ON THE MOTIONS AND SOUNDS OE THE HEART. 249 
in the diastole, and receded from it in the systole. This differ¬ 
ence between the movements of the heart in that animal and in 
the others which were submitted to experiment, may be ex¬ 
plained by considering that in the heart of the latter the swell¬ 
ing of ventricles during systole is produced by the thickening 
of their muscular fibres, which are then in a state of contraction, 
and of which the mass bears a large proportion to the size of 
the internal cavities : while, in the heart of the frog, the sides 
of the ventricle are thin, and its cavity is large; and the thick¬ 
ening of its sides produced by the contraction of their fibres, 
does not counterbalance the diminution of the volume of the 
ventricle attendant on the expulsion of its blood. 
§ 4. Conclusions respecting the Sounds of the Heart . 
From the experiments on the sounds of the heart it appears 
to follow: 1. That the sounds are not produced by contact of 
the ventricles with the sternum or ribs, but are caused by mo¬ 
tions within the heart and its vessels. 2. That the sternum and 
front of the thorax, by their contact with the ventricles, in¬ 
crease the audibleness of the sounds. 3. That the first sound 
is connected with the ventricular systole, and coincides with it 
in duration. 4. That it is not produced by the friction of the 
internal surfaces of the ventricles against each other, as such 
friction cannot exist until the blood has been expelled from the 
ventricles, whereas the first sound commences with the beginning 
of the ventricular systole. 5. That the cause of the first sound 
is one which begins and ends with the ventricular systole, and is 
in constant operation during the continuance of that systole. 
6. That the first sound does not depend upon the closing of the 
auriculo-ventricular valves at the commencement of the ventri¬ 
cular systole, as that movement of the valves is of an instanta¬ 
neous character, and is much shorter in duration than the sy¬ 
stole. 7. That it is produced by the rapid passage of the blood 
over the irregular internal surfaces of the ventricles, on its way 
to the mouths of the great vessels. 8. That the ‘bruit mus- 
culaire 3 may contribute to the production of the first sound. 
9. That the second sound coincides with the termination of the 
ventricular systole, and requires for its production the integrity 
of the semilunar valves of the aorta and pulmonary artery; 
That it is caused by the sudden check given by the action of 
those valves to the motion of the columns of blood driven to¬ 
wards the heart after each ventricular systole, by the elasticity 
of the arterial trunks. 
The Committee wish to express their opinion, that although 
