CHEMICAL PHENOMENA IN LIFE 



tinctly that every cell contains such enzymes 

 which are not to be extracted from protoplasm, 

 and which never diffuse from intact living cells. 

 Such enzymes were named Intracellular Enzymes 

 or Endo-Enzymes. Other enzymes, such as the 

 cane sugar inverting enzyme of yeast, or the 

 digestive enzyme of the mucous membrane of the 

 stomach are abundantly secreted and conse- 

 quently may be obtained without difficulty in 

 any quantity from living tissue. These are the 

 enzymes which we call Secretion Enzymes. 



We understand that chemists were very anxious 

 to isolate pure enzymes and to study the pro- 

 perties of these most remarkable substances in 

 the hope of being able to explain why they act in 

 that way. In spite of the very advanced technical 

 achievements of experimental chemistry, it was 

 not possible to prepare a pure enzyme, not even 

 in one case. The difficulties of preparation are 

 very great. All enzymes have proved to be 

 typically colloidal substances, and they readily 

 show alterations of their properties, coagulate, 

 are destroyed by heat, show a high degree of 

 adsorption of other substances, and are mixed 

 with very many similar colloidal substances, so 

 that the chemist, in his endeavour to separate 

 the effective agent from its companions, loses 

 more of it the longer he treats it with reagents, 

 and often finally has before him a white powder, 

 looking quite satisfactorily pure, but of much 

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