412 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



performed upon the dog as follows : The heart was exposed during 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 heart 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 precluded error resulting from adventi- 

 tious sounds ; moreover, the heart before excision had pumped itself free of 

 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 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 ven- 

 tricular systole. Later experiments, in which the auriculo-ventricular valves 

 have been rendered incompetent by mechanical means, have seemed to confirm 

 the importance of muscular contraction as a cause of the first sound. 1 



Acoustic Analysis of the First Sound. By the use of a stethoscope 

 combined with a peculiar resonator, the German physician Wintrich of Erlan- 

 gen 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 contraction of the heart. The other experi- 

 ments 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. 



K. THE FREQUENCY OF THE CARDIAC CYCLES. 3 



In a healthy full-grown man, resting quietly in the sitting posture, the 

 heart beats on the average about 72 times a minute. In the full-grown 



1 L. Krehl : " Ueber den Herzmuskelton," Archiv fiir Anatomic und Physiologic, Physiolo- 

 gische Abtheilung, 1889, p. 253 ; A. Kasem-Bek : " Ueber die Entstehung des ersten Herztones," 

 Pfliiger's Archiv fiir die gesammte Physiologic, 1890, Bd. xlvii. p. 53. 



2 Wintrich : " Experimentalstudien iiber Resonanzbewegungen der Membranen," Sitzungs- 

 berichte der phys.-med. Societal zu Erlangen, 1873; Wintrich: "Ueber Causation und Analyse 

 der Herztone," Ibid., 1875. 



3 Tigerstedt : Lehrbuch der Physiologic des Kreislaufes, Leipzig, 1893, pp. 25-35 ; Vierordt : 

 Daten und Tabellen zum Gebrauchefiir Mediciner, 1888, pp. 105-109, 259. 



