~3. Germs.~--The chief reason why bad odors are dangerous is that they
almost always have with them little living things called _germs_. Germs
are so small that they cannot be seen by the naked eye: it takes a
strong microscope to enable us to see them, but they are so powerful to
do harm that if we receive them into our bodies they are likely to make
us very sick, and they often cause death.

~4. Contagious Diseases.~--You have heard about diphtheria and scarlet
fever and measles, and other "catching diseases." When a person is sick
with one of these diseases, the air about him is poisoned with germs or
something similar, which may give the same disease to other persons who
inhale it. So when a person is sick from one of these diseases, it is
very important that he should be put in a room by himself and shut away
from every one but the doctor and the nurse. It is also necessary that
all the clothing and bedding used by the sick person, and everything in
the room, as well as the room itself, should be carefully cleansed and
disinfected when the person has recovered, so as to wipe out every trace
of the disease. The writer has known many cases in which persons who
have been sick with some of these diseases were careless and gave the
disease to others who died of it, although they themselves recovered. Do
you not think it very wrong for a person to give to another through
carelessness a disease which may cause his death?

~5.~ Unhealthful vapors and odors of various sorts arise from cisterns
and damp, close places under a house. Rooms which are shaded and shut up
so closely that fresh air and sunshine seldom get into them should be
avoided as dangerous to health.

~6. Breath-Poisoned Air.~--The most dangerous of all the poisons to