THE HEART. 



169 



We may begin our study of these curves at any point in the cycle ; let 

 it be the point b' in Fig. 56. From this point the curve rises very abruptly, 



FIG. 56. 



Curves of Endocardiac Pressure from Left Ventricle of Dog: A, a quickly beating, B, a 

 more slowly beating, heart. The letters in this and the succeeding Figs. 57, 58, are explained in 

 the text. 



almost in the vertical line, to a maximum at c, and the same sudden large rise 

 to a maximum occurs in the front-to-back diameter of the ventricles (Fig. 



FIG. 57. 



(See Fig. 52.) 



57) and in the pressure of the apex against the chest wall (Fig. 58). There 

 can be no doubt that this corresponds to the first part of the systole of the 

 ventricles. By the sudden onset of the contraction of the ventricular 

 fibres pressure is brought to bear on the contents of the ventricle, and 

 there being as yet no escape for the blood, by the increasing contraction 

 of the fibres the pressure becomes greater and greater. At the point c a 



