966 



PHYSIOLOGY 



w. The screw on this works on a small cogged wheel at o, which is also the axis of the 

 writing lever I. The movements of the button b thus transmitted to a point near the 

 axis of / are reproduced by this lever highly magnified, and as such are recorded on a 

 blackened surface. The pressure on the artery can be adjusted by means of a screw. 



Dudgeon's sphygmograph (Fig. 423) is rather easier to use than Marey's, and is there- 

 fore largely employed for clinical purposes. It is provided with a dial by which the 

 pressure on the artery can be graduated, and has a small clockwork arrangement for 



FIG. 422. 



moving, along the slip of smoked paper on which the records are taken. The arrange- 

 ment of the levers in this form of sphygmograph is shown in Fig. 424, where F is the 

 (adjustable) spring bearing by its button P on the artery. The up-and-down move- 

 ments of P are transmitted to s, being much magnified and converted into side-to-side 

 movements. The point of s rests on the blackened surface represented in section at A, 

 and scratches on this, when moving, a magnified record of the expansion of the artery 

 under the knob P. 



Fia. 423. Dudgeon's sphygmograph, showing its mode of application to 

 the radial artery. 



In all these sphygmographs, even the most perfect, the moving parts have a con- 

 siderable amount of inertia, so that the curve they give is always more or less deformed. 

 This fact must be borne in mind when comparing the pulse curves obtained by inc.-ms 

 of a sphygmograph with those given by the more perfect forms of manometer, such as 

 Frank's or Piper's. 



Either form of sphygmograph is generally applied to the radial artery 

 since this U near the surface and is supported by bone, and the arm is well 

 adapted for the application of the sphygmograph. The pulse curve obtained 

 by means of a sphygmograph varies according to the artery employed and 

 the force with which^the lever pn-s<<>s on the artery, but all the curves 

 present the saine'genexa] features. 



