PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 



ever, sufficiently marked to be significant. Figs. 15 and 16 show 

 the results obtained when the pH was alternated from 6.6 to 8.2 

 and vice versa. The same piece of skin was used under the same 

 conditions of temperature and concentration of cyanide ; the con- 

 centration of cyanide was M/I73, made by adding liquid HCN to 



.14- 



.12 



JO 



to 



t- 



.08 



.06 



.04- 



.02 



10 20 30 4-0 60 



MINUTES 



60 



FIG. 15. Curve showing the effect of alternating the pH of a solution of 

 HCN in borax on the same piece of frog skin. pH changed from 8.5 to 6.6 

 then back to 8.5. Period of exposure at various pH value indicated in curve. 

 For the first ten minutes the skin was exposed in minutes and the ordinates, 

 the P.D. in volts. 



a borax buffer. The skin was placed in a borax solution for ten 

 minutes, then removed and placed in the cyanide solution at a pH 

 of 8.5 for 15 minutes (Fig. 15). The characteristic curve was 

 obtained an increase in P.D. followed by a gradual decrease. 



