The principles of physiology applied to the preservation of health and to the improvement of physical and mental education / by Andrew Combe.

  • Combe, Andrew, 1797-1847.
Date:
1860
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Licence: Public Domain Mark

Credit: The principles of physiology applied to the preservation of health and to the improvement of physical and mental education / by Andrew Combe. Source: Wellcome Collection.

    316/366 (page 292)
    Nature of the Nervous Influ- ence.—The nervous energy is con- sidered by many to be identical with electricity; and this opinion at first sight seems countenanced to some ex- tent by the fact, that muscular con- traction and other results arising from nervous action can be produced also by means of electricity. But the sub- ject is still involved in great obscurity, and physiological researches must be greatly extended before we shall be able to determine in what manner the nervous system produces its eifects on the living functions, and what is the exact nature of the influence which it exerts. There can be no doubt that electricity may be deve- loped in the animal body, for this is proved indisputably in the case of the electric fishes; and it is also clear that this power is in close connection with the nervous system. Hunter showed that the most characteristic feature of the organisation of the electric battery in the torpedo is its enormous supply of nervous matter, each electric nerve being generally as thick as the spinal cord ; and Mr Faraday has demon- strated by experiments on the gym- notus that was long preserved at the Adelaide Gallery in London, the identity of the imponderable se- cretion of the battery of the fish with electricity. Needles, says Profes- sor Owen, who was present at the experiments, were converted into magnets; iodine was obtained by polar decomposition of iodide of potassium ; and, availing himself of this test. Pro- fessor Faraday showed that any given part of the organ is negative to other parts before it, and positive to such as are behind it. Finally, heat was evolved, and the electric spark ob- tained. A stimulus to the battery is necessary for the discharge of elec- tricity, precisely as a stimulus to the muscles is necessary to produce con- traction. The electric, like the motory nerves, says Professor Owen, *' rise from the anterior myelonal* tracts. An impression on any part of the body of the torpedo is carried by the sensory nerves either directly, ♦ From fjc^viXos, myelos, the spinal cord. or through the posterior myelonal tracts, to the brain, excites there the act of volition, which is conveyed along the electric nerves to the organs, and produces the shock : in muscular contraction, the impression and voli- tion take the same course to the mus- cular fibres. If the electric nerves are divided at their origin from the brain, the course of the stimulus is interrupted, and no irritant to the body has any effect on the electric organs any more than it would have under the like circumstances on the muscles. But if the ends of the nerves in connection with the organ be ir- ritated, the discharge of electricity takes place, just as irritating the end of a motor nerve in connection with muscles would induce its contraction. If part of the electric nerves be left in connection with the brain, the sti- mulus of volition cannot, through these, excite the discharge of the whole organ, but only of that part of the organ to which the undivided nerves are distributed. So, likewise, the irritation of the end of a divided nerve in connection with the electric apparatus, excites the discharge of only that part to which such nerve is distributed.* There exists, then, a close analogy between the electric ac- tion and muscular contraction, and this analogy is further seen in the increase of both by augmented respi- ration and circulation, in their ex- haustion by exercise, and recovery by repose. The same close resemblance is shown by the direct action of strychnia on the nervous centres ; its application causing simultaneous con- vulsive contractions of the muscles, and a rapid succession of involuntary electric discharges. These facts, how- ever, are far from proving the identity/ of the nervous force with electricity, or even the mutual convertibility of these two agents. The nervous sti- mulus which enters the electrical organ acts simply as an exciter of cliemico-vital changes, the result of which is a development of electricity. When the nervous stimulus enters a * Owen's Lectures on the Comp. Anat. of the Vertebrate Animals, p. 216.