CONTAMINATION OF FOODS 151 



Straining and clarifying milk. It might bo thought that 

 I lie foreign matter introduced into milk could lc removed, 

 thus reducing the bacterial content as well. For the re- 

 moval of dirt, straining the milk is generally resorted to. 

 This practice may be carried out so as to remove the in- 

 soluble material that has found its way into milk, but it 

 will have little if any influence on the reduction of bac- 

 teria, since they are readily washed off from the surface 

 of solid matter, and are able to pass the pores of the finest 

 strainer that may be used. All processes of straining can 

 serve only to improve the appearance of the milk, but can 

 have little if any influence on its keeping quality or health- 

 fulness, 



Much of the milk now sold in cities is subjected to a proc- 

 ess known as clarification by passing it through a machine 

 that is comparable to a cream-separator. The insoluble 

 material that has been introduced into the milk will be 

 completely removed by the strong centrifugal force ap- 

 plied to the milk in the rapidly revolving bowl of the clari- 

 fier. This material will be supplemented by cellular ele- 

 ments from the udder, and by casein, the whole forming 

 a slimy mass known as separator slime. The color is white 

 if the milk treated is relatively free from dirt. Usually it 

 is grayish in color, because of the dirt therein. Since the 

 bacterial content of the slime is much higher than that of 

 the untreated milk, the process serves to remove a portion 

 of the bacteria from the milk. The actual reduction is, 

 however, so small as to be of no practical importance in 

 influencing the keeping quality or the healthfulness of the 

 milk. Like straining, it improves only the appearance of 

 the product. 



Influence of feed on contamination of milk. The bac- 

 terial content of the feed or water consumed by the cow 

 can not have a direct influence on the kinds or number of 



