316 



THE BLOOD AND ITS CIRCULATION 



have worked their way between the cells that form the walls of 

 the blood tubes. 



A Russian zoologist, Metchnikoff, after studying a number of 

 simple animals, such as medusae and sponges, found that in such 

 animals some of the cells lining the inside of the food cavity take 

 up or engulf minute bits of food. Later, this food is changed into 

 the protoplasm of the cell. Metchnikoff ])elieved that the colorless 

 corpuscles ot the blood have somewhat the same function. This 



he later proved to be true. Like the 

 amoeba, they feed by engulfing their 

 prey. This fact has a very important 

 bearing on the relation of colorless cor- 

 puscles to certain diseases caused by 

 bacteria within the body. If, for ex- 

 ample, a cut becomes infected by bac- 

 teria, inflammation may set in. Color- 

 less corpuscles at once surround the 

 spot and attack the bacteria which 

 cause the inflammation. If the bac- 

 teria 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 quan- 

 tities, they may prevail and kill the 



A colorless corpuscle catching i ,1 • • xi, rni, 



and eating germs. phagocytes by poisonmg 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. 



Antibodies and their Uses. — In case of disease where, for 

 example, fever is caused by poison given off from bacteria we find 

 the cells of the body manufacture and pour into the blood a 

 substance known as an antibody. This substance does not of 

 necessity kill the harmful germs or even stop their growth. It 

 does, however, unite with the toxin or poison given off by the 

 germs and renders it entirely harmless. 



