ACTION OF THE HEART. 305 



dog was chloroformed, and the heart being exposed, its movements were 

 maintained by artificial respiration. In this state, the sounds being plainly 

 audible, the superior and inferior vena? cava?, and the pulmonary veins, were 

 suddenly compressed, so that the current of blood into both ventricles was 

 arrested : " The heart continuing its action, a stethoscope was again applied, 

 when neither first nor second sound was heard ; after a short space of time 

 the veins were allowed to pour their contents into both sides of the heart, 

 and both sounds were instantly reproduced. The veins being again com- 

 pressed, all sound was extingushed, notwithstanding that the heart con- 

 tracted vigorously." Excellent observers, however, as Ludwig and Dogiel, 

 Bibson and Broadbent, maintain that though much reduced in intensity the 

 first sound is still audible during the contractions of an empty heart. It 

 must not be overlooked that the susurrus of ordinary muscles is due to the 

 vibration into which they are thrown during contraction, whilst Marey has 

 shown that when the heart is excited to contract the shortening of the fibres 

 is a single and sudden act. In regard to the third event considered as a 

 cause, it has been well remarked, 1 that there is no abrupt contraction of the 

 passages through which the blood flows from ventricles to vessels ; and it 

 may be added, that there would be no sound if there were; sound being 

 only produced at that point in a vessel conveying a stream of fluid, where a 

 sudden enlargement occurs. In regard to the fourth event, strongly advo- 

 cated as a cause by Sibson and Broadbent, it may be argued that during 

 other periods of the heart's rhythm, such collision produces no sound, as in. 

 the passage of the blood from the auricles to the ventricles; and in reference 

 to the fifth cause, which has been advanced by Dr. Leared, it appears from 

 Dr. Halford's experiments, that at the moment when the systole of the ven- 

 tricle is about to take place, the active and passive columns of blood, ar 

 those below and upon the semihmar valves, are not separated by any space; 

 that there is no propulsion of the blood from a distance against the passive 

 column, but that when the ventricles contract, the fluid pushes open the 

 valves and communicates its force to the column in the vessels, a circum- 

 stance which does not appear likely to be accompanied by much, if any 

 sound. The sixth aud seventh events doubtless materially aid in the pro- 

 duction of the first sound, and on the whole its chief factors appear to be 

 the sudden tension of the auriculo-ventricular valves, and the contraction 

 of the muscular walls of the ventricle, aided, as just stated, by the vibration 

 of the walls of the chest, and the friction of the heart against them.- 2 



240. That the second sound is produced in the act of closure of the Semi- 

 lunar valves, is now almost universally admitted ; the simple hooking back 

 one of these valves by a curved needle against the side of the artery, so as to 

 permit a reflux of blood into the ventricle, being sufficient to suppress this 

 sound altogether. Whether it proceeds from the tension of the valves them- 

 selves, or from the recoil of the blood against them, or from both causes com- 

 bined, has not been clearly determined ; probably the 1 last is the true account 

 of it. When the first sound is altered by disease of the semiluuar .valves, 

 occasioning obstruction to the exit of blood, the second sound also is affected 



1 By a writer in the Med.-Chir. Rev., April, 1860, p 354. 



2 Billing's remarks upon this subject in his Principles of Medicine, Halford's 

 pamphlet, On the Sounds of the Heart, and the observations of Sibson and Broadbent 

 in Sibson's Medical Anatomy, are deserving of careful perusal. For some excep- 

 tional statements, as that the second sound is due to a contraction of the auricles, see 

 Paton, On Sounds of Heart, in Dub. Quart. Journ., vol. xcix, p. 8-i et seq. The 

 various treatises on practical medicine and auscultation may also be referred to. Dr. 

 Dunglison, Human Physiology, vol. i, 185(5, p. 397, has tabulated the opinions of a 

 large number of authors. They exhibit an extraordinary amount of discordance 

 upon a matter of pure observation. 



