the blood would constantly lessen, the body would shrink or become emaciated, as we say, and death would at length result. The same thing would happen if the stomach stopped digesting the food, for then no chyle would be formed, and therefore no new blood would be made.

22. There are many things that are very wonderful in all this process of blood-making, which is executed by this complicated machinery of digestion. It is especially wonderful that a simple milky fluid should be separated from such a great variety of food as we eat from day to day, and then that this whitish fluid should be changed into red blood.

23. The apparatus of digestion differs in different animals according to the kinds of food that they eat. If the food that an animal eats is very much like his body, the apparatus or machinery is quite simple; for the food in this case does not need to be changed much to make his blood. But if the food which an animal lives on is very much unlike his flesh, the apparatus of digestion is very complicated, because the food must be much changed before blood can be made out of it.

24. For these reasons the digestive machinery in such animals as the dog, the tiger, and the lion, is simple, for they live on flesh, which is of course very much like their own flesh. But in such animals as the cow and the sheep, this machinery is complicated.

In what ways can the supply of chyle to the blood be stopped? What things are there in the process of digestion that are especially wonderful? In what animals is the machinery of digestion most simple? In what animals is it complicated? Illustrate by referring to different animals.

The reason is, that the grass which they eat is not at all like their flesh. It must therefore go through a great change to fit it to make the blood and flesh of such animals. And this cannot be done without considerable machinery. The flesh-eating lion has a single stomach, and the length of its intestines is only three times that of its body. But the grass-eating sheep has really four stomachs, and the length of its intestines is twenty-eight times that of its body. Fig. 16 represents the four stomachs of the sheep. In man

there is but one stomach, and the length of his intestines is about six times the length of the body.

25. In birds that eat grains and seeds there is a peculiar arrangement of the digestive machinery. They have no teeth, and their mill for grinding their food, instead of being in the mouth, is in the stomach. The gizzard, which is the stomach, is truly a mill for crushing the food to pieces. It has on the inside two

How long are the intestines in the lion? In the sheep? In man! How many stomachs has the sheep?

very hard surfaces, which are rubbed and pressed together by stout muscles. The grain is thus broken up just as it is done between two mill stones. While this is going on the gastric juice comes down from above, and dissolves and digests the broken grain.

What is there peculiar in the digestive machinery of grain-eating birds!

the stomach of a turkey. At b is the gizzard cut open, showing the two hard grinding surfaces, and at a above is the part from which oozes the gastric juice. In those birds that live on flesh or fish there is no such grinding machinery, but the stomach is a thin bag, just as it is in all animals that live on such food.

CHAPTER IV.

CIRCULATION OF THE BLOOD.

1. In the last chapter you saw how the supply of blood is kept up in the body. In this chapter I shall show you how the blood is circulated everywhere, in order that it may be used in building and repairing. The machinery that thus circulates the blood is called the circulating system. It has its pipes everywhere. There is no part of the body where the blood does not go. And this machinery keeps the blood everywhere in motion. It nowhere rests for a single moment.

2. This circulating machinery has a great central organ, the heart, situated in the chest. This forces the blood out all over the body through the arteries. It receives it back again by the veins. It forces the blood out through a large artery, called the aorta, and from this go branches in every direction. These

Describe the arrangement of the digestive organs in the turkey. What kind of stomach have birds that eat flesh or fish? What is the machinery that circulates the blood called? Is the blood ever still anywhere? What are the different parts of the machinery? Through what does the heart send out the blood? Through what does it receivo it back!

branches divide more and more, just like the branches of a tree, till the extreme branches are exceedingly small.

3. These small arteries end in a network of vessels that are so small that they are called capillaries, from the Latin word capilla, hair. They are really smaller than any hair. When you prick or cut your finger you wound a large number of these capillaries, and they let out their blood.

4. The heart acts like a forcing and suction pump. It pumps out the blood through the arteries, and by suction it draws the blood back by the veins. It forces out the blood by contracting itself, or making itself smaller. It draws in the blood by dilating itself, or making itself larger.

5. I will make these two actions of the heart plain to you by certain comparisons. When you press the two sides of a pair of bellows together by the handles, as represented in Fig. 18, you contract the bellows

FIG. 18.

that is, you make the room in it smaller. A part of

Illustrate

What are the capillaries? Like what does the heart act? How does it force out the blood? And how does it draw it in? by comparison with a pair of bellows.