TEN FIGURES
I n 1879, Biedermann observed that a curarized frog's sartorius placed in a 0.5 per cent NaCl solution, made weakly alkaline by addition of Na,C03, showed spontaneous ' pulsation and contractions'; he also found that the irritability of the muscle to break and make galvanic stimulations was increased. It seems, therefore, that the occurrence of these spontaneous twitches is accompanied by a condition of hyperexcitability in the muscle. Loeb (1899), however, was of the opinion that these contractions in the pure Na-salt solution are not dependent on an increase in irritability, for he found that a muscle which has been in a 0.7 per cent NaCl solution for 24 hours still contracts spontaneously, although its irritability to induction shocks is decreased. More extensive work of Mines ( '08) showed, however, rather conclusively that while the threshold irritability of a muscle to break induction shocks is not altered in pure isotonic NaCl solution, its threshold irritability to galvanic stimuli of relatively long duration is markedly increased.
Lillie ('10) found that the irritability of the frog's skeletal muscle to various forms of chemical stimulation is also increased by a preliminary treatment with pure isotonic Na-salt solutions (compare also Chao, '34 a). Similar action of these Na-salt solutions in increasing the irritabiIity of the skeletal muscle has also been demonstrated by Chao ('34 b) with the 'cold' stimulation. I n the experiments described in the present paper a similar study has been made of the changes in