BLOOD VESSELS 



43& 



passes any point in an artery the shape of the wave may be 

 deduced from the tracing. 



This may be done by any of the various forms of 

 sphygmograph (fig. 185), {Practical Physiology). 



Such a tracing is not a true picture of the wave, but 

 simply of the eifect of the wave on one point of the arterial 

 wall. Its apparent length depends upon the rate at which 

 the recording surface is travelling, and not upon the lengtli 

 of the wave. 



Its apparent height depends (i.) upon the length of the 



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Fig. 186. — Three Sphygmographic Tracings made from the Radial Artery of 

 a healthy man in the course of one hour without removing the 

 sphygniograph. 1 was made immediately after muscular exercise ; 2 

 was made after sitting still for half an hour ; and 3, after an hour. 



recording lever, (ii.) upon the resistance offered by the instru- 

 ment, (iii.) upon the degree of pressure with which the instru- 

 ment is applied to the artery, and (iv.) on the thickness of 

 the arterial wall. 



Such a trace (figs. 184 and 186) shows — 



ist. That the pulse waves generally follow one another 

 without any interval. 



2ncZ. That the rise of the wave is much more abrupt 

 than the fall. 



37tZ. That there are one or more secondary waves upon 

 the descent of the primary wave. 



