HOW THE BODY FIGHTS DISEASE 



munity is always essentially fermentive in charac- 

 ter; the germicidal properties of the serum from 

 an inoculated animal are due to the presence 

 of fermentive substances secreted by the "phago- 

 cytes," just as the stomach cells secrete pepsin and 

 free hydrochloric acid, the liver cells bile and other 

 ferments, and so on. These are thrown into the 

 blood-stream and carried about through the body, 

 and may act there in destroying the microbes, or in 

 disturbing their normal functions, or simply by 

 neutralizing the bacterial poison. The effect of the 

 inoculation of a fresh animal or the injection of the 

 serum from an inoculated animal is to stimulate 

 the white corpuscles to greater activity, and hence 

 of the production of greater quantities of the bac- 

 tericidal ferments. 



It will be seen that in view of Metchnikoff the 

 whole process is one of vital action. We need not 

 attribute intelligence to the white corpuscles in 

 their war upon the microbes, but they nevertheless 

 comport themselves in many ways like living be- 

 ings, and seem like independent units colonized in 

 the organism. 



But modern physiology is no longer content with 

 merely " vitalistic" explanations of the bodily proc- 

 esses. For it, the vital processes, whether of di- 

 gestion, absorption, growth, or reproduction, are 

 simply and solely a complex series of chemical re- 



279 



