THE CIRCULATION. 



necessarily tends, at the moment of its contraction, to straighten or 

 untwist the spiral. At the time of the ventricular contraction, there- 

 fore, the apex of the heart rotates upon its axis, from left to right ante- 

 riorly and from right to left posteriorly. This twisting movement at 

 the apex is very perceptible at each pulsation of the heart when exposed 

 in the living animal. 



The impulse of the heart is a stroke, more or less forcible, of the 

 apex of the organ against the walls of the chest, taking place at the 

 time of the ventricular systole. This impulse is readily perceptible 

 externally, as a general rule, both to the eye and to the touch. In the 

 human subject, when in the erect position, it is located in the fifth inter- 

 costal space, midway between the left edge of the sternum and a line 

 drawn perpendicularly through the left nipple ; while in the supine posi- 

 tion of the body, the heart subsides, in a measure, from the anterior part 

 of the chest, so that its external impulse may become for the time very 

 faint, or may even disappear altogether. 



This alternate recession and advance of the apex of the heart, corre- 

 sponding with its relaxation and contraction, is visible in the organ when 

 exposed by opening the walls of the chest. According to the descrip- 

 tion given by Harvey, at the time of its motion " 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." If we allow the end of the 

 finger to rest lightly upon the apex of the exposed heart, the protrusion 

 of this part of the organ at the time of the ventricular systole is dis- 

 tinctly felt, lifting the finger at each beat with a somewhat forcible 

 impulse ; and if a light rider of white paper be placed upon the apex, it 

 is also seen to be thrown forward and backward at each alternate con- 

 traction and relaxation of the heart. 



The immediate cause of the protrusion of the heart's apex at the time 

 of the ventricular systole has been variously regarded, first as an actual 

 elongation of the ventricle, and secondly, as a forward movement of the 

 whole heart, due to a recoil from the blood expelled from it under pres- 

 sure, or to a reaction of the distended arteries at its base. Galen, who 

 was the first to study the action of the heart by inspection in the living 

 animal, found the transverse diameter of the organ increased during 

 relaxation and its length diminished, while during the systole its width 

 was diminished and its length increased. 1 Of subsequent observers, 

 some believed the heart to be lengthened, others that it was shortened at 

 the time of the ventricular systole. Nearly all the more recent physio- 

 logical writers of eminence (Longet, Carpenter, Flint, Ranke, Burdon- 

 Sanderson) are of the opinion that the ventricles when contracting 

 diminish in size in every direction, that the apex of the organ approaches 

 the base, but that the whole heart is thrown forward by the impulse of 

 recoil above mentioned. Prof. Flint 2 cut out the heart suddenly from 



1 Galen, De Usu Partium, vi. 8. 



2 Physiology of Man. New York, 1866, p. 189. 



