70 



PHYSIOLOGY. 



Sounds of the heart. — When the ear is placed over the prcecordial 

 region, two sounds are heard, following each other in quick suc- 

 cession, at each beat of the heart. These sounds are followed 

 by a short interval of repose, after which they recur, again fol- 

 lowed by repose, and so on. The sounds are of different lengths ; 

 ihQ first being the longest. If the whole interval, from the beginning 

 of one pulsation to the beginning of the next, be divided into four 

 equal spaces of time, the first two will be occupied by the first sound, 

 the third by the second sound, while the fourth will represent the 

 period of repose. 



The first sound coincides with the systole of the ventricles, the pulse 

 in the arteries, and the impulse against the walls of the chest. The 

 second, with the first stage of the diastole of the ventricles. The 

 first is a dull, prolonged sound, the second is short and sharp, and 

 follows so immediately upon the first, that it can hardly be imagined 

 to occur during the systole of the auricles, as has been supposed. 



The causes of these sounds have given rise to much discussion. 

 The first is evidently complex, having several elements in its com- 

 position. The principal cause of it is found at the orifices of the 

 aorta and pulmonary artery, and is produced by the rush of the 

 blood through these comparatively narrow outlets. Another element 

 is found in the passage of the blood over the rough internal surface 

 of the heart ; a third element, in the sound of muscular contraction 

 accompanying the systole of the ventricles ; and a fourth in the im- 

 pulse of the heart against the walls of the chest ; for when the 

 impulse is prevented, the sound is much diminished. 



In regard to the seco;2(^ sound, which accompanies the first stage 

 of the diastole of the ventricles, there is not so much doubt. It is 

 produced by the sudden shutting dowji of the semilunar valves at 

 the orifices of the aorta and pulmonary artery, the function of which 

 valves is, tc prevent the reflux of the blood into the ventricles during 

 their dilatation. 



2b sum up^ the causes of \\\q first sounds are : 1st. The rush of 

 blood through the narrow orifices of the aorta and pulmonary artery ; 

 2d. The passage of the blood over the rough internal surface of the 

 ventricles; 3d. The sound of muscular contraction; 4th. The im- 

 pulse against the chest. The cause of the second sound is, the sud- 

 den shutting down of the semilunar valves at the orifices of the aorta 

 and pulmonary artery. 



The followiniT table from Dr. Carpenter's Human Physiology, will 

 perhaps assist the student in connecting the sounds of the heart with 

 its movements : 



First Sound. Ventricular systole, and auricular diastole. Impulse against 

 the chest. Pulse in arteries. 



Second Sound. First stage of ventricular diastole. 



Interval. Short repose; then auricular systole, and second stage of ven- 



tricular diastole. 



