SUCCESSION OF THE MOVEMENTS OF THE HEART. 43 



at right angles to and touching the point during the diastole, and a small silver tube 

 was introduced through the walls into the left ventricle. At each contraction, a jet 

 of blood spurted out through the tube, and the point of the heart receded from the 

 knife about an eighth of an inch. The animal experimented upon was a dog a little 

 above the medium size. These simple experiments demonstrate that, in the dog at 

 least, the ventricles shorten during 

 their systole. The arrangement of 

 the muscular fibres is too nearly 

 identical in the heart of the warm- 

 blooded animals to leave room for 

 doubt that it also shortens in the 

 human subject. The error which 

 has arisen in this respect, and which 

 obtained in our first experiments 



made in 1861 is due to the loco- FlG> ^-Diagram of the shortening of the ventricles during 



systole. 

 motion and protrusion of the entire The dotted lines show the position of the heart during contraction. 



organ, so as to make the point strike 



against the chest. A little reflection indicates the mechanism of this phenomenon. 

 During the intervals of contraction, the great vessels, particularly the aorta and pul- 

 monary artery, which attach the base of the heart to the posterior wall of the thorax, 

 are filled but not distended with blood; at each systole, however, these vessels are 

 distended to their utmost capacity ; their elastic coats permit of considerable enlarge- 

 ment, as can be seen in the living animal, and this enlargement, taking place in every 

 direction, pushes the whole organ forward. We have also considerable locomotion of 

 the heart from recoil. It is for this reason that, observing the heart in situ, the 

 ventricles seem to elongate. It is only when we examine the heart firmly fixed, or 

 contracting after it is removed from the body, that we can appreciate the actual changes 

 which occur in the length of the ventricles. During the systole the ventricles are short- 

 ened and are narrowed in their transverse diameter, but their antero-posterior diameter 

 is slightly increased. 



In addition to the marked changes in form, position, etc., which the heart undergoes 

 during its action, we observe, on careful examination, that the surface of the ventricles 

 becomes marked with slight longitudinal ridges during the systole. This was not noted 

 by Harvey but is mentioned by Haller. 



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 left of the 

 median line. Vivisections have demonstrated that the 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 we have 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 arterial 

 system. The impulse is due to the locomotion of the ventricles. In the words of Harvey, 

 "the heart is erected, and rises upwards to a point, so that at this time it strikes against 

 the breast and the pulse is felt externally." In the case of the son of the Viscount Mont- 

 gomery, already referred to, Harvey gives a most graphic description of the manner in 

 which the heart is "retracted and withdrawn" during the diastole, and "emerged and 

 protruded " during the systole. 



Succession of the Movements of the Heart. "We have already followed, in a general 

 way, the course of the blood through the heart and the successive action of the various 

 parts ; but we have yet to consider these points more in detail, and to ascertain, if possi- 

 ble, the relative periods of activity and repose in each portion of the organ. 



