THE BACTERIA IN DIFFERENT MEDIA. 145 



The most suitable temperature seems to be 35° 

 (95° Pah.). 



We know but little about this fermentation. 

 " It merits, however, to be better studied. It 

 is this which causes the spontaneous coagulation 

 of milk: sugar of milk is transformed into lactic 

 acid, which coagulates the caseine. We often see it 

 occur in beef juice or in sour starch water; it must 

 play a part in the formation of sour krout, and 

 intervenes very certainly, and perhaps more than 

 the alcoholic fermentation, in the preparation of 

 bread. Finally, it very easily invades beer, which 

 of our domestic drinks is most exposed, because of 

 its slight acidity, to become the seat of this fer- 

 mentation. All of these facts render it interest- 

 ing, so much the more as it is rarely exempt from 

 complication, and is frequently accompanied, for 

 example, by a commencement of butyric fermenta- 

 tion, far more disagreeable in its products " (Du- 

 claux). 



2. Butyric Fermentation. — This is, in fact, al- 

 ways preceded by a lactic transformation, and it is 

 by an ulterior modification that the lactic acid 

 produces the butyric acid. The organism which 

 accompanies it is a bacterium very nearly allied 

 to Bacillus subtilis, Cohn. 



The reaction represented by the phenomena, 

 from a chemical point of view, is the follow- 

 ing:— 



2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 + H 4 . 



lactic ac. butyric ac. 



