311 



Sleep, is a state, if not altogether passive, in which, at least, the activity 

 of most of the organs, is remarkably diminished, and that of some of 

 them are completely suspended. It is erroneously then, that some au- 

 thors have viewed it as an active phenomenon, and a function of the 

 living economy: it is only a mode or manner of being. It is to no pur- 

 pose they have maintained, that to sleep required some measure of 

 strength. Excessive fatigue hinders sleep, merely by a sense of pain in. 

 all the muscles, a pain that excites anew the action of the brain, which 

 it keeps awake, till it is itself overpowered by sleep. 



It has been attempted to show the proximate cause of sleep. Some 

 have said that it depends on the collapse of the lamina of the cerebellum, 

 which, as they conceive, are in a state of erection during waking; and 

 they argue from the experiment in which, by compressing the cerebel- 

 lum of a living animal, sleep is immediately brought on. This sleep, 

 like that produced by compression of any other part of the cerebral 

 mass, is really a state of disease; and no more natural than apoplexy. 

 Others, conceiving sleep, no doubt, analogous to this affection, ascribe 

 it to the collection of humours upon the brain during waking. This or- 

 gan, say they, compressed by the blood which obstructs its vessels, falls 

 into a state of real stupor. An opinion as unsupported as the other. As 

 long as the humours flow in abundance towards the brain, they keep up 

 in it an excitement winch is altogether unfavourable to sleep. Do we 

 not know, that it is enough that the brain be strongly occupied by its 

 thoughts, or vividly affected in anyway, to repel sleep? Coffee, spiritu- 

 ous liquors, in small quantities, will produce sleeplessness, by exciting 

 the force of circulation, and determining towards the brain a more con- 

 siderable afflux of blood. All, on the other hand, that may divert this 

 fluid towards another organ, as copious bleedings, pediluvium, purges, 

 digestion, copulation, severe cold, or whatever diminishes the force with 

 which it is driven towards it, as inebriation, general debility, tends power- 

 fully to promote sleep. In like manner, it is observed, that while it lasts, 

 the cerebral mass collapses: a sign that the flow of blood into it is re- 

 markably lessened. 



The organs of the senses, laid asleep, in succession, awake in the same 

 manner. Sounds and light produce impressions, confused at first, on the 

 eyes and ears; in a little time these sensations grow distinct; we smell, 

 we taste, we judge of bodies by the touch. The organs of motion prepare 

 for entering into action, and begin to act, at the direction of the will*. 

 The causes of waking operate by determining a greater flow of blood 

 into the brain : they include all that can affect the senses, as the return 

 of light and of noise with the rising of the sun; at times, they act within 

 us. Thus, urine, fecal matter, other fluids accumulated in their reser- 

 voirs, irritate them, and send up, towards the brain, an agitation which 

 assists in dispelling slumber. Habit, too, acts upon this phenomenon, 

 as on all those of the nervous and sensitive system, with most remarka- 

 ble influence. There are many that sleep soundly amidst noises which, 

 at first, kept them painfully awake. Whatever need he may have of 

 longer repose, a man that has fixed the daily hour of his awaking, will 

 awake every morning to his hour. It is as much under the controul of 

 the will. It is enough to will it strongly, and we can awake at any hour 

 we choose. 



* See tbp CHAPTER on Motion, Art. CLXXII. 



