120 MICRO-ORGANISMS AND FERMENTATION. 



Lafar isolated from the sour yeast mash a species which he 

 named Bac, acidificans longissimus, and since 1894 it has been 

 applied in practice for souring the yeast " goods." It ferments 

 saccharose, galactose, dextrose, laevulose, and maltose, but 

 not lactose, and it occurs both in short rods and in very long 

 threads. A short time afterwards, Leichmann described a 

 bacterium occurring under similar conditions, Bac. Delbriicki, 

 which is believed to be identical with Lafar 's species. It 

 shows great resemblance to Leichmann's Bact. lactis acidi, and 

 both species produce laevo-lactic acid. It cannot, however, 

 like the latter, ferment lactose. In a lactose broth it produces 

 no acid, and grows with difficulty, whereas in grape-sugar 

 broth or maltose broth, as weh 1 as in sweet wort, it grows 

 vigorously. According to Henneberg this species has its 

 optimum for acid production at 46-47 C. In the mash it 

 forms up to 1-79 per cent, of lactic acid. The amount of acid 

 is reduced with free access of air. Its optimum for growth 

 lies between 40-48 C. In the mash,' it occurs with both 

 short and long cells, single or grouped two and three together. 

 On solid substrata it forms small, flat, clear colonies. 



Henneberg has isolated a number of other species of lactic 

 acid organisms from mash and pressed yeast, which he has 

 described as " wild," some of which may produce direct 

 damage in the industry, if care is not taken to secure a vigorous 

 yeast fermentation, for they not only carry on the production 

 of acid throughout the fermentation, but form at the same 

 time volatile acids, especially acetic acid, which damages the 

 yeast and reduces the output of alcohol. Other members of 

 this group appear to be harmless. 



All the species examined grow and produce acid in presence 

 of yeast at 27'5-30 C. Amongst the dangerous kinds may 

 be named Bac. Hayducki, which occurs in mash in small short 

 cells, mostly single, and forms round white colonies on gelatine 

 (its optimum for acidification is first at 45-46 C. : later at 

 33-35 C.), and Bac. Buchneri, with similar cells in the mash 

 and white or yeUowish colonies on gelatine (optimum for 

 acidification first 39-40, and afterwards 23-30 C.). 



There appears to be no doubt that the lactic organisms 

 occurring in the mash have a tendency to variation, and that 



