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THE DECAY OF THE TEETH. 143

from a fish tooth, the third with dentine from human teeth. The
pieces of human dentine were made in pairs, both members of
each pair being obtained from the same tooth by making a cross-
section of a sound, hirge molar, removing all traces of pulp-
cavity and of the enamel, and then dividing the section symmet-
rically into halves. In this way the two pieces of each pair were
as nearly alike as they could well be made.
In some of the experiments the pieces were filled with differ-
ent materials ; in others they were suspended to equal depth in
the solution by means of wires of different metals and of silk
thread, the latter method being equivalent to making fillings of
the same materials, the silk thread corresponding to a filling of
wax; the wires were all of the same diameter. In the sixth
column of figures I have given the results which would have
obtained in accordance with the experiment of Chase, on the
theory that if gold causes a certain loss in Aveight, amalgam
will cause two-thirds the same ; tin, one-half; gutta-percha, one-
sixth; wax, one-sixth, while the piece filled with zinc-oxychlo-
ride suffers no loss in weight. The balance used was capable of
noting a variation of two-tenths of a milligram.

Wkight Loss IN Compari-
Substance. Solution. Time. Suspended by
IX Mgs. Weight. son.
1. Ivory 115.6 Sulphuric Six weeks Gold wire 30.6 30.6
acid. 1 per
cent.
"
2. Sulphuric Silk thread 31.1 5.1
acid. 1 per
cent.
III.
1. Ivory 204.0 Vinegar Two weeks Gold wire 76.0 76.0
2. " " " " " Platinum wire 76.4
3. " " " Copper 76.0
4. " " ,Tin 75.0 38.0
5. •' Silk thread 76.8 12.7
1. Dentine from U12.0 Lemon-juice Eight days Gold wire 248 248.0
fish tooth
2 Dentine from Silk thread 244.0 I 41.3
fish tooth
VII.
1. Dentine from 39.3 Acetic acid, i Ten days Gold wire 5.0 5.0
human tooth 20 per cent.
" "
2. Dentine from Acetic acid, Silk thread 4.6 0.8
human tooth 20 per cent. I