EN'DOSMOSE AND EX'OSMOSE (Gr. inward motion and outward motion), terms applied by Dutrochet, the first investigator, to the transfusion that takes place when two liquids or two gases of different densities are separated by an animal or a vegetable membrane. As the transmission has no necessary relation to out wards or inwards, the term osmose, or osmotic action, is now preferred. See DIFFUSION.
This action performs a very important part in living organisms, and explains many phenomena of the circulation of sap and the processes of nutrition, which were previously referred only to the wonderful action of vital energy. Thus, the blood continually streaming through the capillary vessels gives forth a portion to the surrounding cells, and so supplies them with the necessary chyle. This may, however, by the expansion of the capillary vessels (see lead to immoderate exudation. On the other hand, the blood, in passing by, takes up a number of worn-out constituents of the juices of these cells, and in this way serves, by the exchange which it effects, to restore the body, and to disburden it of products which have become uscless.—In plants also,
osmose performs an important part in the process of nutrition and the motion of the sap. The substances in the cells of plants are usually denser than the fluids without, and thus a process of endosmose takes place, by which the plant is supplied in the first instance from the soil, being incapable, however. of appropriating any nourishment which is not presented in a liquid state to the fibrils of its roots; whilst that which the roots give off by exosmose, is supposed gradually to unfit the soil for the growth of the same kind of plant. The bursting of the capsules of some kinds of plants is owing to a process of endosmose going on in the cells, as in the fruit of the claterium or squirting cucumber. Some of the entozoa, as tape-worms, seem to live entirely by endosmose. See OSMOSE.