ON NERVE-EXCITATION BY THE NERVE-CURRENT. 145 



of this investigation. In the first place the specifically lighter 

 nerve frequently fails to sink into a fluid which is of greater density 

 than it, and rests on the surface, so that the external closure of the 

 nerve-current is relatively slowly and incompletely established. In 

 the second place one rarely succeeds in again obtaining the con- 

 traction by a renewed contact of the same transverse section with 

 a fluid. I have already mentioned above, that the clinging of fluid 

 to a nerve, and the permanent derivation thereby established, cause 

 still more interference in this case than in that of muscle. Eckhard 

 says indeed (loc. cit. p. 318), ' that one never succeeds in eliciting re- 

 peated contractions by repeated immersion of the surface of section.' 

 I have, however, succeeded several times in obtaining repeated con- 

 tractions at the instant of immersion, still this was, on the whole, a 

 rarity. As regards the question merely of demonstrating the action 

 of the nerve-current, it would be of little interest to prosecute 

 these experiments ; but in relation to the question of chemical 

 excitation it would be of considerable importance if one could dis- 

 tinguish between the electrical and the possibly coincident chemical 

 stimulation at immersion of the transverse section. If anyone chose 

 to maintain that the so-called chemical excitation is only electrical, 

 and is efficient only in so far as it gives rise to current as well as 

 chemical alteration, this could hardly be disproved in the present 

 state of our knowledge. 



The same difficulty which is presented by the contraction occur- 

 ring at contact of the transverse section, repeats itself as regards 

 the subsequent irregular contractions. For when the nerve-current 

 was externally closed by other means we saw the same thing occur, 

 provided the preparations were very excitable. The question must 

 eventually arise as regards such preparations, what is to be regarded 

 as due to the electrical, and what to the chemical excitation, when a 

 long-enduring agitation results from dipping the nerve into a fluid. 

 If it is possible (as in the experiment with normal saline, described 

 at p. 139) to repeat, with always the same effect, the immersion 

 of an electromotive portion of nerve, it is allowable to exclude 

 any chemical action. But if the experiment succeeds only at the 

 first immersion, its interpretation remains very doubtful. The 

 experiments of Eckhard, which cannot but awaken the keen interest 

 of any one who repeats them, and especially the remarkable action 

 of the fixed alcalies, were well worth a renewed methodical inves- 

 tigation. 



