THE CIRCULATION OF THE BLOOD. 



3*9 



viz., a line of ascent from a to b, and a line of descent from b to d (Fig. 

 152). In normal tracings the former is almost vertical and caused by 

 the sudden expansion of the artery immediately following the ventric- 

 ular contraction; the latter *is in general oblique, due to the recoil of 

 the arterial walls, occupies a longer period of time, and is marked 



FIG. 151. VON FREY'S SPHYGMOGRAPH. G. S. Metal framework. P. Button 

 attached to spring. F. Vertical rod. U. Clock-work which turns the recording 

 cylinder. VI. Time marker. 



by several elevations and depressions, both of which indicate that the 

 restoration to equilibrium is neither immediate nor uncomplicated. 

 One of these elevations is quite constant and known as the dicrotic 

 wave, c; the depression or notch just preceding it is known as the 

 dicrotic notch. Pre- and post-dicrotic waves are not infrequently 

 present. The summit is generally 

 sharp and pointed. 



The vertical direction of the line of 

 ascent is taken as an indication that 

 the arterial walls expand readily, that 

 the blood is discharged quickly, and 

 that the ventricular action is not im- 

 peded. An oblique direction of the 

 line of ascent is an indication that the 

 reverse conditions obtain. The height 



varies inversely as the arterial pressure, other things being equal; 

 being high with a low pressure, and low with a high pressure. 



The dicrotic wave shows that a second expansion wave is devel- 

 oped which interrupts temporarily the recoil of the arterial walls. 



FIG. 152. THE PULSE CURVE OR 

 SPHYGMOGRAM. 



