156 PROTECTION OF THE CONSUMER. 



comprise a majority, indicate no material reduction of the 

 bacteria, and sometimes there is an apparent increase (283). 

 When such milk is placed side by side with a sample of the 

 same milk not treated, it is found that the centrifugalized 

 milk does not keep longer than the control. Indeed, in many 

 experiments the centrifugalized milk sours and curdles an 

 hour or two before the untreated sample (183). The centri- 

 fugal treatment is quite unreliable, therefore, as a means of 

 removing bacteria, and is of no use whatsoever in rendering 

 less dangerous milk which contains pathogenic bacteria. The 

 fact that such treatment removes filth and improves taste is 

 certainly sufficient to recommend the employment of the 

 centrifugal force where feasible, but it does not, to any 

 appreciable extent, remove the bacteria. 



Filtering. The plan of filtering the milk has been fre- 

 quently adopted. Various kinds of filtering apparatus have 

 been constructed. In most of the machines the actual filter- 

 ing material is some form of sand of a fine texture through 

 a tolerably thick layer of which the milk is forced to pass. In 

 some machines the milk passes through from its own weight 

 as in ordinary filtering, while in others the milk is by pres- 

 sure forced upwards through the filtering layers. In all of 

 the machines there is a convenient device for removing the 

 sand filter for washing and sterilizing. Without such a 

 sterilization the filter would be worthless, since the sand 

 would soon become filled with filth and bacteria. These filter- 

 ing machines have been sometimes adepted by milk com- 

 panies and used on a large scale to filter great quantities of 

 milk for general distribution. But smaller machines are also 

 on the market. They have not come into very general use 

 and most of them, indeed, are inventions of recent date, 

 whose efficiency is not yet tested. 



Concerning the efficiency of the filtering machines, almost 

 the 'same is to be said as concerning centrifugalizing. The 

 filters are quite efficient in removing the dirt and filth, 



