154 A TEXTBOOK OF PHYSIOLOGY 



The shifting is due to the effect of gravity on the heart. In each 

 position a different part of the heart is brought in close contact with 

 the chest wall. The chest wall is driven out by the systole only 

 where the heart-muscle touches it; at other places it is slightly drawn 

 in. This indrawing is believed to be due to the expulsion of the blood 

 from the thorax by the left ventricle. The thorax being a closed 

 cavity, negative pressure is produced by each systole when the 

 blood passes out by the arteries of the head, limbs, and abdomen. 

 This vacuum is filled by (1) the drawing of air into the lungs; hence 

 the cardio-pneumatic movement, which may be detected by connecting 

 a water manometer with one nostril, and closing the other nostril; 



(2) the drawing of venous blood into the great veins and right auricle ; 



(3) the slight indrawing of the chest wall. The impulse may be re- 

 corded by placing a small cup or receiving tambour over the spot 

 where it is most evident, and connecting the inside of the cup by a 

 tube to the recording tambour. The cup need not be closed by a 

 rubber dam, for an air-tight junction can be effected by pressing it 

 upon the skin. The stroke of the heart is transmitted as a wave of 

 compression to the air within the system of tambours. The recording 

 tambour writes on a drum moved by clockwork, and covered with a 

 smoked paper. From the record so obtained we can obtain informa- 

 tion as to the time-relations of the heart -beat, but no accurate in- 

 formation as to its energy or amount of contraction. 



The Sounds of the Heart. When the ear is applied over the cardiac 

 region of the chest, or a stethoscope is employed, two sounds are 

 heard. The first, heard most intensely near the apex, is a duller and 

 longer sound than the second, which is shorter and sharper, and is 

 heard best over the base of the heart. The syllables li'tb, dilpp, express 

 fairly well the characters of the two sounds, and the accent is on lub 

 when the stethoscope is over the apex thus, li'tb-dupp, lub-dupp, 

 lub-dupp and on the second sound when over the base thus, lub- 

 dupp, lub-d-ipp, lub-diipp. 



The first sound is caused by the sudden tension (1) of the cardiac 

 muscle; (2) of the diaphragms formed by the closed auriculo-ventricular 

 valves; (3) of the papillary muscles and chordae tendineae. This 

 sound is heard in an excised mammalian heart empty of blood ; there- 

 fore it is largely muscular in origin. It is not heard in a turtle's 

 heart, because this contracts too slowly. 



When the sounds and the contraction are recorded* together, the 

 record shows that the first sound begins about 0-01 second before the 

 cardiogram marks the beginning of the systole, and for the first 0-06 

 second of its duration this sound is heard only over the apex (Fig. 61). 

 Over the base of the heart the first sound is heard just at the time 

 when the semilunar valves open and the output begins. The first 

 sound ceases before the ventricular contraction is over, for it is the 

 sudden tension, not the continuance, of contraction that causes it. 

 The beginning of the second sound marks the sudden tension of the 

 semilunar valves, which immediately follows their closure. 



For clinical purposes it is important to bear in mind what is 



