CIRCULATION 



79 



their way through the walls of the blood vessels and 

 escape into the tissues, where they wander about doing 

 valiant service for the body. They are very sensitive 

 chemically. Wherever poisonous substances are pres- 

 ent they gather in great numbers and by eating up 



From artery 



Pig. 51.— Migration of the white blood corpuscles from the capillaries of a frog in- 

 to the tissues during inflammation, a, white corpuscle penetrating wall of capil- 

 lary; b, white corpuscle in tissue; c, red corpuscle. (From Fitz, after Warren.) 



microbes and other foreign particles, they are often able 

 to combat successfully severe disease. Matter from 

 festered places is made up largely of these corpuscles. 



Coagulation. — The white corpuscles are also impor- 

 tant because of their influence on the coagulation, or 

 clotting, of blood. They contain an enzyme which has 

 the power to hasten the physical process of coagulation so 

 that it takes place at a much lower temperature than 

 would otherwise be possible. 



AVhen the corpuscle comes in contact with any foreign 

 substance like dust or air the enzyme is rendered active. 



