CHAPTER V.
STERILIZATION AND DISINFECTION.

BEFORE considering the cultivation of bacteria and
the preparation of media for that purpose it is necessary
to discuss methods of destroying bacteria whose acci-
dental presence might ruin our experiments.

The dust of the atmosphere, as has already been shown,
is almost constant in its inicro-organismal contamination,
so that the spores of moulds and bacilli, together with
yeasts and micrococci, constantly settle from it upon our
glassware, enter our pots, kettles, funnels, etc., and would
ruin every culture-medium, with which we operate did
we not take measures for their destruction.

Micro-organisms maybe killed by heat or by the action
of chemicals, the processes being genetically termed
sterilization. The term sterilization is usually employed
to denote the destruction of bacteria by heat, in contra-
distinction to disinfection, which usually means the
destruction of the bacteria by the use of chemical
agents. A chemical agent causing the death of bacteria
is called a germicide. An object which is entirely free
from bacteria and their spores is described as sterile.
Certain substances whose action is detrimental to the
vitality of bacteria and prevents their growth amid other-
wise suitable surroundings are termed antiseptics.

The study of sterilization, disinfection, and antisepsis
will naturally lead us through the following subdivisions :

I. The sterilization and protection of instruments and
glassware used in experimentation.

II. The sterilization and protection of culture-media.

III. The disinfection of the instruments, ligatures, etc.
and the hands of the surgeon, and the use of antiseptics.

IV. The disinfection of sick-chambers and their con-
tents, as well as the dejecta and discharges of patients
suffering from contagious and infectious diseases.

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