( 1231 
As in the Elevation of the CoJj£, the Blood, by the pai- ' 
fage that is open'd for it^ 'is ia a manner foUicieed into the 
Lungs, fo in the Depreffion of em, by the fubfidence of 
the Lungs and the Contraftion of the Blood Veffels^ both 
which are Gonfequent thereof, the Blood is forcibly driven, 
aS: it were with an Embohm^ thro the Pulmonary Vein into 
the Left Ventricle of the Heart. And this, together with 
the general Comprejjlon of the Bady by the weight; of the At- 
'mofphere, which lurrounds and prefles upon the whole Sur- 
face of it, is that Power which caufes the Blood to mount 
in the Veins, after the force imprefs'd upon it by the 
Heart is broken and fpent, and which is fufficient to 
force the Heart from its natural State to dilatation. 
He thatis aMe to compute the weight of a Column of 
Air,, equal to the Surface of the whole Body, will readily 
grant it a Power- fufficient for the Effects, which are here 
afcrib'd to it. And, when he confiders, that the Bodies of 
Animals are comprefTible Machines, he will find that it 
muft of neceffity afFe£l them in the manner here laid down. 
But tho pur Bodies be entirely composed of Tubulin or Vef- 
felsffird with Fluids, yet this Prefiure, how great foever^ 
being equal, cou d have no efFed upon 'em, if the fuperfi- 
cial iOiraenfions v/ere not eafily variable^ becaufe being 
comprefs'd on all parts with the fame degree of Force, the 
contain d Fluids cou d not any where begin to recede, and 
make way for the reft to follow, but wou'd remain as fixt 
and immovable as if chey were aftually folid. But by the 
[)ilatation of the Thorax^ room is maide xfor the Fluids to 
move, and by the Coardation of it frefh motion is imprelV,, 
which is the main Spring whereby the Circulation is fet . 
and kept going. 
This reciprocal Dilatation and Contraftion of the Super- 
ficial Dimenfions of the Body feems fo neceffary to Animal 
Life, that there is not any Animal fo imperfeft as to want 
it, at leaft none to the inward Strudure, of which 
our Anatomical Difcoveries have yet reach'do For, the 
moft 
