TESTING THE BACTERIAL CONDITION OF MILK 117 



Precautions. Two points must be carefully ob- 

 served in carrying out this test : ( i ) The temperature 

 must be kept as near 98 F. as possible, in order that 

 the bacteria may develop as desired. This can be 

 done by keeping the temperature of the water sur- 

 rounding the jars at 100 to 102 F. The tempera- 

 ture must be watched. (2) The thermometer and the 

 knife used should be made not only clean but sterile 

 each time after using in one sample before placing 

 them in another. 



GERBER'S FERMENTATION TEST 



This test consists in heating milk in tubes 6 hours 

 at 104 to 106 F. and then observing the odor, ap- 

 pearance, taste, etc., for abnormal qualities. The milk 

 is heated a second time for 6 hours at 104 to 106 F. 

 Any abnormal coagulation of the milk is noticed, such 

 as holes due to gas, Gerber states that milk coagu- 

 lating in less than 12 hours is abnormal, due either 

 to the abnormal character 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 containing preservatives and should 

 be examined for such substances. 



METHOD OF TESTING MILK FOR SUSPENDED 

 DIRT 



The amount of dirt in suspension in milk can be 

 estimated without serious difficulty. The best way is 

 to provide a small centrifugal machine that is made 

 to run at higher speed than the Babcock tester. A 



