Endosmose

(-dos-mōz.) [Gr. end on, and osmos, impulsion.] (Physiol.) When two different liquids are separated by a thin porous partition, either inorganic or organic, a current sets in from each liquid to the other; to these currents the names endosmose and exosmose are respectively given. These terms, which signify impulse from within, and impulse from without, were first introduced by M. Dutrochet, who first drew attention to these phenomena. They may be well illustrated by means of the endos mo meter. This consists ofa long tube, at the end of which a membranous bag is firmly bound (Fig. 305). The bag is then filled with a strong syrup, or some other solution denser than water, such as milk or albumen, and is immersed in water. The liquid is found gradually to rise in the tube, to a height which may attain several inches; at the same time, the level of the liquid in which the endosmometer is immersed becomes lower. It follows, therefore, that some of the external liquid has pa ed through the membrane and has mixed with the internal liquid. The Fig.305. ENDOSMOMETER. external liquid moreover is found to contain some of the internal liquid. Hence two currents have been produced in opposite directions. The flow of the liquid towards that which increases in volume is endosmose, and the current in the opposite direction is exosmose. If water be placed in the bag, and immersed in syrup, endosmose is produced from the water towards the syrup, and the liquid in the interior diminishes in volume while the level of the exterior is raised. The height of the ascent in the endosmometer varies with different liquids. [s. 330]