48 BIOLOGY AND TECHNIQUE 



of saccharose subjected to heat, without kacalyzer or ferment, a 

 similar change would occur, but by the mediation of these substances 

 the inversion is produced without other chemical or physical rein- 

 forcement. 



This analogy between enzymes and katalyzing agents is very 

 striking. Thus, as stated, both katalyzers and enzymes bring about 

 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 

 reversibility 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 quan- 

 tity 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 

 animals 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 all enzymes depends most intimately upon environ- 

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

 essential. All of them depend for the development of their activity 

 upon the existence of a specifically suitable reaction. Strong acids 

 or alkalies 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 common 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. 2 



Proteolytic Enzymes. In nature, the decomposition of dead ani- 

 mal and vegetable matter occurs only when the conditions are favor- 



-OppenJieimer, "Die Fermente," etc. Leipzig, 1900. 



