226 GENERAL CHARACTERISTICS. 



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

 show that one hundred 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, sauerkraut, &c. Con- 

 firming the results of Mayer and Baginsky, he showed that 

 volatile acids, also, are produced in the course of lactic fermenta- 

 tion, 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 aerogenes to be as 85 : 1 5 ; 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 phos- 

 phates in the lactic fermentation of milk. The optimum fermenta- 

 tion 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 fermentation is highly improbable. 



