162 THE VASCULAR MECHANISM. 



may be seen in an inspection of the beating heart. For there is evidence 

 that the apex, though, as we have seen, it is during the systole somewhat 

 twisted round and at the same time brought closer to the chest-wall, does 

 not change its position up or down i. e., in the long axis of the body. If 

 in a rabbit or dog a needle be thrust through the chest-wall so that its point 

 plunges into the apex of the heart, though the needle quivers its head 

 moves neither up nor down, as it would do if its point in the apex moved 

 down or up. 



118. Cardiac impulse. If the hand be placed on the chest, a shock or 

 impulse will be felt at each beat, and on examination this impulse, " cardiac 

 impulse," will be found to be synchronous with the systole of the ventricle. 

 In man, the cardiac impulse may be most distinctly felt in the fifth costal 

 interspace, about an inch below and a little to the median side of the left 

 nipple. In an animal the same impulse may also be felt in another way 

 viz., by making an incision through the diaphragm from the abdomen, and 

 placing the finger between the chest-wall and the apex. It then can be dis- 

 tinctly 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 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 move- 

 ment to the front and to the right, of which we have already spoken, it 

 suddenly grows tense and hard. 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 become suddenly 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 

 of shock both to the chest-wall and to the diaphragm, which may be felt 

 readily both on the chest-wall, and also through the diaphragm when the 

 abdomen is opened and the finger inserted. If the modification of the 

 sphygmograph (of which we shall speak in dealing, later on, with the pulse), 

 called the cardiograph, 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. 58), of 

 which we shall have to speak more fully immediately (see 122). 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 sys- 

 tole. While at the spot of impulse itself the contact of the ventricle is 

 increased during systole, away from the spot the ventricle retires from 

 the chest-wall (by the diminution of its right-to-left diameter), and hence, 

 by the mediastinal attachments of the pericardium, draws the chest-wall 

 after it. 



119. 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 



