The Significance of Gelation in the Systole of the Contractile Vacuole of Amoeba dubia.

Abstract

I. MECHANICAL SUPPORT DURING SYSTOLE.

Observations of the position and behavior of the contractile vacuole of Amoeba dubia, lead to the conclusion that, under normal conditions, the vacuole, at systole, is lodged in a region, which, judged by certain optical and experimental criteria, is gelated. The optical evidences of this gelation are: first, tinder ordinary transmitted illumination, the absence of translatory movement, and the relative fixed position of the granules and crystals involved; second, on dark field examination, the absence of Brownian movement, and the appearance of fibrillar lines in this region. The experimental evidence is derived from: first, testing the consistency of the endoplasm by means of a microneedle; second, repeated local agitation of an endoplasmic region, which causes it to change from a motionless (and apparently gelated) to a distinctly flowing state. This last is interpreted as due to a reversal of phases.

The constant occurrence of this encapsuling area of gelation in the normal ameba, suggests that it functions as a source of mechanical support for the vacuolar membrane during systole. It is not unreasonable to assume that a phenomenon analogous to syneresis in the gelated region may initiate systole. Experimental evidence confirms the first of these assumptions. The microinjection of urea∗ greatly increases the fluidity of the internal protoplasm, so that the ameba takes on a limax form. The lack of gelation results in the absence of internal mechanical support for the vacuole, which becomes greatly dilated.

II. EFFECT OF INJECTED WATER.

In accordance with the results of Chambers and Reznikoff, 1 the gradual injection of distilled water at a pH of approximately 6.6 to 6.8, affects the physiological state of the organism but slightly.