( ) 
idly, I conc^ive, that when^the Branches of the Arteries 
begin to grow very finall, tbey fend cffreveni! dufts. whofe 
Orifices are ot different Dimenfions, Tiicfe Dad« are of 2 
forts. 
Tk Firfi of thefe, which in the fame Artery are always 
fmaller than the 2d, pafs immediately from the Artery, and 
open into the Vcifis. 
The Secend which pafs off nearer to the extremity of the 
Arteries^ unite and carry off a Liquor from theMafs of Blood 
for particular ends in feveral parts ot the Body. It is to be 
obferved, tjiat in one cafe the fecond fort are only to be 
found.- 
I imagine, that a thin Fluid may be fecern'd from a thick 
one, when the Orifices of the fecretory Duds are lb fmali, as 
to admit no other but that thin Fluid, and that at the fame 
time the remaining parts of the Blood which are thicker, 
continue their courfe in the VeffeL 
Again, I imagine that a thick Fluid may be feccrn'd, whert 
the thinner parts are carried off fome other way, fo that the 
Liquor to be fecerned will be the thinneftof the remaining 
Mafs. 
Upon thefe principles I think it will be eafie to cxplaiii 
the Dodrine of Secretions. And now In the fir (i place Let 
us examine how the thinner Secretions are performed : As 
for inftance, the Urine. 
When the Blood by the Contraftiorl of the Heart is puflit 
into the Arteries, they are dilated, which again contrafting 
themfelves puQi it forward into all the parts of the Body, 
and amongfl: the reft into the Ramifications of the Arteries 
of which the Glands of the Kid^/ejis are compGs'd. By this 
means the Blood paffes by the Orifices of the Secretory duiis ^ 
when thefe Arteries contraft themfelves they prefs the Blood 
and force the thinner parts into the Orifices of thofe Dufts, 
(which will admit no Thicket Fluid ) and carry it toward 
the Pc///^ and the remaining part of the Blood, into the 
Veins, by them to be carry 'd back to the Heart, Thus % 
Tbiu 
