BACILLUS BUTYEICUS (PRAZMOWSKI). 369 



t'ered with when considerable quantities of that gas are 

 present. The spore formation and the sprouting of the 

 spores appears also to occur only when oxygen is 

 absent. Hence it differs markedly in its physiological 

 characters from the bacillus subtilis, which in other 

 respects resembles it. Further, the spores of bacillus 

 butyricus do not show the same resisting power as the 

 spores of bacillus subtilis. The boiling temperature 

 continued for five minutes is sufficient to kill them. 



Intense fermentation can be readily set up by the Conditions of 

 bacillus butyricus. In solutions containing starch, dex- e 

 trine, sugar, or lactates, a considerable quantity of butyric 

 acid is formed in the course of a few days as the result 

 of the action of the bacillus butyricus, carbonic acid 

 and hydrogen being at the same time given off. The 

 vessels containing the nutrient solutions in which these 

 fermentation experiments are made should be kept 

 hermetically sealed, and freed as far as possible from 

 air before the bacilli are introduced ; the high pressure 

 which the accumulated gases exert after a short time 

 does not at all interfere with the development of the 

 bacillus and the progress of the fermentation. The 

 same bacillus is the cause of the butyric acid fermenta- 

 tion which occurs in old milk, and in the ripening of 

 cheese. In the case of milk this fermentation com- 

 mences after the active growth of the lactic acid bacteria 

 has converted a large portion of the milk sugar into 

 lactic acid, either because the necessary removal of the 

 oxygen is accomplished by the previous development of 

 the aerobic lactic bacilli, or because the milk sugar is 

 dehydrated by the lactic bacilli and thus converted into 

 good fermentescible material. The best temperature for 

 the fermentation is between 35 and 40 C. Just as 

 in the lactic fermentation so here we must add chalk 

 to the fermenting mixture in order to prevent the dis- 

 turbing effect on the bacillus of the accumulation of 

 acid. According to Fitz the bacilli are also able to 

 dissolve casein slowly, but not to cause the direct 

 fermentation of sterilised milk, or its coagulation, 

 because they are not able to break up milk sugar. 



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