158 MODERN METHODS OF TESTING MILK 



Gerber's fermentation test. This test consists in 

 heating milk in tubes 6 hours at 104 to 106 F. and 

 then observing the odor, appearance, taste, etc., for 

 abnormal qualities. The milk is heated a second time 

 for 6 hours at 104 to 106 F. Any abnormal coagula- 

 tion of the milk is noticed, such as holes due to gas. 

 Gerber states that milk coagulating in less than 12 

 hours is abnormal, due either to the abnormal char- 

 acter of the milk itself when drawn or to improper 

 care after being drawn. Milk that does not curdle 

 within 24 to 48 hours is open to the suspicion of con- 

 taining preservatives and should be examined for such 

 substances. 



METHODS OF TESTING FOR ENZYMS IN MILK 



Enzyms are chemical ferments; they have the 

 power to produce changes in other substances without 

 themselves undergoing appreciable change. Enzyms 

 are the products of living cells ; those in milk have their 

 origin, in part, in the animal producing the milk and 

 usually, in larger part, in the bacteria contained in 

 the milk. Under this head we shall consider the fol- 

 lowing tests: (i) Reductase, (2) catalase, (3) dis- 

 tinction between heated and unheated milk. 



Reductase test. Ordinary normal milk possesses 

 the power of decolorizing certain coloring-substances 

 by reduction or removal of oxygen ; this property ap- 

 pears to depend upon the presence of micro-organisms 

 in milk since the larger the number of bacteria, the 

 shorter the time required to produce decolorization. 

 The coloring-substance that has been found especially 

 useful in this test is a compound known as methylene- 



