TESTING THE SANITARY CONDITIONS OF MILK l6l 



of 2 hours is observed. Milk older than 2 to 6 hours 

 giving 4 cc. of oxygen by this test is regarded as ab- 

 normal. 



This test has been found useful in detecting ab- 

 normal conditions in the milk of individual cows. A 

 high catalase content in fresh normal milk is a sign 

 of diseased udder after the colostral period is over. 

 Increase of catalase in milk several (6 to 12) hours 

 old indicates bacterial activity and may be used as a 

 test of the keeping power of milk. 



Methods for testing heated milk. It is often desir- 

 able to know whether milk has been heated or not. 

 In the case of pasteurized milk, it is important to learn 

 whether it has been heated sufficiently to be really 

 pasteurized. 



Several tests have been devised for distinguishing 

 between heated and unheated milk. They are based 

 on the following facts: Unheated milk contains 

 enzyms which, in the presence of peroxides, such as hy- 

 drogen peroxide, set free oxygen and this oxygen 

 produces marked coloration when certain compounds 

 are present. These enzyms, when subjected to a tem- 

 perature above 172 to 176 R, are so changed that 

 they lose the power of setting free oxygen from a 

 peroxide and therefore they produce little or no color 

 in milk so heated. Several different substances have 

 been used, giving rise to as many tests, of which we 

 will describe the following: (i) Para-phenylene-dia- 

 mine test, (2) Guaiac test, (3) Methylene-blue test. 



Para-phenylene-diamine or Storch test. Into a cup 

 or test-tube one puts about 5 cc. of milk, then one drop 

 of a 0.2 per cent, solution of hydrogen peroxide and 



