e a foothold
and produce the disease. Unlike tuberculosis, which attacks chiefly
those in the vigor of life, from fifteen to forty-five years of age,
pneumonia attacks generally the very young and the very old; those under
five and those over forty-five, the time of life when the vital
resistance is the least.

_Weather not the cause of pneumonia._

One of the sources formerly believed to be largely responsible for
pneumonia, that is, exposure to severe weather, is curiously negatived
by the fact that children and old people are not those generally exposed
to weather. Perhaps no fallacy in any disease has been more prevalent
than that pneumonia is usually contracted by exposure to wet or to cold.
It has, indeed, been noticed that the disease has been practically
non-existent under conditions where it would be prevalent if exposure
alone were the cause. For instance, in the Arctic zone, where the
temperatures are very low and where no adequate provision against the
rigors of a severe climate are possible, pneumonia is practically
unknown. During Napoleon's retreat from Moscow, when thousands of
soldiers died from physical exposure, from frost bite and starvation,
where if exposure were the predisposing cause of pneumonia, it would
have raged as an epidemic, it seldom appeared, proving this opinion.

Perhaps one reason why the disease has been supposed to result from
exposure is the undoubted fact that it is chiefly prevalent in the
winter and spring rather than in the summer. This argument is, however,
modified by the fact that the majority of cases do not occur in January
or February when the temperature is lowest, but in March, when the
opening of spring is in sight. The reason for this is evident when we
remember that the cause of the disease is a germ, generally present in
the body and needing only a reduced vitality for its successful inroad
on the human system. When, therefore, a person shuts himself up in an
overheated house, without ventilation, takes insufficient exercise, and
lives with an apparently determined effort to do everything possible to
reduce his bodily vigor, then it is no wonder that the germ, almost in
exultation, finds an opportunity for successful development.

_Preventives in pneumonia._

Much as in tuberculosis, then, the best remedy and the best prevention
for pneumonia is a careful attention to the needs of the body in order
that it may preserve its normal vigor. Regular hours, sufficie