LACTIC ACID FERMENTATION 105 



ditions under which the ferment acts are very similar to those we 

 have already considered (see also p. 196). There is frequently car- 

 bonic acid gas formed ; there is a cessation of fermentation when the 

 medium becomes too acid ; there is the same method of starting the 

 process by inoculation of milk or cheese or any such substance with 

 the specific bacillus. It is probable that such inoculated matter will 

 contain a mixture of micro-organisms, but if the lactic bacillus is 

 present, it will grow so vigorously and abundantly that the fermen- 

 tation will be readily set up.* 



In 1877 Lister was able, by means of the " dilution method," to 

 isolate from sour milk, in a form of pure culture, an organism to 

 which he gave the name B. lactis, and which he believed gained 

 access to milk from the air of dairies and similar places.f For some 

 time this organism was held to be causally related to lactic 

 fermentation. But in 1884, by means of culture on solid media, as 

 introduced by Koch, Hueppe was able to isolate a bacillus which he 

 named the Bacillus acidi lactici. This was probably identical with 

 Lister's bacillus, and is now a term used to cover a whole family of 

 organisms having somewhat similar characters, and possessing the 

 property of setting up lactic fermentation.^ In 1894 Giinther and 

 Thierfelder published the result of .their work on lactic acid 

 fermentation, from which they concluded that Lister and Hueppe 

 had discovered one and the same species, and that it was the causal 

 agent of lactic acid production in Europe. Esten found a similar 

 organism to be the cause of lactic acid fermentation in America, and 

 Conn holds that three organisms, or rather types of species, are the 

 chief agents in the production of lactic fermentation, namely B. acidi 

 lactici, Nos. L and ii., and B. lactis ccrogenes. The first named forms 

 between 75 to 90 per cent, of the bacteria present. No. ii. is also 

 very abundant. B. lactis cerogenes is found almost universally, 

 although never in large numbers. It is a type of a species which 

 produces intense acid on litmus gelatine cultures, produces much 

 gas in milk or milk-sugar broth, curdles milk at high temperatures, 

 and produces a distinctive odour in the milk, which it ferments. 

 According to Escherich, the formation of lactic acid by this 

 organism prevents fermentation in the stomach and intestines. 



It was Hueppe who made the important discovery that many 



* For full discussion of the subject of lactic fermentation of milk, see Bacteriology 

 of Milk, 1903 (Swithinbank and Newman), pp. 149-159. 



t Trans, of Path. Soc., 1878, p. 437. 



I Hueppe isolated five forms of his lactic acid bacillus, and Fliigge described 

 eleven forms. Maddox, Beyer, Fokker, Krueger, Grotenfeld, and other workers 

 isolated lactic acid organisms. 



Storr's Agricultural Expt. Sta. Rep., 1899, p. 22. Others than those named 

 are B. acidi lactici of Giinther, B. acidi lactici of Leichmann, Bacillus XIX. of 

 Adametz, Bacillus a. of Freudenreich, B. and M. acidi la^volactici of Leichmann, 

 Grotenfeld's B. acidi lactici (Nos. i. and ii.), No. 8 of Eckles, and B. casei. 



