36 STUDIES ON RESPIRATION. XII 



of hydrogen peroxide, while in the experiments with the fungus the 

 hydrogen ion concentration was varied during the experiment. The 

 results are nevertheless comparable in the two cases. 



In the final experiments the same bottle of "Dioxygen" was used 

 throughout, so that the results would be exactly comparable. It 

 was found that the contents of two bottles which titrated the same 

 with permanganate did not give the same results in respect to the 

 amount of CO2 produced. For this reason all the data here published 

 were obtained by the use of hydrogen peroxide from the same bottle. 



The time required to cause a standard change in the indicator tube, 

 when the other tube contained 0.5 per cent dextrose but no hydrogen 

 peroxide, was taken as 100 per cent. This change may have been 

 caused by a leak in the apparatus or by the breaking down of the 

 dextrose or by both. The source of the CO2 is of no importance for 

 the measurement. It is only necessary that in the absence of hydro- 

 gen peroxide the rate of production of CO2 should be constant so that 

 the rate found after the introduction of the hydrogen peroxide could 

 be compared with it. For convenience the rate in the absence of 

 hydrogen peroxide is called the normal rate; the rate after the addi- 

 tion of hydrogen peroxide is expressed in terms of the normal. This 

 normal change was very slow and varied between 20 and 35 minutes. 



In beginning an experiment the 0.5 per cent dextrose solution was 

 made up to the desired hydrogen ion concentration; 60 cc. of this 

 solution were put into the apparatus and the air was caused to circu- 

 late for 2 hours or more till all dissolved CO2 had been pumped out. 

 Several readings were then taken to get the normal rate of change. 

 Then 8 cc. of hydrogen peroxide were added by opening the flask 

 holding the dextrose solution; 3 minutes were allowed to elapse 

 before the first reading was taken so as to allow a thorough mixing 

 of the solution. In the first few minutes the production of CO2 was 

 very great, but as will be seen from Fig. 1 , it fell off very rapidly in 

 the solution having a pH of 1, while in the neutral solution the fall 

 was not so rapid. 



The experiments with the alkaline solutions were made with the 

 direct method (without the apparatus for the circulation of air) as 

 described in a previous paper.^ Experiments were first made with 

 neutral solutions. The dextrose solution was placed in a tube, 



