S50 ON SLEEP, DREAMING, 



If a stimulus affecting the organs of sense, at which end soever applied 

 be intolerably pungent or forcible, the sensorial power will be exhausted im- 

 mediately, and the organ directly affected will become instantly torpid. 

 Hence sounds, intolerably loud, make us deaf; excessive light blinds us j 

 acrimonious smells or savours render us incapable of smelling or tasting. 

 And hence an abrupt shock of joy or grief, a sudden and intense paroxysm 

 of fever, large quantities of wine or spirits, as internal causes, produce mor- 

 bid lethargy, palsy, apoplexy, which are only so many modifications of the 

 sleep or torpitude of the sensitive and irritative fibres. If the same abrupt 

 and violent cause be sufficient to act upon the vital organs, as well as upon 

 those of external sensation, the torpor becomes universal, and the sleep is 

 once more the sleep of death. It is in this manner that death is produced by 

 a stroke of lightning. 



As violent stimuli produce sudden and occasionally irrecoverable torpitude, 

 either general or local, stimuli less violent induce a tendency to the same 

 effect. Hence the nostrils of persons not accustomed to snuff are more forci- 

 bly agitated by its application, than those that have been in the use of it : 

 the eyes of persons accustomed to sleep in the glare of the sun, find no in- 

 convenience from exposure to the light of the morning ; while those who 

 usually sleep in total darkness are awoke by its stimulus. And so of the rest. 

 On this account a very small portion of light, of sound, or of exercise, 

 are sufficient sources of exhaustion to those who are not in the habit of using 

 great external or internal activity. Hence savages and quadrupeds, who use 

 but very little internal activity, and no more external activity than is neces- 

 sary to gratify their passions and satisfy their hunger, become torpid upon 

 very slight excitements.- Hence infants become exhausted upon still slighter 

 excitements; as the exercise of being carried, the mere breath of the air, or 

 the digestion of milk alone in the stomach ; either of which, but especially 

 the whole collectively, is sufficient to make them sleep soundly : so soundly, 

 indeed, that no common stimulus is able for a long time to rouse them from 

 their torpor. In other words, it requires a period of many hours for the ex- 

 ternal organs to recover from their exhaustion. The smallest undulatory 

 motion in the uterus, perhaps, or the very action of the vital organs them- 

 selves, may be sufficient to wear out, from time to time, the sensorial power 

 of the fetus on its first formation : and hence the fetus sleeps, with few inter- 

 missions, through the whole period of parturition. 



For the same reason, persons in advanced age are far less impressed by 

 common stimuli than in any former part of their lives ; from a long series of 

 exposure to their influence, the organs of sense are become more torpid, and 

 hence they require less sleep, and at the same time less food. The vital 

 orgnns partake of the same disposition, and they are in consequence less 

 liable to violent "or inflammatory disorders. But the general torpitude increas- 

 ing, the heart is stimulated with greater difficulty; a smaller portion of sensorial 

 fluid is secreted by the brain ; a smaller portion of nutriment is thrown into the 

 circulation from the digestive organs ; the pulse and every other power gra- 

 dually declines, till at length, if ever man were to die of old age alone, he 

 would die from a total torpor or paralysis of the heart. But debilitated as 

 every organ is become long before such a period can arrive, the general frame 

 is incapable of resisting the smallest of the more trivial shocks, whether 

 external or internal, to which man is daily exposed : in other words, there is 

 no reservoir of sensorial power to supply the local or temporary demand ; 

 and the man dies, even at last, from sudden exhaustion, rather than from pro- 

 gressive paralysis. 



Sleep, then, is a natural torpitude or inertness, induced upon the organs 

 of the body and the faculties of the mind, by fatigue and exhaustion ; and 

 in a physiological survey, consists of the three stages of slumber, dreaming, 

 and lethargy. In slumber, the exhaustion is slight, and is almost confined to 

 the organs of external sense, the will only inclining to their inertness : in 

 dreaming, the exhaustion is usually more considerable, the will altogether 

 associating in their Alertness : in lethargy, the exhaustion extends to and 



