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240 PATHOLOGICAL CONDITIONS.

lant; Peruvian bark, and gum myrrh, the tonic;
tannin the astringent ; and opiates the sedative prin-
ciple. Astringents, stimulants, and sedatives all tend
to counteract inflammation. The agents of this
class are not very extensively used in the treatment
of dentine, not because they are not ultimately effi-
cient, but because their action is less vigorous than
that of some other agents. When, however, time
and circumstances will permit, mild treatment, if
efficient, is to be preferred.

But there are many cases in which, for want of
time, something more rapid in its action is required.
Of this character is the second class of therapeutic
agents, namely, escharotics, or those which, by their
action, destroy a portion of the tissue with which
they come in contact. It may be well to notice,
separately, the preparations commonly used for this
purpose.
Tannin, or Tannic Acid.—This is the active prin-

ciple of vegetable astringents, and is found most
abundant in nutgalls. It unites with albumen, fibrin,
and gelatin, forming with them insoluble tannates.
Its medicinal influence is almost necessarily topical,
since the promptness of its action on albuminous sub-
stances, and the insolubility of its compounds with
them, prevent its admission into the general circula-
tion. The action of tannin on dentine has been