BACTERIA COMMONLY FOUHD IK COWS* MILK. 105 



a term also used in the following pages for the sake of 

 brevity. All these bacteria decompose albuminoid sub- 

 stances and produce an unpleasant smell; the final prod- 

 ucts in the substrata are carbonic acid, ammonia, and 

 water. In the dairy they generally have an injurious in- 

 fluence; some play a part in the ripening of certain kinds 

 of cheese, however. They are of the greatest importance 

 and value to the agriculturist in other domains, since 

 they split up the complicated albuminoids of the manure' 

 into such substances as may serve as nutrients for cul- 

 tivated plants. These bacteria are therefore especially 

 numerous in solid and liquid manure, and their presence 

 in milk shows that this has been contaminated with these 

 substances. 



This applies especially to the bacteria included in the 

 third subdivision. The more macroscopic impurities 

 coming from the manure, the greater is the probability 

 that these bacteria will appear in large numbers. The 

 most common of them belong to the family Proteus (Hau- 

 ser), and are characterized by a rapid power of locomotion; 

 they are often supplied with cilia, and generally somewhat 

 curved, staff-like bacteria. They seem to attack the casein 

 of the milk directly without precipitating it, and dissolve it 

 under decomposition. Although they do not develop spores, 

 they are very tenacious of life. They can stand both pro- 

 longed drought and a cold of - 4 to - 22 F. (20 - 30 C.). 

 The fermentation produced by these bacteria in milk gives 

 it sometimes a bad and insipid, sometimes a bitter, taste. 

 If the cream from such milk is allowed to grow old it will 

 yield a rotten odor, and air-bubbles will form both in the 

 inner portion and on the surface of the skim-milk. 



All the milk bacteria enumerated in the preceding are 



