2 3 8 



THE CIRCULATION OF THE BLOOD 



card moved by the clock-work of the instrument. 



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. 



FIG. 195. Diagram of the Lever of the Sphygmograph. 



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 bridge over the radial artery. Within this is a flexible bag, q, filled with water, 



FIG. 196. Dudgeon's Sphygmograph. 



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 hydro- 

 static 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 appropriate holder, and the pressure is raised to 



