366 * OF THE CIRCULATION OF BLOOD. 



seemed ready to burst, so great was its distension, and so thin were its walls. 

 Moreover, the large Veins near the heart contract simultaneously with the 

 auricular Systole, and not with its Diastole ; so that they can have no influence 

 in causing its dilatation. The Ventricular diastole is accompanied with a 

 projection of the heart downwards ; this motion was at its maximum when 

 the child was placed vertically, and was very strongly marked. 



484. When the ear is applied over the cardiac region, during the natural 

 movements of the Heart, two successive sounds are heard ; each pair of which 

 corresponds with one pulsation. The whole interval between one beat of the 

 Heart, and the next, may be divided into four parts ; of which ^ie two first 

 are occupied by what is commonly known as the first sound ; the third, by 

 the second sound ; whilst the fourth is a period of repose. The first sound 

 is dull and prolonged ; it is evidently synchronous with the impulse of the 

 Heart against the parietes of the chest, and also with the pulse, as felt rtfear 

 the heart ; it must, therefore, be produced during the Ventricular Systole. 

 The second sound follows so immediately upon the conclusion of the first, 

 that it can scarcely be imagined to take place during the auricular systole, as 

 some have supposed, but must be assigned to the period of the first stage of 

 the Ventricular Diastole. This, indeed, may now be regarded as clearly 

 established ; for it has been fully demonstrated, that the second sound is due 

 to the sudden filling-out of the Semilunar valves of the aorta and pulmonary 

 artery, with blood ; when the outward current through them has ceased, and 

 the incipient dilatation of the ventricles occasions a vacuum behind them. If 

 one of these valves be hooked back by a curved needle against the side ofthe 

 artery, so that a reflux of blood is permitted, the sound is entirely suppressed. 



485. The first sound cannot be so readily or satisfactorily accounted for. 

 That it is partly due to the Impulse of the apex of the Heart, seems proved by 

 the fact that, when this impulse, is prevented, the sound is much diminished 

 in intensity ; and also by the circumstance, that, when the Ventricles contract 

 with vigour, the greatest intensity of the sound is over the point of percussion. 

 But that it is not entirely due to this cause is also evident, from the fact, that 

 a sound may still be heard, when the Heart is contracting out of the body : as 

 in the case observed by Prof. Cruveilhier. This sound has been attributed by 

 some experimenters to the flapping-back of the auriculo-ventricular valves ; 

 by others, to the muscular contraction of the walls of the ventricles; by 

 others again to the rush of blood along the irregular walls of the ventricles, 

 and through the comparatively narrow orifices of the aorta and pulmonary 

 artery. This last is probably the most consistent with truth ; as would appear 

 from the following interesting observations made by Cruveilhier. By apply- 

 ing the finger to the origin of the pulmonary artery (which is situated in front 

 ofthe aorta, and completely conceals it), a perfectly distinct vibratory fremisse- 

 ?nent, corresponding with the ventricular diastole, was perceived : but no such 

 vibratory thrill could be felt by the finger, when applied to any part of the 

 base of the ventricles : whence it was evident, that no action takes place in 

 the mitral and tricuspid valves, which can give rise to the same palpable effects 

 as those produced by the semilunar valves. The same was ascertained regard- 

 ing the valvular sound, which could be distinctly heard by laying the finger 

 against the origin of the pulmonary artery, and applying the ear to it as to 

 a stethoscope : whilst nothing of the kind could be perceived in the region 

 of the auriculo-ventricular valves. Hence it seems quite certain, that the 

 natural first sound cannot be dependent in any way upon the action of the 

 mitral and tricuspid valves. It appeared, on the contrary, that the maximum 

 intensity of the first sound was in precisely the same situation as the maximum 

 intensity |f the secondnamely, at the origin of the large arteries; and that 

 it diminished, as the ear was carried from the base towards the apex of the 



