a good means of disinfection, but can be applied only
to very few objects; all bacteria need moisture for their existence
and multiplication, hence absolute dryness acts as a good germicide.
Meat and fish, certain cereals, and also fruit, when dried, become at
the same time disinfected.

_Heat_ is the best, most valuable, all-pervading, most available, and
cheapest disinfectant. The various ways in which heat may be used for
disinfection are burning, dry heat, boiling, and steam.

=Burning= is of course the best disinfectant, but it not only destroys
the germs in the infected materials, but the materials themselves; its
application is therefore limited to articles of little or no value,
and to rags, rubbish, and refuse.

=Dry Heat.=--All life is destroyed when exposed to a dry heat of 150 deg.
C. for one hour, although most of the bacteria of infection are killed
at a lower temperature and in shorter time. Dry heat is a good
disinfectant for objects that can stand the heat without injury, but
most objects, and especially textile fabrics, are injured by it.

=Boiling.=--Perhaps the best and most valuable disinfectant in
existence is boiling, because it is always at command, is applicable
to most materials and objects, is an absolutely safe sterilizer and
disinfectant, and needs very little if any preparation and apparatus
for its use. One half hour of boiling will destroy all life; and most
bacteria can be killed at even a lower temperature. Subjection to a
temperature of only 70 deg. C. for half an hour suffices to kill the germs
of cholera, tuberculosis, diphtheria, plague, etc. Boiling is
especially applicable to textile fabrics and small objects, and can
readily be done in the house where the infection exists, thus
obviating the necessity of conveying the infected objects elsewhere,
and perhaps for some distance, to be disinfected.

=Steam.=--Of all the physical disinfectants steam is the most valuable
because it is very penetrating, reliable, and rapid; it kills all
bacteria at once and all spores in a few minutes, and besides is
applicable to a great number and many kinds of materials and objects.
Steam is especially valuable for the disinfection of clothing,
bedding, carpets, textile fabrics, mattresses, etc. Steam can be used
in a small way, as well as in very large plants. The well-known
Arnold sterilizers, used for the sterilization of milk, etc., afford
an example of the use of steam in a small apparatus