Page:First course in biology (IA firstcourseinbio00bailrich).pdf/518

 Experiment 9. Let another pupil stop the flow from an imaginary cut artery marked red. See text. Experiment 10. In a case of nose bleed do not let pupil lean over a bowl. (Why?) Cause him to stand rather than lie. (Why? See Exp. 2.) Apply cold water to contract arteries to nose, also have pupil hold a small roll of paper or a coin under upper lip (to make muscular pressure on arteries to nose). Experiment 11. Let one pupil treat another for a bruise (see p. 62). Experiment 12. Emergency drill, restoration from fainting (see p. 57).

The Cells have a Liquid Home.—The cells in the body of man, like the ameba, live in a watery liquid. This liquid is called lymph. The cells cannot move about as the ameba does to obtain food, so the blood brings the food near them and it soaks through the blood tubes into the lymph spaces next to the cells (see colored Fig. 3). The ameba gives off waste material into the water; the cells of the body give it off into the lymph to be carried off by the circulation. The blood, then, has two functions: (1) to take nourishment to the tissues; (2) to take away waste material from them.

The Organs of Circulation.—These are the heart, which propels the blood; the arteries, which take blood away from the heart; the veins, which take the blood back to the heart; and the capillaries (Fig. 53), which take the blood from the arteries to the veins.

, connecting artery (b) with vein (a).

The heart is a cone-shaped organ about the size of its owner's fist. It lies in a diagonal position behind the breastbone, with the small end of the cone extending toward the left. The smaller end (Exp. 1) taps or beats against the chest wall at a point between the fifth and sixth ribs on the left side. The breastbone and ribs protect it from blows. An inclosing membrane called the pericardium secretes a serous fluid and lessens the friction from its beating.

Why the Heart is Double.—There must be a pump to move the impure blood from the body to the lungs to get oxygen