146 



THE CIRCULATION. 



the beat of any two arteries never exceeds probably ^ to ^ 

 of a second. 



A great deal of light has been thrown on what may 

 be called the form of the pulse by the sphygmograph (figs. 

 42 and 43). The principle on which the sphygmograph 

 acts is very simple (see fig. 42). The small button re- 

 places the finger in the ordinary act of taking the pulse, 

 and is made to rest lightly on the artery, the pulsations of 

 which it is desired to investigate. The up-and-down 

 movement of the button is communicated to the lever, to 

 the hinder end of which is attached a slight spring, which 

 allows the lever to move up, at the same time that it is 



Fig. 42.* 



Fiy. 43-t 



just strong enough to resist its making any sudden jerk, 

 and in the interval of the beats also to assist in bringing it 



* Fig. 42. 

 t Fig. 43- 



Diagram of the mode of action of the Sphygmograph. 

 The Sphygmograph applied to the arm. 



