408 THE CHEMICAL COMPOSITION OP THE BODY [CH. XXV. 



robic in contradistinction to those which require oxygen, and are 

 called aerobic. 



The chemical nature of the enzymes, or unorganised ferments, is 

 very difficult to investigate ; they are substances that elude the grasp 

 of the chemist to a great extent. So far, however, research has taught 

 us that they are either proteid in nature or are substances closely 

 allied to the proteids. 



