THE CARDIAC IMPULSE. 



33 



of the valves, thrown after closure into sudden tension, from the 

 vibrations of the blood columns in the multitudinous branches of 

 the arteries, and from vibrations of the arterial walls. Although both 

 the first and second sounds are double in origin, yet the constituent 

 sounds are normally so far synchronous as not to be separable by the 

 ear. 



Hsemic murmurs. Experimenting on the flow of fluids through tubes 

 of glass, thin rubber, and intestines and arteries of animals, Nicolls found that 

 even with velocities much greater than that of the blood-flow, it is impossible 

 to produce sounds in a moving liquid, so long as it is free from air, no matter 

 what dilatations or contractions occur in the pipes. Hence he concludes that 

 hseniic murmurs, such as are heard over the pulmonary artery in cases of 

 oligocythaemia, are produced like vocal sounds, by the vibrations of elastic 

 substances. Likewise the sounds of the heart are produced in all cases by 

 membranous vibration, and not by fluid friction, as the velocity is too small to 

 produce audible sounds by this means. 1 



THE CARDIAC IMPULSE. 



Synchronously with the systole of the ventricles, the chest wall 

 receives a blow from the heart, at the point where the mass of the ven- 

 tricle comes in contact 

 with the parietes. 



The position of the 

 impulse varies con- 

 siderably with the po- 

 sition of the body. 

 Although it is gener- 

 ally stated that the 

 cardiac impulse is 

 normally visible in the 

 fifth left intercostal 

 space, 2 in. below the 

 nipple, and 1J in. to 

 its sternal side, yet in 

 67 per cent, of men it 

 is stated to be visible 

 in the fourth inter- 

 costal space that is 

 to say, when the body 

 is in the supine posi- 

 tion. 2 The impulse is 

 felt slightly lower in 

 men than in women, 

 and in the old than 



f i -p FIG. 22. Areas of cardiac impulse, when supine (black), and 



young. 13V when ,. Qn the left gide (]ightly shaded). Sequeira. 



Ransome 3 it was found 



that the seat of the impulse varied much more when the body was 

 rolled from one side to the other, than when the body was raised from 

 the horizontal to the vertical position. In rising from the supine to 



1 Nicolls, Journ. Physiol., Cambridge and London, 1896, vol. xx. pp. 413 and 426. 



2 Mariaunini and Namias, Arch. ital. de biol., Turin, 1883, vol. iv. p. 143. 



3 Journ. Anat. and Physiol., London, 1895, vol. ix. p. 137. 



VOL. II. * 



