432 ELECTRIC FISHES ELECTRICITY OP MUSCLES. 



parts of the same surface, at an equal distance from the electric organ, 

 are touched, no effect is produced, as they are equally charged with the 

 same electricity ; but if one point be further from it than the other, 

 a discharge occurs, the intensity of which is proportioned to the diffe- 

 rence in the distance of the points from the electric organ. However 

 much a Torpedo is irritated, no discharge can take place through a 

 single point ; but the fish makes an effort to bring the border of the 

 other surface in contact with the offending body, through which a shock 

 is then transmitted. This, indeed, is probably the usual way in which 

 the discharge is effected. The identity of animal with common Elec- 

 tricity is proved, not merely by the similarity of the effects upon the 

 ' feelings produced by the shock of both ; but also by the fact that a 

 spark may be obtained, and chemical decompositions effected, by the 

 former, precisely as by the latter. 



774. The power of the animal over the actions of its Electric organs, 

 is dependent upon their connexion with the nervous centres. If all 

 the nerve-trunks supplying the organ on one side be divided, the ani- 

 mal's control over that organ will be destroyed; but the power of the 

 other may remain uninjured. If the nerves be partially divided on 

 either or both sides, the power is retained by the portions of the organs 

 which are still connected with the centres by the trunks that remain. 

 Even slices of the organ, entirely separated from the body except by a 

 nervous fibre, may exhibit electrical properties. Discharges may be 

 produced, by irritating the part of the nervous centres from which the 

 trunks proceed, so long as the latter are entire ; or by irritating the 

 portions of the divided trunks which remain in connexion with the 

 electric organs ; or even by irritating portions of the electric organs 

 themselves, when separated from the nervous centres. In all these 

 respects, there is a strong analogy between the action of the nerves on 

 the Electric organs, and their action on the Muscles. The connexion 

 of the organs specially appropriated to each of these actions with the 

 Nervous system, the dependence of their functions upon the integrity of 

 this connexion and upon the state of activity of the central organs, 

 the influence of stimulation applied to the nervous centres or trunks, 

 the results of ligature or section of the nerve, and the effects of poi- 

 sonous agents, are all so remarkably analogous in the two cases, that 

 it seems scarcely possible to doubt that the Nervous force is the agent 

 which is instrumental in producing both sets of phenomena. Still, 

 however, no proof whatever can be derived from this source, of the 

 identity of nervous influence with any form of Electricity ; since all that 

 Can be legitimately inferred from it is, that Nerve-force acting through 

 a particular organic structure developes Electricity, in virtue of the 

 correlation formerly explained ( 396). 



775. It is another interesting point of analogy between the action 

 of Muscles, and that of the Electrical organs, that the former (as is 

 now fully proved by the elaborate and exact researches of Matteucci) 

 is attended with electric disturbance. In any fresh vigorous muscle, in 

 a state of passive or tonic contraction, there is a continual electric 

 current from the interior to the exterior, sufficient to excite the leg of 

 a frog to energetic contraction, when its nerve is so applied to the 



