240 Journal of Agricultural Research voi. xiii.no. 4 



that small quantities of volatile acids, chiefly acetic, were produced by 

 this organism. In an earlier work {10) it was shown that some strains 

 of streptococci which did not give a reduction of litmus characteristic of 

 S. lacticus produced large quantities of acetic acid in milk cultures. 

 This suggested that differences in acetic-acid production might serve as a 

 basis for the differentiation of cheese streptococci. Therefore volatile- 

 acid determinations were made on milk cultures of five strains of 5. 

 lacticus, four of which produced between 9.90 and 11.27 c. c. Njio acetic 

 acid in 500 c. c. of milk. The other strain produced 7.25 c. c. of acetic 

 acid. Cultures of S. lacticus agree, therefore, in producing a small and 

 fairly constant quantity of acetic acid in milk cultures, equivalent to 

 about o. 1 2 gm. , calculated for i liter of milk. 



Jensen {12) found that 5. lacticus could develop in peptone broth 

 without any carbohydrate, and that when growing thus it was able to 

 decompose the peptone with the formation of amino acids and ammonia. 

 This is a definite reaction when measured in terms of the hydrogen-ion 

 concentration. Cultures of 5. lacticus inoculated into carbohydrate-free 

 yeast peptone broth with a hydrogen-ion concentration of Ph = 6.o 

 grew abundantly, reducing the hydrogen-ion. concentration to Ph = 6.8. 

 This indicates a vigorous proteolytic activity. Two cultures varied 

 slightly from this final hydrogen-ion concentra.tion ; and two cultures, 

 96ga and 2am were atypical in failing to grow in the carbohydrate-free 

 medium. 



S. lacticus cultures isolated from Cheddar cheese were reported in an 

 earlier work {8) to be positive in their fermentation of lactose in broth 

 cultures, negative in glycerin broth, and either positive or negative in 

 salicin, raannite, and sucrose broth. The fermentation reactions of the 

 5. Lacticus cultures isolated for the present study agreed with the earlier 

 description. The order of availability of the test substances was the same 

 as noted in the earlier publication — viz, lactose, salicin, mannite, sucrose. 

 Glycerin and raffinose were not fermented. The fermentation reactions 

 of each of the 1 2 cultures which were studied in detail ware presented in 

 Table I. The final hydrogen-ion concentrations are given only for those 

 cultures which hydrolyzed the test substance. The minus sign ( — ) does 

 not indicate a. failure to grow, but a failure to form acid. As would be 

 expected, if the test substance is not attacked, the same reaction would 

 take place as in the plain-yeast-peptone broth. The table shows that 

 there is a considerable variation in the final hydrogen-ion concentration 

 of any one strain in the different broths, and also that there is a variation 

 in the final hydrogen-ion concentration of the different strains in any one 

 of the broths. The final hydrogen-ion concentrations varied from 

 Ph = 4.o to Ph = 5.o. The same was the case in dextrose broth, not in- 

 cluded in the table. The succeeding tables show that the same thing is 

 true of the other cheese streptococci, and that the different species cover 

 the same range of variation. Therefore the determination of the final 



