nly of the many environmental and personal factors affecting the health
of individuals.

The home constitutes the important part of environment for most persons,
and for children in particular, since they spend the greater part of
their time in or about it, and get there the foundation on which their
health in later years depends. For persons employed away from home,
industrial and occupational hygiene is hardly less important; but those
subjects are too extensive to be considered here.

Most people live where they must, and few have any part in planning the
construction of their own houses. In choosing a house, however, one
should remember that rooms where sunshine never enters are unfit for
continued occupation. For children in particular fresh air and sunshine
are essential, and it may be economy in the end to pay a comparatively
high rent for an apartment having sunshine during at least a part of the
day. Ignorance and carelessness, unfortunately, can spoil the best
living conditions, and sometimes even in the country fresh air and
sunshine are excluded from sleeping and living rooms.

VENTILATION.--Ventilation has a direct bearing on health, although,
contrary to former belief, the actual amount of oxygen in the air is not
ordinarily the most important factor; even badly ventilated rooms
contain more than enough oxygen to support life. The factors of prime
importance in ventilation are temperature, humidity, air movement, and
the number of persons in a given space since the greater the distance
from one another the less is the probability that diseases will be
spread.

Room temperature should not be above 70 deg. F. and, except for the aged
or sick, it is better to be between 60 deg. and 65 deg. Some moisture in
the air is desirable; the amount needed is from 50% to 55% of the total
moisture that the air can hold at a given temperature. We have no
apparatus to decrease humidity in the air of houses, and in summer we
are obliged to endure humidity, if excessive, no matter how
uncomfortable we may be. But in winter the air in most houses is too
dry, so that the mucous membranes of the nose and throat often become
irritated and susceptible to infection. Most heating systems,
particularly in small buildings, make no provision for supplying
moisture. Keeping water in open dishes on or near radiators is often
recommended, and would greatly improve the condition of the air, if
people remembered to keep the dishes fill