ON SOME APPLICATIONS OF THE THEORY 

 OF OSMOTIC PRESSURES TO PHYSIO- 

 LOGICAL PROBLEMS. 



IN a huge proportion of the most important functions of 

 the animal body, and especially those classed under the 

 heads of nutrition and secretion, the essential phenomenon 

 consists in a transference of fluid, containing" solids in a 

 condition of solution or semi-solution, across a membrane of 

 varying degrees of permeability. It is therefore natural 

 that experiments by chemists on the phenomena of osmosis 

 should have attracted the attention of physiologists and 

 incited them to further investigations on the subject ; and 

 we find in the earlier text-books, of which I may especially 

 instance the one by Ludwig, that the subject of osmosis 

 occupies a large section of the work. Until recent years, 

 however, our knowledge of the factors and forces involved 

 in the interchange of substances in solution across animal 

 membranes, was so meagre and inexact that the application 

 of them to physiology could merely serve as a pretext for 

 hazy speculation. 



Our first exact knowledge of the forces concerned in 

 osmotic phenomena was furnished by PfefTer when he 

 measured experimentally the osmotic pressure exerted by 

 various solutions when enclosed in semi-permeable cells. 

 The brilliant generalisations of Van t' H off have enabled us 

 to form a correct estimate of the forces involved and of the 

 work done in the osmotic transference of fluid from one 

 side of a membrane to the other, although we do not yet 

 know how it is that these solutions are able to attract 

 water through the cell-wall in order to exert an osmotic 

 pressure equal to that which the molecules of the dissolved 

 substance would exert if in the form of a gas. It was in 

 1877 that PfefTer 1 and De Vries - published papers on the 



1 Osfnoiische Untersuchungen. Leipzig, 1877. 



2 Die Mechanischen Ursachen der Zellstreckung. Leipzig, 1877. 



