ABSTRACT
It is generally accepted that the cytoplasm of fresh-water Protozoa is hypertonic to the medium. This is based on circumstantial evidence and indirect measurements of the osmotic pressure of the body fluids. Inorganic ions are likely to account for a large part of the osmotic pressure, and in certain Protozoa radioactive isotopes may be used to determine the concentrations of ions. The isotope technique has been used to demonstrate that cells in Metazoa, namely nerve, muscle and erythrocytes, accumulate ions and carry out ionic regulation. Evidence is presented in this paper concerning the tonicity of the body fluids of the heterotrichous ciliate Spirostomum ambiguum and concerning its powers of ionic regulation.
Copyright © 1957 The Company of Biologists Ltd.
1957
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