THE subject of SLEEP, like many other subjects in medicine, cannot be reduced to the principles of ma­thematical certainty; but, that it may be illustrated by a complete induction of the effects of all the exciting powers producing sleep, I imagine, will not be denied.

"SLEEP, without dreaming," says Mr. Locke, ‘is rest from all study^*’ of the mind and operation of the animal functions of the body. In "sleep", when "quite complete," says Dr. Cullen, ‘the motion and mobility of the nervous power, with respect to the whole of what are called the animal functions, en­tirely cease; or, as I would express it, are in a state of collapse, and are very different from the state of waking, which, in healthy persons, I would call a state of general and entire excitement^†.’ That there is a certain degree of excitement, necessarily ex­isting in the animal system, to constitute perfect and uninterrupted health, is agreed on by all. There must also be, I conceive, a certain point, or degree, of ex­citement, different from the foregoing, favouring pro­found sleep, which is produced by certain powers ope­rating on the living property inherent in every animal. This property has received different names, from diffe­rent authors. It is called by Baron Haller the vis in­sita; by Dr. Cullen, the nervous power; by Mr. John Hunter, [Page 8] stimulability; and by Dr. Brown, the excitabi­lity. The exciting powers acting on the excitability, producing excitement favourable to health, and in­viting sleep, if carried beyond their proper bounda­ries, or withheld, occasion morbid sleep, disease, and even death itself. The sleep-inviting point, or that de­gree of excitement necessary to constitute profound sleep, appears to exist in a kind of indirect debility of the system, or partially-exhausted excitability to the powers producing it, which it is very difficult to ex­plain. ‘Sleep, then, is the effect of the actions of the day, at first always giving more and more ex­citement, but less and less in proportion to the con­tinuance of their operation, but in such a sort as al­ways to add some excitement, till at last the matter comes to a point, where the degree of excitement necessary to constitute the waking state no longer ex­ists.’ Every day's experience teaches us the effects of the exciting powers, in producing sleep: It teaches us, that, if they are applied in excess, or, though mo­derate, are long continued, they run the excitement on to actual indirect debility, and occasion morbid sleep. And, that sleep may be brought on sooner or later, by the excessive or deficient application of the causes pro­ducing it, is certain. By all unusual exertions, those unaccustomed to fatigue, &c. will have their sleep hur­ried or produced sooner than in common, and it is ge­nerally of the morbid kind.

A MAN of science and of genius, in the pursuit of mental acquirement, stimulated by the spirit of emu­lation, or any other exciting emotion, will have his excitability considerably wasted, and his excitement increased beyond the point constituting profound sleep, but favouring the waking state; and this state may be kept up, or rendered more tolerable, a considerable time, by the assistance of the diffusible, together with the durable, stimuli, given at proper intervals, and changed frequently in kind, and in quantity, and ac­commodated [Page 9] to the excitability then existing in the system, favouring the waking state^*.

I THINK it has been sufficiently proven, that the causes producing profound sleep, or sleep without dream­ing, deprive the mind of reflex-sensation. Mr. Locke (on the Human Understanding, in the first volume) observes, that the soul does not think during profound sleep, and that this cannot be proven, as there appears to have been a suspension of time to the sleeping man. The Chevalier Ramsay observes, ‘It is false to maintain, with the Cartesians, that the soul thinks always. They never did, nor can, give any solid reason for this as­sertion. Experience shows the contrary, when we are in a swoon, or in deep sleep. To think, know, and feel always, are privileges of a pure and unfallen state, when the living images shall have a perfect re­semblance to him who never slumbers. This is one of the principal changes made in nature since the fall, and a law established in the sphere of lapsed souls.’

THE reason why children sleep so much, has been supposed, by some, to be owing to their wanting reflex-sensation. May not the phaenomenon of sleep in chil­dren be explained upon other physical causes, and not upon the want of reflex-sensation? That the excita­bility of a child is more abundant, cannot, or will not, I imagine, be denied; and from this I may justly in­fer, that the waking and sleeping states of children do more easily run into each other than they do in adults. Their excitability, therefore, is more susceptible of the action of stimuli of every kind, and the sleep-inviting point is, consequently, produced, or brought on, sooner in children, by fewer causes, in a given time, than in adults.

[Page 10] A PATIENT in a convalescent state of a typhus-fever is considerably debilitated, and very excitable to any stimulus over-proportioned to the abundant excitability then existing in the system. The point at which sleep begins is sooner produced by stimulant powers, and the waking state is likewise sooner brought back; the in­tervals between the two stages of sleeping and waking are of less duration, and sleep is less profound than in a state of perfect and uninterrupted health^*.

THE sudden transition from sleeping to waking, and vice versa, is more observable in some persons, under certain circumstances, than in others; and these sud­den changes may apply to the above-mentioned cases. It has been observed in other persons, that the approach of sleeping and of waking is more gradual, and, in these cases, the ‘ears are often awake before the eyes are opened, or see clearly, and the senses are often awake before the power of voluntary motion is reco­vered.’ From the theory of sleep which I have en­deavoured to establish, may not these facts be resolved upon the same physical causes partially influencing the system, and producing an unequal excitement and mor­bid sleep?

IN a typhus mitior, the patient sleeps much, with a kind of stertorous breathing, and is easily wakened by an address not louder than common; withholding it, he soon falls into an involuntary sleep. This kind of sleep, for the most part, is the consequence of a certain degree of debility, produced by some powers acting with considerable stimulant effect; the reason is, this sleep depends upon less debility than that which consti­tutes [Page 11] the disease. How does it come about, that every thing which stimulates produces that effect by its sti­mulant, and not by its sedative, virtue? Let those ac­customed to all the causes producing the sleep-inviting point, be removed from these causes, and exposed to the directly-debilitating powers, as darkness, silence, cold, rest, and abstinence; these causes lessening the excitement (and accumulating the excitability), will increase a disposition to involuntary morbid sleep.

THERE are many facts which may be adduced in proof of this point. Even daily observation furnishes us with arguments in support of the position. Let us turn our attention to the industrious labourer, who is fatigued from his daily pursuits, exposed to the stimu­lating rays of light, and the noise of the busy world, who eats and drinks his hard earnings with a good ap­petite, and lays down to rest, attended with profound, refreshing sleep. Dr. Zimmerman says, ‘the soldier sleeps even amidst the thunder of the cannon, when he is worn out with excessive fatigue^*.’—Change the order; give him a day's rest, silence, darkness, &c. and he will fall into sleep of the morbid, restless kind.

THE regular returning time of sleeping and waking, is to be explained upon principles similar to the fore­going, and not upon the effects of habit. Habit is the effect of causes producing sleep, and not the cause of sleep; which is too obvious to need any further ex­planation.

FROM what has already been said, we may explain the reason why all simple sounds, as the sound of a gentle cascade, the beating of rain upon a house, vocal or instrumental music, induce a disposition to sleep. They are to be resolved, likewise, upon the same phy­sical principles as all other stimuli, producing partial exhaustion of the excitability, and favouring th [...] sleep-inviting [Page 12] point, and not upon the effects of sound sim­ply preventing reflex-sensation, and causing sleep.—Sound and uninterrupted sleep refresh the bodily and mental powers, by accumulating, or bringing back, the greatly-wasted excitability to the stimuli of the preced­ing day, and preparing, or fitting it, for the operation of the exciting powers of the succeeding day.

IN the latter part of night, and towards morning, the excitement is considerably diminished, the body in some degree weakened, and more easily affected by any sti­mulus, or hurtful power, that may be applied.

THIS living principle, inherent in the world of ani­mals, upon which all natural stimuli exert their effects, in supporting the living existence, is not confined to them alone, but is likewise extended to the vegetable kingdom. The greatest physiologist^* the world has hitherto produced, did not, indeed, admit of irritability in vegetables; but the industry and sagacity of the Bo­tanists have shewn us, that there is a very considerable number of vegetables, which exhibit signs of irritabi­lity, more or less obvious in proportion to their age, to their strength, or to the part to which the irritating cause is applied. This has been observed in the leaves and flowers of several plants. Mr. Bonnet, of Geneva, has, I think, incontestibly demonstrated, that the leaves of vegetables possess the power of voluntary motion. He has shewn us that these parts, or organs, always pre­sent their upper surface to the air, and that whenever a branch is turned out of its natural position, the leaves of that branch immediately assume a new direction. May we not venture to add, that the voluntary and in­voluntary motions of plants are more conspicuous, and remarkable in the organs of fructification, especially in the stamina and pistils, than in the leaves, or any other parts, of vegetables; for in many plants, as soon as these generative organs have arrived at maturity, the [Page 13] stamina embrace the pistil, with a seemingly-venereal ap­petite, and discharge their fecundating influence, from the cells of the antherae, upon the female organ—after this the stamina resume their former position, and, in a short time, pine, wither, and die? The involuntary and voluntary motions of vegetables, are observable in the Berberis vulgaris, or common berberry, and many others; the filaments of these plants, when touched by a pin, or any other mechanical stimulus, are immediately put in motion, and apply themselves to the pistillum, on which they discharge a portion of their fertilizing dust. The wonderful irritability of the stamina of the Cistus Helianthemum ^*, is remarkable, chiefly, about sun rise; in the evening the irritability is nearly extinguished, and on the following morning, this great, unequivocal, never-failing characteristic of life, returns again, and so on through the whole course of the vegetable life. All vegetables are more irritable in the morning than in the evening, to any stimuli that may be applied. The leaves of many vegetables, in the day, assume an ap­pearance very different, from that which they do at night time. They are folded up, or contracted in the night; but in the day time, they are generally expand­ed; and, hence arises that particular state of vegeta­bles, which constitutes what Linnaeus and other na­turalists have denominated Somnus Plantarum, or the sleep of plants. During the continuance of this vegeta­ble-sleep, the appearance of the plant is so much chang­ed, that the most experienced botanist is sometimes at a loss to know it, without a very minute examination. In some plants, the inviting sleeping point may be induced by robbing them of light for a time, but upon the re­turn of light, they resume their waking state. We may lay it down as a pretty constant and certain axiom, that the sleep of vegetables, is more or less profound in proportion to their vigour or debility.^†

[Page 14] IF the vigour and debility depend upon the effects of stimuli acting on the irritability in vegetables: If the motions likewise depend upon, and are subservient to a "vegetable will;" and if sleep more or less profound, depends upon the application of stimuli, which, I think has been sufficiently proven; would it be unphiloso­phical to infer, that vegetables, in time of morbid sleep, are disturbed with dreams peculiar to themselves?

THE connection of causes and effects, traced in the vegetable world, and compared with those of the animal kingdom, point out the striking analogy between the two; and proclaim that Nature is uniformly the same in all her operations.

AN accurate knowledge of the effects of sleep, upon the human system, will enable us to see the propriety of fortifying the body, in the morning, with either the durable or diffusible stimuli, against the noxious quality of the air at certain seasons of the year; it like­wise will further enable us, to point out the impropri­ety of the conjugal pair gratifying or indulging the hymeneal pleasures in the morning. Thus, the tem­perature and purity of the air, food and drink, labour of body or of mind, the stimulus of light and sound, ‘the exercise of passion and emotion, when their sti­mulus neither stops short of the proper point, nor goes beyond it, all give a disposition to sleep,’ of the most salutary kind.

BEFORE I conclude the subject of sleep, I beg leave to mention a few remarkable, important, and valu­able facts, concerning the Hybernation of animals, which will, beyond all scruple, help to resolve many phoeno­mena in nature, shew the great sedative power of cold, and the effects it has in producing sleep, in many fami­lies of the animal kingdom. By the term Hybernation, is to be understood, that dormant state in which ani­mals of many different kinds, subsist in winter without [Page 15] food, without any apparent motion, and without sense, seemingly sound asleep, and not recoverable from it unless placed in a warmer atmosphere. It is to be ob­served, that this faculty is confined to those animals that are the inhabitants of the colder regions of the earth; at least we know of no instance of Hybernation of ani­mals, which dwell in the intratropical parts of the earth. This state of torpidity is most remarkable in the amphibious animals, such as the frogs, the toads, the lizards, and, I suspect, the serpents. There are like­wise several quadrupeds, which are remarkable for re­maining during winter in a torpid state, such as the bear, the badger, the squirrel, the hedge-hog, the dor­mouse, the bat, &c. The Count de Buffon, and several other naturalists, ascribe this state to the coldness of their blood; but, according to Mr. John Hunter's ex­periments, it does not appear that the blood of the bear, of the hedge-hog, of the badger, or of the dor­mouse, is a degree colder, than what we find to be in general the case, in animals of the same class. It has been found by experiments made by Mr. Hunter, that a frog receives and digests food, when it is in an atmosphere in which the thermometer stands at 60°. but that it does not digest food when the cold comes down to 40°. It has from thence been supposed, that those dormant quadrupeds, the bear, the badger, the hedge-hog, the dormouse, and perhaps the squirrel, when the heat of their blood is reduced from 90°. and 100°. by cold to 70°. that then they lose the power of digestion, and that the excretions, as well as the secre­tions, are very much diminished. This is the most plau­sible explanation of the fact hitherto offered.

DOCTOR Pallas says, the fuslik becomes torpid in a great degree of cold; and that the heat of this ani­mal is reduced from 103 to 80 of the scale of Fahren­heit.^*—In the hamster, Sulzer has shewn us, that, during the summer season, the pulse beats one hundred [Page 16] and fifty strokes in a minute; but that, if the animal is examined in the winter months, when in its torpid state, the heart hardly pulsates fifty times in a minute^*. This last observation does not apply merely to the ham­ster, but, I believe, it may be assumed as a fact, that, during the torpid state of all hybernating animals, the pulsation of the heart is very slow. This remarkably-sedative power of cold is not confined solely to the in­ferior animals: the influence of a cold climate on the human pulse is prodigious. It has been found, for in­stance, that the heart of the Greenlander does not beat more than thirty, or forty, strokes in a minute^†.

FROM comparing these facts and experiments, and the fifth and sixth experiments of William Hewson's Inquiry into the properties of the blood, may we not venture to draw the following conclusions? 1st. That cold is a great debilitating or sedative power: 2d. That if the blood of some of the hybernating animals be ac­tually at rest for a considerable length of time, it may be rendered fluid by the gradual introduction of heat, and the animal restored to life. With these facts and ob­servations, I finish the subject of sleep, and now pro­ceed, in the second place, to the inquiry of Dreams.

FROM the theory of sleep already given, I am enabled to prosecute with more propriety the subject of Dreams. It has been made to appear, that profound sleep de­pends upon causes producing a certain degree of ex­citement favourable to the point at which sleep com­mences, and that dreams are the effects of morbid sleep, which depend upon the same stimulus either stopping short of the proper point, or going beyond it. It is in this state of sleep, that the soul does think (according to Mr. Locke), when the intellectual functions are par­tially suspended. Dreams may be explained, likewise, upon the same method of reasoning, as sleep. Certain [Page 17] powers do exert their effects on the principle of life, and produce an excitement unfavourable to refreshing sleep, which will be strictly attended to in the course of this subject; and, I think, the old adage of philoso­phers, will apply equally well here, as in many other cases, "that Nature does nothing in vain."

I PRESUME, from what has been advanced, it will obviously appear, that a complete excitement of the brain, does necessarily take place in time of profound sleep, different from that excitement, which takes place, in order to the proper exercise of the intellectual func­tions in the waking state, and that, in time of morbid sleep, there is either a deficiency or an excess of ex­citement, with respect to the different functions, in different degrees. In such an intermediate state of de­ficiency or excess of excitement in the brain, there always occurs more or less of dreaming: ‘There are, in this state, false perceptions, false associations, false judgments, and disproportionate emotions.’ In short, the circumstances attending dreaming, are observed to take place in delirium, only differing in degree.

IN sthenic and asthenic diseases, when attended with delirium, the excitement in the former is carried be­yond that point at which inviting sleep commences, and, in the latter, stops short of it.

THUS, I conceive, it will evidently appear, that there are two kinds of delirium, depending upon dif­ferent degrees of excitement: the one is owing to an excessive, and the other to a deficient, degree of excite­ment in the brain. Further, it may, perhaps, serve to illustrate the analogy between dreaming and delirium; and the latter is only a bridge for the former to travel over to Insania, if I may be allowed the expression.

DREAMS affect those most, who are of a debilitated and delicate habit, and those easily affected by slight [Page 18] and trifling causes. A labouring man seldom dreams much. ‘The sleep of a labouring man in sweet, whe­ther he eats little or much, but the abundance of the rich will not suffer him to sleep^*’. Besides these, there are some healthy persons who seldom or never dream at all. Mr. Locke tells us, ‘he once knew a man that was bred a scholar, and had no bad me­mory, who told him, he had never dreamed in his life, till he had that fever he was then newly reco­vered of, which was about the five or six and twen­tieth year of his age.’ And, as a farther corroborat­ing circumstance, I have been informed by a gentleman of my acquaintance, that Dr. William Pitt Smith, of New-York, was acquainted with a lady of that city, who, at the age of twenty-three years, declared, she had never dreamed in her life, and further, that the idea of dreaming appeared so absurd to her, that she did not believe there were any such things as dreams.—I have no doubt, the world affords many more such instances.

‘THE dreams of sleeping men are, as I take it, all made up of the waking man's ideas, though, for the most part, oddly put together^†’. That this is not always the case, may, I presume, be proven upon Mr. Locke's own principles of reasoning, that if all our ideas are derived from sensation and reflexion, which he endeavours to maintain, and if, in time of profound sleep, the soul does not think, then dreaming most un­questionably must be, in time of morbid sleep, when the powers of the mind are only partially suspended; therefore, at that time, the organs of sense are excita­ble to new impressions from causes suggested from without, and certainly they may beget new ideas with­in, and likewise excite those into action already fixed in the mind, though, for the most part, incoherent.

[Page 19] It has been observed, in the former part of this dis­sertation, that the excitability is more abundant in the latter part of night, and towards morning, than in the fore part of the evening, consequently more easily af­fected by any stimuli, that may be at that time applied. This will, perhaps, enable us to explain more satisfac­torily the phaenomenon of dreaming, at the approach of day, than at any period of the night; for it is ge­nerally remarked, that thieves make choice of what is vulgarly called the dead hour of the night, to make their depredations, when people are supposed to be fast locked in the arms of profound sleep.

FURTHER, in support of this subject, I beg leave to adduce the following fact, from Dr. Beattie's Disserta­tions Moral and Critical. He observes, that ‘particular dreams might be accounted for from impressions made in time of sleep on the organs of sense, parti­cularly those of touch and feeling. A very slight hint, suggested from without, or in any way suggest­ed, is sufficient for fancy to work upon, in produc­ing multitudes of visionary exhibitions. I have heard from good authority, of a gentleman in the army, whose imagination was so easily affected in sleep with impressions made on the outward senses, that his companions, by speaking softly in his ear, could cause him to dream of what they pleased: once, in particular, they made him go through the whole procedure of a duel, from the beginning of the quar­rel to the firing of a pistol, which they put in his hand for [...]hat purpose, and which, by the explosion, awaked him.’ I take the liberty of mentioning another fact, which will help to illustrate the very point in question. It is a fact I obtained of a gentle­man of my acquaintance, of extensive observation and unblemished moral character, who related his dream in the following words. ‘I imagined I saw, at ten o'clock in the morning, a moon in the east, shoot from itself like one meteor from another, fall to the horizon, [Page 20] and assume the appearance of a rising full moon. Upon the appearance of this singular phaenomenon, I thought my dog started in pursuit of it. Immedi­ately my imagination was changed to the west, where I fancied I saw a person descending from heaven, in a flame of fire. When it came in contact with the earth, a very great smoke issued, which seemed to spread far and wide. This was soon dissipated, and I thought my companions said they observed a man, who had descended in that flame of fire. They went off to meet him, and, behold, returned with a person dressed in a sailor's grab: I asked him from whence he came? he answered, he was taken up in a water spout, in a river (where he was fishing for his living) about sixty miles from this spot; and he observed fur­ther, that he should have descended much faster, if it had not been for a large windlass he had hold of in his passage from above.’ A complete and judi­cious induction of the effects of these facts, are suffi­cient to prove the astonishing vivacity of the imagina­tion, the absurdity and incoherence of the ideas in time of dreaming, and that they are not always made up of the waking man's thoughts.

I SHALL, in the third place, proceed to animadvert upon the effects of dreams on the faculties of the mind.

DOES not the excessive or deficient degree of excite­ment, constituting the morbid state of sleep, wherein certain faculties of the mind are awakened, seem to argue in favour of the different powers of the mind oc­cupying different parts of space in the brain? If so, it will help to resolve the causes, why, sometimes the imagination, the memory, and the judgment, are parti­ally excited, and sometimes deranged and impaired in dreams, and in diseases. There are numberless facts that may be adduced, in proof of the effects of diseases and accidents, in destroying, or impairing, the intel­lectual [Page 21] faculties. But, this is rather foreign to the present inquiry. I shall, therefore, confine myself to the effects of dreams on the faculties of the mind.

"THE imagination, or fancy, seems to be" one of all our mental powers, or faculties, the least suspended in its operation by sleep. Of the other powers, or facul­ties, some are more, others less, affected, and some ap­pear to be, for a time, wholly suspended. That the memory is at times impaired or partially excited in sleep, may be proven from this, that a person will dream of transacting business with a deceased friend, without recollecting any thing of his death. The judgment is frequently impaired in dreams, as well as in diseases, and the imagination retains its vigour in tolerable force. That there is sometimes an association of ideas in sleep, I presume, will not be disputed; and it may be made to appear from this, that, if I dream of the object of my affection, it transports my imagination back to the place where she most commonly resides; but, for the most part, the association of ideas is false and delusive, in our dreaming moments. Sometimes, the understand­ing is so deranged, and has so forsaken us, that we are entirely deprived of the power and freedom of the will. Hence, in dreams, we seem to experience a false necessity of running into trouble, pain, and many other perplexi­ties, though, with a vigorous exertion of that power of the understanding, the will, we should find a remedy or an antidote to all such harrassing ideas.

BUT sleep has a wonderful power over all our facul­ties, besides those mentioned above. Sometimes such a change takes place in the state of the brain, from the influence of certain powers, that we seem to have en­tirely lost our moral faculty. Hence, we sometimes dream of perpetrating crimes without scruple or re­morse; crimes, both repugnant to law and to gospel, and at which we should shudder when awake. Would [Page 22] it be admitted, if I were to ascribe this to the deser­tion of the judgment?

AN attempt to explain all the dreams recorded in the Old and New Testament, upon the same physical causes as we do those of the present day, would, perhaps, suggest a hint favourable to deistical principles, throw some objections in the way, and have a tendency to o­verturn, and retard the progress of, the Christian reli­gion, with some weak and wavering minds. Far be it from me, however, that I should entertain, or even wish to support, an idea, so unfriendly to the moral science, to the happiness, and to the good order, of society: For we are warranted by the same sacred history to be­lieve, ‘that dreams have given information of future events,’ and that they were revealed to some persons, for certain purposes, by the Deity. Hence, weak and ignorant people infer, that they are still prophetical, and ominous of their future events; but, what can be more absurd than such superstitious notions? ‘Su­perstition is one of the worst diseases of the soul. It is generally unfriendly to happiness, to rational pie­ty, and to sound philosophy^*’. Then, ‘as nature has done nothing in vain,’ may I not infer, that dreams are frequently of service to some people? for, according to the Chevalier Ramsay, the Deity institut­ted physical evil for the eradication of moral evil. May not, then, bodily and mental pain, which are fre­quently experienced in dreams, be of use to those per­sons in the way of physical admonition, and that they may be serviceable as means of moral improvement? ‘For we find that bodily and mental pains were the remedies, employed in the Old Testament, for extir­pating vice and promoting virtue^†’.

[Page 23] ‘HE is chastened also with pain upon his bed, and the multitude of his bones with strong pain^*’. The wise and the learned will not despise instruction, how­ever mean and trifling the vehicle may be that conveys it; for great advantages may, perhaps, be derived even from an extravagant flight of the imagination, or of any other faculties of the mind, in a dream.

HAVING finished the subject of dreams, and the ef­fects of dreams on the faculties of the mind, and hav­ing also proven that they occur in a state of morbid sleep, it now remains, in the fourth place, to point out the causes of dreams. These may be divided into external and internal causes.

FIRST. Under the head of the external causes, I shall consider those which affect the outward senses, ei­ther from an excess or deficiency of their stimulant powers: And,

SECONDLY. Under the head of the internal causes, I shall mention those which affect the internal senses likewise, either from their excess, or deficiency, of sti­mulant properties, and convey new impressions to the sensorium commune, and beget new ideas, or excite those into action, already established in the mind.

FIRST. I shall consider those external causes, which, if applied in excess, run the excitement beyond that point at which profound sleep commences.

THESE are such as excessive bodily fatigue, too great heat accumulated in the room, either from the sun, fire, or bed-clothes, excessive eating of rich and nourishing food, and too free use of fermented, or spirituous, li­quors; too pure or dephlogisticated air; worms in the alimentary passage; a ‘great abundance and velocity of rich blood;’ an accumulation of urine in the [Page 24] bladder; an accumulation of the venereal stimulus; a retention of the perspirable matter under the cuticle: In short, a retention of any of the excretions, may prove causes of dreams.

SECOND. I shall mention those external causes whose stimulant effects stop short of that point, at which sleep of the salutary kind begins.

THESE are such as idleness, cold, any way introduced, darkness, silence, too long abstinence either from eat­ing or drinking, or, rather, a deficiency of the stimu­lant effects of these powers; an uneasy position of the body in time of sleep; tumors situated externally on, or in the neighbourhood of, the trachea; ligatures on any part of the body; air rendered very impure, from its being impregnated with any noxious particles; ob­structed nares, either from mucous, or polypi, or any other substance impacted in, and shutting up, their pas­sage; a penury of blood, and an excessive evacuation of any kind.

I SHALL proceed, in the last place, to take notice of the second head, under which the internal causes are to be mentioned.

FIRST. I shall mention those internal causes, which operate from their excessive stimulus, favouring that degree of excitement which constitutes morbid sleep. These are, long and intense applications of the mind to study or business of any kind, violent passions of the mind, as love, joy, and anger.

SECOND. I shall conclude this subject, with pointing out those internal causes, whose stimulus stops short of that point, at which refreshing sleep commences. These are, a kind of inactivity, sluggishness, or rather a vacan­cy of the mind; the depressing passions, as grief, fear, and shame, or rather an abstraction of confidence.

[Page 25] HAVING concluded this dissertation, I cannot lay down my pen without embracing this favourable oppor­tunity, of publicly returning my sincere thanks to the worthy Professors of the College of Philadelphia, and of acknowledging the many valuable and important truths delivered from their different chairs in this semi­nary—Hoping, that her sons may have treasured up in their minds the true principles of the science; that they may live as rising monuments, to the honor of medi­cine; and not conclude their earthly existence, till af­ter they have extended their improvements to such a length, as will mark a glorious epoch in the annals of time.