ANIMAL ELECTRICITY. 



81 



ELECTRICITY, ANIMAL. A power, 

 or imponderable agent, possessed by and 

 evolved from certain living animals, which 

 enables them, independently of the operations 

 of external agents on their structures, to pro- 

 duce several of the phenomena exhibited by 

 common and voltaic electricity, generated in 

 inorganic matter. 



The animals so endowed, with which we are 

 at present acquainted, are all fishes ; and the 

 effect by which their power is most sensibly 

 made known to us is the feeling of a shock, or 

 momentary stunning, which is experienced in 

 the hand that touches their surface. 



It is still doubtful whether the agent which 

 produces this effect be absolutely identical 

 with those which produce the various pheno- 

 mena of common and voltaic electricity, ther- 

 mo-electricity, &c.; but the most recent re- 

 searches on the subject render it probable that 

 it is the same in its nature, although different 

 in intensity. 



When Galvani discovered the possibility of 

 exciting muscular contraction by establishing 

 an external communication between the nerves 

 and muscles by means of metals, he imagined 

 that the contraction was produced by the sti- 

 mulus of a peculiar agent (or fluid) existing in 

 the nerves in a state of accumulation, which, 

 being attracted by the metals, passed along 

 them to the external surface of the muscles. 

 The agent, which was supposed to remain latent 

 in the nerves, was called by some " the nervous 

 fluid," as it was imagined to be identical with 

 that power which animates the nerves during 

 life. Galvani seems to have entertained this 

 notion. Other philosophers, avoiding a name 

 derived from a theory, denominated the agent 

 Galvanism. Afterwards it was called Animal 



dinal axis, bat a real change of place of the 

 upper extremity of the radius on the outer con- 

 dyle of the humeius. The elbow was but slightly 

 deformed, and all its motions were perfect ex- 

 cept extension, which was not complete, but the 

 girl had perfect use of both arms and fore-arms, 

 which were exactly similarly formed. The ra- 

 dius seemed principally in fault, and the motions 

 of the upper head corresponded much to the de- 

 scription given of tLe subluxation. (Vide p. 74.) 

 I was afforded an opportunity of examining the 

 joints in consequence of the child having died of 

 scarlet fever. Both joints were exactly alike. 

 The radius was large, the great sigmoid cavity 

 of the ulna was not half its usual size, and the 

 coronoid process did not exist. The trochlea on 

 the humerus, corresponding to the diminished 

 sigmoid cavity, was one-half less than its natural 

 size so that the lower extremity of the humerus bore 

 so striking a resemblance to tne condyles of the 

 femur, when viewed posteriorly from the popli- 

 teal space, that nobody could look at it without 

 observing the striking resemblance in miniature 

 of the humerus to the femur. There were fibrous 

 bands representing the crucial ligaments, and all 

 the fibres around were yellow and stronger than 

 na tural. The annular ligament of the head 

 of the radius was wider than natural but much 

 stronger, and accounted for the passing to and 

 fro of this head in pronation and supination. 

 That the deformity was congenital no one can 

 doubt : the appearance the history the exis- 

 tence of the same malformation on both sides, all 

 prove it." Dec. 12, 1836.] 



VOL. If. 



Electricity. These views were supported by 

 Valli, Carradori, Aldini, and Fowler. But, 

 since Volta and others demonstrated that the 

 contractions of the muscles in Galvani's expe- 

 riments were owing to electricity developed by 

 the contact of the metals employed, and not 

 to any fluid pre-existent in the nerves, the 

 term Animal Electricity has had its meaning 

 changed. At present, most physiologists use 

 it in the sense which is implied in the defini- 

 tion given above. 



That is not called Animal Electricity which 

 is generated by the friction of animal sub- 

 stances one upon the other, or by the mere 

 contact of animal tissues of dissimilar natures. 

 The phenomena so developed have their source 

 in common and voltaic electricity. They are 

 phenomena exhibited by animals in common 

 with inorganic matter. As the study of these, 

 however, may ultimately lead to the elucidation 

 of some points connected with the electricity 

 of living fishes, they shall be noticed in the 

 course of the following article. 



It is in the mode of its development that 

 the chief peculiarity of Animal Electricity 

 consists. None of the usual excitants of elec- 

 tricity are concerned in it. There is no che- 

 mical action, no friction, no alterations of tem- 

 perature, no pressure, no change of form. The 

 exercise of the animal's will, and the integrity 

 of the nervous system, as well as of certain 

 peculiar organs which exist in all the animals 

 endowed with electrical power, seem to be 

 alone sufficient for its evolution. 



The following are the systematic names of 

 the electrical fishes at present known: 

 Torpedo narke. 



unimaculata. Risso. 



marmorata. Ditto. 



Galvanii. Ditto. 



Gymnotus elect ricus. 



Trich iurus elect ricus. 



JMalapterurus electricus. 



Tetraodon electricus. 



The four species of Torpedo inhabit various 

 parts of the Atlantic and Mediterranean. They 

 were formerly regarded as constituting one 

 species, (Raia Torpedo, of Linnaeus;) and now 

 Dr. John Davy proposes to reduce them to 

 two ; having satisfied himself (and in this he is 

 supported by the opinions of Cuvier and of 

 Rudolphi) that the T. marmorata and T. Gal- 

 vanii are merely varieties of the same species, 

 for which he suggests the name of T. diversi- 

 color. It is known in Italy by the name of the 

 Tremola. The other species (the Occhiatella 

 of the Italians) Dr. Davy thinks would be 

 better named T. oculata. Both pass in Malta 

 under the term Haddayla. The first of these 

 species (T. vulgaris, of Fleming,) occurs on 

 the south coast of England, where it some- 

 times attains a great size. Pennant mentions 

 one which measured four feet in length and 

 two and a half in breadth, and weighed fifty- 

 three pounds. And Mr. Walsh describes an- 

 other which was four feet six inches in length, 

 and of the weight of seventy-three pounds.* 



* Phil. Trans. 1774. 



