world. Both of these instances differ from common dreams in this peculiarity. In these instances, the mind actually issues its mandates whether obeyed or disobeyed. In common dreams, a current of thought passes through the mind like a train of realities, but the mandates of the mind and the motions of the limbs are equally imaginary.

In his chapter upon Trance, Mr Macnish details a similar case, but in which the symptoms were much more aggravated and protracted. Both cases differ altogether from the six cases of protracted sleep detailed in Mr Macnish's eleventh chapter. There is no reason for supposing that these persons were not under the influence of intense slumber, during the greater part of the interval engaged in the paroxysm. Nor is there any reason for rejecting as its cause the continued deposition of new nervous substance to an unusual extent. "The right hand and arm of Mary Lyall appeared completely dead and bereft of feeling; and even when pricked with a pin, so as to draw blood, never shrunk in the least degree. At the same time she instantly drew back her left arm whenever it was touched by the point of the pin. After an interval of seven days she began to move her left hand, and, by pointing to her mouth, signified a wish for food. She took readily what was given to her; still she discovered no symptoms of hearing, and made no other kind of bodily movement than of her left hand.*"

Thus, according to my theory, every kind of nerve connected with the organs of digestion, and the nerves of volition of the left arm, were occasionally released from the oppression of the assimilative particles, while the other nerves of the body continued under their influence, and particularly the nerves of sensation of the right arm. As to those last mentioned nerves, I would not be understood as maintaining that this cause alone occasioned the numbness of the limb in question.

The case of Elizabeth Perkins differs from the others in its fatal termination. After a profound slumber of eleven or twelve days, she "awoke of her own accord, to the great joy of her relatives, and wonder of the neighbourhood. On recovering, she went about her usual business; but this was only for a short period, for in a week after she relapsed again into a sleep which lasted some days. She continued, with occasional intervals of wakefulness, in a dozing state for several months, when she expired."+ Is it not natural to suppose that, in this case, the secerning vessels of the head were in such a diseased state as to effuse upon the brain much more than the quantity of nervous matter usual in the healthy state? If the torpor had arisen from the pressure of overloaded bloodvessels, or an effusion either of

Philosophy of Sleep, p. 209.

+ Id. p. 210.

water or blood, it would have been called apoplexy, and not sleep.

Mr Macnish observes, that the cause of drowsiness, or the "constitutional disposition to doze upon every occasion, seems to be a certain want of activity in the brain, the result of which is, that the individual is singularly void of fire, energy, and passion. He is of a phlegmatic temperament, generally a great eater, and very destitute of imagination. Such are the general characteristics of those who are predisposed to drowsiness. The cases where such a state coexists with intellectual energy, are few in number."* Every word of this description reminds you of the assimilating process, and its effects; and affords a marked difference to another cause, which he notices, of a similar result, viz. that drowsiness sometimes proceeds from a fulness of blood in the head, or a disordered state of the digestive organs." It sometimes, however, arises from both these causes, as in that instance which Mr Macnish, but without reference to either of them, adduces from Boerhaave, of an eccentric physician who took it into his head that sleep was the natural state of man, and accordingly slept eighteen hours out of the twenty-four, till he died of apoplexy, a disease which, according to Mr Macnish, is always apt to be produced by excessive sleep.‡

Mr Macnish adverts to many facts, tending to support my theory, and particularly those respecting the use of food, the very material which supplies and puts in motion the assimilating process. "A heavy meal" (he says), " especially if the stomach be at the same time weak, is apt to induce sleep."§ "Those who eat heartily, and have strong digestive powers, usually sleep much. The great portion of sleep required by infants, is owing, in part, to the prodigious activity of their digestive powers. The majority of animals sleep after eating; and man has a strong tendency to do the same thing, especially when oppressed with heat, In the summer season, a strong inclination is often felt to sleep after dinner, when the weather is very warm. A heavy meal, which produces no uneasy feeling while the person is awake, will often do so if he fall asleep." || Besides the effects of the assimilating process, may we not, in the two latter instances, look to the effects of heat and of a heavy meal as increasing the velocity or the quantum of the blood, and thus creating a pressure more than natural on the substance of the brain, and partaking more of the character of apoplexy than of sleep?

His contrast of Dr Reid with General Ellict has also the same tendency. The former "could take as much food, and immediately afterwards as much sleep, as were sufficient for two days." T The latter "6 never slept more than four hours out of

+ Id. p. 206.

+ Id. p. 206.

Id. pp. 35, 36.

¶ Id. p. 32.

Philosophy of Sleep, p. 205. § Id. p. 16.

the twenty-four. In all other respects he was strikingly absti nent; his food consisting wholly of bread, water, and vegetables."

The very purposes which he ascribes to SLEEP, correspond in every particular with my theory. "Its main object is to restore the strength expended during wakefulness, to recruit the body by promoting nutrition and giving rest to the muscles, and to renovate the mind by the repose which it affords the brain. Action is necessarily followed by exhaustion; SLEEP, by checking the one, restrains the other, and keeps the animal machine in due vigour." The strength expended during wakefulness can only be restored by replacing, with new particles, those carried off by the wear and tear of exertion. Nutrition can only recruit the body by replacing the substance it has lost-the mind can only be renovated in a metaphorical sense; it is the brain which is really renovated, and that by means of the assimilating process. Action is necessarily followed by exhaustion; but the very operation which causes sleep remedies the exhaustion, while it restrains the action, and, by repeatedly renewing their composition, keeps every nerve, every muscle, every bone, every organ of the animal machine, in due and healthy vigour.

He throws considerable light on the subject when he observes, that "where there is no excitement, sleep is sure to follow. We are all kept awake by some mental or bodily stimulus, and when that is removed our wakefulness is at an end."+ "The finished gratification of all ardent desires has the effect of inducing slumber. Hence, after any keen excitement, the mind becomes exhausted, and speedily relapses into this state." "Remove those stimuli which keep it employed, and sleep ensues at any time." Not that these stimuli can prevent or interrupt the usual progress of the assimilative process. They merely urge into the vortex of their influence each particle as it is deposited, and do not permit the accumulating matter to paralyse the energy and activity of the thinking brain. But when these stimuli are withdrawn, when desire or reflection ceases, then the new and scarcely-assimilated substance acts with a dead weight on the living nervous texture, every moment adds to its mass and power, and the seat of thought and feeling feels and thinks no longer-it is paralysed-IT SLEEPS.

All that I ascribe to the presence of the ASSIMILATING PROCESS, Mr Macnish attributes to the absence of the SENSORIAL POWER,-all that I attribute to the diminution of the former, he ascribes to the increase of the latter. In this respect we are like Lavoisier and Stahl, contending for the presence or absence of oxygen and phlogiston in their respective theories of combustion. Thus, in his chapter on Sleeplessness, he says, "Sleep takes

Philosophy of Sleep, p. 33. § Id. p. 15.

+ Id. p. 39.

+ Id. p. 13.

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 power, 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 can 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 particles 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.

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.

66

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, notwithstanding which he enjoyed good health, and reached the seventy-third year. He adds, "I strongly sus pect there must be some mistake in this case, for it is not con ceivable 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, 66 especially if the stomach is at the same time weak, is apt to induce sleep. In ordinary circumstances, the nervous energy or sensorial 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