Apr. 22, iQis Streptococci Concerned in Cheese Ripening 237 



strains, for they develop in the presence of the by-products of 5. lacticus 

 and other cheese organisms; in certain types of cheese they develop in 

 the presence of a high concentration of sodium chlorid (10 per cent in 

 Roquefort cheese); in the manufacture of other types of cheese they 

 survive the "cooking" of the curd (from 52° to 60° C. for about an hour 

 in the making of Emmental cheese). 



The tests ordinarily used for the differentiation of streptococci reveal 

 nothing peculiar about the cheese streptococci. After applying the 

 tests, therefore, it was necessary to study the cultures biochemically 

 along such lines as observation of their conduct pointed out to be pos- 

 sibly fruitful. The result has been the recognition of two distinct species 

 of cheese streptococci in addition to 5. lacticus. Having recognized the 

 species, and knowing something of their food requirements, the way is 

 opened to a chemical investigation of their by-products which should 

 yield interesting results. This paper presents the bacteriological differ- 

 entiation between 5. lacticus and the two other species, with a few funda- 

 mental facts about their peculiar physiological activities and the relation 

 of the organisms to cheese ripening. 



METHODS OF STUDY 



All cultures were incubated at 30° C. For the study of morphology 

 smears were made from 24-hour cultures from the condensation w^ater 

 of agar slopes. The smears were stained according to the Gram-Weigert 

 method, and drawings were made with the aid of the camera lucida. 



The methods for determining the liquefaction of gelatin, decomposi- 

 tion of asparagin and urea, and reduction of nitrate are described in a 

 previous publication (6) to which the reader is referred. All cultures 

 studied reacted negatively to these tests, and therefore they will not be 

 mentioned again. The fermentation reactions were determined in the 

 following test substances: Dextrose, lactose, saccharose, raffinose, sali- 

 cin, mannite, inulin, and glycerin. Every strain reacted positively to 

 dextrose and negatively to inulin. These substances therefore had no 

 differential value and will not be mentioned again. One per cent of the 

 test substance was added to a yeast-peptone broth made of 10 gm. of 

 peptone, 5 gm. of desiccated yeast, and 5 gm. of dibasic potassium 

 acid phosphate in a liter of water. Desiccated yeast was used in place 

 of the usual meat extract because it is in general use in these laboratories 

 and not because it was peculiarly adapted to the problem at hand. 

 Sodium hydroxid was added to bring the medium to a hydrogen-ion 

 concentration of Ph = 6.8. The cultures v^^ere incubated for seven days. 



The hydrogen-ion concentration was then determined by the colori- 

 metric method, with the standard solutions described by Clark and Lubs 

 (j) and the indicators described by them {14). 



The same yeast broth, without addition of a fermentable substance, 

 and without the addition of sodium hydroxid, was found to be a very 



