244 



Journal of Agricultural Research 



Vol. XIII, No. 4 



a The minus sign ( — ) indicates failure to form acids. 



The best medium found for the growth of 5. kefir is digested milk, in 

 which there is a vigorous gas production. Quantitative and quahtative 

 gas analyses were made according to the method described by Rogers, 

 Clark, and Davis (/(5). In 20 c. c. of the digested milk, with an initial 

 hydrogen-ion concentration of Ph = 6.6, 26.80 c. c. of gas were produced 

 by culture 96fi. This culture produced only 3.82 c. c. of gas in 20 c. c. of 

 dextrose-yeast broth, and 2.82 c. c. of gas was produced in 20 c. c. of a 

 lactose-yeast broth culture of this same strain. The growth in the sugar 

 broths was abundant, with a vigorous acid formation. In all these 

 media the gas produced was pure carbon dioxid, with only a trace of some 

 other gas, undoubtedly due to experimental error. The source of the 

 carbon dioxid has not yet been determined. 



The gas production of this group of cheese streptococci served to 

 identify it with the organisms described by Freudenreich (9) and Saito 

 (77). Freudenreich reported that his streptococcus produced 12 c. c. of 

 gas in 50 c. c. of a lactose-peptone broth; lactic acid also was formed. 

 Saito reported that his organism produced carbon dioxid, lactic acid, and 

 alcohols. 



Culture 96gq of 5. kefir grown in 500 c. c. of skim milk produced 

 57.14 c. c. of Njio acetic acid. The milk had not been acidified to the 

 point of curdling. In 500 c. c. of a milk culture to which 0.5 per cent of 

 peptone had been added culture 96gq produced 80.50 c. c. of Njio acetic 

 acid, equivalent to 0.97 gm. of acetic acid per liter. 



S. kefir will not grow in peptone-yeast broth without a carbohydrate. 

 Lactose and sucrose were fermented by every one of the 23 strains on which 

 the tests were made. Raffinose was fermented by most of the strains. 

 Salicin was fermented by only one strain, culture 96dd. The order of 

 availability of the test substances for 5. kefir, therefore, is as follows: 

 Lactose and sucrose, raffinose, salicin. Mannite and glycerin are not 

 fermented. To judge from the limited number of cheese streptococci 

 which have been studied, it appears that the fermentation of lactose and 



