THE BLOOD AND ITS CIRCULATION 369 



corpuscles of the blood have somewhat the same function. This 

 he later proved to be true. Like the amoeba, they feed by ingulfing 

 their prey. This fact has a very important bearing on the relation 

 of colorless corpuscles to certain diseases caused by bacteria within 

 the body. If, for example, .a cut becomes infected by bacteria, 

 inflammation may set in. Colorless corpuscles at once surround 

 the spot and attack the bacteria. If the bacteria are few in 

 number, they are quickly eaten by certain of the colorless cor- 

 puscles, which are known as phagocytes. If bacteria are present 

 in great quantities, they may prevail and. kill the phagocytes by 

 poisoning them. The dead bodies of the phagocytes thus killed 

 are found in the pus, or matter, which accumulates in infected 

 wounds. In such an event, we must come to the aid of nature 

 by washing the wound with some antiseptic, as weak carbolic 

 acid or hydrogen peroxide. 



The Amount of Blood and its Distribution. The protoplasm of the 

 body, as we know, is composed largely of water. Blood forms, by weight, 

 about one thirteenth of the body. Its distribution varies somewhat ac- 

 cording to the position assumed by the body, and the amount of undigested 

 food in the stomach and intestines. Normally, about one hah* 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 temperature 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. In fevers, the temperature of the 

 body sometimes rises to 107 or higher ; but unless this temperature is 

 soon reduced, death follows. Any considerable drop in temperature be- 

 low the normal also would mean death. Body heat, as we know, results 

 from the oxidation of food ; the constant circulation of blood keeping the 

 temperature nearly uniform in all parts of the body. The body tempera- 

 ture may be from two to three degrees higher immediately after violent 

 exercise. Why ? 



Cold-blooded Animals. In animals which are called cold-blooded, 

 the blood has no fixed temperature, but varies with the temperature 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. 

 HUNT. ES. BIO. 24 



