Kansas Academy of Science. 61 



THE INFLUENCE OF THE SEPARATOR UPON DISTRI 

 BUTION OF BACTERIA IN MILK AND CREAM. 



L. D. BisiixKLL and O. W. Hunter. 

 INTRODUCTION. 



IT IS a common practice to clarify milk by passing it through 

 some kind of a centrifugal machine. The rapid rotation 

 throws out most solid filth and many of the bacteria. There 

 are at present several special machines for this purpose on the 

 market. Some concerns consider that clarification aids the 

 keeping quality by reducing the number of bacteria, and some 

 milk producers think that clarification may replace pasteuri- 

 zation. If this is true the installation of these machines would 

 be of value. However, special machines add to the expense of 

 production, and we have received several inquiries as to the 

 use of the separator for this purpose. 



Beside the practical bearing of this problem upon the keep- 

 ing quality of milk, a few authors have studied it in its relation 

 to the modification of milk for infant feeding. In the latter 

 case it is a common practice to make a modified milk by adding 

 a certain percent of cream to skim milk. It is important, 

 therefore, to obtain a skim milk or a cream low^ in bacterial 

 content. 



The results of Wilckens (1894), Anderson (1909), Stocking 

 (1911), and Roadhouse (1914), indicate that when milk was 

 separated, a larger percentage of microorganisms was found 

 in the cream as compared with skim milk. On the other hand, 

 Heinemann, Luckhardt and Hicks (1910), Swinthinbank and 

 Newman (1903), Heinemann and Class (1911) assert that the 

 separated milk contained a higher bacterial content than the 

 cream. Swinthinbank and Newman estimated that 60 percent 

 of the bacteria is thrown into the slime, 25 percent in the skim 

 milk and 15 percent in the cream. Wilckens states that the 

 centrif uged milk contains fewer bacteria than the original milk, 

 and that this decrease is accounted for by the death of the cells, 

 due to rotation. Heinemann, Luckhardt and Hicks and Road- 

 house assert that the bacterial content was higher in the mixed 

 separated milk than in the original milk. Heinemann and 

 Class, after investigating the relation of cream to the bacterial 



