Pasteurisation. 55 



teria, more especially those commonly contained in 

 milk, conld be killed at a temperature as low as 176 

 or -even 167, if only they conld be kept in this tem- 

 perature for a sufficiently protracted period. This 

 conclusion having been reached and confirmed, it 

 was at once plain that the apparatus to be used would 

 have to abandon the aim of continuous operation and 

 adopt the principle of periodic filling and emptying. 

 In his exhaustive researches in this direction, Bitter 

 reached most conclusive results. Beginning again 

 with milk to which bacteria of tuberculosis were 

 added, he heated this in an apparatus of his own in- 

 vention to 154 F. for fifteen, twenty and thirty min- 

 utes respectively, in separate lots. Corroborating not 

 only the result of his previous experiments in the 

 laboratory, which had shown that thirty minutes 

 were sufficient to kill these bacteria exposed to 154, 

 it was found that even half of this period, fifteen min- 

 utes, sufficed to attain the same result. After this 

 the experiments were extended to examine the effects 

 of pasteurizing on the ordinary bacteria of milk 

 under varying degrees of heat and varying periods of 

 -exposure to such heat. 



It was of the greatest importance to attain a stand- 

 ard of comparison, not only for the preservation of 

 the milk, but also as to its fitness for consumption. 

 The investigations were, therefore, extended to the ap- 

 pearance, smell and taste of the milk treated, and to 

 detect every change in these properties on which the 

 value of milk as an article of consumption so largely 



