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Mufcles, is the fame as when I do it voluntarily : 
Therefore by any external or adventitious Force, the 
Blood and Spirits will be derived upon the Part thus 
forced into Action. 
But all the natural and vital Parts have fuch an 
•external or adventitious Force continually aiding upon 
them. In the Prim# Kite the Weight and other 
Qualities of our Food and Drink, mixed with Air 
and Bile, excite the periftaltic Motion, as necelfarily 
as the Weight of a Clock, or Spring of a Watch 
wound up, keeps the Wheels and Pendulum, c"Y, 
in Motion. 
The Chyle forced from thence, together with the 
Blood returning into the Heart, as necelfarily fet its 
elaftic Springs at work, and the fame Blood and 
Chyle forced into the Arteries by it, make their 
Diajtole and following Syjtole inavoidable. 
The Air by its Elafticity, and the whole Weight 
of the Atmofphere, forceth itfelf into the elaftic 
Pipes and Velicles of the Lungs, and dilates them ; 
which by their Elafticity and Mechanifm, aflifted 
by various Mufcles, and the Ribs and Cartilages 
of the Thorax , as necelfarily repel it in Expi- 
ration. 
It is therefore evident, that all thefe natural and 
vital Parts are a&ed upon, and fet at Work by an 
external adventitious and irrefiftible Force, continu- 
ally exciting them whether we will or not, whether 
awake or afleep ; therefore the Blood and remaining 
Spirits after Labour, will be mechanically and ne- 
ceffarily led to all thefe Parts that are thus forced in- 
to Action at all times, but efpecially moft regularly 
and copioufly in Sleep, when all external Objects 
C ceafe 
