PROTEOLYTIC FERMENTS. 59 



cause materials are only fermented after they are tal<:en 

 into the bacterial cell. Fermentation products are meta- 

 bolic products produced under tlie influence of special 

 nutrition. (Compare p. G4. ) 



I. The Bacterial Ferments and the Changes Produced 

 by Them. 



Under ferments in the restricted sense — enzymes — 

 (the custom of calling micro-organisms " living ferments " 

 is passing into disuse) one understands certain chemical 

 bodies, which, in a minimal quantity and -without being 

 thereby destroyed, are able to split up large quantities of 

 definite elaborate organic molecules into smaller, simpler, 

 more soluble, and more diffusible ones. ^ 



Wq can only properly speak of chemical ferments after 

 the following properties have been demonstrated: 



1. Fermentation continues in the presence of materials 

 which are surely bactericidal, but do not injure ferments; 

 for example, phenol, 3%; thymol, 0.1%; chloroform, 

 ether ; or 



2. The power of producing fermentation is possessed by 

 the germ-free filtrate, obtained by passing cultures of the 

 bacteria through clay or porcelain cylinders ; or 



3. This activity is possessed by the pulverized and ster- 

 ile ferment-preparation obtained from cultures. 



Of the extraordinarily numerous details which have 

 been taught by Fermi's ^ methodical and exhaustive stud- 

 ies, only the most important can here be given. All fer- 

 ments dialyze a little, like ordinary albuminous bodies, 

 through good parchment paper. 



Proteolytic or albumin=dissoIving enzymes are widely 

 distributed. The liquefaction of the glue in gelatin (closely 

 related to albumin chemically) is a sure indication of 

 the presence of a proteolytic ferment. Since the reaction 

 of the gelatin when dissolved is always or may be alka- 

 line, the liquefaction is not due to pepsin (which is active 



^ This definitiou evidently does not apply to rennet ferment, wMch 

 coagulates milk. 



^ A. H. X, 1 ; XII, 240 ; C. B. Xll, 713 ; C. B. L. I, 482. 



