60 THE MILK QUESTION 



only diflference being that the visible particles have been 

 strained out. 



It is now customary to take the dirt out of milk in one of 

 three ways: — 



(1) Straining through cotton, cheesecloth, or some simi- 

 lar material; (2) filtering through quartz gravel; (S) clari- 

 fying in a centrifugal machine. 



Practically aU the large dairies depend upon clarifiers 

 to render their milk "clean." These clarifiers whirl the 

 milk at great speed and throw out the dirt by centrifugal 

 force. After several hours' run the dirt removed from one of 

 these machines consists of brownish slime. The amount 

 thus obtained is much greater than the amount obtained 

 by any process of filtering or straining. This does not mean 

 that clarifiers are more effective than straining or filtering. 

 In fact, the purifying action of centrifugal clarifiers is de- 

 ceptive, for these machines throw out some of the normal 

 constituents of the milk which help to make up the dirty 

 slime. The total amount of slime removed depends upon 

 the rate of rotation and the time the milk is subjected to 

 the centrifugal force. 



All these so-called purifying processes render milk more 

 acceptable to the sight, but do not improve the milk from 

 a sanitary standpoint one jot or tittle. The visible dirt 

 and gross particles are taken out, but not the bacteria or 

 the infection. As a matter of fact, milk that has been 

 strained, filtered, or clarified apparently contains a larger 

 number of bacteria than it did before the "purifying" 

 process. The reason for this is that the bacteria are 

 enmeshed in the particles of dirt and are fond of group- 

 ing themselves together in clusters or colonies. When 

 milk is strained, filtered, or centrifuged, the clusters are 

 broken up. Further, the bacteria are washed out of 

 the grosser particles into the milk. Hence, while the 

 strained or clarified milk does, not actually contain more 

 bacteria, they are more generally and more evenly dis- 



