IMPULSE OF THE HEAKT. 191 



siderable enlargement, 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 loco- 

 motion of the heart from recoil. It is for this reason that, 

 observing the heart in situ, the ventricles seem to elongate, 

 and an instrument applied to it apparently indicates removal 

 of the apex from the base. 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. 1 



In addition to these 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 observed by Harvey, but is men- 

 tioned by Ilaller. 2 



Impulse of the Heart. Each movement of the heart pro- 

 duces an impulse, which can be readily felt and sometimes 

 seen, in the fifth intercostal space, a little to the left of the 

 median line. Yivisections 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 placed between the point of the heart and the 

 walls of the thorax, every time we have a hardening of the 

 point the finger will be pressed against the side. If the im- 

 pulse 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, 



1 The observations of Fontana on the shortening of the heart are very con- 

 clusive. He constructed a little instrument consisting of two vertical rules, slid- 

 ing on a horizontal bar like a shoemaker's measure, one of which was applied to 

 the base, and the other just grazed the apex. He estimated the shortening of the 

 heart in a lamb at about two Paris lines (Mem. de Halter, tome iii., p. 226). 



2 Elementa Physiologies, vol. L, p. 889. 



