188 THE CARDIAC IMPULSE. [BOOK i. 



by making an incision 'through the diaphragm from the abdo- 

 men, and placing the finger between the chest-wall and the 

 apex. It then can be distinctly recognized as the result of the 

 hardening of the ventricle during the systole. And the impulse 

 which is felt on the outside of the chest is chiefly the effect of 

 the same hardening of the stationary portion of the ventricle 

 in contact with the chest-wall, transmitted through the chest- 

 wall to the finger. In its flaccid state, during diastole, the 

 apex is (in a standing position at least) at this point in contact 

 with the chest-wall, lying, somewhat flattened, between it and the 

 tolerably resistant diaphragm. During the systole, while being 

 brought even closer to the chest- wall, by the tilting of the ventricle 

 and by the movement to the front and to the right of which we 

 have already spoken, it suddenly grows tense and hard, and becomes 

 rounder. The ventricles, in executing their systole, have to contract 

 against resistance. They have to produce within their cavities, 

 pressures greater than those in the aorta and pulmonary arteries, 

 respectively. This is, in fact, the object of the systole. Hence, 

 during the swift systole, the ventricular portion of the heart 

 becomes suddenly tense, somewhat in the same way as a bladder 

 full of fluid would become tense and hard when forcibly squeezed. 

 The sudden pressure exerted by the ventricle thus rendered sud- 

 denly tense and hard, aided by the closer contact of the apex with 

 the chest-wall (which, however, by itself, without the hardening of 

 contraction, would be insufficient to produce the effect), gives an 

 impulse or shock both to the chest-wall and to the diaphragm. If 

 the modification of the sphygmograph (an instrument of which we 

 shall speak later on, in dealing with the pulse), called the cardio- 

 graph, be placed on the spot where the impulse is felt most 

 strongly, the lever is seen to be raised during the systole of the 

 ventricles, and to fall again as the systole passes away, very much 

 as if it were placed on the heart directly, A tracing may thus be 

 obtained, see Fig. 46, of which we shall have to speak more fully 

 later on, see 115. If the button of the lever be placed, 

 not on the exact spot of the impulse, but at a little distance 

 from it, the lever will be depressed during the systole. While 

 at the spot of impulse itself the contact of the ventricle is 

 increased during systole, away from the spot the ventricle (owing 

 to its change of form and subsequently to its diminution in 

 volume) retires from the chest- wall, and hence, by the mediastinal 

 attachments of the pericardium, draws the chest-wall after it. 



112. The Sounds of the Heart. When the ear is applied to 

 the chest, either directly or by means of a stethoscope, two sounds 

 are heard, the first a comparatively long, dull, booming sound, 

 the second a short, sharp, sudden one. Between the first and 

 second sounds the interval of time is very short, too short to be 

 easily measured, but between the second and the succeeding first 

 sound there is a distinct pause. The sounds have been likened 



