CHAP, iv.] 



THE VASCULAR MECHANISM. 



167 



appears on the ascending portion of the main curve as in Fig. 30 

 and Fig. 33 : such a curve is spoken of as "anacrotic." 



Of these secondary elevations, the most frequent, conspicuous 

 and important is the one which appears some way down on the 

 descending limb and is marked C on most of the curves. It is 

 more or less distinctly visible on all sphygmographic tracings and 

 may be seen in sphygmograms of the aorta as well as of other 

 arteries. Sometimes it is so slight as to be hardly discernible; at 

 other times it may be so marked as to give rise to a really double 

 pulse (Fig. 31), i.e. a pulse which can be felt as double by the finger ; 

 hence it has been called the dicrotic elevation or the dicrotic wave, 

 the notch preceding the elevation being spoken of as the "dicrotic 



FlG. 31. TWO GBADES OF MARKED DICBOTISM IN RADIAL PULSE OF MAN. 



(Typhoid Fever.) 



notch." Neither it nor any other secondary elevations can be recog- 

 nised in the tracings of blood-pressure taken with a manometer. 

 This may be explained by the fact that the movements of the 

 mercury column are too sluggish to reproduce these finer variations; 

 but dicrotism is also conspicuous by its absence in the tracings 

 given by more delicately responsive instruments. Moreover, when 

 the normal pulse is felt by the finger, most persons find themselves 

 unable to detect any dicrotism. Hence some have been led to 



FlG. 32. NOBMAL PULSE-CURVE IN THE AORTA FROM THE DOG. 



maintain that this and the other secondary elevations do not really 

 exist in the normal pulse. But it seems difficult to maintain this 

 view in face of the experiment of Landois, in which the tracing 

 obtained by allowing the blood to spirt directly from an opened 

 small artery, such as the dorsalis pedis, upon a recording surface, 

 shewed in an unmistakeable manner the existence of the dicrotic 

 wave. 



