258 j4n Essay on Dreaming, hicluding 



continue to think — by thinking we exercise the organ of thought 

 — by exercising the organ we may possibly interrupt or defer 

 this process, whose invasion, when effectual, subdues every faculty 

 of the mind. Young children are destitute of this power — they 

 sleep almost incessantly ; but nutrition and assimilation are com- 

 paratively more necessary to them than to adults, and are carried 

 on in a more than proportionate measure in their system. Old 

 persons are drowsy, and find it difficult to keep themselves awake 

 after food, yet court sleep in vain during the hours they have been 

 accustomed in the earlier part of their life to expect it. This 

 may be because their debilitated powers do not enable them to sus- 

 pend the process of assimilation, and they are compelled to sub- 

 mit to its influence as soon as it operates ; while the decay of 

 nature, at the same time, evinces that the function in question is 

 less constantly, regularly, or effectually performed : nor is the 

 fact to be forgotten, that disturbed sleep and frightful dreams 

 have frequently been ascribed to disorder of the digestive organs, 

 whose preparatory office is indispensable to nutrition and assimi- 

 lation. 



It is true, that sleep after meals is most irresistible while the 

 food is still in the stomach, after digestion has commenced, and 

 long before assimilation has taken its turn. But we are ignorant 

 how far the arrival of new matter in the blood-vessels may in- 

 stantly contribute to the deposition of the old ; as an additional 

 number of balls put into a tube, atone extremity, will force out 

 some of their predecessors at the other. 



I enter into no argument on the subject. I repose on the ra- 

 tional presumption that sleep is something more than rest after 

 fatigue — that it is probably the consequence of an important vital 

 process in the dehcate and fragile instruments of the mind — 

 and that no process can be more requisite to those instruments, 

 nor more likely to produce the effect, than the process of assimi- 

 lation. 



That this process is the proximate cause of sleep, receives the 

 strongest confirmation from the facts detailed in the article sleep, 

 in Rees's Cyclopcedia, probably the last and best treatise on the 

 subject, and which evidently points throughout to this cause, 

 though the abl<: writer of the article inadvertently suffered it to 

 escape his attention. He appears to be satisfied with the com- 

 mon explanation, and adopts the unsatisfactory opinion that 

 *' the exhaustion of the powers of the animal organs, by exer- 

 cise, is the determining cause of sleep *." Yet he adverts to two 

 facts, of a general nature and decisive importance, which subvert 

 this opinion. " Some," says he, " have cviWcdJculal existence a 



* Rees's CijchpcBcUa, 23(1 vol. article sleep. 



perpetual 



