Determinations of the pH of Developing Fundulus Eggs.

By the use of a micro-pipette, solutions of Clark and Lubs' indicator dyes were injected into the subchorionic space, the pericardial cavity, and the yolk of developing Fundulus eggs, 4 to 6 days after fertilization, and the colorimetric pH values of the contents were determined. A few injections were also made into the brain vesicles. Single injections were made in most of the eggs. In several cases an injection was made into the subchorionic space, then the pipette was carried into the pericardial cavity, and another injection made in order to detect simultaneously any possible difference in the pH of different spaces in the same egg. The color tints of the indicators were always determined at the horizon of the egg in order to eliminate interference from the yellowish color of the yolk.

The color of the subchorionic space indicated a pH identical with that of sea-water. The critical indicators used were phenol red and cresol red, but the indicators above and below the ranges of these two were also injected. If the developing eggs were placed in distilled water for 18 hours and then injected, the pH of the subchorionic space was found to be that of the surrounding medium, viz., 5.6±1. Controls in sea-water exhibited a subchorionic pH of sea-water. There was no leakage around the pipette at the point of puncture, because the outward diffusion of the injected dye occurred only through the membrane as a whole, and not around the pipette at the site of the puncture.

In his experiments on the permeability of developing Fundulus eggs to acid, Loeb 1 stressed the importance of placing the eggs in distilled water for 24 hours previous to the experiment in order to rid the membrane of adhering electrolytes.