The inhibitory effect of magnesium upon indirect and direct irritability of frog muscle and the antagonistic action of sodium and calcium upon this effect

Several series of experiments were carried out on frogs. In the first series magnesium chloride was injected into a lymph sac and subsequently nerve and muscle were stimulated at various times by induction shocks. Of the results obtained two will be mentioned: One is that indirect irritability gradually disappeared completely while direct irritability remained practically unchanged, that is, on stimulation of the nerve plexus there was no response while on stimulating the muscle directly there was a good contraction. Such a result was seen by many observers and was spoken of as curare-like action. In a previous paper we have called attention to the fact that similar results can be obtained also by perfusion of the leg with solutions of sodium chloride and even with calcium chloride. The magnesium effect, however, is somewhat more pronounced. The second result is that the subsequent infusion of the muscles through the abdominal aorta, with calcium chloride, restores rapidly the abolished indirect irritability. This is similar to the observation of Auer and Meltzer on the antagonistic action of calcium to magnesium in mammals and is also similar to the antagonistic action of calcium to the curare-like action of sodium chloride.