52 



HUMAN BIOLOGY 



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 reins, which take 

 the blood back to the heart ; and the 

 capillaries (Fig. 53), which take the 

 blood from the arteries to the veins. 



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 be- 

 tween 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 



Fig. 53. — Capillaries, 

 connecting artery [b) 

 with vein (a). 



