122 



MILK HYGIENE 



teria. The milk used contained about 9300 bacteria in 

 one c.c. and was kept at 15, 25, and 35 C. : 



At the low temperature, it is seen that the increase 

 is at first very slight. Moore found that the number of 

 bacteria in milk kept at 21 C. (70 F.) did not increase 

 during the first 6 to 9 hours but then increased rapidly ; 

 he also found that in the course of from 36 to 48 hours, 

 no appreciable increase in the number took place, if 

 the temperature did not rise above 12 to 13 C. (53.6 

 to 55.4 F.) and that a still lower temperature, as 4 to 

 5 C. (39.2 to 41 F.), could prevent the increase of 

 bacteria for a longer period. Meyer found, through 

 experiments carried on in Jensen's laboratory, that 

 cooling the milk to 10 to 12 C. (50 to 53.6 F.) checks 

 the growth of bacteria for a long time. 



It is evident, from all of this, that the quick and per- 

 manent cooling of the milk to 10 to 12 C. (50 to 53.6 

 F.) is most important in preserving it. 



Of course the number of bacteria in market milk 

 varies greatly according to its age and care and to the 

 temperature of the air. Experience gained in most of 

 the larger cities shows the bacterial content of market 

 milk to be seldom below 50,000 to 100,000 per c.c. but it is 

 often greater, varying between 1,000,000 to 30,000,000; 

 indeed, not infrequently, even from 100,000,000 to 150,- 

 000,000 have been found. And such milk may not be 

 noticeably tainted. 



