128 THE CIRCULATION. 



teries than can be discharged by the ventricle at each contrac- 

 tion. But the quantity necessary for such a purpose is less 

 than might be supposed. Injections of the arteries prove that, 

 including all down to those of about one-eighth of a line in 

 diameter, they do not contain on an average more than one 

 and a half pints of fluid, even when distended. There can be 

 no doubt, therefore, that the three or four ounces which the 

 ventricle is supposed to discharge at each contraction, being 

 added to that which already fills the arteries, would be suffi- 

 cient to distend them all. 



A distinction must be carefully made between the passage 

 of the wave along the arteries, and the velocity of the stream 

 (p. 131) of blood. Both wave and current are present; but the 

 rates at which they travel are very different, that of the wave 

 being twenty or thirty times as great as that of the current. 



Returning now to the consideration of the pulse-tracings 

 (p. 126), it may be remarked that, in each, the up-stroke cor- 

 responds with the period during which the ventricle is con- 

 tracting ; the down-stroke, with the interval between its con- 

 tractions, or in other words with the recoil, after distension, 

 of the elastic arteries. In the large arteries, when at least 

 there is much loss of tone, the up-stroke is double, the almost 

 instantaneous propagation of the force of contraction of the 

 left ventricle along the column of blood in the arteries, or the 

 percussion impulse, as it is termed by Dr. Sanderson, being 

 sufficiently strong to jerk up the lever for an instant, while the 

 wave of blood, rather more slowly propagated from the ven- 

 tricle, catches it, so to speak, as it begins to fall, and again 

 slightly raises it. 



In the radial artery tracings, on the other hand, we see that 

 the up-stroke. is single. In this case the percussion-impulse is 

 not sufficiently strong to jerk up the lever and produce an 

 effect distinct from that of the systolic wave which immedi- 

 ately follows it, and which continues and completes the dis- 

 tension. In cases of feeble arterial tension, however, the per- 

 cussion-impulse may be traced by the sphygmograph, not only 

 in the carotid pulse, but to a less extent in the radial also (as 

 in Fig. 46). 



In looking now at the down-stroke (Fig. 44) in the tracings, 

 we see that in the case of an artery with deficient tone, it is in- 

 terrupted by a well-marked notch, or in other words, that the 

 descent is interrupted by a slight uprising. There are indica- 

 tions also of slighter irregularities or vibrations during the fall 

 of the lever ; while these are alone to be seen in the pulse of 

 health, or in other words, when the walls of the artery are of 

 good tone (Fig. 45). In some cases of disease the reascent is 



