It is, then, between these parts, that we must place the cerebral organs of the senses, and it is with this part of the cephalo-spinal axis, that the nerves of the senses are actually found to communicate. Mr. Lawrence' saw a child with no more encephalon than a bulb, which was a continuation of the medulla spinalis, for about an inch above the foramen magnum, and with which all the nerves from the fifth to the ninth pair were connected. The child's breathing and temperature were natural; it discharged urine and fæces; took food, and at first moved very briskly. It lived four days.

If we divide the posterior roots of the spinal nerves and the fifth pair, general sensibility is lost; but if we divide the nerves of the senses, we destroy only their functions. We can thus understand why, after decapitation, sensibility may remain for a time in the head. It is instantly destroyed in the trunk, owing to the removal of all communication with the encephalon; but the fifth pair is entire, as well as the nerves of the organs of the senses. Death must of course follow almost instantaneously from loss of blood; but there is doubtless an appreciable interval during which the head may continue to feel; or, in other words, during which the external senses may act.2 M. Julia Fontanelle3 has indeed concluded, from a review of all the observations made on this matter, that, contrary to the common opinion, death by the guillotine is one of the most painful; that the pains of decollation are horrible, and endure even until there is an entire extinction of animal heat! It need scarcely be said, that all these inferences are imaginative, and perhaps equally fabulous with the oft-told story of Charlotte Corday scowling at the executioner after her head was removed from her body by the guillotine; and this conclusion is strongly confirmed by the results of experiments on a robber-who was beheaded with the sword-by Drs. Bischoff, Heerman, and Jolly, who inferred that consciousness must have ceased instantaneously. But if such be the case with man, it most assuredly is not so with the inferior animals. Ample evidence will be afforded hereafter to show, that both sensation and volition may persist in the rattlesnake and alligator long after the head has been removed from the body. Singular facts in regard to the latter animal have been recorded by Dr. Leconte,' and more recently, by Dr. Dowler, of New Orleans.

It has been remarked, that the cerebral hemispheres may be sliced away without abolishing the senses. The experiments of Rolando and Flourens, which have been repeated by M. Magendie, show, however, that the sight is an exception;-that it is lost by their removal. If the right hemisphere be sliced away, the sight of the left eye is lost; and conversely; one of the facts that prove the decussation of the optic 'Medico Chirurg. Transact., v. 166.

2 Bérard, Rapports du Physique et du Moral, p. 93, Paris, 1823.

3 Phœbus, Art. Enthauptung, in Encyclopäd. Wörterb. der Medicin. Wissenchaft. xi. 204, Berlin, 1835.

A condensed account of Dr. Bischoff's Remarks, from Müller's Archiv., by S. L. L. Bigger, is in the Dublin Journal of Medical Science, Sept., 1839, p. 1.

5 New York Journal of Medicine, for Nov., 1845, p. 335, and Sir Charles Lyell, Travels

in North America, Amer. edit., i. 237. New York, 1849.

6 Contributions to Physiology, New Orleans, 1849, from New Orleans Journal of Medi

Fig. 34.

thal

B

nerves. The experiments of these gentlemen show, that vision, more than the other senses, requires a connexion with the organ of the intellectual faculties-the cerebral hemispheres; and this, as M. Magendie has ingeniously remarked, because vision rarely consists in a single impression made by light, but is connected with an intellectual process, by which we judge of the distance, size, shape, &c., of bodies. It has been well suggested and maintained by Dr. Carpenter,' that whilst the cerebral ganglia are the organs of the higher intellectual and moral acts; there is a series of ganglia, connected with the reception of impressions from without, which are seated near the base of the brain, and are hence termed by him sensory ganglia. As we descend in the animal scale, these ganglia become more marked; whilst the cerebral hemispheres become less and less; until ultimately the animal appears to have its encephalic organs limited almost wholly to those that are concerned in the reception of impressions from without, and the originating of motor impulsions from within. These ganglia are seated at the base of the brain: from the origin of the auditory nerves to those of the olfactory.

Brain of Squirrel, laid open.

The hemispheres, B, drawn to either side to show the subjacent

parts. c. The optic lobes. D. Cerebellum. thal. Thalamus opticus. c s. Corpus striatum.

Fig. 37.
Cod.

Dr. Carpenter is disposed to regard the optic thalami as ganglia for the reception of tactile impressions, and the corpora striata as ganglia con

'Principles of Human Physiology, 4th Amer. edit., p. 370, Philad., 1850.

nected with motion. He esteems them to be, moreover, the centre of consensual or instinctive movements, or of automatic movements involving sensation;-a topic which will receive attention elsewhere.

Having arrived at a knowledge that in man and the upper class of animals, perception is effected in a part of the encephalon, our acquaintance with this mysterious process ends. We know not, and we probably never shall know, the action of the brain in accomplishing it. It is certainly not allied to any physical phenomenon; and if we are ever justified in referring functions to the class of organic and vital, it may be those, that belong to the elevated phenomena, which have to be considered under the head of animal functions. We know them only by their results: yet we are little better acquainted with many topics of physical inquiry;-with the nature of the electric fluid for example.

The organs, then, that form the media of communication between the parts impressed and the brain, are the nerves and spinal marrow. M. Broussais,' indeed, affirmed, that every stimulation capable of causing perception in the brain, runs through the whole of the nervous system of relation; and is repeated in the mucous membranes, whence it is again returned to the centre of perception, which judges of it according to the view of the viscus to which the mucous membrane belongs; and adapts its action as it perceives pleasure or pain,

We are totally unacquainted with the material character of the fluid, which passes with the rapidity of lightning along nervous cords; and it is as impossible to describe its mode of transmission, as it is to depict that of the electric fluid along a conducting wire. As in the last case, we are aware of such transmission only by the result. Still, hypotheses, as on every obscure matter of inquiry, have not been wanting. Of these, three are chiefly deserving of notice. The first, of greatest antiquity, is, that the brain secretes a subtile fluid, which circulates through the nerves, called animal spirits, and which is the medium of communication between the different parts of the nervous system; the second regards the nerves as cords, and the transmission as effected by means of the vibrations or oscillations of these cords; whilst the third ascribes it to the operation of electricity.

1. The hypothesis of animal spirits has prevailed most extensively. It was the doctrine of Hippocrates, Galen, the Arabians, and of most of the physicians of the last centuries. Des Cartes3 adopted it energetically; and was the cause of its more extensive diffusion. The great grounds assigned for the belief were;-first, that as the brain receives so much more blood than is necessary for its own nutrition, it must be an organ of secretion; secondly, that the nerves seem to be a continuation of the tubular matter of the brain; and it has already been remarked, that Malpighi considered the cortical neurine to be follicular, and the medullary to consist of secretory tubes. It was not unnatural, therefore, to regard the nerves as vessels for the transmission of these spirits. As, however, the animal spirits had never been met with in a

1 Traité de Physiologie, &c., Paris, 1822; or translation by Drs. Bell and La Roche, 3d Amer. edit., p. 63, Philad., 1832.

2 Fletcher's Rudiments of Physiology, P. ii. b. p. 68, Edinb., 1836.

3 Tractatus de Homine, p. 17, Lugd. Bat., 1664.

tangible shape, ingenuity was largely invoked in surmises regarding their nature; and, generally, opinions settled down into the belief that they were of an ethereal character. For the various views that have been held upon the subject, the reader is referred to Haller,' who was himself an ardent believer in their existence, and has wasted much time and space in an unprofitable inquiry into their nature. The truth is, that we have not sufficient evidence, direct or indirect, of the existence of any nervous fluid of the kind described. Allusion has been already made to the views, in regard to the tubular structure of the white neurine, admitted by most observers: Berres, affirms that the forms, which the nervous substance assumes under the magnifying glass, can only be compared to those of canals and vesicles; but whether they be hollow he does not attempt to decide. M. Raspail3 has concluded, that the opinion of their being hollow, and containing a fluid, is unsupported by facts; for although he admits, that M. Bogros succeeded in injecting the nerves with mercury, he thinks that the passage of the metal along them was owing to its having forced its way by gravity. Modern histologists accord with great unanimity as to the tubular structure of the medullary neurine; but we have no reason for considering the brain the organ of any ponderable secretion. Yet the term "animal spirits," although their existence is not now believed, is retained in popular language. We speak of a man who has a great flow of animal spirits, but without regarding the hypothesis whence the expression originated.

The term nervous fluid is still used by physiologists. By this, however, they simply mean the medium of communication or of conveyance, by which the nervous influence is carried with the rapidity of lightning from one part of the system to another; but without committing themselves as to its character;-so that, after all, the idea of animal spirits is in part retained, although the term, as applied to the nervous fluid is generally exploded. Dr. Good directly admits them under the more modern title; Mr. J. W. Earles firmly believes in the existence of a circulation in the nervous system,-and it is not easy to conceive, that the brain does not possess the function of elaborating some fluid,-galvanoid or other,-which is the great agent in the nervous function.

8

2. The hypothesis of vibrations is ancient, but has been by no means as generally admitted as the last. Among the moderns, it has received the support of Condillac, Hartley," Blumenbach, and others; some supposing, that the nervous matter itself is thrown into vibrations; others, that an invisible and subtile ether is diffused through it, which acts the sole or chief part. As the latter is conceived, by many, to be the mode in which electricity is transmitted along conducting wires,

1 Elementa Physiologiæ, x. 8.

'Oesterreich. Med. Jahrbuch., B. ix., cited in Brit. and Foreign Med. Review, January, 1838, p. 219. 3 Chimie Organique, p. 218. Paris, 1833.

4 Study of Medicine, with Notes by S. Cooper, Doane's Amer. edit., vol. ii., in Proem to Class iv. Neurotica, New York, 1835.

New Exposition of the Functions of the Nerves, by James William Earle, Part. I. London, 1833. 6 Euvres, Paris, 1822.

7 Observations on Man, &c., chap. i. sect. 1. London, 1791. • Institutiones Physiologicae, § 226.

it is not liable to the same objections as the former. Simple inspection, however, of a nerve at once exhibits, that it is incapable of being thrown into vibrations. It is soft; never tense; always pressed upon in its course; and, as it consists of filaments destined for very different functions, sensation, voluntary and involuntary motion, &c.—we cannot conceive how one of these filaments can be thrown into vibration without the effect being extended laterally to others; and great confusion being thus induced. The view of Dr. James Stark' in regard to the structure of the tubes of the nerves, has led him to adopt a modification of the theory of vibrations. Believing, that the matter which fills the tubes is of an oily nature,-and as oily substances are known to be non-conductors of electricity; and farther, as the nerves have been shown by the experiments of Bischoff to be amongst the worst possible conductors of electricity,-he contends, that the nervous energy can be neither electricity nor galvanism, nor any property related to them; and he conceives, that the phenomena are best explained on the hypothesis of undulations or vibrations propagated along the course of the tubes by the oily globules they contain.

3. The last hypothesis is of later date,-subsequent to the discoveries in animal electricity. The rapidity with which sensation and volition are communicated along the nerves, could not fail to suggest a resemblance to the mode in which the electric and galvanic fluids fly along conducting wires. Yet the great support of the opinion was in the experiments of Dr. Wilson Philip' and others, from which it appeared, that if the nerve proceeding to a part be destroyed, and the secretion, which ordinarily takes place in the part be thus arrested,— the secretion may be restored by causing the galvanic fluid to pass from one divided extremity of the nerve to the other. The experiments, connected with secretion, will be noticed more at length hereafter. It will likewise be shown, that in the effect of galvanism upon the muscles, there is a like analogy ;-that the muscles may be made to contract for a length of time after the death of the animal, and even when a limb is removed from the body, on the application of the galvanic stimulus; whilst comparative anatomy exhibits to us great development of nervous structure in electrical animals, which astonish us by the intensity of the electric shocks they are capable of communicating.

3

Physiologists of the present day generally, we think, accord with the electrical hypothesis. The late Dr. Young, so celebrated for his knowledge in numerous departments of science, adopted it prior to the interesting experiments of Dr. Philip; and Mr. Abernethy, whilst ▾ he is strongly opposing the doctrines of materialism, goes so far as to consider some subtile fluid not merely as the agent of nervous transmission, but as forming the essence of life itself. By putting a ligature, however, around a nervous trunk, its functions, as a conductor of nervous influence, are paralyzed, whilst it is still capable

2 Philosoph. Trans. for 1815, and Lond. Med. Gazette for March 18, and March 25, 1837. 3 Med. Literature, p. 93. Lond., 1813.

4 Physiological Lectures, exhibiting a view of Mr. Hunter's Physiology, &c. Lond., 1817.