160 Analyfis of the Air . 
plied with equal quantities of frefh air, 
thro' the doors and windows, or the cranies 
of them. 
And thus many of thofe who have weak 
lungs, but can breathe well enough in the 
frefh country air, are greatly incommoded 
in their breathing, when they come into 
large cities where the air is full of fuliginous 
vapours, arifing from innumerable coal fires, 
and (tenches from filthy lay-ftalls and fewers : 
And even the mod robuft and healthy in 
changing from a city to a country air, find 
an exhilarating pleafure, arifing from a more 
free and kindly infpiration, whereby the 
lungs being lefs loaded with condenfing air 
and vapours, and thereby the veficles more 
dilated, with a clearer and more elaftick air, 
a freer courfe is thereby given to the blood, 
and probably a purer air mixed with it 5 and 
this is one reafon why in the country a fe- 
re ne dry conftitution of the air is more ex- 
hilarating than a moift thick air. 
And for the fame reafon, *tis no wonder, 
that peftilcntial, and other noxious epide- 
mical infedions are conveyed by the breath 
to the blood (when we confider what great 
quantities of the airy vehicle lofes its 
elafticity among the veficles, whereby the 
