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TOOTII-BLEACHING—USE OF ClILORIN. 541

The only agent belonging to the group of reducing bleachers which
has thus far been found available for bleaching teeth is sulfurous oxid,
either in the gaseous coudition or in aqueous solution.
Chlorin as a Bleacher.—The general use of chlorin as a bleaching
agent in the arts no doubt suggested its use in the treatment of tooth
discoloration. Its introduction as a tooth-bleaching agent, as well as the
assembling of the general principles of tooth bleaching into a co-ordi-
nate system, are due to Dr. James Truman, whose method depends upon
the liberation of chlorin from calcium hypochlorite, commonly called
bleaching powder or "chlorinated lime," in the pulp chamber and cav-
ity of decay in the tooth. Chlorin is liberated from the bleaching pow-
der by the action of dilute acetic acid ; this taking place in contact with
the discolored structure, it is rapidly bleached as a result of the action
of the chlorin upon the coloring matter contained in the dentinal tubules.
Numerous modifications of this original method of bleaching tooth struc-
ture have been suggested, but, as the ultimate result in each is accom-
plished through the activity of chlorin, a rational understanding of the
mode of action of chlorin in this relation is of importance as an aid
to the intelligent use of those methods for tooth-bleacliing which are
dependent upon or owe their efficacy to that agent.
Chlorin is an elementary gaseous body, greenish in color, soluble in
water, iiaving a disagreeable odor, intensely irritating to the air-passages
when inhaled, and poisonous when breathed in sufficient quantity. It
has a strong affinity for all metallic bodies, entering into direct combi-
nation with a number of tliem, under favorable circumstances, with
great energy—forming, as a rule, compounds that are soluble in water.
One of its distinguishing features and one which is directly concerned
in its use as a bleaching agent is its strong affinity for hydrogen. So
strong is this affinity, that when a molecule of chlorin is brought into
contact with a molecule of water under favorable conditions, the hydro-
gen of the water molecule is seized upon by the chlorin to form chlor-
hydric acid and the oxygen is set free in the nascent state, a condition
under which its oxidizing powers are exhibited in their greatest intensity.
This powerful affinity of chlorin for hydrogen enables it to decompose
many other hydrogen-containing molecules in a similar manner, form-
ing chlorhydric acid and destroying the identity of the matter acted
upon.
It ha,s been shown that all organic compounds which are the products
of the vital processes of the animal body contain hydrogen as an im-
portant constituent. This applies also to the decomposition products
whose presence in the tubular structure of the dentin is the cause of
tooth discoloration.
These organic stains exhibit the pi-opcrty of" color by virtue of