ABSTRACTS 



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BACTERIOLOGY. — A study of the Streptococci concerned in cheese 

 ripening. Alice C. Evans. Journ. Agr. Res. 13: 235-252, 1918. 



Two species of streptococci are distinguished from the well-known 

 Streptococcus lacticus, and all three species are described culturally and 

 biochemically. 



The most pronounced characteristic which distinguishes S. lacticus 

 from the other two species is the small quantity of acetic acid which it 

 produces in milk cultures. Vigorous strains curdle litmus milk in less 

 than two days, with complete reduction of the litmus beneath the pink 

 surface layer. Crystals of tyrosin are formed in milk cultures after 

 several weeks incubation. Peptone yeast broth of a hydrogen-ion con- 

 centration of Ph = 6.0 is rendered alkaline with a final hydrogen-ion 

 concentration of Ph = 6.8. 



Streptococcus X requires from two to twelve days to curdle milk. 

 The litmus is not reduced, or is only partially reduced. No crystals 

 are formed in milk cultures. The hydrogen-ion concentration of 

 peptone yeast broth is reduced to the same point as in the case of 

 S. lacticus. Streptococcus X produces a comparatively large quantity 

 of acetic acid in milk cultures (0.7 to 0.8 gram per liter). 



Streptococcus kefir is notable among dairy streptococci because of its 

 vigorous production of carbon dioxide when gfown in milk containing 

 peptone, or in trypsin digested milk. It does not produce sufficient 

 acid in milk cultures to bring the milk to curdling. There is no reduc- 

 tion of the litmus. No growth takes place in peptone yeast broth. 



Experimental cheese inoculated with the three species of strepto- 

 cocci alone or in various combinations showed that the flavor of cheese 

 of the cheddar type and of soft cream cheese could be varied according 

 to the species of streptococci used for a starter. A. C. E. 



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