492 ESSAYS AND OBSERVATfONS 



Art. XIS:. 



Of the difference between Refpiration and th 

 Motion of the Hearty hifleeping and waking 

 Perjons^ h^ Robert Whytt, M. D, 



OF all the parts of the human bodfy 

 there is none whofe ftrudlure is 

 more fubtile, and whofe feveral fundlions 

 and ufes are kfs known, than thofe of the 

 brain. It is little to be wondered at, 

 therefore, if authors have failed of giving 

 a fatisfactory account of Sleep, which is 

 one particular ftate of this unknown or- 

 gan. We have elfewhere offered our 



conjedtures concerning the reafon why 

 the vital motions continue in time of 

 fleep ; when the organs of fenfe become 

 lefs fit to receive the impreflions of exter- 

 nal objedls J and when the mufcles of vo- 

 luntary motion are more relaxed and re- 

 main 



