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154 THE TREATMENT OF TEETH

or with hoAV much force the gold may have been
packed into and onto the amalgam. This is pro-
bably due to the destruction of the amalgamated
gold, for a filling of this kind made immediately
really consists of three parts : first, an ordinary
amalgam, then an amalgam composed principally,
if not entirely, of gold and mercury, and finally
a gold filling. In the first edition the writer advo-
cated the " immediate " method of making these
fillings, but now much prefers to insert the amalgam,
and fill up with temporary gutta-percha, then, at a
subsequent sitting, to insert the gold. When amal-
gam and gold are used in connection in the same
cavity, the surface of the amalgam will become per-
fectly black, and for " appearance' sake " it is often
advisable to cut out part of the buccal surface
of the amalg^am, and extend the srold, so as to
cover up this part. It is said that an electrical
action is set up which is beneficial in saving the
tooth ; no doubt the rapid oxidising and blacken-
ing of the surface of the amalgam is due to such
action, but the action ceases as soon as the surface
is oxidised, and beyond the preservative effect
that a black amalgam seems to have, the value
of these fillings is more mechanical than thera-
peutic.
It may not be out of place to here allude to the