500 STUDIES IN GENERAL PHYSIOLOGY 



means that it allows certain substances to pass through and 

 others not. In my opinion, the working out of a theory of 

 semi-permeability is one of the main physiological problems 

 of the day. 



The theory of the dissociation of electrolytes is of funda- 

 mental importance in the analysis of the constitution of living 

 matter. Pharmacology will feel its influence most directly. 

 Everything seems to indicate that the specific physiological 

 effects of inorganic acids are due to the number of positively 

 charged hydrogen ions in the unit of solution, and the spe- 

 cific physiological effects of alkalies to the negatively charged 

 hydroxyl ions. But the universal bearing of the theory of 

 dissociation upon physiology will perhaps be best seen in the 

 field of animal electricity. An active element of living mat- 

 ter is negatively electric to its surrounding resting parts. 

 We may assume that an acid is formed in the active part, and 

 that the passive parts are neutral. The positive hydrogen 

 ions of the acid have a much greater velocity of migration 

 than the anions. Hence the former will diffuse more rapidly 

 into the passive tissue than the anions, and the active tissue 

 will remain negatively charged. 1 



At no time since the period immediately following the 

 discovery of the law of conservation of energy has the out- 

 look for the progress of physiology appeared brighter than 

 at present. But in order to reap the full benefit of our 

 opportunities, we must bear in mind that the fundamental 

 problem of physiology is the determination of the constitu- 

 tion of living matter, and that in order to accomplish our 

 task we must make adequate use of comparative physiology 

 as well as physical chemistry. Pathology, in particular, will 

 be benefited by such a departure. 



1 As far as I am aware, this was the first attempt at applying the principle of 

 batteries of concentration to the explanation of the current of action. [1903] 



