230 MODERN DAIRY PRACTICE. 



sess the quality of producing lactic acid iu the milk ; they 

 are able to develop at temperatures above 52 F. (11 C.) 

 the optimum temperature as regards their power of fer- 

 mentation lying between 82 and 100 F. (28 and 38 C.). 

 The different bacteria show great differences, however, as 

 regards both their optimum temperature and the different 

 substances besides lactic acid which they produce in milk. 

 The majority of the lactic-acid bacteria are aerobic ; the 

 statements made in some text-books to the effect that these 

 organisms cannot give rise to regular fermentations in the 

 presence of air are therefore erroneous. The advantage of 

 stirring the cream during the ripening is apparent from this. 



If the sour milk or cream found in practice is exam- 

 ined bacteriologically, we usually find that several differ- 

 ent kinds of lactic-acid organisms are active in it at the 

 same time, and that neighboring creameries may operate 

 with wholly different forms of lactic-acid bacteria. Storch 

 also says in his comprehensive and valuable work on the 

 " Souring of the Cream " : " Every time I obtained new 

 samples of butter I received new bacteria. The explana- 

 tion that there are no two lots of butter in Denmark pos- 

 sessing exactly the same flavor is found in this." 



This is not the place to treat exhaustively the special 

 qualities and morphological characteristics of the different 

 lactic-acid bacteria.* Some few observations on this point 

 may properly be made here, however. All investigations 



* Those studying these questions are referred to the work by V. 

 Storch, just mentioned, to the special reports by H. Weigmann in 

 Laiidw. WocJienbl. f. Schleswig-Holstein, to G. Marpmann's article in 

 Erganzungsliefte zum Centralbl. f. allgemeine Gesundheitspflege, 1886, 

 to C. O. Jensen's bacteriological investigations reported in Bull. 22 

 of Copenhagen Arg. Exp. Station, to L. Adametz's researches, a 

 summary of which was given at the Agricultural Congress in Vienna, 



