The Effect of Salt Concentration of the Medium on the Rate of Osmosis of Water through T H E Membrane of Living Cells

The present paper reports a further investigation ot' the kinetics of osmosis, using the unfertilized egg of the sea urchin Arbacia punctulata as an osmometer. In a previous communication dealing chiefly with the affect of temperature on osmosis, it was pointed out that the rate of osmosis is influenced by a second external factor, the salt concentration of the medium (1). I t is with this factor that the present investigation is concerned. The technic used was the same as that previously described. In order to understand the mechanism involved it was desirable to study the effect of salt concentration of the medium over a wide range --from 20 per cent to 125 per cent of sea water. 1 Hence it was obviously necessary that for low concentrations endosmosis should be studied, and for high concentrations exosmosis. This procedure was justified since both processes follow the same diffusion equation, l and since their velocity constants are practically identical when the concentration of the medium is the same in the two cases (2).