ANIMAL ELECTRICITY. 



93 



nerve is, for the most part, divided into five 

 distinct branches before entering the electrical 

 organs; and these are again subdivided into, 

 at least, as many branches as there are longi- 

 tudinal septa. Rudolphi describes a nerve 

 formed from branches of the fifth pair and 

 sympathetic, which runs beneath the lateral 

 line, over the surface of the electrical organs, 

 but does not enter them. This has, by some, 

 been supposed to be an electrical nerve, but 

 without sufficient reason.* 



3. The electrical organs in the Silurus. 

 The only organ that can be regarded as con- 

 nected with the electrical function in this fish 

 is a thick layer of dense cellular tissue, which 

 completely surrounds the body immediately 

 beneath the integuments. So compact is it 

 that, at first sight, it might be mistaken for a 

 deposit of fatty matter. But, under the mi- 

 croscope, it appears to be composed of ten- 

 dinous fibres, closely interwoven, the meshes 

 of which are filled with a gelatinous substance. 

 This organ is divided by a strong aponeurotic 

 membrane into t\vo circular layers, one outer, 

 lying immediately beneath the corion, the other 

 internal, placed above the muscles. Both or- 

 gans are isolated from the surrounding parts 

 by a dense fascia, excepting where the nerves 

 and bloodvessels enter. The cells or meshes 

 in the outer organ, formed by its reticulated 

 fibres, are rhombic in shape, and very minute, 

 so as to require a lens to see them well. The 

 component tissue of the inner organ is some- 

 what flaky, and also cellular. 



The nerves of the outer organ are branches 

 of the fifth pair, which runs beneath the lateral 

 line and above the aponeurotic covering of the 

 organ. This aponeurosis is pierced by many 

 holes for the transmission of the nerves, which 

 are lost within the cellular tissue of the organ. 

 The intercostals supply the inner organ : their 

 electrical branches are numerous and remarka- 

 bly fine.f 



The organs of the other known electrical 

 fishes have not yet come under the notice of 

 any anatomist. 



In taking a general view of these interesting 

 organs, we are struck \vith the existence of a 

 certain degree of analogy amongst them, and 

 yet we fail to discover such resemblances as 

 might be expected, and such as exist between 

 the structures of other organs performing the 

 same functions in different animals. Here we 

 have tendinous membranes variously arranged, 

 yet all so as to form a series of separate cells 

 filled with a gelatinous matter. But how great 

 is the difference between the large columnar 

 cell in the torpedo full of delicate partitions, 

 and the minute rhombic cells of the Silurus ! 

 All, however, are equally supplied with nerves 

 of very great size, larger than any others in the 

 same animals; and, indeed, we may venture 

 to say, larger than any nerve in any other ani- 

 mal of like bulk. 



The organs vary in different fishes ; first, in 

 situation relatively to other organs. They 

 bound the sides of the head in the torpedo ; 

 run along the tail of the Gymnotus, and sur- 

 round the body of the Silurus ; secondly, in 

 having different sources of nervous energy ; 

 and, thirdly, in the form of the cells. No 

 other fishes have aponeuroses so extensive, or 

 such an accumulation of gelatine and albumen 

 in any cellular organ. Broussonet remarked 

 that " all the electrical fishes at present known 

 to us, although all belonging to different classes, 

 have yet certain characters in common. All, 

 for instance, have the skin smooth, without 

 scales, thick, and pierced with small holes, 

 most numerous about the head, and which 

 pour out a peculiar fluid. Their fins are 

 formed of soft and flexible rays, united by 

 means of dense membranes. Neither the 

 Gymnotus nor torpedo has any dorsal fin ; 

 the Silurus has only a small one, without rays, 

 situated near the tail. All have small eyes."* 



X. Analogies of animal electricity. Setting 

 aside the vague hypotheses of the older philo- 

 sophers, (some of whom attributed the phe- 

 nomena produced by the peculiar power of 

 electrical fishes entirely to the mechanical effect 

 of certain rapid motions of their surface, and 

 others to the influence of currents of minute 

 corpuscules flowing from the body of the fish 

 in the act of discharging,) we can have no dif- 

 ficulty in referring this very remarkable series 

 of phenomena to the agency of some power 

 very analogous to common or voltaic elec- 

 tricity, which seems to stand in the same rela- 

 tion to these as they do to electricity derived 

 from other sources.f 



It was by Muschenbroek that the effects 

 of the torpedo's discharge were first referred 

 to electricity. He was led to imagine that 

 the agent producing the shock was truly 

 electrical from the similarity of its effects 

 to those of the discharge of the Leydenjar. 

 Succeeding observations, however, as we 

 have seen, have shewn that certain differences 

 exist between the phenomena produced by 

 Animal Electricity and those observed in con- 

 nexion with the discharge of the Leyden jar : 

 the chief of these are its passage through air 

 only to a very small distance; its producing 

 only very slight igniting effects even when con- 

 siderably accumulated; and its manifesting 

 but feebly the phenomena of attraction and 

 repulsion. Further, it affects the multiplier 

 more strongly than common electricity does 

 under ordinary circumstances, and its chemical 

 effects are more distinct. From voltaic elec- 

 tricity it is distinguished by the comparative 

 feebleness of its power of decomposing water; 

 by the greater sharpness of the shock caused 

 by the discharge, and by the weakness of its 

 magnetizing power. 



Only four of the eight experimental effects 

 enumerated by Dr. Faraday \ as characteristic 



* Abhandl. der Acad. v. Berlin, 1820-21. 229, 

 and Blainville, Princ. d'Anat. Comp. i. 232. 



t Rudolphi, (Abhandl. der Acad. v. Berlin. 

 1824.) 140. 



* Mem. de 1'Acad. de Paris, 1782. 693. 

 f It is interesting to know that the Arabic name 

 of the torpedo (Rausch) means also lightning, 

 $ Philo?. Trans. 1833. 



