370 



FLOYD JOHN BRINLEY. 



that entered the cells. However, she states and also Scarth (22) 

 shows that the pH of the sap in the vacuole could be no criterion 

 of the pH of the protoplasm. 



EXPERIMENTS WITH TADPOLES, DAPHNIA AND ELODEA. 



Experiments conducted with young bull frog tadpoles (Fig. 3) 

 and Daphma (Fig. 4) gave the same relative results as the experi- 

 ments conducted with cyanide on frog skin " cells." After being 

 separated from their cultural medium by cheese cloth, the organ- 

 isms were placed in Syracuse watch glasses filled with a solution 



en 



LJ 



ID 

 Z 



51 



4-0 



30 



7 



8 

 P H 



10 



FIG. 3. Curve showing the effect of pH on the toxicity of HCN to young 

 bullfrog tadpoles. Abscissae represents the pH; ordinates the time in min- 

 utes required to produce death. Ten animals were used in each test. 



of HCN in a borax buffer solution. It was previously deter- 

 mined that the animals were not killed in the buffer solution free 

 of cyanide until after an exposure of three to four hours. On ac- 

 count of the anesthetic action of the cyanide, tadpoles did not 

 prove to be good material for this work, since it was difficult to 

 determine the time of death. When Daphnia was used the beat- 

 of the heart could be observed under a binocular microscope and 

 the death point determined at the instant the heart stopped beating. 

 It was noted, that the heart continued beating for some time after 



