THE CIRCULATION OF THE BLOOD 



365 



effect on the arterial wall of the discharge of blood from the ventricle is 

 illustrated in the figure. During the first one-sixth of the systole a certain 

 volume of blood is forced into the artery, which at this moment is already 

 full of blood. Of this volume a portion moves forward while another 

 portion moves sideways as the arterial wall begins to expand under the 

 pressure of the heart. At the end of the first one-sixth of the systole the 

 condition of the arterial wall may be represented by the lines ib. During 

 the second one-sixth the artery expands still more as the volume of blood 

 increases under the increasing force of the heart, so that at the end of the 

 second period the expansion of the arterial wall is not only greater at the 

 point a but in addition has extended over a greater length of the artery so 

 that the condition of the artery may be represented by the lines 20. Dur- 

 ing the third sixth the same process continues; the incoming volume of blood 

 still further expands the artery at a, as well as successive portions further on 

 as far as d, so that at the height of the systolic power the condition of the 

 artery may be represented by the lines 3 d. 



FIG. 171. DIAGRAM SHOWING THE DEVELOPMENT OF A PULSE WAVE. (Rollet.) 



