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THE ANTISEPTIC ACTION OF FILLING-MATERIALS. 241

fillings do not so readily decompose, owing to their becoming
charged with antiseptic cupric salts."
Other materials experimented with by the first method were
gold amalgam, oxychloride of zinc (agate cement), oxyphosphate
of zinc (Caulk's cement), gutta-percha, gold, tin, and tin-gold.
Gold amalgam, freshly mixed, caused a slight retardation in the
development of bacteria ; old pieces had no ejffect. Oxychloride
of zinc, fi-esli, had a very marked action. (See Fig. 107.) Pieces
which had lain twenty-four hours in saliva and bread lost their
antiseptic power. Oxyphosphate of zinc, fresh, had a slight, in-

FiG. 108.

Ixoci'LATED GELATINE PLATE Containing Pack's pellets and Abbey '? foil Xo. 4, folded to
make strips of No. 32. a, h, c, (/.annealed; e,/, g, unannealed. The latter have retarded the
growth of the bacteria in their neighborhood, as is shown by the gelatine remaining clear. Plate
twenty-four hours old.
constant action (Fig. 107), sometimes none at all. After twenty-
four hours' exposure in a mixture of saliva and bread, it showed
no action whatever ; gutta-percha and tin proved completely in-
active.
The results obtained with gold were very peculiar and perplex-
ing. Some preparations of gold manifest a decided restraining
efi'ect upon the development of bacteria, so that if a pellet is
dropped upon the plate it will after twenty-four to forty-eight
hours appear surrounded l)y a perfectly round circle of trans-
parent gelatine, separated from the clouded gelatine by a sharp
16