risks that can be avoided, and there is one other thing that you
should keep on the watch against doing; and that is, touching or
kissing or playing with other children who may be sick. It is better
not even to sit in the same room with them if you can avoid it.

Many of the infectious diseases--and nearly three fourths of all the
diseases that children have are infectious--are caught, as we have
seen, from germs that are carried in the air. That is one reason why
so many infectious diseases are likely to begin with running at the
nose, or sneezing, or cold in the head, or sore throat. The germs,
having been breathed in with the air, catch on the sides of the
nostrils or at the back of the throat, and start inflammation and
soreness wherever they land. This is just the way that _measles_,
_scarlet fever_, _chicken pox_, _whooping cough_, and _diphtheria_
begin. Nearly all colds in the head, and sore throats with coughing,
are infectious; so the best thing to do whenever you have a bad cold
in the head, or a sore throat, is to keep out in the open air as much
as you can, until it is better. Of course, a cold is not such a
serious thing in itself; but, if it is neglected, it may lead to some
very dangerous troubles, particularly to inflammation of the lungs,
and sometimes even of the kidneys or the liver or the heart. Several
of these infectious diseases--measles, chicken pox, and scarlet fever,
for instance--have a rash, or breaking-out, called an _eruption_, upon
the skin. This is another thing easy to look out for; and if you see
anyone with a rash upon his face and hands, it is a good thing to keep
away from him and not let him touch you. Even if he should not have
measles or scarlet fever or chicken pox, but only a disease of the
skin itself, he still might spread the infection of that; for most
diseases that cause a breaking-out upon the surface of the skin are
infectious.