THE KINDS OF MICRO-ORGANISMS IN MILK 347 



enes. From this time on many varieties of lactic acid bacteria 

 have been described, but inasmuch as bacteriologic technic was 

 not sufficiently developed, it is sometimes difficult to realize to 

 which group of organisms the lactic acid bacteria reported by some 

 authors belong. Those described by Clauss, Grotenfelt, Schard- 

 inger, Kozai, and Utz probably are identical with Htippe's Bacil- 

 lus acidi lactici or B. aerogenes. In this country Conn also found 

 an organism that he identified as Htippe's Bacillus acidi lactici, 

 but stated that it was present only exceptionally in sour milk. 

 They all grow luxuriantly on laboratory media; dextrose and 

 lactose are fermented, with the formation of acid and gas; milk 

 is coagulated more or less rapidly and the curd contracts with 

 the liberation of whey. The colonies on agar or gelatin are large, 

 moist, and frequently viscid. These organisms are found chiefly 

 in surface layers of milk. 



Lactic acid bacteria have also been described by Leichmann, 

 Gtinther and Thierfelder, Kozai, Utz, Esten, Schierbeck, and 

 others. These were not distinctly separated from the type de- 

 scribed by Htippe, although Leichmann insisted that his organ- 

 ism was not the same. Later he became convinced that he had 

 discovered an organism wholly different from Hiippe's bacillus, 

 and gave it the appellation Bacterium lactis acidi. While Htippe's 

 organism was the bacillus of lactic acid, Leichmann's was the bac- 

 terium of sour milk. The appellations are so similar that much 

 confusion has resulted, and even in modern publications the two 

 organisms are sometimes hopelessly confused. Gtinther and 

 Thierfelder went so far as to clearly identify their organism with 

 Htippe's, although some properties, according to their own de- 

 scription, were so entirely different that the identification was 

 wholly unjustified. 



Some sort of system was brought out of the confusion by Kruse 

 in 19C3. This author studied the literature and, without experi- 

 mental evidence, separated the lactic acid bacteria previously de- 

 scribed into two groups, namely, the Bacillus aerogenes group 

 with Htippe's B. acidi lactici as chief representative, and the Strep- 

 tococcus lacticus group, with Bacterium lactis acidi of Leichmann 

 as the chief representative organism. Kruse proposed to sub- 

 stitute the name Streptococcus lacticus for this group in order to 

 avoid confusion with the previous one, and because he thought 

 that earlier descriptions warranted the assumption that Bac- 

 terium lactis acidi was really a streptococcus and not a bacillus. 

 Experimental evidence for the correctness of Kruse's view was 

 brought by his pupil Holling and the writer. 



It was shown that the lactic acid bacteria of the Bacillus 

 acidi lactici (Htippe) type when inoculated into sterile milk pro- 



