The Influence of Alcohols on the Protoplasmic Membrane and Colloid Models

As is well known, the protoplast of living cells does not in the least act as a strictly semi-permeable membrane in the sense that it lets water pass, practically unimpeded, into the vacuole, whereas it does not permit the dissolved substance to pass at all; on the contrary, from solutions of a great number of substances in water, when brought into contact with the cell, the dissolved substance passes more or less quickly through the plasma and enters the vacuole: f.e. glycerol, glycol and several dyes. There are some, however, that do not penetrate, not even in the long rim and here a distinction should be made with plant-cells between substances, which, like cane sugar, penetrate into the plasma itself, hut do not, or only very slowly, pass through it into the vacuole and those which do not even enter into the plasma itself. In this research, as far as plant-cells are concerned, the former phenomenon, the so-called intrability, will not be discussed; it deals exclusively with the permeability of the plasma, i.e. the penetrability of the plasma up to the vacuole. Concerning the above mentioned selective permeability of the plasma different explanations were given. These nearly all agree in ascribing to the protoplast a certain boundary layer of special structure and composition and which is supposed to be the bearer of the selective permeability. With Hugo de Vries we take, with plant-cells, the tonoplast to be this layer.