PHYSIOLOGICAL EFFECTS OF HYDROGEN CYANIDE. 



371 



other body movements had ceased and that the organism did not 

 recover after the heart stopped. 



20 



FIG. 4. Curve showing the effect of pH on the toxicity of HCN to 

 Daphnia. Abscissae represents pH ; ordinates time in minutes required to 

 kill 95 per cent, of the organisms. 



It is obvious from Fig. 3 and 4 that less time was necessary to 

 kill the animals in acid solution than in the alkaline solution. It 

 required twenty-two minutes to kill Daphnia at a pH of 5.7 to 7.0 ; 

 forty minutes at a pH of 8.0 and sixty-four minutes at a pH of 

 9.0. The concentration of cyanide used in the above experiment 

 was M/45O. The results indicated what would be expected from 

 the study of the frog skin " cell," where more cyanide entered 

 when the external pH was acid than when alkaline. The animals 

 were killed first in solutions of the same pH values in which HCN 

 penetrated the frog skin cells most quickly. 



The effect of the pH on penetration of cyanide was further 

 checked by studying its effect on the streaming of protoplasm in 

 Elodea cells (in press). The streaming of the protoplasm can be 

 observed under the high power of a microscope while the cells 

 are immersed in a solution of cyanide. The pH was controlled. 



