As before stated, the natural ceaseless heavings of the lungs,
chest, and diaphragm, aided by the muscles inclosing the abdomen, have
the duty assigned them of communicating automatic motion to the uterus
and the other contents of the pelvis. When the diaphragm descends from
A to B, and the lungs are filled with air, the uterus sinks in the
pelvic cavity in obedience to the downward pressure from above, as
before stated; the circulation through the uterus is then for a moment
retarded, but the next instant, when the lungs are emptied of air and
the diaphragm rises, the blood flows forward more freely than if it
had not been momentarily obstructed. Ample provision has thus been
made to maintain a healthy circulation through the uterus.
The uterine motions I have described are fully adequate for the
purposes indicated. But when the natural stimulus of motion is
withheld, the circulation becomes sluggish causing congestion, which
may develop into inflammation. Under these conditions the uterus
gradually becomes displaced, falling backward, forward or downward as
the case may be. The blood vessels by which the uterus is supplied
thus have their caliber diminished by bending; the circulation through
them is retarded just as the flow of water in a rubber tube is
obstructed by a kink. A very good idea of what occurs in the uterus
under the conditions just described may be obtained by winding a
string around the fingers.
As the coats of the arteries are thick, and the pressure exerted by
the ligature has less power to prevent the arterial blood flowing
outward past the string to the end of the finger than it has to
prevent the return of the venous blood toward the heart, therefore the
part beyond the ligature soon becomes congested, the blood stagnating
in the capillaries.
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