The Controlling Influence of Carbon Dioxide. 153 



anaerobic splitting process, only, but in so doing automatically retards also 

 the amount of the following oxidations even in the presence of excess of 

 oxygen. 



On this hypothesis, if the amount of available oxygen be decreased till it is 

 no longer present in excess, but in deficiency, so that the oxidisable 

 substances produced in the first process accumulate faster than they are 

 removed by oxidation, then the rate of the first splitting process will no 

 longer be the limiting factor upon oxidation. In such conditions, if carbon 

 dioxide has no effect upon the oxidation process, as we suppose, the amount 

 of carbon dioxide present, while still retarding the first process, should now 

 have no effect upon the amount of oxygen consumed. 



In the following experiments peas covered with thick water films in order 

 to reduce gaseous exchange were allowed to respire in the presence of 20 per 

 cent, of oxygen. In this condition a large amount of CO2 was produced 

 anaerobically in addition to that accounted for by the loss of oxygen, showing 

 clearly on our assumption that the available oxygen was present in an amount 

 quite insufficient to remove the oxidisable substances as fast as they were 

 produced in the first anaerobic splitting process. 



As the following Table of results shows, carbon dioxide had not, under 

 these conditions, any definite influence upon the amount of oxygen consumed. 



Table XII. — Showing that if Oxygen is present in deficiency, increased 

 concentrations of Carbon Dioxide, while still retarding the rate of 

 Anaerobic C0 2 production, have now no effect in reducing the amount 

 of Oxygen taken in. 



Initial C0 2 in 

 atmospheres N 2 . 



Oxygen 

 consumed. 



Anaerobic C0 2 

 production. 



per cent. 







j 



26 



104 



10 



27 



87 



20 



23 



80 



40 



28 



44 



In each experiment 25 peas, dry weight 8 grin., with sufficient water to form adequate films 

 oyer them when fully swelled. The flasks were shaken at intervals during the experiments. 



The results shown in the Table were obtained after the experiments had been running 90 hours. 

 The percentage of oxygen, initially 20 per cent., had fallen only to about 17 per cent, in each 

 experiment. 



The peas used were sterilised with 1/500 bromine for 30 minutes, and the flasks with weaker 

 bromine for a longer period. 



Temperature of the experiments was that of laboratory, 16° C. (average). 



The increase in volume of the gases in the flasks during the experiments, as calculated from 

 manometer readings, was taken as a measure of anaerobic respiration sufficient to demonstrate 

 clearly the point that carbon dioxide retards anaerobic C0 2 production in these experiments. 



o 2 



