PHILIP H. MITCHELL AND J. WALTER WILSON 55 



dependence of the formation of metallic salts of proteins on hydrogen 

 ion concentration is helpful in forming a conception of the behavior 

 of potassium. If one believes with Robertson (2) that salts of 

 the proteins may be so built that the inorganic constituent is, partly 

 at least, in non-dissociable form then one can readily conceive of how 

 an intracellular change of hydrogen ion concentration such as occurs 

 in a fatigued muscle would markedly alter the distribution of 

 potassium, and doubtless other inorganic constituents, between the 

 dissociable and the non-dissociable forms. 



As to the absorption of potassium a conception of how contraction 

 might be essential to the mechanism involved is difficult. One notes 

 the generally accepted idea that ion movements having definite 

 relation to membranes are concerned in excitation. This idea is, of 

 course, the basis of the Nernst theory of stimulation and is assumed 

 in the conception of the mode of propagation of excitation as developed 

 by Lillie (17). Because ions move during excitation and perhaps 

 penetrate membranes, are we to assume that the potassium ion can 

 penetrate the cell only at that time? In the light of our present 

 knowledge it seems necessary to believe that cell permeability is not 

 merely a matter of passage through an external membrane but that 

 the physiological behavior of the protoplasm as a whole must be consid- 

 ered. The work of Wishart (18) on the distribution of glucose between 

 plasma and corpuscles may be cited as one example of such observations. 

 If contraction, involving migration of ions, causes a sort of fixation 

 of rubidium or cesium within the cell it is fair to suppose that 

 potassium would be similarly affected. That potassium favors 

 excitability by its presence at cell surfaces has been amply demon- 

 strated for a variety of tissues, so that some significant movement of 

 potassium ions is involved, among other things, in a response such 

 as muscular contraction. Our results suggest that movement at the 

 cell surface is not the only factor concerned but that some transforma- 

 tion of potassium into a non-dissociable form occurs, presumably 

 within the protoplasm. In this connection the work of Crozier (19) 

 on sensory activation of cells by acids is of interest since it led him 

 to the view that stimulation does not merely involve an increase in 

 permeability but that the change of condition of materials at the 

 surface of cells is instrumental in determining diffusion of ions within 

 the cell. 



