IMPULSE OF THE HEART. 123 



and forwards, forming part of the septum, then emerge 

 and curve spirally around the apex and adjacent portion 

 of the heart. The whole extent of the movement thus 

 produced is, however, but slight. The condition, which, 

 no doubt, contributes most to the occurrence and character 

 of the impulse of the heart, is its change of shape ; for, 

 during the contraction of the ventricles, and the consequent 

 approximation of the base towards the apex, the heart 

 becomes more globular, and bulges so much, that a distinct 

 impulse is felt when the finger is placed over the bulging 

 portion, either at the front of the chest, or under the 

 diaphragm. The production of the impulse is, perhaps, 

 further assisted by the tendency of the aorta to straighten 

 itself and dimmish its curvature when distended with the 

 blood impelled by the ventricle ; and by the elastic recoil 

 of all the parts about the base of the heart, which, accord- 

 ing to the experiments of Kurschner, are stretched down- 

 ward and backward by the blood flowing into the auricles 

 and ventricles during the dilatation of the latter, but re- 

 cover themselves when, at the beginning of the contraction 

 of the ventricles, the flow through the auriculo -ventricular 

 orifices is stopped. But these last-mentioned conditions 

 can only be accessory in the perfect state of things ; for the 

 same tilting movement of the heart ensues when its apex 

 is cut off, and when, therefore, no tension or change of 

 form can be produced by the blood. 



Although what we generally recognise as the impulse of 

 the heart is produced in the way just mentioned, the beat 

 is not so simple a shock as it may seem when only felt 

 by the finger. By means of an instrument called a cardio- 

 graph, it may be shown to be compounded of three or four 

 shocks, of which the finger can only feel the greatest. 



The cardiograph is a tube, dilated at one end into a 

 cup or funnel, either open-mouthed or closed by an elastic 

 membrane, while at the other it communicates with 

 the interior of a small metal drum, one side of which is 



