CIRCULA TION. 411 



Rouanet in 1832; 1 not long afterward it was conclusively proven by experi- 

 ment l>y the English physician C. J. B. Williams. 2 



Dr. Williams's experiment was as follows : In a young ass the chest was 

 opened and the heart was exposed. It was ascertained that the second sound 

 was audible through a stethoscope applied to the heart itself. A sharp hook 

 was then passed through the wall of the pulmonary artery, and was so directed 

 as to make the semilunar valve incompetent temporarily. By means of a 

 second hook, the aortic semilunar valve was likewise made incompetent. 

 When both hooks were in position, the heart was auscultated afresh, and the 

 second sound was found to have disappeared, and to be replaced by a hissing 

 murmur. The hooks were withdrawn during auscultation, and at the moment 

 of withdrawal the murmur disappeared and the normal second sound recurred. 

 Subsequent clinical and post-mortem observations have shown that the second 

 sound may be altered by disease which cripples the aortic valves. 



Causes of the First" Sound. The causes of the first sound have not 

 been proven so clearly by the available evidence, which is partly experimental 

 and partly derived from physical diagnosis followed by post-mortem verifica- 

 tion. The first sound, like the second, was ascribed by Rouanet 3 to vibrations 

 depending upon valvular closure, the simultaneous closure of the tricuspid 

 and mitral valves ; but the persistence of the sound throughout the whole 

 ventricular systole made this cause less probable than in the case of the second 

 sound. Williams, 4 on the other hand, ascribed the first sound to the con- 

 traction of the muscular tissue of the ventricles, an explanation consistent 

 with the muffled quality of the first sound, and with its persistence through- 

 out the systole of the ventricles. It is now believed by many that both of 

 the foregoing explanations are correct, and that the first sound is composite in 

 its origin, and due both to closure of the valves and to muscular contraction. 

 The evidence in favor of these causes is, briefly, as follows : 



In favor of a valvular element in the first sound, it may be urged : That 

 if the ventricles of a dead heart be suddenly distended with liquid, the mitral 

 and tricuspid valves produce a sound in closing; and that clinical and post- 

 mortem observations show that the first sound may be altered by disease 

 which cripples the auriculo-ventricular valves. 



In favor of an element in the first sound caused by muscular contraction 

 it may be urged : That in a still living but excised heart, the first sound con- 

 tinues to be heard under circumstances which preclude the closure and vibra- 

 tion of the valves, and leave in operation no conceivable cause for the first 

 sound except muscular contraction. Experiments upon the first sound of 

 the excised heart were reported in 1868 by Ludwig and Dogiel, 5 and were 



1 J. Rouanet : Analyse des bruits du cceur, Paris, 1832. 



2 C. J. B. Williams : Die. Pathologic und Diagnose der Krankheiten der Brust, etc. Nach der 

 dritten, sehr vermehrten Auflage aus dem Englischen fibersetzt, Bonn, 1838. (The writer has 

 not seen an English edition.) s Loc. cit. * Loc. cit. 



5 J. Dogiel und C. Ludwig : " Ein neuer Versuch iiber den ersten Herzton," Berichte uber 

 die Verhandlungen der k. sdchsischen Gesellschaft der Wissenschqften zu Leipzig, math.-physische 

 Classe, 1868, p. 89. 



