Licence: Public Domain Mark
Credit: Physiology of the nervous system / by Robert B. Todd. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![inferior to the metals as conductors. And from experiments made on this subject in 1845 by Dr. Miller, Mr. Bowman, and myself, we were led to conclude that nerve was infinitely a worse conductor than copper. The provision for insulation, however perfect for the nervous force, seems most insufficient for electricity, unless, perhaps, for a current of very feeble intensity. Yet we know that the nerve fibres convey the mandates of the will with the nicest precision to the muscles, and propagate the effects of physical stimuli applied to the peri- phery with the greatest exactness to the centre. This could scarcely be if the force so propagated were an imperfectly insulated electric current, for it is evident that in such a bundle of fibres as a nervous trunk disturbances would conti- nually be taking place, from the secondary currents induced in neighbouring fibres by the electricity passing through those in action. 3. The firm application of a ligature to a nerve stops the propagation of the nervous power along that nerve below the point of application; the passage of electricity, how- ever, is not interrupted by these means. The nervous trunk, indeed, is as good a conductor of electricity after the application of the ligature as before it, provided it do not become dry at the point of ligature. 4. If a small piece be cut out of the trunk of a nerve, and its place supplied by an electric conductor, electricity will still pass along the nerve and along the conductor; but the nervous force, excited by a stimulus applied above the section, will not be propagated through the conductor to the parts below. 5. The existence of an organ in certain ani- mals capable of generating electricity is un- favourable to the electric nature of the nervous force. The best examples of this organ are found in the Torpedo and the Gymnotus; and experiment has placed it beyond doubt that the organ generates electricity, which is capable of giving a shock similar to that from a Leyden jar; which developes a spark during the dis- charge, and can effect electrolysis; by which, likewise, the galvanometer may be disturbed, and needles rendered magnetic.* The electrical organs have no resemblance, in point of structure, to nerves; they, however, present a remarkable analogy in that respect, as well as in their physiological action, to the striped variety of muscles. They are composed of a number of prisms, each of which consists of a membrane closed at both extremities, and containing a soft albuminous substance, but subdivided by transverse very delicate septa into a multitude of small compartments. The bloodvessels and nerves are distributed upon the enclosing membrane and upon the septa, but do not penetrate the albuminous material. On these septa, according to Savi, the nerves form a network, in which the disposition of their terminal fibres differs from that in muscle in there being a true anastomosis or fusion of the primitive tubules. The analogy of the struc- ture of the electrical prisms with that of mus- cular fibres is sufficiently obvious, the latter being prismatic columns of fibrine, enclosed by a membrane, the sarcoleinma, and separable into discs, the nerves and vessels being distri- buted upon the sarcolemma, and not penetrating the contained sarcous elements. In both these textures the anatomical disposition has evident resemblance to the artificial arrangements for generating electricity^ and accordingly in one (the electric organ) true electricity is generated; in the other, as we shall see further on, either electricity, or a force in close relation to elec- tricity, is developed. In both cases the genera- tion of the force is independent of the nervous system; its exercise and application, however, are under the influence of that system. The arrangement of the nerves and nervous centres is essentially different from that of muscle or of the electric organ, and so far would suggest a decided difference in the cha- racter of the force which they can developefrom that produced by the latter textures. 6. A comparison of the muscular with the nervous force throws some light on the nature of the latter, and upon its true relation to elec- tricity. Matteucci has established beyond a shadow of doubt that electricity of feeble tension is gene- rated in the ordinary nutrition of the muscles of all animals, and by a particular arrangement this may be made to assume the current form, passing from the interior to the exterior of the muscle. The source of this electricity is no doubt to be found in the chemical action which accompanies the nutrition of the muscular tissue, “ principally that which takes place in the contact of the arterial blood with the muscular fibre.”* The intensity of this cur- rent increases in proportion to the activity of muscular nutrition, and in proportion to the rank the animals occupy in the scale of beings. It requires a particular artificial arrangement to accumulate the electricity in such a manner as that it shall affect the galvanometer; “during life the two electric states evolved in the mus- cle neutralize each other at the same points from which they are evolved;” but in the arrangement of a muscular pile as devised by Matteucci, “a portion of this electricity is put in circulation just as it would be in a pile com- ]3osed of acid and alkali, separated from each other by a simply conducting body.” During the active contraction of a muscle, however, a force is developed which has re- semblance to electricity, and in his early experi- ments was regarded in that light by Matteucci. This power is capable of affecting the nerve of the frog in the same manner as electricity. The following experiment displays this:—Take the lower extremity of a frog and skin it; dissect out the sciatic nerve from among the muscles on the posterior part of the thigh, and then sepa- rate the thigh by cutting it across just above the knee-joint, leaving the nerve connected with the knee and leg; this preparation is the galvunoscopicj'rog, so called by Matteucci from the readiness with which it indicates an elec- tric current; next prepare the lower extre- mities of a frog according to Galvani’s method :](https://iiif.wellcomecollection.org/image/b22332807_0014.jp2/full/800%2C/0/default.jpg)
