PULSE-TRACIXGS. 1 5 1 



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. 



In the radial artery tracings, on the other hand, we see 

 that the up-stroke is 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 continues and 

 completes the distension. In cases of feeble arterial 

 tension, however, the percussion-impulse may be traced 

 by the sphygmograph, not only in the carotid pulse, but 

 to a less extent in the radial also (fig. 46). 



In looking now at the down-stroke (fig. 44) in the 

 tracings, we see that in the case of an artery with defi- 

 cient tone, it is interrupted by a well-marked notch, or, in 

 other words, that the descent is interrupted by a slight 

 uprising. There are indications also of slighter irregu- 

 larities or vibrations during the fall of the lever ; while 

 these are alone to be seen in the pulse of health;, or, in 

 other words, when the walls of the artery are of good 

 tone (fig. 45). In some cases of disease the re-ascent is 

 so considerable as to be perceptible to the finger, and this 

 double beat has received the technical name of "dicrotous" 

 pulse. As a diseased condition this has long been recog- 

 nized, but it is only since the invention of the sphygmo- 

 graph that it has been found to belong in a certain degree 

 to the normal pulse also. 



Various theories have been framed to account for the 

 dicrotism of the pulse. By some, it is supposed to be due 

 to the aortic valves, the sudden closure of which stops the 

 incipient regurgitation of blood into the ventricle, and 

 causes a momentary rebound throughout the arterial 

 system ; while Dr. Sanderson considers it to be caused by 

 a kind of rebound from the periphery rather than from 

 the central part of the circulating apparatus. 



