[ 29 ] 
Let us therefore inquire after the Agents which are 
capable of producing fuch furprifing ‘Phenomena* 
and at the fame time fhall be confiftent with every 
other Operation in the Animal Oeconomy. 
LXVI. 
; i ;■ ;* '■/'-* ' V - * * " * **' w * ' '*■ '• *• * • ' 
From what has been faid it appears, that Contrac* 
tion, or mufcular Adion, does not depend upon any 
Fluid dilating or diftending the Fibres $ but, on the 
contrary, they fhrink up and grow lefs. The in- 
ftantaneous Alternations from Conftridion to Dila- 
tation, and vice verfa , manifeftly difeover that muf- 
cular Motion cannot be caufed by fuch Juices as 
the Bloody Lymph , and fuch-like,- but it muft be 
fromfome more fubtile athereal Matter, which may 
be mix’d with the Blood in general, and fecreted 
from it by the Glands of the Brain. 
LXVII. 
Let us but carefully confider the exquifite Appa- 
ratus of the Brain, the Quantity of Blood it receives, 
the infinite Number of its excretory Duds, and the 
great Divifibility and Subtilty of Matter, and we 
fhall find great Reafon to conclude that there is a 
moft fubtil, ethereal, volatile Fluid, of great Force 
and Elafticity, perpetually fecreted from the Blood, 
by the Glands of the Brain, and continually flying 
into the Nerves, for the Ufes of mufcular Motion, 
and many other great Purpofes of the Animal Oeco* 
nomy» 
LVIIL 
