54 EXPERIMENTAL DAIRY BACTERIOLOGY 



and is especially important to the milk producer and handler, 

 and also to the consumer. If in any practical way the contam- 

 ination may be lessened and the keeping quality improved, 

 the value of the product will be enhanced. Entirely apart 

 from the economic and hygienic relations of the contamina- 

 tion of milk may be considered its relation to general clean- 

 liness. Wholesome food prepared in a cleanly manner is 

 desirable, not because unclean food may cause sickness or 

 may not keep so long, but simply for the sake of cleanli- 

 ness alone. 



When it is considered that milk is largely produced for 

 human food, either in the form of milk, or as butter or cheese, 

 it must be admitted that the circumstances surrounding its 

 production are, even under the best of stable conditions, far 

 from what would be looked upon as desirable in the prepara- 

 tion of any other food product. Especially is this true when 

 it is kept in mind that meat, fruits, vegetables, etc., -^- food 

 products likely to be soiled with dirt, can be washed and 

 rendered clean and wholesome. The mud, manure, and dust 

 which fall into milk are partially dissolved and cannot be 

 removed. Straining removes the grosser pollution, such as 

 straw and hair, but does not remove the bacteria which are 

 attached to these objects. Milk is a food product that, once 

 rendered dirty, cannot be made clean. Many of the sources 

 of contamination are wholly preventable, some partially, and 

 still others to a very slight extent. The student should become 

 thoroughly familiar with all the sources of contamination and 

 with the different practical means for overcoming or removing 

 the same. 



Contamination from barn air. Dust particles floating in 

 the air invariably carry a larger or smaller number of bac- 

 teria, depending upon the nature of the surface from which 



