MMD 1M7 MEMCA PHYSIOLOGY FOR NURSES —Skull \ — Cervical vertebra; :- — Scapula — Dorsal vertebrae — Lumbar vertebrae PROFILE OF SKELETON. A TEXTBOOK OF PHYSIOLOGY FOR NURSES BY WILLIAM GAY CHRISTIAN, M.D. Professor of Anatomy, Medical College of Virginia AND CHARLES C. HASKELL, M.A., M.D. Professor of Physiology and Pharmacology, Medical College of Virginia ILLUSTRATED ST. LOUIS C. V. MOSBY COMPANY 1918 COPYRIGHT, 1918, tty C. V. MOSBY COMPANY Press of C. J'. Mosby Company 1918 PREFACE It is presumed that the pupil nurse, for whom this book has been compiled, is familiar with the writer's Anatomy for Nurses, and has a similar knowledge of physics and chemistry. Technical terms have been em- ployed, without full explanation, upon this assump- tion. A brief appendix containing an outline of some physical and chemical phenomena has been added for those who have not received a proper introduction to these subjects. In the preparation of the work we have chiefly re- lied on the work of Luciana, Howell, Pearce-Macleod, Jones and Bunce, Mallet's Syllabus of Chemistry, Ganot's Physics, and Bliss and Olive's Physics and Chemistry for Nurses. The work is an elementary one and has no claim to originality except in arrangement and treatment. W. G. CHRISTIAN. C. C. HASKELL. Richmond, Va. 560;" CONTENTS CHAPTER I - CIRCULATION 17 CHAPTER II RESPIRATION i 34 CHAPTER III FOOD AND DIGESTION , 43 CHAPTER IV THE FUNCTIONS OF THE LIVER 76 CHAPTER V THE SPLEEN 80 CHAPTER VI FUNCTIONS OF THE KIDNEY 82 CHAPTER VII THE FUNCTIONS OF THE SKIN 90 CHAPTER VIII THE DUCTLESS GLANDS 94 CHAPTER IX THE NERVOUS (SYSTEM 1M) U 12 CONTENTS CHAPTER X THE SPECIAL SENSES 122 CHAPTER XI SLEEP 138 CHAPTER XII • REPRODUCTION 142 CHAPTER XIII GROWTH AND OLD AGE 145 APPENDIX APPENDIX 147 ILLUSTRATIONS FIG. PAGE Profile of Skeleton Frontispiece 1. Simple tissues 18 2. White blood corpuscles from man 20 3. Diagram of entire circulation 22 4. Diagram of valves of the heart 25 5. Cross section of small artery and veins: A, artery; V, vein 27 6. The aorta and its branches 28 7. Apparatus for measuring the arterial blood pressure in man 31 8. The position of the lungs in the thorax ....... 35 9. Diagram of structure of lungs showing larynx, bronchi, bronchioles, and alveoli 36 10. Front view of organs. Semidiagrammatic 49 11. Diagram of the alimentary tube and its appendages . . 52 12. The stomach and duodenum opened 56 13. Schema of simple reflex arc 58 14. Cross section of pancreatic tubule 60 15. Injected lacteal vessels in two villi of human intestine . 63 16. The microscopic structure of the liver 77 17. Portion of transverse section of human liver 78 18. Vertical section of human spleen 80 19. Longitudinal section through the kidney 85 20. Diagrammatic representation of the course of the urinifer- ous tubules and the kidney vessels 86 21. The thyroid gland 95 22. Schema of simple reflex arc 100 23. B-rain, lateral view 101 -4. Cortical centers in man 103 25. Brain, mesial view 104 26. Diagram of section of spinal cord, showing tracts . . . Ill 13 14 ILLUSTRATIONS FIG. FAfiK 27. The simplest reflex arc in the spinal cord 112 28. Orbital muscles 126 29. Section through the anterior portion of the eye .... 127 30. Formation of image on retina 129 31. Errors in refraction 132 32. Tympanum of right side with the auditory ossicles in place 134 33. Semidiagrammatic section through the right ear .... 136 34. Diagrammatic view of the organ of Corti ...... 136 PHYSIOLOGY FOR NURSES PHYSIOLOGY FOR NURSES CHAPTER I CIRCULATION Just as anatomy is a study of form, physiology is a study of function. Anatomy studies the appearances of the bones, ligaments, muscles, vessels, nerves and vis- cera, by dissecting the dead body. Physiology explains that bones are supports and levers; ligaments, binding tissue ; muscles, moving agents ; vessels, channels for cir- culating fluids; nerves, conducting agents; viscera, agents of secretion or excretion necessary for life and growth. Physiology can not be learned from the dead body, though some of it can be guessed at, but must be discovered by observation of the living animal or plant. Examination and analysis of the cells of which bodies are composed may reveal their physical and chemical character, but the more thorough the analysis, the more complete the destruction of the cells and the more impos- sible it is to investigate their vital activities. Hence many vital phenomena are still unexplained, though the num- ber is daily decreasing. The most widely distributed of all the tissues of the body is the blood. It is the universal solvent for all ma- terial used in building other tissues, in keeping them iii a state of health by carrying food to them and by remov- ing worn out or injurious material from them. The func- tions of the blood and the forces of the circulation make, 17 18 PHYSIOLOGY FOR NURSE8 I CIRCULATION 19 therefore, a convenient point of departure in beginning the study of physiology. The blood consists of a liquid, plasma, and solid bodies, red corpuscles, or erytlirocytes, blood platelets; and white corpuscles, which are of two kinds, leucocytes and lymphocytes. The plasma is all of the liquid part of the blood as it exists in the living animal and is to be distinguished from " serum, " which is the liquid part after coagulation Jias occurred. Plasma consists chiefly of water, but contains other substances of the greatest importance. The inor- ganic salts, such as sodium chloride, calcium chloride, and potassium chloride, as well as compounds of these bases with other acid radicals, are of importance in re- gard to the phenomena of osmosis, as influencing the ir- ritability of muscle and nerve, and are supposed to play an important role in the maintenance of the heart beat. Calcium salts cause an increased vigor of contraction and if present alone, cause the heart to stop tightly con- tracted; while the salts of potassium tend to cause re- laxation. It is suggested that the presence of these salts in proper concentrations causes the alternate con- traction and relaxation of the heart during life. Among the organic constituents are proteins, which are known as fibrinogen, serum albumin, and serum glob- ulin or paraglobulin. In addition, there are what may be designated as temporary constituents of the plasma, sub- stances on their way from the digestive canal to the tissues, such as fat, sugar, the results of protein digestion; as well as waste products on their way to the organs of excre- tion; bodies known as hormones, which are produced at one part of the body and sent elsewhere to influence other structures; substances which are manufactured to enable the animal to overcome bacterial invasion; and 20 PHYSIOLOGY FOR NURSES certain substances which resemble ferments in their ac- tion. Among the latter may be mentioned protlirom- bin, which, as we shall see, is active, in causing blood- clotting or coagulation. Of the formed elements of the blood, the red corpus- cles or erythrocytes are the most numerous. There are about five million of these to the cubic millimeter of the blood of a healthy man ; women are supposed to have about five hundred thousand less. They contain a sub- stance known as hemoglobin, which, by virtue of its iron content, is capable of forming unions with gases, especially with oxygen, and to a less extent with car- bon dioxide. These unions, as we shall find, are essen- Small Large Polymorphic Polynuclear. Eosinophile. mononudear. monomiclear. Fig. 2. — White blood-corpuscles from man. (Hill's Histology.) tial for the processes of respiration. The number of these corpuscles is reduced under certain pathologic condition, as in the various anemias; and may be in- creased when there is a great loss of fluid from the body, as in cholera or where there is a diminution in the amount of oxygen in the surrounding air, as in ascents to great heights. The white cells serve an entirely different function in the body. There are from five to ten thousand to the cubic millimeter of blood on the average, but this num- ber is subject to wide variations under altered condi- tions. The white cells are of assistance in the digestion of protein and in the transportation of fat in the blood, CIRCULATION 21 which probably explains the increase in their numbers following a meal. Cold baths and pregnancy are other ''physiologic" causes of increased numbers of leuco- cytes. A very important duty of the white cells is to combat bacterial invasion, and it is found that many in- fectious diseases are accompanied by an increase in the number of the leucocytes., this leucocytosis often being of value in the diagnosis. In pneumonia, for instance, the number not infrequently is increased to forty or fifty thousand to the cubic millimeter. In the leucemias, there is often a still larger increase ; while in some other diseases, such as typhoid fever, there is a reduction in the number, this being known as a leucopenia. There are about three hundred thousand platelets to the cubic millimeter. These are small disc-shaped bodies when examined with proper care, but usually disinte- grate and appear simply as detritus in the ordinary stained specimens of blood. Their functions are imper- fectly understood; they appear to be of importance in the coagulation of the blood, and it is claimed that their number is reduced in the hemorrhagic diseases. Lymph. — It must be understood that the tissue cells are not bathed direct in blood. The blood, carried in its system of vessels, has been likened to a wholesaler, and the pnrt of the retailer, coming in intimate contact with the consuming tissue cells, is taken by the lymph. The lymph is derived from the blood by the processes of fil- tration and osmosis, and is poured out into the spaces surrounding the cells. Containing the nutritive sub- stances derived from the blood, it turns these over to the cells and receives waste products from the latter. It is forced into special vessels, knoAvn as lymphatic chan- nels, and finally is carried back into the blood stream through the right and left lymphatic ducts. Along the 22 PHYSIOLOGY FOR NURSES course of the lymphatic channels are found the lym- phatic glands, which act as niters, attempting to prevent the entrance of bacteria or toxins into the circulation. The "waxen kernels" are lymphatic glands that have become inflamed and swollen as the result of the action of some toxic agent. Coagulation. — The clotting or coagulation of the blood is nature 's way of stopping hemorrhage and where there is derangement of the process, serious or even fatal hemorrhage may occur from an apparently trivial wound. A substance known as prothrombin and salts of calcium is found in the blood. If calcium acts on pro- thrombin, it converts the latter into thrombin and throm- bin causes fibrinog'en, a soluble protein of the blood plasma, to assume an insoluble form, known, as fibrin, this latter constituting the clot, enclosing the red corpus- cles in its meshes. The white cells possess the power of movement, so they are not included in the clot to any considerable extent. That blood does not normally clot in the vessels, is explained by the presence of a substance known as antithrombin, which prevents the action of the calcium salts on the prothrombin. When tissues are wounded, another substance, known as kephalin or "thromboplastic'' substance, neutralizes the antithrom- bin and allows the conversion of prothrombin into active thrombin. If blood is obtained by puncturing a vein and drawing the blood into a perfectly clean syringe, contact with wounded tissue is prevented and coagulation is de- layed, because the thromboplastic substance is not de- rived from passing over wounded tissue. Clotting will oc- cur, however, because the platelets will gradually dis- integrate and furnish the requisite thromboplastic ma- terial. The hemorrhagic diseases which have been men- tioned, are accompanied by a marked increase in the Fig. 3. — Diagram of entire circulation. CIRCULATION 23 coagulation time, so that individuals have bled to death after the extraction of a tooth or the production of sim- ilar small wounds. The circulatory apparatus consists of a central pump- ing station, the heart; a set of vessels leading from the heart to all portions of the body, the arteries; an im- mense number of small thin-walled vessels, the capilla- ries, in which the arteries terminate; and a set of ves- sels, the veins, which return the blood to the heart. The schematic drawing shows that arteries constantly dimin- ish in size as they get further from the heart, that the capillaries are the terminations of arteries and begin- ning of veins, and that the veins, by one vein joining an- other, increase in size as they approach the heart. The total area of capillaries is greater than that of the veins and much greater than that of the arteries. If the blood in the arteries differs from that in the veins, it is obvious that there must be a sort of midpoint in the capillary system where arterial changes to venous blood; and if this is true, it is apparent that the arteries carry some- thing to the tissues which they need and that the veins take something away which is either useless or inju- rious. The object of the circulation of the blood is, there- fore, briefly, to feed or irrigate the tissues through the arteries and to drain them through the veins. But the veins can not pour out the blood so charged, because it would waste the blood which can be purified; so the lungs liave been provided to burn up the waste material and change venous back to arterial blood which is fur- ther cleansed by the liver and kidneys. The course of the circulation is then from the heart through the arter- ies and capillaries to the tissues where arterial is changed to venous blood; through venous capillaries and veins to the heart and thence to the lungs where 24 PHYSIOLOGY FOR NURSES venous is changed to arterial blood and thence back to the heart to go over the same route as long as life lasts. The heart is, therefore, the main force of the circula- tion. Anatomy has taught us that it is a four-chambered hollow muscle. The two thin-walled chambers at the base are called auricles, the two thick-walled chambers forming the apex, the ventricles. Both the left auricle and ventricle are thicker than the right, but the left ventricle is much thicker than any other part of the or- gan. The right half is concerned with venous blood and the pulmonary circulation. The blood from the upper extremities, head and neck is collected and poured into the right auricle through the superior vena cava; that from the lower part of the body enters the same cavity through the inferior vena cava. From the right auricle the course is into the right ventricle through the auric- iiloventricular opening, thence through the pulmonary artery into the lungs whence it is collected by the four pulmonary veins and carried into the left auricle from which it flows through the left auriculoventricular opening into the left ventricle from which it is pumped through the aorta to all parts of the body. The auriculoventricular openings are guarded by valves composed of triangular flaps, the right — tricuspid —having three, and the left — bicuspid, or mitral — hav- ing two. The two auricles fill at the same time. As the blood flows in through cavse or pulmonary veins, it passes through the auriculoventricular openings into the cor- responding ventricle until that cavity is nearly full. As the blood rises in the ventricle it floats the valve flaps away from the walls of the ventricles and toward the opening. This action continues until there is but a slit- like aperture between the flaps. Just at this moment the auricle contracts, forces into the ventricle all the CIRCULATION 25 blood it will hold and presses the valves tightly across the opening- into which it would project if the papillary muscles did not contract and hold the edges of the valve at just the right angle. This action of the auricles is called auricular systole (from a Greek word meaning to contract). With a barely perceptible pause ventricular systole begins, the blood is forced into the aorta and pul- monary artery, whose openings are guarded by three cuplike folds called semilunar valves. As the blood rushes between these cups some of it gets into three lit- Fig. 4. — Diagram of valves of the heart. The valves are supposed to be viewed from above, the auricles having been partially removed. A, aorta with semilunar valve; B, pulmonary artery and valve; C, tricuspid, and D, mitral valve; E, right, and F, left coronary artery; G, wall of right, and H, of left auricle; /, wall of right, and /, of left ventricle. (Stewart's Physi- ology.) tic pockets, sinuses of Valsalva, between the valve folds and the arterial Avails, so that when the force from be- hind ceases the weight of the blood and the elastic re- coil of the vessels force each flap towards the opening, and, the three flaps coming together, the return of blood to the heart is prevented. This completes the contrac- tile or systolic period of the heart cycle and the period of rest, diastole, begins. A cardiac cycle, therefore, con- 26 PHYSIOLOGY FOR NURSES sists of two distinct parts; i.e., auricular systole, ven- tricular systole, and diastole, or rest. The closure of the auriculoventricular valves takes place at the same instant; that of the semilunar valves a little later. The sound of the first, dull and low pitched and confused with the sound made by contracting muscle, is called the first sound of the heart; the sharp, high, short click of the semilunar valves, make the second sound. Cardiac systole lasts about the tenth of a second, diastole about five tenths; so that the heart is at rest about sixty per cent of the time. Exact closure of all the valves is necessary to prevent leakage. It follows, therefore, that if any valve is too short or too long, has a rough place on it either through the presence of a foreign body or a wound, it will not meet its fellows exactly and there will be a falling back of blood into the chamber which that valve guards. Or if the opening is too small from any cause, there will be greater difficulty in driving the blood through, or it would take a longer time. Either defect would cause a change in the heart sounds. Various infectious processes are apt to cause such damage to the valves through the production of "endo- carditis," an acute inflammatory process involving the inner lining of the heart. When the inflammation sub- sides, scar tissue appears and, as is always the case with such tissue, contraction causes a distortion of the leaf- lets with a resultant leakage. Rheumatic fever, tonsil- litis, chorea, and pneumonia are the commonest predis- posing causes for endocarditis. The heart is the chief, but not the only, force of the circulation. The arteries are lined by a thin coat — the Mima — continuous with the lining membrane of the heart ; but around this their wralls are composed of fi- CIRCULATION 27 brous, muscular and elastic tissue. The latter is partic- ularly important. If fluid is put into an iron pipe until it is full, 110 force will get any more of the liquid in ; but if the same experiment is tried with a rubber tube, not only can an additional amount be forced into the stretched tube, but, as soon as the power is withdrawn, the additional fluid will be squeezed out, even against gravity, by the elastic contraction of the tube. When the heart forces blood into the aorta, that tube expands. As soon as the heart ceases to contract, the elastic coat .•f'^'^&ij&S&S^^'' v"^^%£^i? -" :-M A ftoi v \ Fig. 5. — Cross section of small artery and vein: A, artery; V, vein. (Hill's Histology.) of the artery contracts. If the semilunar valves hold, no blood can return to the heart and the contraction of the elastic artery must drive the blood onward into the smaller arteries. The elastic recoil of the arteries them- selves, is, therefore, the second great force of the circula- tion and one which acts continuously. The heart acts only during systole, the recoil of the arteries continues during diastole. As the arteries diminish in size they offer greater resistance, partly by friction, to the pas- sage of the blood ; and as their distance from the heart increases and their strength diminishes, the heart's im- 28 PHYSIOLOGY FOR NURSES pact and the elastic recoil both lose power until, in mi- nute arteries the blood flow approaches the character of a steady stream instead of the jet-like type of the larger arteries. In the arteries the blood leaps in jets ; in the capillaries it oozes; in the veins it flows. It is like a swift torrent which spreads into a marsh where move- ment is barely perceptible until its outlet is found in a deep, dirty, sluggish stream. The venous current is collected by the veins from the capillaries. The blood, through capillaries and veins, still receives an impulse from the heart, but not in suf- ficient strength to complete the return circulation. Cer- tain accessory forces are, therefore, called into play. The first of these is the suction of the thorax caused by inspiration, and described under that head. A more widespread factor is that of the valves in the veins, par- ticularly those so located that gravity habitually retards the flow. These valves are half cup shaped, concavity upward, very much like the semilunar valves, so ar- ranged that the blood flows easily over their free sur- face, but is caught in the hollow cup when it attempts to fall back. From this position it is forced on to the next valve partly by the push of the heart from behind, partly by suction of the thorax in front and largely by the massage-like action of the muscles which squeeze and compress the veins and drive the blood to the next valve, where the same process is repeated. Circulation Time. — The circulation time can not be definitely stated. The usual estimate is that from twen- ty-five to thirty beats of the heart are required to com- plete the circulation ; i.e., to drive the blood throughout the body. About a fourth of this number completes the pulmonary circulation. The velocity through different vessels also varies as does the quantity supplied to each . 6 — The aorta and its branches. CIRCULATION 29 organ. The latter lias been determined by experiments which prove that in every minute each hundred grams of the leg receive 5 c.c. of blood ; while the same weight of spleen would receive 58 c.c., of brain 136 c.c. and of the thyroid no less than 560 c.c. in the same time. Circulation Velocity. — Circulation velocity does not refer to the rapidity of flow through any given vessel, but to the time it takes for a given portion of blood to pass between two points as from one jugular vein through the heart, pulmonary artery, veins, left heart, aorta and capillaries of the head to the opposite jugular. This is determined by putting some methyleiie blue in one jugular and watching for its appearance in the other. This has been accurately determined in many lower animals and is estimated to be about thirty-two seconds in man. As the rate of flow is much more rapid in the largest than in the smallest arteries, in the arteries than in the capillaries, and in the veins than in the capil- laries, it can not be calculated by simply watching the speed with which corpuscles pass through one of the vessels. Of course the velocity of the blood current will not be confounded with the rate of the pulse, which is an impact rather than a current. The Pulse. — The pulse is seen and normally felt only in the arteries. The capillary and venous systems are so much wider than the arterial, that the force of the heart- beat is not displayed in the pulsatile or expansile man- ner so characteristic of the latter. The column of blood extending from the heart throughout the arteries may be compared to a series of balls suspended by strings and each touching the other. If the first of the series is struck sharply the power will be transmitted through- out the series, but it will visibly affect the last only. If fresh blood is pumped into the aorta, that particular 30 PHYSIOLOGY FOR NURSES blood will immediately flow but a short distance, but the force will be applied to every drop of blood in every artery. Each artery will expand and contract just as the aorta does and the expansion will be synchronous with the heartbeat; but that particular jet of blood will not reach the artery being felt for several seconds. It follows from this that the greater the power of the heartbeat the stronger will be the pulse; the more fre- quent the heartbeat, the more rapid the pulse, the more the capillaries are expanded, the less the resistance to the outflow, the more compressible the pulse and the lower the blood pressure. In the lungs the blood circulates under the same gen- eral conditions as in other parts of the body. Pressure is less in the pulmonary vessels because the right ventri- cle is weaker than the left. Inspiration and expiration also affect both the systemic and pulmonary circulation. In inspiration about one-twelfth of all the blood in the body is in the lungs, while expiration reduces this to one-fifteenth or eighteenth. Blood Pressure. — If liquid be pumped into an inelas- tic tube, the pressure will be exactly proportionate to the quantity of fluid and the force of the pump. As soon as the pump ceases to act, the pressure falls to zero. If the same experiment be conducted with an elastic tube pressure will again be equal to force and quantity, but the elastic recoil of the tube will maintain some pressure after the pump ceases to act. If the tube be converted into two whose combined area is as great as that of the single tube, but with thinner walls, pressure will de- crease because friction will be greater ; and if the proc- ess of division be continued until each tube is of micro- scopic size, but their combined area is much greater than that of the original tube, pressure will be very greally CIRCULATION 31 diminished. If now several small tubes unite to form one, and this is joined by another formed in the same way and the process is repeated until there is but one tube, the pressure in that will be less than the pressure in the numerous microscopic tubes, and much lower than it was in the one large elastic tube because friction so Fig. 7. — Apparatus for measuring the arterial blood pressure in man. The pressure in the cuff is raised by means of the syringe until the pulse can no longer be felt at the wrist. This pressure is read off on the mercury manometer (systolic pressure). (Pearce-Macleod, Fundamentals of Hitman Physiology.) retards the flow that the larger tube can never be filled. The arteries, capillaries, and veins form such a set of tubes and blood pressure varies in these sets of vessels. 32 PHYSIOLOGY FOR NURSES As ordinarily understood blood pressure means arterial pressure and is taken during systole, systolic pressure or, during diastole, diastolic pressure. The method of determining pressure is to encircle the arm (because there is but one bone and the muscles, when compressed, squeeze the arteries uniformly) with a long rubber sac, enclosed in leather, which is connected by tubing Avith a column of mercury and an air pump. "When air is pumped into the sac until the blood can no longer pass under it, as shown by disappearance of the radial pulse, the height of the column of mercury is read. This is systolic pressure and, in healthy young men, varies be- tween 110 and 130 mm. of mercury. Pressure Forces. — Pressure forces are three in num- ber: i.e., the power of the heart, the resistance ot the vessels, and the quantity of blood. In normal animals, the two former change with changing conditions, so that a practically constant level of pressure is main- tained the greater part of the time. Decrease in the vol- ume of the blood tends to lower the pressure, but, within certain limits, this is compensated for by increase in the rate of the heart and a constriction of the vessels. Like- wise, if fluid is introduced into the vessels, it does not cause a marked and persistent rise in the pressure, due to the same factors working in the opposite direction. The volume of the blood remaining the same, certain drugs are capable of causing vascular contraction, as epinephrine, which, uninterfered with, would cause an enormous rise in pressure. Injecting this drug into the circulation does cause a rise in the pressure, but when this reaches a certain level, the heart is slowed, in or- der to prevent an undue strain. On the other hand, when the vessels are caused to dilate by nitrites, the CIRCULATION 33 heart, beats more rapidly in the attempt to raise the pressure back to the normal level. Occasionally, this compensatory action fails. Such is the case in fainting or syncope. Here, the vessels, es- pecially in the abdominal region, dilate, and insufficient pressure is maintained to supply the brain properly with blood, so unconsciousness occurs. In moderate hemor- rhage, the loss of blood is compensated for in the man- ner described, but when the loss has assumed very se- rious proportions, the pressure falls and unconsciousness results. It is obvious that this fall of pressure is con- servative ; if it did not take place, great difficulty would occur in regard to clotting. Therefore, it may be un- wise to resort to measures aimed to raise the blood pres- sure before the bleeding point has been located and the hemorrhage checked. Diseases which harden the walls of small vessels, con- verting them into inelastic tubes, have the effect of con- stricting vessels, increasing resistance and raising blood pressure. Many drugs affect blood pressure either, like digitalis, increasing the power of the heart, or, like the nitrites (amyl, sodium, etc.) by dilating peripheral vessels and causing a fall of blood pressure. Others act upon the nervous mechanism of the heart, which, roughly, consists of a set of sympathetic fibers which accelerate or augment the action of the heart and a set of vagus or pneumo gastric fibers which slow or inhibit its action. This subject will be discussed under the nervous system. CHAPTER II RESPIRATION The air which surrounds us is in the main composed of two gases, oxygen and nitrogen, thoroughly mixed but not chemically combined. Of these the nitrogen is inert while the oxygen is essential to animal life. The organ which enables us to bring this gas in contact with the blood is the lung, while its use in the animal econ- omy is called respiration. But taking oxygen into the lungs, would be of no service if the process stopped there. It is, therefore, carried by the blood into all parts of the body where the oxygen is used and inju- rious matter taken up and removed. If two gases be placed one on either side of a wet membrane, like parch- ment, they will mix with each other by a process called osmosis. If, therefore, a liquid, like blood, containing oxygen be brought in contact with tissues containing carbon dioxide, the two gases would interchange even if there were no chemical activity to promote the change. Blood going to all parts of the body carries oxygen in combination with hemoglobin. When in contact with live tissue this oxygen is given up to the tissue and car- bon dioxide is taken up and carried by the venous blood to the lungs where, in the cells of those organs, a re-ex- change is effected, the carbon dioxide being given up and oxygen, derived from the inspired air, takes its place. The last exchange is called the external and the first the internal respiration. The organs of respiration are the nose, pharynx, larynx, trachea and lungs. Except the last, and in all 34 RESPIRATION 35 but the ultimate air cells of the lungs, these organs are but variously modified tubes through which the air is drawn, heated and moistened. It is in the air cells that the thin Avails of the pulmonary capillaries bring the blood close enough to the inspired air for the exchange to take place. Respiratory Forces. — For normal respiration the re- spiratory forces are the diaphragm and certain muscles Fig. 8. — The position of the lungs in the thorax. (T. Wingate Todd.) (Pearce-Macleod, Fundamentals of Human Physiology.) which move the ribs. Essentially the lungs are a pair of elastic bags, communicating with atmospheric air through the breathing tubes, enclosed in a movable bony framework which is covered by soft tissues and lined, for each lung, by a frictionless membrane completely air-tight. If the framework increases in size, the lungs must either follow it or leave a vacuum between lung •°>f> PHYSIOLOGY FOR NURSKS and frame. Aii increase in the si/c of tlie thorax, there- fore, makes the air pressure in the lungs less than the pressure of the atmosphere and air enters the lungs un- til the pressure is equalized. Forced inspiration means simply forced increase in the size of the thorax requir- ing a corresponding amount of air to establish equilib- rium. The ribs slope downward and forward and are fixed behind. Consequently, when the anterior end is pulled upward they must push the sternum forward and increase the diameter of the chest from before back- wards. At the same time the spaces between them in- Fig. 9. — Diagram of structure of lungs showing larynx, bronchi, bronchioles, and alveoli. (Pearce-Macleod, Fundamentals of Unman Physiology.) crease and the chest grows from above downwards. If, now, the diaphragm, which is fastened around the bar- rel-like chest, convex upwards, contracts, it must flatten the dome and greatly increase the space within the thorax. It must be borne in mind that this space con- tains not only the heart and lungs, but the great vessels, and that the force which causes inrush of air can not but produce some suction (aspiration) which will influence their contents. As soon as the inspiratory muscles cease to act, the abdominal contents, resting against the under surface of the diaphragm, and held in place by RESPIRATION 37 the powerful and elastic muscles of the abdominal wall, begin to press on the diaphragm and force it to resume its dome shape. The ribs drop back into their position of rest, the elastic lungs contract and drive out the air and thorax, diaphragm and lungs are ready to repeat the act of inspiration. The descent of the diaphragm pushes the abdominal viscera downwards and forward and this movement communicated to the abdominal wall gives its name to this type of breathing, abdominal, which is most noticed in children. When the lower ribs only move the type is said to be inferior costal; when the clavicles and upper ribs move the type is superior costal. The latter is characteristic of civilized women and is a possible provision for pregnancy, though many observations indicate improper dress as a cause of this type of inspiration. In forced inspiration, as in asthma, other muscles are brought into play. The same is true of forced expi- ration where the abdominal muscles play a large part. Respiratory Cycle. — This consists of two parts, the in- take of air, inspiration, and the output or expiration. Inspiration takes a slightly shorter time than expiration, the average difference being the proportion of five to six; though in children, women, and the aged the pro- portion may be six to eight or even nine. There is a slight pause after expiration. Respiratory Sounds. — If the ear be applied to the chest during inspiration a soft murmur, like the rust- ling of leaves in a gentle wind, is heard, followed, dur- ing expiration, by a similar sound during a shorter lime. Note the apparent contradiction: The time of inspiration is shorter than that of expiration, but the in- spiratory sound lasts three times as long as the expir- atory. Both sounds seem to be caused by the friction of 38 PHYSIOLOGY FOR NURSES air entering and leaving the infundibula and alveoli. If the air vesicles are filled up, or the listening is done over large bronchi, the second is modified and becomes tubular. It is the difference in sound caused by the air moving in small tubes and large ones. Quantity of Air.— The total quantity of movable air in the lungs of an average man is about 230 cubic inches. Of this amount about 20 cubic inches is taken in at each inspiration, about 110 cubic inches can be taken in after an ordinary inspiration and about 100 cubic inches is the amount which can be forcibly expelled after an or- dinary expiration. The amount passing in and out in each ordinary respiratory cycle is called tidal air, that taken in by forced inspiration, complemental air and that which can be expelled by the greatest effort supple- mental. Tidal, complemental, and supplemental air to- gether constitute one's vital capacity. Not the utmost effort will expel all the air from lungs which have once been filled, a fact which causes lung tissue to float in water, which no other tissue will do. The fact that once filled lung tissue floats and that never filled sinks, often enables experts to determine whether a dead child has ever breathed or was born dead. The air remaining after fullest expiration is termed residual air and amounts to about 100 cubic inches. Number of Respirations. — Within the limits of health respirations may vary from sixteen to twenty-four per minute, or one respiration to four heartbeats. In child- hood breathing is more rapid and at all ages it varies with exercise or the position of the body, while in feb- rile diseases the rate greatly increases. Some patho- logic conditions diminish the rate. Modifications of Respiration. — When breathing is dif- ficult for any reason it is termed dyspnea, from two RESPIRATION 39 Greek words signifying "bad breathing;" when it is totally arrested, the condition is called asphyxia and when there is an excess of oxygen or too little carbon dioxide in the blood, so that respiration can be sus- pended without injury, a condition of apnea exists. Modifications of respiration are seen in sighing, yawn- ing, laughing and sobbing, snoring, hiccoughing and coughing. Sighing is a slow, large inspiration, followed by an audible rapid expiration. Yawning is practically an involuntary sigh accom- panied by a widely opened mouth. It may be caused by stomach pain (hunger) as well as the torpor which precedes sleep. Hiccough is a spasmodic contraction of the diaphragm accompanied by closure of the glottis. It is often patho- logic and uncontrollable. Coughing is a reflex act caused by irritation of the nerves of the larynx. The mechanism of the act is a full inspiration followed by a sudden strong expiration. Laughing and sobbing are, mechanically, identical. The diaphragm is the muscle employed in each act and the face is the organ of expression. Snoring is the vibration of the soft palate. CHEMISTRY OF RESPIRATION If two or more gases are confined in the same vessel they will mix or diffuse throughout the space. If water or other fluid be in the space, some of each gas will en- ter the fluid, or be dissolved in it; and, under some con- ditions, some of the gases may enter into chemical com- bination with the liquid. The amount of gas dissolved ;ni (I the amount in combination, will vary somewhat 40 PHYSIOLOGY FOR NURSES with the pressure applied. As the essential function of the respiratory act is to convey one gas to the tissues and another away; and as experiments prove that some of the gas is in solution, but most of it in combination, there must be pressure changes, or differences, in the lungs and in the tissues to facilitate the exchange. If the tidal air is analyzed we shall find that inspired rich in oxygen and that expired rich in carbon dioxide. The reserved air must, therefore, contain a larger amount of C02 than the complemental. Now as tidal air enters the alveoli and finds them filled with air con- taining a high percentage of C02, there must be a dif- fusion or mixing of air in the alveoli. This process of mixing goes on at all times. When arterial blood passes to the tissues it finds them filled with C02 existing under a pressure which causes it to enter into chemical combination as well as solution. The oxygen in the arterial blood, chiefly in combination with hemoglobin, finds the pressure lowered as soon as it reaches the tissues. Pressure on the oxygen being low, it escapes into the tissues ; that on C02 being high, it com- bines with the blood. Upon reaching the lungs the re- verse of this action takes place, venous blood giving up its C02 and taking oxygen instead because the air in the alveoli is rich in oxygen and poor in C02, while the blood is rich in C02 and poor in oxygen, the tendency being for oxygen to escape from the alveoli and C02 to escape from the blood into the alveoli until the pressure on each gas is equalized. Oxygen and carbon dioxide are the chief, but not the only, gases inhaled and exhaled. Atmospheric air con- tains, in a hundred parts, approximately 79 parts of ni- trogen, 20.96 parts of oxygen, .04 parts of carbon diox- ide and minute quantities of other gases with about 1 RESPIRATION 41 per cent of water. Nitrogen has no injurious effect, ex- cept by excluding oxygen. Like all nonpoisonous gases it may cause asphyxia if breathed pure, but would cause it no more quickly than lack of oxygen if the nitrogen were absent. Carbon dioxide is poisonous, but less fatal than carbon monoxide which acts by combining with the hemoglobin of the blood and excluding oxygen, because its compound with hemoglobin is much more stable than that of oxygen. The injurious effects of rarefied air, like that on high mountains, is due to lack of oxygen in the blood. Ventilation. — Briefly stated the problem of venti- lation is to maintain, in a closed space like a room, the nearest possible approximation to atmospheric condi- tions. The problem would be simple if it were not for the necessity of heating. A healthy adult gives off about six-tenths of a foot of C02 per hour, that is he changes the contents of a hundred feet of air from four-tenths to one foot of C02. If this process be carried too far, he will not only increase the actual C02 but, by using up the oxygen, still more increase the relative content. If a supply of 1,000 cubic feet of fresh air is furnished per hour for each well person, the room is sufficiently ven- tilated ; but in hospitals the amount required is 3,000 cubic feet. Nervous Mechanism. — Nervous mechanism is almost automatic. A center to control respiration is located in the medulla. The normal stimulus to which it responds is carbon dioxide. When the venous blood is sufficiently charged with that gas, the center sends a message, which is carried by the nerves to the muscles of inspiration which contract and cause an inrush of air. If there be an impediment to the intake, accessory muscles of in- spiration are called upon until the obstacle is overcome. 42 PHYSIOLOGY FOR NURSES If part of the lung is occupied by a foreign substance, as in pneumonia, the respiratory efforts are made more frequently because there is more C02 in the blood and the center is stimulated to greater activity. If there is too little C02, the center is less excited and the number of inspirations per minute will decrease, to rise again as soon as the proper amount of C02 is restored. CHAPTER III FOOD AND DIGESTION Digestion is the process by which physical and chem- ical alterations of foodstuffs, which fit them for absorp- tion, are effected. Animal and vegetable tissues contain foodstuffs of the same chemical composition; but some animals can not convert certain forms of vegetable mat- ter into food, while others can. When an animal feeds upon other animals it is called carnivorous and feeds upon tissues similar to its own. When it feeds upon vegetables it is called herbivorous and feeds upon tis- sues containing the same chemical elements but so ar- ranged as to be not easily digested by carnivorous ani- mals. With the aid of light, heat and moisture, vege- tables take up chemical elements from air and soil and combine them into the proper constituents of food for herbivorous animals, and these in turn, convert them into the similar, but more digestible foodstuffs required by man. Of the elements of the chemist, only about twenty en- ter into the composition of our tissues ; and of these, five form so much of our bulk that the others may be men- tioned as traces. The elements which chiefly concern us occur as follows, in every hundred parts : Carbon, 53 Oxygen, 22 Nitrogen, 16 Hydrogen, 7 Sulphur, 2 43 44 PHYSIOLOGY FOR NURSES The various constituents of the body may be divided into two great classes, organic and inorganic, and the first into those which contain nitrogen and those which do not. The Inorganic constituents are water and the various salts, that is minerals like iron, potash, soda, etc., in com- bination with some acid. Water is the most widely distributed inorganic mate- rial, constituting more than half the body weight. It is the solvent for all materials which are carried from one part of the body to another for its nourishment or to re- move the worn-out, useless or injurious substances which result from our life processes. We get water by drink- ing it in the form of water, milk, tea or coffee, soups, etc. ; but a small portion is made in the body by burning up hydrogen. Salts are combinations of soda and lime with hydro- chloric or some other acid and of soda, potash, lime and magnesium with phosphoric acid. In the first case we have chlorates or chlorides of soda, lime, etc. ; and in the latter, phosphates of potash, magnesium, etc. The most important and widely distributed of the salts is the one with which we are most familiar, chloride of soda, or common table salt. Phosphate of lime is a nec- essary element of bone and iron is an indispensable ele- ment of hemoglobin. Organic Compounds consist of nitrogenous com- pounds which are subdivided into proteins, like the red flesh of animals, white of eggs, etc.; albuminoids like gelatin and some bodies of simpler composition, like urea, which are largely for excretion; and nonnitrog- < nous compounds which are fats (butter, fat meat etc.), carbohydrates (starch, sugar) and certain other organic bodies like alcohol not so widely used as the FOOD AND DIGESTION 45 preceding. Translated into simple language this means that we require for health lean meat (protein), fat meat, (hydrocarbon or fat) and vegetables (starch and sugar), with enough water to dissolve them after digestion and carry the products of digestion to every part of the body. Carbohydrates. — Carbohydrates are, chemically, com- pounds of carbon, hydrogen and oxygen, the last two occurring in the proportions found in water. Thus glu- cose (C6H1206) is composed of six elements of carbon, twelve of hydrogen, and six of oxygen, which is practi- cally the same as saying six elements of carbon in three of water, which is composed of hydrogen two and oxy- gen one (H2'0). There are various types of carbohy- drates— glucose, amylose — but special attention need here be called to none but glycogen which is the pecul- iar form of starch formed in animals. Fats or Lipoids, are found, in varying amounts, in ani- mal tissues, lying under the skin in large amounts, be- tween the muscles, in the marrow of bones and in smaller amounts in other situations. Fats, in the form of oils, are found in many vegetables — olive, cottonseed, nuts, etc. Chemically, fats are compounds of glycerin and a fatty acid. They are insoluble in water, and, be- ing bad conductors, serve to keep the other tissues warm. Normal fats belong to one of three types. Stearin, solid and melting only at comparatively high temperatures. Mutton suet is a fine example of this type. Palmitin, is the principal constituent of most animal and vegetable fats. It melts at a lower temperature than stearin. Olein, always fluid except in low temperatures, is found chiefly in vegetable fats, but occurs in that of animals. 46 PHYSIOLOGY FOR NURsi.S Fats, \vluMi boiled with soda or potash, break up into glycerin and fatty acids, which latter combine with soda or potash and form soap. If fats, soap and water be thoroughly shaken together the fat breaks up into small particles which are held in suspension in the water forming an emulsion. Milk is an excellent emulsion whose fat gradually rises to the top in the form of cream. Nitrogenous Bodies. — The chief constituents of mus- cles, glands, nervous tissue, serum, blood and lymph are complex bodies called proteins. They occur in vegeta- bles as well as in animals, but much vegetable protein is indigestible by human organs and comes to us only after furnishing food for the lower animals. Thus peas and beans contain 23.7 per cent protein as compared Avith 22.7 in fowls and 20 per cent in beef; but so much of the protein of peas is unusable by the human diges- tive organs, that this vegetable can not be used as a sub- stitute for meat. Various names are employed to desig- nate the protein derived from different sources. One found in milk or cheese is called casein; that in the yolk of eggs vitellin and that in muscle either myosin, or sj/ntonin. Not all bodies which contain nitrogen are capable of maintaining health. The familiar body called gelatin, derived from the skin and connective tissue, contains a considerable proportion of nitrogen and yet an animal fed upon it alone will starve almost as quickly as one deprived of food entirely. This seems to be due to the absence of certain amino bodies which are formed of nitrogen and hydrogen in the proportion of one part of N to two of H or NH2. That it is the absence of these amino bodies, or amino acids, which keeps gelatin from maintaining a nitrogen balance, is proved by feed- FOOD AND DIGESTION 47 the animal on gelatin plus a suitable amount of an ammo acid, which diet maintains health. The follow- ing tables copied from Jones and Bunce will be useful for reference : COMPOSITION Or MILK HUMAN cow's Protein, 70 1.7 7o 3.5 Butter (fat), 3.4 3.7 Lactose (carbohydrate), 6-2 4.9 Salts, 0.2 0.7 COMPOSITION OF EGGS % Total solids, 13.3 Protein, 12.2 Sugar, 0.5 Fats, lecithin, cholesterin (traces), salts, 0.6 MEATS OX CALF PIG FOWL PIKE Water, 76.7 75.6 72.6 70.8 79.3 Solids, 23.3 24.4 27.4 29.2 20.7 Proteins, 20.0 19-4 19.6 22.7 18.3 Fats, 1.5 2.9 6.2 4.1 0.7 Carbohydrates, 0.6 0.8 0.6 1.3 0.9 Salts, 1.2 1.3 1.1 1.1 0.8 VEGETABLE FOODS WHEAT BAPvLEY OATS RICE PEAS POTATOES Water, 13.6 13.8 12.4 13.1 14.8 7o 76.0 Protein, 12.4 11.1 10.4 7.9 23.7 2.0 Fat, 1.4 2.2 5.2 0.9 1.6 0.2 Starch, 67.9 64.9 57.8 76.5 49.3 20.6 Cellulose, 2.5 5.3 11.2 0.6 7.5 0-7 Mineral salts, 1.8 2.7 3.0 1.0 3-1 1.0 Theoretically peas should be more valuable than any other vegetable, particularly the potato, because they 48 PHYSIOLOGY FOR NURSES are rich in protein, starch, fat and salts; while the po- tato is poor, comparatively, in everything but water. Practically the high protein value of the pea is not available while its large percentage of indigestible cel- lulose renders it objectionable when eaten to excess. DIGESTION That digestion is chiefly a chemical process is per- fectly true; but it involves a process, which may be called vital chemistry, which the test tube has not, and may not, imitate completely. An essential part of di- gestion is carried out by bodies called enzymes or fer- ments. Another is the production, in proper proportion, of the acid or alkali in the presence of which alone these ferments will act ; while yet another is the prepa- ration of food, by chewing, SAvallowing, etc., and its agi- tation in the intestinal canal where it is exposed to the ferments on the one hand and on the other is brought in contact with the vessels by which the products of di- gestion will be carried into the body. The Enzymes, or ferments without which food can- not be digested, are of three chief types: (1) amylo- lytic, which convert starch into sugar; (2) fat splitting, which convert fats into glycerin and fatty acids; and (3) proteolytic, or those which convert protein into simpler bodies. Besides these there are sugar splitting ferments which change the nonabsorbable into absorbable sugars, and a body which coagulates protein, as in the change of milk to clabber. The ferments which act on starchy foods are ptyalin, secreted by the salivary glands, and amylase, formed by the pancreas. Transverse colon — 1 Ascending colon — j FOOD AND DIGESTION I — Descending colon ! — Jejunum J?ig. 10. — Front view of organs. Semidiagrammatic. 50 PHYSIOLOGY FOR NURSES The fat splitting enzyme, lipase, or steapsin, is formed by the pancreas. Proteolytic ferments are pepsin, formed in the glands of the stomach and acting only in the presence of an acid, and trypsin, formed by the pancreas and acting in an alkaline medium. Besides these well-known ferments, the glands in the wall of the small intestines furnish various enzymes which act upon the partly digested food poured into the intestinal canal by the stomach. Their action is not so well understood as is that of the secretions of the stom- ach and pancreas. Before considering the action of the digestive fer- ments, an account of the mechanics of the alimentary canal will be given. The simplest form of feeding and digesting is in an unicellular organ, a single cell of protoplasm, which wraps itself around its food and becomes, in its entirety, a chewing, swallowing, digesting, absorbing and dis- charging organism. In man, and the higher animals, af- ter food has been procured, the successive steps are chewing (mastication), swallowing (deglutition), and di- gestion. The organs concerned are the mouth, contain- ing the teeth, tongue, and salivary gland; the pharynx and esophagus, the swallowing organs ; the stomach and intestines which are the digesting, absorbing and evacu- ating organs. Food is held between the grinding teeth by the mus- cles of the cheek (chiefly the buccinator) on the outside and the tongue between the teeth. Here it is not only thoroughly crushed, but is mixed with the saliva which begins the digestion of starchy food. When this proc- ess is completed, the larynx is pressed up under the hyoid bone and the base of the tongue, the top of which organ, FOOD AND DIGESTION 51 aided by the mylohyoid muscles, crowds the food against the roof of the mouth and, exerting pressure from before backwards, forces the food under the soft palate, which it drives upward to protect the back entrance of the nos- trils, and over the epiglottis, which is pressed down over the air passage (larynx) and the food is driven within the grasp of the pharynx and esophagus over which a wave of contraction passes from above downward until the bolus is forced into the stomach. Stomach Movements.— The walls of the stomach, when empty, are in close contact, like any other empty bag. When food enters it separates these walls only in pro- portion to the bulk of the food, and closely adheres to them. Hence, when the next mouthful is swallowed, it does not come into direct contact with the stomach, but with the coating of food which has already lined that organ. Successive deposits of food will form successive layers, millers' law of "first come first served" deter- mining the order of digestion. It follows that the hydro- chloric acid of the stomach, essential to the action of pepsin but fatal to that of ptyalin, does not necessarily come in contact with any but the first food swallowed; and that the action of saliva on starch may continue for an indeterminate time in the stomach. This result is further promoted by the peculiar action of the stomach muscle, which does not communicate a churning move- ment to all the food contained in the organ, but seems to divide into two sets of activity, one confined to the large or cardiac end of the stomach and the other to the small, pyloric, extremity. At the large end there is lit- tle muscular action, this portion of the organ acting as a reservoir for the undigested food; while, about the middle of the stomach, the waves of contraction start which force the food toward the pyloric end, mix it with 52 PHYSIOLOGY FOR NURSES the gastric juice and reduce it to the thin liquid, chyme, which is the end of stomach digestion. Between the ad- mission of food to the stomach and the appearance of chyme in the intestine, several hours elapse. During this time contraction waves, at intervals of about twenty SMALL INTESTINE ANUS Fig. 11. — Diagram of the alimentary tube and its appendages. (After Testut.; seconds, press the liquefying food against the pyloric valve, which does not yield until the food is in a liquid form. It then opens and the liquid part escapes into the FOOD AND DIGESTION 53 duodenum, where the reaction is alkaline and where in- testinal digestion begins. Finally undigested arid indi- gestible articles are allowed to pass. Intestinal Movements. — The muscular coats of the in- testine are arranged in two layers, an outer longitudinal and an inner circular. Obviously if each band of circu- lar fibers contracted in succession a wave of constriction would finally pass over the entire length of the tube from stomach to large intestine; and, if each band re- laxed directly after contraction, there would be an in- active or dilated area always both above and below the wave of contraction — the dilated area above constantly increasing and the one below decreasing in length. This is the normal or peristaltic movement of the intestine. At the same time the longitudinal fibers seem to con- tract and draw the entire tube over the advancing food. If, from disease or other cause, a wave can be excited below and made to pass upwards, the contents of the in- testine wrould be forced into the stomach, as in obstruc- tion of the bowel when fecal vomiting is seen. This ac- tion is termed antiperistalsis. There seem to be local constrictions at various points, in addition to normal peri- stalsis, which serve to break the column of food into many segments and both promote mixing with the in- testinal and pancreatic ferments and exposure to ab- sorptive channels. Nervous Control. — Both the stomach and intestines re- ceive nerve fibers through the vagi (pneumogastric or tenth cranial nerve) and the sympathetic system of nerves. Movements of Large Intestines. — The opening of the small intestine into the large is guarded by the ileocecal valve and by a sphincter muscle, normally in a state of contraction. Food passing into the large intestine is 54 PHYSIOLOGY FOR NURSES still in a semifluid state, but becomes solid about the middle of the transverse colon. Waves of contraction of the same general character as those seen in the small intestine determine the onward movement in the large. There seems to be a normal antiperistaltic Avave from the middle of the transverse colon back to the ileocecal valve to retard movement and allow longer time for ab- sorption. Beyond the transverse colon we can properly speak of feces instead of food. The material continues to lose water until the sigmoid flexure is reacned. This is a sort of reservoir for fecal matter where it remains until just before defecation, the rectum apparently remain- ing empty until that time. Defecation. — This is partly a voluntary and partly an involuntary act. The normal stimulus seems to be the passing of fecal matter from the signioid into the rec- tum. This excites the center for defecation in the lum- bar part of the spinal cord, the sphincters of the rectum, only partly under the control of the will, are relaxed, the diaphragm contracts drawing a full supply ot air into the lungs, and remains fixed while the abdominal muscles contract forcibly and force out the contents of the bowel. Vomiting1, — Vomiting is the ejection of the contents of the stomach through the esophagus and mouth. The order of events is, a feeling of nausea, a flow of saliva, a contraction of the stomach from the middle towards the esophageal opening, descent of the diaphragm so as to press on the stomach, a sudden and violent contraction of the abdominal muscles, exerting still further pres- sure on the stomach whose contents are forced along the esophagus and out of the mouth. As the soft palate can not be so well carried over the posterior nares from FOOD AND DIGESTION 55 behind, these cavities are often unprotected and some of the ejected matter is forced into them. Nervous Mechanism. — The nervous mechanism is a very complex reflex action. A vomiting center may ex- ist in the medulla. Many sensory nerves may be con- cerned, particularly those connected with vision and equi- librium. Irritation of the sensory nerves of the stomach is, however, the most constant cause. Hunger and Thirst. — These sensations are the cry of cells throughout the body for food and drink, with a local manifestation in the stomach and throat. The empty stomach contracts at irregular intervals and these contractions are attended by slightly painful sensations, "hunger pains," until food or some substitute is taken. Thirst is felt whenever the total amount of water in the body falls beloAV a certain point. It occurs, therefore, as a symptom following loss of blood, perspiration or fre- quent urination. The sense of distress is felt in the pharynx chiefly and is transmitted by the ninth cranial (glossopharyngeal) nerve. Action of Digestive Secretions The Salivary Glands. — These are three in number, parotid, much the largest, situated between the lower jaAv and the base of the skull; submaxillary, under the body of the lower jaw, and the sublingual, just under the tongue. The mixed secretion of these glands contains 994 parts of water and only six parts of solid material in a thousand parts. The solids are some salts of potash, soda and magnesia, mucin and ptyalin. Nervous Mechanism. — As the nervous control of these glands is well understood and is very similar to other complex reflexes, it is explained at some length as an example. The simplest form of reflex arc is a spot in 56 PHYSIOLOGY FOR NURSES the central nervous system connected by at least two nerves with a given gland or other structure. On© nerve conveys impulses from center to organ and is called an efferent nerve; the other carrying impulses from pe- riphery to center, is called an afferent nerve. Thus if a little salt be placed on the tongue a message is sent to the center which controls secretion which acknowledges it by sending a message to the gland cells to begin se- cretion. Two other nerve impulses, however, are Cardiac Orifice (Esophagus Funclus Great Curvature Ductus Communis.- Choledochus — Duct of Wirsung Duodenum Fig. 12. — The stomach and duodenum opened. (Buchanan's Anatomy.) needed before the gland can function properly — one in- creasing and one decreasing the blood supply. These are called vasodilator and vasoconstrictor fibers. The function of the first is to increase the amount of blood on which the gland can act. Vasodilator fibers are car- ried along with the secretory fibers in the cranial nerve called chorda tympani, while vasoconstrictor fibers come from the sympathetic. Afferent fibers are carried by FOOD AND DIGESTION 57 many nerves, chiefly those of smell and taste, stimula- tion of which will excite a flow of saliva. Dilatation of the blood vessels in a gland will produce two chief ef- fects. First it brings into contact with the gland cells a larger quantity of blood containing the material from which that particular secretion is made ; and, second by increasing the pressure it will force a larger quantity of the watery constituents of the blood through the vessel wall and into the glandular structure. There are thus two distinct acts, filtration, which is mechanical, and se- cretion, or manufacture, which is a vital function per- formed by living tissue. Mouth Digestion Saliva. — The salivary secretion acts mechanically to moisten dry food, thus getting it into a suitable condi- .tion for swallowing; through the mucin contained to lubricate the mass, and by the ptyalin, to digest some of the starch. This is accomplished by causing the starch molecules to take up water, in chemical combination, thus converting it into maltose and dextrine, two forms of sugar which are not absorbed as such but have to be converted into dextrose in the intestines. Ptyalin diges- tion, therefore, is simply preparatory. Food is retained in the mouth for too short a time to be digested, but re- cent evidence shows that it may be held in the fundus of the stomach for more than an hour before the hydro- chloric acid arrests ptyalin digestion. Stomach Digestion Gastric juice is secreted by glands in the mucous lin- ing of the stomach. It is a watery solution containing pepsin, and rennin, the first to act on proteins, the sec- 58 PHYSIOLOGY FOR NURSES ond to coagulate the albumin of milk. In addition about five-tenths of one per cent of gastric juice is hydro- chloric add, a strong mineral acid which promotes the activity of pepsin. Mechanism of Secretion. — The mere smell or taste of appetizing food is enough to start gastric secretion and, indeed, seems to be its normal stimulus. Some foods, however, appear to contain substances called secreto- gogucs, which continue to excite secretion after intro- duction into the stomach. Meat extracts and juices ap- Fig. 13. — Schema of simple reflex arc: r, receptor in an epithelial mem- brane; a, afferent fiber; s, synapsis; c, nerve cell of center; e, efferent fiber; in, effector organ. (Pearce-Macleod, Fundamentals of PI it man Physiology.) pear to possess these substances in a high degree, while they seem almost absent from bread and white of egg and present in but small quantity in milk. Pepsin can not act in an alkaline solution and acts best in the presence of hydrochloric or other mineral acid. It acts on protein alone which it finally converts into pep- tones, a soluble protein more ready for absorption than pure protein. There are intermediate steps before the FOOD AND DIGESTION 59 peptones appear. First the protein swells up and changes into an acid albumin called syntonin, which passes through two successive stages — primary and sec- ondary proteoses — before peptone is produced. Rennin is the ferment which changes milk to clabber. It acts well in the presence of hydrochloric acid. Cow's milk forms a solid mass, or firm clot, not unlike the clot of blood save in color, which squeezes out the wliey af- ter standing. Human milk forms a loose flocculent clot, probably more easily mixed with gastric juice. Rennin does not digest the casein, which is digested by pepsin as are other proteins. The clotting is probably to pre- vent the immediate passage of milk into the duodenum before stomach digestion could begin. There seems to be no other food substance on which rennin acts. The stomach has no power of digesting starchy foods which leave it in the condition in which mouth digestion has left them. Fats are not appreciably acted upon by the gastric ferment, but are more or less liquefied and mixed with the other foods in the chyme. By soaking into and around particles of bread or other food, fats may interfere with stomach digestion. Stomach digestion is more preparatory than complete. Apparently about half of the proteins pass into the duodenum as either peptones or proteoses, 20 per cent as unchanged proteins while but a small part of the re- mainder is absorbed from the stomach. Some native proteins are not acted on by the pancreatic juice and must receive preparatory treatment in the stomach. Mixing the foods, warming them, separating the fats from other foods with which they are mechanically mixed, emulsifying them, partly digesting protein and regulating the amount poured into the duodenum seem the chief functions of the stomach. 60 PHf SIOLOGY FOR NURSES Absorption' from the stomach seems to be slight, even water passing into the duodenum almost at once. Al- cohol, however, is readily and rapidly absorbed. Chyme is denned as "the semiliquid mass of partly digested food passed from the stomach into the duo- denum." It contains: (1) digested protein in the form of peptones or proteoses; (2) carbohydrates which have been partly digested by plyalin; (3) fat warmed and © Fig. 14. — Cross section of pancreatic tubule (modified from Sabotta). mixed in an emulsion but otherwise not appreciably changed; (4) undigested proteins and carbohydrates; and (5) indigestible substances which enter the duo- denum late and are not proper constituents of chyme but are mixed with it. Pancreatic and Intestinal Digestion The product of stomach digestion meets, in the in- testines, with three digestive fluids; i.e., pancreatic FOOD AND DIGESTION 61 juice, succus entericus (intestinal juice) and bile. The action of the three is simultaneous, but a separate de- scription must be given of each to be intelligible. Pancreatic juice contains three ferments, trypsin, amylase and lipase to act on proteins, carbohydrates and fats. The pancreas is an elongated body reaching from the hollow of the duodenum to the spleen and is a compound tubular gland like the salivary glands. Its secretion is poured through a long tube (duct of Wirsung) which, after joining the common bile duct, opens into the duodenum. The secretion is a clear, watery fluid in man, very abundant, amounting to from 500 to 800 c.c. a day. The nerve supply is derived from the vagus and the celiac plexus. The secretion appears to begin soon after food is placed in the stomach and continues from two to four hours; the first acid chyme which enters the duodenum appears to incite the pan- creas to activity. This activity is probably not pro- duced by reflex nerve action, but by the production of a chemical body, secretin, which is absorbed by the blood, carried to the pancreas and stimulates the organ. A similar explanation is given of the secretion of gas- tric juice. Bodies which are thus formed and act in this manner are termed hormones. The character of the food determines the type of the secretion; i.e., if meats alone are eaten the juice will be rich in trypsin ; if fats, in lipase; if bread, in amylase. Trypsinogen alone, the immediate enzyme of the pan- creas, is not able to act on proteins but requires the presence of another substance, kinase or entcrokinase, which is formed by. the mucous membrane of the small intestine, by which it is converted into trypsin. Trypsin differs from pepsin in the following particu- 62 PHYSIOLOGY FOR NURSES lars: It can act in neutral, slightly acid or distinctly alkaline solutions. Its effect on proteins is not only more powerful but more rapid than that of pepsin. It breaks up the protein molecule more completely. The joint action of trypsin and pepsin changes the com- plex structure of the many kinds of protein into simple bodies of the ammo-acid type more soluble than the original form and prepares them for the action of erep- sin (the protein enzyme of the intestinal juice) which breaks up the products of peptic and tryptic digestion into such simple forms that the human body can use them as building stones out of which its own peculiar form of proteins can be constructed. Amylase acts upon starches in the same way as ptyalin, converting them into maltose and achroodex- trin, a preparatory step to their final conversion into dextrose by the maltose of the intestinal juice. This digestion is completed by the time the food gets to the ileocecal valve. Lipase or Steapsin is the first of the fat splitting fer- ments. This ferment splits fats into glycerin and a fatty acid and the latter combines with some of the salts present to form a soap which is used to hold the fats in an emulsion, in which form they are more readily acted on by the lipase. This is the only ferment which seems to have the power of acting in either direction; i.e., it can either split fats or it can take the component parts (glycerin and fatty acid) and combine them to form fat. Lipase acts best in the presence of bile. Succus entericus, intestinal juice is secreted by the tubular glands, crypts of Lieberkiihn, Avhich line the intestinal canal. It seems to act only on starchy foods ; but there are several enzymes in the juice which can POOD AND DIGESTION 63 be extracted from the mucous membrane of the intes- tines which act 011 various foods, breaking the products of gastric and intestinal digestion into simpler bodies, better fitted either for absorption or to be employed as tissue builders. The action of enterokinase, erepsin and secretin have been alluded to. Fig. 15. — Injected lacteal vessels in two villi of human intestine. (Teich- mann.) X 100. I,acteals filled with white substance and blood vessels with dark. Bile is not a digestive fluid, but it so largely promotes the splitting and absorption of fats that its presence as an auxiliary is essential to health. Absorption in Small Intestines Absorption of Proteins. — The greater part of digested proteins is absorbed by the blood vessels of the intes- 64 PHYSIOLOGY FOR NURSES tinal villi. This is proved by tying the thoracic duct so the fluid it carries can not get into the blood. Animals thus treated continue to absorb and utilize proteins as before. The actual form in which nitrogenous foods enter the blood current is that of the ammo acids, which are carried to the various tissues which, in turn, select such acids as are suitable for their repair or upbuilding. Some of the organs, notably the liver, have the power of converting these acids not into tissue but into some other nitrogenous compound — urea in the case of the liver. If the contents of the small intestine be examined at the ileocecal valve, it will be found that from 97 to 99 per cent of such foods as milk, eggs and meats have been absorbed, while the proportion of vegetable protein absorbed is much smaller — from 70 to 80 per cent. This seems due to the entanglement of the vegetable pro- teins in indigestible cellulose. Absorption of Carbohydrates. — Starchy food is ab- sorbed as simple sugars. Rather more than a pound (500 grams) may be utilized in a day, all, in the form of dextrose, is stored up as glycogen, keeping the amount of sugar in the blood constant about 15 per cent. When excessive amounts of starchy food or sugar are eaten, the liver may be, for the time, overworked and sugar may temporarily appear in the urine. Absorption of Fats. — The fatty acids and glycerin of intestinal digestion are absorbed as such and appear, to some extent at any rate, to be recombined in the epithelial cells of the villi. After passing the epithelium the fat is taken up by the lacteals of the villi and carried by the thoracic duct to the beginning of the left in- nominate vein where it is poured into the blood stream. A small amount, however, appears to be absorbed directly FOOD AND DIGESTION 65 by blood vessels of the villi. Different fats are absorbed in varying degrees — of olive oil nearly 98 per cent is absorbed while only about 90 per cent of mutton fat is so accounted for. Large Intestine — Digestion and Absorption The secretion of the large intestine contains no enzyme. Hence, such digestion as occurs in that area is simply a continuation of activity of the ferments car- ried in from the small intestine. Absorption, particu- larly of water, does take place. Water is absorbed in the small intestine, but is replaced by osmosis, since the contents of the intestine at the ileocecal valve are as fluid as at the pylorus; but, there being no such com- pensation in the large intestine, fluid is rapidly lost and the contents quickly attain the fecal character. The reaction in the large intestine, as in the small, is alka- line and promotes the growth of bacteria, particularly those which attack protein. Putrefaction, therefore, is a normal activity in the large intestine. By it the rem- nants of proteins are split into end products some of which are carried off in the feces, others in the urine. Some of these products may be injurious if absorbed in the blood, explaining some of the ill effects of constipa- tion. Composition of Feces. — The amount of fecal matter will vary with the amount and character of the blood. When meats alone are used, small dark colored actions result. If the diet consists largely or wholly of vege- tables, particularly of those containing much cellulose or woody fiber, the amount of fecal matter will increase in amount up to even 500 grams — a little more than a pound — as compared with 170 grams— about a third of a pound. Fecal matter is composed of indigestible 66 PHYSIOLOGY FOR NURSES bodies, seeds, grains of corn, ligaments; undigested fragments of digestible food; some results of intestinal secretion; inorganic salts, mucus, pigment, the results of putrefaction, etc. End Results — Summary The processes of digestion are merely preparatory: the food is reduced by these processes to such a form that it may be absorbed. Changes fully as important take place after the food has left the alimentary canal, constituting what is known as "metabolism." Unfor- tunately, our knowledge regarding these changes is still very poor, but it is to be hoped that much more will be learned about them in the near future and more light shed on the etiology (science of cause of disease) of the diseases which are the result of "metabolic disturb- ances." When starch has been digested; that is, has been re- duced by the action of ptyalin, amylase, and maltase to the absorbable dextrose, it enters the capillaries of the intestinal villi and is carried in the portal circulation to the liver. Normally, AVC have 1 to 2 per cent of dex- trose in our blood, but it is evident that after a meal containing much starch or sugar, the amount in the portal vein must be much more than this. Should this sugar-laden blood escape into the general circulation and eventually pass through the kidneys, these organs would not be able to retain the sugar in the blood, and it would be passed out in the urine, giving rise to a " glycosuria. " The liver, however, has the power of fixing this dextrose in a form in which it may be stored ; changing it into the glycogen or animal starch which has already been mentioned. Therefore, after a meal containing carbohydrate, this compound can be easily FOOD AND DIGESTION 67 detected in increased amounts in the liver. The volun- tary muscles also possess the same "glycogenic" func- tion, and glycogen is deposited in them also. If exces- sive amounts of a readily absorbable sugar is fed, the amount entering the portal circulation is too great for the liver and muscles to handle, and some of the dex- trose appears in the urine. This condition is known as "alimentary glycosuria" to distinguish it from the forms of glycosuria due to disease. When need arises the glycogen is reconverted into dextrose and is used to yield energy to contracting muscles or secreting glands or to other functioning tissues. This energy-yielding process is strongly suggestive of a similar yield of en- ergy when fuel containing carbon and hydrogen is burned outside the body, and the end results of the combustion of carbohydrate either in the body or out- side are the same, namely, water and the gas, carbon dioxide. Occasionally, we see persons whose tissues can not utilize the dextrose furnished them, and here, as in the alimentary glycosuria, the amount of dextrose in the blood increases beyond the amount that the kid- neys can hold back and sugar appears in the urine. This condition constitutes "diabetes mellitus." The wasting away that usually accompanies severe cases illustrates the importance of the carbohydrates in the diet. When larger amounts of carbohydrates are fed, amounts larger than are needed for the energy require- ments, much of it may be converted into fat and stored. The well-known effects of excessive candy eating are explainable on this basis. To a verj^ small extent, carbo- hydrate may be used to help build up the tissues of the body, but this occurs in such a limited way as to be negligible. 68 PHYSIOLOGY FOR NURSES Under the influence of lipase, fats are broken up into glycerin and free fatty acid. Alkaline salts of sodium, potassium, magnesium, and calcium are present in the small intestine, and these bases unite with the fatty acids to form soaps. The ordinary toilet soap is a similar union of sodium with fatty acid. The soaps of sodium and potassium, certainly, pass into the small lymph channels of the intestinal villi, being reconverted, in passing through the absorbing cells, back into neu- tral fat; i.e., the union of glycerin and fatty acid. This food fat passes on in the lymph channels until it finally gains entrance to the veins by means of the thoracic duct and the right lymphatic duct, and by this means it is distributed to the various parts of the body. Fat, like carbohydrate, is an important source of energy. In the body, it is finally reduced to the same forms that carbohydrate is, carbon dioxide and water, being ex- creted by the lungs and kidneys. A considerable amount of the fat, if fed in excess, may be deposited in the tissues, to serve as a reserve for possible subsequent need. The amount of fat that is used for constructive purposes may be disregarded. Under certain circumstances, there may be a disturb- ance in the process of changing the fats to carbon diox- ide and water. Inj such cases, incompletely oxidized substances accumulate in the blood ; the so-called ' ' ace- tone bodies," acetone, diacetic, and /^-oxybutric acid. This condition is known as "acidosis," and may arise in the course of diabetes mellitus or even in simple starva- tion. The sodium carbonate of the blood plays an im- portant part in carrying carbon dioxide from the tissues to be excreted by the lungs, but these acetone bodies require a considerable amount of alkali to neutralize them, so that the normal sodium carbonate content of FOOD AND DIGESTION 69 the blood is reduced and carbon dioxide is not carried away promptly. This explains the cyanosis and the labored breathing. As has been stated, protein may be broken up in the body to yield energy, but this is extravagant for two reasons; first, because protein food is actually much more expensive and, second, that it probably causes more wear and tear than carbohydrate on the body when used in excessive amounts. The most important role of protein is to serve as tissue-building material, a role for which it is indispensable, carbohydrate and fat being unable to replace protein for this purpose. Under normal conditions, all, or nearly all, of the protein is absorbed in the form of what is known as "ammo acids." These are organic acids containing the NH or amid group, and are known as the "building stones" of the proteins. Under the combined action of pepsin, trypsin, and erepsin, this decomposition takes place, and the amino acids enter the blood vessels of the intestinal villi and are carried to the liver in the portal vein. It is probable that the liver does not effect any change in them at this time, but allows them to pass through the tissues where they may be utilized. Wherever there is need of building material, the "build- ing stones" are taken from the blood and utilized to construct the particular kind of protoplasm needed. Even with the ordinary amounts of protein in the diet, only a part is used for tissue building or repair; a considerable portion being burned to yield energy. The end products of this breaking up of protein are not so simple as are those representing the final results of car- bohydrate and fat decomposition. Under the action of tissue enzymes, the nitrogen is split off and is carried to the liver. Here it is converted into "urea," which 70 PHYSIOLOGY FOR NURSES passes in. the blood to the kidneys and is excreted in the urine, constituting; the chief organic substance in the urine under normal conditions. Tissues which wear out and are broken down likewise give rise to the pro- duction of urea, since they are protein material. Though under normal conditions, proteins are broken down into amino acids before absorption, nevertheless the tissues possess the power to break down more com- plex protein bodies that may enter the circulation. The occurrence of anaphylaxis (literally "without a guard") or anaphylactic shock is explained in this way. A com- plex protein body is introduced into the circulation, either by subcutaneous or intravenous injection or by passing through an abnormal mucous membrane. Hav- ing entered the circulation, the tissue cells elaborate an enzyme capable of decomposing it into its constituent "building stones." It is assumed that this process is rather slow and gradual; the enzyme is produced in small amounts so that there is no poisoning as a result of the first introduction of the foreign protein. Once the enzyme is produced by the tissue cells, however, it remains active for some time. Now, at some later time, if the same protein is introduced into the circulation, its decomposition starts rapidly, since there is still the necessary enzyme present. As a result of this rapid action, intermediate products of the decomposition are produced in large enough numbers to produce mild, severe, or even fatal poisoning. The urticaria (nettle rash) often seen after injection of diphtheria antitoxin, asthmatic attacks, and similar manifestations are now considered to be instances of anaphylaxis. It has already been pointed out that carbohydrate, fat, and protein are required for proper nutrition. Pro- tein is absolutely essential for constructive processes ; FOOD AND DIGESTION 71 any of the three may yield energy, but on an exclusive protein diet, serious disturbances soon arise. There- fore, we may regard protein as the material from which new tissue is built or by which old, worn-out tissue is to be replaced, while fats, and especially carbohydrates, are the fuel foods; all three being needed in order that growth may occur or that health may be preserved. It becomes a matter of much practical importance as to how much of each constituent should be included in the diet and what the total should be. Fortunately, most individuals in health instinctively select the proper amounts needed for nutrition, but where it is necessary for the physician to select a diet, the importance of this knowledge is obvious. It has been learned that when a substance is burned, it gives off a definite amount of heat, and by suitable means, this heat can be measured. The amount of heat required to raise one gram of water one degree centi- grade is known as the small calorie, and is designated by the symbol "cj" the amount to raise the temperature of a kilogram of water a similar amount is known as the large calorie, and its symbol is "C." If one gram of carbohydrate is burned under suitable conditions, it is found that it yields approximately 4.1 large calories ; while a gram of fat under similar conditions yields over twice as much heat, namely, 9.3 large calories. More- over, the amount of heat produced in the animal body by the oxidation of foods can be measured, and it is found that this is the same for carbohydrate and fat as that produced by burning these substances outside the body. In the oxidation of protein in the body, it has been found that a gram also yields about 4.1 large calories, though the combustion of this amount of pro- tein outside the body gives off more heat. This is due 72 PHYSIOLOGY FOR NURSES to the fact that protein is not completely burned in the body but some of the end results of its metabolism are still capable of further oxidation. By studying the diets of large numbers of individuals engaged in different vocations, it has been learned what the average amount of each constituent in the diet is and what the total caloric value of the food taken in 24 hours should be. The following are samples of average dietaries : TOTAL INVESTIGATOR CARBOHYDRATE FAT PROTEIN CALORIES Moleschott. 550 gm. 40 gm. 130 gm. 2980 Ranke. 240 " 100 " 100 " 2324 Voit. 500 " 56 « 118 " 3053 It is seen from these figures that the amount of pro- tein is not subject to wide variations, while reduction in the amount of carbohydrate in some of the diets is accompanied by increase in the amount of fat and vice versa. These energy-yielding foods are to a certain extent mutually replaceable, but there is a limit to this : fat being more difficult of digestion and also more ex- pensive. On the other hand, when fat is not absorbed properly or not handled properly after absorption, even though there be no evidence of disturbance with the metabolism of protein and carbohydrates, severe nutri- tional disturbances occur, as illustrated by cases of injury to the thoracic duct or of faulty fat digestion, the latter occurring in infancy. Agreement has not yet been reached in regard to the amount of protein required in the diet. As shoAvn above, in no instance is it below 100 grams in 24 hours in the average diet. This amount is in excess of what is re- quired for repair of tissue in the adult under normal conditions, a considerable part of the ingested protein being split up to yield energy. Since protein is more FOOD AND DIGESTION 73 expensive, both in actual cost and, possibly, on account of its influence on the cells of the animal using it, the ques- tion has arisen whether we could not advantageously re- duce the amount in our diets. It has, indeed, been shown that for considerable periods of time the amount may be reduced to less than a half of the amount given in the dietaries above with no apparent impairment of the per- son's health or efficiency. Against this, however, is the fact that, left to himself, normal man takes the larger amount of protein in his diet, regardless of his condition or occupation. When one is engaged in work necessitating much muscular exertion, a greater number of calories is required, but when this is the case, the increase is made largely with the carbohydrate and fat, the laborer using actually little more protein than the clerk who leads a sedentary life. Since urea, resulting from protein decomposition in the body, is excreted by the kidneys, it has been sug- gested that large amounts of protein in the diet will throw extra work on these organs and tend to injure them. Then, too, it has been pointed out that the putre- faction of proteins that may take place in the intestines, gives rise to poisonous substances, which entering tiie circulation, may damage both liver and kidneys. These are theoretical conditions, however, which are still far from proved. Tn some recent work, it has been pointed out that not all proteins are li adequate" for nutrition. It is essen- tial that certain of the "building stones" be present, and if the protein is deficient in these it does not suffice for the purposes of maintenance or for the promotion of growth. Gelatin is an illustration of one of the inade- quate proteins. It was formerly believed that gelatin was capable of supplying the protein in the diet, and 74 PHYSIOLOGY FOR NURSES the experiment was tried 011 a large scale in France, but this experiment was a failure, for the reason already given. The mineral salts are absolutely indispensable in the diet, and it is stated that death will occur in an animal fed on an abundance of salt-free food sooner than with one deprived entirely of all food. This is because the organic food leads to the excretion of the salts in the tissues. Sodium chloride, or ordinary salt, is the only one of the salts that we consciously add to our diet. When the diet consists of a considerable amount of vegetable food, the need of sodium chloride becomes more apparent, and herbivorous animals show the same desire for salt that human beings do. The sodium chloride plays a very important role in our bodies. It is the chief inorganic constituent of our blood plasma and it is essential for the production of hydrochloric acid of the gastric juice. It is also sup- posed to exert an influence on the contractions of the heart. The urine contains a considerable amount of this salt, and in certain cases of diseased kidneys, diffi- culty is experienced by these organs in eliminating the sodium chloride. As a result of this, there occurs a salt retention and the salt also retains fluid, giving rise to the accumulation of fluid in the tissues, known as edema or dropsy. Salts of calcium are also important. They influence the contraction of the heart and also the irritability of muscle and nerve. Calcium is found in large amounts in the bones, and clotting of blood and curdling of milK can not take place in the absence of calcium. Potassium salts influence the heart, while the salts of iron are of FOOD AND DIGESTION 75 importance in constituting an essential part of hemo- globin, the oxygen-carrying pigment of the blood. Even if the diet contains sufficient amounts of carbo- hydrate, fat, and protein, with an adequate supply of mineral salts and water, it is found that nutritional disturbances will occur eventually, unless certain or- ganic substances in addition be included. These sub- stances may be nitrogenous in nature or may be free from nitrogen. They are not energy-yielding foods, nor are they used for constructive purposes; but, ap- parently, they exert a very marked influence on the processes of metabolism. They are known as "vita- mines " or as " growth-promoting factors. ' ' The first one to be studied is that occurring in the pericarp (the part which surrounds the kernel) of rice, the absence of which gives rise to the peculiar disease known as "beri- beri." Scurvy, also, was formerly held to be a disease due to the absence of vitamines from the diet, though this has been denied recently. Certain fats contain the requisite "growth-promoting" factors, while others do not; butter and cod-liver oil being instances of the former, while lard is an example of the latter class. CHAPTER IV THE FUNCTIONS OF THE LIVER That the liver plays an important part in the nutri- tion of the body might be inferred both from the size of the organ and the enormous stream of blood poured into it by the portal vein; for in addition to the hepatic artery, which carries blood to nourish the tissue of the organ, the portal vein, which receives blood from the entire digestive and absorptive tract, ' pours this great stream of blood into the doorway of the liver, plainly not for the benefit of that organ, but that it may effect necessary changes in tiie material of which this blood alone is the bearer. Three such changes appear; i.e., the secretion of bile and the formation of glycogen and urea. Bile is partly an excretion of substances to be re- moved and partly a secretion of a product useful but not essential to digestion. Ii is secreted at all times but, in man, is stored in the gall bladder and ejected into the duodenum only when needed. The quantity formed in a day is from 500 to 800 c.c. The color, in man, is a greenish yellow. It contains about 97l/2 per cent water and about 21/2 per cent solids of which the chief are bile pigment, derived from broken-down red blood cor- puscles, bile acids, taurocholate, and glycocholate of soda,- — fats, soaps, lecithin, a substance which occurs in greatest quantity in the white matter of the nervous system, and cholestcrin. Bile pigment is called ~bilirubin when red, and bili- verdin when green. The pigments appear to be re- 73 FUNCTIONS OF THE LIVER 77 absorbed from the intestines into the portal circulation and carried to the liver which again extracts them from the blood. This is called the circulation of the bile. Secretion of Bile. — It is believed that there are no special secretory nerve fibers whose stimulation excites the secretion of bile. Apparently the flow is automati- cally regulated by the blood flow, since stimulation of the splancJiic nerves, which carry vasomotor fibers to the liver, increases the flow of bile. Secretin, whose Fig. 16. — The microscopic structure of the liver. (Highly magnified.) A, Lobule, showing the intralobular plexus; B, Lobule showing the hepatic cells. (Buchanan's Anatomy.) action on pancreatic secretion has been related, stimu- lates the flow of bile. As soon as the acid chyme is thrown into the duodenum, not only is the activity of the liver excited, but the gall bladder is stimulated to contract and there is an outflow of ready formed bile into the duodenum. When this is prevented, as by a gallstone plugging the bile duct, or from any cause, bile gets into the blood and the condition of jaundice is produced. 78 PHYSIOLOGY FOE NURSES Function of Bile. — Whatever its other effects, the chief known use of bile is in promoting the digestion and absorption of fats. It, in some way, prevents putre- faction in the intestines, though this is not the result of germicidal action, which bile does not possess. i ,>«. ;w b.d. Fig. 17. — Portion of transverse section of human liver. X. 100. h.a., hepatic artery; v.c., intralobular vein; v.p., interlobular vein; b.d., bile duct. FUNCTIONS OF THE LIVER 79 Glycogenic Function of the Liver. — Glycogen, or ani- mal starcli can be detected by the microscope in the cells of the liver, increasing after meals and decreasing during the hours of fasting, and varying with the kind and quantity of food, exercise, etc. The amount in the liver varies between 1.5 and 4 per cent of the weight of the liver. Glycogen is chiefly derived from starchy foods, though proteins may furnish small amounts. Fats seem to increase the amount of glycogeii in the liver by preventing its consumption in other parts of the body. GLYCOGEN THEORY. — The theory of this function of the liver is that it maintains the sugar equilibrium of the body; that is, that an increase of carbohydrate food would always be followed by an increase of sugar in the blood if the liver did not convert the dextrose and other sugars into animal starch which it stores up until a fasting period, or at least decrease of the normal sugar content of the blood, calls for a renewal of the supply, when the stored glycogen of the liver is recon- verted into sugar and given up to supply the deficiency. This conversion appears to be accomplished by a special enzyme formed for the purpose, in the liver. The liver is not the only store house for glycogen. It is estimated that the red muscles of the body contain as much of this starch as the liver itself, and that it is used up more rapidly when the muscle is active than when passive. Urea-Forming Function of the Liver. — Urea is the chief form in which nitrogen is removed from the body. This product of protein food is eliminated from the blood by the kidneys, but it is formed in the liver and sent to the kidneys only to be extracted. No doubt the liver is not the only source of urea, but it is at least a demonstrated source of this end product of protein digestion. CHAPTER V THE SPLEEN A chapter on the physiology of the spleen may be al- most as brief as the history of snakes in Ireland, for al- Y^0"1 Fig. 18. — Vertical section of human spleen (modified from Kolliker), low power, t, trabeculae; m, Malpighian corpuscles; b,\ injected arterial twigs; s.p., spleen pulp. The clear spaces are the venous sinuses. most nothing is positively known of the function of the organ. It not only has, in proportion to its size, a very abundant blood supply, but its return circulation is car- 80 THE SPLEEN 81 ried into the portal vein and thence through the liver, indicating that it effects some changes in the blood which the liver must perfect; yet its removal neither causes the death of the animal nor effects any perma- nent changes in the character of the blood. That it is associated with digestive processes is shown by the fact that it slowly increases in size after a meal for about five hours and then returns to its normal size. Its activity is supposed to be directed to I. The formation of new red blood corpuscles, a work which it certainly does during fetal life. II. The destruction of old and damaged red blood cor- puscles, a supposition founded largely on the spleen's richness in iron. III. The production of uric acid, an inference from the presence of other bodies from which uric acid can be the presence of other bodies from which uric acid can be formed. CHAPTER VI FUNCTIONS OF THE KIDNEY All the waste matter of digestion and of bodily activ- ity is not carried away in the feces. Some elimination, particularly of water, takes place through the lungs, some through the skin, but the major part through the kidneys. The product of the activity of this pair of or- gans is the urine. Urine, in man, is a more or less straw-colored fluid, the color varying greatly even in health and still more in disease, from an almost colorless liquid to a dusky red. Urine, in health, shows a slightly acid reaction, i.e., turns blue litmus paper red, due to the presence of salts, chiefly sodium, so combined as to form acid phosphates. This activity is increased on an animal diet and dimin- ished on a vegetable diet, sometimes even disappearing so that the urine is neutral, — has no action on litmus pa- per or even turns red litmus blue; the urine becomes alkaline in reaction. The average specific gravity of urine is 1.020. The amount passed in a day is from two to three pints but varies under so many conditions, even in health, that a specific amount can not be stated. In general the statement may be made that the amount of urine varies more from the activity of the skin than from any other single condition. Thus, in warm weather, when one perspires freely, the amount of urine will decrease and the color will be high. Exercise, or any other condition, which increases the formation of sweat, will decrease the amount of urine. A cold bath or a sudden change of weather to a lower temperature, 82 FUNCTIONS OF THE KIDNEY 83 increases the urinary secretion. Children discharge more urine than adults, and women, relatively more than men. Even mental conditions affect the flow, as is evidenced in hysteria when loss of nervous control enor- mously increases the output. Diet largely affects both the quantity and the contents; and, of course, the amount of liquid taken will act even more decidedly and more rapidly. Drinking a quantity of water will increase the flow ; but drinking the same amount of beer will not only cause a greater flow, but the increase will occur earlier. Many drugs, called diuretics, produce the same effect, while others will diminish the quantity. Composition of Urine. — Urine holds a large number of different bodies in solution, but is chiefly notable be- cause it takes away the product of the digestion of ni- trogenous food in the form mainly of urea. Urea is the most important nitrogenous element in the urine. That urea, or some antecedent substance, is formed largely in the liver seems certain. It is present in the blood and other tissues and so large a part of the total output is removed by the kidneys that the removal of both of these organs ahvays causes death. The aver- age amount excreted in twenty-four hours is from 350 to 450 grams. Drinking large quantities of water will decrease the relative but increase the actual amount of urea, while an increase in nitrogenous food increases, and of vegetable food, diminishes, the output of urea. Exercise, or anything which increases metabolism of tis- sue, increases the amount of urea. Uric acid as such does not occur in urine in health, but in the form of urates, chiefly of sodium though sim- ilar salts of potash, lime, magnesia and ammonia are found. From ten to fifteen grains of urates are ex- creted daily. They are not formed in the kidneys, but 84 PHYSIOLOGY FOR NURSES exist in the blood and are merely extracted from it by those organs. They increase greatly in gout. Creatinin, xanthin, hypoxanthin are other nitroge- nous bodies which exist in small quantities in the urine. Hippuric acid, in the form of hippurates, has the pe- culiarity of being a body formed by the kidneys and not preexisting in the blood. It is increased by a vegetable diet. Of the nonnitrogenous bodies occurring in normal urine, sodium chloride, common table salt, is the most abundant. About 151 grains are eliminated daily. Some mucus derived from the bladder, is a constituent of normal urine. Urochrome, said to be formed from hemoglobin, is the coloring matter of the urine. Any of the bodies mentioned above, may be increasod or decreased in diseased conditions and others may be present, from disease or injury, which do not exist in normal urine. The examination of the urine in health and disease is, therefore, a routine matter for the doc- tor and one with which the nurse should be familiar. Some of the chief abnormal constituents are blood, pus or cells derived from any part of the urinary tract — kidneys, ureters, bladder or urethra; albumin, wnich coagulates when urine is heated; sugar, in the form of fjrapc sugar most frequently; casts from the tubules of the kidney; free uric acid; stones formed of salts nor- mally found in the urine and many others too numerous to mention. The tests for these substances will be found in works on urinary analysis. Urinary Organs. — The urinary organs are the kidneys, which extract urine from the blood; the ureters, ducts of the kidneys, one for each, which convey urine to the bladder or reservoir which retains the fluid until its dis- FUNCTIONS OF THE KIDNEY 85 tention calls for relief, and the uretlira, or tube, or duct, of the bladder through which the urine is voided. The kidney is a compound tubular gland which, when split from outer to inner border, is seen to consist of an outer or cortical portion; an inner pyramidal or medul- lary portion and a deep concavity, the Jiilum, filled by Fig. 19. — Longitudinal section through the kidney: /, Cortex; i' , med- ullary rays; i" , labyrinth; 2. medulla; 2', papillary portion of medulla; 2", boundary layer of medulla; 3, transverse section of tubules in the boundary layer; 4, fat of renal sinus; 5, artery; *, transverse medullary rays; A, branch of renal artery; C, renal calyx; U, ureter (after Tyson and Henle). blood vessels and the pelvis or beginning of the ureter. The cortical area, about two-thirds of the organ, is the active, secretory portion of the kidney, the remainder being the collecting area. In the cortical portion are found the glomeruli and convoluted tubules which re- move the urine from the blood, while in the medullary 86 PHYSIOLOGY FOR NURSES s ID op Fig. 20. — Diagrammatic representation of the course of the uriniferous tubules and the kidney vessels. FUNCTIONS OF THE KIDNEY 87 substance are seen the pyramids of Malpighi, whose apices open into the caUces or first branches of the ure- ter. Histology must be consulted for the minute anat- omy of the organ. As no distinct secretory nerve fibers have been demon- strated in the kidney, the mechanism of the secretion of urine can be explained only by supposing that a part of the process is simple filtration or osmosis, depending on an abundant blood supply with sufficient pressure, while the remainder is due to the " vital action" of the cells lining the glomeruli and tubules. "Assuming that nearly all the constituents of urine preexist in the blood and are simply taken out of the circulation by the kid- ney, it may be stated that, for the most part, the water and salts are extracted by the cells of the Malpighian bodies, while the urea and related nitrogenous solids are removed by the cells of the convoluted tubes ; so that the specific gravity of the fluid is raised by passing down the tubes." (Jones and Bunce). Diuretics may act, therefore, by increasing the amount of blood flowing through the kidney, by increasing the pressure of the blood, by promoting osmosis or by stimulating cell ac- tivity. After urine has been formed in the kidney it is col- lected in the pelvis of the ureter, which contracts to the ureter proper, a long slender tube partly composed of nonstriated muscle fiber, which runs behind the perito- neum to the bladder, and enters the bladder so obliquely that the weight of urine in that organ presses on and closes the ureteral openings and prevents any back flow of urine. It is well to remember that, in the female the neck of the uterus is between the two ureters just be- fore they enter the bladder. The bladder is an ovoid muscular sac which receives 88 PHYSIOLOGY FOR NURSES and retains the urine until distended moderately when there is a desire to urinate. The neck of the bladder is surrounded by a thickening of plain muscle fiber form- ing a spliincter, or ring-like, muscle, whose constant con- traction prevents the dribbling away of urine as fast as it enters the bladder. Micturition is the act of emptying the bladder. The urine is forced along the ureters by contraction of the muscular coats of those tubes every ten or twenty sec- onds so that it enters the bladder in small jets and not as a steady flow. When the bladder is being filled, the pres- sure causes a stimulation of the fibers of the sphincter, through the sensory nerves, and the contraction of this muscle prevents the escape of the urine. A further ac- cumulation of urine increases the pressure on the sen- sory nerves and, by a reflex act, causes a contraction of the muscular coats of the bladder, an inhibition of the center in the lumbar part of the spinal cord which con- trols the sphincter, which is consequently relaxed, al- lowing the urine to flow freely along the urethra. Fullness of the bladder is not the only stimulus that causes a desire to urinate. An irritating quality in the urine itself, which may be caused by some drugs, men- tal conditions, like anxiety or other emotion, may create a desire to void the urine when the bladder is not only not full, but when nearly empty. This seems to be due to changes of tone in the bladder muscle itself. The urethra in the female is a much shorter channel than in the male. As the catheter is an instrument very frequently used by the nurse, she should be familiar with the normal urethra. In woman the canal is so short and wide that the passage of the catheter is usually very easy. In man, however, the contraction of the muscular fibers around the bulbous part of the urethra frequently FUNCTIONS OF THE KIDNEY 89 offers a temporary obstacle which is overcome by gentle pressure. The elongated urethra of old prostatic cases need only be mentioned. Nerve Control. — The subject of nerve control is not completely understood. That there is a center control- ling micturition in the lumbar cord and that sensory nerves pass from the bladder to the cord and motor nerves from the cord to the bladder, is clear, but the ex- act paths are not so well known. That this center, like that for defecation, is under the control of the will in adult life is a matter of daily observation ; but that this control is acquired is plain from the habits of infancy and from the involuntary passages of urine and feces in the unconsciousness of severe illness, is equally obvious. CHAPTER VII THE FUNCTIONS OF THE SKIN The importance of the skin is made apparent when one considers that the destruction of a third of that cover- ing is nearly always fatal. Primarily its function is pro- tective, as is shown by its position between the easily in- jured inner tissues and the outer world. It contains those nerve terminals which give the inner consciousness warn- ing against pain, pressure, heat or cold, sharp, rough or otherwise injurious objects. It contains the sweat glands which aid in the elimination of harmful matter and as- sist in regulating the body temperature; and, in the fe- male, through the mammary gland, it supplies nourish- ment to the infant. Sweat, or Perspiration, is the secretion of the sweat glands which are found in nearly every part of the SKHI, though most abundant in the palms of the hands and soles of the feet. The number for the entire body is es- timated to be about two million. They are simple tubu- lar glands, lined by columnar epithelium, usually coiled and having a thin muscular coat surrounding the larger ducts. The average quantity of sweat in twenty-four hours is from 700 to 900 grams, though the amount va- ries greatly with the temperature and moisture of the at- mosphere and the exertion of the individual. It is a thin watery fluid with a low specific gravity and an al- kaline reaction, which contains chloride of soda, urea, uric acid and various other organic bodies. The influ- ence of profuse sweating on the amount of urine has al- ready been stated. To a limited degree the skin, through 90 FUNCTIONS OF THE SKIN 91 the sweat glands, can relieve the overburdened kidneys, a fact which is taken advantage of to induce sweating, by drugs or other means, when the kidneys do not prop- erly perform their function, as in the condition of ec- lampsia which sometimes endangers a woman in child- bearing. Nerve Control. — There is reason to conclude that there is a sweat center, probably, in the medulla and perhaps subsidiary centers in the cord. Secretory fibers are car- ried directly to the glands and are ordinarily excited by high temperature, which acts reflexly through the cen- tral nervous system. Heat alone will not cause sweat- ing. In the high temperatures of fever, sweating is notably absent, while ' present in profuse degree in the pale skin of the terror stricken. This proves, also, that an increase in the amount of blood in the skin is not enough to cause sweat, and that a decrease does not prevent its secretion. Many drugs, like pilocarpin will increase the activity of the sweat glands and some, like atropin will paralyze the secretory fibers. Sebaceous Glands .—These simple or compound alve- olar glands are usually found associated with the hairs, when their ducts open directly into the hair, follicles. The cells which line them are cast off apparently as a part of the secretion of the glands, sebum, which is an oily semiliquid which sets into a cheesy mass, such as can be squeezed from the pimples or comedones, which disfigure many people when the ducts become stopped. The secretion of those glands located in the ear, when mixed with that of other glands, forms ear wax. The secretion of the sebaceous glands probably forms an oily coating for the SKin and hairs which protects the former by preventing too rapid evaporation and keeps the latter from becoming too dry and brittle. 92 PHYSIOLOGY TOR NURSES Iii addition to these active and important excretory functions of the skin, there is a slight power of remov- ing carbon dioxide. Cutaneous Sensations. — Everyone is aware of a capac- ity to feel; i.e., a sense of touch, or tactile sense; and to distinguish between rough and smooth, sharp and blunt, hot and cold, heavy and light objects, etc. These are among our cutaneous sensations, though the last two are more properly muscle sensations. The capacity to feel pain is more widely distributed than the other skin sen- sations. Nerves which convey information to the brain from any portion of the body are called sensory, or afferent, and each nerve ending responds to but one stimulus; i.e.. can carry information of but one kind. Thus if the nerve of sight is cut, no pain is felt, but only a riash of light will be recognized by the brain. Observation has proved that there are four stimuli which can excite the nerves distributed to the skin, which will convey four kinds of information to the brain. These four sensations are heat, cold, pressure or touch and pain. Careful experiments have shown that minute areas of skin are sensitive to one or another of these stimuli and to no other. Such areas are designated lieat spots, cold spots, pressure or pain spots. If one touches, with a delicate instrument, a cold spot, a sen- sation of cold will be experienced, even if the instrument itself is u'unHf'r Hum the skin.. Cold spots are more nu- merous than warm; pressure points more numerous than either and pain spots the most numerous of all. Some portions of the body envelope, like the membrane cover- ing the eyeball, have no nerve spots except those of pain, which are present in great numbers. Pressure spots, supposed to number about half a million for the FUNCTIONS OF THE SKIN 93 entire body, are found in rings around hair follicles, the hairs acting like levers can thus give rise to the sense of pressure or touch when nothing has touched the skin, as when an insect crawls over the hair or when the wind moves it. Certain areas, like the tips of the fingers, and the tip of the tongue are very abundantly supplied with touch nerves, while other parts, like the middle of the back, have pressure spots only at comparatively wide inter- vals, and it would seem that the number may be in- creased by use, as is seen in the delicate sense of touch possessed by the blind, or in the fingers of a trained sur- geon. At least the nerve terminals may be educated and become more sensitive. Skin sensations are as much or- gans of special sense as the eye or ear and capable of as much improvement by training. From this it would appear that some persons not only cry out more than others under the effects of pain, but that they actually suffer more pain. Two modifications of cutaneous sensibility, itching and tickling, deserve particular mention. Neither is clearly explained, but it would appear that itching is never a normal nerve impulse, but is always the result of in- jury or disease; while tickling seems to be a modifica- tion of tactile sensation due to rapidly repeated stim- ulation. Some observers think itching a mild stimula- tion of nerves conveying painful sensation. The function of the mammary gland will be described with the reproductive organs. CHAPTER VIII THE DUCTLESS GLANDS The glands the functions of which have been studied have ducts which carry the results of their labor to the point at which it is to be used in the animal economy. There remain a number of glandular organs, with no ducts, which, nevertheless, exert a great influence on the vital changes of the body, in some instances being of such power that their removal is followed by death within a brief period of time. These glands are the thyroid, with its accompanying parathyroids, situated on the trachea near the root of the neck ; the thymus, located in front of the great ves- sels just above the heart ; the adrenal bodies, or supra- renal capsules, perched on the top of each kidney; the pituitary, located at the base of the brain in a peculiar depression of the skull called sella turcica; the pineal gland imbedded in the brain substance near the con- necting link between the third and fourth ventricles ; and the spleen in the abdominal cavity, the largest of all the ductless glands. The secretion of each of these glands is poured directly into the current of the blood and acts through that organ. It is designated an internal secre- tion because there is no obvious apparatus for its dis- charge. Some of the work done by glands with ducts, like the formation of urea by the liver, partakes of the nature of internal secretion. Like the secretin, noticed in the discussion of digestion, these internal secretions 94 THE DUCTLESS GLANDS 95 excite activity in other organs, except in a few cases where they inhibit such activity. They have, therefore, been named hormones, meaning to excite, and chalones when they inhibit or prevent activity. Fig. 21. — The thyroid gland. (Gray's Anatomy, after Spalteholz.) While no adequate explanation of the function of the thyroid and parathyroids can be given, it seems clear that the former forms a hormone which stimulates other 96 PHYSIOLOGY FOR NURSES tissues and increases their metabolism; i.e., the process by which living cells incorporate substances taken from blood into parts of their own bodies, a sort of cellular digestion or rather building up. Feeding thyroid extract will cause an increase in the output of nitrogen and an increase in the oxidation, or burning up, of fat, That the gland is intimately connected writh nutrition is shown by the production of idiocy and arrested growth when it atrophies in the young. The parathyroids are even less understood. Their complete removal causes rapid death. That they are connected with the metabolism of calcium (lime) salts, seems clear. When the thyroid fails to develop in early childhood, a condition called cretinism occurs, in which there is a failure to grow in height or intelligence. In fact the person, though reach- ing adult life, remains an idiotic dwarf. Removal of the parathyroids results in a condition of tetany. muscular tremors, which end fatally after pro- ducing convulsive movements especially of the respir- atory muscles. The condition is called liypotJiyroidism and may be relieved by calcium salts. Hyperthyroidism is produced by overactivity of the thyroid and is attended by nervousness, muscular wast- ing, weakness and protrusion of the eyeballs, from which symptom the name exoplitlialmic goiter has been derived. The active principle of the adrenal bodies is called epinephrine (the trade name of which is adrenalin) which slows the heart ultimately by acting reflexly through the central nervous system, and at the same time causes a great rise in blood pressure by exciting constricton of the arterioles. It also seems to affect car- THE DUCTLESS GLANDS 97 bohydrate metabolism. While so little can be said oi the exact functions of the adrenal bodies, their importance in our economy is obviously immense, since their entire removal always ends fatally. Nothing need be said of the thymus except that its partial atrophy and disappearance at puberty indicates that it is connected with the development of the organs of reproduction. The pituitary consists of lobes having different func- tions, if, indeed, they are not separate glands. The hor- mone of the anterior lobe presides over and stimulates growth of the skeleton and perhaps all connective tis- sues; while that of the posterior lobe seems directed to the activity of some glands and to preside over the gly- cogen store in the liver which it appears to dole out in appropriate measure. An extract of the pituitary body called pituitrin excites contraction of plain muscle fiber, so especially marked in the uterus that it has been used in obstetric work to augment uterine power. Of the pineal body too little is known positively to justify a statement of its functions, though possibly they are concerned with growth. In the pancreas certain masses are found called is- lands of Langerhans. There is some evidence that these furnish an inhibitory chalone which prevents the too rapid use of the glycogen in the liver. Not a great deal, it must be confessed, is positively known about the function of the ductless glands. But there is at least enough undisputed to warrant the as- sertion that they are of very great, and, until recently, of unsuspected importance in the general work of keep- ing in repair and regulating many of the most essential organs. When the removal of an organ weighing only 98 PHYSIOLOGY FOR NURSES a few grains produces such changes that an animal wastes away and dies, its vital necessity is demon- strated. To state then that we can not explain its mode of action does, indeed, expose our ignorance, but does not lessen the need which our bodies have of the organ in question. CHAPTER IX THE NERVOUS SYSTEM The nervous system may be compared to the tele- phone system of a large community — the brain repre- senting the central office, where calls are answered and connections made; the spinal cord corresponding to the large cables conducting the mass of wires to and from the office, the peripheral nerves to the wires of the in- dividual subscribers. The analogy is, of course, imper- fect, but serves the same purpose as a diagrammatic drawing. Nerves carrying impulses from the periphery to center are like wires running from individual to cen- tral ; while those which run to muscles, glands, etc., would resemble wires running to the individuals called, after the connection has been made — central in this in- stance resembling the function of a nerve cell in a re- flex arc in its simplest form — i.e., an afferent nerve pass- ing to a cell and an efferent nerve from another con- nected cell to periphery. Such an arc w^ould be com- plete if we conceive of an organism possessed of a skin with a sensory nerve, a muscle to move the organism, a nerve cell to respond to an appeal from the surface and a nerve fiber from cell to muscle. If we imagine that such an organism encounters something painful, the course of the nerve impulse would be from the nerve ending in the skin to the cell, where the danger is rec- ognized and an order sent along the efferent nerve to the muscle to contract and remove the organism from daner. 100 PHYSIOLOGY FOR NURSES The elements of the central nervous system are the brain, divided into the two hemispheres of the cerebrum, two crura, connecting links between the cerebrum and the lower portions of the nervous system, the pons, the medulla or ~bulb, the two hemispheres of the cerebellum and the spinal cord. All of these component parts, ex- cept the last, are found in the skull, enclosed in. the three membranes of the brain, while the cord, also en- closed in three similar membranes, continuous with Fig. 22. — Schema of simple reflex arc: r, receptor in an epithelial mem- brane; a, afferent fiber; s, synapsis; c, nerve cell of center; e, efferent fiber; m, effector organ. (Pearce-Macleod, Fundamentals of Human Physiology.) those of the brain, is in the spinal canal which runs through the vertebral column. The peripheral nervous system is made up of the cra- nial and spinal nerve trunks and ganglia and their nu- merous endings in various parts of the body. The sympathetic system is a chain of ganglia and con- necting fibers situated on each side of the spinal col- umn, connected with both cranial and spinal nerves, and witie 102 PHYSIOLOGY FOE NURSES A broad view of the entire nervous system reveals that the brain is the highest development of the system, presiding over the work of the rest, thinking, ordering, and governing through its subsidiaries. Some of its impressions are received directly, and some of its orders given, through the medium of the cranial nerves; but from the larger portion of the body its various ssnsa- tions and actions must be transmitted to the brain through the spinal cord. In this transmission the cord, like a good subordinate officer, finds many things of such simple and routine nature that the conscious brain need not be troubled with them and itself interprets the information and gives the necessary instructions. Thus it appears that while much of the tissue of the cord is solely employed in conducting impulses to or from the periphery of the body, it is capable of action, not ab- solutely independent, but under general orders of the brain. The sympathetic, or more properly autonomic system is much more independent. While connected with the brain and spinal cord, its functions are, in large meas- ure, performed without the conscious will of either. The Cerebral Hemispheres. — In these subdivisions of the fore brain we find the higher centers. Here reside those intellectual functions which we are thinking of when we say "we 'think." In that part of the cortical matter — like bark, surrounding other matter — whicli is found over the anterior part of the frontal lobe probably originate the highest philosophic conceptions; in front of the central sulcus (fissure of Rolando) lies the long area stretching from the top to near the bottom of the brain which presides over all motor activity, with the special centers for the lower extremity at the top, those for the upper extremity in the middle and for the face THE NERVOUS SYSTEM 103 at the bottom. Behind the same fissure lies an area of nearly like size and shape which receives and interprets those sensations communicated from the periphery, like pain, pressure, heat and cold, which were discussed with the skin. Around the end of the Sylvian fissure is an angular area concerned in word and object seeing. Just below the same fissure lies the center for hearing and one still lower for the interpretation of words. In the Fig. 24. — Cortical centers in man. Of the three shaded areas bordering on the Rolandic fissure (hoi.), the most anterior is the precentral associational area, the middle one is the motor area (the position of the body areas are indicated on it), and the ma,st posterior is the sensory area, to the cells of which the fillet fibers proceed. The centers for seeing and hearing are also shown. The unshaded portion in front cf the Rolandic area is the precentral; the portions behind, the parietal and temperosphenoidal. (Pearce-Macleod, Fundamentals of Human Physiology.) occipital lobe is the center for vision, while the centers for smelling and tasting, closely associated, appear to be on the inner surface of the temporosphenoidal lobe near its anterior end. A glance at the surface of the brain, or a good picture of the cortex, will show how small a surface is employed in the functions of motion 104 PHYSIOLOGY FOR NURSES and in receiving sensations from the skin and tissues. This indicates that the amount employed in the mere sensations of seeing, hearing, tasting and smelling is equally small, and that the remainder of the cortex, a very large portion of the whole, must be occupied, as association areas in analyzing the sensations brought in I Corpus callosum — Vision Olfactory gustatory Pens] Medulla oblongatal Fig. 25. — Brain, mesial view. — Cerebellum by these highly trained and developed nerves. Thus, the uneducated may see a word as distinctly as the trained, but it conveys no meaning, any more than would a word in an unknown tongue. We can, therefore, read- ily comprehend that we have not only memory for words and their definitions, but that special areas of the brain may be taught to preside over these functions and so associate certain characters, which we call letters, with THE NERVOUS SYSTEM 105 a certain meaning, when combined in a definite way, which always conveys the same idea to one's mind. Edu- cation, therefore, would be, in this sense, simply the formation of certain habits; and as the frequent repeti- tion of the same act leaves each time a firmer impress on the mind, the habit may finally become automatic and be performed without definite consciousness. As the thoughts of at least a large majority of mankind are al- ways dependent on sensations received from without, it is apparent that without the association areas the high- est intellectual functions, which are entirely dependent on such associations, can not be performed; and it fol- lows that disturbance in any of the areas, or in the con- ducting paths which lead between them, may give rise to an interruption of function, or at least such a dis- turbed condition, that connected thought becomes im- possible. Temporarily such an interruption occurs in the delirium of illness and permanently in various types of insanity. Neither is it surprising that parts of an area alone may be affected. Thus a symptom of "word blindness" may, and does occur in which there is a com- plete failure to recognize printed or written words though speech is not affected. The association areas referred to must not be con- founded with those fibers — the corpus callosum — which run between the two halves of the cerebrum and associ- ate, or coordinate, the action of similar centers, for ex- ample, make the centers for the two upper extremities act in concert, as in swimming. The most widely scattered, and one of the most im- portant, association areas is that called the "language area." In order that the fullest use may be made of a language, it must be spoken, heard, written and read. This necessitates not only the highly specialized nerves 106 PHYSIOLOGY FOR NURSES of vision and hearing, but the use of all muscles in- volved in uttering articulate sounds, moving the eye- balls in unison or the hand in Avriting, and the centers for each must not only be associated with each other, but each in turn must be closely connected with those cen- ters which originate the thought to be expressed, select words with the proper shade of meaning, or comprehend the full meaning of a writer or speaker; while the sen- sory nerves of lips and tongue must also be in harmony. The area involved, therefore, would be large segments of the frontal, parietal, occipital and temporosphenoidal lobes. Probably, too, special sections are devoted to musical sense, associated with language, at least in vo- cal music, since we find some children devoid of all ideas of music while others, at an equally early age, have what wo call a "good ear" for musical sounds. THE CRURA, PONS, CEREBELLUM, MEDULLA Our knowledge of the remaining segments of the brain is neither so extensive nor so definite as that which we possess of the cerebrum. The crura cerebri are in the main composed of white fibers which convey nerve impulses to and from the cor- tex through the pons to the medulla, and thence to the spinal cord; though they contain gray matter supposed to be concerned in coordinating the movements of the eyeball and iris. The pons consists, superficially, of transverse fibers which connect the hemispheres of the cerebellum with each other and deeply of longitudinal fibers, derived from the crura, running to the medulla. It may assist in regulating automatic voluntary movements (Flint). The corpora striata and optic thalami are masses of THE NERVOUS SYSTEM 107 gray matter imbedded in the cerebrum, the first inti- mately connected with the anterior part of the internal capsule and the latter with its posterior third. Since these bundles carry respectively motor (efferent) and sensory (afferent) impulses, the corpora are supposed to be connected with motion and the thalami with sen- sation. Four small bodies — corpora quadrigemina — are sit- uated just back of the thalami. The first pair are con- nected with vision and the posterior with hearing. The cerebellum is so much larger than the portions of brain just discussed that mere size would indicate its possession of important functions. We are, however, al- most entirely ignorant of its work and so many theories have been advanced that one hesitates to speak of knowledge of the subject. Its removal certainly causes a loss of the power of coordinating voluntary muscular action in animals; so that if a coordinating center for this purpose exists, it is highly probable that it is located in the cerebellum, and aids in maintaining equilibrium. The Medulla Oblongata. — Here we are on firmer ground. This somewhat pear-shaped body seems to con- tinue the conducting fibers from all parts of the brain lying above it into the spinal cord. Its conducting func- tion, a large part of its work, is, therefore, obvious. The paths of conduction of motor impulses are in the an- terior pyramids, whose fibers cross to the opposite side of the cord as the crossed pyramidal tracts — explaining why an injury to the motor area of one Cerebral hemi- sphere causes paralysis of the other side of the body. The sensory fibers finally pass through the medulla into that region of the cord around the posterior roots of the spinal nerves with which they are connected. 108 PHYSIOLOGY FOR NURSES They do not all cross at one point, but successively as they pass down the spinal cord. The medulla is an important reflex nerve center dif- fering somewhat from a similar action of the cord which will be discussed later. Respiratory Center. — Among these centers that pre- siding over respiration is so important that the point at which it is located has long been called the ' ' vital spot. ' ' To carry on a function so essential as breathing, a mech- anism must be employed which can act independently of the will, which functions when one is asleep or uncon- scious— as in anesthesia. This center is located in the lower part of the medulla and consists of two parts, one on each side of the midline, each presiding over its own side of the body. Its neurons descend in the spinal cord and are connected through the gray matter witli the spinal nerves at their points of origin at different levels. Motor impulses, therefore, originate in the medullary center and are distributed to the lower centers in the cord, or to the centers of the vagus or facial nerve. Es- sentially the center is automatic and is normally stim- ulated by the amount of carbon dioxide in the blood ; i.e., if the amount of C02 is small, the respirations will be fewer, if the amount is increased the respiratory move- ments will increase in number. This fact, and the ex- tent of the control which the brain exerts over the cen- ter, is illustrated in "holding the breath." One may voluntarily cease to breathe for a time, but when C02 has sufficiently accumulated in the venous blood in the center, an inspiration takes place regardless of one's attempts to prevent it. The chief motor (efferent) nerve which carries the im- pulses of the center is the phrenic, a branch of the cer- vical plexus, though the intercostal, lumbar and other THE NERVOUS SYSTEM 109 nerves also play an important part. The sensory nerve chiefly concerned is the tenth cranial or vagus which is in part distributed directly to the lung tissue, but al- most any sensory nerve may convey impulses to this center. The vagus appears to carry two sets of fibers, inspiration stimulating the inhibitory fibers by expan- sion of the lung, while the partial collapse of the lung at expiration stimulates the inspiratory fibers. That the sensory nerves of the skin affect the center anyone may prove by dashing cold water over the person and noting the "gasp for breath" which immediately follows. The sensory nerves of the face, breathing and swallowing passages (fifth and ninth) can inhibit inspiration. This is a protective arrangement whose action can be shown by swallowing when the reflex through the ninth tem- porarily arrests respiratory movements; by breathing or attempting to breathe, any irritating gas, like am- monia, the inhibitory impulses in this case following the fibers of the fifth in the nose. At birth the first inspiration of the newborn child seems to be caused mainly by the accumulation of C02 in the infant's blood as a result of cutting off its connec- tion with the mother through the placenta; though a contributing stimulation is the exposure of the skin, with its sensory nerves, to the air. Obstetricians must often take advantage of this to start the inspirations which do not always begin at once after prolonged and difficult labor. Apnea and Dyspnea. — The first of these terms means absence of breathing literally, but is employed in physi- ology to describe a condition of respiratory rest when the lungs and blood are full of oxygen. A fleeting con- dition of apnea is produced by a very full inspiration. Dyspnea, difficult or labored breathing, is the condi- 110 PHYSIOLOGY FOR NURSES tion produced by a marked increase of carbon dioxide or a similar decrease in oxygen. It could be produced by diminishing the amount of oxygen in the respired air, by blocking up the air passages, as by choking, or decreasing available lung space. When carried to ex- cess as by hanging, a condition of aspliyxia results. The vagus nerve carries two sets of fibers to the mus- cles of the bronchioles — those which excite contraction when stimulated, and those which cause dilatation. They are called broncho constrict or and bronclwdilator fibers. Cardiac Center. — This center is found in the neighbor- hood of the roots of the vagus nerve, through which it exerts a slowing and regulating influence on the heart- beats, and is, therefore, called the cardioinhibitonj cen- ter. Whether there be a distinct accelerating center in the medulla is disputed. It is certain that nerve fibers sent to the heart by the sympathetic system increase the rate of the heartbeat. Other nerves affect the action of the heart reflexly. Painful sensations, particularly from the viscera, slow the heart, These sensations are carried into the central nervous system and act reflexly on the inhibitory center stimulating it to greater activity. On the other hand, emotion may stimulate the accelerator center and cause a more rapid beat, sometimes attended by less power. Hence it has been inferred that acceler- ator nerves carry two sets of fibers, one simply to in- crease the rate of action of the heart and the other to augment its power. Fear, therefore, might increase the rapidity with loss of strength, while anger could aug- ment both. Vasomotor Center. — The action of the blood vessels consists in dilating to increase and constricting to di- minish their capacity. A vasoconstrictor center in the medulla is demon- THE NERVOUS SYSTEM 111 strated, but there seems to be no vasodilator center. Changes in the size of the blood vessels are caused by the constriction of the muscular coat to reduce the size and relaxation to increase size. Constriction dimin- ishes and dilatation increases the quantity of blood in the area of distribution of the vessels involved. The im- pulses are carried by the sympathetic autonomic sys- Fig. 26. — Diagram of section of spinal cord, showing tracts. (After K61- liker) ; g, posterior median, and b,) postero-lateral columns; p.c., crossed pyramidal, and p.d., direct pyramidal tracts; f, cerebellar tract. (After Ho well.) tern and are not under the control of the conscious will, though the higher centers of the brain can excite them as may be seen in blushing — a vasodilatation of the ves- sels of the face. Ordinarily the center is excited re- flexly, as when exposure to cold causes a constriction of the vessels in the part affected. Fright, grief, the recep- tion of bad news may cause the temporary unconscious- 112 PHYSIOLOGY FOR NURSES ness called fainting by inhibiting the constrictor center and allowing such dilatation of the great venous chan- nels, particularly those of the abdomen, that there is too little blood in the brain to maintain its normal state. Nature indicates the remedy by throwing the fainting person down. Parts of the medulla are supposed to contain various other centers, such as for the control of salivary secre- tion, swallowing, vomiting, etc. The Spinal Cord.— Like other parts of the central nervous system, the spinal cord consists of gray and white matter, the gray being in the center and the white on the outside, a converse arrangement to that of the brain. While mainly employed in conducting impulses to and from the brain, the cord contains many reflex centers more or less under the control of the higher cen- ters. The fissures on the front and back of the cord indi- cate a partial subdivision into hemispheres, similar to ihe subdivision of the cerebrum, while the large mass stretching from one half to the other suggests the pres- ence of commissural fibers connecting and coordinating the two. The gray matter, projected in the form of ir- regular horns into the front and back of each half of the cord, contains the cells, the branches of which connect on the one hand with the fibers of the entering nerves and on the other with branches of other cells in turn con- nected with the fibers of nerves leaving the cord either on the same or the opposite side. Such an arrangement completes the formation of a reflex arc, composed of a nerve fiber connecting a sensory terminal with the re- ceiving branch of the cell in the gray column, the dis- patching branch of which connects with the receiving branch of a cell in the motor area, the dispatching branch Fig. 27. — The simplest reflex arc in the spinal cord. (After Kolliker.) The afferent fiber in the posterior root (in black) gives off collaterals, which end by synapses around the cells of the anterior horn (in red), the axons of which form the efferent fibers of the anterior roots. (Howell's Physi- ology.) THE NERVOUS SYSTEM 113 of which in turn joins a departing — motor or secretoi-y— fiber, the peripheral termination of which is in the muscle or gland which is to receive the stimulus to activity. Moreover there are ascending branches connected with similar cells which put the entire arc in communication with the brain, and radiating branches which form con- nections with other sensory and motor centers, so that all may be under the control of the higher centers and all coordinated with each other. The conducting fibers for descending impulses — effer- ent— cross at the lower part of the medulla and form the anterior pillars or columns of the cord. The ascending impulses are carried in the posterior columns and cross at various levels as they ascend, though many cross in the lower part of the medulla forming the posterior or sensory, decAissation. Other afferent fibers are con- nected with lateral tracts of the cord, near the entrance of the posterior roots of the spinal nerves, and are car- ried through the restiform bodies of the medulla into the cerebellum on the same side. Apparently the paths in the cord along which tactile impressions are carried are not the same as those traveled by pain and temper- ature sensations, as indicated by a disease in which there is, in affected regions, loss of the power of feeling pain or detecting differences in temperature, while the pres- sure sense is not affected ; but these paths are not clearly defined. As the motor fibers all decussate (cross to the oppo- site side) near the junction of the medulla and cord, and many of the sensory fibers are crossing all the way from the entrance of the sensory roots upward, injury to one- half of the cord will produce total motor paralysis of the same side and partial sensory paralysis of the same side, but all sensation is not abolished below the injury. 114 PHYSIOLOGY FOR NURSES Injury to the area of the surface matter of the brain governing; these paths causes both motor and sensory paralysis of the opposite side, because all the fibers of both kinds cross before reaching the origin of the spinal nerves which convey these impulses to or from the tis- sues. Centers of the Spinal Cord. — There are two enlarge- ments of the spinal cord, one situated in the cervical and the other in the lumbar portion. While these ''second- ary brains" can not be located with exactness, there is sufficient evidence to show that the cervical enlargement contains groups of cells or centers which preside over the movements of the upper extremity, accelerate the ac- tion of the heart, cause dilatation of the pupil, and reg- ulate or prescribe the activity of the cervical sympa- thetic system of nerves. There is here also a spinal res- piratory center. In the lumbar enlargement are centers controlling the rectum, bladder and the genital organs and the move- ments of the lower limbs. THE CRANIAL AND SPINAL NERVES The cranial nerves — twelve pairs — differ from the spinal in being directly attached to some part - of the brain and, usually, in carrying, in each pair, either af- ferent or efferent fibers alone. They are known by num- bers from before backwards and also have synonyms in- dicating their function. The first, or olfactory; second or optic; eighth, or auditory; and ninth, or glosso- pharyngeal, are concerned with smelling, seeing, hear- ing and tasting and are described with the organs of special sense. The third, or motor oculi; fourth, or patheticus; and THE NERVOUS SYSTEM 115 sixth or abducent all carry motor impulses to the mus- cles which move the eyeball. Their function is, there- fore, sufficiently indicated by their distribution. The fifth, or trifacial, resembles a spinal nerve in ris- ing by a motor and a sensory root, only the sensory is in front and the larger of the two. It is emphatically the neuralgic nerve, so frequently does this painful af- fection attack the sensory branches of this widely dis- tributed nerve. Its synonym of trifacial is derived from its splitting into three divisions and leaving the skull by three openings. One division, the ophthalmic conveys news from the mucous membrane and part of the skin of the nose, the eyeball and lacrimal gland, forehead and upper eyelid; the next, upper maxillary (jaw) is the afferent nerve from the skin covering the upper jaw, side of the nose, upper lip and lower lid and from the teeth and gum of the upper jaw the tonsils .and nasal and throat mucous membrane. The third division, in- ferior maxillary, does the same work for the lower jaw and its surroundings, including the tongue and salivary inlands, the skin at the back of the ear running to the top of the head, and takes all the efferent fibers which are distributed to the muscles which move the lower jaw. The nerve resembles a spinal nerve also in possessing an enlargement called a ganglion on its afferent root in which these fibers arise, the branches or roots of the ganglion furnishing the connection with the brain. This arrangement is identical with that of the spinal and other cranial nerves which contain mixed fibers. The eleventh and twelfth, or hypoglossal, nerves con- tain none but efferent (motor) fibers. The eleventh is distributed to very important muscles of the neck and back and is often connected with the surgical affection called wry neck. 116 PHYSIOLOGY FOR NURSES The twelfth conveys efferent impulses to those mus- cles which depress the hyoid bone, to the tongue and many of the muscles which move that organ. While the seventh, or facial, nerve proper contains none but efferent fibers, mainly distributed to those small bundles which move the face and change its ex- pression— hence muscles of expression, — it is connected with a part intermediate between itself and the auditory called chorda tympani or nerve of Wrisberg, which sup- plies the salivary glands with vasodilator and secretory fibers. The seventh is the nerve concerned in facial paralysis. The ninth, or glossopharyngeal, is also a mixed nerve. The motor fibers are distributed to the muscles of the pharynx and base of the tongue, while secretory fibers are carried to the parotid gland. The sensory fibers conduct impulses from part of the mucous membrane of the tongue, the pharynx, Eusta- chian tube and tympanic cavity. The origin of this nerve is from the medulla. The tenth, vagus or pneumogastric, also springs from the medulla just below the ninth and is, like it, a mixed nerve. It is the most widely distributed of all the cra- nial nerves, some of its branches reaching such function- ally different organs as the larynx, heart, lungs, stom- ach, and intestines, even so far as the large intestine. The motor (efferent) fibers go to the intrinsic muscles of the larynx, while others go to the plain muscles of the digestive tract, including part of the large intestine ; while the afferent fibers bring sensory impulses from the mucous membrane of the larynx, trachea and lungs, esophagus, stomach, intestines, gall bladder and its duct. The nerve carries inhibitory fibers to the heart and secretory fibers to the pancreas and the glands of THE NERVOUS SYSTEM 117 the stomach. It is the agent, therefore, by which the voice is produced, the air passages guarded against ir- ritants and excited to expel them; the heart regulated, glands of the stomach and the pancreas incited to activ- ity and the musculature of the swallowing and digestive organs stimulated to perform their functions. The spinal nerves, unlike the cranial, always spring from the spinal cord by two roots, an anterior, motor, connected with the anterior column and adjacent gray horn, and a posterior sensory connected with the poste- rior columns and the gray matter of the posterior horn. After emerging there is formed, on the posterior root only, a ganglion from whose cells the posterior root really springs. This ganglion is the trophic center of this root; i.e., that mass of cells which is so essential to the health and activity of a tissue that without it death of the tissue and degeneration will occur. This is proved by cutting one nerve between the ganglion and the cord and another between the ganglion and periphery, in the latter case only will the nerve degenerate. Beyond the ganglion the two roots unite to form the spinal nerves as we dissect them. In all regions except the thoracic, spinal nerves thus formed communicate more or less in- timately with one another to form anatomic plexuses, from which the ultimate branches of distribution are de- rived. In these plexiform communications there is a re- distribution of fibers in such a way that some nerves emerge which are entirely afferent, some entirely effer- ent, but most are, like the parent trunks, mixed. The plexuses are cervical, brackial, lumbar and sacral and coccygeal. The cervical plexus supplies the skin over the neck, upper part of the chest, back of the head and thorax and muscles in the same region. 118 PHYSIOLOGY FOR NURSES One branch, of more importance, is the phrenic, or chief inspiratory nerve since it carries motor impulses to the most important of the inspiratory muscles, the diaphragm. The brachial plexus is largely devoted to the upper ex- tremity. One of its branches supplies the serratus mag- nusf an accessory respiratory muscle, but most of them are mixed nerves some of the fibers of which convey cu- taneous sensations from all parts of the upper extrem- ities, while motor branches supply all the muscles which move this great lever, even those muscles which spread out over the back and chest. The thoracic nerves run mainly between the ribs — in- tercostal nerves — supplying motor impulses to the mus- cles of the same name, which makes them respiratory nerves, while their sensory fibers convey cutaneous sen- sations from the skin of the thorax and a large part of the abdomen. The lower thoracic nerves supply ths broad muscles of the abdomen and are thus expiratory agents. The lumbar plexus gives rise to those nerves which supply sensation to the skin from where the last inter- costal leaves off to where the sacral plexus takes up the work, and motor impulses in the same area. The first of the lumbar nerves supplies the skin over the upper, outer part of the hip and others carry the distribution over the front and inner side of the thigh and, by one long branch, along the inner side of the leg as far as the big toe. The skin over the external genitals is supplied in part by this plexus. The muscles supplied are those forming the lower part of abdominal wall, some in the back of the abdomen and pelvis and those on the front and inner side of the thigh. Briefly the muscles which THE NERVOUS SYSTEM 119 flex or adduct the thigh or extend the knee, receive their impulses through the lumbar plexus. The sacral and coccygeal nerves supply motor and sensory fibers to the external genitals, the hip, back of the thigh and all of the leg and foot, except the inner side of these parts which receive their supply from the lumbar plexus. THE AUTONOMIC SYSTEM The chain of ganglia and nerve fibers which lies on each side of the vertebral column is usually called sym- pathetic, because it was formerly supposed that sympa- thetic or reflex impulses wrere carried by it. The more recent name, autonomic is derived from words meaning "a lawr unto itself," and is appropriate because this sys- tem of nerves is entirely independent of the conscious will ; i.e., is independent of that portion of the brain which consciously directs. That some of these fibers are connected with the brain through cranial nerves is ap- parent and all are under the control of some portion of the brain ; but that only means that there are brain areas over which man exercises no control. Some of the gan- glia of this system are found in the skull and are con- nected with cranial nerves, notably the ciliary which gives branches to the iris or pupil ; but the larger num- ber lie along the spinal column and are connected with nearby spinal nerves by two roots — a white (medul- lated) fiber which runs from nerve to ganglion and a gray (nonmedullated) fiber which passes from ganglion to nerve which afterwards distributes it to nonstriated muscle fiber. Through the spinal and cranial nerves, the sympathetic ganglia are connected with the central nervous system in these regions (1) through the third nerve with the midbrain, (2) through the seventh, ninth, 120 PHYSIOLOGY FOR NURSES and tenth with the medulla, and (3) through the spinal nerves, from the first thoracic to the second lumbar, with the spinal cord. The branch connecting the spinal nerve and ganglion is called preganglionic, while the branch passing from the ganglion to the muscle fiber is the post- ganglionic. There are three autonomic ganglia in the neck, but their motor fibers are derived from the upper thoracic nerves and, after joining the sympathetic trunk in the thorax, ascend in it to the cervical ganglia ; which, however, give off gray communicating branches to the cervical nerves which in turn carry them to the plain muscle fibers in the regions to which they are distrib- uted. Other ganglia, the collateral are found in the thorax, abdomen and pelvis, and still others, the ter- minal, in the walls of the viscera. The activities of this extensive nervous system are directed to plain muscle fiber wherever situated. The muscle in the walls of blood vessels, however remote from the ganglia, that in the bronchi and their subdi- visions, in the intestinal canal, in the iris and the geni- tourinary tract, in glands and other plain muscular or- gans throughout the body, all is innervated by the auto- nomic system. Two opposed activities are characteristic of muscular fiber contraction, by which its ends are brought nearer together, and relaxation by which the ends are sepa- rated. Most plain muscle is arranged in circular or lon- gitudinal layers around some tubular body. Contrac- tion of the circular fibers diminishes the size of the tube ; relaxation enlarges it. Contraction of the longitudinal fibers shortens the tube ; relaxation lengthens it. Apply this to a blood vessel and one sees that contraction is equivalent to constriction and relaxation to dilatation. The best known fibers of the sympathetic are those THE NERVOUS SYSTEM 121 which excite constriction of blood vessels, hence called vasoconstrictor fibers. The less well understood are the relaxers, hence called vasodilator. The two are vaso- motor. Emotions may excite the activity- of these nerves. The face pales with fear and flushes with shame or an- ger— vasoconstriction and vasodilatation. Exercise will excite the dilators, cold the constrictors. It is obvious that this is a form of reflex action, but of reflex action controlled by higher nervous centers, neither under the control of the will nor independent of the subconscious brain. Enlarging- or decreasing the size of the intestines; con- tracting the bladder or uterus, changing the amount of blood which flows through the kidneys, the salivary and other glands, altering the size of the pupil or of the bronchioles are among the many activities of these widely distributed nerves. The nerve fibers derived from the tenth cranial, which inhibit, or slow, the heartbeat, are carried to the heart muscle through the sympathetic plexus situated on the aorta. They are designated bulbar autonomic fibers, as distinguished from the accelerator fibers derived from the upper thoracic spinal nerves and joining the same cardiac plexus before distribution. Other bulbar autonomic fibers are carried by the ninth, seventh, and third nerves. Those from the latter pass to the ciliary ganglion and from it to the muscle of the iris which regulates the amount of light entering the pupil; or to the ciliary muscle which regulates ac- commodation of the eye for near or distant vision, while the similar fibers of the seventh and ninth probably reach the tongue, through the chorda tympani and lin- gual for the anterior two-thirds and the ninth for the posterior third, and supply vasomotor fibers to those or- gans. CHAPTER X THE SPECIAL SENSES We have already seen that the recognition of pain, pressure, heat, and cold and muscular sensibility are conducted by nerve paths as much specialized for their purposes as is the nerve of vision; but long habit has applied the term special senses to the organs of taste, smell, vision, and hearing. TASTE AND SMELL These special senses are so intimately associated that it is difficult to make a clear distinction between them, except that the four qualities, sweet, salt, sour and bit- ter or combinations of the four are appreciated without assistance from the olfactory sense. Except these four, all our so-called taste sensations, are really olfactory sensations, the nerves of smell being stimulated by the substance eaten either before it is placed in the mouth or after it has been swallowed, the odoriferous particles, in the latter case, entering the back of the nose in the current of expired air which follows the act of swal- lowing. The nerves which carry sensations of taste to the brain are the glossopharyngeal for the posterior one- third of the tongue, fauces and palate, and the lingual, or gustatory, branch of the fifth for the anterior two- thirds of the tongue. The taste fibers- in the gustatory, however, are derived from the clwrda tympani of the seventh. The lingual really carries fibers of cutaneous THE SPECIAL SENSES 123 sensibility which endow the tongue with painful, tactile, or pressure and temperature sensations. One's sense of taste, then, is highly complex, being easily associated with, or influenced by, temperature, touch and odor. The numerous papillae of the tongue are provided with certain cells ending in hairlike projections which are peripheral taste organs. From these the sense of taste is conveyed along the nerve paths mentioned to a point in the temporospJienoidal lobe, just behind the smell center, where the center for taste is thought to be located. Because of their number and complexity, it is difficult to classify taste sensations. The bitter, sweet, acid and salt may be, and are, so often mingled not only with each other, but with odors which wre associate with things tasted in the past that we can not separate the various classes of stimulation. An apple, for instance, is usually a combination of sweet and sour, but the flavor so highly appreciated wrould be lost if the olfac- tory nerves were destroyed. It is for this reason that food "loses its taste" when we suffer from colds, par- ticularly if both the back and front of the nose is stopped by secretion. The distribution of the four car- dinal tastes is not clear, but the back of the tongue and fauces are more sensitive to bitter and the front to sweet stimuli. There is some evidence that there are four separate end organs and nerve fibers for the four fundamental tastes. A substance which is insoluble can not be tasted. A piece of clean metal or glass stimulates the cutaneous sensations when applied to the tongue, but gives no sense of taste. Substances in solution, or capable of be- ing rapidly dissolved in the saliva, give rise to sensa- tions of taste, probably through a chemical reaction in 124 PHYSIOLOGY FOR NURSES which the hairlikc process is involved. Heat or cold, when excessive, interferes with the acuteness of taste. Smaller quantities of bitter substances can be tasted than of any other, while acid, sweet, and salt each re- quire larger amounts, salt the largest. Some substances give different sensations on different parts of the tongue, as sulphate of soda which is merely salty at the tip of the tongue, but bitter at the back. Certain sub- stances dissolved in the blood give rise to sensations of taste. The bile in the blood in jaundice causes a bitter taste, while the sugar in diabetes causes a sweet tas'.e. THE OLFACTORY SENSE The course of olfactory sensations is from the end or- gans of smell in the roof and upper part of the sides of each nostril, along the olfactory nerves to the bulb and thence to the base of the brain at the lower and inner part of the temporosphenoidal lobe just in front of the center for taste. The smell sense is one of the oldest in the history of life. When highly developed it was not only of great defensive strength in enabling its possessor to detect the presence of enemies, but was of equal offensive serv- ice in the pursuit of prey. In man it has dwindled to such an extent that he vaguely defines odors as pleas- ant or disagreeable, while a dog can still detect the odor, of a man, imperceptible usually to himself and as- sociates, and follow him unerringly after hours have elapsed and pick him out of a crowd of others. The substances which arouse, or stimulate, the sense of smell, give off inappreciable particles, probably gas- eous in form, which are carried by inhaled air to the end organs of the olfactory nerve, are there dissolved by the moisture present and chemically stimulate the THE SPECIAL SENSES 125 hair processes. Many odors, like those of fruits, wines, and many foods are habitually confounded with the sense of taste. Some disagreeable, or foul odors are simply associated in our memories with disagreeable im- pressions and may be agreeable to other persons. The garlic or onion odor and that of musk, excite pleasur- able sensations in some and only disagreeable sensation in others. These effects are probably memories and not differences in the character of the chemical reaction in different individuals. The olfactory nerves are easily fatigued, when stimulated for too long a period, or with too much of the odor. The amount of gaseous material which can be detected is innnitesimally small. Camphor can be detected when only one part is present in four hundred thousand, vanillin (the active principle of vanilla), one part in ten million, while other substances can l)e detected in amounts still more minute. VISION Essentially the organ of vision is an apparatus by which an image of objects may be thrown on a mirror, composed of nerve terminals sensitive to light, the sen- sation, or impulse, thus produced being conducted along paths of nerve tissue to the gray matter covering a cer- tain area of the brain. The particular region of the brain is the cuneate portion of the occipital lobe, and the path of conduction is by the optic tracts, chiasm and nerves from the retina, the concave nervous mirror in which the object is reflected. We actually see with the brain, just as we feel with the brain. If the cuneate area be destroyed we are blind no matter how perfect the remainder of the seeing apparatus may be. Bays of light are vibrations of the ether which sur- rounds us, differing in length and rapidity for different • - 3 0 ' It V 1 V L, ru w }- }~ \ S