ABSTRACT
The influence of some foreign ions and non-electrolytes on the relation between the chloride concentration and vapour pressure of the blood of Carcinus and the external solution has been studied. The added substances showed interesting specific effects, which are discussed in the text, but no general conclusion can be drawn. It is very probable, however, that the gill membrane is almost impermeable to water, so that osmotic forces, as such, play no part in producing the observed relationships between blood and the external medium. There is no evidence for active water regulation in Carcinus.
The latter conclusion is supported by experiments on the effects of cyanide and hypertonic solutions. In the latter case, in spite of “osmotic” regulation being abolished, no significant water transfer occurs.
Miscellaneous experiments on the result of varying pH and temperature are described ; in each case the effects are surprisingly small.
In a single experiment, the isolated gill tissue of Carcinus showed no secretory activity. The method used, based on Hill’s “bound water” technique, is described in detail.
An analysis of the dilution-time curves for Carcinus in dilute solutions suggests that the process is accompanied by considerable changes in the properties of the gill membrane, before the beginning of the real regulatory mechanism. The same data permit the calculation of the work done in maintaining the steady state, but the result is improbably high.
A direct study has been made of the vapour pressure of the body fluid of Ligia oceánica living under various conditions. For short periods of immersion in dilute solutions the animals show a high degree of osmotic independence, but their resistance breaks down on prolonged immersion.
A method was tested for the study of internal concentration changes in animals too small for direct measurement. The results of an experiment on Gammarus locusta are discussed.
