Expulsion of Injected Solute by Contractile Vacuole of Amoeba.

Although it has long been the presumption that the contractile vacuole expels substances in solution in the endoplasm of the protozoon, the actual taking up and expulsion of a definite solute by the organoid has never been demonstrated. This now has been accomplished by means of the micrurgical apparatus.

If a moderate amount of saturated aqueous solution of picric acid is injected into an ameba (Amoeba dubia) the course taken by the solute may be traced by its yellow color. The effect on the cytoplasm has already been described by Pollack. 1 Though a part of the colored region is often injured by the pipette and thereupon pinched off by the ameba, a certain quantity of the solute diffuses into the remaining endoplasm before this occurs. This is taken up by the vacuole, the intensity of the yellow color of the vacuolar fluid increasing in proportion to the fading out of color in the endoplasm.

When a 2% solution of picric acid in 95% alcohol is injected, diffusion throughout the endoplasm is much more rapid, and the yellow color appears more quickly in the vacuolar fluid. In the small percentage of cases where the injected region is not pinched off and the entire amount of the solute is retained, the fluid in the enlarging vacuole becomes an intense yellow. Such vacuoles progressively become very flaccid. Contact with the least obstacle, or stress exerted by endoplasmic currents easily causes their deformation. Their limp membranes may temporarily infold deeply, and the vacuoles often appear bean-shaped, long ovoid, or pyriform.