Boiling and Pasteurizing 389 



by temperatures of from 150° to 160° Fahr. On the 

 other hand, the spore-bearing organisms are not thus 

 destroyed, even at higher temperatures, and prolonged 

 boiling becomes necessary for their destruction. When 

 pressure and high temperatures are combined, the most 

 resistant spores can be killed in a comparatively short 

 time, as is done, for instance, in the autoclave at 1.5 to 

 2.0 atmospheres of pressure. Milk sterilized in this 

 manner, and protected against fresh infection, will 

 remain unchanged for an indefinite length of time. 

 But a very serious objection is raised against such treat- 

 ment in that milk thus sterilized is really boiled milk 

 and, as such, is not likely to be acceptable to the con- 

 sumer. 



Pasteurization. — In order to meet this objection, 

 it becomes necessary to heat the milk to a point below 

 that at which the cooked taste becomes perceptible. 

 Such heating possesses no value if inadequate for the 

 destruction of the objectionable bacteria. Extensive 

 experiments have been carried on, therefore, to deter- 

 mine, on one hand, the limit to which milk may be safely 

 heated without producing a distinctly cooked taste, and, 

 on the other, the effect of different temperatures on the 

 various organisms frequently or occasionally occurring 

 in milk. 



The results secured by investigators in different 

 countries show that temperatures of 155° to 160° Fahr. 

 should not be exceeded in the heating of milk. They 

 show, also, that the bacillus of tuberculosis, regarded 

 as the most resistant of the non-spore-forming disease 

 bacteria, may be killed by exposure to a temperature of 



