'ON SLEEP, DREAMING, &c. 243 



LECTURE VIT. 



ON SLEEP, DREAMING, REVERY, AND TRANCE ; SLEEP-WALKING, AND SLEEP-TALKING. 



WE are proceeding to a subject of much difficulty in theory, though of the 

 greatest familiarity in fact ; and I freely confess to you, that although I have 

 endeavoured to investigate almost every opinion that has been offered upon 

 it, from the time of Aristotle to our own day, I have never met. with any- 

 thing in the least degree satisfactory, or capable of unravelling the perplexi- 

 ties in which it lies entangled. 



What can possibly be more opposite to each other than the two states of 

 wakefulness and sleep? the senses in full vigour and activity, alive to every 

 pursuit, arid braced up to every exertion, and a suspension of all sense 

 whatever, a looseness and inertness of the voluntary powers, so nearly akin 

 to death, that nothing but a daily experience of the fact itself could justify 

 us in expecting that we could ever recover from it. 



And yet, while such is the lifelessness without, the mind, now destitute of 

 the control of the will, is often overwhelmed with a chaos of ideas, rushing 

 upon each other with so much rapidity, that the transactions of ages are 

 crowded into moments, and so confused and disjointed, that the wildest and 

 most incongruous fancies flit before us, and every thing that is possible be- 

 comes united with every thing that is impossible. 



Such, however, are the ordinary means devised by Infinite Wisdom to 

 revivify the animal frame when exhausted by the labours of the day ; to 

 recruit it for new exertions, and enable it to fill up the measure of its 

 existence. 



The order I shall take leave to pursue in discussing this abstruse subject 

 will consist, first, in a brief examination of the more prominent hypotheses 

 on sleep and dreaming that have been offered to us by ancient and modern 

 schools : secondly, in a minute analysis of the feelings and phenomena by 

 which these operations are characterized, agreeably to the series in which 

 they occur: thirdly, in submitting the outline of a new theory to explain the 

 entire process : and, lastly, in an application of such theory to a variety of 

 other subjects of a similar and equally extraordinary nature. 



Sleep may be either natural or morbid. The former is usually produced by 

 whatever exhausts the principle of life ; as great muscular excitement, vio- 

 lent pain, vehement use of the external senses ; or great mental excitement, 

 as intense thought or severe distress. Morbid sleep is commonly occasioned 

 by compression or commotion of the brain, and is hence often the result of 

 congestion, plethora, or local injury to the skull. 



Compression and commotion, though less frequent, are more direct and 

 obvious causes : and hence the greater number of physiologists believe com- 

 pression to take place, also, though in a slight degree, in every case of natu- 

 ral sleep; and in reality to constitute the immediate, while sensorial exhaus- 

 tion only constitutes the remote, cause of this phenomenon. They appeal 

 to the lethargic effect of a full stomach in infants, and of drunkenness in 

 adults, which they refer to congestion in the brain, in consequence of a 

 greater influx of blood into this organ: and hence they reason that a similar 

 sort of pressure is produced by some means or other in every case of sleep. 



But what are the means of pressure thus referred to'? And here a consi- 

 derable difficulty is felt by every school of physiologists : and two distinct 

 schemes are devised to get rid of it. By the one we are directed to the arte- 

 rial system, which, we are told, becomes peculiarly excited and overcharged 

 in the organ of the brain during' wakefulness, from the activity of the internal 

 senses.* By the other we are directed to the absorbent system, which from 



* This explanation is partly, though not chiefly, adopted by the author of the elaborate article on steep, 

 IP Rees's Cyclopedia: and has since been fully embraced by Mr. Carnu'chael, in his learned Essay on 



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