A CONTHrBUTION TO THE PHYSICAL ANALYSIS OF THE 



PHENOMENA OF ABSORPTION OF LIQUIDS 



BY ANIMAL TISSUES 



Ralph W. Webster 



I. INTRODUCTION 



The following paper is, as the title indicates, intended to be a contribution to the 

 physical analysis of phenomena of absorption by living tissues. That the older exper- 

 iments on absorption could not lead to any satisfactory explanation of the processes 

 involved seems evident from the fact that only recently has there been discovered one 

 of the most fundamental theories concerning the exchange of liquids separated by mem- 

 branes, more or less semi-permeable. Only such papers can be expected to throw a 

 light on this subject as take cognizance of this theory of osmotic pressure. 



Van't Hoff, applying certain facts brought out by Traube and Pfeffer regarding 

 the influence of semi-permeable membranes upon processes of osmosis, showed that sub- 

 stances in solution obey the ordinary laws of gases, as brought forth by Boyle, Henry, 

 Gay-Lussac, and Avogadro. In consequence of this similarity between gases and sub- 

 stances in solution, the latter will exert a pressure upon the walls of a containing vessel 

 equal to the pressure which the dissolved substance would exert were it present in the 

 gaseous form under the same conditions of temperature and molecular aggregation. 

 Whether this pressure, which van't Hoff calls" osmotic pressure," be due to the 

 impacts of the dissolved particles against the walls of the containing vessel, as the 

 kinetic theory of gases would demand, or whether it be an expression of the attraction 

 of the dissolved particles for water, concerns us, in these experiments, only in so far as 

 our work has to do with the dynamics of the process of absorption. 



From these facts it is evident, as van't Hoff shows, that the pressure of a sub- 

 stance in solution depends both upon the concentration of the substance and upon the 

 temperature at which the observation is made. By the concentration we mean, not the 

 number of molecules, as such, contained in a definite amount of the solvent, but, rather 

 the total number of " active " particles contained in a definite (usually 1 liter) amount 

 of solvent. This fact was made clear by the endeavor to collate the pressures of various 

 salt solutions with those of organic substances, or, in other words, of electrolytes with 

 those of non-electrolytes. Clausius had shown that the molecules of substances con- 

 ducting electricity, viz., of electrolytes, are dissociated into ions, which have a move- 

 ment independent of one another. Arrhenius, in his work on Dissociation of Sub- 

 stances Dissolved in Water, advanced the hypothesis that the molecules of substances 

 in solution suffer a dissociation into their electrically-charged ions (an ion being con- 

 sidered as an atom, or group of atoms, carrying an electric charge -|- or — , according 



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