SOUNDS OF THE HEART. 203 



aortic semilunar valves oppose the passage of the liquid so 

 effectually that the aorta may be ruptured before the valves 

 will give way, a considerable degree of insufficiency exists, 

 under a high pressure, at the orifice of the pulmonary artery. 

 There is at this orifice a safety-valve function as important 

 as that ascribed by King to the tricuspid valve. It is evi- 

 dent that the slight insufficiency at the pulmonic orifice may 

 be even more directly important in protecting the lungs than 

 the insufficiency of the tricuspid valve. The difference in 

 the sufficiency of the semilunar valves on the two sides is 

 fully as marked as between the auriculo-ventricular valves, 

 and it is surprising that since the observations of King, this 

 fact has not attracted the attention of physiologists. 1 



It is probable that the corpuscles of Arantius, which 

 are situated in the middle of each valvular curtain, assist in 

 the accurate closure of the orifice. The sinuses of Yalsalva, 

 situated in the artery behind the valves, are regarded as facil- 

 itating the closure of the valves by allowing the blood to pass 

 easily behind them. 



Sounds of the Heart. If the ear be applied to the prse- 

 cordial region, it will be found that the action of the heart is 

 accompanied by certain sounds. A careful study of these 

 sounds, and their modifications in disease, has enabled the 

 practical physician to distinguish, to a certain extent, the 

 conditions of the heart. This increases the purely physiologi- 

 cal interest which attaches to the audible manifestations of 

 the action of the great central organ of the circulation. 



The appreciable phenomena which attend the heart's 

 action are connected with the systole of the ventricles. It is 

 this which produces the impulse against the walls of the 

 thorax, and, as we shall see further on, the dilatation of the 

 arterial system, called the pulse. It is natural, therefore, in 



1 This observation was first made, and the fact publicly demonstrated, in 

 the course on physiology at the Bellevue Hospital Medical College, session of 

 1864-'65. 



