INORGANIC SALTS 171 



such as the electrical conductivity of protoplasm and 

 medium and the electrical polarization of the plasma 

 membranes. These conditions will be considered later 

 under the subject of stimulation. 



The special relations of the three chief cations of 

 the protoplasmic media, Na, K, and Ca, to protoplasmic 

 activity appear to depend on chemical conditions of a 

 kind still imperfectly understood. The differences 

 between the physiological actions of Na (and Li) and of K 

 (and Rb and Cs) in their relation to vertebrate muscle 

 and nerve cannot be satisfactorily explained on the basis 

 of the physico-chemical constants of these ions. Na 

 and K, though chemically closely similar, appear in 

 many forms of protoplasm, e.g., vertebrate muscle, to 

 act as physiological antagonists; in others their physio- 

 logical differences are relatively slight; e.g., in the case 

 of fish eggs (Fundulus) and sea-urchin eggs (Arbacia) 

 isotonic KCl solution is even less toxic than NaCl solu- 

 tion; both solutions are antagonized by Ca. 



It is remarkable that the striated muscle cells of 

 vertebrata appear to be readily permeable to some K 

 salts (KCl, KBr, KI, KNO3) but not to others (K2SO4, 

 K- tartrate, K-phosphate) ;^ in this respect K salts 

 exhibit a striking contrast to Na salts. The special 

 permeabihty to KCl is shown in frog's muscle by rapid 

 increase in the weight of the tissue when it is immersed 

 in isotonic solutions of this salt; similar conditions have 

 been found by Seebeck^ in the frog's kidney, which, like 

 muscle, shows normal semi-permeability toward Na and 

 Li salts. The special physiological action of K is prob- 



^ Overton, Arch. ges. Physiol., CV (1904), 176. 

 ' Seebeck, ihid., CXLVIII (1912), 443. 



