36 Hcemajlatics. 
the Veins and Arteries of Animals, as they 
lay horizontally on their Backs, or on one fide 
in the Cafe of the Mare, Exper. III. But 
when an Animal (lands on its Legs, a Column 
equal to the perpendicular Height of the Ani- 
mal, muft be added to the feveral Heights of 
the Blood in the glafs Tubes, in order to ef- 
timate the Force, with which the Blood 
preffes againfl: the Coats of the Blood-VefiTels, 
at the lower Parts of the Body, and Co in pro- 
portion for any other Parc that is higher. So 
that thefe Columns of Blood in the Arteries 
and Veins, communicating with each ocher 
below, are on account of their equal Heights, 
equipollent to each ocher : The progreffive 
Motion of them being determined by the Ener- 
gy of the Heart. And tho' Valves in Tubes 
in which a Fluid is propelled upwards with 
an equable Force, would rather retard than 
promote its Progrefs; yet in Tubes where the 
Fluid does not afeend equably, but by Rea- 
fon of frequent Motions of the whole Ma- 
chine, it is fubjeft to many Agitations ; in this 
cafe Valves are of great Importance to check 
the Repercuffion and Regurgitation of the 
Fluid: And accordingly the allwifc Framer 
of animal Bodies has provided Valves in the 
I Veins, 
