50 THE CIRCULATION OF THE BLOOD 



the resistance offered in peripheral vessels. We judge the ten- 

 sion by the force necessary to obliterate the impulse. 



(3) Regularity, which tells whether the heart is regular in 

 either its force or rhythm. 



(4) Its strength, which tells as to the force with which the 

 heart is acting. 



(5) Its length, whether the beat is long or slow and continuous. 



FIG. 31. Dudgeon sphygmograph. 



(6) The condition of the vessel wall, whether sclerotic or not. 

 In the study of the pulse an instrument called the sphygmograph 

 is used, which receives the impulse from a beating artery and 

 transmits it by means of a finely adjusted lever to a smoked sur- 

 face of paper. Thus a graphic representation of the impulse is 

 given, the height to which the writing end of the lever goes denot- 

 ing the force of the impulse of the heart beat at the time of the 

 writing. 



