Abstract
In previous papers 1 the writer has described the accumulation of brilliant cresyl blue in the sap of Nitella and has discussed certain theoretical explanations. The present paper deals with the possibility of explaining accumulation on the basis of dissociation as recently discussed by Osterhout. 2 For this purpose we may assume that the dye enters in the form of dye hydrate (DOH) but that ions are unable to pass in or out. At equilibrium DOH has the same concentration inside the cell as in the outside solution, but if the pH value is lower in the sap there will be more dissociation, and consequently the total concentration of the dye (ions plus undissociated molecules) will be greater than in the outside solution. The difference in concentration can be calculated if the dissociation constant of the dye and the pH values inside and outside are known. When the previous papers were published, such calculations were attempted but at that time the experiments were not sufficiently complete for this purpose. Since then the writer has been able to secure the necessary data.
Living cells of Nitella were placed at 25 ± 0.5° C. in 0.00002 M dye solutions at different pH values, from pH 6.4 to pH 9.2 (M/150 phosphates or borates). At definite intervals the cells were removed from the solutions. The end 3 of each cell was then cut and the sap was squeezed out upon a glass slide. The sap was then drawn up into a capillary tube, the color of which was matched with that of the capillary tube containing the standard dye solution.
It was found that the greater the pH value of the outside solution, the higher was the rate of penetration, and the greater the concentration of the dye in the cell sap at equilibrium.
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