INSTRUMENTS FOR INVESTIGATING THE PULSE. 135 



lengthwise on the forearm, where it is steadied by means of two short metallic 

 supports (S) and fastened with a tape, which must not be drawn too tight. The 

 apparatus is also provided with a secondary screw (H), which can be made to 

 act on the spring (A). If the screw is tightened the spring is compressed and 

 rendered shorter, less yielding and movable with greater difficulty; when the pres- 

 sure is entirely released, the spring (A) has free play, is more yielding and the 

 position of the pad (y) is higher. 



FIG. 43. Marey's Sphygmograph (Diagrammatic). 



Marey's Sphygmograph with Transmission of Air of which many modifications 

 have been made, for example by Knoll; Fig. 44 illustrates the modification de- 

 signed by Brondgeest and designated "pansphygmograph" is constructed on the 

 principle of the pneumatic telegraph. Two pairs of shallow metallic cups (S S 

 and S' S') so-called Upham's capsules are each pierced from below at their center 

 by a small tube. The ends of these tubes are connected with rubber tubes (K 

 and K') . Over the mouth of each of the four cups a delicate rubber membrane is 



7' 



FIG. 44. Brondgeest's Pansphygmograph Constructed on Upham's and Marey's Principle of the Propagation of 

 Movement through Air-containing Drums Covered with Elastic Membranes. The figure represents also 

 diagrammatically Marey's cardiograph. 



stretched and from the middle of each of the two rubber membranes S and S' 

 there projects a button-shaped process (p and p'), which is applied to the pulsating 

 artery and held in place by metallic arches B B', the extremities of which rest 

 on the surrounding skin. From the center of each of the other two rubber mem- 

 branes, which are directed horizontally upward, there projects a knife-edge, which 

 is applied close to the balancing center (h and h') of the delicate writing levers 

 Z and Z'. It is evident that any pressure applied to the buttons will cause a 



