TREATMENT OF CREAM PREVIOUS TO THE CHURNING. 207 



tubercle bacilli as well as other infectious bacteria that may 

 be found in it. According to Bang's investigations the 

 tubercle bacilli in milk are killed by heating to 176-185 

 F. (80-S5 0.).* This occurred if the milk was only 

 heated up to the last temperature given, and not kept at 

 this temperature for any length of time. A temperature 

 of 144 F. (62 C.) made the infected milk greatly less 

 dangerous, and at 162 F. (72 C.) it generally grew en- 

 tirely harmless. This matter is of importance, for Gas- 

 perini has directly proved that the butter can contribute 

 to the spreading of tuberculosis. Even 122 days after the 

 milk was infected with tubercle bacilli the butter made 

 from it contained virulent bacilli which killed animals in- 

 oculated with it. 



Lafar also found that spores of typhus, cholera, and 

 tubercle bacilli would retain their vitality for a sufficiently 

 long time in butter to carry these diseases to living beings. 



Sour-cream Butter. In the manufacture of sour-cream 

 butter, other methods than those given must be followed 

 in severa-l respects. It is here necessary that a lactic-acid 

 fermentation shall have taken place in the cream. 



As is well known, there are two different kinds of sour- 

 cream butter in the market, viz., farm (or dairy) butter 

 and creamery butter. In case of the former kind the 

 lactic-acid fermentation has usually taken place slowly 

 during the creaming in shallow wooden pans, while in the 

 manufacture of the latter kind all fermentations were 

 checked by cooling during the cream separation, and a 

 comparatively rapid lactic-acid fermentation was started in 

 the cream after the skimming. The lactic-acid fermenta- 



* See foot-note on page 158. 



