288 THE CIRCULATION IN THE BLOOD-VESSELS [dl. XXI. 



3. Its regularity or irregularity ; irregularity may occur owing to 



irregular cardiac action either in force or in rhythm. 



4. Its tension ; that is the force necessary to obliterate it. This 



gives an indication of the state of the arterial walls and the 

 peripheral resistance. 



In disease there are certain variations in the pulse, of which we 

 shall mention only two ; namely, the intermittent pulse, due to the 



Fio. 287.- Diagram of the lever of the Sphygmograph. 



heart missing a beat every now and then; and the water hammer 

 pulse, due either to aortic regurgitation or to a loss of elasticity of 

 the arterial walls; either of these circumstances diminishes the 

 onward flow of blood during the heart's diastole, and thus the sudden- 

 ness of the impact of the blood on the arterial wall during systole is 

 increased. When this condition is due to arterial disease, such as 

 atheroma or calcification, this sudden pulse, combined with the 

 decreased extensibility of the arteries, may lead to rupture of the 



FIG. 288. The Sphygmograph applied to the arm. 



walls, and this is especially serious if it occurs in the arteries of the 

 brain (one cause of apoplexy). 



In order to study the pulse more fully, it is necessary to obtain 

 a graphic record of the pulse-beat, and this is accomplished by the 

 use of an instrument called the Sphygmograph. This instrument 

 consists of a series of levers, at one end of which is a button placed 

 over the artery ; the other end is provided with a writing-point to 

 inscribe the magnified record of the arterial movement on a travelling 

 surface. 



