INORGANIC SALTS i6i 



the normal uninjured resting muscle is impermeable to 

 sodium salts. Solutions of sodium and lithium salts 

 leave the normal electrical potential of the external 

 muscle-surface unchanged; while salts like those of K, 

 Rb and NH4 (which give other evidence of penetrating 

 the muscle) produce an injury-current or local negativity. 

 Absence of penetration is indicated by failure to change 

 the external potential of the muscle; the alkali earth 

 salts and in part those of caesium are thus indifferent. 

 Nevertheless, they alter the properties of the tissue; 

 thus Mg salts have a strongly anti-stimulating or narcotic 

 action, and Ca and Sr salts in pure isotonic solution 

 similarly render muscle resistant to stimulation; all of 

 these effects are reversible if the exposures are not too 

 prolonged. 



Loss of contractility in non-electrolyte solutions and 

 its prompt return in solutions of sodium salts — especially 

 if some Ca is also present — are characteristic of many 

 varieties of muscle. Among invertebrates the larvae of 

 Arenicola show this phenomenon in a striking manner;^ 

 here also, as with vertebrate muscle, Li and Na salts are 

 alone capable of preserving contractility for prolonged 

 periods, and K salts have a paralyzing action. Mg 

 salts repress contractility very promptly and completely, 

 and the action is readily reversed, especially by solutions 

 of Na salts containing a little Ca.^ The resemblance of 

 Li to Na in its power of maintaining the normal properties 

 of muscle (though less perfectly than Na) seems to be 

 general for both vertebrate and invertebrate muscle; 

 for example. Mines describes this phenomenon in the 



^ R. S. LiUie, American Journal of Physiology, XXIV (1909), 459. 

 2 Op. cit.f p. 485. 



