ON THE MOTIONS AND SOUNDS OF THE HEART. 205 
the depressed or collapsed parts of the ventricles, and favours 
the systolic shortening of the organ, and the closure of the 
auri-ventricular valves; and this reaction of the fluids mainly 
contributes, under various circumstances, to cause the motion 
that has been described as tilting of the apex; this tilting 
being principally, if not exclusively, a result of the elevation 
of the long axis of the heart in systole, owing to the assumption 
of a convex or globular form in the body of the organ, instead 
of its superiorly and inferiorly compressed state in the previous 
diastole. 
And the ventricular diastole or dilatation is wholly passive, 
exerting no influence over the venous current or arterial valves, 
and is effected by a rapid influx of blood from the veins, com- 
mencing at the moment of relaxation of the ventricles, and 
continuing until their succeeding systole, and reinforced imme- 
diately before the latter action by an abrupt discharge from 
the auricles. 
6th. That the pulsations of the veins are of two kinds, at 
least in some animals, viz. both active and passive; and the 
latter or passive pulsations (which, on the authority of Haller 
especially, may be held to exist in all animals), are attributable 
to reflux from the auricles in their systole. 
7th. The precordial throb or pulsation is caused, imme- 
diately, by the undulation of the blood in its resistance to 
sudden muscular compression in the systole of the ventricles. 
This reaction of the fluids is first perceived about the fundus 
of the ventricles, and last about the apex, towards which it 
seems to be propagated by a continuous undulation from the 
fundus with extreme rapidity. In consequence of this re- 
action of the blood, the heart’s sides are rendered convex, 
instead of compressed or flattened as in diastole, and are, in 
the middle parts more especially, heaved outwards from the 
central axis abruptly and with great force. Thus on all parts 
of the surface of the organ an impulse is felt in systole, which 
is greatest there, where, in addition to passive flaccidity of 
walls, there has been collapse in the diastole (viz. the central 
parts), and which is least where such collapse has previously 
been wanting or slight (viz. the apex). This cardiac impulse 
is usually perceived, in the healthy subject, over the apex 
only, owing to its being absorbed and neutralized over other 
parts of the heart by an interposed thick mass of spongy 
lung. The heart does not oscillate on the aorta, or move to 
and fro in the chest from systole to diastole, and vice versd ; 
nor does it suffer any changes in consequence of its own 
efforts, and exclusively of movements of the lungs and dia- 
