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FILLING TEETH 31

completed filling, and no satisfactory explanation
is forthcoming.
Semi-cohesive gold, if manipulated with a mallet,
can be condensed into a perfectly coherent mass, the
density of which (density and hardness are not
synonymous terms) cannot be surpassed with cohesive
gold. But if hand pressure is used with both of
these kinds of golds the cohesion produced with
the semi-cohesive variety will usually be inferior,
although in many cases it ma}^ be sufficient for all
practical purposes. The advantage of semi-cohesive
gold is that it is a little more adaptable than cohesive
gold, and consequently excellent adaptation, and an
even condensation, may be produced with larger
pieces or with broader ended pluggers.
Crystal Gold. — So much misconception exists
concerning crystal gold, and so many misleading
statements have been made in the past, and continue
to be made at the present day, about this form of
gold, that it may not be out of place to quote from
an article ' ' On the Value of Crystal Gold in Den-
tistry," by the late Dr, N, W. Williams, in the Inter-
nafional Dental Journal, February 1892, After
stating that crystal gold was first brought to the
notice of the dental profession in 1855 or 1856,
and was the invention of Professors George Watt
and J. Taft, and describing the process of its manu-