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Class IV. more conscious of an excitement in this organ of sense I. Nature of the
than in any other: and, from the anomaly and rare ocbrain, its currence of the sensation itself, find no terms by which ramifications and to express it. substitutes. In Germany it has of late been attempted to be shown
that every man is possessed of a sixth sense, though of a
II. As the nerves thus generally communicate with ple of sensation and each other, and with the brain where this organ exists, motion.
it has been a question in all ages by what means they maintain this communication, and what is the nature of the communicated influence ? or, in other words, what is the fabric of the nerves, and the quality of the nervous power ?
* Comment. de Cænesthesi. Dissert. Aug. Med. Auct. Chr. Fred. Hubner, 1794.
Nature and Origin of Mental Derangement, by A. Crichton, M. D. 2 vols. 8vo. 1798.
Upon these points two very different opinions have been Class IV. entertained from an early period of the world, which ple of senunder different modifications have descended to our own se
sation and times : for by many physiologists, both ancient and mo- Nervous dern, the nerves have been regarded as solid capillaments, fabric, or tense and elastic strings, operating by tremors or oscil solid chords lations, like the chords of a musical instrument; and by or hollow others as minute and hollow cylinders conveying a pecu
cylinders. liar fluid. The word NERVE, which among the ancients Original
meaning of was applied to tense chords of every kind, and especially the term to bow-strings and musical strings, affords a clear proof nerve. how generally the former of these hypotheses prevailed
Hypothesis among the Greeks. It was not, however, the hypothesis of Hippo either of Hippocrates or Galen; for by them, while the crates and
Galen; nerves were regarded as the instruments of sensation and motion, the medium by which they acted was supposed to be a fine etherial fluid, elaborated in the organ of the brain ; to which they gave the name of animal spirit, to distinguish it from the proper fluid of the arteries which was denominated vital spirit. “Not”, says Galen, “ that suppo
an etherial this animal spirit is of the substance of the soul, but its Huid; prime agent while inhabiting the brain”* But with respect to the manner in which the animal spirit operates upon the nerves they spoke with great modesty ; for though they thought they had been able to trace a tubular form in some of the nerves, and particularly those of vision, they had not been able to succeed in others. And hence, says Galen," it is impossible for us to pronounce
ed themabsolutely and without proof, whether a certain power selves unmay not be transmitted from the brain through the nerves to the different members; or whether the material of the ed a comanimal spirit may not itself reach the sentient and mov
o munication ing parts; or, in some way or other, so enter into the rest of the nerves as to induce in them a change which is afterwards body. extended to the organs of motion” t.
"De Hippocratis et Platonis Decretis, Lib. vii. A. Tom. I. p. 967. Ed. Basil, 1542.
| Id. Sect. C. p. 969.
Class IV. In a state not much less unsettled, remains the subject II. Principle of sens at the present moment. Dr. Hartley, in the beginning sation and of the seventeenth century, revived the hypothesis that
the nerves are bundles of solid capillaments conveying The question still in motion, sensation, and even perception, by a vibratory
power, and supported his opinion with great ingenuity tled state. Hartley's
and learning * ; but the opposite hypothesis that they are hypothesis minute tubes filled with the animal spirit of the Greek
ratory physiologists, had acquired so extensive a hold ever since strings,
the discovery of the circulation of the blood, which pre
supposes the existence of tubular vessels too subtle to be not able to traced by the senses, that it never obtained more than a subvert the hypothesis partial and temporary assent; and hence, from the times of Syden- of Sydenham and Boerhaave almost down to our own day ham and
the last has been the popular doctrine; is to be traced in
the general tenour of medical writings; and has been espeare hollow cylinders
cially maintained by Sabatier and Boyer. conveying In effect, no fibres of the animal frame can be less an animal spirit. adapted to a communication of motion by a series of viNervous brations than those of the nerves, since none exhibit a fibres unadapted to smaller degree of elasticity ; and though we have little vibrations,
reason to confide in their tubular structure, or to believe as inelastic: yet no proof that any kind of Auid is transmitted in this way, the close of their being tubu
affinity which the nervous power' is now known to hold
a lar. with several of the gasses that chemistry has of late years Little doubt unfolded to us; and the wonderful influence which some however of of them possess over the moving fibres of the animal
frame, seem to leave no question that the nervous power liar fluid; itself is a fluid, though not, perhaps, of their precise
nature, yet resembling the most active of them in its which, like subtilty, levity, and rapidity of movement. Nor is there various
upon this supposition any difficulty in conceiving of its not stand transmission by solid fibres or capillaments of a particular in need of :
kind, the neurilemma of Bichat, whilst we behold the sels for its etherial fluids, now referred to, transmitted in the same transmis
way by substances still more solid and unporous.
But there is another question, closely connected with • Observations on Man, his frame, &c. his duty, and his expectations. 2 vols. 8vo. 1749.
a nervous and pecu
The two effects must
tinct sets of
the present subject, that has also greatly interested phy- Class IV.
II. Princisiologists both in ancient and modern times, and is not
ple of senyet settled in a manner altogether satisfactory.
sation and It has appeared that the nerves are instruments both
Whether of sensation and motion. Are these two effects produced sensation by the same nervous fibres or by different ? or by the
a common same fluids or by different? That there must be two dis- power, or tinct kinds of fibres, or of fluids, is clear, because, as we
tinct shall have more particularly to observe when we come to sources ? treat of paralysis, the muscles of a limb are sometimes deprived of both sensation and motivity at the same pe- proceed riod, sometimes of sensation alone while motivity conti
tinct fibres nues, and sometimes of motivity alone while sensation of fluids. continues. And hence Hippocrates and Galen, the last to
cot According of whom has treated of the subject with great minuteness Greeks,
from disin many of his writings, while they speak of only one ti kind of animal spirit, speak of two kinds of nerves, those fibres ope
rated upon of sense and of motion ; equally issuing from the brain, by the and mostly accompanying each other, and forming parts same ner,
vous fluid. of the same organs.
This distinction is supported by the concurrent obser- How far vations and experiments of physiologists, and especially su by the curious investigations of many of those of our own siologists. day, among whom should be particularly noticed the names of Fleurens, Rolando, Charles Bell, Magendie and Shaw. M. Rolando attempted to show by a long train Rolando's
w distinct proof interesting, but very painful, and hence unjustifiable in experiments, carried on through animals of almost every rebrum and kind, that the cerebrum is the ordinary source of sensation, and the cerebellum of motion : for, according to his observations, in every instance in which the former is much broken down, or in any other way injured, drowsiness, stupor, or apoplexy, is sure to follow; the animal being still capable of exercising locomotive power, but without any guidance or knowledge of what it is about, or where it is moving to. But the moment the cerebellum is wounded, the locomotive power is instantly lost *. These
mainly supported by
Saggio sopra la vera Struttura del Cervello, &c. e sopra le Fonzioni della Sistema Nervosa. Sassari, 1809.
Class IV. investigations were valuable as leading on to others more II. Principle of sen
accurately conducted and followed up by more correct consation and clusions. That these distinct portions of the brain are en
dowed with separate powers, as observed by Rolando, has Such sepa. rate powers been sufficiently ascertained by other pathologists; and since con
especially by M. Fleurens *, who does not seem, at the firmed, but conversely time to have been acquainted with Rolando's experiments, ascribed.
and consequently gives us the weight of an unconnected testimony. But it seems to have been better established, as M. Magendie remarks t, since these experiments, that the converse of M. Rolando's constitutes the law and order of nature: for sensation seems now proved to be dependent upon the cerebellum, instead of upon the cerebrum, while motivity takes its rise from the cerebrum instead of from
the cerebellum. Followed up Mr. Charles Bell has successfully followed up these by C. Bell into the
dem distinct and established powers of the two departments of spinal mar- the brain f, into the spinal marrow, which he has suffi
ciently proved to consist of a double chord; an anterior His demonstration. connected with the crura of the cerebrum, and productive Double
of locomotion, and a posterior connected with the crura of chord of the spinal chain. the cerebellum, productive of sensation. And he has furLike me ther shown that these two distinct powers are communi
to cated to every part of the body by nervous fibres accordcontinued to every part of ing as they issue from the one or the other of these rethe body.
spective channels: that, for the most part, every nervous fascicle distributed over the body and limbs, has a double
origin, and issues equally from both the anterior and Strikingly posterior trunk of the spinal medulla ; and is conseexemplified in the portio quently aulke sensic an
quently alike sensific and motific : while those which produra of the ceed from one alone, are limited in their power to the
peculiar property of their source, of which the portio dura of the seventh nerve affords a striking example : being, when uncombined, simp:y a nerve of motion, without the
* Archives Générales de Médecine, 1. II.
+ Experiences sur les Fonctions, &c. Journ. de Physiologie, Tom. II, II. passim, 1822, 1823.
Idea of the Anatoiny of the Brain. 1809.