17.Its final importance? Starch? How effected? Ptyalin?17.Finally, the saliva has the property of acting chemically upon the food. As we have before stated (Chap. IV.), starch, as starch, cannot enter the tissues of the body; but, in order to become nutriment, must first be changed to grape sugar. This change is, in part, effected by the saliva, and takes place almost instantly, whenever it comes in contact with cooked starch. This important function is due to an organic ingredient of the saliva calledptyalin. This substance has been extracted from the saliva by the chemist, and has been found, by experiment, to convert into sugar two thousand times its own weight of starch.18.Each of the processes? Why is a knowledge of the digestive functions important? How shown?18. Importance of Mastication and Insalivation.—Each of these processes complements the other, and makes the entire work available; for, by their joint action, they prepare the food in the best possible manner for further digestive changes. The knowledge of these preliminary functions will appear the more important, when we reflect that they are the only ones which we can regulate by the will. For, as soon as the act of swallowing begins, the food not only passes out of sight, but beyondcontrol; and the subsequent acts of digestion are consequently involuntary and unconsciously performed.19.Rapid eating? Describe the process and effects.19.It is generally known that rapid eating interferes with digestion. How does this occur? In the first place, in rapid eating, the flow of the saliva is insufficient to moisten the solid parts of the food, so that they remain too hard and dry to be easily swallowed. This leads to the free and frequent use of water, or some other beverage, at meals, to "wash down" the food,—a most pernicious practice. For these fluids, not only cannot take the place of the natural digestive juices, but, on the contrary, dilute and weaken them.20.Loss of taste? Another effect of rapid eating? Mistakes?20.Secondly, the saliva being largely the medium of the sense of taste, the natural flavors of the food are not developed, and consequently it appears comparatively insipid. Hence the desire for high-seasoned food, and pungent sauces, that both deprave the taste and over excite the digestive organs. Rapid eating also permits the entrance of injurious substances which may escape detection by the taste, and be unconsciously received into the system. In some instances, the most acrid and poisonous substances have frequently been swallowed "by mistake," before the sense of taste could act, and demand their rejection.21.Effect of imperfectly broken food in the stomach? Dyspepsia? Overeating?21.Thirdly, the food, being imperfectly broken up by the teeth, is hurried onward to the stomach, to be by it more thoroughly divided. But the task thus imposed upon the stomach, it is not at all adapted to perform; so that the crude masses of food remain a heavy burden within the stomach, and a source of distress to that organ, retarding the performance of its legitimate duty. Hence persons who habitually eat too rapidly, frequently fall victims to dyspepsia. Rapid eating also conduces to overeating. The food is introduced so rapidly, that the system has nottime to recognize that its real wants are met, and that its losses have been made good; and hence the appetite continues, although more nutriment has been swallowed than the system requires, or can healthfully appropriate.Fig. 22.--Section of Chest and Abdomen.Fig. 22.—Section of Chest and Abdomen.A, Heart. B, The Lungs. C, Stomach. D, The Liver. E, Large Intestine. G, Small Intestine.22.Gullet? Describe the stomach and its location. Effects of gormandizing?22. The Stomach.—As soon as each separate portion of food is masticated and insalivated, it is swallowed; that is, it is propelled downward to the stomach, through a narrow muscular tube about nine inches in length, called theœsophagus, or gullet (Fig. 23). The stomach is the only large expansion of the digestive canal, and is the most important organ of digestion. It is a hollow, pear-shaped pouch, having a capacity of three pints, in the adult. Its walls are thin and yielding, and may become unnaturally distended, as in the case of those who subsist on a bulky, innutritious diet, and of those who habitually gormandize.23.Heart-orifice? Gatekeeper? Coins, etc.? Indication of the soft and yielding texture of the stomach?23.The stomach has also two openings; that by which food enters, being situated near the heart, is called thecardiac, or heart orifice; the other is thepylorus, or "gatekeeper," which guards the entrance to the intestines,and, under ordinary circumstances, permits only such matters to pass it as have first been properly acted upon in the stomach. Coins, buttons, and the like are, however, readily allowed to pass, because they can be of no use if retained. The soft and yielding texture of this organ—the stomach—indicates that it is not designed to crush and comminute solid articles of food.Fig. 23.--The Organs of Digestion.Fig. 23.—The Organs of Digestion.O, Œsophagus. S, Stomach. L, Liver. M, Pylorus. C, Large Intestines. P, Pancreas. I, Small Intestines. N, Spleen. G, Gall-bladder.24.What is meant by the gastric juice?24. The Gastric Juice.—We have seen how the presence of food in the mouth excites the salivary glands, causing the saliva quickly to flow. In the same manner, when food reaches the stomach, its inner lining, the mucous membrane, is at once excited to activity. (At first its surface, which while the stomach is empty presents a pale pink hue, turns to a bright red color, for the minute blood-vessels which course through it, are filled with blood. Presently a clear, colorless, and acid fluid exudes, drop by drop, from its numerous minute glands or "tubules," until finally the surface is moistened in every part, and the fluid begins to mingle with the food. This fluid is termed the gastric juice.25.What is the office of the gastric juice? Acidity of the gastric juice? Quantity of gastric juice used? What becomes of it?25.The gastric juice is the proper solvent of certain articles of food, especially those belonging to the albuminoid class. This solvent power is due to its peculiar ingredient,pepsin; in digestion, this substance acts like a ferment; that is, it induces changes in the food simply by its presence, but does not itself undergo change. The acidity of the gastric juice, which is due tolactic acid, is not accidental; for we find that the pepsin cannot act in an alkaline solution—that is, one which is not acid or neutral. The quantity of gastric juice secreted daily is very large, probably not less than three or four pints at each meal. Though this fluid is at once used in the reduction of the food, it is not lost; since it is soon re-absorbed by the stomach, together with those parts of the food which it has digested and holds in solution.26.Muscular coat of the stomach? Expansion and contraction of its fibres? Action of the fibres?26. Movements of the Stomach.—The inner coating of the stomach is the mucous membrane, which, as we have seen, furnishes the gastric juice. Next to this coating lies another, called the muscular coat, composed of involuntary muscular fibres, some of which run circularly, and others in a longitudinal direction. These expand to accommodate the food as it is introduced, and contract as it passes out. In addition, these fibres are in continual motion while food remains in the stomach, and they act in such manner that the contents are gently turned round from side to side, or from one end of it to the other.27.Peristaltic movements? What is said of our consciousness of and power over these movements? Describe the movements of the pylorus.27.By these incessant movements of the stomach, called theperistalticmovements, the gastric juice comes in contact with all parts of the food. We are, however, not conscious that these movements take place, nor have we the power to control them. When such portions of the food as are sufficiently digested approach the pylorus, itexpands to allow them to pass out, and it closes again to confine the residue for further preparation.28.How has the knowledge and the workings of the stomach been ascertained? St. Martin? How else?28.The knowledge of these and other interesting and instructive facts has been obtained by actual observation; the workings of the stomach of a living human being have been laid open to view and examined—the result of a remarkable accident. Alexis St. Martin, a Canadianvoyageur, received a gun-shot wound which laid open his stomach, and which, in healing, left a permanent orifice nearly an inch in diameter. Through this opening the observer could watch the progress of digestion, and experiment with different articles of food. Since that occurrence, artificial openings into the stomach of the inferior animals have been repeatedly made, so that the facts of stomach-digestion are very well ascertained and verified.29.What was formerly thought? What do we now know? What else do we now know? Water, salt, and sugar? Absorption?29. Gastric Digestion.—What portions of the food are digested in the stomach? It was formerly thought that all the great changes of digestion were wrought here, but later investigation has taught us better. We now know that the first change in digestion takes place in the mouth, in the partial conversion of starch into sugar. We also know that, of the three organic food principles (considered in Chapter IV.) two—the fats and the sugars—are but slightly affected by the stomach; but that its action is confined to that third and very important class, from which the tissues are renewed, the albuminoids. A few articles need no preparation before entering the system, as water, salt, and grape-sugar. These are rapidly taken up by the blood-vessels of the stomach, which everywhere underlie its mucous membrane in an intricate and most delicate network. In this way the function of absorption begins.30.Albuminose? The process? Chyme?30.The albuminoid substances are speedily attacked anddigested by the gastric juice. From whatever source they are derived, vegetable or animal, they are all transformed into the same digestive product, calledalbuminose. This is very soluble in water, and is readily absorbed by the blood-vessels of the stomach. After a longer or shorter time, varying from one to five hours, according to the individual and the quantity and quality of his food, the stomach will be found empty. Not only has the digested food passed out, but also those substances which the stomach could not digest or absorb have passed little by little through the pylorus, to undergo further action in the intestines. At the time of its exit, the digested food is of a pulpy consistence, and dark color, and is then known as thechyme.31.What are the intestines? The small intestines? The large intestines? Their structure?31. The Intestines.—The intestines, or "bowels," are continuous with the stomach, and consist of a fleshy tube, or canal, twenty-five feet in length. The small intestine, whose diameter is about one inch and a half, is twenty feet long and very tortuous. The large intestine is much wider than the former, and five feet long (Fig. 23). The general structure of these organs resembles that of the stomach. Like it, they are provided with a mucous membrane, or inner lining, whence flow their digestive juices; and, just outside of this, a muscular coat, which propels the food onward from one point to another.32.Peritoneum? The work of digestion?32.Moreover, both the intestines and stomach are enveloped in the folds of the same outer tunic or membrane, called theperitoneum. This is so smooth and so well lubricated, that the intestines have the utmost freedom of motion. In the small intestines, the work of digestion is completed, the large intestine receiving from them the indigestible residue of the food, and in time expelling it from the body.33.The presence of food in the intestines? Bile?33. Intestinal Digestion.—As soon as the food passes the pylorus and begins to accumulate in the upperpart of the intestines, it excites the flow of a new digestive fluid, which enters through a small tube, orduct, about three inches below the stomach. It is formed by the union of two distinct fluids—thebileand thepancreaticjuice. The bile is secreted by the liver, which is the largest gland of the body, and is situated on the right side and upper part of the abdomen (Fig. 22). The bile is constantly formed, but it flows most rapidly during digestion. During the intervals of digestion it is stored in thegall-bladder, a small membranous bag attached to the under side of the liver. This fluid is of a greenish-yellow color, having a peculiar smell, and a very bitter taste.34.The pancreatic juice? The joint action of these fluids?34.The pancreatic juice is the product of a gland called thepancreas, situated behind the stomach. This fluid is colorless, viscid, and without odor. Like the digestive juices previously described, it owes its solvent power to its peculiar ferment principle, calledpancreatin. By the joint action of these fluids, the fatty parts of the food are prepared for absorption. By previous steps of digestion the fats are merely separated from the other components of the food; but here, within the intestines, they are reduced to a state of minute division, oremulsion, resembling the condition of butter in milk, before it has been churned. There results from this action a white and milky fluid, termed thechyle, which holds in solution the digestible portions of the food, and is spread over the extensive absorbent surface of the small intestines.35.The mucous membrane? Experiments on inferior animals?35.The mucous membrane of the intestines, also, secretes or produces, a digestive fluid by means of numerous "follicles," or minute glands; this is called the intestinal juice. From experiments on the inferior animals, it has been ascertained that this fluid exerts a solvent influence over each of the three organic food principles, and in this way may supplement and complete the action of thefluids previously mentioned, viz.:—of the saliva in converting starch into sugar, of the gastric juice in digesting the albuminoids, and of the pancreatic juice and bile in emulsifying the fats.36, 37.How much thus far has been done with the food? The next process? Give the first way.36. Absorption.—With the elaboration of the chyle, the work of digestion is completed; but, in a certain sense, the food is yet outside of the body; that is, the blood is not yet enriched by it, and it is not in a position to nourish the tissues. The process by which the liquefied food passes out of the alimentary canal into the blood is called absorption. This is accomplished in two ways; first, by theblood-vessels. We have seen how the inner membrane of the stomach is underlaid by a tracery of minute and numerous vessels, and how some portions of the food are by them absorbed. The supply of blood-vessels to the intestines is even greater; particularly to the small intestines, where the work of absorption is more actively carried on.37.The absorbing surface of the small intestines, if considered as a plane surface, amounts to not less than half a square yard. Besides, the mucous membrane is formed in folds with an immense number of thread-like prolongations, calledvilli, which indefinitely multiply its absorbing capacity. These minute processes, the villi, give the surface the appearance and smoothness of velvet; and during digestion, they dip into the canal, and, by means of their blood-vessels, absorb its fluid contents, just as thespongioleswhich terminate the rootlets of plants, imbibe moisture from the surrounding soil.38.How is absorption effected in another way? Describe it. Name of the lacteals? Thoracic duct?38.Secondly, absorption is also effected by thelacteals, a set of vessels peculiar to the small intestines. These have their beginnings in the little villi just mentioned, side by side with the blood-vessels. These two sets of absorbents run in different courses, but their destination is the same,which is the right side of the heart. The lacteals receive their name from their milky-white appearance. After a meal containing a portion of fat, they are then distended with chyle, which they are specially adapted to receive: at other times they are hardly discernible. The lacteals all unite to form one tube, thethoracic duct, which passes upward through thethorax, or chest, and empties into a large vein, situated just beneath the left collar-bone.Fig. 24.--The Lacteals.Fig. 24.—The Lacteals.A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents. E, Blood-vessel.39.The absorbents? Lymph? What further of the lymph?39. The Absorbents.—The lacteals belong to a class of vessels known as absorbents, or lymphatics, which ramify in nearly all parts of the body, except the brain and spinal cord. The fluid which circulates through the lymphatics of the limbs, and all the organs not concerned in digestion, is calledlymph. This fluid is clear and colorless, like water, and thus differs from the milky chyle which the lacteals carry after digestion: it consists chiefly of the watery part of the blood, which was not required by the tissues, and is returned to the blood by the absorbents or lymphatics.40.What can you state as to the time required for digestion?40. Circumstances affecting Digestion.—What length of time is required for the digestion of food? From observations made, in the case of St. Martin, the Canadianalready referred to, it has been ascertained that, at the end of two hours after a meal, the stomach is ordinarily empty. How much time is needed to complete the digestion of food, within the small intestines, is not certain; but, from what we have learned respecting their functions, it must be evident that it largely depends upon the amount of starch and fat which the food contains.41.Circumstances affecting duration of digestion? Fresh food?41.In addition to the preparations which the food undergoes in cooking, which we have already considered, many circumstances affect the duration of digestion; such as the quality, quantity, and temperature of the food; the condition of the mind and body; sleep, exercise, and habit. Fresh food, except new bread and the flesh of animals recently slain, is more rapidly digested than that which is stale; and animal food more rapidly than that from the vegetable kingdom.42.Food in concentrated form? A large quantity of food? Experiment on the dog? Ice-water? Variety of articles?42.Food should not be taken in too concentrated a form, the action of the stomach being favored when it is somewhat bulky; but a large quantity in the stomach often retards digestion. If the white of one egg be given to a dog, it will be digested in an hour, but if the white of eight eggs be given it will not disappear in four hours. A wineglassful of ice-water causes the temperature of the stomach to fall thirty degrees; and it requires a half-hour before it will recover its natural warmth—about a hundred degrees—at which the operations of digestion are best conducted. A variety of articles, if not too large in amount, is more easily disposed of than a meal made of a single article; although a single indigestible article may interfere with the reduction of articles that are easily digested.43.Strong emotion? The tongue of the patient?43.Strong emotion, whether of excitement or depression, checks digestion, as do also a bad temper, anxiety, long fasting, and bodily fatigue. The majority of theseconditions make the mouth dry, that is, they restrain the flow of the saliva; and without doubt they render the stomach dry also, by preventing the flow of the gastric juice. And, as a general rule, we may decide, from a parched and coated tongue, that the condition of the stomach is not very dissimilar, and that it is unfit for the performance of digestive labor. This is one of the points which the physician bears in mind when he examines the tongue of his patient.44.Eating between meals? Severe exercise? Sleep after meals?44.The practice of eating at short intervals, or "between meals," as it is called, has its disadvantage, as well as rapid eating and over-eating, since it robs the stomach of its needed period of entire rest, and thus overtasks its power. With the exception of infants and the sick, no persons require food more frequently than once in four hours. Severe exercise either directly before or directly after eating retards digestion; a period of repose is most favorable to the proper action of the stomach. The natural inclination to rest after a hearty meal may be indulged, but should not be carried to the extent of sleeping; since in that state the stomach, as well as the brain and the muscles, seeks release from labor.QUESTIONS FOR TOPICAL REVIEW.PAGE1. What do you understand by nutrition?802. How is the process of nutrition carried on?803. What further can you state on the subject?80,814. Describe the general plan of digestion.815. How is the process of mastication carried on?80,826. State what you can in relation to the formation of the teeth.82,867. What, in relation to their arrangement?83,848. What, in relation to the process of "shedding?"82,83,849. In relation to the different forms of teeth in different animals?8510. What causes operate to injure or destroy the teeth?85,8611. What suggestions and directions are given for the preservation of the teeth?85,8612. What do you understand by insalivation?80,8613. How is the process of insalivation carried on?86,87,8814. Of what importance is the saliva to the process?87,8815. Of what importance are mastication and insalivation?88,8916. Describe the consequences of rapid eating.89,9017. What becomes of the food directly after it has undergone mastication and insalivation?9018. Describe the location and formation of the stomach.90,91,9219. Describe the process by which the gastric juice is formed.9120. What are the properties and uses of the gastric juice?9221. What are the movements of the stomach, and what their uses?92,9322. What further can you state on the subject?9323. What portions of the food are digested in the stomach?93,9424. What are the first changes of digestion?9325. Describe the location and formation of the stomach.9426. What further can you state in relation to the stomach?9427. Describe the process of intestinal digestion.94,95,9628. What do you understand by absorption?80,9629. How is the process of absorption effected?96,9730. What are the lacteals and of what use are they?96,9731. What length of time is required for the digestion of food?97,9832. What circumstances, of food, affect digestion?9833. What circumstances, of emotion, affect digestion?98,9934. What suggestions and directions are given upon the subject of eating and drinking?98,99CIRCULATION OF THE BLOOD.CIRCULATION OF THE BLOOD.[Heart, Lungs, Arteries & Veins.]CHAPTER VII.The Circulation.The Blood—Its Plasma and Corpuscles—Coagulation of the Blood—The Uses of the Blood—Transfusion—Change of Color—The Organs of the Circulation—The Heart, Arteries, and Veins—The Cavities and Valves of the Heart—Its Vital Energy—Passage of the Blood through the Heart—The Frequency and Activity of its Movements—The Pulse—TheSphygmograph—The Capillary Blood-vessels—The Rate of the Circulation—Assimilation—Injuries to the Blood-vessels.1.What is required by every living organism? In plants? Insects? Reptiles? Man?1. The Blood.—Every living organism of the higher sort, whether animal or vegetable, requires for the maintenance of life and activity, a circulatory fluid, by which nutriment is distributed to all its parts. In plants, this fluid is the sap; in insects, it is a watery and colorless blood; in reptiles and fishes, it is red but cold blood; while in the nobler animals and man, it is the red and warm blood.2.Importance and abundance of blood? Dependence of life? Abel? Mosaic law? In what part of the body is blood not found? Quantity of blood in the body?2.The blood is the most important, as it is the most abundant, fluid of the body; and upon its presence, under certain definite conditions, life depends. On this account it is frequently, and very properly, termed "the vital fluid." The importance of the blood, as essential to life, was recognized in the earliest writings. In the narration of the death of the murdered Abel, it is written, "the voice of hisbloodcrieth from the ground." In the Mosaic law, proclaimed over thirty centuries ago, the Israelites were forbidden to eat food that contained blood, for the reason that "the life of the flesh is in the blood." With the exception of a few tissues, such as the hair, the nails, and thecorneaof the eye, blood everywhere pervades the body, as may be proven by puncturing any part with aneedle. The total quantity of blood in the body is estimated at about one-eighth of its weight, or eighteen pounds.3.Color of blood? Its consistence? Odor?3.The color of the blood, in man and the higher animals, as is well known, is red; but it varies from a bright scarlet to a dark purple, according to the part whence it is taken. "Blood is thicker than water," as the adage truly states, and has a glutinous quality. It has a faint odor, resembling that peculiar to the animal from which it is taken.4.What is stated of the blood as viewed under the microscope?4.When examined under the microscope, the blood no longer appears a simple fluid, and its color is no longer red. It is then seen to be made up of two distinct parts: first, a clear, colorless fluid, called theplasma; and secondly, of a multitude of minute solid bodies, or corpuscles, that float in the watery plasma. The plasma, or nutritive liquid, is composed of water richly charged with materials derived from the food, viz., albumen, which gives it smoothness and swift motion; fibrin; certain fats; traces of sugar; and various salts.Fig 25.--The Blood Corpuscles.Fig 25.—The Blood Corpuscles.5.State what you can of the little bodies called corpuscles.5. The Blood Corpuscles.—In man, these remarkable "little bodies," as the wordcorpusclessignifies, are of a yellow color, but by their vast numbers impart a red hue to the blood. They are very small, having a diameter of about 1/3500 of an inch, and being one-fourth of that fraction in thickness; so that if 3,500 of them were placed in line, side by side, they would only extend one inch; or, ifpiled one above another, it would take at least 14,000 of them to stand an inch high. Although so small in size, they are very regular in form. As seen under the microscope, they are not globular or spherical, but flat, circular, and disc-like, with central depressions on each side, somewhat like a pearl button that has not been perforated. In freshly-drawn blood they show a disposition to arrange themselves in little rolls like coins (Fig. 25).Fig. 26.--Corpuslces.Fig. 26.a, Oval Corpuscles of a fowl.b, Corpuscles of a frog.c, Those of a shark.The five small ones at the upper part of the figure, represent the human corpuscles magnified 400 times.6.The size and shape of corpuscles? Why is the fact important?6.The size and shape of the blood corpuscles vary in different animals, so that it is possible to discriminate between those of man and the lower animals (Fig. 26). This is a point of considerable practical importance. For example, it is sometimes desirable to decide in a court of justice the source, whether from man or an inferior animal, of blood stains upon the clothing of an accused person, or upon some deadly weapon. This may be done by a microscopical examination of a minute portion of the dried stain, previously refreshed by means of gum-water. Certain celebrated cases are recorded in which the guilt of criminals has been established, and they have been condemned and punished upon the evidence which science rendered on this single point, the detecting of the human from other blood.7.The character of the blood of dead animals? Means of detecting such blood?7.The character of the blood of dead, extinct, and even fossil animals, such as the mastodon, has been ascertained by obtaining and examining traces of it which had been shut up, perhaps for ages, in the circulatory canals of bone. A means of detecting blood in minute quantities is foundin the spectroscope, the same instrument by which the constitution of the heavenly bodies has been studied. If a solution containing not more than one-thousandth part of a grain of the coloring matter of the corpuscle, be examined, this instrument will detect it.8.White corpuscles? Total number of corpuscles in the body?8.The corpuscles, just described, are known as the red blood corpuscles. Besides these, and floating along in the same plasma, are the white corpuscles. These are fewer in number, but larger and globular in form. They are colorless, and their motion is less rapid than that of the other variety. The total number of both varieties of these little bodies in the blood is enormous. It is calculated that in a cubic inch of that fluid there are eighty-three millions, and at least five hundred times that number in the whole body.9.The blood in its natural condition in the body? Describe the process by which the coagulation of blood takes place?9. Coagulation.—The blood, in its natural condition in the body, remains perfectly fluid; but, within a few minutes after its removal from its proper vessels, whether by accident or design, a change takes place. It begins to coagulate, or assume a semi-solid consistence. If allowed to stand, after several hours it separates into two distinct parts, one of them being a dark red jelly, the coagulum, or clot, which is heavy and sinks; and the other, a clear, straw-colored liquid, called serum, which covers the clot. This change is dependent upon the presence in the blood of fibrin, which possesses the property of solidifying under certain circumstances; one of these circumstances being when the blood is separated from living tissues. The color of the clot is due to the entanglement of the corpuscles with the fibrin.10.If coagulation were impossible? How is it in fact?10.In this law of the coagulation of the blood is our safeguard against death by hæmorrhage, or against undue loss of blood. If coagulation were impossible, theslightest injury in drawing blood would prove fatal. Whereas now, in vastly the larger proportion of cases, bleeding ceases spontaneously, because the blood, as it coagulates, stops the mouths of the injured blood-vessels. In another class of cases, where larger vessels are cut or torn, it is simply necessary to close them by a temporary pressure; for in a few minutes the clot will form and seal them up. In still more serious cases, where the blood-vessel is of large size, the surgeon is obliged to tie a "ligature" about it, and thus prevent the force of the blood-current from washing away the clots, which, forming within and around the vessel, would close it effectually.
17.Its final importance? Starch? How effected? Ptyalin?
17.Finally, the saliva has the property of acting chemically upon the food. As we have before stated (Chap. IV.), starch, as starch, cannot enter the tissues of the body; but, in order to become nutriment, must first be changed to grape sugar. This change is, in part, effected by the saliva, and takes place almost instantly, whenever it comes in contact with cooked starch. This important function is due to an organic ingredient of the saliva calledptyalin. This substance has been extracted from the saliva by the chemist, and has been found, by experiment, to convert into sugar two thousand times its own weight of starch.
18.Each of the processes? Why is a knowledge of the digestive functions important? How shown?
18. Importance of Mastication and Insalivation.—Each of these processes complements the other, and makes the entire work available; for, by their joint action, they prepare the food in the best possible manner for further digestive changes. The knowledge of these preliminary functions will appear the more important, when we reflect that they are the only ones which we can regulate by the will. For, as soon as the act of swallowing begins, the food not only passes out of sight, but beyondcontrol; and the subsequent acts of digestion are consequently involuntary and unconsciously performed.
19.Rapid eating? Describe the process and effects.
19.It is generally known that rapid eating interferes with digestion. How does this occur? In the first place, in rapid eating, the flow of the saliva is insufficient to moisten the solid parts of the food, so that they remain too hard and dry to be easily swallowed. This leads to the free and frequent use of water, or some other beverage, at meals, to "wash down" the food,—a most pernicious practice. For these fluids, not only cannot take the place of the natural digestive juices, but, on the contrary, dilute and weaken them.
20.Loss of taste? Another effect of rapid eating? Mistakes?
20.Secondly, the saliva being largely the medium of the sense of taste, the natural flavors of the food are not developed, and consequently it appears comparatively insipid. Hence the desire for high-seasoned food, and pungent sauces, that both deprave the taste and over excite the digestive organs. Rapid eating also permits the entrance of injurious substances which may escape detection by the taste, and be unconsciously received into the system. In some instances, the most acrid and poisonous substances have frequently been swallowed "by mistake," before the sense of taste could act, and demand their rejection.
21.Effect of imperfectly broken food in the stomach? Dyspepsia? Overeating?
21.Thirdly, the food, being imperfectly broken up by the teeth, is hurried onward to the stomach, to be by it more thoroughly divided. But the task thus imposed upon the stomach, it is not at all adapted to perform; so that the crude masses of food remain a heavy burden within the stomach, and a source of distress to that organ, retarding the performance of its legitimate duty. Hence persons who habitually eat too rapidly, frequently fall victims to dyspepsia. Rapid eating also conduces to overeating. The food is introduced so rapidly, that the system has nottime to recognize that its real wants are met, and that its losses have been made good; and hence the appetite continues, although more nutriment has been swallowed than the system requires, or can healthfully appropriate.
Fig. 22.--Section of Chest and Abdomen.Fig. 22.—Section of Chest and Abdomen.A, Heart. B, The Lungs. C, Stomach. D, The Liver. E, Large Intestine. G, Small Intestine.
A, Heart. B, The Lungs. C, Stomach. D, The Liver. E, Large Intestine. G, Small Intestine.
22.Gullet? Describe the stomach and its location. Effects of gormandizing?
22. The Stomach.—As soon as each separate portion of food is masticated and insalivated, it is swallowed; that is, it is propelled downward to the stomach, through a narrow muscular tube about nine inches in length, called theœsophagus, or gullet (Fig. 23). The stomach is the only large expansion of the digestive canal, and is the most important organ of digestion. It is a hollow, pear-shaped pouch, having a capacity of three pints, in the adult. Its walls are thin and yielding, and may become unnaturally distended, as in the case of those who subsist on a bulky, innutritious diet, and of those who habitually gormandize.
23.Heart-orifice? Gatekeeper? Coins, etc.? Indication of the soft and yielding texture of the stomach?
23.The stomach has also two openings; that by which food enters, being situated near the heart, is called thecardiac, or heart orifice; the other is thepylorus, or "gatekeeper," which guards the entrance to the intestines,and, under ordinary circumstances, permits only such matters to pass it as have first been properly acted upon in the stomach. Coins, buttons, and the like are, however, readily allowed to pass, because they can be of no use if retained. The soft and yielding texture of this organ—the stomach—indicates that it is not designed to crush and comminute solid articles of food.
Fig. 23.--The Organs of Digestion.Fig. 23.—The Organs of Digestion.O, Œsophagus. S, Stomach. L, Liver. M, Pylorus. C, Large Intestines. P, Pancreas. I, Small Intestines. N, Spleen. G, Gall-bladder.
O, Œsophagus. S, Stomach. L, Liver. M, Pylorus. C, Large Intestines. P, Pancreas. I, Small Intestines. N, Spleen. G, Gall-bladder.
24.What is meant by the gastric juice?
24. The Gastric Juice.—We have seen how the presence of food in the mouth excites the salivary glands, causing the saliva quickly to flow. In the same manner, when food reaches the stomach, its inner lining, the mucous membrane, is at once excited to activity. (At first its surface, which while the stomach is empty presents a pale pink hue, turns to a bright red color, for the minute blood-vessels which course through it, are filled with blood. Presently a clear, colorless, and acid fluid exudes, drop by drop, from its numerous minute glands or "tubules," until finally the surface is moistened in every part, and the fluid begins to mingle with the food. This fluid is termed the gastric juice.
25.What is the office of the gastric juice? Acidity of the gastric juice? Quantity of gastric juice used? What becomes of it?
25.The gastric juice is the proper solvent of certain articles of food, especially those belonging to the albuminoid class. This solvent power is due to its peculiar ingredient,pepsin; in digestion, this substance acts like a ferment; that is, it induces changes in the food simply by its presence, but does not itself undergo change. The acidity of the gastric juice, which is due tolactic acid, is not accidental; for we find that the pepsin cannot act in an alkaline solution—that is, one which is not acid or neutral. The quantity of gastric juice secreted daily is very large, probably not less than three or four pints at each meal. Though this fluid is at once used in the reduction of the food, it is not lost; since it is soon re-absorbed by the stomach, together with those parts of the food which it has digested and holds in solution.
26.Muscular coat of the stomach? Expansion and contraction of its fibres? Action of the fibres?
26. Movements of the Stomach.—The inner coating of the stomach is the mucous membrane, which, as we have seen, furnishes the gastric juice. Next to this coating lies another, called the muscular coat, composed of involuntary muscular fibres, some of which run circularly, and others in a longitudinal direction. These expand to accommodate the food as it is introduced, and contract as it passes out. In addition, these fibres are in continual motion while food remains in the stomach, and they act in such manner that the contents are gently turned round from side to side, or from one end of it to the other.
27.Peristaltic movements? What is said of our consciousness of and power over these movements? Describe the movements of the pylorus.
27.By these incessant movements of the stomach, called theperistalticmovements, the gastric juice comes in contact with all parts of the food. We are, however, not conscious that these movements take place, nor have we the power to control them. When such portions of the food as are sufficiently digested approach the pylorus, itexpands to allow them to pass out, and it closes again to confine the residue for further preparation.
28.How has the knowledge and the workings of the stomach been ascertained? St. Martin? How else?
28.The knowledge of these and other interesting and instructive facts has been obtained by actual observation; the workings of the stomach of a living human being have been laid open to view and examined—the result of a remarkable accident. Alexis St. Martin, a Canadianvoyageur, received a gun-shot wound which laid open his stomach, and which, in healing, left a permanent orifice nearly an inch in diameter. Through this opening the observer could watch the progress of digestion, and experiment with different articles of food. Since that occurrence, artificial openings into the stomach of the inferior animals have been repeatedly made, so that the facts of stomach-digestion are very well ascertained and verified.
29.What was formerly thought? What do we now know? What else do we now know? Water, salt, and sugar? Absorption?
29. Gastric Digestion.—What portions of the food are digested in the stomach? It was formerly thought that all the great changes of digestion were wrought here, but later investigation has taught us better. We now know that the first change in digestion takes place in the mouth, in the partial conversion of starch into sugar. We also know that, of the three organic food principles (considered in Chapter IV.) two—the fats and the sugars—are but slightly affected by the stomach; but that its action is confined to that third and very important class, from which the tissues are renewed, the albuminoids. A few articles need no preparation before entering the system, as water, salt, and grape-sugar. These are rapidly taken up by the blood-vessels of the stomach, which everywhere underlie its mucous membrane in an intricate and most delicate network. In this way the function of absorption begins.
30.Albuminose? The process? Chyme?
30.The albuminoid substances are speedily attacked anddigested by the gastric juice. From whatever source they are derived, vegetable or animal, they are all transformed into the same digestive product, calledalbuminose. This is very soluble in water, and is readily absorbed by the blood-vessels of the stomach. After a longer or shorter time, varying from one to five hours, according to the individual and the quantity and quality of his food, the stomach will be found empty. Not only has the digested food passed out, but also those substances which the stomach could not digest or absorb have passed little by little through the pylorus, to undergo further action in the intestines. At the time of its exit, the digested food is of a pulpy consistence, and dark color, and is then known as thechyme.
31.What are the intestines? The small intestines? The large intestines? Their structure?
31. The Intestines.—The intestines, or "bowels," are continuous with the stomach, and consist of a fleshy tube, or canal, twenty-five feet in length. The small intestine, whose diameter is about one inch and a half, is twenty feet long and very tortuous. The large intestine is much wider than the former, and five feet long (Fig. 23). The general structure of these organs resembles that of the stomach. Like it, they are provided with a mucous membrane, or inner lining, whence flow their digestive juices; and, just outside of this, a muscular coat, which propels the food onward from one point to another.
32.Peritoneum? The work of digestion?
32.Moreover, both the intestines and stomach are enveloped in the folds of the same outer tunic or membrane, called theperitoneum. This is so smooth and so well lubricated, that the intestines have the utmost freedom of motion. In the small intestines, the work of digestion is completed, the large intestine receiving from them the indigestible residue of the food, and in time expelling it from the body.
33.The presence of food in the intestines? Bile?
33. Intestinal Digestion.—As soon as the food passes the pylorus and begins to accumulate in the upperpart of the intestines, it excites the flow of a new digestive fluid, which enters through a small tube, orduct, about three inches below the stomach. It is formed by the union of two distinct fluids—thebileand thepancreaticjuice. The bile is secreted by the liver, which is the largest gland of the body, and is situated on the right side and upper part of the abdomen (Fig. 22). The bile is constantly formed, but it flows most rapidly during digestion. During the intervals of digestion it is stored in thegall-bladder, a small membranous bag attached to the under side of the liver. This fluid is of a greenish-yellow color, having a peculiar smell, and a very bitter taste.
34.The pancreatic juice? The joint action of these fluids?
34.The pancreatic juice is the product of a gland called thepancreas, situated behind the stomach. This fluid is colorless, viscid, and without odor. Like the digestive juices previously described, it owes its solvent power to its peculiar ferment principle, calledpancreatin. By the joint action of these fluids, the fatty parts of the food are prepared for absorption. By previous steps of digestion the fats are merely separated from the other components of the food; but here, within the intestines, they are reduced to a state of minute division, oremulsion, resembling the condition of butter in milk, before it has been churned. There results from this action a white and milky fluid, termed thechyle, which holds in solution the digestible portions of the food, and is spread over the extensive absorbent surface of the small intestines.
35.The mucous membrane? Experiments on inferior animals?
35.The mucous membrane of the intestines, also, secretes or produces, a digestive fluid by means of numerous "follicles," or minute glands; this is called the intestinal juice. From experiments on the inferior animals, it has been ascertained that this fluid exerts a solvent influence over each of the three organic food principles, and in this way may supplement and complete the action of thefluids previously mentioned, viz.:—of the saliva in converting starch into sugar, of the gastric juice in digesting the albuminoids, and of the pancreatic juice and bile in emulsifying the fats.
36, 37.How much thus far has been done with the food? The next process? Give the first way.
36. Absorption.—With the elaboration of the chyle, the work of digestion is completed; but, in a certain sense, the food is yet outside of the body; that is, the blood is not yet enriched by it, and it is not in a position to nourish the tissues. The process by which the liquefied food passes out of the alimentary canal into the blood is called absorption. This is accomplished in two ways; first, by theblood-vessels. We have seen how the inner membrane of the stomach is underlaid by a tracery of minute and numerous vessels, and how some portions of the food are by them absorbed. The supply of blood-vessels to the intestines is even greater; particularly to the small intestines, where the work of absorption is more actively carried on.
37.The absorbing surface of the small intestines, if considered as a plane surface, amounts to not less than half a square yard. Besides, the mucous membrane is formed in folds with an immense number of thread-like prolongations, calledvilli, which indefinitely multiply its absorbing capacity. These minute processes, the villi, give the surface the appearance and smoothness of velvet; and during digestion, they dip into the canal, and, by means of their blood-vessels, absorb its fluid contents, just as thespongioleswhich terminate the rootlets of plants, imbibe moisture from the surrounding soil.
38.How is absorption effected in another way? Describe it. Name of the lacteals? Thoracic duct?
38.Secondly, absorption is also effected by thelacteals, a set of vessels peculiar to the small intestines. These have their beginnings in the little villi just mentioned, side by side with the blood-vessels. These two sets of absorbents run in different courses, but their destination is the same,which is the right side of the heart. The lacteals receive their name from their milky-white appearance. After a meal containing a portion of fat, they are then distended with chyle, which they are specially adapted to receive: at other times they are hardly discernible. The lacteals all unite to form one tube, thethoracic duct, which passes upward through thethorax, or chest, and empties into a large vein, situated just beneath the left collar-bone.
Fig. 24.--The Lacteals.Fig. 24.—The Lacteals.A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents. E, Blood-vessel.
A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents. E, Blood-vessel.
39.The absorbents? Lymph? What further of the lymph?
39. The Absorbents.—The lacteals belong to a class of vessels known as absorbents, or lymphatics, which ramify in nearly all parts of the body, except the brain and spinal cord. The fluid which circulates through the lymphatics of the limbs, and all the organs not concerned in digestion, is calledlymph. This fluid is clear and colorless, like water, and thus differs from the milky chyle which the lacteals carry after digestion: it consists chiefly of the watery part of the blood, which was not required by the tissues, and is returned to the blood by the absorbents or lymphatics.
40.What can you state as to the time required for digestion?
40. Circumstances affecting Digestion.—What length of time is required for the digestion of food? From observations made, in the case of St. Martin, the Canadianalready referred to, it has been ascertained that, at the end of two hours after a meal, the stomach is ordinarily empty. How much time is needed to complete the digestion of food, within the small intestines, is not certain; but, from what we have learned respecting their functions, it must be evident that it largely depends upon the amount of starch and fat which the food contains.
41.Circumstances affecting duration of digestion? Fresh food?
41.In addition to the preparations which the food undergoes in cooking, which we have already considered, many circumstances affect the duration of digestion; such as the quality, quantity, and temperature of the food; the condition of the mind and body; sleep, exercise, and habit. Fresh food, except new bread and the flesh of animals recently slain, is more rapidly digested than that which is stale; and animal food more rapidly than that from the vegetable kingdom.
42.Food in concentrated form? A large quantity of food? Experiment on the dog? Ice-water? Variety of articles?
42.Food should not be taken in too concentrated a form, the action of the stomach being favored when it is somewhat bulky; but a large quantity in the stomach often retards digestion. If the white of one egg be given to a dog, it will be digested in an hour, but if the white of eight eggs be given it will not disappear in four hours. A wineglassful of ice-water causes the temperature of the stomach to fall thirty degrees; and it requires a half-hour before it will recover its natural warmth—about a hundred degrees—at which the operations of digestion are best conducted. A variety of articles, if not too large in amount, is more easily disposed of than a meal made of a single article; although a single indigestible article may interfere with the reduction of articles that are easily digested.
43.Strong emotion? The tongue of the patient?
43.Strong emotion, whether of excitement or depression, checks digestion, as do also a bad temper, anxiety, long fasting, and bodily fatigue. The majority of theseconditions make the mouth dry, that is, they restrain the flow of the saliva; and without doubt they render the stomach dry also, by preventing the flow of the gastric juice. And, as a general rule, we may decide, from a parched and coated tongue, that the condition of the stomach is not very dissimilar, and that it is unfit for the performance of digestive labor. This is one of the points which the physician bears in mind when he examines the tongue of his patient.
44.Eating between meals? Severe exercise? Sleep after meals?
44.The practice of eating at short intervals, or "between meals," as it is called, has its disadvantage, as well as rapid eating and over-eating, since it robs the stomach of its needed period of entire rest, and thus overtasks its power. With the exception of infants and the sick, no persons require food more frequently than once in four hours. Severe exercise either directly before or directly after eating retards digestion; a period of repose is most favorable to the proper action of the stomach. The natural inclination to rest after a hearty meal may be indulged, but should not be carried to the extent of sleeping; since in that state the stomach, as well as the brain and the muscles, seeks release from labor.
QUESTIONS FOR TOPICAL REVIEW.
CIRCULATION OF THE BLOOD.CIRCULATION OF THE BLOOD.[Heart, Lungs, Arteries & Veins.]
[Heart, Lungs, Arteries & Veins.]
CHAPTER VII.
The Blood—Its Plasma and Corpuscles—Coagulation of the Blood—The Uses of the Blood—Transfusion—Change of Color—The Organs of the Circulation—The Heart, Arteries, and Veins—The Cavities and Valves of the Heart—Its Vital Energy—Passage of the Blood through the Heart—The Frequency and Activity of its Movements—The Pulse—TheSphygmograph—The Capillary Blood-vessels—The Rate of the Circulation—Assimilation—Injuries to the Blood-vessels.
1.What is required by every living organism? In plants? Insects? Reptiles? Man?
1. The Blood.—Every living organism of the higher sort, whether animal or vegetable, requires for the maintenance of life and activity, a circulatory fluid, by which nutriment is distributed to all its parts. In plants, this fluid is the sap; in insects, it is a watery and colorless blood; in reptiles and fishes, it is red but cold blood; while in the nobler animals and man, it is the red and warm blood.
2.Importance and abundance of blood? Dependence of life? Abel? Mosaic law? In what part of the body is blood not found? Quantity of blood in the body?
2.The blood is the most important, as it is the most abundant, fluid of the body; and upon its presence, under certain definite conditions, life depends. On this account it is frequently, and very properly, termed "the vital fluid." The importance of the blood, as essential to life, was recognized in the earliest writings. In the narration of the death of the murdered Abel, it is written, "the voice of hisbloodcrieth from the ground." In the Mosaic law, proclaimed over thirty centuries ago, the Israelites were forbidden to eat food that contained blood, for the reason that "the life of the flesh is in the blood." With the exception of a few tissues, such as the hair, the nails, and thecorneaof the eye, blood everywhere pervades the body, as may be proven by puncturing any part with aneedle. The total quantity of blood in the body is estimated at about one-eighth of its weight, or eighteen pounds.
3.Color of blood? Its consistence? Odor?
3.The color of the blood, in man and the higher animals, as is well known, is red; but it varies from a bright scarlet to a dark purple, according to the part whence it is taken. "Blood is thicker than water," as the adage truly states, and has a glutinous quality. It has a faint odor, resembling that peculiar to the animal from which it is taken.
4.What is stated of the blood as viewed under the microscope?
4.When examined under the microscope, the blood no longer appears a simple fluid, and its color is no longer red. It is then seen to be made up of two distinct parts: first, a clear, colorless fluid, called theplasma; and secondly, of a multitude of minute solid bodies, or corpuscles, that float in the watery plasma. The plasma, or nutritive liquid, is composed of water richly charged with materials derived from the food, viz., albumen, which gives it smoothness and swift motion; fibrin; certain fats; traces of sugar; and various salts.
Fig 25.--The Blood Corpuscles.Fig 25.—The Blood Corpuscles.
5.State what you can of the little bodies called corpuscles.
5. The Blood Corpuscles.—In man, these remarkable "little bodies," as the wordcorpusclessignifies, are of a yellow color, but by their vast numbers impart a red hue to the blood. They are very small, having a diameter of about 1/3500 of an inch, and being one-fourth of that fraction in thickness; so that if 3,500 of them were placed in line, side by side, they would only extend one inch; or, ifpiled one above another, it would take at least 14,000 of them to stand an inch high. Although so small in size, they are very regular in form. As seen under the microscope, they are not globular or spherical, but flat, circular, and disc-like, with central depressions on each side, somewhat like a pearl button that has not been perforated. In freshly-drawn blood they show a disposition to arrange themselves in little rolls like coins (Fig. 25).
Fig. 26.--Corpuslces.Fig. 26.a, Oval Corpuscles of a fowl.b, Corpuscles of a frog.c, Those of a shark.The five small ones at the upper part of the figure, represent the human corpuscles magnified 400 times.
a, Oval Corpuscles of a fowl.b, Corpuscles of a frog.c, Those of a shark.
The five small ones at the upper part of the figure, represent the human corpuscles magnified 400 times.
6.The size and shape of corpuscles? Why is the fact important?
6.The size and shape of the blood corpuscles vary in different animals, so that it is possible to discriminate between those of man and the lower animals (Fig. 26). This is a point of considerable practical importance. For example, it is sometimes desirable to decide in a court of justice the source, whether from man or an inferior animal, of blood stains upon the clothing of an accused person, or upon some deadly weapon. This may be done by a microscopical examination of a minute portion of the dried stain, previously refreshed by means of gum-water. Certain celebrated cases are recorded in which the guilt of criminals has been established, and they have been condemned and punished upon the evidence which science rendered on this single point, the detecting of the human from other blood.
7.The character of the blood of dead animals? Means of detecting such blood?
7.The character of the blood of dead, extinct, and even fossil animals, such as the mastodon, has been ascertained by obtaining and examining traces of it which had been shut up, perhaps for ages, in the circulatory canals of bone. A means of detecting blood in minute quantities is foundin the spectroscope, the same instrument by which the constitution of the heavenly bodies has been studied. If a solution containing not more than one-thousandth part of a grain of the coloring matter of the corpuscle, be examined, this instrument will detect it.
8.White corpuscles? Total number of corpuscles in the body?
8.The corpuscles, just described, are known as the red blood corpuscles. Besides these, and floating along in the same plasma, are the white corpuscles. These are fewer in number, but larger and globular in form. They are colorless, and their motion is less rapid than that of the other variety. The total number of both varieties of these little bodies in the blood is enormous. It is calculated that in a cubic inch of that fluid there are eighty-three millions, and at least five hundred times that number in the whole body.
9.The blood in its natural condition in the body? Describe the process by which the coagulation of blood takes place?
9. Coagulation.—The blood, in its natural condition in the body, remains perfectly fluid; but, within a few minutes after its removal from its proper vessels, whether by accident or design, a change takes place. It begins to coagulate, or assume a semi-solid consistence. If allowed to stand, after several hours it separates into two distinct parts, one of them being a dark red jelly, the coagulum, or clot, which is heavy and sinks; and the other, a clear, straw-colored liquid, called serum, which covers the clot. This change is dependent upon the presence in the blood of fibrin, which possesses the property of solidifying under certain circumstances; one of these circumstances being when the blood is separated from living tissues. The color of the clot is due to the entanglement of the corpuscles with the fibrin.
10.If coagulation were impossible? How is it in fact?
10.In this law of the coagulation of the blood is our safeguard against death by hæmorrhage, or against undue loss of blood. If coagulation were impossible, theslightest injury in drawing blood would prove fatal. Whereas now, in vastly the larger proportion of cases, bleeding ceases spontaneously, because the blood, as it coagulates, stops the mouths of the injured blood-vessels. In another class of cases, where larger vessels are cut or torn, it is simply necessary to close them by a temporary pressure; for in a few minutes the clot will form and seal them up. In still more serious cases, where the blood-vessel is of large size, the surgeon is obliged to tie a "ligature" about it, and thus prevent the force of the blood-current from washing away the clots, which, forming within and around the vessel, would close it effectually.