82 Diffusion and Osmotic Pbessuee 



of this nature which are of general occurrence in animal and 

 plant cells, when in certain mixtures, absorb water. He 

 suggests that the tonoplast and ectoplast may be merely 

 layers of such substances, and gives reasons why it is not 

 plausible to suppose that a simple aliphatic oil plays this 

 part of surface layer, as was supposed by Quincke.' The 

 difference, however, between oils and lecithins is so slight 

 that Quincke's theory is not fundamentally modified by 

 these facts. 



On the purely physical side Meerburg's work^ on the 

 passage of fuchsin through membranes of copper ferro- 

 cyanid seems to present evidence in favor of the solution 

 theory. The dye could not pass the membrane, even in a 

 slight degree, until the latter had become fully irapregnated 

 with it. Flusin also showed ' that the rapidity of diffusion 

 of various substances through a membrane of caoutchouc 

 varies in the same degree as does the absorptive power of 

 the membrane for these substances. The same was found 

 to be true for pig's bladder. 



c) The chemical theory. — The chemical explanation of 

 the phenomenon of semi-permeability supposes that the 

 membrane takes an active chemical part in the transmission 

 of substances from one side to the other. In all its free- 

 dom of indefiniteness this theory offers the only escape from 

 the dark problem of glandular secretion, wherein the solute 

 moves from the weaker to the stronger solution against its 

 own diffusion tension. This is one of the most difficult of 

 physiological problems, and upon it absolutely no light has 



1 Quincke, "Ueber Emulaionsbildung nnd d. Einfluss der Galle bei der Ver- 

 danung," PflUgers Arch./, d. ges. Physiol., Vol. XIX (1879), pp. 129-44. 



2 J. H. Meeeboeo, " Zur Abhandlung Tammanns : Ueber die Permeabilitat der 

 Niederscblagsmembranen," Zeitschr. f. physik. Chem.., Vol. XI (1893), p. 446-8. 



3 G. Fldsin, " Sur Tosmose des liquides & travers une membrane de caoutchouc 

 Tulcanlsfi," Compt. rend.. Vol. CXXVI (1898), pp. 1497-1500; IDEM, "Sur I'osmose des 

 liquides h travers une membrane de vessie de pore," ibid.. Vol. CXXXI (1900), pp. 

 1308, 1309. 



