436 ESSAYS ann OBSERVATIONS 
AR Tol 
Of the difference between Refpiration and the 
Motion of the Heart, in fleeping and wa- 
king Perfons, by Roprt Wuytt, M. D. 
Se, 
\F all the parts of the human body, there 
is none whofe ftru€ture is more fub- 
tile, and whofe feveral functions and ufes are 
lefs known, than thofe of the brain. It is 
little to be wondered at, therefore, if au- 
thors have failed of giving a fatisfactory ac- - 
count of /leep, which is one particular ftate 
of this unknown organ.—We have elfewhere 
offered our conjectures concerning the reafon 
why the vital motions continue in time of 
fleep ; when the organs of fenfe becomes lefs 
fit to receive the impreffions of external ob- 
jects ; and when the mufcles of voluntary mo- 
tion are more relaxed and remain at reft *, 
But, as refpiration and the motion of the 
heart, 
* Effay on the Vital and other Involuntary motions of a- 
nimals, fect, xii. 
