58 Agricultural Bacteriology. 



putrefactive ones produce an enzyme similar to rennet. 

 When these forms are numerous, i. e., more abundant 

 than the sour milk bacteria, the milk may curdle, al- 

 though remaining quite sweet. If the milk is kept for 

 some time after curdling, it will be noted that the curd 

 becomes soft and reduced in amount due to its digestion 

 by other enzymes that resemble trypsin found in the pan- 

 creatic juice of animals. 



Many of the putrefactive bacteria form spores. These 

 spores are not destroyed in the pasteurization of milk. 

 Due to the development of these spores, the pasteurized 

 milk often curdles although it still tastes sweet. The- 

 curd is soft and large amounts of whey separate from it. 

 Such milk is not wholesome, even before it shows any 

 signs of curdling, and it may be dangerous to human be- 

 ings, especially to children. The organisms producing 

 these changes get into milk from manure and dirt. They 

 are especially numerous in dust from hay, straw, and 

 corn fodder. Such feeds should not be fed until after 

 milking. These bacteria do not find such favorable con- 

 ditions for growth in milk as do the lactic organisms. 

 The latter by the acid they produce render the milk still 

 less favorable for the putrefactive germs. 



Slimy fermentation of milk. One of the most fre- 

 quent abnormal fermentations is the slimy or ropy 

 change. Such a condition may appear when the milk is 

 drawn from the cow, in which case it is usually due to in- 

 flammation of one or more quarters of the udder. When 

 the trouble is due to bacteria, the milk becomes slimy a 

 day or so after it is withdrawn from the animal. The 

 causal organisms produce a slimy substance in milk, 

 sometimes in such abundance that the milk can be drawn 

 out into long threads. 



