140 HANDBOOK OF PHYSIOLOGY. 



or more sphygmographs upon such a system of tubes at increasing dis- 

 tances from the pump, we may demonstrate that the rise of the lever 

 commences first in that nearest the pump, and is higher and more sud- 

 den, while at a longer distance from the pump the wave is less marked, 

 and a little later. So in the arteries of the body the wave of blood 

 gradually gets less and less as we approach the periphery of the arterial 

 system, and is lost in the capillaries. By the sudden injection of blood 

 two distinct waves are produced, which are called the tidal and percus- 



Fio. 126. Diagram of the formation of the pulse-tracing. A, percussion wave; B, tidal wave; 

 c, dicrotic wave. (Mahomed.) 



sion waves. The tidal wave occurs whenever fluid is injected into an 

 elastic tube (Fig. 126, B), and is due to the expansion of the tube and its 

 more gradual collapse. The percussion wave occurs (Fig. 126, A) when 

 the impulse imparted to the fluid is more sudden; this causes an abrupt 



FIG. 127. -Pulse-tracing of radial artery, somewhat deficient in tone. (Sanderson.) 



upstroke of the lever, which then falls until it is again caught up 

 perhaps by the tidal wave which begins at the same time, but is not so 

 quick. 



In this way, generally speaking, the apex of the upstroke is double; 

 the second upstroke, the so-called pre-dicrotic elevation of the lever, 

 representing the tidal wave. The double apex is most marked in trac- 

 ing from large arteries, especially when their tone is deficient. In 

 tracings, on the other hand, from arteries of medium size, e. g., the 



