IV 



BEHAVIOUR OF BACTERIA IN MILK 49 



Development of Bacteria in Incubated Milk Samples. 

 (All samples collected at the cowsheds). 



In view of the practical importance of keeping milk cool, 

 the effect on the bacterial content of storing milk at C. has 

 been studied by a number of investigators. It is generally 

 assumed that little or no bacterial alteration takes place at the 

 freezing temperature of water, but this cannot be accepted as 

 true without qualification. For fresh samples of milk kept 

 for only 24 to 48 hours at C. it will generally be found 

 that there has been no increase in the number of bacteria but 

 a slight decrease. Park's table, given above, illustrates this 

 decrease, which is no doubt due to the germicidal action of 

 the milk and the suppression of certain types which are in an 

 unsuitable temperamental environment. 



When, however, the milk samples are maintained at C. 

 for many days and weeks, it will be found that a great 

 increase in the number of bacteria has taken place. For 

 example, Pennington, 1 working with both pure and ordinary 

 market-milks, found great increase after long periods in 

 samples kept at 29-32 F. For example, one sample, containing 

 only 300 organisms per c.c. to start with, was found to contain 



1 Journal of Biol. Chem., 1908, vol. iv. p. 353. 



E 



