troy those germs which are carriers of
disease may be divided into two groups, namely, heat in its various
forms, and chemicals. Literally, the word "disinfection" means "doing
away with infection," so that to disinfect a room is to do away with the
infection present in the room. It has, however, come to have a more
general meaning than this and is commonly used instead of the word
"destroy," so that a disinfecting solution is the same thing as a
destroying solution, applied, of course, to bacteria.

It has already been explained that by far the majority of bacteria are
useful if not essential to human life, and one of the difficulties in
employing disinfecting or destroying solutions is that they put an end
at the same time to both useless and useful bacteria. As an example,
the fermentation processes in the human intestines are accompanied if
not produced by certain kinds of bacteria, although on occasion these
harmless or useful bacteria may develop into most obnoxious germs,
producing unpleasant fermentation. It might be easy enough for a doctor
to make a patient swallow some antiseptic solution, like carbolic acid
or corrosive sublimate or nitrate of silver, for the purpose of getting
rid of certain undesirable bacteria in the intestines, but it does not
need a doctor to know that for a patient to swallow such active poisons
as these would not merely kill the harmful bacteria and the good ones as
well, but probably the patient himself.

_Antiseptics._

There is another word often used in connection with bacteria, namely,
"antiseptic," and the common significance of this word applies to a
substance which interferes with or retards the growth of bacteria
without actually destroying them. Doctors, for instance, use antiseptic
instead of disinfecting solutions on wounds, not because they do not
wish to kill the pus-forming bacteria, but because the antiseptic
solution will prevent their growth and not be, as a disinfecting
solution, harmful to the cells which he is trying to repair. It would be
folly, for example, to inject a strong 50 per cent solution of carbolic
acid into a wound on the arm produced by a saw, because all the energy
of the vital forces at the seat of the wound are needed for repairs, and
there is none to spare for so active a detergent as carbolic acid. An
antiseptic, on the other hand, is mild enough so that it does not act on
the tissue at all, but merely prevents any undesirable growth of
bacte