120 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



performed upon the dog as follows: The heart was exposed daring arti- 

 ficial respiration, and loose ligatures were placed upon the venae cavae, the 

 pulmonary artery, the pulmonary veins, and the aorta. Next, the loose 

 ligatures were tightened in the order above written, during which process 

 the beating heart necessarily pumped itself as free as possible of blood. 

 The vessels were then divided distally to the ligatures, and the heart was 

 excised and suspended in a conical glass vessel containing freshly drawn defi- 

 brinated blood, in which the hearl was fully immersed without touching the 

 glass at any point. Under these conditions the excised heart might execute 

 as many as thirty beats. The conical glass vessel was supported in a " ring- 

 stand." The narrow bottom of the vessel consisted of a thin sheet of india- 

 rubber, with which last was connected the flexible tube and ear-piece of a 

 stethoscope. By means of the latter any sound produced by the beating 

 heart could be heard through the blood and the sheet of rubber. The second 

 sound was not heard ; but at each contraction of the ventricles the first sound 

 was heard, not of the same length or loudness as normally, but otherwise unal- 

 tered. The conditions of experiment were held to preclude error resulting 

 from adventitious sounds ; moreover, the heart before excision had pumped 

 itself tree from all but a fraction of the amount of blood required to close the 

 valves, and had been so treated that no more could enter. It was therefore 

 believed to be practically impossible that the sound heard could have its 

 origin at the valves; and no origin remained conceivable other than in the 

 muscular contraction of the ventricular systole. Later experiments, in which 

 the auriculo-ventricular valves have been rendered incompetent by mechani- 

 cal means, have seemed to confirm the importance of muscular contraction as 

 a cause of the first sound. 1 



By the use of a stethoscope combined with a peculiar resonator, the Ger- 

 man physician Wintrich of Erlangen 2 satisfied himself that he could analyze 

 the first sound upon auscultation, so as to detect in it two components, one 

 higher pitched, which he attributed to the vibration of the auriculo-ventricular 

 valves, and a component of lower pitch, attributed to the muscular contrac- 

 tion df the heart. The other experiments above referred to, however, which 

 sustain muscular contraction as a cause of the first sound, did not reveal a 

 change of pitch following incompetence of the valves, but only a diminution 

 in loudness and duration. 



Both the closure of the cuspid valves and the contraction of the muscular 

 tissue of the ventricles are rejected by a recent observer as causes of the first 

 sound, which he ascribes to the opening of the semilunar valves. 5 



1 L. Krehl: '' Ueber den Herzmuskelton," Archiv fur Anatomie und Physiologic, Physiolo- 

 gische Ahtheilung, 1889, 8. 253 : A Kasem-Bek : " IJeber die Kntstebung des ersten Herztones," 

 /' ger 1 8 Archiv fur die gesammtt Physiologic, L890, Bd. xlvii. 8. 53. 



1 Wintrich : " Experimentalstudien iiber Resonanzbewegungen der Membranen," Sitzwngs- 

 phys.-med. Societal eu Erlangen, 1st.!; Wintrich: " Ueber Causation und Analyse 

 der Iler/.etune," Ibid., 1875. 



■'■ K. Quain: "On tbe Mechanism by which tbe First Sound of the Heart is Produced," 

 lings of the Royal Society, vol. lxi. p. 331. 



