BEHAVIOUR OF BACTERIA IN MILK 



53 



of the number of bacteria present. In one sample at 37 0. 

 the milk curdled with only 8,000,000 per c.c., while in others 

 there have been found 4,000,000,000 per c.c., without any- 

 curdling. These differences are due partly to the development 

 of enzymes, and partly to the products of some species neutral- 

 ising the actions of others. The amount of acid present at 

 the time of ordinary acid curdling does not widely vary. 



(10) Milk is not necessarily wholesome because it is 

 sweet, especially if it has been kept at low temperatures. At 

 the temperature of an ice-chest milk may remain sweet for 

 a long time, and yet contain enormous numbers of bacteria, 

 among which are species more likely to be unwholesome than 

 those that develop at 20 C. "From this standpoint the 

 suggestion arises that instances of ice-cream poisoning are 

 perhaps due to the preservation of cream for several days 

 at a low temperature, such treatment keeping the milk sweet, 

 but favouring the development of species of bacteria that are, 

 at higher temperatures, checked by the lactic organisms." 



The difficulty of laying down standards of the number of 

 bacteria, or of special kinds, such as R coli, to allow in vended 

 milk, is discussed in Chapter XIV. In this connection the 

 importance of studying the rate of multiplication in milk 

 of organisms, and particularly of standard organisms, is 

 obvious; 



Bacillus coli communis and its allies multiply rapidly in 

 milk. The following table illustrates its multiplication in 

 pasteurised milk kept at different temperatures. The milk 

 was heated to 80 C. for 10 minutes, and care was taken to 

 add only a few B. coli. 



All results are per standard platinum loopful. 



