[macallum] cellular OSMOSIS AND HEREDITY 153 



These speculations of Overton, while veiy interesting, do not solve 

 the problem of osmosis wholly, for they offer in themselves difficnlties 

 wliieh Traube luis pointed out.^ For instance, if tliere must be soluition 

 in the lipoid material of the cell w-all before the substance can enter the 

 cell protoplasm, then even the most rapid osmosis would be a very slow 

 process. Further, it is impossible to understand why this lipoid material 

 should not hold tliis dissolved material all tJie more tenaciously, the more 

 forcibly it has attracted it, instead of passing it on to the interior of the 

 cell. It is above all impossible, Traube holds, to understand how water 

 ■can penetraite lipoid-holding membranes since it is not soluble in lipoids, 

 and further, salts, as in the case of renal and other secretions, readily 

 penetrate cells, which is quite irreconcilable with Overton's theorv. 



Moore ^ has also criticized the lipoid theory of osmosis in practically 

 the same terms as Traube, pointing out also that it does not furnish any 

 basis of explanation of how energy is expended in concentrating any 

 secreted or absorbed substance, and he also holds with Traube that a 

 lipoid as a good solvent for a given constituent does not give it the power 

 to pass tûiat substance through the cell in a more concentraited condition, 

 or indeed, to alter the concentration of the solute anywhere save in the 

 solvent itself. 



The criticism of Traube that a lipoid-holding membrane is imper- 

 meable to water will not hold wholly, for lecithin, cerebrin and protogon 

 swell up greatly in water and they are consequently permeable to water, 

 but Xathansohn ^ points out that when lecithin swells up in water it 

 (thereby loses the capacity to dissolve the substances soluble in lipoids. 

 He, however, would still accept Overton's theory, but would modify it 

 to account for the diffusion through lipoid-holding membranes of both 

 water and lipoid-soluble material. This, he does by postulating that the 

 membnane is a composite or mosaic structure in which a portion of the 

 component elements consists of unswellable cholesterin impermeable 

 to water and the remainder of pnotoplasmic material which has the pro- 

 perties of a typical semi-permeable membrane. 



In support of this view of Nathansohn, there are facts which Pas- 

 cucci * has determined. The latter found that the stromata of red blood 

 cells is consitituted, one-third of lecithin and cholesterin with a minute 

 quantity of a oerebrin-liTce compound, and the remainder, two- thirds, of 

 proteid. As the stromata consists in large part of the membranes of the 



1 1 c. 



^ Recent Advances in l^hy.siology and Biochemistry, edited by Leonard 

 Hill, p. 156. 



* Pringsheim's Jahrbuch. Vol. 39, p. 607, 1904. 



* Hof nneister's Beitrage, Vol. 6, p. 543, 1905. 



