314 ELECTRO-PHYSIOLOGY. 



and placed one of tte halves in opposition to the other. And, in fact, when I 

 apply the nerve thus prepared to the galvanometer, I find a strong differential 

 current, which is in the direction of the piece of the nerve which was next to the 

 positive pole. 



Hence it is a plain consequence deduced from a known physical theory, that, 

 namely, of the secondary polarity, that a nerve becomes an electro-motor by the 

 passage of the current, and is therefore in a condition to give a secondary current 

 when the current of the battery has ceased. In a word, a nerve after having 

 been traversed by a voltaic current is traversed by the secondary current, 

 which is in an opposite direction to that of the battery, and which may circulate 

 in those parts of the nerve in which the secondary polarization is not developed, 

 and which is certainly neutralized and produces a discharge through, the great 

 difference of the secondary electro-motor power in different points of the same 

 nerve. Thus is explained, with all probability, in what consists the state which 

 we termed unknown, into which the nerve traversed by the inverse current 

 which excites the tetanic contraction in the muscles of the frog is thrown. This 

 nerve is none other than that portion next to the positive pole which is traversed 

 by the current, and which has been shown to have acquired the strongest second- 

 ary electi'O-motor power ; it is therefore that piece of the nerve which, after the 

 opening of the circuit, is traversed by the discharge or by the secondary current, 

 which is at once the strongest and most prolonged ; and as the secondary cur- 

 rent is always in an opposite direction to the current of the battery A\hich has 

 excited it, it follows that in the inverse nerve the secondary current is direct — 

 that is to say, is in the direction which was shown from the first of our propo- 

 sitions to have the strongest electro-physiological action. Moreover, the effect 

 of this secondary current must be further enhanced, because we know that the 

 inverse current maintains the excitability of the nerve, and this perhaps in turn 

 arises from the fact that the inverse current does not excite contraction, and 

 does not, so to speak, consume the muscle, as does the direct current. 



In conclusion, the contractions occasioned in a muscle, the nerve of which has 

 been traversed by the continuous inverse current, are attributable, in all proba- 

 bility', to the physiological effect of the secondary current, which is direct. And 

 that this current or direct secondary discharge exists is proved by the galvano- 

 meter, as has been already made apparent, and is proved also by the galvano- 

 Bcopic frog. In effect, if I apply the nerve of this frog to the nerve of the fowl 

 which was traversed by the inverse current, we see, immediately after opening 

 the circuit, the galvanoscopic frog undergo contraction, and especially if we 

 place its nerve close to those points which are nearest to the positive pole and 

 in a suitable direction. 



I must not omit to cite an imjjortant observation recently made by Plluger, 

 which will perhaps some day find a place among the electro-physiological phe- 

 nomena, depending on the secondary electro-motor power of the nerves. Pfluger 

 has found that while a nerve is traversed by a continuous current, "the excita- 

 bility is augmented beyond the region or points touched by the negative electrode, 

 and so much the more as the point observed is nearer to the electrode. The 

 contrary is the case beyond the positive electrode, where, on the other hand, the 

 excitability is diminished." To make this experiment, Pfluger causes a contin- 

 uous current to pass in the sciatic nerve of a galvanoscopic frog, and then sub- 

 mits this nerve at the points not traversed by the current to the action of different 

 stimulating bodies, as, for instance, water impregnated more or less with salt, and 

 the action of which had been previously determined. He then finds that the 

 stimulus, which applied to a certain point of the nerve does not excite contraction, 

 is capable of producing that effect when the nerve is traversed by the current, 

 if that point be near the negative electrode. On the other hand, a stimulus, capable 

 of exciting contraction, excites it no longer when the nerve is traversed by the 

 current, if applied towards the positive electrode. These curious facta have 



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