The osmotic force must be distinguished from DIFFUSION ; for in the latter case, if a saline solution were in the interior reservoir, liquid salt particles would ooze through the membrane, and a certain quan tity of water would flow back and take their place; but if this were a case of diffusion the water would not be more than five or six times the weight of the escaping salt, whereas the water entering the osmotneter may exceed the weight of the escaping salt 100 times or inure. Nor can osmose be identified with capillarity. [Catua.anr ATTRACTION AND REPULSION.] Many of the saline solutions which exhibit the greatest osmose are not distinguishable in capillary pheno mena from pure water. The force uf the osmotic current may also be measured in the following manner, devised by Liebig :—Close the open end of the short limb of a glass syphon by means of a piece of bladder ; pour a little mercury into the bend of the tube, and fill the shorter limb with the saline liquid. Immerse the bend of the tube and the membrane in water, leaving the extremity of the longer limb open ; and as the water enters the tube the mercury will rise in the longer limb, and when the column reaches a certain height the two liquids will intermingle without change of volume. The length of the column which has been raised above the level of the surface of the mercury is to be measured, and this, when compared with the lengths of the columns obtained with other liquids, will give a comparative measure of the osmotic force in each case. Thus it will be seen that chemical affinity
(shown by the action on the diaphragm) is converted into motive power, capable of numerical expression. It seems most probable that in the animal system there is an arrangement by which motive power is obtained from the decomposition of the tissues. All parts of living structures are in a condition of incessant change, decomposition, and renewal. It may one day be demonstrated that the osmotic injection of fluids is the associating link between muscular movement and chemical decomposition.
The flow of liquids through capillary tubes presents phenomena closely connected with diffusion. They are well discussed in M. Poiseuille'a memoirs (' Annales do Chimie; 3 aerie, xxi ). They are also stated in a briefer form in Professor Miller's ' Elements of Chemistry,' part i., 2nd edition, 1860, where the following remarks occur Osmotic phenomena are constantly going on both in plants and in animals ; for in their tissues liquids of very different natures, sometimes acid, still more often alkaline, are circulating through vessels necessarily constructed of flexiblo and porous materials, and in the ecooumy both of the vegetable and of the animal creation such actions are of the highest importance to the due performance of tho vital functions. In fact, we as yet know not how intimately the entire processes of absorption, nutrition, and secretion are connected with the operations of liquid diffusion and of endoemosis."