On Muscular Motion and Animal Spirits 263 



movement. It certainly seems to have been arranged 

 by the good providences of nature that when the 

 saUne-sulphureous particles are nearly exhausted by 

 vigils, what remains of these particles should be 

 reserved for the natural functions — those really 

 necessary for life. Hence it is necessary that the 

 membrane surrounding the brain should sometimes 

 cease from its motion, so that the small remaining 

 portion of motive particles should be employed for 

 the motion of the membrane surrounding the cere- 

 bellum, and the other natural functions. For it nmst 

 he noticed that although the spontaneous animal 

 functions which are performed by means of the brain 

 are for a time interrupted during sleep, yet the function 

 of the cerebellum and the natural motions go on no 

 less, nay, rather better, when we are asleep than when 

 we are awake. 



It goes to confirm what has been said, that when 

 we have recently awakened from sleep we feel our 

 brain turgid with blood and somewhat heavy. The 

 reason of this seems to be that in sleep, the membranes 

 of the brain ceasing from their pulsation, the motion 

 of the blood is not promoted by the contraction of 

 the said membranes as when one is awake, and there- 

 fore the blood must be somewhat detained, and 

 stagnate in the membranes of the brain. Buc mean- 

 while during sleep the arterial blood, its passage 

 through the brain being to some extent obstructed, 

 is carried in greater abundance to the cerebellum ; 

 hence the nitro-aerial particles pass in sleep in greater 

 abundance to the cerebellum and the nerves arising 

 from it, and thus it is that the natural functions 

 presided over by the cerebellum are better performed 

 in sleep than when one is awake. What has been 

 said also gives us a reason why, in diseases character- 



