PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 



383 



HCN at their respective pH values. The period of exposure to 

 was greater at a pH of 8.5 than at 6.8. It is also apparent that 

 the drop in the P.D. after a return to normal was somewhat more 

 cyanide is represented on the curve by the time between the 

 arrows. From Fig. 13, it is obvious that the initial stimulation 

 pronounced under the acid conditions than under the alkaline. 



.06 



.05 



.04- 



>.02 



.0 



BORAXt BORAX4HCN 



10 20 30 4-0 

 MINUTES 



FIG. 13. Curve showing the effect of the pH of a solution of HCN in 

 borax on the P.D. of frog skin. Period of exposure to cyanide represented 

 as the time between arrows, at other times the skin was exposed to borax 

 alone. pH values used were 6.8 and 8.5. Abscissas represents the exposure 

 in minutes and the ordinates the P.D. in volts. 



There actually are fewer molecules of cyanide in a solution with 

 a pH of 8.5 than with a pH of 6.8 (Fig. i). So if the molecules 

 were the toxic units, it would be expected that there would be less 

 stimulation and more toxicity when the solution contains the 

 greatest number of molecules than under the reverse conditions of 



