36G 



BACILLI WHICH CAUSE FERMENTATION. 



Kennet-like 



spondingly larger amount of oxygen present. The 

 optimum of temperature lies between 35 and 42 C. ; 



Inoculation on at 45'4 C. fermentation ceases. If a small portion of a 

 pure cultivation is introduced into milk, previously 

 sterilised at 100 C., the latter becomes uniformly 

 gelatinous in 15 to 24 hours at the body temperature. 

 Here and there small spaces are visible in the coagulum, 

 containing bubbles of carbonic acid. At a later period 

 the coagulum contracts somewhat, and clear serum 

 collects around it. The coagulum does not become 

 peptonised subsequently. 



Dehydrating- It appears that the lactic acid bacilli dehydrate the 

 milk and cane sugar before they cause their fermenta- 

 tion. They are also able to convert starch into sugar 

 in the same manner as a diastatic ferment. (See under 

 "Ferments.") 



It must be borne in mind that the casein of milk is 

 not only coagulated by lactic acid, but also by rennet- 



by bacteria, like ferments, and that, as Duclaux first showed, a 

 number of bacteria are able to furnish these ferments, 

 and thus without the formation of lactic acid to coagu- 

 late the casein ; the reaction of the material is am- 

 photeric, that is to say, slightly acid, and slightly 

 alkaline. This property occurs, for example, in the 

 bacillus butyricus, in the so-called potato bacillus to be 

 described below, in sarcina lutea, in a large coccus 

 cultivated by Hueppe from water, and causing liquefac- 

 tion of the gelatine, and probably also in many other 

 bacteria. The same bacteria frequently exert a subse- 

 quent peptonising action on the coagulated casein. 



Bacillus butyricus. 

 (Clostridiiun butyricum, Bacillus amylobactcr.) 



In the case of the butyric acid fermentation we must 

 probably also come to the same conclusion as in that of 

 the lactic acid fermentation, viz., that several kinds of 

 bacteria can cause this fermentation of carbo-hydrates, 

 and this without reckoning those bacteria which form 

 butyric acid from other materials (for example, the 



Butyric acid 

 bacillus. 



