146 HAND-BOOK OF PHYSIOLOGY. 



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

 the second upstroke, the so-called predicrotic elevation of the lever, 

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

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



FIG. 128. Pulse-tracing of radial artery, somewhat deficient in tone. (Sanderson.) 



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

 upstroke is usually single. In this case the percussion-impulse is not 

 sufficiently strong to jerk up the lever and produce an effect distinct 

 from that of the systolic wave which immediately follows it, and which 



FIG. 129. Pulse-tracing of radial artery, with double apex. (Sanderson.) 



continues and completes the distension. In cases of feeble arterial ten- 

 sion, however, the percussion-impulse may be traced by the sphygmo- 

 graph, not only in the carotid pulse, but to a less extent in the radial also 

 (Fig. 129). 



The interruptions in the downstroke are called the katacrotic waves, 

 to distinguish them from an interruption in the upstroke, called the an- 

 acrotic wave, which is occasionally met with in cases in which the predi- 

 crotic or tidal wave is higher than the percussion wave. 



FIG. 130. Anacrotic pulse from a case of aortic aneurism. A, anacrotic wave (or percussion 

 wave). B, tidal or predicrotic wave, continued rise in tension (or higher tidal wave). 



There is considerable difference of opinion as to whether the dicrotic 

 wave is present in health generally, and also as to its cause. The balance 

 of opinion appears to be in favor of the belief of its presence in health, 

 although it may be very faint; while, at any rate, in certain conditions 

 not necessarily diseased, it becomes so marked as to be quite plain to the 

 unaided finger. Such a pulse is called dicrotic. Sometimes the dicrotic rise 

 exceeds the initial upstroke, and the pulse is then called liy per dicrotic. 



As to the cause of dicrotism, one opinion is that it is due to a recovery 



