54 A Neiv Dairy Industry. 



temperatures of 165 to 170 P., it must be con- 

 cluded that the application of a temperature under 

 170, but during a more protracted period, must be 

 the right thing, and experiments accordingly made 

 have confirmed this conclusion. 



We know that all changes which take place in 

 milk must be traced to the presence and activity of 

 spores, ferments, etc. We must conclude herefrom 

 that the keeping quality of milk is dependent upon the 

 quantity of such germs contained therein, and that 

 also the success of pasteurization must depend on the 

 efficiency with which it has killed the majority of 

 germs or not. If we, therefore, wish to study the ef- 

 fect of heating on the durability of milk, we have to 

 study the effect which heating produces on the milk 

 fungi, and such experiments have to be carried on by 

 purely bacteriological methods, which in their sim- 

 pler forms we shall have to adopt when testing milk 

 to be prepared for infants' food ; a closer description 

 of the apparatus used will be brought in the chapter 

 treating of the manufacture of artificial mothers' 

 milk. 



The defects attached to pasteurizing apparatus 

 liave been clearly demonstrated by a large number 

 of experiments. It has been proven that certain bac- 

 teria which had been introduced into the milk, for 

 instance, bacteria of tuberculosis, can be killed at a 

 temperature of 154 to 155 if they are only exposed 

 to this temperature for about thirty-five minutes. 

 From this it was. correctlv concluded that other bac- 



