PHTSIOLOGT 47 



more will diffuse in until the concentration of 

 undissociated molecules again becomes the same 

 within and without. This process may continue 

 until the inside concentration of total weak 

 base (ionized plus non-ionized) becomes much 

 greater inside than outside. A weak acid would 

 accumulate in the cell in the same way if the 

 cell produced alkali. We may extend this hy- 

 pothesis to include not only weak acids and bases 

 but all other substances, organic or inorganic, 

 which are able to change with changes in the 

 concentration of hydrogen ions. Such changes 

 (including tautomerism, formation of complex 

 salts, hydration, hydrolysis, etc.) may affect sub- 

 stances to a greater extent than is at present sus- 

 pected. 



It may seem possible in some cases that accu- 

 mulation may be due to a Donnan equilibrium. 

 This exists when one or more non-diffusible ions 

 are present in the cell or in the external solution 

 and it requires that the following ratio should 

 exist for any pair of diffusible ions: 



cone, cation inside cone, anion outside 

 cone, cation outside cone, anion inside 



