When cells of Nitella are placed in buffer solutions at pH 9, there is a very slow and gradual increase in the pH of the sap from pH 5.6 to 6.4 (when death of the cells takes place). If the living cells are placed in 0.002 per cent dye solutions of brilliant cresyl blue at different pH values (from pH 6.6 to pH 9), it is found that the rate of penetration of the dye, and the final equilibrium attained, increases with increase in pH value, which can be attributed to an increase in the active protein (or other amphoteric electrolyte) in the cell which can combine with the dye.

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