Section IV., 1908. [ 14S ] Trans. R. S. C 



VIII. — CeUuIar Osmosis and Heredity. 

 By A. B. Macallum, Ph.D., Sc.D., LL.D., F.R.S. 



(Read May 26th, 190S.) 



The constant review of the concepts of science, the testing of them 

 at ever}' point and the consequent revision of their accepted values con- 

 tribute a special feature which distinguishes the scientific thought of our 

 da}^ and measures the vigour of the scientific spirit. Science no more 

 than dogma can be infallible, for though it may aim at infallibility, it 

 ehoidd never claim to have attained it. Science is acceptable only because 

 its tenets are being constantly subjected to the closest scrutiny by a per- 

 petual procession of researchers whose verdict is always being rendered, 

 but whose final A^'ord on all points may never be uttered. 



/To question any doctrine or concept commonly received in science 

 is therefore, not evidence of heresy in the critic and it may, however, be 

 an imperative duty, for only in the questioning spirit may be found the 

 true attitude of mind which in the final sunmaing up will prove of ser- 

 vice to science. 



These introductor}- remarks are to constitute an explanation of the 

 position which I, am to take in the following pages, for I am to discuss 

 in the questioning spirit the application of two of the doctrines of 

 physical chemistry to the physiological phenomena of osmosis. 

 One of these doctrines is that in solutions, the substance dissolved is in 

 such a condition that its molecules are separated from each other as they 

 wouM be if such substance were in a gaseous condition, occupying the 

 same volume as the solution, and that it, in such solutions, illustrates all 

 the gas laws. The other doctrine is associated witii tlie first, and indeed, 

 inseparable from it. In all the discussions and speculations of the last 

 thirty years on the nature of physiological osmosis, it has occupied a cen- 

 tral point, and it is now almost a common place in physiological text- 

 books and treatises. This second doctrine is that of the semi-permeable 

 membrane. 



The concept of a semi-permeable m^embrane postulates a diaphragm 

 which is freely permeable to water, for example, but not to any substance 

 dissolved in it. If, for instance, sugar is the solute, the membrane will 

 not permit it to pass through to the other compartment, but the water 

 of the latter diffuses through to dilute the solvent of the sugar. The 

 membrane is so constituted as to retard completely the passage of the 

 molecules of the solute, but not the solvent. 



Sec. IV., 1908. 10. 



