624 STUDIES ON RESPIRATIOX, XI 



These experiments showed that in acid solutions the rate of respira- 

 tion was increased at certain concentrations. The next step was to 

 determine the effect of alkaline solutions. 



The first concentration to be tried was pH 8. As it was found 

 that this concentration had no effect on respiration the normal rate 

 in the succeeding experiments was measured between pH 7.52 and 

 7.25 as the color change in phenolsulfonephthalein is much easier to 

 determine at this range. 



The next concentration chosen was pH 9. As phenolsulfon- 

 ephthalein is not sensitive in this range phenolphthalein was used 

 instead; this indicator is not toxic to the fungus. The concentra- 

 tions were first standardized and it was found that the same amount 

 of COo caused a change from pH 7.52 to 7.25 and from 8.92 to 8.68. 

 The time required for normal respiration to change the solution from 

 pH 7.52 to 7.25 was determined; then the fungus was put in a solu- 

 tion slightly higher than pH 8.92 and the time required to change 

 from pH 8.92 to 8.68 noted. It was found to be much longer than 

 the normal, thus showing that respiration was decreased. Not only 

 the first reading but all the succeeding ones showed a decrease, and 

 at no time was there an increase. 



When the pH value was less than 7 and there was a decrease to 

 considerably below normal, no recovery back to normal (or nearly 

 normal) followed, after the material had been replaced in ordinary 

 nutrient solution at pH 4 or in sugar solution at pH 7. After the 

 respiration had been depressed to 60 per cent of normal by pH 8.80 

 and kept there for an hour, there was nearly complete recovery when 

 put back in sugar solution at pH 7. It is therefore evident that any 

 considerable decrease produced by acid solutions is irreversible, 

 while a similar decrease produced by alkahne solutions is reversible. 



Some experiments have also been made by measuring the consump- 

 tion of oxygen by the fungus. Winkler's method, as modified by 

 Osterhout and Haas,^^ was employed. 



It was found that in a solution of pH 9 the fungus uses less than 

 one-half as m.uch oxygen as in a neutral solution, while in a solution 

 of pH 2 the consumption of oxygen is nearly four times as great as 



1^ Osterhout, W. J. V.. and Haas, A. R. C, /. Biol. Cliem., 1917, xxxii, 141. 



