Some individuals exhibit electrical pheno mena much more readily than others. Some persons, for instance, hardly ever pull off articles of dress worn next the skin without sparks and a crackling noise being produced. It is related of a certain monk that sparks were always emitted from his hair when it was stroked back wards ; and of an Italian lady that her skin, when rubbed with a linen cloth, gave out sparks, attended with a crackling noise. The same phenomenon, as exhibited by the cat, and by other animals covered with a soft fur, is daily observed. Butt it has been stated that the vat's electricity may be accumulated in its own body and given off suddenly, so as to produce a shock. Romer says,• "If one take a eat in his lap, in dry weather, and apply the left hand to its breast, while with the right he strokes its back, at first he obtains only a few sparks front the hair; but, after continuing to stroke for some time, he receives a sharp shock, which is often felt above the wrists of both arms. At the same moment, the animal runs off with expressions of terror, and will seldom subunit itself to a second experiment." In repeating this experiment, we have obtained the like result.
We are not aware of any other observer having met with any thing resembling an accumulation of electricity in quadrupeds, excepting Cotugno, who asserted that, in dissecting a living mouse, he felt an electric shock when its tail touched his finger.f XI. Uses of animal cleetricity.—The pur pose which the electrical function is fitted to serve in the animal economy is proba bly not single. It is very evident that the discharge from the organs frequently strikes terror into the enemies of their possessors, and thus it may be regarded as a means of defence; while, in certain circumstances, it may be useful in enabling the fish more easily to secure its prey. But this, probably, is not all. It is very likely, as Dr. Roget has suggested,/ that the electrical organs communicate to the fish perceptions of electrical states and changes in surrounding bodies, (very different from any that we can feel,) in the same way as other organs of sense convey perceptions with regard to light and sound. Such perceptions we can conceive to be very useful and pleasunible to animals living in the dark abysses of the waters.
Some of Dr. John Davy's observations make it very doubtful whether the electrical function is ever subservient to that of prehension of food. Ile kept young torpedos for a period of five months or more, in large jars of salt water, during which time they ate nothing, although very small fishes, both dead and alive, were put into the water. Yet they grew, and their elec trical energies and general activity increased.* The small fishes seemed to have no dread of the torpedos. On one occasion, however, when a lively torpedo was placed in a small vessel along with a smelt, and excited to discharge, the smelt was evidently alarmed, and once or twice, when exposed to the shock, leaped nearly out of the vessel, but it was not injured by the electricity. It has also been frequently ob served of the gymnotus that it eats very few of the fishes that it kills by its discharge.
The electrical power of the young fish is proportionally very much greater than that of the old, and can be exerted without exhaus tion and loss of life much more frequently. After a few shocks, most of the old fish which Dr. Davy has endeavoured to keep alive have become languid, and died in a few hours, whilst young ones, from three to six inches long, remained active during ten or fifteen days, and sometimes lived as many weeks. Hence
Dr. Davy concludes that the chief use of the electrical function is to guard the fish from its enemies, rather than to enable it to destroy its prey, and so provide itself with food. lle fur ther conjectures that, besides its defensive use, the electrical function may serve also to assist in respiration by effecting the decomposition of the surrounding water, and so supplying the gills with air when the fish is lying covered with mud or sand, in which it is easy to con ceive that pure air may be deficient. And Dr. Davy has often imagined that he saw something of this kind going on. After repeated dis charges, lie has observed, all around the margin of the pectoral fins, an appearance as if very minute bubbles of air were generated in it and confined. That this may be one purpose which the electrical function is designed to serve, is rendered still more probable by the circumstance, that the gills (in the torpedo at least) are largely supplied with twigs of the electrical nerves. In fishes in which he had cut the electrical nerves, Dr. Davy found the secretion of the cutaneous mucus considerably diminished or altogether arrested ; and hence he supposes that the electricity assists in the production of this fluid.
Lastly, it has been conjectured that the elec trical function is subservient to tbat of digestion. This idea was started by Mr. J. Couch some years ago.t lie says, " Without denying that the torpedo may devour that which it disables by the shock, I conceive that the principal use of this power has a reference to the functions of digestion. It is well known that an effect of lightning or the electric shock is to deprive animated bodies very suddenly of their irrita bility ; and that thereby they are rendered more readily disposed to pass into a state of disso lution than they would otherwise be; in which condition the digestive powers of the stomach can be much more speedily and effectually exerted on them. If any creature may seem to require such a preparation of the food more than another, it is the torpedo, the whole intes tinal canal of which is not more than half as long as the stomach." These views receive some support from the fact that the nerves of the stomach are derived from those supplying the electrical organs; and perhaps also from the fact, reported by Dr. Davy regarding a torpedo, in which, after it had been frequently excited to give shocks, diges tion seemed to be completely arrested.
The only conclusion to which, in the present state of our knowledge, we can come on this point is, that although the electrical organs form a very efficient means of defence from their enemies for the fishes which possess them, this is not the only purpose they are intended to serve ; what, however, their other uses are is at present only matter of conjecture.
There remains yet unentered upon a large field of enquiry connected with the physiology of those wonderful organs, which, we doubt not, will yield to future ages very striking examples of that nice and close adaptation of means to ends which so clearly proves to us the existence and continued exercise of Wisdom Supreme," upholding all things by the word of his power," making the smallest of his works " very good," and " to be thought upon."