TESTING THE SANITARY CONDITIONS OF MILK 163 



such milk. This can be remedied by adding a few 

 drops of hydrogen peroxide to the solution. 



A modification of this test can be used : To I cc. of 

 milk, one adds I cc. of a water solution of guaiacol 

 and i drop of hydrogen peroxide solution (3 per cent.). 

 In unheated milk a strong orange color appears, but 

 not in case of milk previously heated to 176 F. 



Methylene-blue or Schardinger's test. The re- 

 agent used in this test is a mixture of 5 cc. of a satu- 

 rated solution of methylene-blue, 5 cc. of formalin and 

 190 cc. of distilled water. The test is performed as 

 follows : To 20 cc. of milk add i cc. of Schardinger's 

 reagent, warm to 113 to 122 F. and observe the time 

 it requires to lose the color completely. Ordinary 

 normal milk is decolorized in about 10 minutes with 

 this test. 



The reaction depends upon a specific enzym in milk 

 called aldehyde-reductase, which is more or less quick- 

 ly destroyed at temperatures above 158 F., while with 

 milk heated above 176 F. decolorization is complete. 

 When milk is pasteurized either 2 minutes at 167 F. 

 or about 15 minutes at 158 F. the color disappears in 

 about 30 minutes with the test. 



METHODS OF TESTING MILK FOR SUSPENDED 



DIRT 



In making an examination of milk with reference 

 to its sanitary condition, dirt in suspension or sedi- 

 ment should always be tested for. There are several 

 satisfactory methods. It is sufficient for most pur- 

 poses to get a rough idea of the amount of sediment. 

 There are three general methods in use : ( i ) By filtra- 



