114 MODIFIED MILK AND MILK PRODUCTS 



succumb to acute infections when inoculated with cream than 

 when inoculated with the sediment of whole milk. In examina- 

 tions of milk samples for pathogenic bacteria, such as B. diph- 

 theriae, B. tuberculosis, etc., the examination of the cream should 

 never be neglected, while it follows that market-cream itself 

 should be more often examined than is the case. 



Anderson 1 gives the following figures as to the number of 

 bacteria in cream. In 26 samples of milk the average number 

 of bacteria in the sediment and in the cream layer obtained 

 from gravity and centrifugally raised cream was 



. J cream layer 68,690,000 bacteria. 



Gravity raised j sediment layer ^^ ^ 



f cream layer 06,840,000 



Centnfugahsed | ^.^ layer 18,840,000 \\ 



Whole milk ... 14,388,000 



In Washington, U.S.A. 2 , the examination of 130 samples of 

 cream between February and July, 1907, showed that while all 

 showed over 10,000 organisms per c.c. only three contained less 

 than 50,000, while 10 per cent, contained between 10 and 

 25 million bacteria per c.c. The average for all the samples 

 was 12,130,000 bacteria per c.c. 



The bacterial content of cream varies enormously with its age. 

 Quite fresh centrifugalised cream usually has a bacterial content 

 lower than that of the milk from which it is obtained. Ac- 

 cording to Swithinbank and Newman the result of centrifugalising 

 milk is that roughly 60 per cent, of the organisms will be found 

 in the sediment, 25 per cent, in the separated milk, and 

 15 per cent, in the separated cream. Subsequently, however, 

 on keeping the bacteria multiply enormously, cream being a 

 good nutrient medium. The Commission on Milk Standards 

 appointed by the New York Milk Committee recommended as 

 a standard for cream that it should not contain more than 

 300,000 bacteria per c.c. 



Cream can be bacteriologically examined by methods similar 

 to those used for milk, the cream being diluted with sterile 

 water. For examination for tubercle bacilli the cream itself 



1 Bulletin 56 Washington Treasury DcJ>arttttent y 1909, p. 739. 

 a Ibid. p. 259. 



