[ 46 ] 
C. 
As tb the Sphincter Mufclcs, they feem to be ah 
ways in the fame natural contractile State; and 
whenever they are ft retched out, by fame fuperior 
Power, they recover their ufual Dimenfions merely 
by their rcftitutive or elaftic Property. The fame 
may be faid of the Stomachy Uterus , Vefica , which 
contract by the fame means, into a narrower Capa- 
city, a$ foon as their Contents are diicharged. 
CL 
I (hall confine my Thoughts therefore to the Ac- 
tion of the Heart only, as being the moft perfect 
involuntary Mufcle. 
€ 11 . 
The Heart is a Vi feus which has given the Lite- 
rati a great deal of Trouble to find out its real 
Mechanifm, and the true Caufe of its regular Alter- 
nations of Contraction and Dilatation. I have of- 
tentimes laid open the Breaft of a Dog, and kept 
his Lungs playing with a Pair of Bellows, in order 
to obferve how regularly and alternately the Syftole 
and Diajlole , both of the Heart and its Auricles, 
followed each other; that is, when the Ventricles 
were contracted, the Auricles were dilated, and vice 
verfa ; ib that the Articles feem, in fome meafure, 
to act as Antagonifts to the Ventricles, and the re- 
fluent Blood may be of the fame Service to the Au- 
ricles. 
