APPLICATIONS OF LACTIC ACID FERMENTATION 103 



which, on account of its high sugar content, is well adapted for 

 alcoholic fermentation, being capable of developing up to 3 per 

 cent, of alcohol. According to Rubinsky's investigations l a 

 yeast which ferments milk sugar and a rod bacterium which 

 produces over 1 per cent, of lactic acid are the organisms which 

 play the most important part in the production of Kumys. In 

 pure cultures the lactic acid rod does not grow under 23 C., but in 

 conjunction with the yeast it grows at the ordinary room tem- 

 perature. Kumys should, however, not be made at too low a 

 temperature. Kefir presents the greatest interest, for the so- 

 called Kefir grains, which resemble small cauliflowers (Fig. 62), 

 are produced by the symbiotic growth of the active organisms. 

 Sectional preparations (Fig. 63) show them to consist of a net- 

 work of small or large rods, in which yeast cells are enclosed. The 



FIG. 62. Kefir Grains, natural size. (After Kern.) Above, dried. Below, swollen. 



rods are chiefly Betabacterium caucasicum, a lactic acid bacterium 

 resembling that of Leben in its chief characteristics, while the 

 yeast also resembles that of Leben in fermenting saccharose and 

 maltose, but not lactose without the help of lactic acid bacteria. 

 Kefir grains generally also contain strongly acidifying Strepto- 

 bacteria. The Betabacteria are best found by inoculating into 

 yeast water, which is the only medium in which they thrive well. 

 In this symbiosis, the lactic acid bacteria appear to be more 

 dependent on the yeast than conversely. In good Kefir, only rod 

 bacteria and yeast will be found, and the former always collect 

 round the latter, showing a mutual attraction. Kefir grains 

 imported direct from the East exhibit vigorous growth, and have 

 often been regarded as a miraculous remedy for many ills. Grains 

 obtained from several European depots wers of quite a different 

 nature ; all of these contained a torula which fermented lactose 



1 " Studien uber den Kumiss," Inaugural Dissertation, Leipzig, 1910, 

 Verlag Gustav Fischer, Jena. 



