164 PROTECTION OF THE CONSUMER. 



bacteria; but we must remember that the two chief objects to 

 be accomplished are to increase the keeping quality of the 

 milk and to remove the danger of disease bacteria. Will the 

 pasteurizing temperature produce these two results? 



Such temperatures certainly do increase the keeping prop- 

 erty of the milk. Although 155 does not destroy bacteria 

 spores, it does destroy most of the non-spore-bearing bac- 

 teria. We have already seen that the lactic bacteria, which 

 are the cause of the souring, do not produce spores and, since 

 these will be killed by the pasteurizing temperature, the total 

 number of bacteria in milk is immensely reduced, and its 

 keeping quality correspondingly increased. Experiment 

 shows that pasteurization kills from 95% to 99% of the bac- 

 teria present, and such milk will frequently remain good for 

 two days longer than similar milk not pasteurized. Pasteur- 

 ization, therefore, does accomplish one purpose, for although 

 the milk will not keep indefinitely it will keep sweet much 

 longer than usual. 



Most of the disease germs which are liable to be distributed 

 by milk are destroyed by the temperature of pasteurization. 

 Typhoid fever and diphtheria bacteria are killed by this tem- 

 perature, and the same is probably true of scarlet fever. The 

 tuberculosis bacillus, however, will, under some conditions, 

 stand a higher heat without injury, and it has therefore been 

 claimed that, to free the milk from the danger of distributing 

 tuberculosis, a temperature as high as 185 F. is necessary. 

 At this temperature, however, the cooked taste appears. 

 There has been much dispute over the question whether lower 

 temperatures will destroy the tubercle bacillus. Into the 

 details of this matter we cannot enter. The present con- 

 clusion seems to be that, if the milk is heated in such a manner 

 as to avoid the formation of a scum on its surface, a com- 

 paratively low temperature is sufficient to destroy the viru- 

 lence of the tubercle bacillus (113, 134). A temperature no 

 higher than 140, if continued for twenty minutes, has been 



