinian corpuscles are specialized nerve-endings found in the genital organs of both sexes, also in the palms of the hands and the soles of the feet. CHAP, xxi] REPRODUCTION 48i PHYSIOLOGY OF REPRODUCTION Reproduction. The purpose of reproduction is the continu- ation of the species, and is accomplished by means of the reproduc- tive organs, whose importance is in their adaptation to produce another being. The reproduction of all living organisms is ac- complished in two ways : (1) Asexually; (2) sexually. (1) In the asexual type one individual divides into two or more, as is seen in the budding of plants and animals, also in the unicel- lular organisms when one organism constricts itself into two, either directly, or indirectly by mitosis, or divides itself up into a number of spores. (2) In the sexual type, the individuals fuse either temporarily or permanently before cell division, or else they make sex cells (gametes) which fuse to form the new individual. In many of the lower organisms these sex cells are shed into the water and there unite. In most of the higher organisms the female sex cells or ova remain in the female organism, and the male sex cells are placed in the reproductive tract. In the human species the sperma- tozoa are placed in the vagina at the mouth of the uterus and swim upward through the uterus and the Fallopian tubes, in or near which union w r ith the ova takes place. Impregnation. The term impregnation or fertilization is applied to the union of the spermatozoon or male cell with the ovum or female cell. The ovum. The ovum is a minute globular cell about -^-5 inch (0.2 mm.) in diameter. (See Fig. 6 for cell structure.) The spermatozoon. The spermatozoon is much smaller than the ovum, being only ^5- inch (0.05 mm.) in length. It consists of an elliptical head, a rod-shaped middle piece, and a tail that gradually tapers. The head contains nuclear material and chro- matin. There is an active vibratory motion of the tail which allows it quite free motion in the seminal fluid. Because of this free motion the spermatozoa are able, when deposited in the vagina, to travel upward into the uterus, and into the tubes even against the current produced by the cilia of the tubes. Maturation of sex cells. Before union the maturation of the sex cells takes place. In this process the number of chromosomes 2i 482 ANATOMY AND PHYSIOLOGY [CHAP. XXI is reduced to one-half the original number. Note that in Fig. 8 each chromosome is divided longitudinally into halves so that each new cell has the same number of chromosomes as the original cell. In maturation the division is such that each new cell has one-half the original number of chromosomes. Fusion or fertilization re- stores the normal number of chromosomes. Much of our theory of inheritance is based upon these chromosomes, and the fact that they are contributed to the individual, half by the sperm cell and half by the ovum. Site of impregnation. It is thought that impregnation takes place in the Fallopian tubes or near the wall of the ovaries. When the Graafian follicle ruptures and an ovum escapes into the ab- dominal cavity, the current produced by the cilia of the tubes is thought to draw it into the tube. Once in the tube the peristaltic action of the tube and the action of the cilia propel it slowly along to the uterus. If the ovum does not become impregnated it passes into the uterus and is cast off in the next menstrual flow. If, however, it is impregnated, segmentation or the process of cell division begins at once. Segmentation. The impregnated cell (zygote) rapidly divides into two, each of these two into other two, and so forth, until we have a number of cells where formerly there was one. At this stage the collection of cells is called the blastoderm. Gradually these cells which constitute the blastoderm become arranged in three layers, the outer called the ectoderm, an inner called the ento- derm, and a middle layer called the mesoderm. 1 Later the organs are formed by the folding off of these tissues, and as the embryo grows it takes on the form of the adult. The passage of the fertilized ovum through the tubes requires about eight days, and during this time many thousands of cells are formed and enclosed in a' sac called the amnion. The collec- tion of cells surrounded by the amnion is called an embryo. After entering the uterus the embryo attaches itself to the mucous mem- brane, in the upper portion, usually near the opening of the Fal- lopian tubes. Changes in the uterine lining. The preparation of the mucous membrane of the uterus for the reception of the impregnated ovum includes changes that are similar to those that precede menstrua- 1 See page 28. CHAP. XXI] REPRODUCTION 483 tion. The mucous membrane becomes softer, thicker, and highly congested. In this condition it is known as the decidua vera, and the point to which the ovum becomes attached and which later develops into the placenta is called decidua serotina. Intrauterine growth. During the period of intrauterine life growth takes place rapidly. From the union of the ovum, which is ri? m ch (0.2mm.) in diameter, and the spermatozoon, which is much smaller, there is developed in two weeks' time an embryo which is about -J- of an inch (6.25 mm.). At the end of four weeks it is about inch (12.5 mm.) long, and at four months it is called a foetus, because it has the appearance of a human being, with well-developed eyes, fingers and toes separated, and the external genitals sufficiently formed to determine the sex. The usual du- ration of pregnancy is ten lunar or nine calendar months. At the end of six months the foetus is sufficiently developed to live out- side the mother's body, but it is frail and requires a great deal of care. For further details on the subject of reproduction the student is referred to standard works on physiology and obstetrics. 484 ANATOMY AND PHYSIOLOGY [CHAP. XXI Female Generative Organs Internal Organs External Organs SUMMARY Ovaries two glandular organs in which the ova are formed. Fallopian tubes two canals through which the ova reach the uterine cavity. Uterus a hollow, pear-shaped organ which receives the ovum. Vagina a canal that extends from the uterus to the vulva. Mons Veneris a cushion of areolar, fibrous and adipose tissue, in front of pubic bones, covered with skin and after puberty with hair. Labia majora two folds that extend from the mons Veneris to within an inch of the anus. Labia minora two folds situated between the labia majora. Clitoris small body, situated at apex of the triangle formed by junction of labia minora. Well supplied with nerves and blood-vessels. Hymen fold of mucous membrane that sur- rounds vaginal orifice. Vulvo-vaginal oval bodies situated on either side of the vagina. Urethral glands found chiefly be- neath the walls and floor of urethra. Attached Size Ovaries Two almond-shaped glandular bodies. Situated in posterior fold of broad ligament. To uterus by ligament of ovary. To tubes by fimbria?. 1^ inches long. | inch wide. inch thick. Weight 1-2 drachms. Fibrous tissue. Blood-vessels. Lymphatics. I Nerves. Graaf- ian fol- licles Covering of germinal epithelium. | Produce, develop, mature, and discharge ova. I Form an internal secretion. Structure Stroma 1. Outer coat fibrous tissue. 2. Inner layer of cells contain ovum. Function CHAP. XXI] SUMMARY 485 Location Divisions Three Coats Enclosed in layers of broad ligament. Extend from upper angles of uterus to sides of pelvis. 1 . Isthmus or inner constricted portion near uterus. 2. Ampulla dilated portion which curves over ovary. 3. Infundibulum trumpet-shaped extremity fimbrise. 1. External, or serous. 2. Middle, or muscular. 3. Internal, or mucous, arranged in longitudinal folds and covered with cilia. Function Convey ova to uterus. Hollow, thick-walled organ, placed in pelvis between bladder and rectum. Fundus = rounded upper portion, above the entrance of the tubes. Body = portion below fundus, above neck. Cervix = lower and smaller portion which ex- tends into vagina. External, or serous, derived from peritoneum. Circular layer j Interlaced in Muscular Longitudinal layer \ every direc- Spiral layer J tion. Mucous membrane, lines the uterus. Uterine arteries from internal iliacs. Ovarian arteries from aorta. Remarkable for tortuous course and frequent anastomoses. Broad, or lateral two layers of serous mem- brane. Round two fibro-muscular cords. Utero-sacral two partly serous, partly mus- cular, ligaments. Anterior peritoneal floor of the utero-vesical pouch. Recto-vaginal peritoneal floor of the recto - vaginal pouch. To receive ovum, and if it becomes fertilized to retain it until developed and then to expel it. Canal Extends from uterus to vulva. Outer coat is fibrous. Middle coat is muscular. Mucous coat, or lining, arranged in rugae. Location Placed between urethra and rectum. Divisions Three Coats Blood- vessels Ligaments Function Three Coats 486 ANATOMY AND PHYSIOLOGY [CHAP. XXI Function Ovulation Formation and development of ovum. Retention and sustenance of fecundated ovum. Puberty Age at which sexual organs become matured and functional. Girl changes to woman. Process of development and maturation of fol- licle and ovum, and discharge of ovum. from the uterus. Occurs on an y twenty-eight days. Extends ? (14 years) to the menopause, 3 (about 45 years). This repre- .d-bearing period of a woman's 1. General congestion of gener- ative organs, including breasts. 2. Hypertrophy and congestion of mucous membrane of uterus. 3. Capillary hemorrhage. Epi- thelium is cast off. 4. Following menstruation a new epithelium is formed. Probably dependent on internal secretion of ovaries, and pos- sibly is aided by power in- herent in uterine muscle. ,ure's way of preparing uterine iption of fertilized ovum. Menopause Physiological cessation of the menstrual flow. Accessory organs of generation. Function To secrete milk to nourish infant. f Extend from second to sixth rib. 1 Sternum to arm-pit. Outer surface convex papilla projects from centre called nipple contains openings of milk ducts. Nipple surrounded by areola. 1 . Consists of connective tissue framework which divides the gland into about twenty lobes. 2. Lobes are subdivided into lobules. 3. Lobules are made up of terminal tubules of the duct. 4. Each lobe possesses its own excretory duct, which is called lactiferous and is sacculated. Axillary. Internal mammary. Intercostal. A flow of blooc average evei from pubert or climacteri sents the chi life. Physiology of Gen- erative Organs Menstrua- Changes in connection tion with men- struation . Connection between ovu- lation and menstruation Purpose Na walls for rec< Location Mammary Glands Structure Blood- vessels CHAP. XXI] SUMMARY 487 Mammary Glands Colostrum Milk Male Generative Organs Nerves Intercostal. Primary development at time of puberty, prob- ably due to internal secretion of ovaries. Functional development follows conception, probably due to chemical substances that result from metabolism of fcetus. Active se- cretion stimulated by emptying milk ducts and influenced by nervous system. Water Secreted from blood. Develop- ment Secretion of milk Salts Sugar Proteins Fat Formed by disintegration of cells lining lactiferous tubules. Thin yellowish fluid secreted during first few days of lactation. Proteins 5.71 per cent Fat 2.04 per cent Composi- \ Sugar 3.74 per cent tion Salts 0.28 per cent Water 88.23 per cent Composi- tion Differ- ences Human Cow's Water 87-88% 87.00% Proteins 2-3% 4.00% Fat 3-4% 4.00% Lactose 6-7% 4.30% Salts 2-3% 0.70% Different relative proportions. \ Caseinogen Human < , . Difference in proteins Difference in reaction I Lactalbumin f . Cow's I Casein g en * \ Lactalbumin . Difference in / Human small flocculi. curds 1 Cow's heavy curds. Human amphoteric. Cow's amphoteric, but more nearly acid. Testes. Vas deferens. Seminal vesicles. Ejaculatory ducts. Spermatic cords. The penis. The prostate gland. Cowper's glands. 488 ANATOMY AND PHYSIOLOGY [CHAP. XXI Testes Structure Two glandular organs which produce the spermatozoa. Testicle proper ovoid body covered by fibrous tissue. Central portion consists of irregular cavities filled with seminiferous tubules and blood-vessels. Epididymis tortuous .tubule, forms long, narrow body which lies along posterior por- tion of testes. f In early foetal life in abdomen below kidneys. Location < Before birth are normally drawn downward to I scrotum, and are suspended by spermatic cord. f Production of spermatozoa. I Production of internal secretion. Function Vas Defer ens Continuation of epididymis, and serves to connect the epididymis and the seminal vesicle of each side. Seminal Vesicles Ejaculatory Ducts Scrotum Spermatic Cords Penis Two pouches located between bladder and rectum on outer side of each vas deferens. Connect vas deferens with ejaculatory duct. Function Serve as reservoirs for semen, to which they add a secretion of their own. Formed by union of seminal vesicles and vas deferens of each side. Run downward, converge, pass between lobes of prostate gland and open into the floor of the prostatic portion of the urethra. Pouch which contains testes and part of each spermatic cord. Covered with thick dark skin. Dartos reddish tunic under skin, consists Structure < of muscular and elastic tissue with numer- ous blood-vessels. Divided by septum into halves. Consists of the vas deferens, arteries, veins, lymphatics, nerves, and layers of fasciae connected by areolar tissue. Serve as pedicles for testes. Extends from the internal abdominal ring to the back of the testes. Consists of three cylindrical f Two corpora cavernosa, and bodies of erectile tissue I one corpus spongiosum. Contains urethra which extends from bladder to the end of penis. Covered with skin and mucous membrane. CHAP. XXI] SUMMARY 489 Urethra Extends from the bladder through the corpus spongiosum to the end of the penis. Length, 8 inches. Prostatic portion. Divisions Membranous portion. Penile or spongy portion. Consists f Mucous lining, of Numerous muscular fibres. The Pros- tate Situated in front of the neck of the bladder and around the commencement of urethra. Shape resembles chestnut. f Fibrous capsule containing glandular and mus- Consists of ] cular tissue. Glandular tissue consists of tubules which empty into urethra. Function Secretion of prostatic fluid. Cowper's Glands Located one on each side of membranous urethra, into which they empty. About the size of a pea. Function Secretion of a fluid which forms part of seminal fluid. Puberty j Age at which sexual organs become matured and functional. 1 Boy changes to a man. Semen f Fluid derived from the various sexual glands in the male. 1 Spermatozoa are the main elements. Reproduc- tion Function Produce another being. Accom- plished in two ways Asexually Sexually 1. Divide into two or more, e.g., budding of plants and animals. 2. Divide in two directly or by mitosis. 3. Divide into spores. 1. Individuals fuse permanently or temporarily. 2. Make sex cells (gametes). (a) In lower organisms shed in water and unite. (6) In higher organisms gamete retained by female, and male gamete is placed in re- productive tract of female. 490 ANATOMY AND PHYSIOLOGY [CHAP. XXI Impregna- tion Sperma- tozoon Consists of Maturation of Sex Cells Union of spermatozoon and ovum. Occurs in the Fallopian tubes or near the wall of the ovaries. Ovum Globular cell formed in ovaries ris inch in diameter. A long, narrow cell formed in testes, -sk* of an inch in length. Elliptical head which contains nuclear material and chromatin. Rod-shaped centre piece. .Tail. Capable of independent motion in a fluid medium. Function to fertilize ovum. Reduction of chromosomes in each sex cell to one-half the original number. Union of sex cells restores original number, hence one-half contributed by each sex. Theory of inheritance based on chromosomes. Develop- ment of Zygote 1. Impregnated cell divides into many cells. called blastoderm. Entoderm. 2. Blastoderm composed of Mesoderm. Ectoderm. 3. Tissues are folded off to form organs. 4. In two weeks time embryo is | inch long. 5. In four weeks tune embryo is \ inch long. 6. At four months called a foetus. Collection METRIC SYSTEM LI Millimetres Square Centi- metre 11 |4 5 Centimetres I 9 10 The area of the figure within the heavy lines is that of a square decimetre. A cube, one of whose sides is this area, is a cubic decimetre or litre. A litre of water at the temperature of 4 C. weighs a kilogramme. A litre is 2.11 pints or 33.81 ounces. A pint is 0.473 of a litre. (Liquid measure.) A litre is 1.76 pint. A pint is 0.568 litre. (Dry measure.) The smaller figures in dotted lines represent the areas of a square centimetre and of a square inch. A cubic centimetre of water at 4 C. weighs a gramme. Square Inch 1 Metre = 39.370432 inches. 1 Decimetre = 3.937043 inches. 1 Centimetre = .393704 inch. 1 Millimetre = .039370 inch. 1 Gramme 1 Decigramme 1 Centigramme 1 Milligramme 1 Dekagramme 1 Hektograinme 1 Kilogramme 1 Kilogramme 1 Kilogramme 15.432 grains. 1.543 grains. .154 grain. .015 grain. 154.323 grains. 1543.235 grains. 15432.350 grains. 35.274 ounces. 2.204 pounds. Avoirdupois weights are used in weighing the organs of the body. One ounce avoirdupois = 28.35 grammes. GLOSSARY Abduc'tion. Drawn away from the middle line of the body. Acromeg'aly. A disease characterized by an overgrowth of the extremi- ties and the face as well as the soft parts. Adduction. Brought to or nearer the middle line. Adre'nal. A small gland situated on the top of the kidneys. Same as supra-renal. Afferent. Bearing or carrying inwards, as from the periphery to the centre. Agglutination. The mutual adhesion or clumping of foreign cells, and loss of motility in the case of motile bacteria, when suspended in fluid containing a suitable agglutinin. Agglu'tinin. A substance occurring in blood plasma which produces ag- glutination by its action on the surface of foreign cells. Aggregated. Formed by a collection of several bodies ; crowded. Ag'minated. Arranged in clusters, grouped together, as the agminated glands of Peyer in the small intestine. Albu'mins. Thick, viscous substances containing nitrogen, that are solu- ble in water, dilute acids, dilute salines, and concentrated solutions of magnesium sulphate and sodium chloride. They are coagulated by heat and strong acids. Examples are : egg albumin and serum albumin of blood. Albuminu'ria. Presence of albumin in the urine. Alimen'tary. Pertaining to aliment, or food. Alve'olus, pi. Alve'oli. Any little cell, pit, cavity, fossa, or socket. Socket of a tooth, or an air-cell. Amito'sis. Fission or direct cell-division. Same as akinesis. Amce'ba. A single-celled organism, which is constantly changing its form by protrusions and withdrawals of its substance. Amphoter'ic. Partly acid and partly alkaline in reaction; having the power of turning red litmus paper blue, and blue litmus paper red. 491 492 GLOSSARY Ampul'la. The dilated part of a canal. Anab'olism. The process by means of which simpler substances are built up into more complex substances. Anastomo'sis. Communication of branches of vessels with one another. An'tigens. Immunizing substances which, when introduced into the body of a susceptible animal, may produce specific antibodies. An'trum. A cavity; applied especially to one in the upper maxillary bone, termed antrum of Highmore. Aponeuro'sis. A flat wide band of fibrous tissue which is attached to a muscle. Arach'noid. Resembling a web. The middle of the three membranes of the brain and spinal cord. Arboriza'tion. A branching distribution of veinlets or of nerve-filaments, especially the branched terminal ramifications of a nerve-axone. Are'olar. That form of connective tissue which fills the interstices be- tween the various parts of the body ; cellular. Asex'ual. Having no distinction of sex; having no relation to sex. Asexual reproduction, reproduction without sexual intercourse. Asphyx'ia. Suspended animation. Assimila'tion. The conversion of food into living tissue. At'las. The first cervical vertebra by which the head articulates with the spinal column, so called because it supports the head as Atlas was fabled to support the world on his shoulders. At'rophy. Wasting of a part from lack of nutrition. Au'ditory. Pertaining to the sense or organ of hearing. Augmenta'tion. The act of increasing or making larger. Aur'icle. A term applied to the ear-shaped cavities of the heart, also to the expanded portion of the external ear. Automatic. Performed without the will; spontaneous. Same as au- tonomic. Autonom'ic. Performed without the will; spontaneous. Same as au- tomatic. Auton'omy. Independence ; the condition of having independent func- tions, limitations, and laws. Ax'is. The second cervical or odontoid vertebra. Same as epistropheus. Az'ygos. Without a fellow ; hence, unpaired, single. Bi'fid. Cleft in the middle. Bifurcation. Division into two branches or forks. GLOSSARY 493 Blas'toderm. The primitive membrane or layer of cells resulting from the subdivision of the germ. Brach'ial. Belonging to the arm. Brach'io-cephal'ic. Of or pertaining to both the upper arm and head; as the brachio-cephalic (innominate) artery and veins. Bron'chiole. A small bronchial tube. Bron'chus, pi. Bron'chi. One of the two main branches of the trachea. Buc'cal. Pertaining to the mouth or cheeks. Buc'cinator. The trumpeter's muscle. A thin, flat muscle that helps to form the wall of the cheek. Bur'sal. Pertaining to bursts, membranous sacs. But'tock. The part at the back of the hip which, in man, forms one of the protuberances on which he sits. Butyr'ic Acid. A colorless liquid having a strong rancid smell and acrid taste. C 3 H 7 COOH. Cae'cum. The first portion of the large intestine a blind pouch. CaTculus, pi. CaTculi. A stone. Calyx, pi. Cal'yces. Small cup-like membranous canals, which surround the papillae of the kidney, and open into its pelvis. Canalic'ulus, pi. Canalic'uli. A small channel, or vessel. Cancellated. A term used to describe the lattice-work texture of bone. Ca'nine. Pointed like the tusks of a dog. Name given to the third tooth on each side of the jaw. Can'thus. The angle formed by the junction of the eyelids, the internal being the greater, the external the lesser, canthus. Car'dio-inhib'itory. An agent which restrains the heart's action. Car'pus. The assemblage of bones forming the wrist. Car'tilage. A solid but flexible material, forming a part of the joints, air-passages, nostrils, etc. Gristle. Casein'ogen. The curd separated from milk by the addition of rennet, constituting the basis of cheese. Cau'da Equi'na. A term applied to the termination of the spinal cord, which gives off a large number of nerves which, when unravelled, re- semble a Worse's tail. Cau'date. Tail-like. Centrifugal. Flying off or proceeding from the centre. Same as efferent. Centrip'etal. Tending or moving toward the centre. Same as afferent. Opposed to centrifugal. 494 GLOSSARY Cen'trosome. A peculiar rounded body lying near the nucleus of the cell. It is regarded as the dynamic element by means of which the machin- ery of cell division is organized. Cephal'ic. Pertaining to the head. Chi' asm. A crossing or decussation ; especially that of the fibres of the optic nerve. Choles'terin. A tasteless, inodorous, fatty substance found in small quantities in the protoplasm of all cells, especially in nerve-tissue, blood cells, and bile. Chon'drin. A kind of gelatin obtained by boiling cartilage. Chor'dae Tendin'eae. Tendinous cords. Chor'da Tym'pani. The tympanic cord, a branch of the facial, or seventh cranial nerve, which traverses the tympanic cavity and joins the gustatory, or lingual, nerve. Chro'mosome. Any one of the chromatin rods into which the spirem breaks during mitosis. Cica'trix. The mark, or scar, left after the healing of a wound. Cil'ia. Hair-like processes of certain cells. Coalesce'. To grow together. Cce'liac. Pertaining to the abdominal cavity. Collaterals. Situated at the side ; hence, also secondary. Colum'nae Car'neae. " Fleshy columns ; " muscular projections in the ventricles of the heart. Com'missure. A joining or uniting together. Something which joins together. Congenital. Born with a person, existing from or before birth. Contiguous. Adjacent; near; in actual contact. Convec'tion. A process of transfer or transmission, as of heat or elec- tricity. The term " convection currents " is used in the text, and applies to currents of air produced by differences in temperature and density. Warm air expands, becomes less dense, and is forced upward by the cooler air, which is heavier, and sinks down. In this way convection currents are established. Convolu'tions. The tortuous foldings of the external surface of the brain. Co'rium. The deep layer of the skin ; the derma. Cor'onary. A term applied to vessels, ligaments, and nerves which en- circle parts like a crown, as the coronary arteries of the heart. Cor'pus Callo'sum. A name given to the white medullary substance join- ing the cerebral hemispheres. GLOSSARY 495 Cor'pus Lu'teum. Yellow body, in the ovary taking the place of a Graafian follicle which has discharged its ovum. Correla'tion. The interdependence of organs or functions ; the reciprocal relations of organs. Cor'tex. External or surface layer of an organ, such as the kidney or brain. Cos'tal. Pertaining to the ribs. Crena'ted. Notched on the edge. Crib'riform. Perforated like a sieve. Cru'ra Cer'ebri. Pillars of the cerebrum. Crypt. A secreting cavity ; a follicle, or glandular cavity. Cul-de-sac. A tube or cavity closed at one end. Cu'ticle. A term applied to the upper, or epidermal, layer of the skin. Cu'tis Ve'ra. The true skin ; that underneath the epidermal layer. Cys'tic. Pertaining to a cyst, a bladder or sac. Decomposi'tion. (1) The separation of compound bodies into their con- stituent parts or principles. (2) Any ordinary process of decay, especially putrefaction. Decussa'tion. To cross in the form of the letter X. Degluti'tion. The act or power of swallowing. Del'toid. Having a triangular shape ; resembling the Greek letter A (delta) . Den'drite. A branching, protoplasmic process of a nerve-cell. Same as dendrone. Denti'tion. (1) The process of cutting teeth. (2) The time during which teeth are being cut. (3) The kind, number, and arrangement of teeth proper to any animal. Diabe'tes Insip'idus. A rare disease characterized by chronic polyuria, the urine having a low specific gravity, and being free from sugar. Diabe'tes Melli'tus. A morbid chronic polyuria, associated with thirst and often with wasting, and with the presence of abnormal con- stituents (sugar) in the urine. DiaTysis. The passage through a permeable membrane of a substance in solution. Diapede'sis. Passing of the red blood cells through vessel walls without rupture. Dias'tole. The dilatation of the heart. Diath'esis. A congenital condition of the system which renders it pecul- iarly liable to some diseases. 496 GLOSSARY Dichot'omous. Divided into two. Pertaining to or consisting of a pair or pairs. Dicrot'ic. Applied to the pulse, when there is a rebounding, like a double pulsation ; having a double beat. Diffu'sion. A property of certain bodies of dispersing or mixing them- selves with the surrounding medium. Diplog. The osseous tissue between the tables of the skull. Dis'cus Prolig'erus or germ disc. A term applied to a mass of cells clinging to the ovum when it is set free from the ovary. More recent term is " ovarian mound." Disintegration. A breaking apart. Distilla'tion. The act of distilling or of falling in drops. The operation of driving off gas or vapor from volatile liquids or solids, by heat in a retort or still, and the condensation of the products as far as possible by a cooler receiver. Dor'sal. Pertaining to the back, or posterior part, of an organ. Du'ra Ma'ter. The outer membrane of the brain and spinal cord. The "hard mother," called dura because of its great resistance, and mater because it is the guardian or protector of the brain. Ec'toderm. The completed outer layer of cells, or outer blastodermic membrane. Same as epiblast. Ectop'ic. Characterized as being out of place. Ectop'ic Gesta'tion. The name given to pregnancy, when the fecundated ovum, instead of entering the uterus, either remains in a Fallopian tube, or the abdominal cavity. Efferent. Bearing or carrying outwards, as from the centre to the periphery. Elemen'tary. Pertaining to or of the nature of an element or elements. Elimina'tion. The act of expelling waste matters. Em'bolus. A portion of a blood clot which has been formed in one of the larger vessels, and has afterward been forced into one of the smaller vessels, where it may act as a wedge. Em'bryo. The ovum and product of conception up to the fourth month, when it becomes known as the foetus. Empir'ical. Relating to a knowledge of medicine obtained by experience alone. Endocar'dium. Lining of the heart. Endogenous. Originating within the organism ; not exogenous. GLOSSARY 497 En'dolymph. The fluid in the membranous labyrinth of the ear. Endos'teum. The lining membrane of the medullary cavity of a bone; the internal periosteum. Endothe'lium. A term applied to single layers of flattened transparent cells, applied to each other at their edges and lining certain surfaces and cavities of the body. In contradistinction to epithelium. En'siform. Shaped like a sword. En'toderm. The completed inner layer of cells, or inner blastodermic membrane. Opposed to ectoderm. Same as hypoblast. Epicra'nial. That which is upon the cranium or scalp. Epider'mis. The outer layer of the skin. Epigas'tric. Lying upon, distributed over, or pertaining to the abdomen or the stomach. Epiglot'tis. The cartilage at the root of the tongue which forms a lid or cover for the aperture of the larynx. Epimys'ium. The sheath of connective tissue surrounding an entire muscle. Equilibrium. That condition of rest which results when all the forces acting in a body are equally opposed. In physiology it signifies the harmonious action of the organs of the body, as in standing. Evaporation. The act of resolving into vapor. In order to produce vapor, heat is necessary and, if not supplied, is taken from near ob- jects. Thus the heat necessary for the evaporation of perspiration is taken from the body. Excre'tion. The separation from the blood of waste particles ; also the materials excreted. Exog'enous. Developed outside of the body. Exuda'tion. The passing out of any liquid through the walls or mem- branes of the vessels containing it. FaTciform. Sickle-shaped. Fallo'pian. A term applied to tubes and ligaments first pointed out by the anatomist Fallopius. Fascic'ulus, pi. Fascic'uli. A bundle of close-set fibres. Fau'ces. The constricted passage at the back of the mouth connecting the oral cavity and the pharynx. Fecunda'tion. The act of making fruitful or prolific. Impregnation. Fenes'tra. A window. Fibril'la, pi. Fibrillae. A little fibre. 2K 498 GLOSSARY Fi'brous. Containing or consisting of fibres. Having the character of fibres. Fil'iform. Thread-like. Fim'bria, pi. Fim'briae. A border, or fringe. Fis'sion. A cleaving, or breaking up into two parts. Flat'ulence. Undue generation of gases in the stomach and intestines. Fo'cus. A point at which the rays of light meet after being reflected or refracted. Point at which an image is formed. Fce'tus. The child in utero from the fourth month of pregnancy till birth. Follicle. A little bag; a small gland. Fontanelle'. A term applied to the membranous spaces existing between the cranial bones in the new-born infant. In these spaces the pulsa- tion of the blood in the cranial arteries was imagined to rise and fall like the water in a fountain. Fora'men, pi. Foram'ina. An opening, hole, or aperture. Fos'sa, pi. Fos'sae. A depression, or sinus ; literally, a ditch. Fo'vea Centralis. Central depression of the macula lutea. The point of most acute vision. Fun'dus. The base or closed part of any organ which has an external opening. Fun'giform. Having the shape of a mushroom. Funic'ulus, pi. Funic'uli. A little cord, or bundle, of aggregated fibres. Fu'siform. Spindle-shaped. Gan'glion, pi. Gan'glia. A collection of nerve-cells in the course of a nerve, having the appearance of a knot. Generative. Pertaining to generation, or propagation. Connected with or resulting from the process of begetting. Gen'itals. Pertaining to the organs of generation. Gen'ito-u'rinary. Relating to the genital and urinary organs. Gesta'tion. The act or condition of carrying young in the womb from conception to delivery. Pregnancy. Glair'y. Like the clear white part of an egg. Gle'noid. A name given to a shallow cavity. Glob'ulins. Protein substances somewhat similar to the albumins, but differing in their solubility. Glomer'ulus. A botanical term signifying a small, dense, roundish cluster : a term applied to the ball-like tuft of vessels in the cortical portion of the kidneys. GLOSSARY 499 Glute'i, pi. of Glute'us. The muscles forming the buttocks. Gly'cogenolysis. Conversion of glycogen into glucose. Glycosu'ria. The presence of sugar in the urine. Graaf'ian Follicles, or Ves'icles. A term applied to the sacs in the ova- ries, which contain the ova, or cells. Granula'tions. Grain-like, fleshy bodies that form on the surface of wounds and ulcers. Gus'tatory. Belonging to the sense of taste. Haemoglo'bin. A compound protein found in the red cells of the blood ; its molecule consists of a protein portion and of a pigment portion, the latter containing one atom of iron. Hsemorrhoi'dal. Pertaining to haemorrhoids, small tumors of the rectum, which frequently bleed. Hem'atin. A proteid-free, pigmented constituent of haemoglobin ob- tained by treating with acids. Hemol'ysis. Destruction of the red blood-cells with a setting free of the haemoglobin. Hemophil'ia. A congenital, morbid condition, characterized by a tend- ency to bleed immoderately from any insignificant wound, or even spontaneously. Hi'lum, sometimes written Hi'lus. It is the depression, usually on the concave side of a gland, where vessels, nerves, and ducts enter or leave. Histol'ogy. That branch of anatomy which is concerned with the micro- scopic structure of the tissues of the body. Homoge'neous. Of the same kind or quality throughout; uniform in nature, the reverse of heterogeneous. Homother'mous. Of equal temperature. Applied to animals whose temperature remains practically constant. Hor'mone. A substance which is produced in one organ, and on being carried by the blood to another organ, stimulates this latter to func- tional activity. Hy'aloid. The name given the membrane which encloses the vitreous humor of the eye. Hydrother'apy. A mode of treating disease by the copious use of pure water, both internally and externally. Hyperglycae'mia. An abnormal amount of sugar in the blood. Hyper'trophy. Excessive growth; thickening or enlargement of any part or organ. 500 GLOSSARY Hypochon'driac. A term applied to the region of the abdomen under the cartilages of the false ribs. Hypogas'tric. Situated below the stomach. Pertaining to the hypo- gastrium. Hypoglos'sal. A name given to the motor nerve of the tongue. Hypoph'ysis. The pituitary body of the brain which is lodged in the cen- tral depression of the sphenoid bone. Il'eum. The twisted portion of the small intestine. ITium, pi. H'ia. The upper part of the os innominatum. Immis'cible. Not capable of being mixed. Inflamma'tion. A morbid condition characterized by pain, heat, redness, . swelling, and usually loss of function. Infundib'ulum, pi. Infundib'ula. A funnel-shaped canal. Ingest'. Taking food into the stomach. In'guinal. Pertaining to the groin. Inhibition. Restraint; the physiological arrest or suppression of any process, effected through nerves and special nerve centres. Innom'inate. A name given an artery, a vein, and a bone. Inocula'tion. The injection of virus into any part of the body, either as an operative procedure or by accident. Inos'culate. To unite, to open into each other. In'sulate. To isolate or separate from surroundings. Integ'ument. The skin, or outer covering, of the body. Intercellular. Lying between cells. Intercos'tal. Situated or intervening between successive ribs of the same side of the body. Interlob'ular. That which lies between the lobules of any organ. In'terstice. The space which stands between things; spaces between parts. Inter sti'tial. Pertaining to or containing interstices. Intes'tine. The part of the alimentary canal which is continuous with the lower end of the stomach ; also called the bowels. Intralob'ular. That which lies within the lobules of any organ. I'ris. The colored membrane suspended behind the cornea of the eye. Is'chium, pi. Is'chii. The lower portion of the os innominatum ; that upon which the body is supported in a sitting posture. Jeju'num. The part of the small intestine comprised between the duo- denum and ileum. GLOSSARY 501 Katab'olism. The process by means of which complex substances are rendered more simple and less complex. The opposite of anabolism. Lacta'tion. The period of giving milk. Lactiferous. Bearing, or conveying milk, as a lactiferous duct. Lacu'na, pi. Lacu'nae. A little hollow space. Lambdoi'dal. Resembling the Greek letter A. Lameria, pi. Lamellae. A thin plate, or layer. Lam'ina. A thin plate ; a germinal layer. Laryn'goscope. The instrument by which the larynx may be examined in the living subject. Lar'ynx. The upper part of the air-passage, between the trachea and the base of the tongue. Latis'simus Dor'si. The widest muscle of the back. Lens. A transparent substance, usually glass, bounded by two curved surfaces, or by one curved and one plain. There are two general classes of lenses : (1) concave, which are thinner at the centre than at the edges ; and (2) convex, which are thicker at the centre than at the edges. (See page 454.) Lob'ule. A small lobe. Lum'bar. Pertaining to the loins. Lu'men. The transverse section of a vessel or cavity. , Lym'phoid. Having resemblance to lymph. Mac'ula Lu'tea. Yellow spot. Malle'olus, pi. Malle'oli. A name given to the pointed projections formed by the bones of the leg at the ankle-joint. Malpi'ghian Bodies (so called in honor of Malpighi, a celebrated Italian anatomist). A term applied to small bodies, or corpuscles, found in the kidney and spleen. Ma'trix. The womb. Producing or containing substance. Matura'tion. The process of bringing, or of coming to maturity. Mea'tus. An opening leading to a canal, duct, or cavity. Mediasti'num. The septum of the pleura which divides the cavity of the thorax into two parts. ^ Medulla Oblonga'ta. That portion of the brain which lies within the skull, upon the basilar process of the occipital bone. Meibo'mian. A term applied to the small glands between the conjunc- tiva and tarsal cartilages, discovered by Meibomius. More recent term is tarsal glands. 502 GLOSSARY Mes'entery. A fold of peritoneum attaching some part of the intestine to the posterior wall of the abdomen. Me'sial. Median, dividing into two symmetrical portions. Mesocolon. A duplicature of the peritoneum covering the colon. Metab'olism. The changes taking place in cells, whereby they become more complex and contain more force, or less complex and contain less force. The former is constructive metabolism, or anabolism; the latter, destructive metabolism, or katabolism. Metacar'pus. The part of the hand comprised between the wrist and fingers. Metatar'sus. That part of the foot comprised between the instep and toes. Mito'sis. Processes of indirect cell-division. Same as karyokinesis. Mi'tral. Resembling a mitre. Mu'cin. The chief constituent of mucus. Myocar'dium. The muscular structure of the heart. My'osin. Chief protein substance of muscle. Na'ris, pi. Na'res. A nostril. Neurilem'ma. Nerve-sheath. Neurog'lia. The supporting tissue of the nervous system, contains the glia cells. Neu'rone. The nerve-cell, inclusive of all its processes. Node. A lymphatic ganglion. Nucle'olus, pi. Nucle'oli. A smaller nucleus within the nucleus. Nu'cleus, pi. Nu'clei. A minute vesicle embedded hi the cell protoplasm. Nutri'tion. The processes by which the nourishment of the body is ac- complished. Odon'toid. Tooth-like. (Ede'ma. A swelling from effusion of serous fluid into the areolar tissue. Or'bital. Pertaining to the orbit, the bony cavity in which the eyeball is suspended. Or'gan. Any part of the body with a special function. Or'ifice. An opening. Os, pi. O'ra. A mouth. Os, pi. Os'sa. A bone. Oscilla'tion. Swinging backward and forward ; vibration. Os Cox'a, pi. Os'sa Cox'se. The hip bone, or os innominatum. GLOSSARY 503 Os'sa Innomina'ta, pi. of Os Innomina'tum. " Unnamed bones." The irregular bones of the pelvis, unnamed on account of their non-resem- blance to any known object. Os'seous. Consisting of or resembling bone. Os'sicle. A small bone. Os'teoblasts. The germinal cells deposited in the development of bone. O'toliths. Particles of calcium carbonate and phosphate found in the internal ear. O'vum, pi. O'va. The human germ-cell. Pal'ate. The roof of the mouth, consisting of the hard and soft palate. Pan'creas. A compound secreting gland; one of the accessory organs of nutrition. The sweetbread of animals. Papillae, pi. of Papilla. Minute eminences on various surfaces of the body. Pari'etal. Pertaining to a wall. Parturi'tion. The act of giving birth to young. Pec'toral. Pertaining to the breast, or chest. Ped'icle. A stalk. Pedun'cle. A narrow part acting as a support. Per'meable. Capable of being passed through ; substances which allow the passage of fluids. Perone'al. Pertaining to the fibula; a term applied to muscles, or vessels, in relation to the fibula. Pe'trous. Having the hardness of rock. Phalan'ges. A name given to the small bones forming the fingers and toes, because placed alongside one another like a phalanx. Phar'ynx. The cavity forming the upper part of the gullet. Phlebot'omy. The opening of a vein ; venesection. Phona'tion. Utterance of vocal sounds. Phren'ic. Pertaining to the diaphragm. Pi'a Ma'ter. The most internal of the three membranes of the brain. Pig'ment. Coloring matter. Pis'iform. Having the form of a pea. One of the carpal bones. Placen'ta. Aflat, circular, vascular body which forms the organ of nutri- tion and excretion for the foetus in utero. Plan'tar. Pertaining to the sole of the foot. Plex'us. A network of nerves or veins. Pneumogas'tric. Pertaining to the lungs and stomach. 504 GLOSSARY Poi'kilother'mous. Changing the body temperature with the temperature of the surrounding medium ; applied to cold-blooded animals, bacteria, and plants. The human foetus is cold-blooded. Polyu'ria. Excessive flow of watery urine. Pons Varolii. " Bridge of Varo'lius." The square portion of medullary substance connecting the cerebrum, cerebellum, and medulla oblon- Poplite'al. The space behind the knee-joint is called the popliteal space. Prismat'ic. Resembling a prism, which, in optics, is a solid, triangular- shaped glass body. Prona'tion. The turning of the hand with the palm downward. Prona'tor. The group of muscles which turn the hand palm downward. Pseudopo'dium. A protrusion of the substance of an amoeba or an amoe- boid cell, as in locomotion. Psy'chical. Pertaining to the mind. Pu'berty. Sexual maturity in the human race ; the age at which repro- duction becomes possible. Pu'bis, pi. Pu'bes. The hairy region above the genitals, also used for os pubis, the portion of the os innominatum forming the front of the pelvis. Pyrex'ia. Elevation of temperature ; fever. Radia'tion. The act of spreading outward from a central point. The diffusion of rays of light. Rale. A rattling, bubbling sound attending the circulation of air in the lungs. Different from the murmur produced in health. Rec'tus, pi. Rec'ti. Straight. A name given to muscles of the eye and abdomen. Reflec'tion. The return of rays, beams, sound, or the like from a surface. Reflection of light is of two kinds, regular and diffused. When a beam of light enters a darkened room through a small opening and strikes a mirror, a reflected beam will be seen travelling along some definite path. This is called regular reflection. Should the light, however, fall on a piece of white paper, it would be reflected and scattered in all directions. This is called diffused reflection, and is caused by the inequalities of the reflecting surface. All rough surfaces, as well as dust and moisture in the atmosphere, serve to diffuse light. If this were not the case, it would be dark everywhere except in the direct path of light from some luminous body. GLOSSARY 505 ^^ Refrac'tion. The bending or deviation in the course of rays of light in passing obliquely from one transparent medium into another of dif- ferent density. Light waves travel with different velocities in mediums of different densities, the more dense the medium, the less the velocity. For in- stance, light will travel /(\ less rapidly in water than in air. For this reason where a ray of light in air strikes a body of water obliquely, it will be bent out of a straight line, as shown in the following diagram; the light ray AC, instead of following the straight line AB, is bent on strik- ing the surface of the dense medium, thereby being bent from its direct path toward C. Resiliency. The act of leaping, or springing back ; the act of rebounding. Res'tiform. In anatomy denoting a part of the medulla oblongata, called the restiform body. Retic'ular. Resembling a small net. Ret'if orm. Having the form, or structure, of a net. Ret'ina. The most internal membrane of the eye ; the expansion of the optic nerve. Ru'gae. A term applied to the folds, or wrinkles, in the mucous membrane, especially of the stomach and vagina. Sag'ittal. Arrow-like. Saliva'tion. An excessive secretion of saliva. Saphe'nous. A name given to the two large superficial veins of the lower limbs. Sap 'id. Possessing savor or flavor. Saponifica'tion. Conversion into soap. Se'bum, or Se'vum. A fatty secretion resembling suet, which lubricates the surface of the skin. jfcr- 506 GLOSSARY Secre'tion. The process of separating from the blood some essential fluid, which fluid is also called a secretion. Secre'togogue. An agent which stimulates secretion. Segmenta'tion. The process of division of the fertilized ovum before differentiation into layers occurs. Se'rum. The clear liquid which separates in the clotting of blood from the clot and blood cells. Ses'amoid. Resembling a grain of sesamum. A term applied to the small bones situated in the substance of tendons, near certain joints. Sig'moid. Curved like the letter s. Soleus. A name given to a muscle shaped like the sole of a shoe. Sphinc'ter. A circular muscle which contracts the aperture to which it is attached. Splanch'nic. Of or pertaining to the viscera. Squa'mous. Scale-like. Sta'sis. Stagnation of the blood current. Stim'ulus, pi. Stim'uli. Anything that excites to action. Sto'ma, pi. Sto'mata. A mouth; a small opening. Strat'ified. Formed or composed of strata, or layers. Stri'ated. That which has stria, furrows, or lines. Stro'ma. The foundation or bed tissue of an organ. Styloid. A long and slender process from the lower side of the temporal bone. Sudoriferous. A term applied to the glands secreting sweat. Sul'cus. A fissure between two convolutions of the surface of the brain. Supina'tion. The turning of the hand with the palm upward. Su'pinators. The muscles which turn the hand with the palm upward. Su'pra-or'bital. Above the orbit. Su'ture. That which is sewn together, a seam ; the seam uniting bones of the skull. Synap'se. Interlacing of terminal arborization of nerves. Sys'tole. The contraction of the heart. Tac'tile. Relating to the sense of touch. Tar'sus. The instep ; also the cartilage of the eyelid. Tem'poral. Pertaining to the temples ; the name of an artery and of a bone. GLOSSARY 507 Ten'do Achillis. " Tendon of Achilles." The tendon attached to the heel, so named because Achilles is supposed to have been held by the heel when his mother dipped him in the river Styx to render him in- vulnerable. Ten'don. The white, fibrous cord, or band, by which a muscle is attached to a bone ; a sinew. Throm'bus. Name given to a clot formed in a blood-vessel. Tibia'lis Ante'rior. The muscle situated at the anterior part of the tibia. Tox'ic. Poisonous. Trabec'ulae. A term applied to prolongations of fibrous membranes which form septa, or partitions. Transversa'lis. A term applied to a muscle which runs in a transverse direction. Trape'zius. A name given to the two upper superficial muscles of the back, because together they resemble a trapezium, or diamond-shaped quadrangle. Trap'ezoid. One of the bones of the wrist. The second one of the distal row on the radial or thumb side. Tri'ceps. A term applied to a muscle having a triple origin, or three heads. Tricus'pid. Having three points. Trigem'inal. Threefold ; triple ; also relating to the fifth nerve. Tu'bular. Having the form of a tube, or pipe. Umbili'cus. A round cicatrix, or scar, in the median line of the abdomen. Unicellular. Composed of a single cell. Va'gus. Pneumogastric nerve. Vas'cular. Relating to vessels ; full of vessels. Ver'miform. Worm-shaped. Ver'nix Caseo'sa. The fatty varnish found on the new-born infant, which is secreted by the sebaceous glands of the skin. Ver'tebra, pi. Ver'tebrae. The bones of the spine. Vibra'tion. The act of moving rapidly to and fro. Villus, pi. Villi. The conical projections on the valvulse conniventes, making the mucous membrane look shaggy. Vit'reous. Glass-like. A name applied to the transparent, jelly-like substance which fills the back part of the eyeball behind the crystal- line lens. 508 GLOSSARY Vo'mer. The thin plate of bone shaped somewhat like a ploughshare which separates the nostrils. Xi'phoid. Shaped like or resembling a sword, ensiform. Zygomat'ic. Of or pertaining to the malar bone, or this bone and its con- nections. Constituting or entering into the formation of the zygome. Zy'mogen. A mother substance or antecedent of an enzyme. INDEX (And see Glossary, pages 491 to 508.) Abdomen, divisions of, 279. muscles of, 119, 136. action of, 120. regions of, 279. Abdominal cavity, 18. ring, external, 121. internal, 121. wall, weak places in, 121. Abducens nerve, 422. Abduction, 94. Absorption, 325, 333. paths of, 325, 333. Accessory thyroids, 344. Accommodation, 453, 462. conditions affecting, 454, 462. Acetabulum, 83. Acetone, in urine, 370. Acid, 7. oxide, 7. Acromegaly, 347. Acromion process, 80. Adam's apple, 73, 252. Adduction, 94. Adductor muscles of thigh, 127. Adenoid tissue, 50. Adenoids, 278. Adipose tissue, 48. Adolescence, period of, 472. Adrenal bodies, 345, 353. Adrenalin, 345. Afferent nerve-fibres, 34, 42, 132. Air, complemental, 262. composition of, 263. effect of respiration upon the, 263. expired, 263. inspired, 263. reserve, 262, 270. residual, 262, 270. tidal, 262, 270. Albumins, 161. as food, 309. in urine, 369. Albuminuria, 369. Alcohol, 341. Alexia, 420. Alimentary canal, 271, 297. divisions of, 272. system, 26, 41. Alkalies, 7. Alveoli of lungs, 255. Amino-acids, 161, 308. Amceba, 23. Amoeboid movement, 23, 158. Amphiarthroses, 92, 96. Ampulla of semicircular canals, 442. Amylase, 320. Anabolism, 23, 325. Anastomosis of arteries, 197, 198. Anatomical position, 13. Anatomy, definition of, 13. divisions of, 13. Anemia, 156. Annular ligaments, 99. Anteflexion, of uterus, 467. Anteversion, of uterus, 467. Antibodies, in blood, 162, 171. Antigens, in blood, 162. Antithrombin, 163, 165. Antitoxins, in blood, 162. Antrum, of bone, 63. of Highmore, 70. Anus, 289. Aorta, 201. abdominal, 203, 207, 225. arch of, 202, 224. ascending, 202, 224. branches, of, 203, 224. descending, 203. thoracic, 203, 206, 224. Aphasia, 420. Apnoea, 264. Aponeurosis, 46, 98. Appendix, vermiform, 289. Aqueduct of Sylvius, 418. Aqueous humor, 452, 462. Arachnoid, 141, 411. Arborizations, end, 36. interepithelial, 36. Arch, palmar, 206. Areas of brain, 419, 428. Areola, 45. of mammary gland, 474. Areolar tissue, 44. Arm bone, 80. Arrector muscles of hairs, 380. Arterial tone, 182. Arterioles, 183. Artery, or arteries, 173, 181, 194, 197, 224. anastomosis of, 197, 198. aorta, 201. axillary, 205. basilar, 204. blood supply of, 182. 509 510 INDEX Artery, or arteries continued brachial, 205. branches of, 198. bronchial, 206. carotid, common, 203. external, 204. internal, 204. coats of, 181. cceliac axis, 207. division of, 198. distribution of, 197. dorsal, of foot, 213. elasticity of, 233. extensibility of, 233. femoral, 210. gastric, 207. hemorrhoidal, superior, 210. hepatic, 207, 295. hypogastric, 210. iliac, common, 210, 225. external, 210. internal, 210. innominate, 203. inosculation of, 198. intercostales, 207. lumbar, 210. mediastinal, posterior, 207. mesenteric, inferior, 209. superior, 208. - nerve supply of, 182. ossophageal, 207. ovarian, 209. pericardial, 207. peroneal, 213. phrenic, 210. plantar, external, 211. internal, 211. ' plexus of, 198. popliteal, 211. pulmonary, 199. radial, 206. renal, 208. sacral, middle, 210. severed, flow of blood from, 235. sheath of, 183. size of, 183. spermatic, 208. splenic, 207, 348. structure of, 181. subclavian, 205. suprarenal, 207. tibial, anterior, 213. posterior, 211. tone of, 182. ulnar, 206. uterine, 210. vertebral, 204. Arthrodia, 96. Articulations, 90 ; and see Joints. Ascending tracts of the spinal cord 406. Asphyxia, 265. Association areas of brain, 421, 428. Astigmatism, 454, 462. tlas, 75. torn, 3, 6. ttraction sphere, 21. Auditory apparatus, 437, 457. canal, 437, 457. nerve, 422, 442. Auricle of ear, 437, 457. Auricles of heart, 176. Auriculo- ventricular bundle of His, 180. Automatic acts, 410. Automaticity of muscle, 99, 231. Autonomic nervous system, 402. Axillary, artery, 205. vein, 216, 226. Axis, 75. cylinder process, 33, 34, 42. Axon, 33. Azygos veins, 221. Bacteria, action of, in large intestine, 324. in small intestine, 323. Bartholin, gland of, 471. Base, 7. Basic oxide, 7. Basilar membrane of ear, 441, 458. Baths, cold, 388. hot, 388. regulation of heat by, 388. Biceps, of arm, 123. of thigh, 127. Bicuspid, teeth, 277. valve, 178, 194. Bile, 322, 332. action of, 323. duct, common, 295. ducts, 295, 303. -secreting function of liver, 296. Bladder, 363, 373. Blastoderm, 27, 41. Blind spot, 450. Blood, 154, 168. antibodies in, 162, 171. antitoxins in, 171. changes, in inflammation, 159, 169. characteristics of, 154. circulation of, 228; and see Circula- tion. clotting of, 163 ; and see Coagulation of blood. coagulability of, 164, 171. composition of, 155, 161, 168. defibrinated, 165. difference between lymph and, 166. distribution of, 235. effects of respiration upon, 261, 270. enzymes in, 162. extractives in, 161, 162. functions of, 155, 168. gases in, 161, 162. haemoglobin, 156. in urine, 370. INDEX 511 Blood continued interchange between lymph and, 167. internal secretions in, 162, 343. opsonins in, 159. plasma, 160, 161, 170. -plates, 160, 170. proteins in, 161. quantity, 154. rate of flow of, 234. regeneration of, after hemorrhage, 165, 172. salts in, 162. serum, 163. special substances in, 162. summary of, 168. Blood-cells, 155, 168. red, 155, 168. differences between white and, 160, 170. function of, 156, 169. life cycle of, 157, 169. number of, 156, 168. white, 157, 169. amoeboid movements of, 158. differences between red and, 160, 170. function of, 158, 169. life cycle of, 160, 169. number of, 157, 169. varieties of, 158, 169. Blood-pressure, 235, 245. arterial, 235, 245. capillary, 235. effect of respiration on, 233. method of determining, 236, 245. normal degree of, 237, 245. venous, 235, 245. Blood- vascular system, 173, 193. Blue baby, 243. Bodily heat, 384. distribution of, 385. loss of, 386, 393. production of, 386, 393. regulation of, 387, 394. variations in, 389. Body, back view of, 15. cavities of, 17. contents of, 17, 18. chemical elements in, 5. front view of, 14. human, 16, 18. structural units of, 20. surfaces of, 13. Bone, or bones, 52. atlas, 74. axis, 75. blood-vessels of, 56. calcaneum, 87. callus, 57. canaliculi of, 55. cancellated, 53. classification of, 60, 88. clavicle, 79. coccyx, 77. compact, 55. composition of, 52, 59. dense, 53. depressions of, 62. digits, of foot, 88. of hand, 82. epistropheus, 75. ethmoid, 67. femur, 85. fibres of Sharpey, 56. fibula, 86. flat, 62. frontal, 65. functions of, 60, 88. growth of, 56. Haversian canals, 55. system, 55. humerus, 80. hyoid, 72. ilium, 83. incus, 439. inferior turbinated, 71 irregular, 62. ischium, 83. lacrimal, 71. lacunas of, 55. lamellae of, 55. long, 60. lower jaw, 72. malar, 71. malleus, 439. mandible, 72. marrow, 55. maxilla, 71. maxillary, inferior, 72. superior, 71. medullary canal of, 55, 61. metatarsus, 88. nasal, 70. number of, 60. occipital, 64. of arm, 80. of calf, 86. of carpus, 81, 82, 89. of cranium, 63. of ear, 88, 439. of elbow, 81. of face, 70, 88. of foot, 87, 88. of hand, 82. of head, 63, 88. of heel, 87. of hip, 83. of instep, 88. of leg, 82. of lower extremities, 82, 89. of metacarpus, 82. of metatarsus, 88. of skull, 63. of sole, 88. of tarsus, 87, 89. of thigh, 85. 512 INDEX Bone, or bones continued of thorax, 77. of trunk, 73, 89. of upper extremities, 78, 89. of wrist, 82. palate, 71. parietal, 65. patella, 86. pelvis, 83. periosteum of, 56. phalanges, of foot, 88. of hand, 82. processes of, 62, 63. pubes, 83. radius, 81. regeneration of, 56. ribs, 78. sacrum, 77. scapula, 79. sesamoid, 60. shin, 86. short, 62. sphenoid, 68. spongy, 53. stapes, 439. sternum, 77. structure of, 53, 54. summary of, 59, 88, 89. table of, 88, 89. temporal, 66. tibia, 86. ulna, 81. upper jaw, 71. varieties of, 59. vertebrae, 73, 74, 89. vomer, 70. Brachial, artery, 205. Brain, 410, 426 ; and see Cerebrum. association areas of, 421. divisions of, 412, 426. function, localization of, 419. membranes of, 410. motor areas of, 419. sense areas of, 420. speech areas of, 420. structure of, 411. summary, 426. ventricles of, 417, 427. weight of, 411. Breast bone, 77 ; and see Sternum. Breasts, 474, 487; and see Mammary glands. Breathing, see Respiration, 258, 267. nasal, advantages of, 249, 267. Broad ligaments of uterus, 468. Bronchi, 254, 268. Bronchial, arteries, 206. tubes, 254. Bronchioles, 254. Brunner's glands, 286. Buccal cavity, 18, 19, 273, 298. Buccinator, 109. Bursse, synovial, 143. Cajcum, 288. Calcaneum, 87. Calculi, 370. Calf bone, 86. Callus, 57. Calorie, 12, 341, 342. large, 12, 341, 342. small, 12, 341, 342. Calyces of kidney, 357. Canal, or canals, 63. auditory, 437. inguinal, 121. semicircular, 441, 458. Canaliculi, of bone, 55. Cancelli, of bone, 55. Canine teeth, 277. Canthus, of eye, 444. Capillaries, 173, 183, 194. distribution of, 183. function of, 184. influence of, on circulation, 233. structure of, 183. Capsule of Tenon, 447. Carbohydrates, 306, 327. function of, 337, 350. metabolism of, 335, 350. Carbon dioxide, 263. Cardiac muscle, 100. Carotid arteries, common, 203. external, 204. internal, 204. Carpus, bones of, 82, 89. Cartilage, 50. cricoid, 250. elastic, 47. hyaline, 50. summary of, 58. thyroid, 250. true, 50. varieties of, 50. white fibro-, 50. yellow, 51. Casts, in urine, 370. Catalysis, 9. Cauda equina, 404. Cavities, abdominal, 18. buccal, 18, 19, 273, 298. cranial, 17. dorsal, 17. glenoid, of scapula, 80. nasal, 18, 19, 248, 267. of body, 17,19.,^ contents of, 19. orbital, 18. pelvic, 18. spinal, 17. thoracic, 18. ventral, 17. Cell, or cells, 20. amoeboid movement of, 158. bipolar, 32. differences in, 25, 41. life activities of, 22, 40. INDEX 513 Cell, or cells continued mastoid, 66. meanings of term, 20, 66. . metabolism of, 23, 335. nerve, 32, 42. prickle, 30. reproduction of, 24. respiration in, 22. summary, 40. wandering, 158. Cell-division, 24. Central canal of cerebro-spinal system, 405, 417. Central lobe of cerebrum, 417. Centres, in medulla, 412. nerve, 412, 427. Centrosome, 22. Cerebellum, 413, 427. functions of, 414, 427. peduncles of, 414. Cerebro-spinal fluid, 411. Cerebrum, 415, 427. areas of, 419. convolutions of, 415, 427. cortex of; 415. fissures of, 415, 416, 427. functions of, 418. lobes of, 416, 427. localization of function in, 419. sulci of, 415, 427. Ceruminous glands, 482. Change, 4. chemical, 4. physical, 4. Chemical change, 4. equation, 6. formula, 6. Chemistry, 3. Chest, muscles of, 114, 135. Cheyne-Stokes respiration, 270. Chordae tendineae, 178. Choroid, 448, 461. Chyle, 167, 172. Chyme, 316. Ciliary body, 448, 461. processes, 448, 461. Ciliated epithelium, 29. Circle of Willis, 204. Circulation, of blood, 228, 244. changes in, in inflammation, 159, 169. diagram of, 229. factors governing, 223, 244. foetal, 240, 246. influence of capillaries on,, 233. influence of elasticity and extensibility of arteries on, 233. pulmonary, 229, 244. rate of, 230. summary of, 244. systemic, 229, 244. Circumduction, 95. Circumvallate papillae, 434. Clavicle, 79. 2L Climacteric, 473. Clitoris, 471. Clothing, regulation of bodily heat by, 388. Coagulation of blood, 163, 171. conditions, affecting, 164, 171. hastening, 164, 171. hindering, 164, 171. intravascular, 165, 172. value of, 164, 171. Coccyx, 77. Cochlea, 441, 458. Cochlear nerve, 442, 458. Coeliac axis, 207. Coenzymes, 312. Collar bone, 79. Collateral ganglia, 401, 425. Collaterals, 34, 36, 42. - Colon, 289. ascending, 289. descending, 289. transverse, 289. Colostrum, 476, 487. Columnar epithelium, 29. Complemental air, 262. Compounds, 3. inorganic, 5. organic, 5. Condiments, 340. Conduction, nerve, 410. Condylarthrosis, 96. Condyles, of bone, 63. of femur, 85. Conjunctiva, 445. Connective tissues, 44. adenoid, 50. adipose, 48. areolar, 44. bone, 52. cartilage, 50. elastic, 47. fibrous, 46. lymphoid, 50. neuroglia, 50. reticular, 49. retiform, 49. summary of, 57. varieties of, 44. Constipation, 325. Contractility, muscular, 100. Cord, umbilical, 240. Corium, 140, 145, 376. Cornea, 448, 460. Coronary arteries, 181. veins, 214. Corpora Arantii, 179. Corpuscles, blood, 155, 168; and see Blood-cells. Malpighian, of kidneys, 360, 372. of Pacini, 480. red, 155, 168. renal, 360, 372. tactile, 378. white, 157, 169. 514 INDEX Corpus callosum, 416. luteum, 465. Corti, organ of, 441, 457. Coughing, 266. Cowper's glands, 480, 489. Cranial cavity, 17, 19. nerves, 421, 428. Cranium, bones of, 63. Creatinin, in urine, 368. Crest, of bone, 63. of ilium, 83. Cretinism, 344. Cricoid cartilage, 250. Crying, 266. Crypts of Lieberkuhn, 286. Crystalline lens, 452, 462. Cutaneous membrane, 147. sensation, 430. Cuticle, 376, 390. Cutis vera, 376, 390. Cystic duct, 295. Cytoplasm, 21. Decidua serotina, 483. vera, 483. Decussation of nerve-fibres, 412. Defecation, 325. Defibrinated blood, 165. Degeneration of nerves, 408. Deglutition, 316. Dehydration, 9. Deltoid, 122. Dendrites, 33, 42. Dentine, 275. Derma, 377, 391. Descending tracts of spinal cord, 406. Diabetes mellitus, 291, 337. Dialysis, 10, 12, 167. Diapedesis, 159. Diaphragm, 18, 19, 117. Diarthroses, 92, 96. Diastase, 320. Diastole, 230. Diet, accessory articles of, 309, 340. regulation of bodily heat by, 387. Diffusion, 9. Digestion, 297, 304, 327. accessory organs of, 290. action of bacteria, 323. chemical, 311. in mouth, 315. in stomach, 315, 331. intestinal, 319, 332. mechanical, 310. necessity for, 311. processes of, 311, 329. summary of, 327. temperature necessary for, 312. Digestive fluids, enzymes in, 311. processes, 310, 329. chemical, 311. mechanical, 310. system, 271, 297. Digits, of foot, 88, 89. of hand, 82, 89. Diploe, 68. Disaccharids, as food, 306. Discs, inter vertebral, 76. Discus proligerus, 464. Dislocation, 95. Distal, 13. Dorsal artery of foot, 213. cavity, 17, 19. surface, 13. Douglas, pouch of, 469. Duct, bile, 295. common bile, 295. cystic, 295. ejaculatory, 479, 488. hepatic, 295. nasal, 445. Stenson's, 274. thoracic, 187, 195. Ductless glands, 343, 352. Ductus arteriosus, 240. communis choledocjms, 295. venosus, 240. Duodenal glands, 286. Duodenum, 284. Dura mater, 410. Dyspnoea, 264. Ear, bones of, 439. external, 437, 457. internal, 440, 458. middle, 438, 458. Ectoderm, 27, 41. Efferent nerve-fibres, 34, 37, 132. Ejaculatory ducts, 479, 488. Elastic tissues, 47. Elasticity of muscle, 100. Elbow bone, 81. Elements, 3, 20. in human body, 5. Elimination, 355, 371. organs of, 355, 371. Embolus, 165, 172. Embryo, 482. Emulsion, 12. Enarthrosis, 96. End arborizations, 36. Endocardium, 176. Endolymph, 440. Endosteum, 55, 59. Endothelium, 140. Energy, 9. value of food, 341. Ensiform process, 77, 78. Enterokinase, 321. Entoderm, 27, 41. Enzymes, 311, 312, 330. in blood, 162, 171. in digestive fluids, 311, 329. Epicritic sensations, 432. Epidermis, 28, 376, 391. Epididymis, 478. INDEX 515 Epigastric region of abdomen, 279. Epiglottis, 250, 251. Epimysium, 98. Epinephrin, in blood, 162. Epiphysis, 347, 353. Epistropheus, 75. Epithelial tissue, 28 ; and see Epi- thelium. Epithelium, 28. ciliated, 29. columnar, 29. functions of, 31, 32. pavement, 29. simple, 28. stratified,- 30. summary of, 41. transitional, 30. varieties of, 28. Equation, chemical, 6. Equilibrium, nitrogen, 340, 351. sense of, 443, 458. Erectile tissues, 479. Erector spinse muscles, 112. Erepsin, 321. Ethmoid bone, 67. Eustachian tubes, 278, 439. valve, 180. Excreta, 355, 371. discharge of, 355, 371. Excretion, 150, 153. table of, 150, 153. Excretory organs, 355, 371. system, 26, 41. Exercise, regulation of bodily heat by, 387. Exophthalmic goitre, 345. Expiration, 258, 269. Expression, muscles of, 109. Extensibility of muscle, 100. Extension, 94. Extensor muscles, of forearm, 124. of leg, 139. External, 13. oblique muscle of abdomen, 110. senses, 429. Extractives, in blood, 161, 162, 170. Extremities, 19. Eye, accessory organs of, 444. canthus of, 444. % muscles of, 133, 446, 459. nerves of, 446, 460. pupil of, 449, 461. white of, 447. window of, 448. Eyeball, 447, 460. dimensions, 447. muscles of, 133, 446. refracting media, 447, 460. tunics, 447, 461. Eyebrows, 444, 459. Eyelashes, 444. Eyelids, 444, 459. Face, 63. bones of, 70. muscles of, 104, 133. Facial nerve, 422. Fallopian tubes, 465, 485. Falx cerebri, 416. Fascia, or Fasciae, 46, 98. deep, 47. lumbar, 119. palmar, 47. plantar, 47. superficial, 47. Fatigue, 103, 132, 455. Fats, action of pancreatic fluid upon, 321. as food, 307, 328. decomposition of, 308. digestion of, 321. function of, 338. in blood, 162, 170. metabolism of, 338, 350. Fauces, 273, 278. Feces, 324. Female generative organs, 463. physiology of, 472. Femoral, artery, 210. vein, 220, 226. Femur, 85. Fenestra, ovalis, 438, 458. rotunda, 438, 458. Fever, 390, 394. Fibrin, 161. ^ Fibrinogen, f61. in blood, 163, 170. Fibro-cartilage, elastic, 51. inter vertebral, 76. white, 51. yellow, 51. Fibrous tissue, 46. Fibula, 86. Filiform papillae, 435. Fimbriae of Fallopian tube, 465. Fissure, 63. Flavors, 340. Flexion, 94. Flexor muscles, of forearm, 124. Fcetal circulation, 240, 246. Follicles, simple, 286. Fontanelles of skull, 69. Food, action of bile upon, 322. of gastric fluid upon, 318. of pancreatic fluid upon, 320. of saliva upon, 314. amount necessary, 342, 352. changes undergone by, in large intes- tine, 323, 332. in mouth, 313, 331. in small intestine, 319, 332. in stomach, 315, 331. classification of, 305, 327. definition of, 304. heat value of, 342, 351. Foot, bones of, 87, 88. digits of, 88. 516 INDEX Foot, bones of continued dorsum of, artery of, 213. phalanges of, 88. Foramen magnum, 65. of bone, 63. of Monro, 418. ovale, 178, 240. Forearm, muscles of, 124. Formula, chemical, 6. Fossa, glenoid, 67. nasal, 248. of bone, 63. Fovea centralis, 451. Fracture, 53. green-stick, 53. Frontal bone, 65. lobe of cerebrum, 416. sinuses, 66. Fungiform papillae, 435. Funiculi, of nerve fibres, 37. Gall-bladder, 297, 303. function of, 297. Ganglia, collateral, 401, 425. on spinal nerves, 408. sympathetic, 401, 425. terminal, 401, 425. vertebral, 400, 425. Ganglion, 39. Gases in blood, 161, 162, 171. Gaster, 299 ; and see Stomach. Gastric, artery, 207. fluid, 317, 330. lipase, 317. secretin, 317. Gastrin, 317. Gastrocnemius, 130. Generative organs, female, 463, 484. external, 470, 484. function of, 472. internal, 463, 484. physiology of, 472. male, 477, 487. Genioglossus, 109. Germinative layer of skin, 376. Gigantism, 347. Ginglymus, 96. Gladiolus, 77. Glands, 147. accessory thyroid, 344. adrenal, 345. Bartholin's, 471. Brunner's, 286. ceruminous, 382, 438. classification of, 148. compound, 148. Cowper's, 480. development of, 148. ductless, 149, 343, 352. duodenal, 286. intestinal, 286. lacrimal, 445. mammary, 474, 487. Meibomian, 444. of stomach, 282. of vulva, 471. parathyroid, 345. parotid, 274. prostate, 480. salivary, 274. sebaceous, 381, 392. secreting, 148. simple, 148. sublingual, 274. submaxillary, 274. summary of, 152. suprarenal, 345. sweat, 382, 392. tarsal, 444. thymus, 345. thyroid, 344. urethral, 471. vulvo-vaginal, 471. Glenoid cavity, 80. fossa, 67. Glisson's capsule, 296. Globulins, 161. Glomerulus, 360. Glossopharyngeal nerve, 423. Glottis, 251. Glucose, in urine, 369. Gluteus maximus, 127. medius, 127. minimus, 127. Glycogenic function of liver, 296. Glycogenolysis, 347. Glycosuria, 369. Goitre, 345. exophthalmic, 345. "Goose flesh," 381. Graafian follicles, 464, 484. Green-stick fracture, 53. Gristle, 50 ; and see Cartilage. Gullet, 278, 299. Haemoglobin, 156. Hair, 379, 392. Hamstring muscles, 128. Hand, body of, 82. bones of, 82. Haversian, canal, 54, 55. system, 55, 59. Head, 63. bones of, 63. muscles of, 104. of bone, 63. Hearing, 437, 442, 457. Heart, 173, 193. auricle, 176. auriculo-ventricular bundle of His, 180. -beat, 230, 244. cause of, 231. blood supply of, 181, 194. cavities of, 176, 193. chordae tendineae, 178. INDEX 517 Heart continued endocardium, 175. murmurs, 231. muscle, 100, 174. myocardium, 174. nerve supply of, 181, 194, 232. orifices of, 177, 193. papillary muscles, 178. pericardium, 175. sounds of, 231, 244. causes of, 231. summary, 193. valves of, 178, 194. bicuspid, 178, 194. function of, 179, 194. influence of, on circulation, 233. mitral, 179, 194. semilunar, 179, 194. tricuspid, 178, 194. ventricles, 176. Heat, bodily, 384. centres for, 386. distribution of, 385. loss of, 385. production of, 384. regulation of, 387, 394. variation in, 389. where produced, 384, 393. Heel bone, 87. Hemophilia, 164, 171. Hemorrhage, regeneration of blood after, 165, 172. Hemorrhoidal artery, superior, 210. Hepatic, artery, 207, 295. cells, 294. duct, 295. flexure, 289. vein, 223. Hernia, 121. Hiccough, 265. . Highmore, antrum of, 70. Hip, bones of, 83. Hippuric acid, 368. Hormones, 149, 343. Humerus, 80. Humor, aqueous, 452, 460. vitreous, 453, 460. Hunger, 433, 456. Hyaline cartilage, 50. Hyaloid membrane, 453. Hydrate, 8. Hydration, 8. Hydrochloric acid in gastric juice, 317. Hydrolysis, 8, 309, 311. Hymen, 471. imperf orate, 471. Hyoid, bone, 72. Hypermetropia, 454, 462. Hyperpncea, 264. Hypertonic, 11. Hypochondriac regions of abdomen, 279. Hypogastric, artery, 210. region of abdomen, 279. Hypoglossal nerve, 423. Hypophysis, 346, 353. Hypotonic, 11. Iced food or drinks injurious, 314. Iliacus, 126. Ileo-csecal valve, 289. Ileum, 284. Iliac, arteries, 210, 225. regions of abdomen, 279. veins, 220, 226. Iliopectineal line, 83. Ilium, 83. Images, inversion of, 455. Immune bodies, in blood, 162, 171. Impregnation, 481, 490. site of, 482. Incisor teeth, 277. Incus, 439. Indican, in urine, 369. Inferior maxillary nerve, 422. mesenteric artery, 209. turbinated bones, 71. Inflammation, circulatory changes in, 159, 169. Infundibulum of lungs, 255. Infusion, intravenous, 165, 172. Inguinal canal, 121. ligament, 119. regions of abdomen, 279. Inhibition, 33, 410. Innominate artery, 203. vein, 217, 226. Inorganic compounds, 5. Inosculation of arteries, 198. Insalivation, 313. Inspiration, 258, 269. Intercellular substance, 44. Intercostal arteries, 207. muscles, 115, 117. Interepithelial arborizations, 36. Interlobular veins, 294. Internal, 13. oblique muscle of abdomen, 119. secretions, 149, 343. in blood, 162, 343. senses, 429. Intervertebral discs, 77. Intestinal digestion, 319. fluid, 321. glands, 286. Intestine, discharge of waste matters from, 150. large, 288 ; and see Large intestine. small, 283 ; and see Small intestine. thick, 288 ; and see Large intestine. thin, 283 ; and see Small intestine. Intralobular veins, 294. Intravenous infusion, 165, 172. Inversion of images, 455. Invertase, 322. Ion, 7. Iris, 448, 461. 518 INDEX Irritability, 100. Ischium, 83. Island of Reil, 417. Islands of Langerhans, 291. Iso tonic, 11, 165. Jejunum, 284. Joints, 90. ball-and-socket, 93. classification of, 90. condyloid, 94. freely movable, 92. gliding, 93. hinge, 93. immovable, 90. movements of, 94. pivot, 94. saddle, 94. slightly movable, 92. summary of, 96. sutures, 90. Jugular veins, 214, 225. Karyokinesis, 24 ; see Mitosis. Katabolism, 335. Kidneys, 356, 372. blood supply of, 361, 372. calyces, 357. capsule, 356, 358, 360. function of, 362, 372. glomerulus, 360, 361, 362. Malpighian corpuscles, 360, 372. matter eliminated by, 355. nerves of, 362, 372. papillae, 358. pelvis, 357. pyramids, 360. structure, 357, 372. supports, 356. uriniferous tubules, 358, 372. Kinetic theory, 10. Knee-cap, 86. Labia majora, 470. minora, 470. Labyrinth, 440, 458. bony, 440, 458. membranous, 440, 458. Lacrimal apparatus, 445, 459. bones, 71. gland, 445. sac, 445. Lactase, 322. Lacteals, 188, 189, 195. Lactose, 476. Lacunae of bone, 55. Lamellae of bone, 55. Langerhans, islands of, 291. Language, basis of, 420. Large intestine, 288, 301. action of bacteria in, 324. changes undergone by food in, 323. coats of, 289. divisions of, 288. functions of, 290. movements of, 323. secretion of, 324. Larynx, 250, 267. Lateral, 13. Latissimus dorsi, 112. Laughing, 266. Leg, bones of, 82. Leucocytes, 158. Leucocytosis, 157. Leucopenia, 157. Levatores costarum, 115, 117. Levator palpebrae superioris, 108, 444. Lieberkuhn, crypts or follicles of, 286. Ligamenta flava, 47, 76. Ligaments, 46. annular, 99. inguinal, 119. of uterus, 468, 469, 485. Ligamentum nuchae, 111. Light, perception of, 451. rays of, in hypermetropic eye, 454, 462. in myopic eye, 454, 462. in normal eye, 453, 462. Limbs, 19. Linea alba, 120. Lipase, 318, 321. Liver, 292, 302. discharge of waste matters by, 296. fissures, 293. functions of, 296. ligaments, 292. lobes, 293. lobules of, 293. lymphatics, 296. minute anatomy, 293. nerves, 296. vessels, 293. Localization of brain function, 419. Lower extremities, bones of, 82. muscles of, 124, 139. Lower jaw-bone, 72. Lumbar arteries, 210. fascia, 119. regions of abdomen, 279. Lungs, 254, 268. anatomy of, 255. blood-vessels of, 257. capacity of, 262, 270. infundibulum of, 255. lobule of, 255. matters eliminated by, 355. nerves of, 259. Lymph, 154, 166, 172, 239, 246. differences between blood and, 166. flow of, 239, 246. formation of, 239, 246. function, 167, 172. interchange between blood and, 167. nodes, 185, 189, 195, 196. sources of, 166, 172. vascular system, 185, 19b. INDEX 519 Lymphatic duct, right, 187, 195. part drained by, 186, 187. Lymphatics, 185, 187, 195. classification of, 188. function of, 189. Lymphatic vessels, 185, 187, 195; and see Lymphatics, function of, 191, 196. location of, 191, 196. Lymph nodules, aggregated, of Peyer, 287. solitary, 286. Lymphocytes, 158. Lymphoid tissue, 50. Lymph spaces, 185, 187, 195. Macula lutea, 451. Malar bone, 71. Malleolus, external, 87. inner, 86. lateral, 87. medial, 86. Malleus, 439. Malpighian corpuscles, of kidney, 360, 372. Malpighian layer of skin, 376, 391. Maltase, 322. Mammary glands, 474, 487. Mandible, 72. Manubrium, 77. Marrow of bone, 55, 59. Mastication, 312. muscles of, 108, 134. Mastoid, cells, 66, 439. process, 66. Matter, changes in, 4. definition of, 3. forms of, 3. Maturation of sex cells, 481. Maxilla, 70. Maxillary bones, 70, 71. Meatus, external auditory, 437. of bone, 63. Medial, 13. Median line, 13. vein, 216. Mediastinal arteries, 207. Mediastinum, 257, 269. Medulla oblongata, 412, 427. centres in, 412. functions'of, 412, 427. Medullary canal of bone, 61. sheath, 34. Medullated nerve-fibres, 34, 42. Meibomian glands, 444. Membrana tympani, 439. Membrane, or membranes, 46, 140. basement, 145. classification of, 140. cutaneous 147. hyaloid, 453. mucous- 143 ; and see Mucous mem- branes. permeable, 11. pituitary, 248. Schneiderian, 248. semipermeable, 11. serous, 141 ; and see Serous membranes. summary of, 150. synovial, 142 ; and see Synovial mem- branes. Meninges of brain, 410. of spinal cord, 406. Menopause, 473. Menstruation, 472, 486. and ovulation, 472, 486. changes in connection with, 473. purpose of, 474. Mesenteric artery, inferior, 209. superior, 208. Mesentery, 272. Mesoderm, 28, 41. Metabolic changes, 335. factors promoting, 334. Metabolism, 22, 334, 349. changes occurring in, 335. factors promoting, 334. functions of, 334. of carbohydrates, 335, 350. of fats, 338, 350. of proteins, 339, 351. Metacarpus, bones of, 82. Metaplasm, 22. Metatarsus, 88. Metric system, 25, 491. Micturition, 364, 373. involuntary, 365. Milk, composition of, 477, 487. human and cow's, 477. secretion of, 476, 487. Milk sugar, 476. Mineral matter as food, 327. Mitosis, 24. Mixtures, 4. Modiolus, 441. Molar teeth, 277. Molecule, 3, 6. Monosaccharids, 306. Monro, foramen of, 418. Mons Veneris, 470. Motor areas of brain, 419, 428. nerve-fibres, 34, 37, 42, 395. plates, 37. tracts of spinal cord, 406. Motor-oculi nerve, 422. Mouth, 249, 273, 298; and see Buccal cavity. changes undergone by food in, 313, 331. digestion in, 315, 331. Mucous membranes, 143. function of, 146. gastro-pulmonary, 143. genito-urinary, 144 structure of, 144. summary of, 151. Mucus, 153. 520 INDEX Muscles, or muscular tissue, 97. adductors of thigh, 127. arrector, of hairs, 380. attachment of, to skeleton, 98. automaticity of, 231. biceps, of arm, 123. of leg, 127. blood supply of, 103. buccinator, 109. cardiac, 100, 174. cells of, 97. characteristics of, 100. classification of, 97, 131. contractility of, 100, 102. contractor of pupil, 449. deltoid, 122. diaphragm, 117. dilator of pupil, 449. elasticity of, 100. erector spinse, 112. extensibility of, 100. extensors of forearm, 124. external oblique, of abdomen, 119. fatigue of, 103. flexors of forearm, 124. gastrocnemius, 130. genioglossus, 109. glutei, 127. gluteus, maximus, 127. medius, 127. minimus, 127. gracilis, 127. hamstring, 128. heart, 174. iliacus, 126. inferior oblique, of eyeball, 107. insertion of, 99. intercostals, 115, 117. internal oblique, of abdomen, 119. involuntary, 99. irritability of, 100. latissimus dorsi, 112. lavatores costarum, 115, 117. levator palpebrae superioris, 108, 444. nerves of, 102. non-striated, 99. occipito-frontalis, 104. of abdomen, 119, 136. action of, 120. of arm, 122. of back, 111, 135. of chest, 114, 135. of expression, 109, 134. of eyeball, 104, 446. of face, 104, 133. of forearm, 124. of head, 104. of lower extremity, 125, 138. of mastication, 108, 134. of neck, 110, 134. of orbit, 104, 133. of shoulder, 122. of thorax, 115, 136. of tongue, 109, 134. of trunk, 111. of upper extremity, 121, 137. orbicularis oris, 109. palpebrarum, 444. orbital, 104. origin of, 99. oxidation of glycogen, 103. pectoral, 114. pectoralis major, 114. minor, 114. plain, 99. platysma, 110. posterior femoral, 128. pronators, of forearm, 124. properties of, 100. psoas magnus, 125. quadratus lumborum, 120. quadriceps extensor, 129. recti, of eyeball, 104, 105. rectus abdominis, 120. femoris, 129. sacrospinalis, 112. sartorius, 127. semimembranosus, 128. semite ndinosus, 128. serratus magnus, 115. Skeletal, 97, 98, 103 soleus, 130. sterno-cleido-mastoid ,110. stimuli of, 101. storage of glycogen, 103. striated, 97. striped, 97. styloglossus, 110. summary, 131. superior oblique, of eyeball, 106. supinators, of forearm, 124. tables of, 133-139. tetanus of, 102. to ni city of, 100. trans versalis, 120. trapezius, Ml. triceps, 123. varieties of, 97. vastus, externus, 129. intermedius, 129. intcrnus, 129. visceral, 99. voluntary, 97. Muscular contractility, 100. sense, 433, 456. system, 26, 41. tissue, 97 ; and see Muscle. Muscularis mucosse, 145. Myelin sheath, 34. Myocardium, 174. Myopia, 454, 462. . Myxcedema, 344. Nails, 379," 392. Nasal bones, 70. breathing, advantages of, 249, 267. INDEX 521 Nasal bones continued cavities, 18, 19, 248, 267. duct, 445. fossae, 248, 267. Neck, muscles of, 110, 134. Nerve, or nerves, abducens, 422. auditory, 422, 442, 458. -cell, 32, 42. centres, 38, 412. cochlear, 442, 458. cranial, 421, 428. degeneration of, 408. -endings, 36, 399, 424. reaction of, 399. . facial, 422. -fibres, 34, 42. afferent, 34, 42, 132. decussation of, 420. efferent, 34, 42, 132. funiculi of, 37. medullated, 34, 400, 424. motor, 37, 42, 132. non-medullated, 36, 400. secretory, 275. sensory, 36, 42, 132. ganglia, 39, 400, 424. glossopharyngeal, 422. hypoglossal, 423. impulse, 398. direction of, 399. identity of, 399. nature of, 398. speed of, 399, 424. .stimulus necessary for, 399, inferior maxillary, 422. mixed, 407. motor oculi, 422. of eye, 446. of nose, 436. of tongue, 435. olfactory, 421, 436. ophthalmic, 422. optic, 422. pathetic, 422. peripheral, 409. plexus, 37, 402, 425. pneumogastric, 423. processes, 33. regeneration of, 408. spinal, 407, 426. spinal accessory, 423. stimulation, artificial, 399. physiological, 399. superior maxillary, 422. tissue, properties of, 40, 43. varieties of, 399. trifacial, 422. trochlear, 422. trunks, 38. formation of, 37. Nerve-vagus, 423. vasoconstrictor, 182, 194. vasodilator, 182, 194. vasomotor, 182, 194. vestibular, 442, 458. Nervous system, 21, 39, 41, 395, 423. autonomic, 402. central, 39, 400. interdependence of, 403. divisions of, 400, 424. functions of, 423, 428. gray matter of, 38, 400. parts of, 400, 424. peripheral, 39. reaction circuit, 397. reflex concept, 395. regulation of bodily heat by, 386. sympathetic, 39, 40, 400. synapse, 396. white matter of, 38, 400. Sfeucleolus, 21. SJeuraxon, 33. Neurilemma, 34, 42. Neuroglia, 32, 50, 58. Neurones, 32, 35, 42. Neutralizat on, 8. Nipple, 474. Nitrogen equilibrium, 340, 351. Nodes of Ranvier, 34, 42. Non-medullated nerve-fibre, 36. Nose, 247, 267. external, 247, 267. functions of, 247, 267. internal, 248, 267. nerves of, 436. sinuses communicating with the, 144, 267. Nucleus of cell, 21. Obesity, causes of, 339, 350. Oblique muscles, of eyeball, 106. Occipital bone, 64. lobe of cerebrum, 417. Occipito-frontalis, 104. Odontoid process, 75. Odors, 435, 457. (Edema, 240, 246. CEsophageal arteries, 207. (Esophagus, 278, 299. Olecranon process, 81. Olfactory bulb, 437. nerve, 436. Omentum, 272, 282, 297. Ophthalmic nerve, 422. Opsonins, 159. Optic chiasm, 452. foramen, 452. nerve, 422, 446. Orbicularis oris, 109. Orbit, 446, 460. bones of, 446, 460. Orbital cavity, 18, 19. muscles, 104, 133. Organ, 26, 41. of Corti, 37, 441, 442. Organic compounds, 5. 522 INDEX Organules, 36, 42. Os coxae, 82. Osmosis, 12, 167. Osmotic pressure, 11. Osseous tissue, 52 ; and see Bone. Ossicles of ear, 439, 458. Osteoblasts, 56. Otoliths, 440. Ovarian arteries, 209. Ovaries, 463, 484. Overeating, effects of, 352. Oviducts, 465, 485. Ovulation, 472, 486. and menstruation, 472, 486. Ovum, 472, 481, 486. fecundated, development of, 482, 490. segmentation of, 482. Oxidation, 8. Oxide, 7. acid, 7. basic, 7. Oxyhsemoglobin, 156. Pacini, corpuscles of, 480. Pain, 432, 456. Palate, 273. Palate bones, 71. Palmar arch, deep, 206. superficial, 206. fascia, 47. Pancreas, 290, 301. functions of, 291. structure of, 290. Pancreatic fluid, 320. action of, upon food, 327. secretion of, 320. Papillae of skin, 377. of tongue, 434, 457. on mucous membrane, 146. Papillary muscles, 178. Paraglobulin, 161, 170. Parathyroids, 345, 353. Parietal bones, 65. lobe of cerebrum, 416. Parotid glands, 274. Patella, 86. Pathetic nerve, 422. Pavement epithelium, 29. Pectoral muscles, 114 Pectoralis major, 114. minor, 114. Pelvic cavity, 18. Pelvis, 83. brim of, 83. false, 83. female, 84, 85. inlet of, 85. male, 84. outlet of, 85. strait of, 83. true, 83. Penis, 479, 488. Pepsin, 318. Pericardial arteries, 207. Pericardium, 141, 175. Perichondrium, 52. Perilymph, 440. Perineum, 471. Periosteum, 56, 59. function of, in growth of bone, 57. Peripheral nervous system, 39. Periphery, 16. Peristalsis, 315, 319. Peritoneum, 141, 272. Peroneal artery, 213. Perspiration, 382, 392. insensible, 383. quantity, 383, 392. sensible, 383. Peyer's glands, or patches, 287. Phagocytosis, 159. Phalanges, of foot, 88. of hand, 82. Pharynx, 249, 277, 299. Phrenic arteries, 210. Physical change, 4. sciences, 3. Physics, 3. Physiological saline solution, 165. Physiology, definition of, 13. Pia mater, 410. Pinna, 437, 457. Pituitary body, 346. membrane, 248. Placenta, 240. Plantar, arch, 213. arteries, 211. fascia, 47. Plasma, 160, 161, 170. Platysma, 110. Pleura, 141, 257, 269. Plexus, arterial, 198. nerve, 37, 402, 425. Pneumogastric nerve, 423. Polysaccharids, 306. Pons Varolii, 414, 427. functions of, 414, 427. Popliteal artery, 211. Portal system, 223. vein, 223, 294. Position, anatomical, 13. Poupart's ligament, 119. Presbyopia, 454, 462. Pressure sensation, 430, 432. Prickle cells, 30. Process, acromion, 80. ensiform, 77, 78. mastoid, 66. nerve-cell, 398. odontoid, 75. of bone, 62. olecranon, 81. xiphoid, 77. Pronator muscles, of forearm, 124. Prostate, 480, 489. Protecting sheaths, 46, 367. INDEX 523 Proteins, adequate, 339. as food, 308, 328. classification of, 309, 328. conjugated, 309. derived, 309. digestion of, 308. function of, 339. inadequate, 340. in blood, 161, 170. metabolism of, 339, 351. simple, 309. Prothrombin, 163. Protopathic sensations, 432. Protoplasm, 5, 21. Proximal, 13. Psoas magnus, 125. Ptyalin, 314. Puberty, in female, 472, 486. in male, 480, 489. Pubes, 83. Pulmonary, artery, 199. system,' 198, 224. veins, 200. Pulse, 238, 245. frequency of, 239, 245. locations where it may be felt, 238, 245. points to note, in feeling, 238, 245. ratio of, to respiration, 239. variations in, 239. Pupil, of eye, 449, 461. contraction of, 449. dilatation, 449. Purin bodies, in urine, 368. Purkinje fibres, 189. Pus, in urine, 370. Pylorus, 281. Quadratus lumborum muscle, 120. Quadriceps muscle, 129. Rachitis, bones in, 53. Radial artery, 206. veins, 216. Radius, 81. Rales, 261. Rami communicantes, 401, 425. Ranvier, nodes of, 34, 42. Reaction circuit, 397. Receptaculum chyli, 187. Reciprocal reception, 96. Recti muscles, of eyeball, 104, 105. Rectum, 289. Rectus abdominis, 120. femoris, 129. Reflex action, 410, 423. concept, 395. Reflexes, classified, 398. Refracting media, 452. Refraction, 453, 462. Refractive apparatus, 453. Regeneration of blood, 165. of nerves, 408. Reil, island of, 417. Remak, fibres of, 36. Renal arteries, 208. corpuscles, 360, 372. Rennin, 318. Reproduction, 481, 489. Reproductive system, 26. Reserve air, 262. Residual air, 262, 270. Respiration, 258, 267. abnormal types of, 264, 270. cause of, 243, 269. cause of first, 260, 270. Cheyne-Stokes, 264. control of, 259. effect of, on air, 263. effect of, on blood, 261, 270. effect of, on blood pressure, 233. effect of, on lymph flow, 240. external, 258, 269. frequency of, 261. function of, 258, 269. heat regulation by, 386. internal, 258, 269. redematous, 265. rate of, 261, 270. ratio of, to pulse, 239, 270. Respiratory centre, 259, 269. reflex stimulation of, 244. movements, modified, 265. sounds, 261. system, 26, 41, 250, 267, 269. Restiform bodies, 414. Reticular tissue, 49. Retiform tissue, 49. Retina, 450, 461. layers of, 450. Retroflection, of uterus, 467. Retroversion, of uterus, 467. Ribs, 78. Rickets, bones in, 53. Rods and cones, 450. Rotation, 94. Round ligaments, of uterus, 469. Rugae, of stomach, 282. of mucous membrane, 145. of scrotum, 479. of vagina, 470. Rupture, 121. Saccule, 440, 458. Sacral artery, middle, 210. Sacrospinalis muscle, 112. Sacrum, 77. Saline solution, physiological, 165. Saliva, 314. functions of, 314. secretion of, 313. Salivary glands, 274, 298. Salt, 7. as food, 305. in blood, 161, 162, 171. Saphenous veins, external, 220. internal, 220. 524 INDEX Saponification, 321. Sarcolemma, P8. Sartorius, 127. Scapula, 79. Scarpa's triangle, 210. Schneiderian membrane, 248. Sclera, 447, 460. Scrotum, 479, 488. Sebaceous glands. 381, 392. Sebum, 381. Secretin, 317, 322. Secreting glands, 148. Secretions, 149. external, 149. internal, 149. summary of, 152. table of, 153. Secretory nerve-fibres, 275. Segmentation of ovum, 482. Semen, 480, 489. Semicircular canals, 441, 458. Semilunar valves, 179, 194. Semimembranosus, 128. Seminal vesicles, 479, 488. Semitendinosus, 128. Sensations, 430, 455 ; and see Senses. classification of, 430, 455. definition of, 429. epic ri tic, 432. organs necessary for, 429, 455. protopathic, 432. where interpreted, 430. Sense or senses ; and see Sensations. areas of brain, 420, 428. cutaneous, 430. exterior, 430, 455. external, 429, 455. interior, 430, 455. internal, 429, 455. muscular, 433. df equilibrium, 443, 458. of fatigue, 455. of hearing, 437. of hunger, 433. of pain, 432. of pressure, 430, 432. of sight, 444, 451, 459. of smell, 435. of taste, 433. of temperature, 430, 432. of thirst, 433. of touch, 430. visceral, 430. Sensory area of brain, 420, 428. fibres, 34, 36, 42, 132. tracts of spinal cord, 406. Serous cavities, 189. membranes, 141, 151. arachnoid, 141. classes of, 141. function of, 141. of capsule of Tenon, 141. of cavities, 141. of cerebrospinal axis, 141. of vascular system, 141. proper, 141. secretion, 151. Serratus magnus muscles, 115. Serum, 171. albumin, 161, 170. Sesamoid bones, 60. Sharpey, fibres of, 56. Sheath, myelin, 34. Shin-bone, 86. Shoulder blade, 79. muscles of, 112, 115. Sighing, 265. Sight, 444, 459. Sigmoid flexure, 289. Simple epithelium, 28. Sinews, 46. Sino-auricular node, 180. Sinuses communicating with nose, 144, .267. of bone, 63. of head, 70. venus, of skull, 214. Sinusitis, 70. Skeletal muscles, 97, 98. system, 26. Skeleton, 60. ^attachment of muscles to, 98. divisions of, 63. Skin, 376, 391. appendages, 379, 391. blood-vessels of, 378, 391. discharge of waste matters by, 383, 384. functions of, 376, 391. heat regulation by, 385. layers of, 376, 391. nerves of, 378, 391. summary, 391. Skull, 63. as a whole, 68. bones of, 63. diploe of, 68. Small intestine, 283, 300. action of bacteria in, 323. changes undergone by food in, 319. coats of, 284. digestion in, 319, 332. divisions of, 284. functions of, 288. glands of, 286. lymph nodules of, 286. movements of, 319. Smell, 435, 457. necessary conditions for, 435, 457. Sneezing, 266. Sobbing, 266. Soleus, 130. Solute, 12. Solution, 8. physiological saline, 165. Solvent, 12. INDEX 525 Speaking, 266. Specific gravity, 9. Speech areas in brain, 420. Spermatic arteries, 208. cord, 479, 488. Spermatozoon, 478, 481, 490. Sphenoidal fissure, 446. Sphenoid bone, 68. Sphygmomanometer, 236. Spina bifida, 77. Spinal-accessory nerve, 423. Spinal canal, 17, 19, 404. cord, 403, 426. central canal of, 405. functions of, 410, 426. membranes of, 406, 426. section of, 405. structure of, 404, 426. tracts of, 406. ganglia, 401. nerves, 407, 426. degeneration of, 408. distribution of terminal branches of, 409. ganglion on dorsal root of, 408. regeneration of, 408. roots of, 407. Spinous processes, of bone, 63. of ilium, 83. Spleen, 347, 354. Splenic artery, 207. flexure, 289. Sprain, 95. Stapes, 439. Starch, action of saliva on, 314. of pancreatic fluid on, 320. Steapsin, 321. Stenson's duct, 274. Sterno-cleido-mastoid ,110. Sternum, 77. Stimulants, 340. Stimuli, muscular, 101. nerve, 399, 424. Stomach, 280, 299. blood-vessels of, 283. coats of, 282. component parts, 282. curvatures, 282. digestion in, 315, 331. functions of, 283. glands of, 282. nerves of, 283. openings, 281. peristaltic action of, 316. Stratified epithelium, 30. Styloglossus, 110. Subarachnoid space, 407. Subclavian arteries, 205. veins, 216, 226. Subcutaneous tissue, 378. Sublingual glands, 274. Submaxillary glands, 274. Succus entericus, 321. Sucrase, 322. Sugar, 306. in blood, 162, 170. regulating centre, 336. Summation, 33. Superior maxillary nerve, 422. Superior mesenteric artery, 208. Supinator muscles, of forearm, 124. Suprarenal arteries, 207. capsules, 345, 353. Sutures, 90, 96. ' coronal, 90. frontal, 92. lamboidal, 90. of skull, 91. sagittal, 90. Swallowing, 314. Sweat, 382 ; and see Perspiration. Sweat-glands, 382, 392. Sylvius, aqueduct of, 418. Sympathetic ganglia, 401, 425. system, 40, 400, 425. interdependence of, 403. Symphysis, 92, 96. pubis, 83. Synapse, 396. Synarthroses, 90, 96. Synchondrosis, 92, 96. Syndesmosis, 92, 96. Synovia, 142. Synovial membranes, 93, 142. articular, 142. bursal, 143. function of, 143. vaginal, 142. System, 41. Systole, 230. Tactile corpuscles, 37, 378. Tarsal cartilages, 444, 459. glands, 444. Tarsus, bones of, 87, 89. Taste, 433, 456. buds, 433, 456. necessary conditions for, 433. organ of, 433, 456. sense of, 433, 456. Taste buds, 433, 456. Tears, 445. Teeth, 275, 298. function of, 277. permanent, 276. temporary, 276. Temperature, necessary for digestion, 314. sense of, 432. subnormal, 390. variations in, 389, 390, 394. Temporal bones, 66. mastoid portion of, 66. petrous portion of, 66. squamous portion of, 66. lobe of cerebrum, 417. 526 INDEX Tendo Achillis, 130. Tendons, 46, 98. Tenon, capsule of, 447. Terminal ganglia, 401, 425. Testes, 477, 488. descent of, 478. Testicle, 477 ; and see Testes. Tetanus of muscle, 102. Thigh, adductor muscles of, 127. bone, 85. Thirst, 433, 456. Thoracic cavity, 18, 19. duct, 187, 195. parts drained by, 186, 187, 195. Thorax, 76, 77. bones of, 77. muscles of, 115, 136. Thrombin, 163. Thrombus, 165, 172. Thymus, 345, 353. Thyroid, accessory, 344. cartilage, 250. foramen, 83. gland, 344, 352. Tibia, 87. Tibial arteries, 211. veins, 218. Tidal air, 262. Tissue, or tissues, 26, 41. adenoid, 50. adipose, 48. areolar, 44. cartilage, 50. classification of, 27. connective, 44 ; and see Connective tissues. definition of, 26. elastic, 47. epithelial, 28; and see Epithelial tissue. fibrous, 46. lymphoid, 50. muscular, 97 ; and see Muscle. nerve, 32, 40 ; and see Nerve. neuroglia, 50. origin of, 27. osseous, 52 ; and see Bone, reticular, 49. retiform, 49. Tone, arterial, 182. Tongue, 274, 280, 434, 457. muscles of, 109, 134. nerves of, 435, 457. papillae of, 434, 457. sensations in, 435, 457. Tonicity of muscle, 101. Tonsils, 273, 298. Torticollis, 111. Touch, sense of, 430, 432. Trachea, 253, 268. Transference of impulses, 410. Transitional epithelium, 30. Trans versalis, 120. Transverse fissure of cerebrum, 416. Trapezius, 111. Triceps, 123. Tricuspid valve, 178, 194. Trifacial nerve, 422. Trochanters of femur, 85. Trochlear nerve, 422. Trochoides, 96. Trunk, bones of, 73", 89. muscles of, 111. Trypsin, 320. Tubercle of bone, 63. Tuberosity of bone, 63. Tunics of eye, 447, 460. Tympanum, 438. ossicles of, 439. Ulna, 81. Ulnar artery, 206. veins, 216. Umbilical cord, 240. ^region of abdomen, 279. Under-nutrition, 252. Upper extremities, bones of, 78, 89. muscles of, 121, 137. Upper jaw-bones, 71. Urea, 296, 335, 367. Ureters, 363, 373. Urethra, female, 364, 373. jmale, 480, 489. Urethral glands, 471. Uric acid, 368. Urine, 365, 374. abnormal constituents of, 369. amount of, 366, 374. composition of, 367. excretion of, 364. reaction, 366. retention of, 365, 374. secretion of, 362, 372. specific gravity, 366. .suppression of, 365, 374. toxicity of, 371. Uriniferous tubules, 358, 372. Uterine artery, 210. Uterus, 463, 466, 485. blood supply of, 467, 485. cervix, 466. changes in, following impregnation, 466, 482. coats of, 467. divisions of, 466, 485. function of, 469. fundus, 466. ligaments of, 468, 485. os, 466. position of, 467. structure of, 467. Utricle of ear, 440, 458. Uvula, 273. Vagina, 463, 469, 485. Vagus nerve, 423. INDEX 527 Valve, or valves, Eustachian, 180. ileo-ca3cal, 289. of heart, 178, 194, 233. of veins, 184. Valvular conniventes, 145, 285. Vasa vasorum, 182, 194. Vascular system, 26, 41, 154, 168, 195, 201. changes in, at birth, 243, 246. Vas deferens, 478, 488. Vasoconstrictor nerves, 182, 195, 412. Vasodilator nerves, 182, 195, 412. Vasomotor centres, 412. jierves, 182, 195, 412. Vastus externus, 129. intermedius, 129. internus, 129. Veins, 173, 184, 194, 213, 225. axillary, 216, 226. azygos, 221, 227. basilic, 216. cava, inferior, 220. superior, 217. cephalic, 216. coronary, 214. deep, 213. femoral, 220, 226. hepatic, 223, 295. iliac, common, 220, 226. external, 220, 226. internal, 220, 226. influence of, on circulation, 223. innominate, 217, 226. interlobular, 294. intralobular, 294. jugular, external, 214, 225. internal, 214, 225. median, 216. popliteal, 211. portal, 223, 294. portal system, 223, 227. pulmonarv, 200. radial, 216. saphenous, external, 220. internal, 220. structure of, 184. subclevian, 216, 226. superficial, 213, 215. systemic, 214. thoracic, 217. tibial, anterior, 213. .posterior, 211. ulnar, 216. valves of, 184. Vena cava inferior, 218, 220, 226. superior, 214, 217, 225. Venae comites, 214. Ventilation, 263, 270. Ventral cavity, 17, 19. Ventral surface, 13. Ventricles, of brain, 417, 418, 427. of heart, 176. Venules, 183. Vermiform appendix, 289. Vernix caseosa, 382. Vertebra, 74, 75. false, 74. number of, 74. regions of, 74. true, 74. Vertebral artery, 204. column, 73. abnormal conditions of, 77. bones of, 74, 75. curvatures of, 75, 77. structure of, 75. ganglia, 400, 425. Vesicles, seminal, 479, 488. Vesicular follicles of ovary, 464. Vestibular nerve, 442, 458. Vestibule, of ear, 440, 458. Villi, 146, 285. Viscera, 17. Visceral muscles, 99. sensations, 430, 455. Viscus, 17. Visual apparatus, 444. Vital capacity, 262. centres, 412. Vitamines, 343, 352. Vitreous humor, 453, 462. Vocal cords, 251. Voice, 252, 268. difference between that of male and Jemale, 252. Vomer, 70. Vomiting, 315. Vulva, 470. glands of, 471. Vulvo-vaginal glands, 471. Wandering cells, 158. Waste products, 162, 170, 355, 371. discharge of, 355, 371. Water, as food, 305, 327. Wharton's jelly, 241. Willis, circle of, 204. Windpipe, 253. Wisdom teeth, 277. Wrist, bones of, 82. Wry neck, 111. Xiphoid process, 77, 78. Yawning, 265. Yellow spot, 451. Zygote, 27. Printed in the United States of America. RECENT IMPORTANT BOOKS FOR NURSES Materia Medica for Nurses Second Revised Edition BY A. S. BLUMGARTEN, M.D. ASSISTING VISITING PHYSICIAN TO THE LENOX HILL HOSPITAL ; LECTURER TO THE TRAINING SCHOOLS OF THE LENOX HILL HOSPITAL AND THE SKIN AND CANCER HOSPITAL, NEW YORK ; FIRST LIEUTENANT MEDICAL OFFICERS* RESERVE CORPS, U.S. ARMY Illustrated, Cloth, 8vo. Cross Index. $2.60 The announcement of a new edition of this very suc- cessful book is of particular interest to training schools desiring a thoroughly adequate text in this subject. The work has been thorougJily revised and entirely reset, with the addition of a chapter on the Administration of Medicines, the application of the Harrison Law to nurs- ing, and other important new features. Blumgarten's text is in pla n, simple English, intensely interesting in style, and is written along strictly teaching lines. It therefore contains clear, concise instructions throughout. Stress has been laid upon teaching facts, not words, with the result that, while thoroughly scien- tific, the book is free from the technical terminology in which seems to lie the fault of so many text-books for nurses. It will assist and train the nurse in the observation of the effects of drugs as produced upon actual patients in the wards. The physiological action is particularly arranged to facilitate the retention of the facts presented. A special feature will be found in an original and very elaborate chapter on Solutions. It enables the nurse to handle any problem in the calculation and administration of a required dose of a drug, or to make up any required solution. There is also a chapter on Prescription Read- ing, and there are numerous tables such as Saturation Points, Comparative Action of Various Drugs, etc., scat- tered throughout the text. It also contains all the new and non-official remedies in common use. THE MACMILLAN COMPANY Publishers 64-66 Fifth Avenue New York RECENT IMPORTANT BOOKS FOR NURSES Public Health Nursing BY MARY S. GARDNER, R.N. WITH AN INTRODUCTION BY Miss M. ADELAIDE NUTTING PROFESSOR OF NURSING AND HEALTH, TEACHERS COLLEGE COLUMBIA UNIVERSITY, NEW YORK Cloth, i2mo, 372 pp., %i.?$ Probably the best description of this unusual new book is contained in the following from the introduction by Miss Nutting : " Miss Gardner has performed an important service in placing at our disposal the first really comprehensive presen- tation of so timely a subject. She knows her subject from' within every stage of it. She reveals herself as a woman of quite exceptional administrative insight and her book is a contribution, indeed, to the literature of nursing and service." This work is the only one covering exactly this field and the new developments in public health nursing. Some of its most important chapters are on " The History of the Public Health Nursing Movement " ; " Modern Problems " ; " Duties of the Superintendents of Nurses and of the Staff Nurses " ; "How to Organize a Visiting Nurse Association"; "The Board of Managers " ; " The Staff Nurse " ; " Methods of Organization, Administration, etc." There are, in addition, chapters covering the special branches of public health nursing. THE MACMILLAN COMPANY Publishers 64-66 Fifth Avenue New Tork Elements of Anatomy and Physiology For Nurses BY PERCY M. DAWSON, M.D. ASSISTANT PROFESSOR OF PHYSIOLOGY, UNIVERSITY OF WISCONSIN Illustrated with many colored and half-tone plates. Cloth, I2mo, $1.75 The desire of many hospital training schools for a more condensed outline of this course has led Dr. Dawson to prepare this work. It contains many unusual features and the matter is presented in a very original way, the physiology being developed according to the method of teaching at the University of Wisconsin. The book will prove particu- larly valuable to those training schools in which the time devoted to these two subjects is somewhat limited. Bacteriology for Nurses Second Edition, Revised. Including Schedule for Laboratory Exercises, etc. BY ISABEL McISAAC LATE SUPERINTENDENT UNITED STATES ARMY NURSE CORPS Author of " Hygiene for Nurses," etc. Cloth j illustrated, $1.25 This is a completely revised edition of the well-known text-book which was, for years, the only book written distinctly for the use of nurses, and much new material has been added. The author has carefully confined herself to the needs of the class for whom it is intended and she has been singularly successful in avoiding unnecessary digression, making clear the practical as well as the theoretical. The scheme of the original work has been maintained. There are chapters on Structure, Mode of Development, and Composition of Bacteria; The Effect of Physical and Chemical Agents Upon Bacteria, and the Effects of Bacterial Growth; The Rela- tions of Bacteria to Disease; Immunity; Inflammation, Suppuration, Pneumonia, Epi- demic Cerebro-Spinal Meningitis; Typhoid Fever (Enteric Fever); Asiatic Cholera, Relapsing Fever; Infectious Diseases of Unknown Cause and Bacteria in Air, Soil, Water, and Food. Hygiene for Nurses BY ISABEL McISAAC Cloth, i2mo, $1.25 The pages of this book are full of just the information that every woman in charge of souls and bodies needs. The chapters on food, ventilation, sewage, causes and dissemi- nation of disease, household, personal, and school hygiene, the hygiene of occupation, disinfection, etc., are all of the most vital interest and value to the nurse. Primary Nursing Technique For First-Year Pupil Nurses BY ISABEL McISAAC Cloth, I2mo, $1.25 A valuable and thorough book for nurses starting on their course of study. It is written with the one object in view of inculcating into the minds of its readers the fact that an accurate knowledge of the human body is the first essential to successful nursing. THE MACMILLAN COMPANY Publishers 64-66 Fifth Avenue New Tork Chemistry for Nurses - BY REUBEN OTTENBERG, A.M., M.D. FORMERLY LECTURER TO THE NURSES* TRAINING SCHOOL, MT. SINAI HOSPITAL; INSTRUCTOR IN BACTERIOLOGY, COLLEGE OF PHYSICIANS AND SURGEONS, COLUMBIA UNIVERSITY, AND ASSISTANT IN CLINICAL MICROSCOPY, MT. SINAI HOSPITAL Cloth, i2mo, $1.00 Only within recent years has it been recognized by instructors in nurses' training schools that an elementary knowledge of chemistry is indispensable if students are really to understand what is taught them in the subjects of " Materia Medica" and " Dietetics." This has re- sulted in many states making chemistry a required study and it is rapidly becoming recognized, in an increasing number of states, as a necessary part of the course. This was the first text-book on elementary chemistry published distinctly for nurses. Dr. Ottenberg has pre- pared this splendid little book which presents the sub- ject, for the course in training schools, with simplicity and thoroughness. The fault of the elementary text- books on chemistry, previously used in this course for want of a distinct text for nurses, seems to lie in the fact that they do not take up the special points without which a knowledge of Dietetics or food values is impos- sible, while the more advanced texts are entirely too difficult for nurses, since they presuppose an amount of preliminary training which very few nurses have. It is believed that " Chemistry for Nurses " will fill a definite need, as pupil nurses have repeatedly asked for a text-book to answer their peculiar requirements. THE MACMILLAN COMPANY Publishers 64-66 Fifth Avenue New York UNIVERSITY OF CALIFORNIA Medical Center Library THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW Books not returned on time are subject to fines according to the Library Lending Code. Books not in demand may be renewed if application is made before expiration of loan period. 10m-7,'59(A3819h4)4128 ft