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HISTOKY OF DEXT.\L SURGERY 177

and usually stains the tooth to an inky hlackness. At the time, the expansion
was not recognized and the blackness was considered the most serious objection
against its use. All the earlier experiments, therefore, had for their object an
alloy for amalgam that would retain its own color and would not stain tlie
tooth. This result was approximately accomplished by the introduction of a
\ery large proportion of tin, which also made the amalgamation quicker and
easier and tlie mass much more plastic and readily inserted. It also diminished
somewhat the amount of mercury required, which was considered desiralilo.
Dr. Elisha Townsend gave to the profession the formula sixty tin and forty sil-
ver, which came into very extensive use, and was imitated so closely by most of
the makers of amalgam alloys as to make this proportion of silver and tin' a
fair representative, in all essential characteristics, of an overwhelming majority
of all the amalgam fdlings inserted during a very long period of time. Dr.
Amijrose Lawrence made an amalgam alloy which was extensively sold for a
long time and which contained a somewhat larger proportion of silver and
consequently made a rather Ijettcr filling, l)ut it tarnished rather more and
worked less easily. Its use was therefore much less extensive than that of
manv of its competitors. It was not fully recognized for many years that the
comparative freedom from tarnishing and staining had been accomplished by
the acquirement of so objectionable a quality as shrinkage, and that to such a
degree as to make the fillings leaky. It is hardly too much to say that all
the amalgam fillings made in America through a long period of years were
leaky, the exceptions to that being so few as scarcely to be worth consideration.
AVhen tlie profession began to appreciate this shrinkage and consequent leakage
numerous efforts were made to find an alloy that would be free from tliis
objeition and various tests were used to determine leakage. The first ex-
periments of much value were made by .Tohn Tomes of England, in 18G1.
(Transactions of the Odontological Soc, Great Britain. Vol. III.) Holes were
made in ivorv slabs like slides inr a microscope, and these were clamped on an-
other piece of ivory and the fillings made in the holes were examined with the
nucroscope. Seven amalgams were tried, six of which shrank, one, of copper,
did not, but copper amalgam wastes away in the mouth so as to be unfit for
fillings. Dr. Thomas Fletcher, of Warrington, England, made fillings in
short glass tubes and immersed them in ink. or carmine, or Prussian blue dis-
solved in water or alcohol. Tliis te^^t shov.-ed most of them shrank, some so
as to fall out of the tul)es. Dr. Black afterward found these tests very im-
perfect and inadequate, and also found that poor manipulation would cause
the same appearances as shrinkage. In 1871 Charles Tomes determined