PART III. 



RELATION OF BACTERIA TO MILK 

 PRODUCTS. 



CHAPTER VIII. 



BACTERIA IN CREAM AND FACTORY 

 BY-PRODUCTS. 



114. Bacteria in cream due to mechanical causes. 



Cream whether secured by the gravity process or by a 

 cream separator is invariably richer in bacteria than the 

 skim-milk of the same age. A sample of milk might 

 contain less than 100,000 germs per cc. in the skimmed 

 part, while the bacterial contents of the cream layer in 

 the same would be several millions for the same 

 unit of volume. This is largely due to the filtering 

 out of the microbes during the process ' of cream- 

 ing. It is a well-known fact in sewage filtration that 

 the addition of some chemical that will cause the pre- 

 cipitation of certain organic elements always present in the 

 sewage, will take out the majority of bacteria in the set- 

 tling of thispercipitate. The same principle seems to be 

 operative in the process of creaming, except that the 

 fat globules instead of sinking to the bottom rise to the 

 surface. Gravity-raised cream is usually richer in bac- 

 teria than separator cream, because it is materially older 

 when gathered. 



In full milk separated by the centrifugal method, there 

 are three well-marked products, the skim-milk, the 

 cream, and the slime that adheres to the separator bowl. 



[118] 



