THE TYPES OF MILK BACTERIA. 



FIG. 15. 



ever, that these bacteria do produce the rennet ferment, 



although the tryptic ferment is developed too rapidly to make 



it possible for the milk to 

 curdle before it is digested. 

 In all cases the milk is finally 

 converted into a more or less 

 perfect liquid, semi-transpar- 

 ent, having a complex compo- 

 sition of unknown chemical 

 compounds, and showing a 

 variety of tastes and odors 

 which frequently indicate a 

 close alliance to putrefactive 

 products. 



This class of bacteria can 

 be easily distinguished by 

 bacteriologists. One of the 

 culture media in common use 

 is made of gelatin, and the 

 enzyme which digests the 

 casein also liquefies gelatin. 

 The result is that this class 

 of bacteria may all be distin- 

 guished by their power of 

 liquefying gelatin when grow- 

 ing in ordinary culture media, 

 and they are therefore per- 

 haps the most easily recog- 

 nized by bacteriological meth- 

 ods of all of the types of 

 bacteria. The liquefiers, as 

 they are called, are, therefore, 

 in general the bacteria which 



produce enzymes and digest the casein in milk, and this term 



we will hereafter use. (Fig. 15.) 



A B c 



Showing growth of liquefier in gelatin. 

 The lower half of the tube is filled with 

 gelatin which is liquefied by the bacteria in 

 the shaded portion. 



