620 STUDIES ON RESPIRATION. XI 



XaOH was employed for the alkaline solutions. For the acid solu- 

 tions H3PO4 and H0SO4 were used; to get rid of any volatile acid 

 which might be present the acid was boiled for some time before 

 using. 



For preliminary work both H3PO4 and H2SO4 werevemployed, but 

 as both of these acids gave practically the same results, when the 

 H ions were present in the same concentration, the use of H3PO4 was 

 discontinued. All the results here described were obtained by the 

 use of H2SO4. 



In the experiments where the pH was less than 7 the apparatus 

 described by Osterhout^^ was employed. For the alkaline solutions 

 this method could not be used, as the CO2 neutralized the XaOH, 

 and therefore the method described by Haas^^ was employed. The 

 method adopted here was to determine the time required to produce 

 a given amount of CO2 in normal respiration at pH 7.30 and then 

 change the pH and determine the time required to produce the same 

 amount of CO2. 



This necessitated a determination of the change in pH produced by 

 the same amount of CO2 when added to neutral or alkaline solutions. 

 This was accomplished in the following manner. Into a glass tube 

 10 cc. of a solution having a pH of 7.30 were put, and into a second 

 tube 10 cc. of an alkaline solution; both solutions contained indica- 

 tors. As soon as the tubes were filled they were stoppered and 

 compared with standard buffers to get the exact pH. Into each 

 tube one drop of the same solution of CO2 in water was simultane- 

 ously introduced. The tubes were shaken and comparisons with 

 standard buffers were again made in order to measure the change in 

 pH. This procedure was repeated several times and the average 

 of the changes in each solution taken as the change to be produced b}' 

 the fungus. If for example the average of these changes was found 

 to be from pFI 7.30 to 7.10 in one solution, and from pH 8.92 to 

 8.68 in the other, standard buffers were made up for these values. 

 Then the normal rate of respiration was determined by finding how 

 long it took the fungus to change the pH from 7.30 to 7.10. Unless 

 the rate remained constant for at least 20 minutes the material was 

 rejected. (It had been found by experiment that after the respira- 



15 Osterhout, W. J. Y., J. Gen. Physiol.. 1918-19, i, 17. 

 '^ Haas, A. R., Science, 1916, xliv, 105. 



