APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 



13 



According to Park, 1 two samples of milk maintained at different 

 temperatures for 24, 48, 98, and 168 hours, respectively, showed the 

 development of bacteria as indicated in Table VI. The first sample 

 was obtained under the best possible conditions, while the second 

 sample was obtained in the usual way. (The figures of the second 

 sample are heavy face in the table.) When received the first sample 

 contained 3,000 bacteria and the second 30,000 per cubic centimeter. 



Table VI. — Effect of time and temperature on the growth of bacteria in milk. 



Temperature. 



24 hours. 



48 hours. 



96 hours. 



168 hours. 



32° F. (0° C). 

 39° F. (4° C). 

 42" F. (5° C). 

 46° F. (6° C). 

 50° F. (10° C.) 

 55° F. (13° C.) 

 60° F. (16° C.) 

 68° F. (20° C.) 

 86° F. (30° C.) 

 94° F. (35° C.) 



2,400 



30, 000 



2,500 



38, 000 



2,600 



43,000 



3,100 



42, 000 



11,600 



89, 000 



18, 800 



187, 000 



180, 000 



900, 000 



450, 000 



4, 000, 000 



1,400,000,000 



14,000,000,000 



25,000,000,000 



25, 000, 000, 000 



2,100 



27, 000 



3,600 



56, 000 



3,600 



210,000 



12,000 



360, 000 



540, 000 



1,940,000 



3, 400, 000 



38, 000, 000 



28,000 000 



168, 000, 000 



25, 000, 000, 000 



25,000,000,000 



1,850 



24, 000 



218, 000 



4, 300, 000 



400, 000 



5, 760, 000 



1,480,000 



12, 200, 000 



1,400 



19, 000 



4, 200, 000 



38, 000, 000 



In Table VI it will be noted that at 32° F. there is an actual 

 decrease in the number of bacteria in both samples of milk during 

 the 168 hours, while at all other temperatures there is an increase 

 in the number of bacteria. Ordinarily the consumer receives milk 

 when it is from 24 to 48 hours old; hence it becomes an easy matter 

 to deliver the milk in good condition, providing the milk is produced 

 under sanitary conditions and is properly cooled and held at a tem- 

 perature of 50° F. or below. An examination of the tables and fig- 

 ure will show how intimately the two influences of time and tem- 

 perature act and interact in relation to the multiplication of bacteria 

 in milk. Figure 2 is a graphical representation of the relation of 

 temperature to bacterial growth in milk, taken from Bulletin 26 of the 

 Storrs (Conn.) Agricultural Experiment Station. 2 



At a is represented a single bacterium; at b is shown the progeny 

 resulting from the growth of a single bacterium in 24 hours in milk 

 kept at a temperature of 50° F.; at c is represented the progeny 

 from a single bacterium in 24 hours in milk kept at 70° F. At 50° 

 the multiplication was fivefold, at 70° the multiplication was seven 



1 Park, William Hallock. The great bacterial contamination of the milk of cities. Can it be lessened 

 by the action of health authorities? Journal of Hygiene, vol. 1, no. 3, pp. 391-406. Cambridge, July, 

 1901. 



2 Conn, Herbert William. The relation of temperature to the keeping property of milk. Connecticut 

 (Storrs) Agricultural Experiment Station Bui. 26. Storrs, 1903. 



