444 ESSAYS ann OBSERVATIONS 
Tue caufe exciting the alternate contracti- 
on of the infpiratory mufcles, is an uneafy 
fenfation in the Jungs, occafioned by the 
blood pufhed into their veffels by the right 
ventricle of the heart*. If then lefs blood | 
is fent, in a given time, into the lungs, in 
fleep, than when we are awake ; the neceflity 
of new fupplies of frefh air will be leffened, 
- and confequently infpiration will be perform- 
ed at greater intervals. 
FuRTHER, as intime of fleep, the fenfi- 
bility of the lungs, like that of the heart 
and guts, muft be fomewhat impaired, re- 
fpiration muft alfo, on this account, be per- 
formed more flowly; for the infpiratory 
mufcles will not be excited into action till a 
greater degree of irritation, than ufual, be 
occafioned by the blood accumulated in the 
pulmonary veffels. And, to this it is owing, 
that refpiration is not only flower, but fome- 
what deeper in time of fleep, than in a waking 
perfon at reft in a horizontal pofition. 
In comatous and apoplectic cafes, where 
all the feelings of the body are much more 
impaired than in ordinary fleep, refpiration is 
not only much flower and deeper than ufual, 
but 
* Effay on Vital and Involuntary motions, &c. p 176. &e, 
