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PROPHYLAXIS OF DENTAL DECAY. : 233

of time, after whicli they were brought into culture-gelatine aud
the number of colonies which developed determined. The
stronger the antiseptic and the longer the time of exposure, the
less will be the number of colonies which develop in the culture
tube. As control, the experiment was repeated, using sterilized
water instead of an antiseptic solution.
To avoid transferring too much of the antiseptic to the culture
tube, each piece was placed for an instant on sterilized blotting-
paper, to remove the excess of liquid. I give the results of one
of these experiments below. In this solution ~So. 4 was made
use of, and small pieces of bread charged with bacteria subjected
to the action of the solution 20, 35, 55, 70, 90, and 120 seconds
respectively. The control tube developed 4500 colonies
Tube 1 (20 seconds action) developed 420 colonies.
u "
2 (35 " ) " 46 "
" 3 (55 " " ) " 250 "
" 4 (70 " " ) " 13 "
" 5 (90 " " ) " 1 colony.
" 6 (120 " " ) remained sterile.
It may appear strange that tube 3 should develop more colonies
than tube 2, but such irregularities often occur, owing to the
fact that it is not possible to obtain pieces of bread or meat of
exactly the same size and consistency. The result of the experi-
ment is, however, very clear. When large compact pieces were
used (as large as a pea, for example), such as may sometimes be
found in cavities of decay, it required as much as ten to fifteen
minutes to effect a complete sterilization. The lesson is plain.
Even such a powerful wash as the one under consideration will
accomplish but little in sterilizing the human mouth when the
centers of decay are stuffed full of food. This is also the reason
why excessive smoking, notwithstanding the fact that tobacco-
smoke is a powerful antiseptic, does not insure the teeth against
decay ; the smoke passes over the surface, but does not penetrate
to the point of action. It follows that the use of the mouth-
wash should always be preceded by the thorough use of the
brush or toothpick, removing at least all larger particles of food
and opening the spaces between the teeth, so that the wash may