Physiological Effects of a Hypotonic Environment

Abstract

1. The reactions of isolated rhythmic preparations from Arenicola marina, Nereis diversicolor and Perinereis cultrifera to hypotonic saliness are described. 2. The preparations used were (1) the "isolated extrovert" of all three species, (2) ventral longitudinal body-wall strips of the two last named. All these preparations are essentially alike in their reactions to dilution of the bathing medium. 3. On abruptly changing from sea water to a hypotonic fluid, responses of the following general type are seen: first, brief excitement; then a phase of more or less complete inhibition; finally, provide the hypotonic fluid is not below a lower salinity limit characteristic of the preparation, gradual return of activity as the preparation accommodates itself to the new medium. The first two phases are shock effects of sudden dilution. The inhibition phase may last for many hours. 4. Preparations were exposed to salinities which fell gradually at various speeds. From the results of these experiments it is inferred that shock effects of rapid change are unlikely to be evoked under natural conditions, at least in Arenicola and Nereis. 5. The lower salinity limits for spontaneous activity in the tissues of the various species are: Perinereis cultrifera, 20-25% sea water; Arenicola marina, 15-20%; Nereis diversicolor, 5-10%. The results are discussed with reference to the ability to live in brackish water. 6. On suddenly returning from a hypotonic fluid to normal the responses vary. There may be relatively slight excitation (Arenicola marina extrovert) or a cycle of excitation--inhibition--accommodation like that evoked by a sudden downward change (Nereis diversicolor body wall).