312 MANUAL OF PHYSIOLOGY. 



during the closure of the valves; and the dicrotic crest is no 

 doubt produced by the closure of the aortic valves, at which 

 moment the sudden check given to the reflux of the blood column 

 causes a positive centrifugal wave to follow the primary wave of 

 the pulse. 



The view that the reflux of blood and the closure of the valves 

 produce the dicrotic wave is supported by the fact that the con- 

 ditions which increase the dicrotism viz., (1) sharp, strong sys- 

 tole, (2) low tension, and (3) perfect resiliency promote the 

 recoil and closure ; and, on the other hand, the conditions which 

 diminish the dicrotic wave in the most marked degree, are (1) 



FIG. 141. 



I. Scheme of Normal Pulse Curve: a, entrance of ventricular stream into the aorta, 

 the lever is jerked too high to reach * ; a b shows real summit of waves ; 6, point at which 

 stream from ventricle ceases; c, negative wave caused by (1) sudden cessation of inflow 

 and slight reflux of blood; d, point of closure of aortic valves; e. positive wave from 

 valves (dicrotic wave). The time may be measured on abscissa at a' b' d'. 



II. Scheme of High Tension Pulse Curve : A, curve of radial pulse, which is the resultant 

 of positive reflected wave, c, added to the primary curve B. 



III. Scheme of Low Tension Pulse Curve: A, radial pulse curve, which is the resultant 

 of the negative reflectant wave c, subtracted from the primary wave B. (After Grashey). 



inefficiency of the aortic valves, and (2) a rigid calcareous con- 

 dition of the arteries. 



It can be shown by means of an elastic tube, fitted with a 

 suitable pump and sphygmographs, that when its outlet is closed 

 & positive wave is reflected from the distal end back to the pump, 

 and when it is open a negative centripetal wave is reflected. This 

 fact assists us in explaining the variations in the character of the 

 pulse curve of the radial artery where the equidistance of the 

 derived arterioles enables the reflected waves to have considerable 

 effect. When the arterioles are constricted (a condition corre- 



