72 CAUSES OF THE HEART-SOUNDS. 



[It is to be remembered that in reality four sounds are produced in the heart, 

 but the two first sounds occur together and the two second, so that only a single 

 first and a siugle second sound are heard.] 



The causes of the first sound are due to two conditions. As the sound is heard, 

 although enfeebled, in an excised heart in which the movements of the valves are 

 arrested, and also when the finger is introduced into the auriculo-ventricular orifices 

 so as to prevent the closure of the valves (C. Ludwig and Dogiel), one of the chief 

 factors lies in the " muscle sound " produced by the contracting muscular fibres of 

 the ventricles. This sound is supported and increased by the sound produced by 

 the tension and vibration of the auriculo-ventricular valves and their chordae 

 tendinese, at the moment of the ventricular systole. Wintrich, by means of proper 

 resonators, has analysed the first sound and distinguished the clear, short, valvular 

 part from the deep, long, muscular sound. 



The muscle-sound produced by transversely -striped muscle does not occur with a simple con- 

 traction (p. 86), but only when several contractions are superposed to produce tetanus ( 303). 

 The ventricular contraction is only a simple contraction, but it lasts considerably longer than 

 the contraction of other muscles, and herein lies the cause of the occurrence of the muscle-sound 

 during the ventricular contraction. 



Defective Heart-Sounds. In certain conditions (typhus, fatty degeneration of the heart), 

 where the muscular substance of the heart is much weakened, the first sound may be completely 

 inaudible. In aortic insufficiency, in consequence of the reflux of blood from the aorta into 

 the ventricle, the mitral valve is gradually stretched, and sometimes even before the beginning 

 of the ventricular systole, the first sound may be absent. Such pathological conditions seem to 

 show that, for the production of the first sound, muscle-sound and valve-sound must eventually 

 work together, and that the tone is altered, or may even disappear, when one of these causes is 

 absent. [Yeo and Barrett state that the sound is purely muscular (?).] 



The cause of the second sound is undoubtedly due to the prompt closure, and 

 therefore sudden stretching or tension, of the semi-lunar valves of the aorta and 

 pulmonary artery, so that it is purely a valvular sound. Perhaps it is augmented 

 by the sudden vibration of the fluid-particles in the large arterial trunks. [The 

 second sound has all the characters of a valvular sound. That the aortic valves 

 are concerned in its production, is proved by introducing a curved wire through the 

 left carotid artery and hooking up one or more segments of the valve, when the 

 sound is modified, and it may disappear or be replaced by an abnormal sound or 

 " murmur." Again, when these valves are diseased, the sound is altered, and it 

 may be accompanied or even displaced by murmurs.] Although the aortic and 

 pulmonary valves do not close simultaneously, usually the difference in time is 

 so small that both valves make one sound, but the second sound may be double 

 or divided when, through increase of the difference of pressure in the aorta 

 and pulmonary artery, the interval becomes longer. Even in health this may be 

 the case, as occurs at the end of inspiration or the beginning of expiration (v. 

 Du8ch). 



Where the Sounds are Heard Loudest. The sound produced by the tricuspid 

 valve is heard loudest at the junction of the lower right costal cartilages with the 

 sternum ; as the mitral valve lies more to the left and deeper in the chest, and is 

 covered in front by the arterial orifice, the mitral sound is best heard at the apex- 

 beat, or immediately above it, where a strip of the left ventricle lies next the chest- 

 walL [The sound is conducted to the part nearest the ear of the listener by the 

 muscular substance of the heart.] The aortic and pulmonary orifices lie so close 

 together that it is convenient to listen for the second (aortic) sound in the direction 

 of the aorta, where it comes nearest to the surface, i.e., over the second right costal 

 cartilage or aortic cartilage close to its junction with the sternum. The sound, 

 although produced at the semi-lunar valves, is carried upwards by the column of 

 blood, and by the walls of the aorta. The sound produced by the pulmonary artery 

 is heard most distinctly over the third left costal cartilage, somewhat to the left 

 and external to the margin of the sternum (fig. 51). 



