410 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



given to the elucidation of the curve thus recorded ; but, so far, too little 

 agreement has been reached for the subject to be entered upon here. 1 



J. THE SOUNDS OF THE HEART. 



If the ear be applied to the human chest, at or near the place of the apex- 

 beat, the heart's pulsation will be heard as well as felt. This fact was known 

 to Harvey. 2 About two hundred years later than Harvey, in 1819, the 

 French physician Laennec, the inventor of auscultation, made known the fact 

 that each beat of the heart is accompanied not by one but by two separate 

 sounds. He also called attention to their great importance in the diagnosis of 

 the diseases of the heart. 3 



Relations of the Sounds. The first sound is heard during the time when 

 the apex-beat is felt ; it therefore coincides with the systole of the ventricles. 

 The second sound is much shorter, and follows the first immediately, or, to 

 speak more strictly, after a scarcely appreciable interval. The second sound, 

 therefore, coincides with the earlier part of the diastole of the ventricles. 

 The second sound is followed in its turn by a period of silence, commonly 

 longer considerably than the second sound, which silence lasts till the begin- 

 ning of the first sound of the next ventricular beat. The period of silence, 

 therefore, coincides with the later, and usually longer, portion of the diastole 

 of the ventricles, and with the systole of the auricles. It is interesting that 

 the great auscultator, Laeunec, offered no explanation of the cause of either 

 sound, while he made and reiterated the incorrect and misleading statement 

 that the second sound coincides with the systole of the auricles. When the 

 heart beats oftener than usual, each beat must be accomplished in a shorter 

 time; and it is found that, during a briefer beat, the period of silence is 

 shortened much more than the period during which the two sounds are audi- 

 ble ; which latter period may not be altered appreciably. 



Characters of the Sounds. The first sound is not only comparatively 

 long, but is low-pitched and muffled. The second sound is comparatively 

 short, and is high and clear. The two sounds, therefore, are sharply con- 

 trasted in duration, pitch, and quality. A rough notion of the contrasted 

 characters of the sounds may be obtained by pronouncing the meaningless 

 syllables " lubb dup." In other mammals the sounds have substantially the 

 same characters as in man. 



Cause of the Second Sound. Since Laennec's time, the cause of the 

 second sound has been demonstrated by experiment. The second sound is due 

 to the vibrations caused by the simultaneous closure of the semilunar valves 

 of the pulmonary artery and of the aorta, when the diastole of the ventricles 

 has just begun. This cause was first suggested by the French physician 



1 M. von Frey : Die Untersuchung des Pulses, etc., 1 892, p. 102 ; K. Tigerstedt : Lehrbuch der 

 Physiologic des Kreislaufes, Leipzig, 1893, p. 112. 



2 Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, 1628, p. 30 ; Willis's trans- 

 lation, Bowie's edition, 1889, p. 34. 



3 R. T. H. Laennec: De I' auscultation mediate, etc., Paris, 1819. 



