348 HUMAN PHYSIOLOGY 



The Amount of Blood and its Distribution. — Protoplasm of the 

 body, as we know, is composed largely of water. The blood 

 forms, by weight, about one thirteenth of the body. Its distri- 

 bution varies somewhat according to the position assumed by the 

 body, and the amount of undigested food in the stomach and in- 

 testines. Normally, about one half of the blood of the body is 

 found in or near the organs lying in the body cavity, about one 

 fourth in the muscles, and the rest in the heart, lungs, large 

 arteries, and veins. 



Blood Temperature. — The temperature of blood in the human 

 body is normally about 98.5° Fahrenheit, although the tempera- 

 ture drops almost two degrees after we have gone to sleep at night. 

 It is highest about 5 p.m. and lowest about 4 a.m. Any consider- 

 able variation in the temperature of the blood means death. In 

 fevers, the temperature of the body sometimes rises to 107°; but 

 unless this temperature is soon reduced, death follows. Any 

 considerable drop in temperature below the normal also would 

 mean death. Bodily temperature, as we know, results from 

 the oxidation of food ; within the cells of the tissues in all parts 

 of the body, but especially those of the muscles. 



Cold-blooded Animals. — In lower animals which are called cold 

 blooded, the blood has no fixed temperature, but varies with the tempera- 

 ture of the medium in which the animal lives. Frogs, in the summer, 

 may sit for hours in water with a temperature of almost 100°. In winter, 

 they often endure freezing so that the blood and lymph within the spaces 

 under the loose skin are frozen into ice crystals. Such frogs, if thawed 

 out carefully, will live. This change in body temperature is evidently 

 an adaptation to the mode of life. 



Necessity of Good Food, Fresh Air, and Sleep. — Inasmuch as the 

 fluid part of the blood receives its nourishment directly from the 

 foods which are taken into the body, it follows that if food materials 

 contain an ill-balanced proportion of nutrients, the blood and the 

 body may suffer. Proteid must be taken into the blood at all 

 times, for without it, no protoplasm can be formed. More carbo- 

 hydrates and fats are needed in winter. Why? The red cor- 

 puscles, having the important function of carrying oxygen, must 

 be kept in healthy condition. To do this, plenty of fresh air is 



