180 PRODUCTION OF CARBON DIOXIDE 



medium containing the bacteria at different hydrogen ion concen- 

 trations. 



It was found that the rate was at a maximum at pH 7; this was 

 accordingly called 100 per cent, and arbitrarily designated as the 

 "normal" rate. All rates were then designated as per cent of the 

 normal. When, for example, the initial pH was 6, enough alkali was 

 added to make the pH 7. The rate at pH 6 was then divided by the 

 rate at pH 7 in order to express the rate at pH 6 as per cent of the 

 normal rate. 



The initial pH value of the dextrose containing the bacteria was 

 not always the same owing to variations in the organisms them- 

 selves. It was found impracticable to adjust the pH at the beginning 

 of each experiment to a value which would be uniform for all experi- 

 ments (for example to pH 7.0). For this reason the curves in Fig. 1 

 and Fig. 2 do not all begin at 100 per cent, but at different rates 

 of production of CO2 depending on the initial pH value of the dex- 

 trose containing the qrganisms. 



In Fig. 1 and Fig. 2 the acid or alkali respectively were added at 

 the zero point on the abscissae. The first reading in each case denotes 

 the rate of production of CO2 at the instant before the acid or alkali 

 was added, and the pH at this instant is shown by the attached 

 figure. The addition of acid or alkali changed the pH to the value 

 indicated by the figure attached to the first reading. Thus in curve 

 B, Fig. 1, the pH at the start was 7.6 and the addition of acid changed 

 it to 6.7, as shown by the figure attached to the first point on the 

 curve. 



Curve A, in Fig. 1, shows the effects of the addition of acid to 

 bacteria contained in a solution whose initial pH was 7.0. The 

 pH fell at once to 6 .6 then rose to 6 . 7. The production of CO2 fell 

 and rose with the change in pH value. 



Curves C and D illustrate the effect of adding larger amounts of 

 acid: in these cases the pH remains stationary after the addition of 

 acid while the production of CO2 falls steadily until equilibrium is 

 attained. 



Curve B illustrates the effect of adding acid to an alkaline suspen- 

 sion of bacteria (pH 7.6). The pH changed at once to 6.7 and sub- 

 sequently fell. The production of CO2 rose and fell in a character- 

 istic manner. 



