THE EXCITABILITY OF FROG MUSCLE WITH PARTICULAR REFERENCE TO ITS LATENT ADDITION

With a view to indicating that the alpha excitatory state in muscle is not of a special nature it is shown that the alpha strength-duration curves are of the same form as those determined for nerve and other tissues except that in about two-thirds of all cases the rheobase appears to be slightly too low. Also from experiments in latent addition it is found that the alpha excitatory state following an inadequate stimulus subsides exponentially at a rate which is related to the alpha excitability in the same way, approximately, as the subsidence rate in nerve is related to the nerve's excitability. In both tissues the subsidence as measured directly is 2-3 times as fast as it appears to be from the strength-duration curve. The alpha refractory period is at least as short as that of nerve so the alpha chronaxie is unusually long compared to the refractory period. There is no reason at present, however, to consider this as having any bearing on the problem at issue. It is concluded therefore, that the alpha excitability differs from others in the rates of its reactions rather than in its fundamental nature and that any conclusions about excitability drawn from its study will probably be valid quite generally.