618 STUDIES ON RESPIRATION. XI 



M (about pH 11.7) decreased the production of CO2 to 88.8 per cent, 

 0.02 M (about pH 12.3) decreased it to 71.3 per cent. He found 

 Ca(0H)2 more toxic than HCl at equal concentrations. He explains 

 this by supposing that calcium precipitates out phosphates in the 

 tissue. Oxygen consumption was decreased to about the same 

 degree that the production of CO2 was decreased. Thunberg also 

 used a large number of organic acids and found that most of them 

 had only a shght effect in concentrations from 0.01 to 0.2 m. A 

 few, like formic, a-oxybutyric, and pyroracemic acids, decreased the 

 production of CO2 from 40 per cent to 50 per cent at the greatest 

 concentration. On the other hand acids like citric, fumaric, and 

 malic increased the production of CO2 in proportion to the increase 

 in concentration of acid. 



Some work has been done on the effect of H ions on the fermenta- 

 tion by yeast. In most cases, however, the pH of the solutions was 

 not measured. Solutions of 0.1 n HCl and HNO3 seem to inhibit 

 fermentation entirely.^ Hagglund-^ determined the pH of his solu- 

 tions and found that the optimum hydrogen ion concentration for 

 yeast fermentation (using lactic acid, HCl, and H2SO4) was 7 x 10~* 

 (pH 3.16). His criterion of fermentation was the production of CO2. 

 Liiers^ found that the pH of the solution, after fermentation had been 

 in progress for several days, always was from 2.51 to 2.73, though at 

 the beginning it may have been neutral. 



The extent to which oxidase enzymes are concerned in respiration 

 is at present unknown, but it is important to note that they are 

 inhibited by acids. Bertrand,^ as well as Abderhalden and Guggen- 

 heim,* and later Wolff*^ reported inhibition of oxidase reaction by 

 acids. According to Bunzelli" the oxidation of hydrochinone by 

 laccase (from alfalfa) increases with decrease of H ions from 5.6 X 

 10-8 to 7 X 10-8 (pH 7.26 to pH 8.16). Reed^i found that the 



''Drabble, E., and Scott, D. G., Biochem. J., 1907, ii, 340. 

 ^ Hagglund, E., Biochem. Z., 1915, Ixix, 190. 

 *Luers, H., Z. ges. Brauwesen., 1914, xxxvii, 79. 

 •^ Bertrand, G., Compt. rend. Acad., 1907, cxlv, 340. 



8 Abderhalden, E., and Guggenheim, M.,Z. physiol. Chem., 1907-08, liv, 331. 

 MVoUI, J., Compt. rend. Acad., 1909, cxlviii, 500. 

 '° Bunzell, H. H., /. Biol. Chem., 1915, xx, 697. 

 11 Reed, G. B., /. Biol. Chem., 1916, xxvii, 299. 



