THE PHYSIOLOGICAL EFFECTS OF IONS 451 



the work done in growth has never once been considered. 

 We need not go far to find the reason for this. Even in the 

 newer text-books of physiology the attraction of salts for 

 water is still spoken of as was the case fifty years ago; the 

 idea of osmotic pressure and the work of Van 't Hoff have 

 not yet worked their way into this territory. 1 



One of the most fertile results of the theory of dissocia- 

 tion is the idea which has been brought forward, chiefly by 

 Ostwald, that those reactions of acids in aqueous solutions 

 which are common to all acids, and only to these, are 

 dependent upon the activity of the positively charged hydro- 

 gen ion, and that in a similar way the universally specific 

 effects of bases are determined by the negatively charged 

 OH ion. The relative strength of acids and. bases is there- 

 fore dependent upon the number of H and OH ions con- 

 tained in the unit volume of the solution, and this number 

 is determined by the degree of dissociation of the electrolyte 

 under consideration. A further important result of the 

 theory of dissociation is the fact that in completely disso- 

 ciated salt solutions the properties of the solution are the 

 sum of the properties of the ions contained in it. The ion 

 itself, however, represents a new species of molecules, namely, 

 atoms or groups of atoms which are charged with a definite 

 amount of electricity. It is the object of this and further 

 papers to determine the physiological effects of individual 

 ions. 



Kahlenberg and True were the first to make such experi- 

 ments in physiology. 2 These authors investigated the toxic 

 properties of acids and salts in dilute aqueous solutions upon 

 growing plants. As a measure of the toxic effects these 

 authors used that concentration of the given electrolyte in 

 water which just allowed germinating beans to grow sixteen 



1 Since these lines were written matters have changed. [1903] 



2 Botanical Gazette, Vol. XXII (1896), p. 81. 



