OP ARTS AND SCIENCES. 



Ill 



I have experimented with our North American ferment and find 

 the facts to be these: (1.) It causes alcoholic fermentation of milk- 

 sugar or lactose, Ci2H220n. (2.) It causes fermentation of dextrose, 

 CsHioOg. (3.) It does not cause fermentation of saccharose or cane- 

 sugar, which has the same empirical formula as lactose. In addition to 

 these three facts it is also known, as Ilueppe has shown, (1) that the 

 Bacillus of lactic fermentation causes to some extent the inversion of 

 milk-sugar; (2) that lactic acid, according to Hammarsten, by stand- 

 ing with milk-sugar inverts it to dextrose and galactose just as does 

 any mineral acid ; (3) that the Bacillus of lactic fermentation acts 

 further on the galactose, CeHjaOe, convening it into two molecules of 

 lactic acid, CsHgOs. 



From these data it seems evident that alcoholic fermentation of 

 milk takes place in the followiug manner. The Bacillus acidilactis 

 begins the process by forming some lactic acid, which in turn, assisted 

 by the Bacillus itself, inverts the milk-sugar to galactose and dextrose. 

 The galactose is further acted upon by Bacillus acidi-lactis and con- 

 verted into lactic acid ; the dextrose is acted upon by the yeast, and 

 converted into alcohol and carbonic acid gas. In the kephir drink, 

 therefore, we should find plenty of lactic acid, a little milk-sugar, not 

 inverted, the amount depending upon the duration of fermentation, 

 some alcohol, and carbonic acid gas, — precisely what is found. 



One vital objection may, however, still be urged against this theory. 

 If it be true, as I have said, that the Bacillus acidi-lactis to some 

 extent, and the lactic acid to a greater extent, cause the inversion of 

 milk-sugar, then should not ordinary beer yeast, SaccJiaromyces cere- 

 visice, Meyen, cause alcoholic fermentation in sour milk, since the 

 milk-sugar, according to the theory, must be here inverted to fermenta- 

 ble dextrose and to galactose ? It should cause such fermentation ; 

 and if it does, the theory is confirmed. Upon experiment, I found that 

 ordinary beer yeast when added to sour milk or to milk on the point 

 of souring did cause fermentation, much carbonic acid gas being elimi- 

 nated and some alcohol formed ; sweet milk, however, did not ferment 

 with beer yeast. 



It will be observed that I have given no function to the Bacteria of 

 the kephir granules. The very fact that they remain almost wholly 

 in the Zoogloea masses during fermentation, comparatively few going 

 out into the milk, seems to indicate that they have little to do with 

 this alcoholic fermentation ; and this is made still more probable by 

 the additional fact that, though absent in the fermentation of sour milk 

 by beer yeast, still fermentation ensues. 



