A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents.

E, Blood-vessel. ]

[Sidenote: 39. The absorbents? Lymph? What further of the lymph?]

39. THE ABSORBENTS.--The lacteals belong to a cla.s.s 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 called _lymph_. 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.

[Sidenote: 40. What can you state as to the time required for digestion?]

40. CIRc.u.mSTANCES AFFECTING DIGESTION.--What length of time is required for the digestion of food? From observations made, in the case of St. Martin, the Canadian {98} already 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.

[Sidenote: 41. Circ.u.mstances affecting duration of digestion? Fresh food?]

41. In addition to the preparations which the food undergoes in cooking, which we have already considered, many circ.u.mstances affect the duration of digestion; such as the quality, quant.i.ty, 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.

[Sidenote: 42. Food in concentrated form? A large quant.i.ty 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 quant.i.ty in the stomach often r.e.t.a.r.ds 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 winegla.s.sful 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.

[Sidenote: 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 these {99} conditions 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.

[Sidenote: 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 r.e.t.a.r.ds 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.

{100}

QUESTIONS FOR TOPICAL REVIEW.

PAGE

1. What do you understand by nutrition? 80 2. How is the process of nutrition carried on? 80 3. What further can you state on the subject? 80, 81 4. Describe the general plan of digestion. 81 5. How is the process of mastication carried on? 80, 82 6. State what you can in relation to the formation of the teeth. 82, 86 7. What, in relation to their arrangement? 83, 84 8. What, in relation to the process of "shedding?" 82, 83, 84 9. In relation to the different forms of teeth in different animals? 85 10. What causes operate to injure or destroy the teeth? 85, 86 11. What suggestions and directions are given for the preservation of the teeth? 85, 86 12. What do you understand by insalivation? 80, 86 13. How is the process of insalivation carried on? 86, 87, 88 14. Of what importance is the saliva to the process? 87, 88 15. Of what importance are mastication and insalivation? 88, 89 16. Describe the consequences of rapid eating. 89, 90 17. What becomes of the food directly after it has undergone mastication and insalivation? 90 18. Describe the location and formation of the stomach. 90, 91, 92 19. Describe the process by which the gastric juice is formed. 91 20. What are the properties and uses of the gastric juice? 92 21. What are the movements of the stomach, and what their uses? 92, 93 22. What further can you state on the subject? 93 23. What portions of the food are digested in the stomach? 93, 94 24. What are the first changes of digestion? 93 25. Describe the location and formation of the stomach. 94 26. What further can you state in relation to the stomach? 94 27. Describe the process of intestinal digestion. 94, 95, 96 28. What do you understand by absorption? 80, 96 29. How is the process of absorption effected? 96, 97 30. What are the lacteals and of what use are they? 96, 97 31. What length of time is required for the digestion of food? 97, 98 32. What circ.u.mstances, of food, affect digestion? 98 33. What circ.u.mstances, of emotion, affect digestion? 98, 99 34. What suggestions and directions are given upon the subject of eating and drinking? 98, 99

[Ill.u.s.tration: CIRCULATION OF THE BLOOD.

[Heart, Lungs, Arteries & Veins.]

{101}

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--Pa.s.sage of the Blood through the Heart--The Frequency and Activity of its Movements--The Pulse--The Sphygmograph--The Capillary Blood-vessels--The Rate of the Circulation--a.s.similation--Injuries to the Blood-vessels._

[Sidenote: 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 n.o.bler animals and man, it is the red and warm blood.

[Sidenote: 2. Importance and abundance of blood? Dependence of life? Abel?

Mosaic law? In what part of the body is blood not found? Quant.i.ty 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 his _blood_ crieth 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 the _cornea_ of the eye, blood everywhere pervades the body, as may be proven by puncturing any part with a {102} needle. The total quant.i.ty of blood in the body is estimated at about one-eighth of its weight, or eighteen pounds.

[Sidenote: 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.

[Sidenote: 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 the _plasma_; and secondly, of a mult.i.tude 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., alb.u.men, which gives it smoothness and swift motion; fibrin; certain fats; traces of sugar; and various salts.

[Ill.u.s.tration: FIG 25.--THE BLOOD CORPUSCLES.]

[Sidenote: 5. State what you can of the little bodies called corpuscles.]

5. THE BLOOD CORPUSCLES.--In man, these remarkable "little bodies," as the word _corpuscles_ signifies, 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, if {103} piled 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 b.u.t.ton that has not been perforated. In freshly-drawn blood they show a disposition to arrange themselves in little rolls like coins (Fig. 25).

[Ill.u.s.tration: 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.]

[Sidenote: 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.

[Sidenote: 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 ca.n.a.ls of bone. A means of detecting blood in minute quant.i.ties is found {104} in the spectroscope, the same instrument by which the const.i.tution 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.

[Sidenote: 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.

[Sidenote: 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 a.s.sume 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 circ.u.mstances; one of these circ.u.mstances 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.