THE CIRCULATION OF THE BLOOD. 219 



mercurial manometer. The fluid in the box may be raised to any desired 

 pressure, and may then be shut off by tap (c) . At the upper part of the box is 

 a circular opening, and resting upon (6) is a flat button (d) , which by means 

 of a short light rod(e) communicates the movement of (5) to the lever(/). To 

 the axis of rotation of this lever is a spiral watch-spring (g) which can be tight- 

 ened at will, so that the lever can be made to take a vertical position at any 

 desired hydrostatic pressure within the box. The movements of the lever are 

 recorded upon a piece of blackened glazed paper made to move in a vertical 

 direction past it. When in use, the box is fixed upon the end of the radius by 

 an appropriate holder, and the pressure is raised to any desired height to which 

 the lever is adapted by tightening or slackening the spring. The tap (c) is 

 then closed. The pressure within the box acts in all directions, and is correctly 

 indicated by the manometer. 



The tracing of the pulse (sphygmogram), obtained by the use of 

 the sphygmograph, differs somewhat according to the artery upon which 

 it is applied, but its general characters are much the same in all cases. 

 It consists of : A sudden upstroke (fig. 184, A), which is somewhat 



Fig. 184. Diagram of pulse tracing. A, Up-stroke; B, down-stroke; c, pre-dicrotic wave; D, di- 



crotic; E, post-dicrotic wave. 



higher and more abrupt in the pulse of the carotid and of other arteries 

 near the heart than in the radial and other arteries more remote; and 

 a gradual decline (B), less abrupt, and therefore taking a longer time 

 than (A). It is seldom, however, that the decline is an uninterrupted 

 fall; it is usually marked about half-way by a distinct notch (c), called 

 the dicrotic notch, which is caused by a second more or less marked as- 

 cent of the lever at that point and by a second wave called the dicrotic 

 wave (D) ; not unfrequently there is also soon after the commencement 

 of the descent a slight ascent previous to the dicrotic notch: this is 

 called the pre-dicrotic wave (c), and in addition there may be one or 

 more- slight ascents after the dicrotic, called post-dicrotic (E). 



The interruptions in the downstroke are called the Icatacrotic waves, 

 to distinguish them from an interruption in the upstroke, the anacrotic 

 wave, which is sometimes met with. 



The explanation of these tracings presents some difficulties, not, 

 however, as regards the two primary factors, viz., the upstroke and 

 downstroke, because they are universally taken to mean the sudden in- 



