122 OP VITAL MOTION. 



removed, without doing any injury to the vessels, we 

 may be convinced of this; for at each diastole the 

 organ becomes turgid with blood, not merely in the 

 cavity, but in every vessel of the coats ; while at the 

 systole the walls are pale and the cavity emptied. 



It is possible, also, that there may be a pulsatile 

 generation of force in the pulmonary and some other 

 tissues, where from the looseness of the structure, 

 and the comparative absence of the pressure or sup- 

 port of surrounding parts, the flow of blood may be 

 intermittent rather than continuous. Any pulses of 

 vascular force originating in this way may react 

 with the pulse of nervous influence (either through 

 the nervous circle, or else by direct conduction 

 through contiguous tissues), and with the pulses of 

 vascular force belonging to the coronary system, in 

 the induction of the diastole ; while the common pause 

 in the generation of force in all these quarters which 

 is necessitated by the cessation of the jet of blood 

 into the arterial system, may bring about the systole. 

 It is possible, also, that the blood within the cavities 

 of the heart, in so far as its surface is concerned, 

 may act upon the lining membrane, just as it does 

 upon the coats of the capillaries; but this action 

 must be very insignificant when compared with the 

 immense surface acted upon in the walls of the heart 

 itself. Moreover, on the one side of the heart the 

 cavities contain venous blood, and on the other side, 



