90 M. E. COLLETT. 



(Osterhout^2j • the penetration of stimulating salts into a nerve is 

 lessened by CaCl2, presumably by means of a surface action (Loeb 

 and Ewald"); the erosion of Na-glycocholate gels by NaCl is 

 prevented by CaCL and by anaesthetics (Schryver^^). Lillie 

 considers that the protective effect of Ca is due to its stabilizing 

 action on the cell surface (as regards solution-coagulation balance) 

 and in part to the greater solidity or insolubility of Ca-colloid 

 compounds. 



Hober,^* in his extensive monograph on the physiological action 

 of calcium, finds that Ca can be replaced by other alkaline earths 

 (especially by Sr) better than by heavy metals, and still better 

 by certain complex Co ions. In many cases, however, Ca is 

 not wholly replaceable by any cation. Hober therefore concludes 

 that the action is largely colloidal, but must also in part be 

 chemical. Schreiter''^ notes that in the normal polarization of 

 the nerve membrane,* Ca in Ringer's solution can be replaced 

 by Ba and Sr, but not by substances which injure the membrane 

 such as Mg, Mn, Co, Al. Mathews^" would explain the difference 

 in toxicity of various bivalent cations and in their power to antago- 

 nize NaCl, by the differences between them in solution tension, 

 which would determine their ability to alter the surface energy 

 relations of a colloid. The electromotive series runs: H Ni 

 Co Cd Zn Mn Mg Ca Sr Ba Na. Here as in the order for toxicity 

 the heavy metals are at one end of the scale and the alkaline earth 

 metals at the other. This series, however, would not explain the 

 great efficiency of Ca as compared with Sr and Ba nor the varying 

 efficiency of Zn, Co, and Cd with different organisms. For 

 that we must go back to specific chemical action or specific 

 solubility for an explanation. 



The antagonism of acid by salts may be due to protection of 

 the membrane against penetration by the acid as a whole or to 

 protection against the special action of the H ion. Thus the 

 coagulative action of the H ion might be offset by the anticoag- 

 ulative or dispersing action of the strongly adsorbed anion of such 

 a salt as NaCl, or by competition with the strongly adsorbed cation 



*I.e. , alteration in distribution of dyes in axis cylinder when the nerve is stained 

 during passage of a constant current along it. 



