BACTERIA IN BUTTER 



347 



made sample has been found to contain from 15 to 30 

 or 40 millions or more. The number, however, always 

 decreases quickly on account of the want of aeration in 

 the interior and the poor food-supply, for pure fats are 

 not readily attacked by bacteria. 



Jensen gives the following table, which indicates the 

 decrease taking place in a marked sample of butter made 

 from ripened cream, and also the difference in number of 

 organisms on the surface and in the interior : 



The numbers which have been found in butter are many 

 and of various species. Some of them may be considered 

 as accidental impurities introduced from the air or water- 

 supply of the farm and dairy ; others are more or less 

 characteristic of most samples of butter, and come into it 

 from the milk or cream out of which it is manufactured. 

 Among the organisms usually present the following may 

 be mentioned : 



(a) Lactic acid organisms, especially Sir. lacticus and 



its allies. 

 (b} Bs. lactis aerogenes. 



