570 MANUAL OF MILK PRODUCTS 



incorporated in butter and that they may retain their vitality 

 for some time. These authors draw the following conclusions 

 from the results of their investigations : 



"The work recorded in our investigation, as well as that by 

 contemporaneous writers, proves that constant storage in an 

 icy temperature does not destroy the virulence of butter which 

 contains dangerous tubercle bacilli. It should therefore be evi- 

 dent to all that the most satisfactory way of obviating this 

 danger would be to manufacture butter only from cream that 

 is free from tubercle bacilli. The application of the tuberculin 

 test to all cows that supply milk for butter-making purposes, 

 with the subsequent removal of all tuberculous animals from 

 these dairy herds, is desirable, but where this cannot be done 

 recourse may be had to pasteurization, as it has been found 

 that subjecting cream to a temperature of 140 F. (60 C.) for 

 a period of twenty minutes, or of 176 F. (80 C.) momentarily, 

 will effectually destroy all of the tubercle bacilli that may have 

 found lodgment in it. Moreover, the manufacture of butter 

 out of pasteurized cream has other advantages, as set forth in 

 Bureau of Animal Industry Circular 146. 



"No dependence should be placed on the action of the salt 

 that is added to butter as an agent in the destruction of tubercle 

 bacilli. It has been shown that the effect of salt as commonly 

 used in the manufacture of butter is very slight at best. Most 

 of the samples of butter used in the present experiments were 

 salted with the usual amount, yet the butter retained its viru- 

 lence for six months, as already noted/' 



As a safeguard against the transmission of disease through 

 butter, it is the common practice in creameries at the present 

 time thoroughly to pasteurize the cream from which butter is 

 made. This practice serves not only as a protection against 

 the transmission of disease, but at the same time gives butter 

 of more uniform quality. 



