Only four of the eight experimental effects enumerated by Dr. Faraday/ as characteristic of common and voltaic electricity are pro duced by animal electricity; which appears to be sufficient to prove that the latter is as much a peculiar power distinct from these as are the agents called magneto-electricity and Merino-electricity. Perhaps, however, what we at present regard as so many powers dif fering from one another in their natures, may be merely modifications of the same power, varied in its sensible properties by changes in the circumstances under which they are mani fested. This latter view is that taken by Dr. Wilson Philip, who holds that Animal Elec tricity is just common electricity modified in its properties by those of life, under the in fluence of which it operates in the living animal.
Sir llumphry Davy thought he saw a stronger analogy between common and animal electricity, than between voltaic and animal electricity, hut concluded that the latter would be found by more extended researches than he was able to make to be " of a distinctive and peculiar kind."' Cavendish, on the other hand, believed that there is a complete identity between common electricity and that of fishes. And this lie laboured to prove by imitating several of the peculiarities of the discharge of the torpedo by a particular arrangement of small Leyden jars, forming a battery, from which the electricity was discharged in large quantity but of low intensity.f Others, again, have attempted to trace a certain resemblance between the structure of the electrical organs of the torpedo and the formation of the voltaic pile, " inasmuch as they are formed of alter nate layers of moistened conductors of dif ferent natures, to wit, of membranous parti tions, and of gelatinous and albuminous fluid." (Tiedemann.) They suppose that the nerves, being spread over one side of the transverse partitions of the cells, produce opposite states of electrical tension on the two sides of the partition. In the present imperfect state of electrical science, all such hypotheses are un satisfactory.
The only conclusions which, in our opinion, can be legitimately drawn from the accumu lated facts on the subject are—that the shock given by electrical fishes is caused by an agent closely allied in its nature to common elec tricity and other like powers,/ and that the developement and discharge of this agent are strictly dependent on the integrity of the ner vous communication between certain peculiar organs and the great nervous centres.
It is evident that the nervous system plays a very important part in the electrical function. But whether its influence merely stimulates the electrical organs to do what their organic structure renders them capable of doing, or really supplies them with a stream of the im ponderable agent which they accumulate, and then, under voluntary impulses, discharge, is still a point for further investigation. In the structure of the electrical organs, we do not see any arrangement such as researches in elec tricity artificially developed lead us to believe fitted either to produce or to accumulate elec tricity. But this is in •itself no reason why we should conclude that the organs have not such powers. It seems more in accordance with what we know of the actions of other parts of the animal frame, to believe that they do possess such powers. But—if the elec trical organs, by their organic structure, be fitted to develope and to discharge electricity under the nervous influence, just as a gland secretes its peculiar fluid and its ducts eject it, why (it may be asked) are the nerves going to these organs of so very great a size compared with the same parts in other organs of similar bulk and very energetic action ? Is their sub jection to the will of the animal sufficient to account for the difference ? or does it indicate, as some physiologists maintain, that the ner vous influence does more in this case than merely supply the vital stimulus such as is received by all other organs in common ? In other words—is the agent discharged by the fish as electricity first developed in the ner vous centres, and only accumulated in the electrical organs; and is this agent identical with common nervism ? To these questions we cannot yet give a satisfactory reply. They point the way to some very interesting and im portant fields of investigation, and cheer us with the hope of considerably extending our acquaintance with the physiology of the nerves, on the supposition that the phenomena of ani mal electricity shall one day be proved to he owing to an accumulation and discharge of the very same agent that causes contraction of muscles, &c. Such a view appears to have been taken of this subject by Sir II. Davy when he remarked,* " there seems a gleam of light worth pursuing in the peculiarities of animal electricity,—its connexion with so large a nervous system,—its dependence on the will of the animal,—and the instantaneous nature of its transfer, which may lead, when pursued by adequate inquirers, to results very important for physiology." Treviranus, in 1818, suggested the likelihood of the power concerned in the ma nifestation of electrical phenomena by animals, being one of those on which continuance of life in general depends. "Perhaps," said he,t "it is the same power which enables the tor pedo to give electric shocks that is the imme diate cause of the contraction of muscular fibres." The same hypothesis is thus ex
pressed by Carus./ " Numerous nerves are distributed upon the cells of the electrical organs, and as it is through the agency of these nerves that the organs act, it is not im possible that the nervous influence itself is accumulated in these cells as in condensers, and that it is discharged at will, just as this influence is accumulated in the muscular tissue to produce contraction of its fibres." It was reflection on the phenomena of animal elec tricity that led Dr. Wollaston to form the hy pothesis, which lie supported with so much ability, of secretion in general being depen dant on electricity, conveyed by the nerves, and acting on the secreting organs.* Dr. Wilson Philip, also, thinks that the circum stances under which electrical action is mani fested by fishes go to the support of his theory of the nervous influence being identical with common and voltaic electricity. Dr. Faraday says that, from the time that it was shewn that electricity could perform the functions of the nervous influence, he has had no doubt of their very close relation, and probably as effects of one common cause. To the numerous list of learned observers who have speculated on this interesting subject, we have to add the re spected name of Sir John Herschel, who imagines that the present state of electrical science warrants the conjecture, that the brain and spinal marrow form an electric organ, which is spontaneously discharged along the nerves, at brief intervals, " when the tension of the electricity reaches a certain point."-f Meissner, again, supposes that the blood be comes charged with electricity in the lungs, during the chemical process of respiration ; that the electricity immediately traverses the nerves of the lungs, and then the other parts of the ganglionic system ; that hence the cen tral organs of the nervous system become charged ; and that the brain, on and through which the will acts, being charged, excites the several organs to activity through the medium of their respective nerves, along which electric currents are passed. The facts, (in addition to those which have chiefly engaged our atten tion in this article,) upon which such theories are built are,— (1) that the muscles of an animal recently dead contract when common electricity passes through them, just as they do when they are subject to the animal's will; (2) that voltaic electricity acts upon secreting organs, so as to enable them in some degree to carry on their functions after their proper nerves have been cut; and (3) that the same agent appears to influence powerfully the capillary circulation. But, although these facts, taken Mono. with what we know of the phenomena of tric electricity of fishes, certainly do appear to favour the views to which we have just alluded, there are yet other facts which are so hostile to them as to make it probable that they do not express the truth. For instance, the most carefully conducted experiments have failed to demonstrate the existence of electric currents through muscles during their contrac tion; which, from all that is known of the phenomena exhibited by electricity in other circumstances, it may be presumed would not have been the case had it been the immediate stimulant of muscular contraction. M. Per son has applied the poles of a galvanometer to the spinal marrow without obtaining any indi cations of the existence of electrical currents through its substance. The subjects of Per son's experiments were cats, dogs, rabbits, eels, and frogs. The spinal canal having been opened, the piles of the galvanometer were placed in communication with the anterior and posterior columns of the cord. This was done at different parts, after the roots of the nerves had been cut. Small plates of platina, with which the wires of the instrument were armed, were thrust into the cerebellum and into several of the largest nerves. These experiments were repeated after the animals had been placed under the influence of strychnia. But there was no certain indication of electricity ob tained, although the most delicate instruments were used' Person's experiments have been repeated by Muller with the same results. Messrs. Prevost and Dumas, however, state that, having armed the branches of their gal vanometer with two wires of platina, exactly alike, and having plunged one of them into the muscles of a frog's leg, while, with the other, heated to redness, they touched its nerves, they saw considerable deviations of the needle of the instrument follow the contrac tions of the muscles.t But seeing that the electricity made manifest in this experiment may have been developed rather by the con tact of the hot wire and the nerves than by the nervous actions, we cannot admit that it is sufficient to prove the existence of electrical currents in muscles during their contraction. Dr. Faraday, also, has lately experimented on living muscles with the very delicate galvano meter invented by himself, but has entirely failed to obtain indications of moving electri city. Negative results such as these, obtained by so many practised observers, are sufficient to induce us to withhold our assent from those theories which make nervism identical with electricity, until the whole subject shall have been more fully investigated.