Page:Popular Science Monthly Volume 2.djvu/547

Rh peculiar to animals, as Galvani declared. It decides also that electricity produced by external causes has an influence over animals, as Volta taught. From profound study of the two orders of phenomena, it deduces a system of procedure for the cure of very many maladies by electricity. Consequently, an exposition of the relations between electricity and life must begin with examining the electricity that exists naturally, in the same way that heat does in animals, and then go on to explain the action of the fluid on the organism, whether in a healthy or a morbid state. Such a description will complete what has been written in the Review respecting the relations of life with light and heat—relations that we may to-day consider as forming the features of a new science.

The most authentic witnesses to the existence of animal electricity are fish. The torpedo, the silurus, the gymnotus, the ray, and other fishes, develop spontaneously a more or less considerable quantity of electricity. This fluid, the production of which depends upon the animal's will, is identical with that of common electrical machines; it gives the like shocks and sparks at a certain tension. The apparatus for its formation consists of a series of small disks of a peculiar substance, kept apart by cells of laminated tissue. Fine nerve-end fibres are scattered over the surface of these disks, and the whole represents a sort of membranous pile, usually placed in the region of the head, sometimes toward the tail.

These fishes are the only animals provided with an apparatus specially devoted to the production of electricity; but all animals are electric, in this sense, that a certain quantity of that fluid is constantly forming within their organs. The existence of electricity peculiar to the nerves and muscles, and independent of their special modes of action, has been settled by numerous experiments, particularly by those of Nobili, Matteucci, and Dubois-Reymond. To prove the currents of nervous electricity, it is sufficient to prepare a frog's muscle, and touch it at two different points with the two ends of a nerve-filament of the same animal. The muscle then undergoes contraction under the influence of the nervous current. Another experiment, as simple, proves the existence of the muscular current. In an animal living or just killed, a muscle is exposed and cuts made in it perpendicularly to the course of the fleshy fibres, and communication effected by the two wires of a very sensitive galvanoscope between the natural surface of the muscle and the surface made by incision. The needle of the instrument then betrays the passage of a current. This muscular electricity may be obtained in tolerable quantity by placing a number of slices of muscle together in the form of a pile. The positive pole of the system will be the natural surface of one of the terminal slices, and the negative pole the cut surface of the other. Such a battery acts