120 Dairy Bacteriology. 



use of this method for the purification of infected milk. 

 Coupled with this peculiar relation of the tubercle germ 

 to centrifuge slime, is the fact that tuberculosis among 

 swine is much more prevalent in Denmark and North 

 Germany where the centrifugal process in creaming is 

 extensively used, and where, until recently, the swine were 

 fed the uncooked separator slime. Ostertag 1 has pointed 

 out this condition, and has drawn attention to the nu- 

 merous cases of intestinal tuberculosis in hogs. 



116. Bacterial changes in cream. Although cream 

 is numerically much richer in bacteria than milk, yet the 

 changes due to bacterial action are so much slower that 

 the latter product usually spoils sooner than cream. For 

 this reason, cream will sour sooner when it remains on 

 the milk than it will if it is separated as soon as possible. 

 This fact indicates the necessity of early creaming, so as 

 to increase the keeping quality of the product, and is an- 

 other argument in favor of the separator process. 



117. Bacteria in different creaming' methods. The 

 method used in creaming has an important bearing on 

 the kind as well as the number of the bacteria that are 

 to be found in the cream. The difference in species is 

 largely determined by the difference in ripening tempera- 

 ture, while the varying number is governed more by the 

 age of the milk. 



1. Primitive gravity methods. In the old shallow pan 

 process, the temperature of the milk is relatively high, 

 as the milk is allowed to cool naturally. This compara- 

 tively high temperature favors especially the develop- 

 ment of those forms whose optimum growing-point is 

 near the air temperature. By this method the cream 

 layer is exposed to the air for a longer time than any 



1 Ostertag, Milch Ztg., 22: 672. 



