GAS PRODUCTION OF STREPTOCOCCUS KEFIR 



129 



Organic acids naturally suggested themselves as a possible 

 source of carbon dioxid. These were therefore tested in a broth 

 consisting of 2 per cent of peptone, 1 per cent of dried yeast 

 and 0.5 per cent dibasic sodium phosphate. The sodium salts 

 of formic, acetic, propionic, butyric, caproic, lactic, malic, 

 valeric, oxalic, tartaric, citric, and succinic acids were subjected 

 to this test but in no case was there an increase in carbon dioxid 

 over that obtained from the same medium without the addition 

 of an acid. 



The sugar content of the medimii, of course, was considered 

 as a possible source of carbon dioxid and experiments were con- 



TABLE 2 



Relation of lactose concentration to carbon-dioxid production 



* Cubic centimeters of fo Ba(0H)2 neutralized. 



ducted in order to throw some light on this question. The 

 observation of Miss Evans, that a small amount of gas is obtained 

 in ordinary lactose broth whereas a greatly increased volume is 

 given off by the organisms when grown in digested milk, was 

 confirmed. Experiments conducted on this point, using a well- 

 buffered broth and varying the lactose content showed, however, 

 that the carbon dioxid produced increases with the increased 

 concentration of sugar. This is true up to the point where the 

 lactose content results in acid production beyond the amount 

 cared for by the buffer. In table 2 are given the results of an 

 experiment which shows the increase of carbon dioxid evolved 

 with the increase in lactose concentration. This experiment 

 was verified on several occasions. 



