THE CIRCULATION 229 



the resonance- tone of the ear. That the membranous valves 

 play the leading part in producing the first sound cannot be 

 doubted, whether by their first closure or by their subsequent 

 vibration. We should be inclined to attribute to them the 

 whole performance, were it not that the first sound, or at 

 any rate a sound, is heard during the beating of a bloodless 

 heart. If an animal be killed and the heart removed from its 

 thorax with the utmost despatch, it will beat for about a minute 

 while lying in the palm of one's hand. When a stethoscope is 

 applied to the ventricle, a " first sound " is heard. This was 

 described as a muscular sound, owing to a misconception. It 

 is similar to the sound which is heard when a stethoscope rests 

 upon a contracting biceps. Until recently the voluntary con- 

 traction of a muscle was believed to be vibratory a tetanus. 

 The sound corresponds to a rate of about thirty-six vibrations 

 to the second. There being reasons for thinking that muscle 

 contracting naturally does not vibrate as fast as this, the 

 sound was interpreted as the first overtone of the muscle- 

 note. Muscle was said to vibrate eighteen times a second. 

 The similarity of the first sound of the heart and the ordinary 

 muscle-sound led physiologists to infer that the contraction of 

 the heart also was a tetanus. But this was a mistake. Neither 

 voluntary muscular action nor the contraction of the heart 

 is an interrupted contraction in this sense. In the case of the 

 musculature of the heart especially, contraction is a steady 

 shrinking, followed by a steady relaxation. The sound pro- 

 duced by the bloodless heart is due to the various displace- 

 ments which occur when it contracts. Its interior is very 

 irregular, with its columns, papillary muscles, tendinous cords, 

 valves. The displacement of these various structures is re- 

 sponsible for the noise. 



The sounds of the heart afford to the physician a means of 

 ascertaining with the utmost nicety the condition of the valves. 

 If the sounds are altered from the normal in the least degree, 

 the valves are not healthy. Alteration of the structure 

 of a valve is in ordinary parlance heart-disease. It is usually 

 indicated by an addition to the normal sound. Such addition 

 is termed a " murmur "; in French, un bruit de souffle. Either 

 term is somewhat misleading to the tyro. We remember a 

 fellow-student to whom our chief had in vain expounded the 



