102 MILK [vi 



be alive after the lapse of 120 days ; and in cheese 

 after the lapse of 35 days. After such an interval of 

 time as a month, they probably become so attenuated 

 as no longer to be very dangerous. It is noteworthy 

 that the tubercle bacillus is not killed at such a low 

 temperature as the majority of bacteria, which, as 

 we have already noted, are killed at a temperature 

 of under 60 C. (140 Fahr.). Experiments have 

 proved that it is necessary to heat milk for thirty 

 minutes at a temperature of 65 C. (149 Fahr.), 

 fifteen minutes at 68 C. (155 Fahr.), and ten 

 minutes at 75 C. (167 Fahr.) ; but it would be 

 better to boil the milk in cases where the presence 

 of tubercle bacilli is suspected. 



Cholera Bacillus. That milk may be the means of 

 spreading cholera has been proved beyond doubt in 

 several cases. The cholera bacillus (see Fig. 13, p. 77) 

 is not, however, capable of living so long in milk as that 

 of tuberculosis. In ordinary milk, indeed, it seems 

 to be killed in the course of twenty -four hours ; in 

 boiled milk, however, it is capable of multiplying 

 abundantly. The reason of this is to be found in 

 the fact that in unboiled milk the lactic acid formed 

 by the numerous lactic bacteria present exercises a 

 speedily fatal effect on the cholera bacilli ; in boiled 

 milk, on the other hand, the conditions are more 

 favourable, since the lactic ferments have been killed 

 by the process of boiling. In butter, it would seem 



