Decrease in Milk Bacteria 383 



most intense at 70, but which endures longer at lower 

 temperatures. 



The decrease may also be assigned to the dropping out 

 of the bacteria unsuited to their surroundings rather 

 than to any germicidal property in the milk. Although 

 the total number of bacteria suffers a decrease, the 

 latter falls on the non-acid bacteria, rather than on the 

 lactic-acid bacteria. 



Whatever explanation we accept for the decrease 

 in the numbers of bacteria in fresh milk for some hours 

 after it is drawn, the fact is indubitable that the decrease 

 does occur. On the whole, however, the decrease is 

 not uniform, and of comparatively short duration. 

 No reliance, therefore, can be placed on it as a natural 

 means for increasing the keeping quality of milk. It 

 is rather the low temperatures on which we must de- 

 pend for retaining the milk wholesome for more or less 

 considerable lengths of time. Since some of the organ- 

 isms begin to multiply as soon as they enter the milk, 

 and since a single hour of this initial multiplication 

 may mean much in determining the keeping quality 

 of the milk, it follows that milk should be cooled at 

 once rather than allowed to cool gradually. 



Temperature. In some experiments reported by 

 Conn, the influence of temperature is shown to be para- 

 mount in determining the keeping quality of milk. 

 In a portion of milk kept at 50 Fahr., the bacteria 

 multiplied only fivefold in twenty-four hours, whereas, 

 in a similar portion of milk kept at 70 Fahr., the in- 

 crease was seven hundred and fifty fold. 



" Sometimes it is found possible to keep the milk 



