PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 



369 



dropped. Likewise as the pH was increased the degree of ion- 

 ization was increased. At a pH of 7.0 the dissociation is practi- 

 cally 50 per cent, and the concentration of cyanide in the cell is 

 about 40 per cent, of the concentration of the external solution. 



INTERNRL 



8.0 

 - 7.f 



6.8 



6.5 



100 



10 



FIG. 2. Curve showing the effect of pH on the permeability of frog skin 

 to HCN. Abscissae represents the external pH; ordinates the per cent, of 

 total cyanide on the right and the degree of ionization on the left. Calcu- 

 lated degree of dissociations represented by X. Internal pH values indi- 

 cated as follows : short dashes 6.5, solid line 6.8, dotted line 7.4, long dashes 

 8.0. 



At a pH of 9.0 dissociation is practically complete and accordingly 

 little or no cyanide is present in the cell. It is evident that hydro- 

 gen cyanide seems to penetrate frog skin chiefly in the form of 

 molecules and not as ions. It is also apparent from Fig. 2 that 

 the intracellular pH varying from 6.5 to S.o does not affect the 

 permeability of frog skin to hydrogen cyanide. Brooks (21) 

 stated that changing the pH of the sap of Valonia with CO 2 and 

 NH 3 , changed the amount of 2 -- 6-- dibromo phenol indophenol 



