CHAPTER I. SEMI-PERMEABLE MEMBRANES AND OSMOTIC PRESSURE. ALTHOUGH th e process of osmosis, or diffusion . of a liquid through a membrane, appears to have been discovered as early as 1748 by the Abb6 Nollet, l and although many observations on the process of osmosis were made in later years by other investigators, who were attracted to the subject chiefly on account of its physiological interest, it was not till many years later, between I 826 and I 846, that quantitative measurements were carried out by Dutrochet and by Vier rdt. - B y them it was found that when a salt solution is separated from water by means of a membrane of pigs bladder, the water diffused through the membrane more rapidly than the salt. The level of the solution therefore rose, and a hydrostatic pressure was produced and since this pressure was brought about by osmosis, it was called an osnzotic pressure. By Dutrochet and by Vierordt it was established that the difference between the rates of osmosis of pure water and of salt solution depends not only on the nature of the salt but also on the concentration of the solution and, as was found later, on the nature also of the membrane or permeable septum employed. This influence of the membrane, indeed, was utilized at a later time by Thomas Graham for the separation of different substances by dia sis, and led to the characterization of substances as crystalloids and colloids. The. fact discovered by Graham that colloidal substances do not pass through colloidal membranes, was seized on by Moritz The terms endosmosis and exosmosis, applied to the oppositely directed diffusion currents, were first used by Dutrochet. The single term osmosis is now used to denote the whole process of diffusion through a membrane or permeable septum. It has been shown recently that, diffusion does indeed take place but at a very slow rate comparatively, depending on the nature of the membrane and of the diffusing colloid, 1 .. . . . . . . . . OSzWOTZC PRESSURE L . . . . - . L . Traube as pointing to a method for imitating the behaviour of vegetable cells which, as was already known, are surrounded by a membrane through which osmosis can take place...