436 THE PROPERTIES OF STRIPED MUSCLE. 



question are chiefly polar ; for it is at the anode and cathode that the 

 changes of current density are most abrupt. This consideration, how- 

 ever, affords us no explanation of the other fact of which we have such 

 convincing proofs, namely, that in muscle as in nerve, excitation waves 

 start from the cathode at the moment of closure, from the anode at the 

 moment of opening of the current. As regards nerve, the fact just 

 stated has been expressed by Pfliiger in the form of a law as well known 

 as that of du Bois-Reymond, according to which it is an essential 

 condition of the efficiency of a polar change, not only that it should 

 be abrupt, but that it should be towards cathelectrotonus or from 

 anelectrotonus — meaning by these terms the condition or state which 

 exists at the cathode or anode respectively — in other words, from the 

 normal to the cathodic state, or from the anodic to the normal. It is 

 obvious that the changes in the opposite direction, namely, from normal to 

 anodic at the anode on closure, and from cathodic to normal on opening, 

 although they are no less abrupt, have no exciting effect — a fact which 

 will be more advantageously dealt with in connection with the dis- 

 cussion of the corresponding phenomena in nerve. 



As regards the excitatory effects of the second kind, those which are 

 dependent on the duration of the current, nothing further need be 

 added. Attention has, however, not been drawn to the remarkable 

 difference which presents itself in this respect between nerve and 

 muscle. Physiologists are so little inclined to admit that a nerve is 

 continuously excited by the flow along it of a current, that the doctrine 

 of du Bois-Reymond, that so long as a current is of constant strength it 

 has no exciting effect, has the authority of a " law " ; whereas in muscle 

 the contrary has been familiar to us ever since " Wundt's curves " have 

 been copied into every text-book. At first sight the contrast appears 

 very striking. More careful consideration leads us, however, to surmise 

 that the difference may be more phenomenal than essential. In muscle, 

 contraction is the sign of the cathodic state ; in nerve, increased excit- 

 ability. In the former it is transitory, soon giving way to " exhaustion." 

 In nerve, which is incapable of fatigue, it is persistent. These 

 differences seem, however, to afford no ground for doubting that the 

 underlying process is the same in the two cases. 



Secondary muscular and neuro-muscular electrical excitation.— 

 More than half a century ago, du Bois-Reymond l proved by ex- 

 periments, in which conductors of different kinds were interposed 

 between the exciting muscle and the excited nerve of the physiological 

 rheoscope, that the change in the former which evokes the response 

 of the latter, is electrical. In the ordinary form of the experiment it 

 is accordingly found that the secondary neuro-muscular response is 

 best observed when the parts bridged over by the nerve are, either in 

 the unexcited or in the excited state, at considerably different poten- 

 tials. Experience, however, shows that if both preparations are in 

 good condition, the rheoscopic limb reacts even when the position of 

 the nerve is apparently very unfavourable — as, e.g., when it is applied 

 to the sartorius in such a way as to cross the fibres transversely. 2 The 

 best results are, as might be expected, obtained when winter frogs 

 are used, which have been kept at a temperature approaching that of 

 freezing. In this case, if the primary muscle is rhythmically excited 



1 Loc. cit., Bd. ii. S. 87. 



2 Bicdermann, " Elek trophy siologie," S. 355. 



