The Form of Dye Penetrating the Cell as Determined by the Glass Electrode.

Measurements with the glass electrode show that cresyl blue in the form of salt∗ decreases the pH value of distilled water and in the form of free base∗ increases it. The free base also increases the pH value of the sap freshly extracted from the vacuoles of living cells. This difference in the behavior of the dye salt and the free base enables us to determine whether free base of cresyl blue penetrates into the vacuoles of living cells of Nitella.

The pH value of the sap of Nitella (obtained from Maryland) was measured by means of the glass electrode immediately after extraction at about 25°C. The duration of each measurement was about 5 minutes. The pH value of the sap of the control cells was pH 5.77. Using indicator methods previously employed 1 with brom cresol purple (appearing yellowish when dissolved in distilled water) the sap from the control cells was only 0.1 pH lower. Each measurement was made immediately after extraction and took about 5 minutes. As the dye penetrates, the pH value of the sap is gradually increased to the extent of 0.5 pH or more.

The same concentration of brilliant cresyl blue produces approximately the same increase in pH value whether it penetrates the vacuole of a normal cell or is added in the form of free base in vitro to freshly extracted sap.

The work is being continued.

The measurements in distilled water were made by Dr. A. E. Mirsky 2 while those in the sap were made by Dr. M. Dole. 3 I wish to thank them for their kindness and courtesy.