Page 43 - My FlipBook

anvil is as 15 to 28. (Letting the weight fall.) Now I have
the same result that I had upon the heavy anvil. You will
see also that the impulse given to the pencil is not quite
double the, impulse given at the shorter distance of fall.
I will make another experiment to show you the ex-
treme nicety of this thing, using the heavy anvil and this
same point ; then I will speak of the application of it, for all
of this applies directly to our work in filling teeth. Now, in-
stead of setting the block directly upon the anvil, I will put
a thin pad composed of a few thicknesses of ordinary writing
paper under it. It penetrates the paper readily without the
pad. This cuts the paper, but the cut piece falls away.
Now, J will try that by taking hold of the instrument and

making a little pressure at the time the weight falls. You
will notice that the paper is driven into the wood. It does
not fall away ; it doesn't rub off. It wasn't the hand pressure
that drove the paper into the wood, but I compressed the
layers of paper more closely in contact, so as to render it
more firm and solid. I bring this before you for a purpose.
There are a number of pounds more pressure in the blow
on account of the compression of the paper, and the pad is
but little thicker than the peridental membrane. The lesson
is this : If you fix the tooth, render the peridental membrane
tense by pressure at the moment your blow falls, you will
have from one-quarter to one-third more pounds pressure
in your mallet blow than if you do not so fix the tooth
by hand pressure at the time the blow falls, and you need
not strike your gold so hard to produce the same number of
pounds pressure with the mallet. Therefore, this little rapity-
tap-tap-tap over the gold is a very ineflficient means of con-
densing gold and comparatively painful to the patient ; neces-
sarily so ; it is so clinically, and it is so as a scientific fact.
It is the blow that hurts your patient, and you should always
labor to make that blow, whatever it is, just as efficient as
possible.
A word now in regard to the instruments of different
sizes. I will use the same wood block in the manudynamo-
meter, but I will use other instruments. Here is an instru-
ment point one-half millimeter in diameter. I will lay this
same paper on the block, and I will say that we can rarely
pierce the paper with an instrument held in the hand with as

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