ON THE MOTIONS AND SOUNDS OP THE HEART. 271 



8. To those we may add the facts pointed out by Dr. Spittal, 

 which have been repeated and verified by the Reporter, assisted 

 by Dr. Edwin Harrison and other gentlemen not of the Com- 

 mittee, and which seem to prove that if the living heart impinge 

 with any force upon the walls of the thorax sound must result. 



From the whole of those facts, the Committee conclude that 

 impulse is not the principal cause of the first sound, but that it 

 is an auxiliary and occasional cause, nearly null in quietude and 

 in the supine posture, but increasing very considerably the sound 

 of the systole in opposite circumstances. 



M7-st Sound — Muscular Tension. — The facts ascertained by 

 the Committee relating directly to muscular tension as a pos- 

 sible cause of the first sound, are few but striking, and in their 

 judgement decisive. 



1. The heart in systole becomes suddenly, from a compara- 

 tively soft and flaccid body, extremely tense, and to the touch 

 hard as cartilage. Experiments 2 and 12, and many others, in 

 which the fact was not recorded. 



2. The unvarying and uniform character of the systolic sound, 

 however diversified the circumstances in which the heart was 

 placed, furnishes a strong argument in favour of its intrinsic 

 nature. 



3. The voluntary muscles, when suddenly contracted, become 

 tense and hard, and emit sounds resembling strikingly the first 

 sound of the heart. This is especially observable in the action 

 of the abdominal muscles. Experiment 14. 



4. From those experimental facts, taken along with the self- 

 ev-ident fact, that the muscular tension thus experimentally 

 proved to be sonorous is an essential part, and, as it were, the 

 first stage of full muscular contraction, the Committee conclude 

 that the first sound of the heart is, for the most part, a physical 

 result of the sudden transition of the ventricles from a flaccid 

 condition to a state of extreme tension ; that in a word the first 

 sound is essentially a muscular sound. 



Second Nonnal Sound of the Heart. — ^We now proceed to 

 the consideration of the normal second sound, and of the hypo- 

 theses that have been or might be advanced respecting it, and 

 the facts we possess that throw light on its causes and mechanism. 



The Committee had proceeded but a short way in their expe- 

 rimental inquiries when they found the conclusion forced on 

 them that the majority of the hypotheses (above enumerated) 

 regarding the second sound were wholly untenable. In some of 

 their first experiments they found that the second sound might 

 be absent, although the first soimd was present, and the systolic 



