864 THE LYMPHATIC SYSTEM. 



For the same membrane and different solutions of the same substance, 

 the direction and intensity of transudation depend upon the strength of 

 the solutions. With endosmometers containing solutions of sugar or 

 salt, and immersed in pure water, as shown by Dutrochet, the stronger 

 the solution the more rapid is the endosmosis from without ; and if two 

 solutions of salt be employed, with a membranous septum between them, 

 endosmosis takes place from the weaker solution to the stronger, and is 

 proportional to the difference in their densities. Density, however, is 

 not always the condition which determines the direction of the current. 

 For although with saline or saccharine solutions the direction of endos- 

 mosis is from the lighter to the denser liquid, with alcohol and water it 

 takes place from the water to the alcohol ; that is, from the denser to the 

 lighter liquid. It is evident from these facts that the process of endos- 

 mosis does not depend principally upon the attraction of the two liquids 

 for each other, but upon the attraction of the animal membrane for the 

 two liquids. The membrane is not a passive filter through which the 

 liquids mingle, but is the active agent which determines their transu- 

 dation. The membrane has the power of absorbing liquids, and of 

 taking them up into its own substance. This property, belonging to 

 the membrane, depends upon the organic ingredients of which it is com- 

 posed ; and, with different animal substances, the rate of absorption is 

 different. The tissue of cartilage, for example, as shown by the experi- 

 ments of Chevreuil, will absorb more water, weight for weight, than that 

 of the tendons; and the tissue of the cornea will absorb nearly twice as 

 much as that of cartilage. 



The continuance of endosmosis is much favored by renewal of the 

 two liquids. Since the accumulation of fluid on one side of the mem- 

 brane depends on the difference in composition of the liquids employed 

 and the consequent difference in their rate of absorption, when endos- 

 mosis has been for some time going on, and the two liquids have 

 approximated each other in composition, the activity of endosmosis 

 will be diminished in proportion. As the salt or sugar passes out- 

 ward to the water and the water inward to the solution in the endos- 

 mometer, the external liquid acquires a saline or saccharine ingredient, 

 and the interior solution becomes more dilute ; and when the two liquids 

 have thus arrived at the same or nearly the same composition, endos- 

 mosis must cease. But if the exterior liquid be constantly replaced by 

 a current of pure water, and the interior solution maintained at its 

 original strength by the addition of new ingredients, the process of 

 transudation will go on with undiminished activity until. the membrane 

 has lost its absorbent power. The effect of a constantly renewed cur- 

 rent in aiding endosmosis may be readily shown by filling the cleansed 

 intestine of a rabbit with water from a reservoir and then placing it in 

 a shallow glass vessel containing a dilute solution of hydrochloric acid. 

 If the water be allowed to flow through the intestine under pressure 

 from the reservoir, that which is discharged from its open extremity 

 will in a few seconds show the presence of hydrochloric acid by its 



