THE VITAL PHENOMENA OF BACTERIA. 133 



pasteurization as it is called. I was able to de- 

 termine further the exact temperature at which 

 milk can be made germ-free and showed that, 

 in order to obtain milk that would keep and re- 

 main fit for transport, a temperature of 120 

 is necessary ; otherwise, condensation must be 

 resorted to. Shortly before the appearance of 

 my work, Soxhlethad attributed the well-recog- 

 nized success that attends the pasteurization 

 of milk to the subsequent chilling of the fluid ; 

 later, upon the basis of the facts I had ascer- 

 tained, he introduced the method of treating 

 children's milk which goes by his name. This, 

 as a matter of fact, was nothing more than an 

 exploitation of my discoveries, which I had 

 freely placed at the disposition of every one. 



Naegeli observed, as Pasteur had done before 

 him, that milk that has been heated does not 

 afterwards become acid, but, on the contrary, 

 alkaline, and he assumed that the germ that 

 produced acid had been so modified by the heat 

 that its ferment-nature had undergone meta- 

 morphosis. My own investigations have made 

 the following point clear, namely, that the 

 germs producing acid are actually destroyed 

 by the heat, but that resistant spores of other 

 bacteria are present along with them in the 

 milk, and that these spores resist the heat, 

 subsequently germinate and thereby render 



