368 FLOYD JOHN BRINLEY. 



indicator and placed in a dilute solution of HC1 the indicator did 

 not change color. Several tests were conducted by reversing the 

 skin and it was noted that the membrane was slightly more per- 

 meable to HCN when the skin was turned inside out than when 

 it was in a normal position. The difference, however, was so 

 slight that it is not significant (Fig. i). 



The " cells " after being filled with a borax buffer and put in a 

 solution of HCN, were placed in a water bath at a constant tem- 

 perature of 25 C. for one hour. At the end of that time equi- 

 librium was reached between the cyanide inside and outside the 

 cell. Five cubic centimeters of the internal and external solution 

 were titrated with N/$o silver nitrate, using a one cc. pipette as a 

 burette. The concentration of the cyanide solution used was 

 M/3I3. That the skin was not killed at this concentration was 

 easily demonstrated by substituting for the cyanide solution min- 

 eral acids, known not to penetrate living membranes. No change 

 in intracellular acidity was noted in such control experiments. 

 Experiments were conducted using external and internal solutions 

 of various pH values, the external pH varied from 5. to 8.6 and 

 the internal pH from 6.5 to 8.0. The results plotted in Fig. 2, 

 show the relation of concentration of the total cyanide (HCN and 

 CN) found in the cell at equilibrium to the various external and 

 internal pH values. From this figure it may be noted that the 

 penetration curve closely approximates the dissociation curve (.r) 

 and that the total concentration of cyanide inside the cell corre- 

 sponds very closely to the undissociated cyanide in the external 

 solution. The degree of dissociation represented in the curve 

 was calculated from the formula 



log i/H - - pH = = log i/K + log a/i-a ( 19) , 



where a =- degree of ionization : K - = dissociation constant, for 

 HCN =4.7 X icr 7 (20). 



Figure 2 shows that at equilibrium, when the pH is from 5. to 

 5.5, the concentration of total cyanide within the cell is equal to 

 the amount of cyanide in the external solution. From the disso- 

 ciation curve it is evident that at this pH there is practically no 

 dissociation, all of the cyanide being in the molecular condition. 

 As the external pH was increased, the penetration curve rapidly 



