Volume 2

The cyclopaedia of anatomy and physiology / edited by Robert B. Todd.

Date:
1836-1859
Catalogue details

Licence: Public Domain Mark

Credit: The cyclopaedia of anatomy and physiology / edited by Robert B. Todd. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    95/1034 (page 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, but a real change of place of the upper extremity of the radius on the outer con- dyle of the humerus. The elbow was but slightly deformed, and all its motions were perfect ex- cept extension, which was not complete, but the girl had perfect rise 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 the 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 the 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 fib ous 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. II. 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 nurke. unimaculata. llisso. murmoratu. Ditto. Galvanii. Ditto. Gymnolus electricus. Trichiurus electricus. Malapterurus 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. G