THE EQUATION OF LACTIC FERMENTATION 173 



the carbonate of calcium, magnesium, or zinc. In the latter case, the highly 

 characteristic lustrous acicular crystals of zinc lactate ([C 3 H 5 3 ] 2 Zn + 3 aq.) are 

 obtained. 



A few quantitative experiments made by ADOLF MAYER (II.) show that 100 

 parts of fermented lactose produce 



83.9 parts of lactic acid 

 3.7 acetic acid 

 12.4 unknown substances. 



These results, however, were not obtained with pure cultures of lactic acid 

 bacteria, and therefore are not fully conclusive. 



Pure cultures of lactic ferments were first employed by E. KAYSER (I.) in 

 1894, in an investigation of fifteen different species of lactic acid bacteria isolated 

 from French milk, Belgian beer, Danish cream, wine-must, rye infusion, sauer- 

 kraut, &c. Confirming the results of Mayer and Baginsky, he showed that 

 volatile acids, also, are produced in the course of lactic fermentation, their 

 amount depending on the composition of the nutrient medium as well as on the 

 species of ferment. Thus, for example, a greater quantity of volatile acids was 

 produced from a milk qualified with peptone than from a peptonised maltose 

 solution. Cultures grown at the bottom of the nutrient liquid (" lactic bottom 

 fermentation ") yielded less than surface cultures. This fact had been already 

 recorded in 1889 by OPPENHEIMER (I.), who found the ratio of acetic acid 

 to lactic acid produced from milk fermented by Bacterium lactis acrogenes to be 

 as 85 : 15 ; and in the case of Bacterium coli commune as 70 : 30. This ratio is, 

 however, not invariable, but is chiefly determined by the amount of oxygen 

 present. Hence, in the absence of air, only small quantities of the volatile acids 

 are found, lactic acid being almost the only acid present. 



Attempts were made by G. KABRHEL (I. and II.) and H. TIMPE (I.) to 

 investigate the part played by casein and the phosphates in the lactic fermenta- 

 tion of milk. The optimum fermentation temperature is between 30 and 35 C., 

 and the operation proceeds much more actively when air is excluded. Kayser 

 was unable to detect any lactic enzyme excreted by the bacteria and capable of 

 converting lactose into lactic acid. 



In view of these results, it is hardly necessary to say that the establishment 

 of a satisfactory equation to represent the reactions occurring in lactic fermenta- 

 tion is highly improbable. 



