place as soon as the sensorial power that keeps the brain awake is expended, which, under common circumstances, occurs at our ordinary hour of going to rest, or even sooner, if any soporific cause, sufficiently strong, should chance to operate.

“But the above power may be increased by various means, as in cases of physical suffering or excited imagination, and consequently is not expended at the usual time. In this case the person remains awake, and continues so till the period of its expenditure, which may not happen for several hours after he lies down, or even not at all during the whole night. Now," he continues, " whatever increases the sensorial poroer, whether it be balls, concerts, grief, joy, or bodily pain, is prejudicial to repose. By them the mind is exalted to a pitch of unnatural action, from which it is necessary to descend before it ean roll into the calm channel of sleep.**

Does not the excitement of music and dancing, pleasure and pain, joy and grief, sufficiently account for the continued'activity of the cerebral organization, which prevents the accession of sleep (let the cause of sleep be what it may) without resorting to the sensorial power for an explanation ? " What we want to account for is the accession of sleep, not the continuance of wakefulness. Will the subtraction of the sensorial power account for any thing that is not as readily accounted for by the gradual subsidence of the activity of the cerebral organization, after the excitement has been weakened or extinguished ? In either case, the brain' may be ready to submit to the dominion of sleep'; but it has not yet submitted. Another event is necessary to succeed either the increased absorption of the particles of the brain, or the co-relative subtraction of the sensorial power, thus occasioned by the active exertion of the organ ; and that event is, I maintain, the accession of new particles to supply the place of the old, these par. ticles deriving no energy from the exhausted 'mass on which they are deposited, and creating a paralysis of that mass, like any other foreign body.

Again, says Mr Macnish, “ Certain stimulating agents, such as tea or coffee, taken shortly before going to bed, have often the effect of preventing sleep. I would impute this to their irritative properties, which, by supplying the brain with fresh sensorial power, enable it to carry on uninterruptedly all its functions longer than it would otherwise do, and, consequently, prevent it from relapsing into slumber at the usual period.”+

Here also an appeal to the sensorial power seems unnecessary. The irritative properties of these stimulating agents are alone sufficient to account for the phenomena. It is obvious that they excite the nervous system ; and it is probable they thereby continue its power to engage in its own state of activity the new Philosophy of Sleep, p. 193.

+ Id. p. 195,

a

particles which are deposited, - which, if it were in an inactive state, would, in accumulating, press upon the cerebral organization, and thus, as in so many former instances, involve the frame in sleep.

It may not be out of place here to observe, that these stimulating agents, tea and coffee, seem to have an opposite effect to that produced by other food, and even to counteract the natural tendency of less enlivening nutriment to promote the assimilating process, and the encouragement of Somnolency. It is therefore probable, that civilized society has found them of advantage after the substantial meal of the day, which might otherwise “ steep the senses in forgetfulness," while we ought yet to be awake; and no doubt the breakfast of Elizabeth's golden reign, beef-steaks and ale, has, for the same prudential reason, given way to the more light and elegant dejeuné of later times.

Mr Macnish observes, that Gooch gives an instance of a man who slept only for fifteen minutes out of the twenty-four hours; and even this was only a kind of dozing, and not a perfect sleep;, not withstanding which he enjoyed good health, and reached the seventy-third year. He adds, “ I strongly suspect there must be some mistake in this case, for it is not conceivable that human nature could subsist upon such a limited portion of repose. Instances have been related of persons who never slept; but these must be regarded as purely fabulous *."

I am ready to agree with Mr Macnish in his suspicion as to Gooch's case, and his decision as to the others. If, however, these cases were beyond a doubt authenticated, there would be no other mode of accounting for these extraordinary facts, than by boldly maintaining that such a renewal of the brain and nervous system as took place in the waking moments of these individuals, was sufficient for them, though not for other men ; and that they did not sleep, because the new mass of nervous particles was never so great as to resist a co-operation with the old, or act like an extraneous body by creating a paralysis. To say that the sensorial power was never exhausted in these individuals, would be merely to say that the power of remaining awake was never exhausted,-a discovery which would not add much to our information.

One instance more of this exuberant employment of the sensorial power. “ A heavy meal,” says Mr Macnish, “ especially if the stomach is at the same time weak, is apt to induce sleep. In ordinary circumstances, the nervous energy or sorial power of this viscus is sufficient to carry on its functions; but when an excess of food is thrown upon it, it is then un

Philosophy of Sleep, p. 34.

able to furnish from its own resources the powers requisite for digestion. In such case it draws upon the whole body--upon the chest, the limbs, &c., from whence it is supplied with the sensorial power of which it is deficient, and is thus enabled to perform that which by its own unassisted means it never could have accomplished. But mark the consequences of such accommodation! Those parts, by communicating vigour to the stomach, become themselves debilitated in a corresponding ratio, and get into a state analogous to that from which they have extricated this viscus. The extremities become cold, the respiration heavy and stertorous, and the brain torpid *"

There is nothing in these circumstances calling for the intervention of such a machine as the sensorial power. If the brain be torpid, the increased flow of blood and the pressure of the bloodvessels sufficiently explain it. But if the meal be not so heavy as to induce these apoplectic symptoms, it may at least produce sleep by promoting the assimilating process t. If the respiration be heavy and stertorous, the apoplectic state of the brain will at once account for it or if there be no apoplectic tendency, the very pressure of the overloaded stomach against the diaphragm and lungs will disturb and oppress the breathing. And, in fine, if the extremities become cold, it is not by parting with their sensorial power, but their caloric-an agent with which we are much better acquainted; and which, according to Richerand, seems to increase, and in a manner to concentrate itself in the epigastric region, as long as the stomach is engaged in digestion #," a fact confirmed by Blumenbach, who states that the high temperature maintained in the stomach by the quantity of blood in the neighbouring viscera and bloodvessels, is of such importance that at one time the word coction was synonymous with digestion ||

From these observations we may perceive that the term “ sensorial power," does not signify an efficient and definite cause of the phenomena it is brought to explain ; but appears to be rather a general term including many causes. Thus in the instance before us, this power (and occasionally its absence) indicates five different things, and never once itself:-). Caloric, 2. The natural cause of sleep, whatever that may be ; 3. The pressure of the bloodvessels on the brain ; 4. The effects of such a state of the brain on the lungs; and, 5. The pressure of an over-distended stomach on the same organ.

There is no Philosophy of Sleep, p. 16. * See my Essay on Sleep in Tilloch's Phil. Mag. liv. 258, or Transactions of the King and Queen's College of Physicians, ii. 60. t. 62.

# Richerand's Physiology, p. 100.
Il Blumenbach's Physiology, p. 322.

66

+
+

thing so common as deceptions practised on us by words. We are led every day to mistake them for knowledge. Spurzheim and Combe were not so to be deluded. Can we read their motto on a seal, without feeling its force as of a talisman, “ Res, NON VERBA, QUÆso.” It may be a defect, but the constitution of my mind is such, that I have no pleasure in a theory that cannot, as it were, be felt and handled.

Even the sensible, pleasing, tranquil, unpretending words of Mr Macnish cannot persuade me--and my constitutional de fects must plead my excuse with bim, if I continue to prefer my conjecture to his. For his theory, like my own, is not more than a conjecture. But I have not advanced a single observation intended to depreciate his most valuable essay. On the contrary, my anxious desire would be to impress on others my sense of the obligation I owe him for much amusement, and much information, abounding with candour, good nature, and originality. Not to disparage his views, but merely to support my own, has been my object throughout this disquisition: and I owe him still another obligation for furnishing me not only with the opportunity, but the means. Indeed I have not been under the necessity of seeking elsewhere than in his own volume, for the proofs of the reasonableness, if not the validity, of my hypothesis and an acute friend of mine, on reading “ The Phitosophy of Sleep," observed that he supposed it to have been written with a view to recommend my theory, until he unexpectedly lighted on the passage in which it is impugned.

But perhaps the greatest obligation I owe Mr Macnish is the indispensable task he imposed upon me to reconsider my hypothesis and all its corollaries, thus affording me the opportunity of weeding out (if this were a possible achievement) every thing superfluous, inaccurate, and erroneous, that encumbered

Still I must repeat, that, with all its apparent consistency, I am aware that it is but a conjecture, and can never be any thing more,--yet, I trust, a conjecture that future physiologists will not be disposed to pass by as unworthy of notice, or unsupported by a due harmony with nature, and a requisite array of facts and arguments *.

2. Notes on Mr Carmichael's Essay, by Mr Macnish. On perusing Mr Carmichael's Life of Spurzheim, I had certainly the impression that this gentleman meant to represent sleep as the sole period during which assimilation takes place

We have been under the necessity of considerably abridging Mr Car. michael's essay, but are confident that ihis has not materially diminished the force of his arguments. The MS. was with his permission submitted 10 Mr Macnish, who has kindly favoured us with the following Notes.-Ed.

а

in the brain ; nor, on again consulting this work, am I certain that such is not the interpretation which may be legitimately put upon his words. However, as he disclaims such an interence, I shall pass from it, and examine the ground which he has taken up in his present interesting and very ably written essay.

Though I dissent from Mr Carmichael's proposition, “ that the process of assimilation in the brain is the actual cause of sleep," yet I have nowhere in my work made any allusion to this particular doctrine. My remarks refer solely to what I, at the time, conceived to be his meaning, viz. that assimilation occurs in the brain only during sleep. This I objected to on the strong ground of its being at variance with analogy. The question of the assimilative process occasioning sleep is not touched upon at all ; nor from any thing that has been said could it be interred that I either admitted or disallowed the truth of this hypothesis. I am glad, nevertheless, that Mr Carmichael has resumed the subject, as it has turned my attention to a point which did not formerly suggest itself, and given me an opportunity of stating several facts which I think are directly opposed to the opinion he has formed with regard to the proximate cause of sleep,

I cannot conceive how a natural and healthy deposition of new particles should occasion a cessation in the functions of any organ. Before such a deposition can take place, there must be an augmented circulation of blood in the part; and it is generally understood that the greater the quantity of blood sent to an organ, the greater is the energy of its manifestations. During sleep, the blood is propelled in greater abundance into the liver and stomach than in the waking state; the consequence of which is, that these viscera act more vigorously, and that digestion is carried on with increased activity. Why should the brain be an exception to this general law? Why should its functions be suspended, when the very principle which invigorates other parts must be more actively at work within it? When a man is engaged in keen thought; when his passions are violently excited; when he labours under the influence of joy, or love, or revenge, is the blood less vehemently sent to the sensorium, than when his mind is in an unexcited state of tranquillity ? When the brain is roused to its utmost energy, as in madness or delirium, is there less force in its circulation than when it is in perfect repose ? Common observation forces us to answer these questions in the negative. There is more vehement action in the circulating mass, and in proportion to this vehemence is the power of the cerebral manifestations. Mr Carmichael's theory, however, leads us to conclude that the brain is least active when the circulation is most urgently at work within its substance. If he can show, indeed, that assimilation may proceed with in