304 MICROBES AND TOXINS 



than mechanical, physical, and chemical forces. The theory 

 of immunity as being due to phagocytosis calls in the activity 

 of living cells the mechanism of which is not known. It is 

 certain, however, that in vital activities it is not necessary to 

 assume anything beyond physico-chemical phenomena which 

 will some day become clear. ]5iologists no longer talk of a 

 "vital principle." 

 Zymase — vide Fermentation. 



