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AGENTS USED FOR STERILIZATION. 167
" We employed the gas generated by heating over an alcohol lamp
a pastil which contained five grains of paraform. The lamp was placed
in a tin box of nearly one cubic foot capacity . . . (Fig. 141). Among
the instruments employed in the tests were various chisels, excavators,
and burs. These were boiled, shown by cultural method to be sterile,
then either dipped into bouillon cultures or infected from selected cases
found in the operative clinic of the Department of Dentistry, University
of Pennsylvania. After infection each instrument was placed in a sterile
tube and kept at incubator temperature (37.5° C.) for three hours. . . .
In a single test with moist instruments we found sterilization complete.
After the infection and subsequent drying the tubes containing the in-
fected instruments Avere separated into two lots, one to be subjected to

Fig. 141.

Schering's formalin sterilizer.
the method of disinfection and the others to be kept as controls, by
which would be shown tlint no step other than the action of fornialde-
hyd destroyed the vitality of the germs. . . . After exactlv ten or
fifteen minutes, according to the experiment, the door was opened and
the instrument quickly removed. . . . Each instrument (controls like-
wise) was placed in a considerable amount of sterile bouillon and these
cultures, together with the subcultures made from them, observed for
at least one week. ... In all experiments a free growth developed
from the controls. . . . The disinfection of instruments purposely in-
fected in the clinics from cases of caries, pyorrhea, and gingivitis was
satisfactorily accomplished in every ca.se. . . . AVe conclude that infected
dental instruments can be di.sinfected without injury in a closed space
of less than one cubic foot, by an exposure of fifteen minutes to the