INORGANIC SALTS 157 



in fact, enough K in blood plasma to destroy all myoneural 

 transmission, were it not for the Ca also present. Cal- 

 cium is the only metallic ion in plasma (other than Na) 

 required for myoneural transmission; in mixtures of 

 NaCI and CaCL indirect irritabihty is preserved almost 

 as long as in serum. Sr also antagonizes this action of K, 

 but Ba and Mg do not. A similar blocking of myo- 

 neural transmission is caused by BaCl.; this action is also 

 antagonized by Ca. Overton found that in a mixed 

 solution of sodium and calcium chlorides of the same 

 concentration as in serum (0.7 per cent NaCl plus 0.02 

 to 0.03 CaCla) the addition of 0.05 to 0.06 per cent KCl 

 completely paralyzed the nerve-endings without affecting 

 the direct irritability of the muscle; in order to abolish 

 the latter 0.15 per cent KCl was required; when more 

 CaCL was added to the solution more KCl was required 

 to prevent transmission. In the absence of K a mere 

 trace of Ca is all that is necessary; in a K-free NaCl 

 solution one part of CaClz in 20,000 maintained indirect 

 irritability for twenty-four hours and one part in 50,000 

 for twelve hours; even one part in 100,000 had a percep- 

 tible effect. 



Although the nerve-trunk retains its power of conduc- 

 tion for many hours in pure solutions of Na and Li salts, 

 transmission through reflex arcs is quickly prevented 

 by lack of Ca.^ This was shown both in perfusion 

 experiments with intact frogs and in experiments in 

 which the isolated spinal cord with nerves and muscles 

 attached was immersed in the solution. In such a 

 preparation kept at a low temperature in well-oxygenated 



^ Overton, Verhandl. Ges. deutscher Naturf. u. Arzte, LXXV (1903), 

 Theil II, 2te Halfte, p. 416. 



