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2 28 THE TREATMENT OF PULPS

(f) In difficult cases a 50 per cent, solution of sulphuric
acid, or better, phenol-sulphonic acid (which latter more
readily clings to the broach), carried into the canal on the
broach, will, by uniting chemically with the calcium salts of
the dentin, soften the walls of the canals and render the work

easier. Its action should be neutralized on completion of the
operation with a saturated solution of sodium bicarbonate.
Remove all debris.
(g)
(h) After the proper medicinal treatment has been given,
depending, on the conditions present, as already described,

the canals are ready for drying and filling.
Wrapping Cotton on Smooth Broaches.—The method
varies, depending on whether the cotton, containing some
medicament, is to be temporarily left in the canal, or whether
it is to be immediately withdrawn on the broach, as in swab-

bing or drying the canal.
I. When the Cotton is to be left in the Canal.— (a) Place
a few wisps of cotton on the pulp of the forefinger of the left
hand, (b) Lay a round or square smooth broach on the
cotton, allowing the end of the cotton to extend slightly

beyond the point of the broach, (c) Rotate the broach to
right with the thumb and fingers of the right hand, at the
same time rolling the cotton in the same direction with the
thumb and forefinger of the left hand. Roll the cotton fairly
tightly at the point of the broach and loosely the rest of the

way. (d) Fold the slight excess of cotton left at the end of
the broach over that already rolled and roll it in the same
direction as before, so as to thoroughly cover the point of the
broach, (e) Garry the broach containing the cotton as far
as possible into the canal to be treated, (f) Rotate a turn to

the left, at the same time withdrawing it a short distance,
when the cotton will be disengaged, (g) Pack the cotton
further into the canal by pushing the broach slightly forward,