ng this in all its intricate relationary
combination--even through and beneath the closed surface of living
moving nature, is he prepared to estimate the conditions of disease, or
interfere for its removal.

When fluid accumulates on either side of the thoracic compartment to
such an excess that an opening is required to be made for its exit from
the body, the operator, who is best acquainted with the relations of the
parts in a state of health, is enabled to judge with most correctness in
how far these parts, when in a state of disease, have swerved from these
proper relations. In the normal state of the thoracic viscera, the left
thoracic space, G A K N, is occupied by the heart and left lung. The
space indicated within the points A N K, in the anterior region of the
thorax, is occupied by the heart, which, however, is partially
overlapped by the anterior edge of the lung, PLATE 22. If the thorax be
deeply penetrated at any part of this region, the instrument will wound
either the lung or the heart, according to the situation of the wound.
But when fluid becomes effused in any considerable quantity within the
pleural sac, it occupies space between the lung and the thoracic walls;
and the fluid compresses the lung, or displaces the heart from the left
side towards the right. This displacement may take place to such an
extent, that the heart, instead of occupying the left thoracic angle, A
K N, assumes the position of A K* N on the right side. Therefore, as the
fluid, whatever be its quantity, intervenes between the thoracic walls,
K K*, and the compressed lung, the operation of paracentesis thoracis
should be performed at the point K, or between K and the latissimus
dorsi muscle, so as to avoid any possibility of wounding the heart. The
intercostal artery at K is not of any considerable size.

In the normal state of the thoracic organs, the pericardial envelope of
the heart is at all times more or less uncovered by the anterior edge of
the left lung, as seen in PLATE 22. When serous or other fluid
accumulates to an excess in the pericardium, so as considerably to
distend this sac, it must happen that a greater area of pericardial
surface will be exposed and brought into immediate contact with the
thoracic walls on the left side of the sternal median line, to the
exclusion of the left lung, which now no longer interposes between the
heart and the thorax. At this locality, therefore, a puncture may be
made through the t