PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 



379 



stimulation, characterized by a rise in potential difference, is also 

 evident at a concentration of M/i$4 but not nearly to the same 

 degree as with the weaker concentration of cyanide. The drop 

 following stimulation at a concentration of M/I54 is practically 

 of the same magnitude as obtained with a M/225 solution. In 

 the case of the M/i$6 solution there was no stimulation but the 

 potential difference dropped suddenly to the base line. The skin 



10 t 20 



30 4-0 

 MINUTES 



t60 70 



FIG. 10. Curve showing the relation of concentration of HCN to the 

 P.D. of frog skin. Concentration of total cyanide = M/22$, A// 154 and 

 Af/i36. Same solution on both sides of the membrane. The period between 

 arrows indicates the time that the skin was exposed to cyanide, at other 

 times the skin was exposed to borax buffer free from HCN. Abscissae rep- 

 resents the time in minutes ; ordinates the P.D. in volts. Different pieces of 

 skin from the same frog were used. 



26 



