7 8 Hcemajlatks. 
For fincc the Siibfl’ance of the Lungs is of a 
very flaccid Nature, they muft needs collapfe, 
when the Air equally prefTed on them both 
within and without. 
3. Hence alfo we fee that this Dilatation 
of the Lungs, which arifes only from the Force 
of the Blood in the pulmonary Artery, is not 
alone fufficient to promote the Paflage of the 
Blood thro’ them ; but there is alfo requifite 
a farther Dilatation of the Coats of the Veficles 
with infpired Air; thereby probably to unfold 
the corrugated Extremities of the Arteries 
and Veins, and fo to give the Blood a freer 
Courfe thro’ them. For cho’ in Experiment 
the fir ft, it was obferved that on deep figh. 
ing, that is on much dilating the Lungs, the 
Force of the Blood in the Horfe’s Arteries was 
greatly increafed, which was occafioned by 
the Blood's flowing more plentifully thro' 
them when they are dilated than when fallen ; 
yet we cannot hence infer that the Blood flows 
more freely thro’ them alfo when they are thus 
dilated by the Force of the arterial Blood, 
without the joint Dilatation alfo by the in- 
fpired Air. 
4. But when for w^ant of this Dilatation of 
the Veficles by the Air, the Blood's free Courfe 
was 
