macallum] cellular OSMOSIS AND HEREDITY 151 



must be decreased and in consequence the layer of liquid in contact with 

 the Avail will become richer in salt than the rest of the solution.^ When 

 the solution moves through capillar}^ tubes, along a filter or upwards 

 through finely divided quartz, the salt will collect on tlie capillai-y walls, 

 on the fibres of the filter, or on (the particles of quartz, and the cun-ent, 

 as it ascends, will become more and more dilute until finally it is dis- 

 tilled water. J. J. Thomson and Monckmian filtered potassium perman- 

 gajiate from its solution by passing it through finely divided silica and a 

 sjmjlar separation may be obtained by allowing dilute permanganate 

 sohutions to diffuse into filter paper. Perhaps the most striking illus- 

 trations of this plienomeiLon may bie obtained by suspending long strips 

 of filter paper so as merely to dip into a dilute solution of copper acetate. 

 In a few minutes the fluiid runs up several inches, but the upper half 

 inch or inch of the moistened portion does not contain a trace of the 

 copper solution, as may be shovm by treatment with potassium feiTO- 

 C3'anide solution or ammonium sulphide. 



When, in consequence, a septum is in contact with a solution whose 

 air tension is high, the solute wi^l tend to condense on the surface of the 

 septum, while the solvent will pass through. This would cause ;the rerten- 

 tion of such substances as sugar, urea, etc., while pennitting the solvent, 

 water, to transude. 



It mustt, however, be admitted, that surface tension is not a factor 

 fufficient to explain all the phenomena of osmosis, and especially those 

 manifested in cellular absorption and diffusion. It will not explain the 

 ûbsoi'ption of colloids in the intestine, the passage of fats and pro4;eins 

 through the endotheliial lining of capillaries and the diffusion through 

 living membranes of material which is not in solution, but rather in 

 suspension as colloids. The difficulty of explaining these and the in- 

 adequacy of the concept of the semi-permeable membrane has promoted 

 in recent years revival of the old doctrine of vitalism as a distinot force 

 concerned in .the exchange of material through the septa formed by liv- 

 ing cells. To accept an hypothesis postulating the existence of a biotic 

 or vital force distinct from the physical or chemical ones that we know 

 and can examine is, I think, to despair of an intelligible solution of the 

 problem and it does not seem justifiable as yet to adopt that attitude, 

 the more so since the range of facts bearing on the problem has been 

 recently greatly widened. 



Overton,^ who has investigated at great length the velocity with 



^J. J. Thomson, Applications of Dynamics to Physics and Electricity. 



' Vierteljahresschr. Naturforsch. Gesellsch. in Zurich, "Vol. 44. p. 88, 1899; 

 Arch, fur d. ges. Physiol., Vol. 92, p. 261, 1902; Jahrb. fur wiss. Bott., Vol. 34, 

 p. 669, 1900. 



