126 



THE CIRCULATION. 



Before proceeding to consider the formation of the pulse, as 

 shown by these tracings, it is necessary to consider what are 

 the elements combined to produce it. 



Fig. 44. 



FIG. 44. Pulse-tracing of radial artery, somewhat deficient in tone. 



FIG. 45. Firm and long pulse of vigorous health. 



FIG. 46. Pulse-tracing of radial artery, with double apex. 



The above tracings are taken from Dr. Sanderson's work " On the Sphygmograph.' 1 



The heart at regular intervals discharges a certain quantity 

 of blood into the arteries and their branches, already filled, 

 though not distended to the utmost, with fluid. This fresh 

 quantity of blood obtains entrance by the yielding of the 

 artery's elastic walls, and, on the cessation of the propelling 

 force, and when these walls recoil, the blood is prevented from 

 returning into the ventricle whence it is issued, by the shut- 

 ting of the semilunar valves in the manner before described 

 (p. 103). The pressure, therefore, which is exercised on the 

 blood by the contracting arterial walls, will cause it to travel 

 in a direction away from the heart, or, in other words, towards 

 the capillaries and veins. 



It was formerly supposed that the pulse was caused not by 

 the direct action of the ventricle, but by the propagation of a 

 wave in consequence of the elastic recoil of the large arteries, 

 after their distension ; and successive acts of dilatation and 

 recoil, extending along the arteries in the direction of the cir- 

 culation, were supposed to account for the latter appearance 

 of the pulse in the vessels most distant from the heart. The 

 fact, however, that the pulse is perceptible in every part of the 

 arterial system previous to the occurrence of the second sound 

 of the heart, that is, previous to the closure of the aortic 



