THE CIRCULATION 149 



are so delicately constructed that they readily respond 

 when the pressure on one side rises above that on the 

 other. As soon as the aortic pressure rises above the 

 ventricular the valves close. At. the moment this 

 happens the valves are supported by the hard, con- 

 tracted ventricular walls. The withdrawal of the 

 support by the sudden relaxation of these walls will 

 tend to produce a negative pressure wave in the arterial 

 system. But this negative wave is stopped by the sudden 

 stretching of the aortic valves, which, on losing their firm 

 support, have now themselves to bear the resistance of 

 the arterial pressure. This sudden checking of the 

 negative wave starts a second positive wave, which is 

 propagated through the arterial system as the dicrotic 

 wave.' 



This is not the place to describe all the modifications 

 of the pulse curve which may occur in various states of 

 health and disease. It must suffice to point out some of 

 the more general clinical applications which follow from 

 the exposition which has been given of the way in which 

 its different parts are produced. 



The ascent of the curve will obviously be abrupt in 

 proportion as the output from the left ventricle is large, 

 its contraction forcible, and the pressure in the arteries 

 low. All these conditions concur in sthenic fever, and 

 they are also present to an extreme degree in most cases 

 of aortic incompetence, both of which conditions are 

 therefore characterized by a sudden rise of the pulse. 



On the other hand, the ascent will be gradual in pro- 

 portion to the resistance which the heart experiences in 

 expelling its contents into the aorta. Narrowing of the 



