922 



PHYSIOLOGY 



of the artery is registered by means of a lever, which, may be made to rest 

 more or less heavily upon the artery, and the movements of which are 

 recorded on a blackened surface. Such an instrument is called a sphygmo- 

 graph. Of the many forms of sphymographs, Marey's or Dudgeon's is 

 perhaps the most convenient for clinical purposes. 



The principle of Marey's sphygmograph is shown in Fig. 412. The button 6 is 

 adjusted so as to press on the radial artery. Its movements are transmitted to a lever 

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



FIG. 412. 



writing lever I. The movements of the button 6 thus transmitted to a point near the 

 axis of I 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. 413) is rather easier to use than Marey's, and is 

 therefore 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 moving along the slip of smoked paper on which the records are taken. The 



FIG. 413. Dudgeon's sphygmograph, showing its mode of application to 



the radial artery. 



arrangement of the levers in this form of sphygmograph is shown in Fig. 414, where r 

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

 movements 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. 



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 means 

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

 Frank's or Piper's. 



