THE BLOOD 



347 



they feed by engulfing 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 be- 

 comes infected by bacteria, inflammation may set in. The bacteria 

 form a poison known as a toxin, which causes this inflammation in 

 their immediate neighborhood. Colorless corpuscles at once sur- 

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

 in number, they are quickly eaten by the colorless corpuscles, 

 which are known as 'phagocytes. If bacteria are present in great 



Diagram showing how colorless corpuscles pass between the cells that form the walls of 

 the capillaries; 1,2, 3, 4< different stages. Hall. 



quantities, they may prevail and kill the phagocytes by poison- 

 ing them. The dead bodies of the phagocytes thus killed are 

 seen in the pus, or matter which accumulates in infected wounds. 

 In such an event, we must come to the aid of the colorless 

 corpuscle by washing the wound with some antiseptic, as weak 

 carbolic acid or hydrogen peroxide. 



Number and Manufacture of Colorless Corpuscles. — The number 

 of colorless corpuscles, although normally about 17,000 to a drop of blood, 

 may vary, especially in certain diseases. They are formed in large numbeis 

 within the lymph glands (collections of cells which are found here and there 

 along the course of the lymph vessels). The spleen, a gland, and the 

 marrow of bone are also believed to manufacture colorless corpuscles. 



