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 EXAMINATION FOKPKfeSEEVATIVES 237 



of dirt is read from the scale. Stewart lias devised a 

 method that gives good results in the laboratory of the 

 Board of Health in Philadelphia. It consists in the use 

 of small glass tubes, open at each end; the lower open- 

 ing is closed with a small rubber stopper. The tubes 

 are filled with milk, and are centrifuged. The dirt is 

 thrown upon the rubber stopper and adheres thereto 

 when the stopper is withdrawn. It may easily be trans- 

 ferred to a slide for microscopic examination. Pus cells 

 are collected in the same way. L. P.] 



g. Examination for preservatives. One of the most im- 

 portant regulations with regard to the milk trade is 

 that milk shall not be preserved by the use of antiseptics 

 or alkalies, and one of the most important functions of 

 the milk inspector is to see that this regulation is ob- 

 served. An occasional test for preservatives may be 

 made by standing the samples aside at room tempera- 

 ture. If the milk does not change within the time that is 

 customary for good milk, the presence of artificial pre- 

 servatives may be suspected. Methods for the detec- 

 tion of preservatives by chemical means have already 

 been given. 



If the increased keeping power of the milk is due to 

 the addition of alkalies, this may be indicated by a simple 

 test with litmus paper. 



