134 BACTERIOLOGY. 



the milk alkaline and bitter. The bacterial 

 species concerned in this matter, and which be- 

 long in great part to the general group of hay 

 or potato bacilli, were later studied by LofHer, 

 Weigmann, Kriiger and Fliigge. Fliigge and 

 I together ascertained that some of these bac- 

 teria could form not only bitter substances 

 but also proteid-like poisons. Milk usually 

 becomes bitter because of the formation of pep- 

 tones ; according to von Freudenreich, how- 

 ever, certain bacteria may form other bitter 

 substances. 



Important work was done upon the lactic 

 acid fermentation by my pupils, Scholl and 

 Grotenfelt, and later by Weigmann, Kriiger, 

 Conn and Kaiser ; Grotenfelt first, Weigmann 

 later and more accurately, have established the 

 fact that some of the germs which form lactic 

 acid in milk and in various sugar solutions, 

 produce a fine, aromatic odor. 1 I had already 

 in 1889 maintained before the German dairy 

 association that dairymen ought to make use 

 of pure cultures of such bacteria to bring 

 about the souring of pasteurized cream in 

 all places where butter is made out of sour 

 cream (as is the case universally north of the 

 Main and in Scandinavia). Grotenfelt has in- 



1 Cf. Weigmann, Zum Butteraroma. Centralbl. f. Bakt., Abth. II., 

 III., p. 497- 



