128 



THE BACTERIAL CONTENT OF MILK 



Quite recently further investigations have been made in milk 

 maintained at a standard temperature by various workers. For 

 the sake of comparison with other statistics which we have selected, 

 we may take two series recorded by Park. In the first the tempera- 

 ture was 90° F., a temperature common in New York in hot summer 

 weather, and the samples of milk were of three degrees of quality, 

 namely, fresh and good, fair, and bad. The result was as follows : — 



The second series of Park was milk taken from cows in common j 

 dirty stalls, twenty-four, thirty-six, and forty-eight hours afterJ 

 milking. The milk was cooled to 52° F., three hours after milking,] 

 and maintained at that temperature for the forty-eight hours of thej 

 experiment. The result, therefore, shows the effect of time evenf 

 more exactly than the first series : — 



Average Number of Bacteria per 1 c.c. of Milk at 52° F. (six samples). 



After S hours. 

 30,366 



After 24 hours. 

 69,433 



After 36 hours.* 

 348,833 



After 48 hours. 

 1,668,333 



* The figures at thirty-six hours were estimated from the test of one sample 



only. 



Even a cursory examination of the figures already given will 

 have shown how intimately the two influences of time and tempera-| 

 ture act and interact in relation to the multiplication of micro- 

 organisms in milk. They are scarcely separable, and no hard-and- 

 fast line can be drawn by way of comparison of these two' 

 influences. 



We must now, therefore, discuss the numerical changes occurring 

 in the bacterial content of milk in as broad a way as possible. For 

 this purpose reference will be made to two investigations carried 

 out, one by Park of New York, and the other by ourselves 



