40 CIRCULATION OF THE BLOOD ACTION OF THE HEART. 



FIG. 19. Diagram of the shortening of 



the ventricles during systole. 

 The dotted lines show the position of the 

 heart during contraction. 



gate. It is only when the heart is firmly fixed or is contracting after it has been 

 removed from the body, that the actual changes which occur in the length of 



the ventricles can be appreciated. During 

 the systole, the ventricles are shortened and 

 are narrowed in their transverse diameter, 

 but their antero-posterior diameter is slight- 

 ly increased. 



In addition to the marked changes in 

 form, position etc., which the heart under- 

 goes during its action, on careful examina- 

 tion it is seen that the surface of the ventri- 

 cles becomes marked with slight, longitudinal 

 ridges during the systole. 



Impulse of the Heart. Each movement 

 of the heart produces an impulse, which can 

 be readily felt and sometimes seen in the 

 fifth intercostal space a little to the right of the perpendicular line of the left 

 nipple. This impulse is synchronous with the contraction of the ventricles. 

 If the hand be introduced into the chest of a living animal and the finger be 

 placed between the point of the heart and the walls of the thorax, every time 

 that there is a hardening of the 

 point, the finger will be pressed 

 against the side. If the impulse of 

 the heart be felt while the finger is 

 on the pulse, it is evident that the 

 heart strikes against the thorax at 

 the time of the distention of the ar- 

 terial system. The impulse is due 

 to the locomotion of the ventricles. 

 In the words of Harvey, " the heart 

 is erected, and rises upward to a 

 point so that at this time it strikes 

 against the breast and the pulse is 

 felt externally." 



Succession of the Movements of 

 the Heart. The main points in the 

 succession of the movements of the 

 heart are readily observed in cold- 

 blooded animals, in which the pul- 

 sations are very slow. In examining 

 the heart of the frog, turtle or alii- 

 gator, the alternations of repose and * f $S&2fiS!S ; Lud % S? ftaTf systole ' 

 activity are very strongly marked. 



During the intervals of contraction, the whole heart is flaccid and the ven- 

 tricle is comparatively pale ; the auricles then slowly fill with blood ; when 

 they have become fully distended, they contract and fill the ventricle, which 



FIG. 20. Side view of the heart (Landois). 



