178 GENERAL PHYSIOLOGY 



into carbon dioxide, water, and amino-acids. These changes 

 can also be brought about by strong reagents (acids and alka- 

 lies), or by superheated steam under pressure, but not with 

 nearly so great ease as by enzymes. Bacterial enzymes are 

 most active when they come directly from living bacterial 

 cells. The nitrates of cultures of bacteria and dead bacteria 

 possess very little enzyme compared with the live cells. 



The intra-cellular enzymes are divided into two general 

 classes: oxidizing or hydrating, and reducing or dehydrating, 

 enzymes. Oxidation is accomplished by means of catalytic 

 agents, enzymes, within the bacterial cell. One of the most 

 studied of the oxidizing intra-cellular enzymes is catalase. 

 This enzyme, as well as most of the others, has the power of 

 decomposing hydrogen dioxide and liberating nascent oxy- 

 gen. Many bacterial cultures contain substances which can 

 decompose hydrogen dioxide (Bact. tuberculosis, Bact. 

 diphtherias, M. pyogenes var. aureus). Catalase is distinct 

 and separate from the toxin. 



The question of the occurrence of reducing enyzmes of 

 bacterial origin is still an unsettled problem. In all prob- 

 ability they do occur in some species. 



It was formerly supposed by some investigators that all 

 the chemical reactions which occurred when animal and vege- 

 table cells were present, were due to the cells themselves as 

 a whole. The reactions have since been proved to be due to 

 the definite chemical substances which we now know as en- 

 zymes and which are secreted by the cell protoplasm. 



