206 THE CIRCULATION OF THE BLOOD 



Thus a tracing of the pulse is obtained, and in this way much more deli- 

 cate changes can be seen than can be felt by the mere application of the finger. 



The principle of the sphygmometer of Roy and Adami is shown in the diagram, figure 



197. 



The apparatus consists of a box, a, which is moulded to fit over the end of the radius 

 so as to oriage over the radial artery. Within this is a flexible bag, b, filled with water, 

 and connected by a T-tube with a rubber bag, h, and 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 b is a flat button, d, 

 which by means of a short light rod, e, communicates the movement of b to the lever, /. 

 At the axis of rotation of this lever is a spiral watch-spring, g, which can be tightened at 

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



FIG. 196. Dudgeon's Sphygmograph. 



pressure within the box. The movements of the lever are recorded upon a piece of black- 

 ened glazed paper made to move in a vertical direction past it. When in use, the box 

 is fixed upon the wrist 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. 



Sphygmogram. The tracing of the pulse obtained by the use of 

 the sphygmograph, called a sphygmogram, differs somewhat according to 

 the artery from which it is taken, but its general characters are much the 

 same in all cases. It consists of a sudden upstroke, or anacrotic limb, figure 

 198,^4, which is somewhat 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 or catacrotic limb, B, less abrupt, and 

 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, 



