40 



Scientific Proceedings (125) 



a. In phosphate buffers of .033 M the proportion of cells sur- 

 viving in good condition was greatest, (92 per cent.) at P H 6.2, 

 and decreased when the medium was more acid or alkaline. 



b. When atoxyl (in .05 M concentration) was present the 

 number of cells in good condition after 24 hours was greatest, 

 (94 per cent.) at P H 5.6, decreased gradually to 86 per cent, at 

 P H 6.4 and then suddenly to 6 per cent, at P H 7.5. 



c. Arsenate buffers (of .05 M) acted much like phosphate 

 buffers, but showed a greater general toxicity : thus under the 

 most favorable conditions (P H 6.4) 80 per cent, of the ceils sur- 

 vived in good condition as compared with 92 per cent, in the case 

 of the phosphate buffers. 



d. The optimum P H for survival of Nitella when placed in 

 either phosphate buffers or arsenic buffers was 6.2-6.4, and was 

 not the same as the normal P H °f tne ce M sa P of Nitella, which 

 was found to be 5.7. 



2. The conditions affecting arsenic penetration are illustrated 

 by the experiments with solutions containing atoxyl, in which no 

 arsenic penetrations was observed between P H 5.6 and 6.4, while 

 positive tests were obtained at all higher values of the P H with 

 a maximum of 22 mg. in 0.036 c.c. of cell sap at P H 7.5, which 

 was the most alkaline solution used. 



3. The amount of arsenic in living (even though perhaps in- 

 jured) cells was always considerably less than the arsenic con- 

 tent of the solution in which the cells were placed. 



4. Dead cells, i.e., those which were limp and with shrunken 

 cell contents had an arsenic content approximately equal to that 

 of the solution in which they were placed. 



5. The cell walls were found to contain considerably more 

 arsenic than the cell sap. 



From these experiments it may be concluded that the penetra- 

 tion of the arsenic of atoxyl into the cell sap of Nitella is strik- 

 ingly correlated with the H ion concentration of the suspension 

 fluid. This apparent relationship between the H ion concentra- 

 tion of the suspension fluid and the penetration of arsenic may 

 possibly be due to ( 1 ) an influence of the H ion concentration 

 upon the dissociation of atoxyl, or (2) changes in the permea- 

 bility of the cell for arsenic due to the action of either buffer 

 ions or H ions. 



