ON THE MOTIONS AND SOUNDS OF THE HEART. 273 



artery in which a valve had been so hooked up. If a valve in 

 one artery only was so engaged, the second sound was weakened ; 

 but if a valve of each set of sigmoids was fixed, then the second 

 sound wholly disappeared. In some instances there was a mur- 

 mur of the sucking or blowing kind following the systole during 

 the suspension of the valve ; in other instances there was absence 

 of sound simply. Experiments 4, 6, 12, 13. 



5. The arteries were cut across close to the sigmoid valves, 

 the veins being left entire, and the heart beating with consider- 

 able force ; the ear-tube was then applied, but gave only one 

 sound, and that one coincident with the systole. Experiment 14. 



6. In the separated heart the first sound was repeatedly ob- 

 served, but the second sound never. 



Summary of Conclusions. — 1. The first sound of the heart, as 

 heard in the chest, is generally complex in its nature, consisting 

 of one constant or essential sound, and one perceptible only under 

 certain circumstances ; this constant element of the first sound 

 may be considered as intrinsic, appearing to depend on the sud- 

 den transition of the ventricles from a state of flaccidity in dia- 

 stole to one of extreme tension in systole ; while the extrinsic or 

 subsidiary sound, which generally accompanies and increases the 

 intrinsic sound, arises from the impulse of the heart against the 

 parietes, chiefly of the thorax. 



2. The collisions of the particles of the blood amongst each 

 other, or against the interior parietes, valves, &c. of the heart, 

 do not appear to have any share in the normal first sound of the 

 heart ; neither do the motions of the auriculo-ventricular valves ; 

 and the attrition of the opposite interior surfaces of the heart's 

 cavities seems purely hypothetical. 



3. The principal, and apparently only, cause of the second 

 normal sound of the heart, is the sudden closure of the sigmoid 

 valves by the columns of blood that recoil back on them during 

 the diastole, impelled by the elastic contraction of the arteries. 



4. The columnae carnese appear to act simultaneously with the 

 parietes of the ventricles, and in such a manner as to make it 

 apparently impossible that the auriculo-ventricular valves should 

 close with a flap, in the same manner as the sigmoid valves. 



Note. An opinion which is further confirmed by the anatomy 

 of the heart of the domestic cock, in which M. Bouillard appears 

 to have heard both sounds with the naked ear. In that animal 

 there is no tricuspid valve resembling that of man, but the val- 

 vular office is discharged by laminar extensions of the substance 

 of the pai'ietes of the ventricle, which meet in the middle, so as, 

 during the systole, to cover the auriculo-ventricular orifice. 



To conclude, — The Committee feel strongly that the subject 

 VOL. v.— 1836. T 



