324 ABSORPTION. 



tireless. In applying the laws of endosmosis to physiological absorption, it is found that 

 the membranes which are most easily penetrated by fluids are excessively thin and 

 nearly homogeneous. Take, for example, the walls of the capillary blood-vessels, through 

 which the greatest part of physiological absorption takes place. This membrane is 

 from 2 g^oo to -reyor ot an i ncn thick, and is entirely amorphous, with the exception of 

 the lining epithelium with its nuclei. The assumption that invisible capillary orifices 

 exist in these thin, amorphous membranes, aside from the so-calle'd stomata, is purely 

 hypothetical and is unwarrantable. The only circumstance which could lead to such a 

 supposition is the fact that these membranes can be penetrated by liquids. 



It is manifestly unphilosophical and absurd to offer, as an explanation ot endosmosis 

 through structureless membranes, an hypothesis which has its only support in the exist- 

 ence of the phenomena which it is intended to explain. This mode of reasoning is all 

 the more unsound, as the phenomena of endosmosis are very far from being completely 

 understood, and as many important properties of organic structures, which bear directly 

 upon the question under consideration, are ignored. For example, physiological absorp- 

 tion does not always take place in accordance with known physical laws. It undergoes 

 modifications which can at present only be explained on the supposition that the liquids 

 become, for the time, part of the living organic structures and partake of their peculiar 

 properties; one of them, the property by virtue of which they appropriate both the 

 organic and the inorganic principles necessary to their proper constitution and regenera- 

 tion, is called by some, vital ; a word which simply expresses ignorance of its essen- 

 tial character. It must be understood, however, that this remark does not apply to the 

 general phenomena of endosmosis or absorption, but only to certain of its unexplained 

 modifications. 



A most important property of organic tissues, which is ignored by those who explain 

 absorption on the principle of capillary attraction, is that of hygrometricity. All the 

 organic nitrogenized proximate principles are capable of losing their water of composi- 

 tion by desiccation and of regaining it by imbibition. The water which enters into their 

 composition is not necessarily contained in interstices in the tissue, but, in the case of 

 structureless parts especially, is uniformly disseminated, or, we may term it, diffused 

 throughout the organic substance, of which it forms a constituent part. This action of 

 certain liquids upon the organic semisolids is something like the diffusion of liquids ; the 

 difference being that it is the liquid only which is diffused in the semisolid, the semisolid 

 being incapable of diffusing in the liquid. As it has been found that all liquids are not 

 equally subject to capillary attraction, so animal tissues imbibe different liquids with dif- 

 ferent degrees of activity; a fact which will account in a measure for the variations in 

 the end osmotic currents with different solutions. 



Examples are not wanting of endosmosis by imbibition or diffusion, when it cannot 

 be assumed that there is any such thing as porosity in the septum. The following 

 experiment of Lhermite fully illustrates this point. A tube was partly filled with a col- 

 umn of chloroform ; and upon this was poured a layer of water, and above it a layer of 

 ether. The ether gradually penetrated the layer of water and passed to the chloroform, 

 mingling with it. After a certain time, all the ether had thus been diffused in the chlo- 

 roform, and the layer of water retained its original volume. We have repeated this 

 experiment with some slight modifications, using first a layer of sulphuric acid, then a 

 layer of water, and finally a solution of blue litmus in alcohol ; and, in a very short 

 time, the acid penetrated the water and reddened the litmus above. A liquid septum is 

 certainly not porous, in any sense of the word; and the explanation of the phenomenon 

 of endosmosis through liquids depends simply upon the law of diffusion of liquids, the 

 molecules of the liquids being held together so feebly that they will admit the molecules 

 of other liquids with which they are capable of mixing. 



With regard to the passage of liquids through different septa, the following seem to be 

 the facts which can be considered as definitely settled : 



