Streptococci. 



165 



Fig. 24. 



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the growth takes place either with general clouding, or with the formation of flakes and 

 tufts and the bouillon then remains clear. The optimum temperature of the growth lies 

 between 10 and 42 deg. C. Most of the varieties are facultative anaerobes. 



Coagulation of milk may take place with acid formation, or in spite of acid 

 formation it may not coagulate, or again coagulation may take place with only slight 

 acid formation, which in all probability depends on the formation of substances having 

 the properties of rennet. 



Gas formation has never been observed by the author, but it is supposed to occur; 

 slime formation is typical of some of the species. 



Lohnis classifies the varieties of streptococci found in milk as: 



1. Those which coagulate milk and form gas: Micrococcus sornthali (Adametz), 

 Streptococcus "a" from Kefir (Freudenreich), Streptococcus memelcnsis (Leichmann), 

 Streptococcus caucasicus (Migula). 



2. Those which coagulate milk but form no gas: Streptococcus guntlieri, Bacillus 

 lacticus Kruse, Bacillus lactis Lister, Lactococcus 'beijerink, Bacillus acidi lactici Groten- 

 feld, and the streptococci from Armenian buttermilk. 



3. Those which neither co- 

 agulate milk nor form gas : 

 Streptococcus Jcefir, Streptococcus 

 "~b" Freudenreich, Streptococcus 

 soya. 



4. Those which neither co- 

 agulate milk nor form gas: some 

 streptococci of cheese, Strepto- 

 coccus inocuus. 



5. Those which form 

 slime ; some varieties of the 

 Streptococcus pi/ogenes, leuconos- 

 toc varieties, Streptococcus liol- 

 landicus, Bacterium lactis longi, 

 "sticky milk" producers, Micro- 

 coccus mucilaginosus, Bacterium 

 lactis acidi. 



6. Those which in culture 

 form vine or tongue-like shoots. 



7. Those which liquefy 

 gelatine. 



It is well known that the 

 cultural characteristics of the 

 streptococci may readily change : 

 a strong acid forming variety 

 may lose this characteristic by 

 long cultivation in milk, and may 

 become a slime producing variety, 

 so that the distinguishing feature 

 is not absolute. There are transi- 

 tory forms between one and the 



other type, and one type at some time may change into another type by changing its 

 characteristics. 



Some varieties also belong to those streptococci (collective name streptococcus or 

 Bacterium lactis acidi Leichmann), which produce volatile substances and alcohol from 

 milk sugar and which at the moment of their development unite into a fragrant substance, 

 a so-called fruit ester, which reminds one of the odor of a certain fruit or fruits; other 

 representatives of this variety produce other substances with odor and taste, which may 

 be described as straw-like, sorrel-like and especially malt-like. The author never succeeded 

 in producing striking odoriferous substances in sterile milk with the streptococci cultures 

 at his command. He, however, does not wish to refute from his few experiments with 

 about 20 strains from various provinces, the possibility of the production of special 

 odoriferous substances by the Streptococcus lacticus. 



Under certain conditions tremendous quantities of streptococci 

 may occur in market milk from cows which are affected with strep- 

 tococcic mastitis. Special reference has been made in the chapter 

 on affections of the udder, regarding the similarity of these patho- 





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Slreptococcits lacticus. 1 X 1000. 



