264 APPLIED BACTERIOLOGY 



is one of simple decomposition, one molecule of milk-sugar 

 (lactose) becoming converted into four molecules of lactic 

 acid, which latter coagulates the milk by precipitating the 

 albuminoids. This change is shown by the following 

 equation : 



CiAAi+H20 = 4C3H60, 



Lactose. Lactic acid. 



The fermentation ceases after a certain amount of lactic 

 acid has been formed, but it will recommence, however, if 

 the liquid be neutralised with carbonate of lime. 



The Bacillus acidi lactici consists of short, somewhat 

 thick non-motile bacilli 1 to 1'7 fj' long by about 0"3 to 0*4 /i 

 broad, generally occurring in pairs and in strings of 

 4 elements. The bacilli form spores, each situated at one 

 extremity of the bacillus. On the surface of gelatine, in 

 ' streak ' cultures, a thin delicate growth is formed along 

 the whole tract of the needle. The gelatine is not liquefied. 



The Bacillus acidi lactici sets up the lactic fermentation in 

 solutions of milk-sugar, cane-sugar, dextrose and mannite. 

 In the case of the first two sugars, the ferment appears to 

 first exert an ' inverting ' action, whereby one molecule of 

 these two sugars is respectively converted into two mole- 

 cules of dextrose or glucose, which in turn is broken up 

 by the action of the ferment into two molecules of lactic 

 acid. These changes are shown by the two following equa- 

 tions : 



(a) Ci2H2Ai + H20 = 2CeHiA- 

 Milk-sugar. Dextrose. 



(b) C6HiA = 2C3HA 

 Dextrose. Lactic acid. 



The most favourable temperature for the fermentation 

 appears to be from 35° to 42° C, while at 45° C. it ceases. 



4. Fermentation by Reduction.- — It is to this class that the 

 various butyric acid ferments belong, which are the cause 



