REGULATING FACTORS IN BACTERIAL METABOLISM 667 



(1) Effects of different amounts of peptone with and without the 

 addition of phosphate. The object of this experiment was to 

 determine the effects of different concentrations of peptone on 

 the carbohydrate and nitrogen utihzation by bacteria and the 

 influence exerted by the addition of an acid regulator such as 

 primary sodium phosphate (Na2H PO4). The media were made 

 as outlined above and tests for the hydrogen ion concentration 

 run on the second and fourth days. With a little care 1 cc. 

 of the culture can be withdrawn by means of a sterile pipette 

 without contaminating it. By this simple method the progres- 

 sive changes in the same culture tube could be followed for a 

 week or more by daily withdrawals of 1 cc. samples. 



The results of these tests are summarized in table III. They 

 indicate quite clearly that the concentration of peptone plays a 

 rather significant role in accelerating glucose fermentation, as 

 well as in favoring its complete utilization. The former effect 

 is seen in table III, section A, in the differences in the Pj values 

 in the B. cloacae cultures on the second day and in the B. aero- 

 genes cultm-es on the fourth day. A similar effect is noted in 

 table III, section B, in the case of B. coli. The favorable effect 

 on complete utilization of the carbohydrate is brought out espe- 

 cially in the case of B. aerogenes in section A and of B. coli in 

 section B of table III. 



The effect of the regulating action of the acid-phosphate is 

 evident on comparing sections A and B. By keeping down the 

 hydrogen ion concentration of the medium some of the organ- 

 isms are enabled to use up all the carbohydrate (0.5 per cent) 

 without producing sufficient concentration of acid to inhibit 

 their growth. Once this is accomplished, the active utilization 

 of the nitrogenous constituents commences and we obtain a 

 progessively decreasing hydrogen ion concentration (or an in- 

 creasing Pj value). That the regulating effect of the phosphate 

 is not the only factor, however, is evident from the results 

 obtained with B. coli as shown in table III. 



It is interesting to note that in the absence of phosphate the 

 cultures of B. cloacae and B. aerogenes reach a hydrogen ion 

 concentration practically as high as that of B. coli, which does 



