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 blood vessels 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 +. 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:-1. Caloric, 2. The natural cause of sleep, whatever that may be; 3. The pressure of the blood vessels 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.

Blumenbach's Physiology, p. 322.

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 defects must plead my excuse with him, 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 Philosophy 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 it.

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 Carmichael's essay, but are confident that this has not materially diminished the force of his arguments. The MS. was with his permission submitted to Mr Macnish, who has kindly favoured us with the following Notes.-ED.

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 inference, 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 partcular 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 inferred 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

creased activity without any additional impulse being given to the circulation, his doctrine may acquire plausibility; but such a phenomenon is at variance with every thing we know both in the animal and in the vegetable kingdoms. As well may we suppose that plants will grow better without than with water, and that the urine will be as copiously secreted from kidneys that are torpid as from these organs in a case of diabetes.

Mr Carmichael looks upon sleep as being occasioned purely by mechanical compression, or something so closely resembling it, that I must regard the two circumstances as identical, so far as the present argument is concerned. I am perfectly aware that such compression will occasion sleep; but this I hold to be the sleep of disease, and not of health. Effusion of blood, of serum, or of purulent matter upon the brain, a torpid state of the blood vessels of this organ,-or the beating in of a portion of the skull cap,-will throw the person into stupor or sleep, by paralyzing, with their pressure, the cerebral texture. Eating or drinking to excess, by inducing congestion approaching to apoplexy, will do the same; so will foul air or narcotics; but the pure sleep of health has no affinity to these adventitious conditions. So far from there being any increase of blood in the brain during healthy sleep, it is proved that the circulating fluid in that organ is actually lessened, as I have had occasion to shew in a case related by Blumenbach, of a person who had been trepanned, and whose brain was observed to sink when he was asleep, and swell out when he was awake. The abolition of the cerebral functions is, to my mind, sufficient evidence of diminished action going on in the brain. I cannot conceive increased assimilation without increased circulation, nor increased circulation without augmented functional energy. To admit the first without allowing the second, is to presume the existence of an effect without any corresponding cause.

Supposing, however, that healthy sleep is always occasioned by the mechanical compression, or similar cause, spoken of by Mr C., how are we to account for people being so easily awakened? Sleep should be like apoplexy: it should be difficult or impossible to arouse a man till the pressure is removed.—Yet we constantly see people awakened from the most perfect sleep by very trifling causes. What, in such a case, becomes of this pressure? Is the load at once lifted off the person's brain? What becomes of the assimilative particles which are squeezing his senses out of him, and submerging him under the billows of sleep? It is as difficult to conceive that such mechanical pressure could be instantaneously removed, as that any deposit of new matter which ever takes place could have the effect of a foreign body acting upon the brain.

Dreaming is inconsistent with this gentleman's theory. Assi

VOL. IX.-NO. XLII.

M

milation is a general process; but, according to him, one part of the brain may be fattening while another is starving. It seems as rational to infer that the assimilative operation is at work in one leg, and at a stand in the other.

Mr C. endeavours to strengthen his case by the instances of General Elliot and Dr Reid, but these must be looked upon as idiosyncrasies. Generally speaking, the more sleep a man takes the less food can he do with; and a hard-working, active, lightsleeping man will require more food than a great dozer. Dr Reid seems to have acted on the principle of the boa constrictor. By over-eating himself, he induced a plethoric state of the brain, the mechanical compression upon which threw him into a torpor similar to that which falls over the snaky monster of the wilderness, when gorged with food. His two days slumber was not the repose of health-not the sound sleep induced by the spontaneous and periodical exhaustion of nervous energy.

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The theory of the nervous energy, or sensorial power, to which Mr C objects as not sufficiently definite and expressive, appears to me singularly adapted to explain the different phenomena of sleep. I conceive this power to exist in a ratio corresponding to the activity of the circulation. In fever, phrenitis, or mental excitement of any kind, it is excessive, and the person remains awake. My view of the case is, that, to induce sleep, we have only to quell the action of the sensorial power in other words, to relax the force or irritability of the vascular system : According to Mr C, it is necessary that the brain should be compressed by a physical agent operating upon it. This agent is the deposit of new particles, the result of increased activity in the assimilating vessels of the brain. Now, as such an increased action in these vessels cannot take place without augmented energy in the local circulation, it follows that the very circumstances which, according to me, occasion wakefulness, according to him give rise to sleep. A ban

Mr C. has, with no small ingenuity, endeavoured to shew that the facts stated by me, especially those with regard to the effect of food in inducing sleep, bear out his hypothesis; but on this point I think it will not be difficult to show that he labour's under a mistake. I impute the soporific propensity of great eaters to the large quantity of food in the stomach draining the nervous energy of the brain, or inducing an apoplectic state: it may often act in both ways. I do not employ the sensorial power as a mere imaginary agent for the explanation of phenomena which cannot be easily accounted for without it; for I hold its existence, and the way in which circumstances are modified by it, perfectly susceptible of demonstration. We can show that one organ may have an excess, and another a deficiency, with as much ease as that one body may be positively,