182 PRODUCTION OF CARBON DIOXIDE 



Curve B shows the effect when sufl&cient NaOH is added to change 

 the reaction from pH 6.3 to pH 6.8. There is an increase in the 

 rate as the hydrogen ion concentration approaches neutrality; this 

 is followed by a decrease. At the same time there is an increase in 

 the hydrogen ion concentration. The final pH value in this case 

 coincides with the initial pH value. 



Curve C shows the effect when sufl&cient alkali is added to change 

 the pH value from 5.6 to 6.4. There is an increase in the rate followed 

 by a decrease, and the pH value becomes gradually less. 



Curve D shows the effect when the pH value is changed from 7.0 

 to 9.0. There is a complete cessation in the rate for several hours; 

 this is followed by a gradual increase in the. rate as the medium be- 

 comes more acid. The increasing acidity is not attributable to the 

 carbon dioxide produced, as this was frequently removed during 

 the period of experimentation. 



Briefly summarized, when alkali is added to solutions containing 

 Bacillus hutyricus of various hydrogen ion concentrations, the rate 

 of production of CO2 increases as the normal rate (at pH 7.0) is 

 approached and decreases in the opposite direction. 



The experiments performed with Bacillus suhtilis gave results 

 similar to those expressed in Fig. 1 and Fig. 2 {Bacillus hutyricus). 



Both organisms show a tendency to resist changes in the pH value. 

 When acid or alkali is added there is always an initial effect which is 

 quite pronounced, increasing or decreasing the pH value. This 

 result is followed by a return towards the initial pH value. This 

 might be due to absorption of the added acid or alkali by the or- 

 ganism or to the excretion of a neutralizing substance. In the case 

 of change in the rate of CO2 production produced by alkali the time 

 required for recovery is considerable, but the organisms seem to be 

 able gradually to overcome the cause of the depression in the rate. 



Fig. 3 represents composite curves of a number of experiments 

 with Bacillus hutyricus (curve A) and Bacillus suhtilis (curve B). 

 The abscissae are the various pH values, and the ordinates are the 

 corresponding rates of CO2 production. Each point represents the 

 average of a number of experiments. In most cases the rate was 

 obtained after the bacteria had been in contact with the acid or 

 alkali from 30 to 45 minutes and had reached equiHbrium (constant 

 rate of CO2 production). 



