CLASS IV. II. Principle of sen sation and motion. attribute of sensation, but exercising motion over all the organs of the face that are connected with the function of respiration, whether in the cheeks, lips, and nostrils; and hence operating equally in the acts of speaking, singing, sucking, drinking, spitting, coughing, and sneezing. And he has confirmed these discoveries by the striking fact, that the nerves of the head, which issue like the spinal medulla, from both departments of the brain, possess the same double power, and are, in like manner, nerves of sensation and motion; of which the fifth pair offers a notable example, bestowing at the same time sensibility on the head and face, and performing various muscular motions common to all animals: so as to be analogous to a double spinal nerve, or rather to the spine itself, and enriched, like the spine, with ganglions in particular parts. Confirmed Many of these experiments have since been repeated, and porary expethe results to which they have thus led, though in some rimenters. respects opposed by other experiments of M. Fodere*, have generally been confirmed by M. Magendie, Mr. Shaw, Mr. Broughton, and various other anatomists: and we hence see the reason of those frequent decussations, and other interunions of nerve with nerve, by which those possessing a single origin, and consequently a single property, hereby exchange filaments, and become enriched with a new power, the respective filaments being enveloped in the same sheath. by contem cidation still respecting the continu ance of these powers in a disorganized state of There is much, however, in this recondite subject, that Much elustill requires elucidation; and particularly in regard to required that continuation of sense and motion, in many cases which we shall hereafter have to notice, in which the brain, through a very considerable extent, both in its white and cineritious substance, has been found in a mollescent or pulpy state; often indeed entirely disorganized, and as soft as soap; while, in other instances, the spinal marrow, through an extent of six or seven inches in length, has been found equally dissolved, and its chain completely destroyed; one set of limbs being rendered rigid and mo Recherches Experimentales, &c. Journ. de Physiologie. Juillet, 1823. brain or spinal marrow. CLASS IV. II. Principle of sensation and motion. of Glisson, Haller, and Girtanner. tionless, with an augmented sensibility, at the same time that the sensation and mobility of the rest have been scarcely interfered with. And hence a separate and specific power has, from an early age, been ascribed to the nervous fibres themselves, while the brain has been conHypothesis templated as their radix. This, in truth, was the peculiar hypothesis of Glisson, and nearly so of Haller, with respect to the motory power; and Girtanner, who trod in the same footsteps, with a clear and comprehensive mind, considerably enlarged upon it, and gave to the Vis insita as moving energy the name of vIS INSITA, as, by way of tinguished distinction, he applied that of VIS NERVEA to the energy or power of feeling. And as he believed that other organs Why called besides muscles, and indeed plants as well as animals, are possessed of fibres endowed with the same power, and that a brain is by no means essential for their production, he, in like manner, changed the name of muscular to that of irritable fibre; and contended that a principle of irritability is common to fluids as well as to solids, and co-extensive with organized nature*. contradis from vis nervea. irritable fibre. Oxygene conceived to be its principle, By what means these fibres unite into solid masses or hollow coats, and what are their respective powers when thus complicated, shall be glanced at hereafter†; at present, we must confine ourselves to their actuating principle, whatever that may consist in. Oxygene was at this time the popular aura of the phiLalosophers, as caloric had been a short time before. voisier had just proved its close connexion with several of the vital functions, and hence the chemical divinity of Girtanner was oxygene. He paid unbounded homage to its influence, attempted to show that irritability, and even life itself, are dependent upon it; and that in the animal system it is distributed to every part by means of the circulating blood. * Mémoires sur l' Irritabilite, considérée comme principe de vie dans la nature organisée. Journ. de Phys. 1790. See the introductory remarks to Order III. of the present class, NEUROTICA, CINETica. II. Princi motion. and galva discovery. since its Discovery ofarly antiof the last nearly cipated half before. But the still more striking properties of the galvanic CLASS IV. fluid, began now to be discovered and to captivate the ple of sengeneral attention; and the time drew nigh in which sation and oxygene was doomed to fall as prostrate before the shrine of Galvanic aura as caloric had fallen before that of nic fluid oxygene. And it is curious to remark, how nearly this discovery was not only made but completed in all its bearings, and by the very same means, about fifty years before the attention of Galvani was directed to the subject; for as we are told in the Philosophical Transactions a century for 1732*, that the Queen's physician, Dr. Alexander Stuart, being engaged in a course of experiments upon the frog, observed upon thrusting the blunt end of a probe into the spinal marrow, after decapitation, that the muscles of the animal's body were thrown into convulsive contractions; and that the same happened to the muscles of the head when the probe was thrust into the brain. And by additional experiments he advanced so far as to infer that what the nerves contribute in muscular motion, cannot be produced by oscillations or elasticity, but must be owing to a fluid contained in them; but which fluid he was unfortunate enough to conceive was a pure and perfectly defecated elementary water; using the word water, however, in a general sense, as merely opposed to sal volatile, or fermented spirits, which he thought the term animal spirits was calculated to import. Its Whatever be the nature of the active and etherial fluid which was thus traced by Stuart, and has since been fully established by Galvani, there can be no question of its having a powerful influence upon many branches or divisions of the nervous system, though not upon all. effects upon the muscles of an animal for some hours after death are too well known to be particularized: and Dr. Philip seems to have shown, by various trains of experiments †, that it is equally capable of maintaining respira Vol. xxxvII. p. 324. + Phil. Trans. 1815. p. 5–90. Has a close affinity with the nervous inbut not proved to fluence; be the same. CLASS IV. tion, and the operation of several of the animal secretions, II. Princi ple of sen sation and motion. Fanciful and complicated conjecture of Rolando. Result of the inquiry. Nervous system differently elaborated but a secer 66 especially those that induce digestion, for as long a period. But in drawing from such facts the corollary that the IDENTITY of galvanic electricity and nervous influence is established by these experiments"; he seems, like those who have anticipated him in the same doctrine, to proceed farther than he is warranted: for we have no right to say more than that galvanic electricity is a stimulus exciting the nervous influence into a state of continued secretion, or continued action; which may possibly be done by various other stimuli, as well as by that of galvanism. M. Rolando, however, has proceeded farther than this; for while he regards the nervous fluid and that of galvanism as identic, he contemplates the cerebellum and its appendages as a galvanic machine in which the cerebellum itself constitutes the formative pile, the medulla oblongata, the conductor in which the fluid is accumulated, and the spine and nerves the channels through which it is conveyed to the muscles for the purpose of exciting voluntary motion. But this puts us into possession of only one half of the powers of the brain,-the motific. For the sensific powers, M. Rolando has revived the old doctrine of vibrations, already noticed, and conceives that all sensations are commenced at the extremities of the nerves, and are conveyed from the circumference to the centre of the system by vibrating chords *. Upon the whole the nervous system seems to present itself, in the different classes of animals, under various scales of elaboration; but in every scale to be a secernent nent organ: organ through its entire range; operating by means of two or more different sets of fibres, which may be secretories or conductors of as many different fluids or modifications of the same fluid. possesses two or more secretories or conductors of different fluids or modifications of a common fluid. In the higher and more complicated classes of animals it consists of a cylindrical chord, or spinal marrow, a contral or ganglionic compages and a brain, all communicat * Coster, Archives Générales de Médicine, Mass, 1823. CLASS IV. II. Princi sation and ing and acting in harmony*. In some of the inferior classes we find the cylindrical chord alone, and in others the gan- ple of senglionic compages: while in the lowest of all we trace a variety of distinct and granular molecules, which seem to act the part of nervous ganglions, though we cannot discover their connexion. motion. Brain a gland. gene Cullen's hypothesis. The brain has so much of the general structure and rally adcharacter of a gland, as to be admitted to be an organ of mitted to be this kind almost without a dissentient voice in the present day. This is a point conceded even by Dr. Cullen, notwithstanding that by supposing the energy of the brain to be a mere quality rather than a specific essence, and to be incapable of undergoing any change of recruit or exhaustion, he finds no adequate use for its glandular conformation. As we are justified, however, by all the force of analogy in regarding it as a gland, though unquestionably a gland of a peculiar kind, and as we are equally justified on the same ground of analogy in regarding the nervous power or energy by which it maintains a communication with every part of the system, as a fluid of a peculiar kind, we are almost driven to the necessity of contemplating it as the source from which this fluid issues and by which it is supplied as it becomes exhausted. And more especially when we reflect upon the enormous proportion of blood which is sent from the heart to the head, as the most extensive laboratory of the entire frame, and which, according to Haller †, amounts to one-fifth, or or on the lower estimate of Monro ‡, to one-tenth of the entire current poured forth from the left ventricle of the heart, while it is well known that the weight of the human brain is not more than one-fortieth part of the entire body. It is probable that the nervous fluid on its first secretion Nervous and in its simplest state, is as homogeneous as that of the fluid at first perhaps hoblood; but that, like the blood, it becomes changed by mogeneous; → De Nervi Sympathetici humani fabricâ, usu, et morbis, &c. Auctore J. Lobstein, Parisiis, 1823. Elem. Physic. x. v. 20. On the Nervous System. p. 3. |