happen to exist, or to predominate, in their saline habitat. At the same time we still lack (so far as I know) the simple, but crucial experiments which shall tell us whether, in solutions of different chemical composition, it is at equal densities, or at ãisotonicã concentrations (that is to say, under conditions where the osmotic pressure, and consequently the rate of diffusion, is identical), that the same structural changes are produced, or corôÙreôÙsponôÙding phases of equiôÙlibôÙrium attained.
While HûÑber and others84 have referred all these phenomena to osmosis, Abonyi is inclined to believe that the viscosity, or mechanical resistance, of the fluid also reacts upon the organism; and other possible modes of operation have been suggested. But we may take it for certain that the phenomenon as a whole is not a simple one; and that it includes besides the passive phenomena of intermolecular diffusion, some other form of activity which plays the part of a regulatory mechanism85.
Growth and catalytic action.
In ordinary chemical reactions we have to deal (1) with a specific velocity proper to the particular reaction, (2) with variations due to temperature and other physical conditions, (3) according to vanãt Hoffãs ãLaw of Mass,ã with variations due to the actual quantities present of the reacting substances, and (4) in certain cases, with variations due to the presence of ãcatalysing agents.ã In the simpler reactions, the law of mass involves a steady, gradual slowing-down of the process, according to a logarithmic ratio, as the reaction proceeds and as the initial amount of substance diminishes; a phenomenon, however, which need not necessarily {131} occur in the organism, part of whose energies are devoted to the continual bringing-up of fresh supplies.
Catalytic action occurs when some substance, often in very minute quantity, is present, and by its presence produces or accelerates an action, by opening ãa way round,ã without the catalytic agent itself being diminished or used up86. Here the velocity curve, though quickened, is not necessarily altered in form, for gradually the law of mass exerts its