CHAPTER XX 



ON THE PRESENCE OF PATHOGENIC BACTERIA IN BUTTER AND 



CHEESE 



THE utilisation of milk, which is infected witn pathogenic germs, 

 for the purpose of manufacturing butter or cheese has perhaps 

 hardly received the attention which it deserves. There is abundant 

 evidence to show that cream contains a very large percentage of 

 the total bacteria which are present in milk, as the organisms 

 rise to the surface with the cream. This has been shown by 

 Anderson, who in the course of numerous experiments showed 

 that the cream contained many times more bacteria per c.c. than 

 did the rest of the fluid. In one case the figure was 500 times as 

 great for the bacterial content of the cream as for that of the milk 

 below it. It will be sufficient to quote one set of the figures 

 obtained by him : 



Gravity Method: Centrifuged Milk. 



Cream . . . . 68,690,000 96,690,000 



Sediment .... 4,840,000 18,840,000 



Whole milk .... 14,388,000 



These figures demonstrate forcibly the high bacterial content 

 of cream whether obtained by gravity or by centrifugalising. The 

 effect of centrifugalising is to send more bacteria up into the cream ; 

 only a small percentage of the total number are found in the 

 sediment. 



Niederstadt, as quoted by Anderson, has found 75 per cent, 

 of all the bacteria present in the cream. 1 



Considerable evidence has already been given in the preceding 

 pages upon this well-known point. 



Butter. Evidently butter is likely to contain more bacteria than 

 fresh milk when made from fresh cream. If the cream is allowed to 

 go sour before utilising, it may reasonably be supposed that certain 

 strains of bacteria will die out, leaving others in possession of the 



1 Cp. also Scheurlen and others. 



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