76 APPLIED PHYSIOLOGY 



but were its strongest and purest cells which went out to 

 fight enemies and were killed. After they die, they decay 

 and become poisons, and so must be thrown off. 



The same thing happens in a cut. The bacteria grow 

 upon its surface, while the white blood cells fight them 

 until they are killed and flow away as matter. If the cut 



a 



An abceds ( x 50) . 



a epithelium of the skin, softened and bursting. 



b white blood cells which have packed the tissues full and shut out nourishment. 



c blood tube stopped by white blood cells. 



is kept closed and clean so that the germs cannot get in, 

 there will be no cold in the cut, but the white blood cells 

 will devote all their energies to mending the cut. Then 

 the cut will heal in a few days, without pain or much 

 inflammation. 



When you sit in a cold wind after being heated by exer- 

 cise, the tender cells of your nose and mouth are hurt, and 

 you have a sore throat. Perhaps some bacteria grow there 

 too. Then white blood cells and liquid parts of the blood 

 pass out of the capillaries and form the thick matter which 

 we spit out. This does not consist of impurities of the 



