deaths from accidents, therefore, would include a proper
survey of all the roads of a vicinity to make sure that no danger exists
in this regard. Other precautions against preventable accidents will
readily suggest themselves.

CHAPTER XV

_DISINFECTION_

Inasmuch as more than 10 per cent of all deaths are due to bacterial or
to various infectious diseases, it is of considerable interest to study
the various means by which these germ diseases may be prevented. In this
chapter it is proposed to discuss the different ways in which the active
agents concerned in the spread of disease may be captured and put to
death. It has already been pointed out that infectious diseases can be
acquired only by the introduction of the specific germs into the human
body, either through the mouth or lungs or through some skin abrasion.
Further than this, it is quite as definitely known that the vitality of
the germ after leaving a diseased person depends primarily upon its
condition at the time of leaving the body and afterwards upon the
environment which that germ finds outside of the affected person, while
waiting for a chance to make its next human resting place.

It is evident, therefore, that if during the interval which elapses
between the time when the germs leave a sick person and the time when
they enter another person some method could be found by which these
germs could be killed, the progress of the disease would be effectually
stopped.

This, in the most general sense, is what is meant by disinfection. It
is a determined effort to destroy the carriers of disease while
temporarily absent from the human body which is their natural home. This
process of killing bacteria, however, is not so simple a matter as it
might at first seem. They are, unfortunately, such minute beings that
they cannot be seen, so that the warfare is waged against an invisible
enemy, not, however, to be despised on that account. The methods of
warfare must be uncertain, since the exact location of the enemy cannot
be known, and it is manifestly impossible to disinfect the universe.
What is done is to fix upon the location or surroundings where the
original patient was confined, and, assuming that the germs, if any,
which have escaped ready for further infection are somewhere near, to
poison the air and the wall and floor of the room in question so that
happily the germs may be killed.

_Disinfecting agents._

The various agents used to des