CHAP, iv.] THE VASCULAR MECHANISM. 235 



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 pres- 

 sure 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 or 

 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 ob- 

 tained, see Fig. 41, of which we shall have to speak more fully 

 immediately, see 133. 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 retires 

 from the chest-wall (by the diminution of its right-to-left dia- 

 meter), and hence, by the rnediastinal attachments of the peri- 

 cardium, draws the chest- wall after it. 



130. 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 measurable, but between the second and the succeeding first 

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

 to the pronunciation of the syllables lubb diip, so that the cardiac 

 cycle, as far as the sounds are concerned, might be represented 

 by : lubb^ dup, jgause. 



The second sound which is short and sharp presents no difficul- 

 ties. -^Itis coincident in point of time with the closure of the 

 semilunar valves, and is heard to the best advantage over the 

 second right costal cartilage close to its junction with the sternum, 



