This was the special claim set up by Aveling for his Sigmoid forceps.
Tarnier also, in introducing his axis traction forceps to the profession
in 1877 (for an account of which see _British Medical Journal_, May 26,
1878), proves by means of diagrams and figures that, “in pulling on the
classical forceps, it is impossible to make the traction exactly in the
line of the pelvic curve,” and that two forces are actually exerted—one
in the direction of the inferior straight, and the other at right angles
to this in the direction of the pubes, while the head tends downward in
the pelvic curve—the resultant of these two forces. This “vicious
pressure” upon the pubes represents not only so much force lost, but
also tends to injure the maternal soft parts, and can only be overcome
by using the axis traction forceps. As the head descends, the pelvic
curves of the blades become less and less, until, as the head arrives on
the floor of the pelvis, the forceps are nearly straight. At the moment
the head sweeps over the perineum the blades are still further
deflected, until they form an angle with the shafts, as shown in the
dotted lines of Fig. 1, thus forming the perineal curve of Herman's,
Aveling's and Tarnier's forceps.
2. These forceps give the greatest permissible freedom of movement to
the head during traction.
By the loose connection of the blades each possess a degree of
independent movement, but always in a plane parallel to the other, so
that the head may rotate during traction. The carrying out of this
important principle is the chief advantage of this instrument over all
other axis traction forceps.
3. An index is supplied by the arms and pin, which serves to indicate
the advance and position of the head.
The application of Breus' forceps is in no wise more difficult than that
of the ordinary instrument. Having disinfected, warmed and lubricated
the blades, and the patient being prepared by an irrigation of a
solution of bichloride, one part in 2,000, and placed in the lithotomy
position, the handle of the left blade is taken up by the thumb and
three fingers of the left hand (as one would hold a fiddle bow), the
index finger pressing the projecting arm firmly against the shaft, as
the thumb of the right hand guides the blade forward in the groove
between the index and middle fingers introduced into the vagina. The
right blade is then introduced in a similar manner and locked, and the
pin inserted in the eyes of the projecting arms. The traction is made
upon the handles in the axis of the brim, without changing its direction
until the head presses on the perineum. Prof. Braun prefers, at this
point, to remove the forceps and complete the delivery in the ordinary
way.
The same precautions are necessary in using the axis traction as the
ordinary forceps. Especially must it be remembered that, as the force is
exerted directly in the axis of the pelvic curve, and none being lost,
much less is required, and generally the force of one hand is quite
sufficient. To avoid too great compression of the head, the compressing
force should be removed by opening the lock in the interval of each
traction.
Breus' forceps, after being tested successfully in all possible
difficult cases—in many where the operator had failed with the ordinary
forceps, as I myself have seen—is now recognized as the instrument best
adapted to those cases where the head presents high above the pelvic
brim.