228 



THE CIRCULATION OF THE BLOOD 



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 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 wrist by an appro- 

 priate 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. 



To manometer. 



FIG. 197. Diagrammatic Sectional Representation of the Sphygmometer. a, Box 

 by which the portion of the artery is covered; b, thin-walled india-rubber bag filled with 

 water, and communicating through tap, c, with the manometer and thick-walled rubber bag, 

 h; d, piston connected by rod, e, with recording lever,/; g, spiral spring, attached to axis of 

 lever, and by which the pressure in b, against the piston, d, is counterbalanced; k, skin and 

 subcutaneous tissue; m, end of radius seen in section; n, radial artery seen in section. 

 (Roy and Adami.) 



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

 sphygmograph, called a sphymogram, 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, A, 

 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 re- 

 mote; 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 uninter- 

 rupted fall; it is usually marked about half-way by a distinct notch, C, called 

 the dicrotic notch, followed immediately by a second more or less marked 

 ascent of the lever called the dicrotic wave, D. Not infrequently there is 



