110 PROCEEDINGS OF THE AMERICAN ACADEMY 



mation of an enzyme which inverts milk-sugar is a general phenome- 

 non in Bacteria, and Hueppe has shown that it is probable in the case 

 of his Bacillus of lactic acid in particular." De Bary then concludes: > 

 " The inversion required in this case to enable the Saccharoraycete to 

 set up alcoholic fermentation is the work therefore of the Bacillus of 

 lactic acid, or of the Bacterium of the Zoogloea, or of both." 



But De Bary has since revoked this explanation. A. Levy of 

 Hagenau discovered that kephir may be made without any kephir 

 grains "simply by shaking the milk with sufficient violence while it is 

 turning sour. A trial convinced me," says De Bary, " of the correct- 

 ness of this statement. The kephir obtained by shaking was not per- 

 ceptibly different in taste or other qualities from the kephir of the 

 grains, and the determination of alcohol, kindly made for me by Pro- 

 fessor Schmiedeberg gave 1 per cent in some specimens of the former 

 kind and 0.4 per cent in one of the latter; sour milk not shaken con- 

 tained no trace of alcohol or only a doubtful one. Our former expla- 

 nation, therefore, must be abandoned, and there is no other ready at 

 present to take its place." 



Beyerinck has also proposed a theory to account for alcoholic fer- 

 mentation of milk. There are at present, he sa,ys, four yeasts which 

 are known to cause such fermentation: (1) that of Duclaux,* (2) that 

 of Adametz, called Saccharomyces lactis,^ (3) that of the kephir 

 called by Beyerinck Saccharomyces hefyr, and (4) Saccharomyces Ty- 

 rocola.% As a matter of fact there is one other which he overlooked, 

 Saccharomyces galacticola, described by Pirotta,§ of which I intend to 

 speak later. Beyerinck supposes that these yeasts secrete an enzyme 

 which he names lactase, since it inverts lactose or milk-sugar, and 

 which he declares to be in every way analogous with invertine. The 

 inverted milk-sugar is next acted upon by the yeast, carbonic acid gas 

 eliminated, and alcohol formed. Hence, if his supposition be true, 

 Saccharomyces kefyr should ferment sweet milk by first producing 

 its enzyme and then by acting upon the inverted product ; but it is 

 universally agreed by all who have written upon kephir that the lactic 

 acid fermentation must precede the alcoholic, or else the latter will 

 not take place. Beyerinck's theory therefore fails, in that it pays no 

 heed to the Bacteria of lactic fermentation. 



* Ann. d. I'lnst. Pasteur, 1887, I. 573. See Ibid.. 1889, III. 201. 



t Centralblatt. f. Bakt. u. Parasit., V. 116. 



\ Ibid , VI. 44. 



§ Pirotta et Rib. Studii eul Latte. Pavia, 1879. 



