CONTAMINATION WITH BACTERIA 121 



stored in unsterilized vessels or when it is exposed to 

 the air. It is evident that the number of bacteria found 

 in freshly drawn milk varies greatly according to the 

 conditions of cleanliness of the stable and the cows, and 

 as to the cleanliness and carefulness observed during 

 milking. 



Freshly drawn milk possesses a certain bactericidal 

 action which, however, does not seem to affect all forms 

 of bacteria. The number of living bacteria in milk may 

 be lessened appreciably in the course of a few hours as 

 a result of this activity, but the action does not last and, 

 under appropriate temperature conditions, bacteria 

 soon begin to increase and their number, at times, be- 

 comes enormous. The rapidity with which the bacteria 

 increase after milking is dependent entirely upon the 

 temperature at which the milk is kept. 



If the milk is cooled immediately after being drawn 

 and is kept at a temperature not higher than 10 C. 

 (50 F.) there is no material increase of bacteria during 

 the first 24 to 36 hours; even at 14 to 15 C. (57.2 to 

 59 F.) the increase is relatively slight. But as the 

 temperature rises, the number of bacteria increases 

 rapidly and bacteria are very numerous in milk that 

 has stood at 20 to 25 C. (68 to 77 F.) for 12 hours. 



In order to illustrate the importance of cleanliness 

 in the stable and during milking, the following figures 

 determined by Grotenfeld may be of use. In one c.c. of 

 milk from cows particularly well cared for, he found 106 

 bacteria, while the freshly drawn milk of cows in a dirty 

 stable contained 617,000 bacteria per c.c. Therefore, one 

 cannot generalize as to the number of bacteria in freshly 

 drawn milk, but milk from well-cared-for and carefully 

 milked cows will, as a rule, contain hardly more than 

 1000 to 6000 bacteria per c.c. The following results show 

 the potent effect of cold in checking the increase of bac- 



