PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 387 



The P.D. gradually increased suggesting a recovery followed 

 by a gradual decrease to the base line. The curve suggests, that 

 at a pH of 6.6 the cyanide was more toxic than at a pH of 8.2 as 

 was evident from the fact that the P.D. suddenly dropped when 

 the skin was taken from a solution of a pH of 8.2 and placed in a 

 pH of 6.6. When the skin was taken from a pH of 6.6 and placed 

 in a solution of 8.5 a recovery occurred. 



The conditions plotted in Fig. 16 are the reverse from those in 

 Fig. 15. The skin after being placed in a borax buffer solution 

 for ten minutes was removed and put in a cyanide solution of a 

 pH of 6.6. The initial rise followed by a rapid drop was again 

 obtained. When, however, the skin was removed from the pH 

 of 6.6 and placed in a cyanide solution having a pH of 8.5, the 

 P.D. rapidly increased until a point was reached above the initial 

 stimulation suggesting a recovery and a stimulation. At the end 

 of 15 minutes the skin was again placed in the original HCN solu- 

 tion at a pH of 6.6; a rapid fall occurred, suggesting a return to 

 normal, followed by a rapid decline. As previously stated, 98 

 per cent, of the total cyanide is dissociated at a pH of 8.5 and 

 thus the cyanide is present in the ionic condition. When the pH 

 is 6.6 the cyanide is about 40 per cent, dissociated, therefore, the 

 number of molecules and ions is about equal. From the data 

 given, it appears that the cyanide is more toxic to the frog skin 

 when the solution is acid than when alkaline. Thus, it seems that 

 the molecule is actually more toxic than the ion. In dilute con- 

 centrations the physiological effect of hydrogen cyanide on frog 

 skin is first a stimulation followed immediately by a rapid return 

 to the original reading terminating in a toxic effect which will 

 eventually prove fatal. 



SUMMARY. 



The experiments indicate that little or no HCN penetrates frog- 

 skin " cells " except in the form of undissociated molecules. The 

 total amount of intracellular cyanide is proportional to the concen- 

 tration of undissociated molecules in the external solution. The 

 "internal pH value of the " cell " has no effect on the penetrations 

 of HCN through frog skin. 



From a study of the effect of hydrogen cyanide on the potential 



