TIME AND TEMPERATURE 



187 



sake of comparison with other statistics, we may take two series 

 recorded by Park. In the first the temperature was 90° F., a tem- 

 perature common in New York in hot summer weather, and the 

 samples of milk were of , three degrees of quahty, namely, fresh and 

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



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

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

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

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

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

 more exactly than the first series : — 



* The figures at 36 hours were estimated from the test of one sample only. 



Even a cursory examination of these figures with those already 

 given will have shown how intimately the two influences of time and 

 temperature 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. 



Eeference may also be made to two investigations made, one by 

 Park of New York, and the other carried out by Swithinbank and 

 the writer. 



The following figures obtained by Park show the development 

 of bacteria in two samples of milk maintained at different tempera- 

 tures for twenty-four, forty-eight, and ninety-six hours respectively. 

 The first sample was obtained under the best conditions possible, the 

 second in the usual way (the figures of this sample are underlined). 



