116 ATLAS OF BACTERIOLOGY. 



2. The bacteria excrete ferments, designed to make 

 the surrounding nutrient medium more suitable for 

 assimilation. Tho products which develop at this 

 time in the vicinity of the bacteria may be called 

 transformation products. 



3. The bacteria assimilate some substances and 

 excrete others true products of disassimilation. A 

 separation of fermentative products and disassimila- 

 tive products, such as is still attempted at times, is 

 incorrect because the substances are only fermented 

 when they have previously entered the bacterium 

 cell. Hence fermentation products are products of 

 disassimilation under the influence of special nutri- 

 tion (vide page 124). 



I. BACTERIAL FERMENTS AND THE CHANGES PRODUCED 

 BY THEM. 



Under the term ferments in the narrower sense 

 (enzymes) we refer to chemical bodies which, in mini- 

 mum amounts and without being used up, are able to 

 separate large amounts of complicated organic mole- 

 cules into simple, smaller, more soluble and diffusible 

 molecules.* 



Ferments may be regarded as chemical only when 

 we can prove : 



1. That the fermentation continues in the presence 

 of substances (for example phenol, three per cent; 

 thymol, .01 per cent; chloroform, ether) which kill 

 bacteria but do not endanger ferments ; or 



2. That the germless filtrate of the bacterial culture 



* This definition does not hold good for a single ferment, the 

 milk ferment, which coagulates the milk (vide page 123) . 



