PASTEURIZATION OF MILK OR CREAM 281 



REFERENCES 



WARD: Pure Milk and the Public Health (1909), pp. 15-16, 24-25, 



37, 121. 



RUSSELL and HASTINGS: Outlines of Dairy Bacteriology, pp. 54-56. 

 ERNST: Milk Hygiene, transl. by Mohler and Eichhorn (1914), pp. 



148-149, 156. 

 MARSHALL: Microbiology, pp. 318-319. 



EXERCISE 6.x A STUDY OF THE PASTEURIZATION OF 

 MILK OR CREAM BY LABORATORY METHODS 



Apparatus. Water bath; test-tube rack of metal to 

 fit water bath; sterile, large tubes selected for uniformity 

 in diameter (2 cm.); sterile Petri dishes; sterile 1 c.c. pi- 

 pettes, graduated to 0.1 c.c.; sterile litmus lactose agar 

 tubes. 



Method. 1. Secure milk or cream, about 125 c.c. to 

 be used for tubing and pasteurizing. 



Note. If time permits, it is desirable to test pasteurization upon: 



a. Fresh milk or cream. 



b. Milk or cream which has stood for twenty-four hours but is 

 still sweet. 



c. Milk or cream which has reached an acidity of about 22. 



d. Milk or cream from different sources, supposedly having dif- 

 ferent bacterial contents. 



2. Tube the sample or samples of milk or cream, pour- 

 ing 10 c.c. into each tube, filling fifteen tubes for each sample. 



Note. Only one sample should be pasteurized at a time. 



3. Prepare one tube from each sample of milk or cream 

 for the introduction of the thermometer. By so doing, 

 the conditions practically identical, the temperature will 

 be easily read and controlled. 



4. After the tubes are prepared mark tubes in duplicate 

 as follows: 50, 60, 70, 80, 90 and 100, leaving two 

 unmarked as controls. 



5. Place them in the rack so that the marks on the tubes 



