306 MANUAL OF PHYSIOLOGY. 



latiou, or (2) a wave reflected from the periphery. If the former, 

 it should be less marked than the predicrotic, which by this theory 

 is said to be the first wave of oscillation, for each succeeding os- 

 cillation is less than its forerunner. But, as already mentioned, 

 the dicrotic is invariably the larger. 



There are many reasons why it cannot be a wave of reflection 

 from the periphery of the arterial tree; viz.: 1. Its curve is not 

 nearer the primary wave when the peripheral vessels are ap- 

 proached. 2. The arterioles which form the peripheral resistance 

 are at too irregular distances to give one definite wave of reflec- 

 tion. 3. It is seen in the spurting of an artery cut off from the 

 periphery. 4. It increases with the greater elasticity and low ten- 

 sion, while the reflected waves diminish. 



The dicrotic notch depends upon a negative wave caused by the 

 sudden stop of inflow and the momentary reflux of blood before 

 the valves are closed ; 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 condi- 

 tions which increase the dicrotism viz., (1) sharp, strong systole, 

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

 and closure; and, on the other hand, the conditions which di- 

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

 efficiency of the aortic valves, and (2) a rigid calcareous condi- 

 tion 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 

 a 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 equidistauce of the 

 derived arterioles enables the reflected waves to have considerable 

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

 sponding to the closed tube) a positive wave centripetal is re- 

 flected and is added to the pulse- wave so as to diminish the di- 



