Sterilising, 65 



spread and common baccilhis subtilis would have to 

 be heated for a considerable time to 240 to insure 

 any degree of security of its having been killed. 



Pasteur records amongst his experiments of steriliz- 

 ing milk that the hay baccillus was found killed only 

 after a heating of several hours' duration to 2of) c , or 

 after heating for half an hour to 206 F. To such 

 excessive heat we cannot, however, expose milk with- 

 out its palatability being seriously impaired, so that 

 sterilizing at such temperatures is practically not to be 

 thought of. We note that in the beginning all these 

 experiments tended merely to produce a keeping 

 quality in the milk, and only in the course of time 

 the expediency became apparent of combining with 

 it a sanitary amelioration by its thorough disinfection. 

 We shall first review the effects of sterilizing from 

 the standpoint of longer keeping qualities, and turn 

 thereafter to the merits attained by the disinfection. 



Among those that entered the occupation of building 

 sterilizing apparatus, two distinct methods were very 

 soon adopted the one heating to high temperatures 

 and then hermetically sealing the vessels containing 

 the milk, the other advocating a repeated heating and 

 intermediate cooling at different degrees of tempera- 

 ture, which is termed " fractionized sterilization." 

 Tyndall was the first to advocate this method, and 

 Dahl adopted it, cooling milk first to 5.~> and then 

 heating it to 1.~><S for four consecutive times and 

 cooling the milk to 104 between each heating, the 

 separate operation consuming one hour and a half 



