INFLUENCE OF MEMBRANES UPON OSMOTIC CURRENTS. 485 



such thing as porosity in the septum. The following exper- 

 iment of Lhermite fully illustrates this point. A tube was 

 partly filled with a column 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 chloroform, and the 

 layer of water retained its original volume. 1 We have re- 

 peated 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 phenome- 

 non 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 con- 

 sidered as definitely settled : 



The cohesive attraction of the constituent particles of in- 

 soluble solids is so great, that the entrance of fluids is impossi- 

 ble, unless the substance be porous ; and this always involves 

 the law of capillary attraction ; but in liquids, the cohesive 

 attraction is so slight as to admit of the penetration and dif- 

 fusion of certain other liquids. 



Homogeneous animal membranes, which are of a semi- 

 solid consistence, are capable of imbibing certain liquids ; 

 and any liquid which can pass into such membranes, under 

 proper conditions, will pass through them. The cohesive 

 attraction of the particles of the membrane is not such as to 

 allow them to imbibe an indefinite quantity of any liquid ; 

 but it is one of the distinctive properties of organic tissues 



1 LHERMITE, Recherches sur V Endosmose. Comptcs Rendus^axls, 1854, tome 

 xxxix., p. 1179. 



