THE SPHYGMOGRAPH 



227 



The spring is adjusted to the proper tension to follow the movements of the 

 artery wall during the pulse wave. The sphygmograph is bound on the 

 wrist while taking a record. 



It is evident that the beating of the pulse will cause an up-and-down 



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



movement of the lever, the pen of which will write the effect on a smoked 

 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. 196. Dudgeon's 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, 

 b, filled with water, and connected by a T-lube 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 



