SOUNDS OF THE HEAET. 205 



along the oesophagus of a horse when drinking. 1 He divides 

 a single revolution of the heart into four parts : the first two 

 parts are occupied by the first sound ; the third part by the 

 second sound ; and in the fourth part there is no sound. 2 

 He regards the second sound as following immediately after 

 the first. Some authors have described a " short silence " as 

 occurring after the first sound, and a " long silence " after 

 the second. The short silence, if appreciable at all, is so 

 indistinct that it may practically be disregarded. 



Attempts have been made to improve upon this division 

 of Laennec, by dividing the heart's action into three equal 

 parts, as is done by M. Beau ; 3 the first being occupied by 

 the first sound, the second by the second sound, and the third, 

 silence. This hardly needs discussion. JVT. Beau bases this 

 division upon a theory of the production of the sounds which, 

 though pretty generally discussed by physiologists, is, as far 

 as we have seen, adopted by none, and is so entirely opposed 

 to facts that it hardly demands comment. It is evident to 

 any one who has heard the sounds of the heart, that the first 

 is longer than the second. 



Most physiologists regard the duration of the first sound 

 as a little less than two-fourths of the heart's action, and the 

 second sound as a little more than one-fourth. When we 

 come to consider the mechanism of the production of the two 

 sounds, we shall see that if our views on that point be correct, 

 the first sound should occupy the period of the ventricular 

 systole, or four-tenths of the hearths action, the second sound 

 about three-tenths, and the repose three-tenths. 



The first sound is relatively dull, low in pitch, and made 

 up of two elements : one ; a valvular element, in which it 

 resembles in character the second sound ; the other, an ele- 

 ment which is due to the action of the heart as a muscle. 

 It has been ascertained that all muscular contraction is at- 



1 Op. tit., p. 32. 



2 LAENNEC, Traite de I 1 Auscultation Mediate, Paris, 1837, tome iii., p. 48. 



8 BEAU, Traite experimental et clinique c?' Auscultation, Paris, 1856, p. 228. 



