chap, xxi.] THE SPHYGMOGRAPH. 233 



The ctromograpli of Lortet and Chauveau em- 

 bodies the same idea as that of a recording instru- 

 ment. It consists of a tube, represented in the figure 

 (Fig. Ill) in cross section, T, which is interposed in 

 the course of the blood-vessel. A 

 square opening on one side of the 

 tube is closed by a plate of caout- 

 chouc. Projecting into the tube 

 and piercing the caoutchouc is the 

 flattened end s' of a light lever, the Fig. ill. Dromo- 



i . -i . T f 1 ' i 1 graph of Lortec and 



long thin end s 01 which is outside chauveau. 

 the tube, and records movements 

 on a blackened surface. The lever is deflected by the 

 current of blood, and a curve obtained on the moving 

 blackened surface. The extent of the deviation can 

 also be measured by a scale attached to the instrument 

 in the direction of the axis of the tube. . From the 

 upper wall of the tube rises another tube provided 

 with a stop-cock, which can be placed in connection 

 with a sphygmoscope of Marey (page 234), and by it a 

 record of pulse movements is obtained on the same 

 blackened surface as that of the velocity. One great 

 advantage of this instrument is that it records varia- 

 tions of velocity, and these variations can be com- 

 pared with the movements of the heart, etc. 



The spliygiwograpli is an instrument for obtain- 

 ing tracings of the movements in arteries which consti- 

 tute the pulse. While the kymographion records varia- 

 tions of blood pressure, the sphygmograph may be said 

 to record variations of arterial tension. It was originally 

 devised by Yierordt, but in the form given to it by him 

 it was extremely cumbersome. It has been modified 

 and improved by Marey, and is shown applied in Fig. 

 112. An ivory knob on the end of a steel spring is 

 placed over the artery for receiving its movements. 

 The tension of the spring is regulated by a screw. A 

 fine screw b rises from the knob, and has pressed 



