THE GROWTH OF BACTERIA IN T MILK 75 



trouble in the milk. The largest part of the bacteria will be 

 cocci, some of which liquefy gelatin and belong to the pepton- 

 izing group, and some of which do not. These organisms come 

 directly from the udder and can practically never be avoided. 

 Their presence in milk is normal, even in the best dairy con- 

 ditions, and there is no reason for regarding them as injuring 

 the milk, for most of them have no action upon it and are per- 

 fectly harmless to man. In addition to these there will be a 

 varying number of miscellaneous bacteria, liquefiers and non- 

 liquefiers. Their number and types will depend upon the extent 

 of the contamination of milk with manure, dust and other 

 sources of bacteria. These miscellaneous bacteria are the ones 



most likely to produce trouble. 







EFFECT OF TEMPERATURE ON NUMBERS 



The number of bacteria in milk at any subsequent period is 

 more largely dependent upon the temperature and age than upon 

 the original contamination. 1 Milk when fresh from the dairy, 

 even from the slovenly, filthy dairy, will rarely contain more 

 than half a million or so bacteria per c.c.. and usually a much 

 smaller number. By the time the milk is one or two days old 

 the numbers may amount to 50,000,000. to 100,000,000, or even 

 more. Milk from an ordinary cleanly, carefully kept dairy may 

 have no more than from 10,000 to 50,000 per c.c. at the outset. 

 But this milk, also, in the course of one or two days may have 

 numbers as high as 100,000,000. The number of bacteria 

 present at any time is, therefore, more dependent upon the age 

 of the milk and the method of keeping it than upon the original 

 amount of contamination. Milk which originally contained 

 large numbers of bacteria, if kept cold, will in 24 hours show 

 a much lower bacteria count than milk which originally had 

 small numbers but was kept under warmer conditions. This 



1 Conn. Bui. 26, Storrs. Exper. Sta., 1903. 



