THE BACTERIA OF SOIL, AIR, WATER, ETC. 1 57 



lactic bacteria survived pasteurization and multiplied rapidly 

 after 24 hours, completely inhibiting the peptonizing bacteria. 



" Milk held at 10° C. (50° F.).— In unheated milk the growth 

 of bacteria and the consequent curdling of the milk was much 

 retarded. The average milk did not contain sufficient acid to 

 affect the taste until it was over 48 hours old. The propor- 

 tion of peptonizing to lactic bacteria was greater than at the 

 higher temperature and the taste of the milk occasionally 

 showed the influence of the former. 



"In the pasteurized milk the bacteria increased very slowly, 

 and in nearly every case the milk was unchanged in taste and 

 appearance 96 hours after pasteurization. In only two of 

 fourteen cases was there a marked increase of peptonizing 

 bacteria. The predominating bacteria were species having 

 little or no effect on milk. 



"The lactic bacteria inhibited the development of the 

 peptonizing bacteria only when they had developed sufficient 

 acid to render the milk unfit for use. 



"It seems probable that the acid had a distinct inhibitory 

 action on the proteolytic enzymes of the peptonizing bacteria. 



"If milk could be pasteurized commerically in such a way 

 that the bacteria would be reduced to a few hundred per cubic 

 centimeter and held at a low temperature until used, it would 

 be perfectly safe for 48 hours or even 72 hours. Under these 

 circumstances it would probably be in better condition after 

 this long period than ordinary city milk at the time it is delivered. 

 How closely these conditions could be approximated commer- 

 cially is another question." 



Since the publication of the above bulletin, it has been 

 demonstrated in some dairy plants th°at such conditions can 

 be brought about upon a commercially profitable scale, and 

 it would seem justifiable on the part of health authorities to 

 demand that milk dealers comply, or that the municipal 

 authorities should establish pasteurizing plants. 



