190 THE CIRCULATORY APPARATUS 



response of the arterial system which is receiving 

 at every systole or contraction of the ventricle a 

 large volume of blood; the shrinkage of the artery is 

 due to the elastic recoil of the arterial system or their 

 walls upon the volume of blood, forcing it forward, 

 into, and through the arteries, during the diastole 

 or relaxation of the ventricles. The pulse or pulse 

 wave is simply a wave passing from the heart over 

 the arterial system, forcing the blood throughout the 

 body until the capillaries are finally reached, when 

 the column of blood passes into the venous system. 



The number of beats of the pulse is 72 per minute, 

 and varies accordingly. (See Heart-beat, page 183.) 

 The pulse is influenced by the same factors which inter- 

 fere with the heart's action. The pulse is spoken of 

 as frequent or infrequent, depending whether it is 

 above or below the normal rate 72 per minute; 

 quick or slow according to the suddenness with which 

 it strikes the examining finger; hard or soft, tense or 

 easily compressible, depending on the resistance which 

 the artery offers to the compressing finger; large, full, 

 or small, depending on the amount of blood in the 

 arterial system at the time of examination. 



The Blood-pressure. The blood-pressure or arterial 

 tension may be defined as the pressure exerted radially 

 or laterally by the moving blood-stream against the 

 sides of the vessels (Brubaker). 



The blood -pressure is greatest in the aorta and 

 gradually lessens as the blood is forced through the 

 vessels and emerges into the arterioles and capillaries, 

 then passes through the venules into the veins. 



At each contraction of the heart a large volume of 

 blood is thrown into the arterial system, which is 

 already engorged. This mass of blood in the arterioles 

 and capillaries must be forced along to accommodate 

 the next column of blood thrown from the ventricle, 

 to relieve the arterial system of its already over- 

 distended condition, and maintains an even distribution 



