in ELECTRICAL EXCITATION OF MUSCLE 221 



excitability to both directions of current is completely recovered 

 after washing with 0'6 / Q NaCl solution in a short time 

 (10-15 minutes). It need hardly be said that this is as im- 

 possible after the application of substances which produce deep- 

 seated chemical and physical changes in the contractile substances, 

 >'.</. sublimates, strong acids, alcohol, etc., as after mechanical or 

 thermic destruction (26). 



The corresponding sodium salts, which are in such close 

 chemical relation with the salts of potash, exhibit a striking 

 antagonism in their physiological effect upon striated muscle. 

 We have already seen that the excitability of certain contractile 

 substances (spermatic filaments, ciliated cells) is considerably 

 heightened by N"a 2 C0 3 in dilute solutions, and in discussing the 

 possibility of rhythmical excitation of striated muscle by the 

 constant current it was pointed out that the effect was accentuated 

 in a marked degree when the excitability of the kathodic end of 

 the muscle was increased by treatment with Na 2 C0 3 . If the 

 pelvic end of an uninjured curarised sartorius dips into a 

 0'5 1 % solution of this salt, the excitability of the 

 muscle to the closure of weak ascending currents is seen after 

 a short time to be extraordinarily augmented, while the descend- 

 ing current still works quite normally, although break excitations 

 are discharged with such low intensity of current and brief 

 duration of closure, as would not occur in a normal muscle (26) 



(Fig- 89). 



Sometimes under these circumstances, with weak descending- 

 currents, the opening twitch is conspicuously delayed, so that 

 the tolerably long latent period of the opening excitation may 

 be observed directly without further artificial aid. Later on we 

 shall encounter an analogous effect in the indirect excitation of 

 muscle. The significance of these facts to the theory of current- 

 action, and the law of polar excitation in particular, is as clear 

 as possible, and can hardly require further exposition. They 

 afford as direct and salient a proof that the electrical excitation 

 of the muscle is a polar effect of current, as the previous experi- 

 ments in time measurement ; for if all the cross-sections of the 

 intrapolar tract were simultaneously excited there could never 

 be such an extraordinary disparity in the excitatory action of the 

 two directions of current as is exhibited when a sartorius muscle 

 that has been injured at one end, or chemically altered, is 



