186 



BACTERIA IN MILK AND MILK PRODUCTS 



So strongly convinced is Conn of the exceptional influence of 

 temperature on the increase of bacteria in milk, and the subsequent 

 souring, that he holds that " the keeping of milk is more a matter of 

 temperature than of cleanliness." The cooling of milk immediately 

 after mUking, and keeping it at a low temperature, will do more for 

 its preservation than any other practical device. Conn has also 

 pointed out that lactic organisms flourish in milk when it is kept at 

 temperatures above 50° C. He summarises the influence of tempera- 

 ture as follows : — 



(1) Variations in temperature have a surprising influence upon 

 the rate of multiplication of bacteria. At 50° F. these organisms may 

 multiply only five-fold in twenty-four hours, while at 70° they may 

 multiply seven hundred and fifty-fold. (2) Temperature has a great 

 influence upon the keeping property of milk. MUk kept at 95° (heat 

 of the cow's body) will curdle in eighteen hours, while the same milk 

 kept at 70° will not curdle for forty-eight hours, and if kept at 50°, 

 the temperature of an ice-chest, may sometimes keep without curdling 

 for two weeks or more. (3) So far as the keeping property of milk 

 is concerned, the matter of temperature is of more significance than 

 the original contamination of the milk with bacteria. (4) Milk pre- 

 served at 50° or lower wiU keep sweet for a long time, but it becomes 

 filled with bacteria of a more unwholesome type than those that grow 

 at higher temperatures.* 



The influence of time is not less marked than that of temperature, 

 as the following table will show : — 



Milk drawn at 59° 

 After 1 hour 

 2 



4 



7 



9 



24 



153,000 m.o. per cub. inch. 



616,000 



539,000 



680,000 



1,020,000 



2,040,000 



85,000,000 



Freudenreich gives another example, as follows 



Milk drawn at 15-5° C. 

 After 4 hours 



j» y SI 



»» ^4 ,, 



= 27,000 m.o. 

 34,000 

 100,000 

 = 4,000,000 



per C.C. 



Concerning these figures little comment is necessary. But here 

 again, also, we may remember that this rapid multiplication only 

 continues up to a certain point, after which there is a marked reduc- 

 tion owing to products of activity. 



Quite recently further investigations have been made in milk 

 maintained at a standard temperature by various workers. For the 



* Storr's Agric. Expl. Sta. Conn. Bull. 26 (H. W. Conn). 



