An Essay on the Circulation. [Volume: 2, Issue: 12, July, 1861, pp. 651-658]

654

THE DENTAL OOSMOS.

of arguments deduced from observation and experiment that ever appeared
on any subject." This great discovery was received at first with much
dissenting clamor, on account of his differing with or questioning the authority of Aristotle and Galen; but he lived to see his theory triumphant.
Harvey made known the important fact of there being two circulations,
namely, the greater and lesser, or systemic and pulmonic. This may be
more readily understood from a demonstration by means of the numeral
figure eight (8.) The greater circle representing the systemic circulation,
the lesser circle the pulmonic, and the point of contact of the two circles
the heart. By the systemic circulation is meant the passage of the blood
from the left ventricle of the heart through the body and back to the
right auricle by means of the arteries, capillaries, and veins. By the pulmonic circulation, the passage, by a distinct set of arteries, capillaries,
and veins, from the right ventricle through the lungs and back to the left
auricle. Each system thus has its own set of arteries or efferent trunks,
and veins or afferent trunks; these communicating at their central extremity by the heart, at their peripheral extremity by the capillary vessels,
by which are meant the minutest ramifications of the two systems inosculating into a plexus.
The chief impelling power of the blood is due to the heart's rhythmic
motion, which is attributed to the vis insita, though the exciting cause
cannot be positively determined. The contraction of the two auricles is
synchronous, the two ventricles also; but that of the auricles and ventricles is not. The contraction of these parts is followed by their dilatation or diastole, the first being the systole.
The diastole of the heart, according to Cruveilhier, is an active force,
no precise account of the cause being given. It is supposed to be owing
to the presence of the yellow fibrous tissue, interwoven with muscular substance, upon whose elasticity the first stage of ventricular diastole is supposed to depend; the second stage being caused by the ingress of blood
produced by the auricular systole. During the diastole of the heart the
impulse occurs; this is not the arterial pulse, but the shock communicated
by its apex to the walls of the thorax.
The heart has two sounds, one at each beat; they are followed by a
short interval of repose, after which they recur. If the whole interval,
from the beginning of one pulsation to the beginning of the next, be
divided into four equal spaces of time, the first two will be occupied by
the first sound, the third by the second sound, while the fourth will represent the period of repose.
First sound is during the second stage of ventricular diastole, ventricular systole, and auricular diastole. Impulse against the chest. Pulse
in the arteries
Second sound is during the first stage of ventricular diastole.
Interval. Short repose; then auricular systole, and second stage of
ventricular diastole, etc.