THE CIRCULATION. 291 



The anacrotic pulse is seen in Bright's disease, where the peripheral 

 resistance is high, and in stenosis of aorta. 



The more gradual downstroke is interrupted by two completely 

 distinct elevations of secondary waves, though in the lowest part of 

 the descent there may be several minor inequalities. The more dis- 

 tinct of the two occurs at about the middle portion of the line of 

 descent. It represents the dicrotic wave; from its mode of origin it 

 is sometimes called the "recoil wave." Between the apex and the 

 dicrotic wave occurs the predicrotic, or tidal wave, while below the 

 dicrotic wave occurs the postdicrotic wave or waves, since there are 

 very frequently several. 



The line of ascent and the predicrotic wave are caused by systole, 



Fig. 94. Sphygmogram Magnified. (LAHOUSSE.) 



A, B, Correspond to the dilatation. B, D, A, Correspond to contraction of 

 artery. A, C, O, A, Measures the total duration of pulse. B, C, represents the 

 height of the pulse. /), Is the dicrotic pulse. 



while the dicrotic wave takes place during diastole. The postdicrotic 

 waves are a result of vascular tension. 



Origin of the Dicrotic Wave. At one time this wave was be- 

 lieved to have its origin in the periphery, but is now known to be 

 caused as follows: By ventricular systole there is projected into the 

 full aorta a mass of blood so that a positive wave is propagated from 

 the heart toward the periphery, where it becomes extinguished 

 among the smallest arterioles and capillaries. At the closure of the 

 semilunar valves, the arteries from having just been distended begin 

 to contract or recoil upon the contained blood, with the result that 

 this newly exerted pressure sets it into motion in two directions: 

 toward the heart and toward the periphery. In the latter direction 

 the passage is free until the capillaries are reached ; toward the heart 

 thp still closed semilunar valves are met with such force that there 



