CH. XX.] SOUNDS OF THE HEART. 237 



too, that the vibration of the ventricular walls themselves, 

 and of the aorta and pulmonary artery, all of which parts 

 are suddenly put into a state of tension at the moment of ven- 

 tricular contraction, may have some part in producing the first 

 sound. Secondly, the muscular sound produced by contraction of 

 the mass of muscular fibres which form the ventricle. Looking 

 upon the contraction of the heart as a single contraction and not 

 as a series of contractions or tetanus, it is at first sight difficult 

 to see why there should be any muscular sound at all when the 

 heart contracts, as a single muscular contraction does not produce 

 sound. It has been suggested, however, that it arises from the 

 repeated unequal tension produced when the wave of muscular 

 contraction passes along the -very intricately arranged fibres of 

 the ventricular walls. There can.be no doubt, however, that the 

 valvular element is the more important of the two factors, because 

 the sound is loudest at first, when the vibration of the valves 

 commences, and fades away as the vibrations cease. If the 

 sound was mainly muscular, it would be loudest when the mus- 

 cular contraction was most powerful, which is approximately 

 about the middle of the ventricular systole. The facts of disease 

 lend support to the theory that the first sound is mainly valvular ; 

 for when the valves are incompetent, the first sound is largely re- 

 placed by a murmur due to regurgitation of blood into the auricle. 

 After the removal of the heart from the body, the muscular 

 contribution to the first sound is audible but it is very faint. 

 It is stated to have a somewhat lower pitch than the valvular 

 sound. 



The cause of the second sound is more simple than that of the 

 first. It is entirely due to the vibration consequent on the 

 sudden stretching of the semilunar valves when they are pressed 

 down across the orifices of the aorta and pulmonary artery. The 

 influence of these valves in producing the sound was first demon- 

 strated by Hope, who experimented with the hearts of calves. In 

 these experiments two delicate curved needles were inserted, one 

 into the aorta, and another into the pulmonary artery, below the 

 line of attachment of the semilunar valves, and, after being 

 carried upwards about half an inch, were brought out again 

 through the coats of the respective vessels, so that in each vessel 

 one valve was included between the arterial walls and the wire. 

 Upon applying the stethoscope to the vessels, after such an 

 operation, the second sound ceased to be audible. Disease of 

 these valves, when sufficient to interfere with their efficient action, 

 also demonstrates the same fact by modifying the second sound 

 or destroying its distinctness. 



