Contamination of Milk. 23 



bles rapidly undergo changes that render them unde- 

 sirable, or even unfit for human food. Milk is the most 

 perishable food of all. Produced under ordinary con- 

 ditions and with no precautions taken to preserve it 

 during the warmer periods of the year, it is unfit for 

 use in twenty-four hours. 



There are two reasons for this rapid deterioration : 

 (1) gross contamination, (2) its nature and composi- 

 tion. The surroundings in which milk is produced al- 

 ways make infection easy. The high nutritive compo- 

 sition and the dilution of its food ingredients make it 

 admirably adapted as a medium for bacterial growth. 

 Many of the bacteria produce changes in the milk which 

 injure the quality of the butter and cheese. It thus be- 

 comes important to prevent as far as possible the intro- 

 duction of the bacteria and to check their development 

 in the milk. 



Contamination of milk. Tn order to prevent the bac- 

 teria from getting into the milk, it is necessary to know 

 the sources from which they come, and to become ac- 

 quainted with practical means of exclusion. Unless the 

 sources are recognized and something is known of their 

 relative importance, numerous things will be done that 

 are unnecessary, and often the essential things left un- 

 done. 



The subject of the contamination of milk is the most 

 important and fundamental one in dairy bacteriology. 

 At every step in the production of milk and in its treat- 

 ment on the farm the farmer is confronted with this 

 subject. The returns he receives from his milk are 

 often decided by the wisdom with which he meets the 

 problems concerned in the production of clean and 

 healthful milk. 



