162 THE CIRCULATION. 



every artery at the same moment, although the maximum 

 effect of distension, which alone we feel with the finger, is 

 attained more slowly in proportion to the distance of the 

 vessel from the heart. There can be no doubt, therefore, 

 that the contractile force of the ventricle is almost 

 instantaneously propagated through the whole arterial 

 system ; and if we consider that the fluid blood, practically 

 incompressible, contained in the arteries, may be compared 

 to a quasi-solid trunk beginning at the heart, and branching 

 into all parts of the body, it is evident that a force applied 

 at the beginning of the trunk will be immediately propa- 

 gated through all the branches, and, if sufficiently strong, 

 will produce movement at all parts. And this force is 

 applied when fresh blood is forced into the aorta by the left 

 ventricle, and the effect is without doubt instantaneously 

 propagated through the continuous and branching column 

 of fluid in the arteries. These vessels being elastic, how- 

 ever, the force of the ventricle is employed, not only in the 

 instantaneous propagation of an impulse, but in part also 

 in distending the vessels along which the blood, wave-like, 

 rolls on to complete the pulse which has already com- 

 menced in all the arteries at the same moment. 



Returning now to the consideration of the pulse-tracings 

 (p. 159), it may be remarked that, in each, the up-stroke 

 corresponds with the period during which the ventricle is 

 contracting; the down-stroke, with the interval between 

 its contractions, or in other words with the recoil, after 

 distension, of the elastic arteries. In the large arteries, 

 when at least there is much loss of tone, the up-stroke is 

 double, as in fig. 46, the instantaneous propagation of the 

 force of contraction of the left ventricle, or percussion- 

 impulse, as it is termed by Dr. Sanderson, being sufficiently 

 strong to jerk up the lever for an instant, while the wave 

 of blood, rather more slowly propagated from the ventricle, 

 catches it, so to speak, as it begins to fall, and again 

 slightly raises it. 



