THE VASCULAR MECHANISM. 



207 



between the summits of the primary and secondary waves is of the 

 same length in pulse tracings taken from the same individual at the 

 same time, whether the artery examined be near or far from the heart ; 

 for example, it is the same in the carotid and the dorsalis pedis arteries. 



Sec. 



Diastole 



Systole 



FIG. 75. Diagram (after Hiirthle) showing simultaneous cardiographic, 

 endocardiac, and aortic curves. (Starling's Principles of Physiology.} 



I., cardiogram ; II., endocardiac pressure; III., aortic pressure ; IV., aortic- 

 pressure, corresponding with dotted endocardiac curve in II. 



Hence the dicrotic wave must arise at the same point as the primary 

 wave, and since the primary wave starts at the root of the aorta, the 

 dicrotic wave must start there also. 



It is brought about in the following manner. When the left 

 ventricle ceases to contract, the column of blood travelling along the 



