346 MILK 



bulgaricus, B. caucasicum, and B. casei of Freudenreich, B. del- 

 briicki of Leichmann, and others. 



4. Micrococcus pyogenes (Rosenbach): The members of this 

 group are staphylococci; they are Gram-positive, aerobic, Kquefy 

 gelatin; some coagulate milk, some do not; some have a tendency 

 to shme formation. Representatives of this group are: Micro- 

 coccus lactis acidi of Marpmann, M. acidi paralactici liquefaciens, 

 Halensis of Kozai, M. varians lactis of Conn, the acid-coagulating 

 micrococci of Gorini, and others. 



The third group of Lohnis' classification is in no maimer con- 

 cerned in the "normal" souring of milk, but includes bacteria 

 that are chief agents in producing a variety of fermented milk 

 products, such as are prepared in different parts of the world and 

 form important articles of food among a variety of peoples. 



The fourth group, in all probabUity, is also not concerned in 

 the "normal" souring of milk. However, they may not be entirely 

 indifferent in this fermentative process, since the liquefying micro- 

 cocci break up the proteins of milk and render them more suit- 

 able for absorption by the Streptococcus lacticus group. Inci- 

 dentally, members of this group produce some acid from lactose, 

 and may, therefore, contribute to a limited extent to the "normal" 

 souring of milk. 



On the whole, we must consider the first two groups of lactic 

 acid bacteria of Lohnis' classification as the common agents in 

 the fermentative process, usually called the "normal" souring of 

 milk. They are, therefore, the most important "lactic acid" 

 bacteria. 



Pasteur in 1858 was the first to describe an organism which 

 would simulate the souring process normally occurring in miUc 

 under ordinary conditions. His "levure lactique," according to 

 his description, is a variety of Bacillus aerogenes. He observed 

 "small globules or very short particles resembling certain kinds 

 of amorphous precipitates. They are constricted in the middle, 

 occur isolated or in irregular clusters. They ferment lactose with 

 acid and gas formation, and cultures are often viscid." In a 

 later publication Pasteur described the lactic acid bacteria as 

 short bacilli, sometimes joined in short chains, thus giving addi- 

 tional evidence of their identity with Bacillus aerogenes. Lister's 

 Bacterium lactis (1788) is now usually identified with Strepto- 

 coccus lacticus, although the description is too meager to permit 

 proper classification. An exhaustive study of a lactic acid bac- 

 terium was published by Htippe in 1884. He found it in large 

 numbers in all samples of milk examined, and it was considered 

 the lactic acid organism par excellence for some time. There is 

 little doubt that this Bacillus acidi lactici is a variety of B. aerog- 



