MOVEMENT OF THE BLOOD IN THE ARTERIES. 



331 



tions may make their appearance. The presence of the tidal wave in a 

 Sphygmographic tracing indicates, according to Galabin, high tension, di- 

 minished elasticity, and long, laborious action of the heart. It is typically 

 seen in cases of Bright's disease. A second wave that appears in the period 

 of descent is termed the dicrotic wave. The cause of this is not accurately 

 known. It has been held to be a reflection from the periphery, but tracings 



FIG. 131. 



FIG.. 132. 



FIG. 131. This figure shows a modification of Marey's Sphygmograph, by means of which the amount 

 of pressure exerted on the artery can be approximative!)- measured. A, registering lever ; D, knife-edge 

 on which it rests; K N, spring placed over the artery ; T, screw regulating the pressure, the amount 

 of which is ascertained by the index B. 



FIG. 132. Diagram to illustrate the relation of the sphygmographic tracing to the true pulse wave. 

 The thick line represents the true pulse wave, the thin Hue the sphygmographic tracing, the dotted 

 line the tracing drawn by a sphygmograph having a secondary spring to keep down the lever, a, tidal 

 or "first secondary wave ;" 6, dicrotic or "principal secondary wave;" c, d, two small waves into which 

 the tidal wave may be broken by the action of the secondary spring. 



obtained by Galabin show, that in cases where it is well marked, it is not 

 nearer the primary wave in tracings taken from the foot than in those taken 

 from the femoral artery, and he considers it to be due to the inertia of the 

 arterial walls, the acquired velocity of their expansion with each influx of 

 blood passing a little beyond the point of equilibrium, and again passing 

 within it by recoil, so that a series of oscillations occur about the point of 

 equilibrium. The feebler the tension of the vessels the more marked is the 

 dicrotism of the pulse. It is perfectly obvious that the fulness of the pulse, 

 or in other words the amplitude of the pulsation, is in inverse ratio to the 

 tension of the walls of the vessel; whilst tli hardness of the pulse is indica- 

 tive of arterial tension, and may be produced either by the heart acting with 

 great force and injecting more blood than the arteries can discharge through 

 the capillaries, or by the contraction of the capillaries themselves preventing 

 the escape of the blood from the arteries into the veins. M. Marey has 

 clearly shown how these two conditions of the arterial system may be in- 

 duced by acting upon the capillaries alone, and either facilitating the pas- 

 sage of the blood through them, or, on the contrary, rendering it more diffi- 

 cult. Thus the tracing obtained by his Sphygmograph, after exposure to a 

 cold bath of one minute's duration, is shown in Fig. 133. It is that of a 



