494 PROCEEDINGS OF SECTION D. 



in the sulphuric acid solution, and the mercury becomes positively 

 charged, while the sulphuric acid solution becomes negatively charged. 

 The difference of electric potential thus established between the mercury 

 and the sulphuric acid solution tends to slow down the hydrogen ions 

 which are diffusing in and to accelerate the SO^ ions; hence the difference 

 of electric potential increases more and more slowly, and finally reaches 

 a constant value, and a constant excess of hydrogen over SO4 ions is 

 maintained in the mercury. In the case of an electrolyte diffusing into 

 a tissue we have a somewhat different state of affairs. Here the ions, on 

 entering the tissue, combine with some constituent of the tissue in pro- 

 portion to their concentration in the tissue. In so doing they must set 

 free from the tissue other ions bearing the same electric charge, and 

 since, for example, if positive ions enter into the tissue in excess more 

 positive ions will be set free from the tissue than negative ions ; the 

 positive ions thus set free will diffuse out of the tissue more rapidly than 

 the negative ions which are set free. This excess of positive ions 

 diff'using out of the tissue will take the place of the excess of positive 

 ions which has diffused into the tissue from the solution, and no 

 difference of electric potential will arise ; so that the process will be 

 limited only by the power of the tissue to combine with the ions 

 diffusing into it. 



To clarify our conceptions of this process let us consider a concrete 

 example. Suppose we have a tissue in which the chief saline constituent 

 is sodium chloride, and that we place this tissue in a solution of mag- 

 nesium nitrate. In a solution of magnesium nitrate the NO3 has a much 

 higher velocity than the magnesium ion, so that many mor° equivalents 

 of NO3, carrying negative charges, enter the tissue in a unit of time than 

 equivalents of magnesium carrying positive charges. These NO3 ions 

 will displace chlorine, and also, probably, hydroxyl ions from the ion- 

 proteid constituents of the tissue, while the magnesium ion will displace 

 sodium and hydrogen ions. But, since very many more equivalents of 

 NO3 enter the tissue than equivalents of magnesium, very many more 

 chlorine and hydroxyl ions will be displaced from the tissue than sodium 

 and hydrogen ions. Hence many more chlorine and hydroxyl ions, 

 carrying negative charges, will dift'use out of the tissue than sodium and 

 hydrogen ions; and this excess of negative charges carried out of the 

 tissue will tend to neutralise the excess of positive charges left behind in 

 the solution of magnesium nitrate, on account of the excess of NO3 ions 

 which has entered the tissue. Thus the process will go on, if the 

 medium is a solution of pure magnesium nitrate, until nearly all the ion- 

 proteid is in the form of a compound, or of compounds, with magnesium 

 nitrate, and nearly all of the sodium chloride is displaced from the tissue ; 

 then, just as in the case of the capillary electrometer, a potential difference 

 will begin to arise between the tissue and the solution, and the proportion of 

 NO3 and magnesium ions entering the tissue per unit of time will 

 gradually assume equality. 



On the basis of this hypothesis it is evident that the chemical pro- 

 perties and affinities of a tissue must be profoundly influenced by the 

 relative velocities of migration rif the ions in the solution bathing it. We 

 should especially expect to find the acid or basic properties of a tissue 

 profoundly affected by the relative proportions of anions and cations 

 entering the tissue. Just as phenol, by the substitution of three of its 



