378 FLOYD JOHN BRINLEY. 



liana) was used. Since the potential difference of the skin from 

 different frogs and also different pieces of skin from the same 

 frog, varied considerably, it was necessary to repeat each experi- 

 ment many times and only characteristic curves of single experi- 

 ments will be given. There is some evidence at hand to indicate 

 that the conditions under which the frogs are kept influences to 

 some extent the potential difference of the skin. It was observed 

 in several instances, when the temperature of the vivarium dropped 

 several degrees below normal, that the potential difference of the 

 skin also dropped and that on warm days the potential difference 

 was usually higher than that at other times. 



Control experiments were conducted by placing the skin in 

 solutions of borax-boric acid buffer and Ringer's solution. The 

 result of a typical control test is given in Fig. 9. Readings on the 

 potentiometer were taken every minute. The temperature varied 

 during the tests from 20-21 C. The experiments were run in 

 parallel series using different pieces of skin from the same animal. 

 It will be noted from Fig. 9, that there was an initial rise in P.D. 

 followed by a gradual decline. The two curves are approximately 

 parallel indicating that the borax buffer is no more toxic to frog 

 skin than is the Ringer's solution. The pH of the Ringer's solu- 

 tion was about 8.2 and the borax 6.8. 



A series of experiments was undertaken to determine the re- 

 lation of the concentration of cyanide to the potential difference 

 of frog skin. The cyanide solution was made by adding pure 

 liquid HCN to a borax buffer at a pH of 6.8. The concentrations 

 of cyanide used were M/1^6, M/i$4 and M/225. Fig. 10 shows 

 the results of a typical set of experiments. The cells were placed 

 in a borax buffer for ten minutes, then removed and placed in the 

 cyanide solution. The skin was allowed to remain in the cyanide 

 solution for various periods of time, then removed and placed in a 

 borax buffer free from HCN. The period between arrows indi- 

 cates the time that the cells were exposed to cyanide. In all cases 

 it may be observed that the skin completely recovered after being 

 removed from the cyanide solution. After the cells had been re- 

 moved from the borax solution and placed in cyanide solution at 

 a concentration of M/225, a great stimulation occurred, followed 

 by a gradual drop in the potential difference to the base line. This 



