Fermentations of Milk. 103 



cause of abnormal odors or tastes in milk, since methods 

 for overcoming the trouble can be intelligently applied 

 only when the actual cause is known. An abnormal con- 

 dition may be caused either by the direct absorption of 

 odors before or after the milk is drawn from the animal, 

 or it may be due to bacteria. If the milk appears bad- 

 flavored when first drawn, and if such taint becomes less 

 pronounced as the milk becomes older, it is likely that 

 the trouble is due to some characteristic of the feed. 

 Certain feeds, like green rye, rape, cabbage, and certain 

 of the root crops, like turnips, impart a strong odor to 

 milk, if the same are fed shortly before milking. If the 

 tainted condition appears only some time after the milk 

 is drawn, it may be due to the direct absorption of taints 

 from the surroundings in which the milk is kept, or it 

 may be caused by bacteria. These causes can often be 

 differentiated, by noting whether the taint tends to in- 

 crease in intensity with age. If such is the case, it is 

 likely that the cause is of germ origin, but if the reverse 

 is true, it cannot be ascribed with certainty to bacteria 

 and recourse must be had to other methods, such as the 

 transfer of a small quantity of the tainted milk to a 

 sample of perfectly fresh milk, or preferably to some 

 milk that has been heated to the boiling point and then 

 cooled. In the case of an odor due to direct physical 

 absorption, it will not appear in the inoculated sample, 

 since the small amount transferred is not sufficient to 

 be noted. If it is due to living organisms, the inocula- 

 tion of the smallest quantity into a fresh sample* is likely 

 to reproduce the same change as originally noted. 



Tests for the bacteriological condition of milk. 

 Within certain limits milk can be indirectly examined as 

 to its bacterial content without any special equipment. 



