of the

brain, its ramifica

tions and

CLASS IV. the tongue to that of taste, or the ears to that of sound. I. Nature A distinct organ is not always requisite for a distinct sense. In man himself we have already seen this in regard to the sense of touch, which exists both locally and generally : substitutes. the distinct organ of touch is the tips of the tongue and of the fingers, but the feeling is also diffused, though in a subordinate and less precise degree, over every part of the The sense body. It is possible, therefore, in animals that appear probably endowed with particular senses without particular organs general, but dull as that for their residence, that these senses are diffused, like that of general of touch, over the surface generally; though there can be no doubt that, for want of such appropriate organs, they must be less acute and precise than in animals that possess them.

touch.

Whether any tribe possesses

than the

five common?

Suspected in the bat.

migratory

birds or fishes?

Whether there be any other than the five senses common to man and the higher classes of animals, may be other senses reasonably doubted; but we occasionally meet with peculiarities of sensation that can hardly be resolved into any of them. Thus the bat appears to be sensible of the presence of external objects and obstructions that are neither seen, smelt, heard, touched, or tasted; for it will cautiously avoid them when all the senses are purposely closed up. And hence many naturalists have ascribed a Whether in sixth sense to this animal. It is equally difficult, by any of the known senses of fishes or of birds, to account for the accuracy with which their migratory tribes are capable of steering their annual course through the depths of the ocean or the trackless regions of the atmosphere, so as to arrive at a given season on a given coast, or in a given climate, with the precision of the expertest mariner. Whilst, with respect to mankind themselves, we sometimes meet with persons who are so peculiarly affected by the presence of a particular object that is neither seen, smelt, tasted, heard, or touched, as not only to be conscious of its presence, but to be in great distress till it is removed. The presence of a cat not unfrequently produces such an effect; and the author has himself been a witness of the most decisive proofs of this in several instances. It is possible, that the peculiar sense may, in such cases, result from a preternatural modification in some of the branches of the olfactory nerve, which may render them capable of being stimulated in a new and peculiar manner;

Whether even in man?

but the individuals thus affected are no more conscious of.CLASS IV. › I. Nature an excitement in this organ of sense than in any other, and, from the anomaly and rare occurrence of the sensa- brain, its tion itself, find no terms by which to express it.

ramifica

tions and

In Germany it has of late been attempted to be shown substitutes. that every man is possessed of a sixth sense, though of a very different kind from those just referred to; for it is a sense not only common to every one, but to the system at large; and consists in that peculiar kind of internal but corporeal feeling, respecting the general state of one's health, that induces us to exult in being as light as a feather, as elastic as a spring; or to sink under a sense of lassitude, fatigue, and weariness, which cannot be accounted for, and is unconnected with muscular labour or disease. To this sensation M. Hubner has given the name of cænesthesis, and several of his compatriots that of selbstgefühl, and gemeingefühl, "self-feeling or generalfeeling;" and its organ is supposed to exist in the extremities of all the nerves of the body, except those that supply the five external senses*. I scarcely know why these last should have been excepted; for the sensation itself is nothing more than a result of that general sympathy, which appears to take place between different organs and parts of the body, expressive of a pleasurable or disquieting feeling, according as the frame at large is in a state of general and uninterrupted health, or affected by some cause of disquiet.

tion and

II. As the nerves thus generally communicate with each II. Princi other, and with the brain where this organ exists, it has ple of sensa been a question in all ages by what means they maintain motion. 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 +?

1794.

Comment. de Cænesthesi. Dissert. Aug. Med. Auct. Chr. Fred. Hubner,

Nature and Origin of Mental Derangement, by A. Crichton, M. D. 2 vols. 8vo. 1798.

"The question," says Dr. Bostock, "may be thus stated in direct terms. When an impression made upon an organ of sense is transmitted by a nerve to the brain, or when the exercise of volition is communicated to the nerve, so as to produce the corresponding effect upon the muscle, what change does the nerve experience, or in what way is it acted upon so as to admit of this transmission ?" -Elem. Syst. of Physiology, vol. i. p. 250.—Ed.

CLASS IV.

ple of sensa

tion and

motion.

Nervous

fabric, whether

solid chords or hollow

Original

meaning

of the term

nerve.

crates and

Galen ;

etherial

fluid;

Upon these points, two very different opinions have been II. Princi- entertained from an early period of the world, which, under different modifications, have descended to our own times: for by many physiologists, both ancient and modern, the nerves have been regarded as solid capillaments, or tense and elastic strings, operating by tremors or oscil'lations, like the chords of a musical instrument; and by cylinders. others, as minute and hollow cylinders conveying a peculiar fluid. The word NERVE, which among the ancients was applied to tense chords of every kind, and especially to bow-strings and musical strings, affords a clear proof 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 nerves were regarded as the instruments of sensation and supposed an 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 this animal spirit is of the substance of the soul, but its 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," themselves says Galen, "it is impossible for us to pronounce absolutely, and without proof, whether a certain power may not how it be transmitted from the brain through the nerves to the different members; or whether the material of the animal spirit may not itself reach the sentient and moving parts; or, in some way or other, so enter into the nerves as to induce in them a change, which is afterwards extended to the organs of motion +."

but ex

pressed

uncertain

maintained

a communication with the

rest of the body.

The question still in

66

In a state not much less unsettled remains the subject an unsettled at the present moment. Dr. Hartley, in the beginning of the seventeenth century, revived the hypothesis, that the

state.

* De Hippocratis et Platonis Decretis, Lib, vII. A. tom. i. p. 967. Ed. Basil. 1542.

+ld. Sect. C. p. 969.

II. Princi

motion.

Hartley's

nerves are bundles of solid capillaments conveying motion, CLASS IV sensation, and even perception, by a vibratory power, and ple of sensupported his opinion with great ingenuity and learning*; sation and but the opposite hypothesis, that they are minute tubes filled with the animal spirit of the Greek physiologists, hypothesis had acquired so extensive a hold ever since the discovery of vibratory of the circulation of the blood, which pre-supposes the not able to strings existence of tubular vessels too subtile to be traced by the subvert the hypothesis senses, that it never obtained more than a partial and of Sydentemporary assent; and hence, from the times of Sydenham ham and Boerhaave, and Boerhaave almost down to our own day, the last has that they been the popular doctrine.

are hollow cylinders

less conveying vi- an animal spirit.

Nervous

of their

hold yet no proof years being

some tubular.

Little

In effect, no fibres of the animal frame can be adapted to a communication of motion by a series of brations than those of the nerves, since none exhibit a smaller degree of elasticity; and though we have little fibres unreason to confide in their tubular structure, or to believe adapted to vibrations, that any kind of fluid is transmitted in this way, the close as inelastic: affinity which the nervous power is now known to with several of the gases that chemistry has of late unfolded to us, and the wonderful influence which of them possess over the moving fibres of the animal frame, seem to leave no question, that the nervous power itself is ever, of a a fluid, though not, perhaps, of their precise nature, yet nervous and peculiar resembling the most active of them in its subtilty, levity, fluid; and rapidity of movement. Nor is there, upon this sup- which, like position, any difficulty in conceiving its transmission by solid various fibres or capillaments of a particular kind, the neurilemma gases, does of Bichat, whilst we behold the etherial fluids, now re- in need of ferred to, transmitted in the same way by substances still more solid and unporous.

doubt, how.

not stand

hollow

vessels for its trans

But there is another question, closely connected with mission. the present subject, that has also greatly interested physiologists both in ancient and modern times, and is not yet settled in a manner altogether satisfactory.

and motion

It has appeared that the nerves are instruments both of Whether sensation and motion. Are these two effects produced by sensation the same nervous fibres, or by different? or by the same a common fluids, or by different? That there must be two distinct power, or

Observations on Man, his Frame, &c. his Duty, and his Expectations. 2 vols. 8vo. 1749.

† The editor's opinion of this hypothesis will appear in the sequel.

from

distinct

sources?

ple of sensa

tion and

motion.

The two

effects must

CLASS IV. kinds of fibres or of fluids is clear, because, as we shall II. Princi- have more particularly to observe when we come to treat of paralysis, the muscles of a limb are sometimes deprived of both sensation and motivity at the same period, sometimes of sensation alone while motivity continues, and sometimes of motivity alone while sensation continues. And hence Hippocrates and Galen, the last of whom has treated of the subject with great minuteness in many of his writings, while they speak of only one kind of animal spirit, speak of two kinds of nerves, those of sense and of motion; equally issuing from the brain, and mostly acdistinct sets companying each other, and forming parts of the same organs*.

proceed from distinct fibres or fluids. According to the Greeks, from

of fibres

operated upon by the same nervous fluid.

How far

supported by modern physiologists.

distinct pro

cerebellum.

This distinction is supported by the concurrent observations and experiments of physiologists, and especially by the curious investigations of many of those of our own day, among whom should be particularly noticed the names of Flourens, Rolando, Charles Bell, Magendie, and Shaw. M. Rolando attempted to show, by a long train of interesting but very painful experiments, carried on through Rolando's animals of almost every kind, that the cerebrum is the vinces of ce- ordinary source of sensation, and the cerebellum of motion : rebrum and 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 investigations were valuable as leading on to others more accurately conducted and folSuch sepa- lowed up by more correct conclusions. That these distinct rate powers portions of the brain are endowed with separate powers, as firmed, but observed by Rolando, has been sufficiently ascertained by conversely other pathologists; and especially by M. Flourens‡, who

since con

ascribed.

does not seem at the time to have been acquainted with

The curious fact of most of the nerves of motion (though not all) originating from the spinal marrow, has been already stated.-ED.

Saggio sopra la vera Struttura del Cervello, &c. e sopra le Fonzioni della Sistema Nervosa. Sassari, 1809.

Archives Générales de Médecine, 1. 11. Also, Recherches Exp. sur le Syst. Nerveux. Paris, 1824.