78 PRACTICAL DAIRY BACTERIOLOGY 



so slowly indeed that for several days there is practically no 

 increase in numbers. But even if milk is kept only one or two 

 degrees above freezing, the bacteria will increase, and will in 

 the course of time in two or three weeks be found to be 

 extremely abundant. It is important to note that the bacteria 

 which are found at these low temperatures do not produce the 

 ordinary changes in milk. The milk does not sour or curdle 

 and, as a rule, there is no visible sign in such milk that the 

 bacteria have become abundant. Such milk may have a some- 

 what oldish taste, but, as it is neither sour nor curdled, would 

 usually be pronounced sweet and would naturally be used with 

 perfect freedom. The milk, however, may contain bacteria in 

 great numbers, and may become harmful because of them. 



At 40. If the milk is warmed to about 40, nearly the same 

 statement can be made, excepting that the bacteria tend to grow 

 a trifle faster and will become abundant somewhat earlier. 

 It cannot be emphasized too strongly that milk or cream re- 

 tained at these low temperatures, while it will remain sweet 

 for many days, and even for some weeks, cannot after the first 

 few days be looked upon as wholesome, since the bacteria have 

 been growing, even though slowly, and may be present in 

 enormous numbers. It may be possible that some cases of milk 

 poisoning, especially such as come from ice cream, may be 

 attributed to this cause. (See page 109.) The emphatic lesson 

 to be drawn is that no normal milk that has been kept for many 

 days is safe, even though it still remains sweet. 



At 50. If the temperature "is raised to 50, the bacteria 

 develop more rapidly, although very much more slowly than at 

 higher temperatures. At this temperature the species which 

 grow are commonly not lactic bacteria, but a large variety of 

 miscellaneous forms. This is a matter of some importance, 

 since while lactic bacteria are harmless and in some respects 

 useful, the miscellaneous types which develop at 50, though 

 many of them are harmless, are more likely to contain species 



