54 MILK HYGIENE 



tococci and the pyogenic staphylococci. Some of these, 

 in addition to producing an acid, develop a ferment 

 which has an action somewhat similar to that of rennet 

 (see below). 



d. Bacteria may form a rennet-like ferment which 

 causes the milk to form a coagulum of the consistency of 

 jelly, without souring. The ferment, which can be iso- 

 lated comparatively easily from many bacteria, has 

 effect in the same manner and under similar conditions 

 as chymosin. The precipitated casein cannot be dis- 

 solved again by treatment with diluted lime water, and 

 it may be assumed that the ferment has produced a 

 change of the casein into paracasein, whose compound 

 with lime is not soluble, as is well known. A great 

 number of bacteria are known which change the milk in 

 this manner; for example, forms that belong to the 

 typhoid-colon group, many bacilli that are included in 

 the large group of spore-bearing hay bacilli, among 

 them those named by Duclaux, Tyrothrix tennis, scaber, 

 filiformis, etc. Bacilli belonging to this last group are 

 often found in milk, because they are usually frequent 

 in the soil and dust and in the excrement of the 

 cattle, so that they always find their way into the milk 

 when it is drawn. The bacteria under consideration 

 have different influences on the milk. While some, 

 apparently, only cause the milk to curdle (they also 

 separate, at the same time, small quantities of albumose- 

 like substances probably caseoses and peptone), others 

 are able to redissolve the casein curd by means of a 

 peptonizing ferment (" casease ") and thus increase 

 the quantity of caseoses. Still others not only dissolve 

 the curd, but also break up the molecule of albumin, so 

 that in the fluid such products appear as peptone, leu- 

 cm, tyrosin, ammonia, butyric acid, etc. Sometimes the 

 development of butyric acid is so considerable that it 



