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36 THE TECHNICAIi PROCEDUEES IN FILLING TEETH.

should have careful attention. It is to he done in the same way
day after day and correct habits of grasp and movement should
be formed for each instrument.
The chisels and enamel hatchets, which are much used for
chipping enamel and trimming enamel walls, should have a short
bevel similar to that of the hoes. The chisels are ground in a
manner very similar to the grinding of the hoes. They are the
simplest and easiest of the cutting instruments to sharpen cor-
rectly. In grinding the enamel hatchets, the stone should be laid
differently to the hand and the instrument should be grasped
differently. In grinding the right-hand instrimient, lay the stone
crosswise to the length of the arm. Catch the instrument shaft
between the third and fourth fingers, with the point between the
thumb and forefinger. Find the position that will give the cor-
rect bevel and grind with an elbow movement, sweeping from
end to end of the stone. In this grasp, the end of the second
finger may slide on the stone as a rest. In grinding the left-hand
instrument, use the ordinary pen grasp, turn the hand until the
thumb nearly touches the stone, use the third finger as a rest,
find the position that will make the correct bevel and grind with
the elbow movement.
In all of these, the edges should be kept straight and should
be equally sharp in all parts of their length. Too much grinding
should be carefully avoided. Make the edge sharp and no more.
One should be always trying the edges to ascertain the degree of
sharpness, and these trials should include three points on the
edge of each instrimient even to the smallest of the excavators:
the center of the length of the edge and each of the angles of the
edge with the blade. The trials should be made on the thumb or
finger nails. Touch the edge to the nail lightly and see that it
takes, or catches ; if, with this very light pressure, any part of
the edge will slip on the nail instead of taking hold, it is not fully
sharp and needs more grinding. This test on the nails is a very
delicate one and if delicately used will not mar the nails and
will very certainly reveal any lack of perfection in the edge of
the instrument. The correct angle of the edge with the length of
the blade should be very carefully preserved in all of the grind-
ings. Wlien all of this is done carefully, the edges kept in good
form, sharp, and not overground, the instruments furnished us
will do an immense amount of service. An instrirment will occa-
sionally be found that is too hard, so that the edge crumbles, or
is too soft, so that the edge will not hold. Tlie tempering of these
small instrument points is an extremely delicate process and