PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 381 



of exposure to KCN. It is well known that many anesthetics in 

 dilute solutions act as protoplasmic stimulants and in concen- 

 trated solutions their toxic action is established (Osterhout, 9). 

 It is interesting in this connection to determine whether the 

 rapid fall in the potential difference immediately following stimu- 

 lation by dilute cyanide is due to a natural recovery to normal or 

 to the toxic action of the cyanide. Cells were removed from the 

 borax buffer solution at the end of a ten minute exposure and 

 placed in a hydrogen cyanide solution of a concentration of M/i6o. 

 A series of three experiments was conducted ; in the first series the 

 cells were removed from the cyanide solution at the end of three 

 minutes and placed in a borax buffer, at which time the stimula- 

 tion had reached its maximum and started to drop. In the second 

 series the skin was allowed to remain in the cyanide solution for 

 six minutes, then removed and placed in the pure buffer, at which 

 time the drop following stimulation had reached the same reading 

 as when the skin was first placed in the cyanide. In the third 

 series the skin was exposed to the cyanide for a period of nine 

 minutes. At the end of that time, the drop following stimulation 

 had reached a point below the original P.D. The results of a 

 typical series of experiments are plotted in Fig. n. It is evident 

 from this figure that after the removal of the skin from the cya- 

 nide solution, in the three and six minute exposure, the drop in 

 P.D. continued until it had fallen below the P.D. obtained at the 

 time the skin was placed in the cyanide solution; the P.D. then 

 increased to normal. The nine minute exposure showed no 

 further drop in the P.D. after being removed from the cyanide 

 solution but an immediate recovery occurred. It is apparent from 

 the data given that the drop in potential difference immediately 

 following the stimulation was due not to the toxic action of the 

 cyanide but to a natural return to the original reading and the 

 toxic action did not take place until after the drop had surpassed 

 the point where the skin was stimulated. 



EFFECT OF THE pH OF CYANIDE SOLUTION ON THE POTENTIAL 



DIFFERENCE. 



It is apparent from the data given in the first part of this paper 

 that little or no HCN penetrates living membranes except in the 



