LESSON V.

ORGANS THAT PREPARE NOURISHMENT FOR THE BODY. THE STOMACH, Liver, Pancreas, Lacteals, and smaller InteSTINES.

1. It has been stated that the bones and the muscles, and also all other portions of the body, are nourished and sustained by the blood; and that the blood is constantly conveying to them new particles of matter, and carrying away worn-out portions which are of no further use. As the blood has so much to do in the building and repairing of the "house we live in,” it will be both interesting and useful to know something about the organs and the processes by which the blood itself is manufactured.

2. We will begin, therefore, by stating that the blood is manufactured from the food we eat. It may well be supposed, therefore, that the quality of the blood will depend considerably upon the quality of the materials used in its manufacture; for, while it is true that good wholesome food will make good blood, it is equally true that poor food will make poor blood. The "house we live in" can not be a very good one if made of poor materials. This subject, the manufacture of the blood, becomes, therefore, a very important

one.

3. As is well known, the solid portions of our food are first divided by chewing. And here, we may remark, it is very desirable that the teeth should be firm and strong, and that they should be required to do their part of the work well. While they are doing their duty, several little sacs, or glands, near the sides of the mouth, throw into the mouth a liquid called saliva,1 which moistens the food, so that it may glide easily down the throat into the stomach.

4. The next thing is to describe the stomach, and tell what that does toward manufacturing blood. The stomach is a kind of bag that will hold from a quart to three pints, according to the size and age of a person. It is formed chiefly of muscles, some running in one direction, and some in an

other, and the inner side is lined with vessels which contain a fluid called the gastric juice.

5. When food is received into the stomach, the blood-vessels of the stomach carry off any superabundance2 of water that may be found there; then the gastric juice is poured on to the food to dissolve it, and the muscles of the stomach move the food about in every direction, so as thoroughly to mix it with the gastric juice. This operation is continued, with a strong and steady action, from two to four hours after a hearty meal, until the food is reduced to a thin paste. In this state it is called chyme.

6. As soon as any portion of the food is thus suitably prepared, the muscles, seeming to know their duty well, move it along to the small end of the stomach, where a little door or valve opens to let it pass through into the smaller intestines. This valve is a very faithful sentinel, always on duty; and if any portion of food not properly digested-that is, not reduced to chyme-makes its appearance there, this little valve will close against it, and turn it back into the stomach. The ancient Greeks gave to this valve the name pylōrus, which means "a door-keeper." (See Figs. 9 and 10, page 33.)

7. There is one thing more very singular about this everwatchful sentinel. While it will not, unless completely exhausted by fatigue, let indigestible food pass at all, it opens at once to let other substances pass, such as buttons, pieces of money, and little pebbles, that have been swallowed by mistake. For of what use would it be to keep them in the stomach? Mr. Pylōrus seems to know that they can not be digested at all, and that the easiest way to dispose of them is to let them pass on.

rus.

8. It sometimes happens that either too great a quantity of food, or food of a bad quality, has been taken into the stomach. The stomach, after a great amount of labor, and failing to digest it, tries to get rid of it by pushing it past the pylōThe pylorus resists, and a struggle ensues. If the pylōrus yields first, the undigested food passes through, irritating3 the intestines as it moves along, and often producing severe sickness. But if the stomach yields first, its muscles endeavor to expel the unwholesome food in the other direction, and occasion what is called vomiting.

9. But suppose that good wholesome chyme has passed the doorway of the pylōrus, what is the next step in the process? We are looking to see how blood is made from the food we have eaten. First, then, through a little channel the liver pours upon the chyme a quantity of that bitter yellow fluid called bile; then another organ, called the pancreas, pours upon it the pancreatic juice; some other juices are also poured in, and these liquids convert a portion of the chyme into a thin whitish fluid called chyle.*

10. As this chyle is carried along in the intestine it comes in contact with the mouths of numerous little veins, and also the mouths of numerous little hair-like tubes called lacteals,5 both of which absorb it, and convey it to what is called the thoracic duct; and this duct empties it into a large vein, which conveys it to the heart. After this it is sent to the lungs, where it iş acted upon by the oxygen of the atmosphere, as we shall hereafter describe, when it becomes blood -a stock of fresh materials, suitable to aid in repairing, building up, and nourishing the body.

11.

"For this the watchful appetite was given,

Daily with fresh materials to repair

This unavoidable expense of life,

This necessary waste of flesh and blood.
Hence the digestive powers, with various art,
Subdue the ruder aliments' to chyle;
The chyle to blood; the foamy purple tide
To liquors, which, through finer arteries,
To different parts their winding course pursue,
To try new changes, and new forms put on."

12. But what does this blood, which circulates in our bodies, consist of? The blood of man consists of a colorless liquid, composed mostly of water, in which are seen floating a great number of very small, flat, circular atoms, or sacs, called disks or cells, a few of them white, but most of them red. If twelve thousand of these thin, flat cells were placed one upon another, they would make a pile of less than an inch in thickness! These cells seem to be a kind of living atoms, for

* Oils and fats are not digested in the stomach, but only after they have passed into the intestine, and been acted upon by the bile. They are then absorbed by the lacteals. Although we speak of the mouths of the lacteals, they are so small as to be invisible even by the aid of glasses, and may be considered as mere pores leading to those tubes.

they have their periods of birth, of growth, of decay, and of death; and they are nourished by the liquid in which they float. Countless myriads of them come into existence every day; and it is said that at every pulsations of the heart nearly twenty millions of them die. Has not physiology, then, its passing wonders, as well as astronomy? (See Fig. 8.)

13. While the blood, as a whole, has its own peculiar labors to perform in nourishing the body and removing its waste particles, each part of the blood has its separate duty. Thus the liquid in which the blood-cells float carries along the nourishing materials which are dissolved in it; but the business of the cells is to carry the oxygen. They take it in at the lungs, carry it where it is needed to burn up the waste particles of carbon and convert them into carbonic acid gas, and then go back for a new supply. What a wonderful process this is! But when the cells get old, and worn out in this labor, they shrivel up with age, they lose their bright crimson color, and assume a tawny hue like the decaying leaves of autumn, and at length they die-millions of them at every breath we draw. Some portions of their dead remains are used in repairs of the system, while other portions are strained off in the liver, and used for the manufacture of bile.

14. The relative position of the principal organs of the body, and the manner in which they are neatly packed to

Fig. 8 represents a very small drop of human blood, containing the circular blood-cells magnified 500 diameters. As the blood-cells in other animals are not similar in size and shape to those found in man, the microscope will detect the difference.

gether, may be seen in the drawing, Fig. 9, which we have given below. In the drawing Fig. 10 is a separate representation of the principal organs of digestion, which are engaged in manufacturing that life-bearing and life-preserving current, the blood, from the food we have eaten. He who made them, He who planned this curious manufactory, has assigned to them their duties; and faithfully will they keep laboring on in our service through a long life, if we furnish them the proper materials to work with, and guard them

EXPLANATION.-Fig. 9: c the windpipe. Back of the heart it branches to both lungs. B, B, the right and left lungs; A, the heart; d, the diaphragm, the muscle separating the chest from the abdomen; D, the stomach; S, the spleen (or milt), supposed by the ancients to be the seat of melancholy. Its use is not well determined. C, the liver, the largest organ in the body; 7, the gall-bladder, on the under surface of the liver; m, m, the two kidneys, the right one the lowest; V, situation of the pylorus; O, the pancreas; w, w, the small intestine, sometimes called the second stomach; f, f, f, the colon, or large intestine.

Fig. 10: 3, the e-soph'-a-gus, through which the food passes into the stomach; 13, cardiac orifice of the stomach; 14, splenic extremity; 15, pyloric extremity; 18, pylorus; 19, 20, 21, that part of the small intestine called the du-o-de'-num; 22, gall-bladder; 23, cystic duct; 24, hepatic duct; 25, common gall duct; 26, its opening into the du-o-de'num; 27, duct of the pancreas opening into the du-o-de'-num; 28 to 30, that part of the small intestine called the je-ju'-num; 30 to 31, that part called the il-e-um; 31, opening of the il'-e-um into the large intestine, or co'-lon; 36, 37, 38, 39, the colon; 40, rectum.