ICHTHYOLOGY. 



683 



sjusatars 



skctricitr. 



too much neglected. Connected as they are with the 

 existence of the animal, and exercising a powerful con- 

 troul over its habit*, they ought to be examined with 

 care, and their appearances recorded in detail. 



SECT. XI I. Organ* of Electricity. 



FROM the remotest periods, the benumbing powers 

 Qf jjj e torppjo nave bee n the subject of popular admi- 

 ration. In the days of Aristotle and Pliny, some of its 

 curious properties were ascertained ; but it was not 

 until the year 1 772. that any accurate observations were 

 nude on the animal, conducted on scientific prin- 

 ciple*. 



The resemblance between the sensation produced by 

 the torpedo, and that occasioned by the discharge of a 

 jar charged with electricity, was first pointed out by 

 John Walsh, Esq. who determined, at the same time, 

 many of the phenomena which accompany this action 

 of the animil. Nearly about the same tune, and in 

 consequence of examples furnished by Walsh, Mr Hun- 

 ter dissected this animal with care, observed the ap. 

 peannce* of its electrical organs, and pointed out their 

 relation to one another. Previous to these observations 

 of Walth and Hunter, Borrelli, Lorenzini, and Reau- 

 mur, had each of them examined the fish, and arrived 



Since that time 

 of other investi- 

 having received 

 other branch of the 



|/-,N ..ok..;) 



Thestrw 



any 



: structure of the electrical organ* of the torpedo 

 and the other fishes which posses* them, has been al- 

 ready fully explained under the article ELECTRIC ITV, 

 to which we refer our readers. Since the publication 

 of that article, Mr Tod (PhiL Tram. 1 81 6, Part I. 

 p. 120,) baa investigated the influence of the nerves in 

 the production of the electricity which these organs 

 exhibit, and added some new facts to those which had 

 been given to the public by preceding writers. He 

 observes that the columns, when separate and unin- 

 taaawd by external pressure, appear to be of the 

 form of cylinders, as is shown as nearly as possible 

 by suspending them by one of their extremities. The 

 different forms which they exhibit in a horizontal sec* 

 tun of the whole organ, are produced by their un- 

 equal attachment to one another, by the intermediate re. 

 ticulate snrtstancr He adds, that the electrical organs 

 are so placed within the curvature of the semilunar 

 cartilages of the large lateral fins, as to be entirely 

 tinder the influence of the muscles, which are inserted 

 into these organs. 



In order to ascertain the share which the nerves have 

 in producing the phenomena, he made an incision on 

 each side of the cranium and gills of a lively torpedo, 

 and pushed aside the electrical organs so as to expose 

 and divide their nerves. The animal was then placed 

 in a bucket of sea water. On examining it in about 

 two hoars afterwards, he found it impossible to elicit 

 shocks from it by any irritation ; but it seemed to pos- 

 sess as much activity and liveliness as before, and lived 

 as long as those animal* from which shocks had not 

 twen received, and which had not undergone this change. 

 Two of these animals being procured, the nerves of the 

 satirical organs of one of them were divided after the 

 manner above described. They were placed each in 

 separate buckets of sea water, and allowed to remain 

 undisturbed. This was performed in the morning, and 

 when examined in the evening, it was impossible to 



distinguish between the liveliness or activity of either. 

 Of other two of these animals, the nerves of the elec- 

 trical organs of one of them were divided. Being pla- 

 ced each in separate buckets of sea water, they were 

 both irritated as nearly alike as possible. From the 

 perfect animal, shocks were received ; after frequent re- 

 petition, it became weak and incapable of discharging 

 the shock, and soon died. The last shocks were not 

 perceptible above the second joint of the thumb, and 

 so weak as to require much attention to observe them. 

 From the other, no shocks could be received ; it ap- 

 peared as vivacious as before, and lived until the se- 

 cond day. This experiment was frequently repeated 

 with nearly the same results. The nerves of one elec. 

 trie organ only being divided in a lively torpedo, from 

 which shocks had been previously received, on irrita- 

 ting the animal, it was still found capable of communi- 

 cating the shock. Whether there was any difference 

 in the degree of intensity could not be distinctly obser- 

 ved. One electrical organ being altogether removed, 

 the animal still continued capable of discharging the 

 electric shock, and the same circumstance took place 

 when only one of the nerves of each electrical organ was 

 divided. When a wire was introduced through the cra- 

 nium of a torpedo, which had been communicating 

 shocks very freely, all motion immediately ceased, and 

 no irritation could excite the electrical shock. 



The shock is communicated through the same con- 

 ductors as common electricity, and intercepted by the 

 same non-conductors. The sensation may be commu- 

 nicated to several persons at the same instant; and it 

 is of no consequence whether the animal be insulated or 

 not. The shock, however, is much stronger in air than 

 in water; in summer than in winter; when the animal 

 is in vigour, than when in an exhausted state. The 

 shocks generally follow simple contact or irritation ; 

 but, in some instances, when caught by the hand, no 

 shock is discharged until muscular energy has been 

 exerted in vain to extricate itself. 



This electrical discharge is in general accompanied 

 by an evident muscular action. There appears a swel- 

 ling of the superior surface of the electrical organs, 

 particularly towards the anterior part opposite to the 

 cranium. The eyes also appear at the time somewhat 

 retracted. If this action of the fish be too much ex- 

 cited, the animal becomes debilitated, and soon expires. 



Spallanzani, while prosecuting his experiments on 

 this subject, ascertained, that the young fish as well as 

 the old possessed this power ; and, what appears still 

 more surprising, even those still in the egg in the ute- 

 rus were able to communicate a sensible shock. 



Besides the torpedo, there are other fish which pos- 

 sess the same apparatus, and exhibit the same singular 

 phenomena. One of these, the gymnotus ekctricut, has 

 been carefully examined by Hunter ; and the result of 

 his observations, communicated in the 65th volume of 

 the PhiL Tram. A third fish, the Silurus electricus, 

 possesses the same property ; and probably many more 

 with which we are as yet unacquainted ; although to 

 this list there can only be added at present the Trichiurui 

 Indian and Telraodon electricus. 



The use of this singular faculty has often been point- 

 ed out both by ancient and modern naturalists. As an 

 instrument of defence, the exercise of such a power 

 will protect the fish from many of its foes ; and when 

 used in the offensive, it will be equally formidable. 

 Such animals may be able to benumb their smaller and 

 defenceless prey, and employ their electrical energies in 

 procuring fwd. 



Stricture 



and 



Functions 

 of Fishes. 



