262 Jn Essay on Dreami?ig, including 



well-known fact, that corpulency predisposes to sleep, and sleep 

 to corpulency. Does this happen because during sleep the pro- 

 cess of assimilation is most active in every part of the frame ? 

 Having produced an exuberance of flesh and fat, these produc- 

 tions may become in their turn the cause of somnolency, by con- 

 ducing to the more partial activity of the process in the brain ; 

 or at least the superfluous accumulation may form a kind of re- 

 servoir for the essential purpose of renovating the superior vital 

 organs, when the usual measure of nutrition is no longer sup- 

 plied. 



Thus we may clearly comprehend the different, yet strangely 

 analogous modes of action of vegetable poisons, intense cold, ex- 

 ternal injuries, and the assimilating process, on the brain. They 

 all render it comatose, torpid, and paralysed ; but none of them, 

 except the last, are endowed with anv but destructive powers. 

 The assimilating process alone can renovate and restore the 

 drained and exhausted organ : and even though the effect of its 

 activity is to sink us in stupefaction, that very stupefaction is na- 

 tural, refreshing, revivifying sleep. 



A very formidable objection to this theory has, however, oc- 

 curred to me. If the deposition of new matter by the blood- 

 vessels creates such a disturbance in the brain, as to occasion the 

 paralysis of sleep, why should not the action of the absorbents 

 produce a similar effect, and, in removing the old matter, also 

 bring on the same state of torpor and insensibility ? That it does 

 not, must be distinctly admitted; for the action of those vessels 

 cannot but exist as well in the brain as elsewhere during our 

 waking moments, and is probably most powerful during the in- 

 tensity of thinking, as well as of bodily exercise. But if the hy- 

 pothesis be true, this difficulty must admit of a solution. Can 

 we then discover such a difference between the operation of these 

 two actions on the brain, as will sufficiently account for circum- 

 stances so opposite ? 



In absorption, those particles which are removed, may leave 

 the remaining cerebral mass in the very act of thinking, or at 

 least not unfitted for the function. Every particle of the mass has 

 already formed a part of the instrument destined to this office, 

 and subservient tc the exercise of one or other of the mental fa- 

 culties. The new particles have never been exercised in any 

 mode of thinking. They can differ but little, on their first arrival, 

 from so many foreign bodies of equal dimensions ; and is it sur- 

 prising, that the oppression occasioned by their deposition should 

 be felt throughout the delicate volume of the brain, until they are 

 perfectly assimilated with the other particles, and fitted like them 

 for mental operations? — a result which may, perhaps, in some 

 measure be effected by the very sleep which they induce. 



The 



