THE BIOLOGICAL ACTIVITIES OF BACTERIA 43 



changes without themselves being used up in the process, both act 

 without the aid of heat, and the reactions brought about by both 

 have occasionally been shown to be reversible. While this last phe- 

 nomenon has been variously shown for katalyzers, the process of re- 

 versibility has been demonstrated for bacterial enzyme action only in 

 isolated cases. Thus, it has been found that by the action of the yeast 

 enzyme maltase upon concentrated dextrose solutions, a re-formation of 

 maltose may occur. In both cases, moreover, the quantity of enzyme 

 or katalyzer is infinitely small in proportion to the amount of material 

 converted by their action. 



There is a close similarity, furthermore, between the bacterial en- 

 zymes and the ferments produced by specialized cells of the higher ani- 

 mals and plants. For instance, the action of the ptyalin of the saliva or 

 of the diastase obtained from- plants is entirely analogous to the starch- 

 splitting action of the amylase produced by many bacteria. 



The action of aU enzymes depends most intimately upon environ- 

 mental conditions. For all of them the presence of moisture is essential. 

 AU of them depend for the development of their activity upon the exist- 

 ence of a specifically suitable reaction. Strong acids or alkahes always 

 inhibit, often destroy them. Temperatures of over 70° C. permanently 

 destroy most enzymes, whereas freezing, while temporarily inhibiting 

 their action, causes no permanent injury, so that upon thawing, their 

 activity may be found almost unimpaired. Direct sunlight may injure, 

 but rarely destroys, ferments. Against the weaker disinfectants in com- 

 mon use, enzymes often show a higher resistance than do the bacteria 

 which give rise to them. 



The optimum conditions for enzyme action, then, consist in the 

 presence of moisture, the existence of a favorable reaction, weakly acid 

 or alkaline, as the case may be, and a temperature ranging from 35°- 

 45° C 



Proteolytic Enzymes. — In nature, the decomposition of dead animal 

 and vegetable matter occurs only when the conditions are favorable for 

 bacterial development. Thus, as is well known, freezing, sterilizing by 

 heat, or the addition of disinfectants will prevent the rotting of organic 

 material. 



In the laboratory, the presence of proteolytic enzymes is determined 

 chiefly by the power of bacteria to liquefy gelatin, fibrin, or coagulated 

 blood serum. These ferments are not always secretions from the bac- 



' Oppenheimer, " Die Fermente," etc. Leipzig, 1900. 



