230 THE BODY AT WORK 



nature of a murmur. " Surely, Mr. S., you can hear the 

 murmur in this case." We others could hear it as we stood 

 around the bed. After listening for a minute, S. replied : 

 " I think I could hear it, sir, if the heart wasn't making such 

 a thundering noise." The thundering noise was the murmur. 

 It is the business of the physician to recognize that there is 

 a departure from the normal, to analyse its character, to deter- 

 mine the time at which it is heard in relation to the cardiac 

 cycle, and to locate the place on the chest where it is heard 

 most loudly. He is then in a position to state which of the 

 valves is affected and what is the nature of its lesion. Is it 

 a lesion obstructing an orifice, or is it causing regurgitation 

 of blood ? Or is one of the valves, as is commonly the case in 

 heart-disease, imperfect in both respects ? 



A murmur, in the strictest sense, is a sound added to a heart- 

 sound. It is due in all cases to vibration of a fluid column 

 (" fluid vein " is the term in physics). When fluid passing 

 under pressure along a tube of a certain calibre enters a tube 

 of smaller calibre, no vibration occurs. When it passes from 

 a tube of smaller calibre into a larger tube or space, it is thrown 

 into vibration. Under normal conditions no vibration occurs 

 in the heart. The auriculo- ventricular orifices are so large that 

 auricle and ventricle form a single cavity when the valve is 

 open. The ventricles drive the blood into tubes of smaller 

 dimensions than themselves. These are not the conditions which 

 set up vibration in a fluid column. But if one of the orifices is 

 constricted, owing to thickening or partial adhesion of its 

 valve, the fluid column vibrates on entering the space beyond 

 it. The sound is propagated forwards, beyond the constric- 

 tion, not behind it, and transmitted to the wall of the ventricle, 

 aorta, or pulmonary artery, as the case may be. When either 

 of the auriculo- ventricular orifices is constricted, the vibration 

 of the fluid column can be felt as well as heard. The finger 

 placed against the chest-wall at the spot where the impulse of 

 the heart occurs is sensible of a thrill. The vibration may occur 

 whilst blood is flowing through an auricle into a ventricle, 

 before the auricle contracts. In time, it is presystolic. The 

 murmur produced by regurgitation into an auricle is synchronous 

 with systole. The murmur due to regurgitation into a ventricle 

 past an incompetent semilunar valve is post systolic. 



