THE SECOND SOUND. 31 



to the apex, than when it was applied over the region of the arterial 

 orifices. 



It is concluded that the first sound is formed of many component 

 tones, and is caused by the sudden tension and vibration of the cardiac 

 muscle, of the auriculo-ventricular valves, and of the blood, and that the 

 sound may be augmented by the stroke of the heart beating against the 

 parietes of the chest. The vibrations which are seen on the plateau of 

 the curve of the intraventricular pressure probably appear as sound 

 vibrations in the curves of the capillary electrometer, such as are 

 obtained by the microphonic method of Einthoven. 



The second sound. Carswell and Eouanet l were the first to assert 

 that the second sound of the heart was dependent upon the return 

 shock of the blood against the semilunar valves, when, at the end of 

 systole, the intraventricular pressure falls rapidly below zero and the 

 elastic reaction of the arteries comes into play. 



A sound is produced when, in the excised aorta, the semilunar valves 

 are suddenly thrown into tension, and this sound is similar in character 

 to the second sound of the heart. The most satisfactory method of 

 obtaining this result is, after ligaturing all other orifices and placing the 



FIG. 20. Tracing of pulse (P), first (A 1 , B 1 ) and second (A 2 , B 2 ) sounds 01 

 the heart. Einthoven and Geluk. 



>rta and valves in a vessel of water, to connect one coronary artery with 



pressure bottle. On suddenly opening the tap interposed between 

 ihe coronary artery and the pressure bottle, the valves are thrown into 



insion and a sound is heard. A tube connected with the vessel of 



rater is used as a stethoscope. 



To C. <T. B. Williams 2 we owe the first and conclusive experiments 



n the living animal. He noticed that the second sound was suspended 

 on applying pressure over the region of the orifice of the aorta and pul- 

 monary artery, and also when, by laying open the auricles, the heart 



icame emptied of blood. In both cases the first sound continued. 

 Williams further passed an ordinary dissecting-hook into the pulmonary 

 ;ery, and caught up and hooked back one of the semilunar flaps. 



le second sound was then changed in character. He next passed a 

 shoemaker's curved awl into the aorta, and hooked back an aortic flap. 



"he sound now gave way to a hissing noise. On withdrawing the hook 

 ind awl, the second sound of the heart was again heard, and the hissing 



iased. For the purpose of these experiments he used asses, supplied 



1 "Analyse des bruits du coeur," Paris, 1832. 



2 Rep. Brit. Ass. Adv. Sc., London, 1836, p. 269. 



