OF THE VENTRICLES OF THE HEART. 5 
bed 
& bined hemadromometer and sphygmoscope, and confirmed by Lortet, 
va leads me to doubt the correctness of Marey’s explanation, and to 
. advance the following. 
i, 
During the main ventricular descent the aortic pressure increases 
______ (©); probably from the rise of the base of the heart after its contraction, 
: just as at the commencement of the systolé it falls (a) from the oppo- 
4 site cause. — 
4 _ When all contraction has ceased, the only impediment to regurgi- 
tation from the arteries is the passive resistance of the ventricular 
walls, which is comparatively slight; so that blood flows back to the 
heart, compressing the ampoule in the ventricle and causing the eleva- 
tion z in the upper trace, while it necessarily produces asimilar depres- 
sion in the lower one. 
When the reflux of blood has become sufficiently rapid, the aortic 
valve closes, and in so doing puts an abrupt stop to the ventricular 
rise z. Immediately after this the coronary repletion and consequent 
turgescence commences, as shown above, and by opening out the cavi- 
ties of the ventricles, diminishes the pressure on the contained ampoule, 
and so depresses the trace below zero. 
The tendency to the formation of a vacuum, together with the 
associated raising of the base of the heart, causes so great a rush of Page 393. 
blood from the auricles, which as Mr. Bryant has shown are then quite 
full, that a slight undulation is produced in the ventricular trace z. 
The increase in bulk of the ventricular walls, consequent on the 
coronary repletion, takes place in all directions, and by expanding the 
whole conical heart, pushes the base up into the cavity previously. 
occupied by the full auricles, which it simultaneously empties by the 
absorptive force. 
This theory being true, the heart is a machine in which simplicity 
of action and economy of force are most marked. The systolic move- 
ments fill the reservoirs which are to feed the cavities they empty ; and 
all the diastolic forces are expended in active preparation for the suc- 
ceeding systolé ; the circulation in its walls, besides its primary object, 
even aiding its mechanical function. 
