494: ABSORPTION. 



cations of physical laws to the phenomena of absorption as it 

 occurs in the living body. 



Modifications of Endosmosis. 



Modifications due to the Extent and Thinness of the Per- 

 meable Membrane. It has been found in endosmotic experi- 

 ments, that the activity of the currents is in proportion to the 

 extent of the endosmotic surface and the thinness of the per- 

 meable membrane. In physiological absorption, the most 

 favorable conditions for endosmosis are realized in the capil- 

 lary system of highly vascular parts. The extent of absorb- 

 ing surface is here enormous ; and the walls of the vessels are 

 exceedingly delicate and permeable. The experiments of 

 Hagendie and others on vascular absorption, which have al- 

 ready been considered in detail, demonstrate the great ra- 

 pidity with which soluble substances are absorbed from the 

 highly vascular mucous membrane of the intestinal canal ; 

 and the experiments upon absorption through the walls of 

 the jugular vein show how much more slowly this takes place 

 when the membrane is thick, and the surface comparatively 

 restricted. 1 



Modifications due to Pressure and the Density of 

 Liquids. The force of the endosmotic current is frequently 

 so great as to overcome a very considerable pressure. This 

 is illustrated in all experiments in which the liquid in an 

 endosmometer is made to rise in a long tube. If a closed 

 membranous sac containing a highly endosmotic liquid be 

 immersed in water, the force with which the liquid pene- 

 trates will often be sufficient to rupture the membrane itself; 

 as is shown when an egg, with a part of its shell removed, is 

 placed in water. This forcible character of the endosmotic 

 current early attracted the attention of Dutrochet, whose 

 experiments on this point were very interesting. He intro- 

 duced into the reservoir of an endosmometer a saccharine 

 1 See page 472. 



