144 THE SOUNDS OF THE HEART. [BOOK i. 



The second short sharp sound presents no difficulties. It is 

 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, i. e. at the 

 point where the aortic arch comes nearest to the surface. Its 

 characters are such as would belong to a sound generated by the 

 sudden tension of valves like the semilunar valves. It is obscured 

 and altered, replaced by ' murmurs ' when the semilunar valves are 

 affected by disease, the alteration being most manifest to the ear 

 at the above-mentioned spot when the aortic valves are affected. 

 When the aortic valves are hooked up by means of a wire intro- 

 duced down the arteries, the second sound is obliterated and 

 replaced by a murmur. These facts prove that the second sound 

 is due to the sudden tension of the aortic (and pulmonary) semi- 

 lunar valves. 



The first sound, longer, duller, and of a more 'booming' 

 character than the second, heard with greatest distinctness at the 

 spot where the cardiac impulse is felt, presents many difficulties 

 in the way of a complete explanation. It is heard distinctly when 

 the chest-walls are removed. The cardiac impulse therefore can 

 have little or nothing to do with it. In point of time, and in the 

 position in which it may be heard to the greatest advantage (at 

 the spot of the cardiac impulse where the ventricles come nearest 

 to the surface), it corresponds to the closure of the auriculo-ven- 

 tricular valves. In point of character it is not such a sound as one 

 would expect from the vibration of membranous structures, but 

 has, on the contrary, many of the characters of a muscular sound. 

 In favour of its being a valvular sound, may be urged the fact that 

 it is obscured, altered, replaced by murmurs, when the tricuspid or 

 mitral valves are diseased ; and according to some authors clamp- 

 ing the great veins so as to shut off the blood supply stops the 

 sound though the beat continues. The first argument may be met 

 by the consideration that a murmur though itself undoubtedly of 

 valvular origin, might largely or completely hide a sound occurring 

 at the same time as the closure of the valves but due to other 

 causes ; and the second is directly contradicted by an experiment 

 of Ludwig and Dogiel. These observers tied in succession, in the 

 order of the flow of blood, the great veins and arteries of the heart 

 of a dog so as to completely deprive the heart of blood, and 

 listened to the heart both within the body and after removal. 

 For the short time that the heart continued to beat, the first sound 

 was heard, feeble but with its main characters recognisable. From 

 this they inferred that the sound was of muscular origin. But 

 there is a great difficulty in regarding the sound as a muscular 

 one, for a muscular sound is the result of a tetanic contraction, 

 the height of the note produced varying with the rate of re- 

 petition of the simple contractions which go to make up the 



