458 THIRD REPORT — ISoo. 



4th. An explanation of the sounds of the heart has become 

 necessary smce the employment of the stethoscope in ascer- 

 taining the state of internal parts. Laennec has well described 

 these sounds, and properly refers the first to the rush of blood 

 from the ventricles during their systole. But, in supposing 

 that the second sound is produced by the auricular systole, he 

 has fallen into an extraordinary error, as the second sound 

 follows immediately after the first one, whereas the auricular 

 systole precedes the ventricular. This mistake has been no- 

 ticed by different writers since Laennec's time, who have re- 

 jected his explanation, and substituted others in its place. 



From the observations which the author has made, he has 

 no doubt that the second sound is caused by the obstacle which 

 the semilunar valves present to the passage of the blood from 

 the arteries back into the heart, at the termination of the ven- 

 tricular systole. 



At each contraction of the ventricles a quantity of blood is 

 driven by them into the trunks of the arteries, which, being 

 already full, accommodate the addition to their contents by a 

 lateral expansion of their parts nearest to the heart. When 

 the systole of the ventricles is at an end, the elastic force of the 

 arteries, acting upon their contained blood, drives it towards 

 the heart, its entrance into which is prevented by the sudden 

 closing of the semilunar valves : and thus a shock is communi- 

 cated to the front and upper part of the ventricles, and to the 

 adjacent trunks of the arteries, which may be heard by the 

 ear placed over the region of the heart. The relation, as to 

 time, which the second sound has to the first, its abrupt cha- 

 racter, and its coincidence with the end of the ventricular systole, 

 have led the author to adopt the foregoing opinion. 



Mr. Carlile then described the experiments from which the 

 greater number of the preceding conclusions have been dra^n, 

 and having detailed the circumstances of some made upon living 

 subjects, proceeded to relate those which follow. 



1. Artificial respiration having been established in a rabbit 

 which had been strangled, and the heart having been exposed, 

 the following observations were made. 



The finger being applied successively to the front, back, and 

 each side of the ventricles, conveyed the sensation of hardness 

 and impulse when the ventricles assumed the globular form, and 

 of softness and flaccidity when they became flattened and ex- 

 panded. The end of a probe being laid on the front surface 

 of the ventricles, was raised nearly a quarter of an inch during 

 the former of these states, and sank, causing a slight depression 

 on the surface, in the latter. The probe was more elevated 



