BIOLOGICAL APPLICATIONS 193 



stituent of the protein salts affords, I believe, an explanation of 

 an important physiological phenomenon; I refer to the well- 

 known power which living tissues possess of "selecting" or storing 

 up certain inorganic constituents in a concentration greater than 

 that in which these substances are found in the surrounding 

 liquid medium (23) (25) (26). Thus the skeletal muscles and the 

 red blood corpuscles contain a marked excess of potassium over 

 sodium, while the plasma which bathes them contains much less 

 potassium than sodium. Again, although in fresh- water streams 

 the concentration of potassium salts is often very low, the plants 

 which live in them are capable of storing up a comparatively 

 large amount of potassium in their tissues. 



If we place within a dialyser an excess of diffusible potassium 

 salts over diffusible sodium salts and dialyse against a solution 

 containing excess of diffusible sodium salts, the proportions of 

 sodium to potassium within and without the dialyser sooner or 

 later readjust themselves, approaching equahty. Hence the above- 

 mentioned phenomenon, which is met with in living tissues, 

 admits, as Loeb has pointed out (14) of only one explanation, — 

 the inorganic constituents of a tissue which are found therein in 

 excess of their concentration in the fluids which bathe it must 

 exist within the tissue in the form of non-dissociated non-diffu- 

 sible compounds. "If a tissue utilizes one kind of metal in this 

 way, for example K, while another metal, for example Na, is 

 chiefly used for the formation of dissociable compounds with 

 Na as the free ion, the consequence will be that the ashes of the 

 tissue contain K and Na in altogether different proportions from 

 those in which they are contained in the surrounding solution. 

 I think we may take it for granted that, at least, potassium forms 

 a non-dissociable constituent of the protoplasm of a number of 

 tissues of animals and plants" (Loeb. loc. cit.). 



If we admit that, as many investigators now believe (13) (14) 

 (32) (26), the inorganic constituents of living tissues are partly 

 united with proteins, the fact that such unions dissociate only 

 into protein and not into protein and inorganic ions affords a 

 sufficient explanation of the above phenomenon, 



Loeb (13) (14) and W. A.' Osborne (21) have advanced an 

 analogous explanation of the "oligodynamic" (16) (19) action of 

 many highly toxic heavy metals. 



