1038 PHYSIOLOGY 



In a branching system of tubes, such as the arterial system, reflec- 

 tion of waves must take place at every dividing place. All the condi- 

 tions for the origin of reflected waves and interference of such waves 

 are present in the arterial system. It is impossible a priori, however, 

 to say whether any reflected wave will form a marked feature on the 

 pulse- tracing. It is possible that the multitudinous reflections which 

 must occur in every part of the arterial system may interfere with any 

 one to such an extent that they mutually annul each other. The 

 origin of any secondary wave in the pulse- tracing must therefore be 

 determined by experiment. 



To study the pulse more fully it is necessary to obtain a graphic 

 record of the expansion of the arteries, or, what comes to the same 

 thing, of the exact changes in pressure which produce this expansion. 

 The curve obtained with the mercurial manometer shows elevations 



FIG. 412. 



corresponding to the pulse ; but the instrument is far too sluggish 

 to record the finer variations of pressure. For this purpose a 

 manometer such as Hiirthle's, which has very little inertia, must be 

 used. The expansion 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 sphygmograph. Of the many forms of 

 sphygmographs, Marey's or Dudgeon's is perhaps the most con- 

 venient for clinical purposes. 



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

 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 writing lever I. The movements of the button b thus trans- 

 mitted 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 arrangement of the levers in this form of sphygmograph 

 is shown in Fig. 414, where F is the (adjustable) spring bearing by its button P 

 on the artery. The up-aiid-dowii 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, 



