more frequently among children is, as
will be seen later, that one attack of a disease frequently confers
immunity upon the patient, so that, for example, a child having scarlet
fever is not likely to have the disease later on in life; but this is no
argument for exposing one's self to contagion, since it is quite
possible that even the first attack may be avoided. Tuberculosis or
consumption is preeminently a disease of youth, as is also typhoid
fever. It is very rare for the latter disease to appear in children or
in adults over forty-five, and for the former to develop until maturity.

In old age, diseases occur due to the gradual failure of the different
organs to perform their normal functions. Some of these diseases are
connected with the heart and the circulation, others with the liver or
with the mucous membranes, so that among those advanced in life,
rheumatism, gout, cancer, and diseases of the kidneys are very apt to
occur.

One of the objects of sanitation is to eliminate disease due to bacteria
and to prolong the normal life, so far as is possible, past the early
period when diseases are easily contracted. It is not hoped that death
can in any case be prevented, but hygiene will have done its utmost when
death occurs only among the aged and when the diseases then causing
death are only those which are consequent upon the wearing out of the
body.

So far as sex is concerned, the ordinary rules of hygiene or the
violation of those rules seem to have but little concern. It is
generally understood that males are on the average shorter-lived, by a
few months, than females, and all statistics support this position. Some
diseases, like typhoid fever, attack males more than females in the
ratio of three to two, while cancer attacks females to a greater extent
than males at about the same ratio reversed. Generally speaking,
however, excepting in so far as their occupations and manners of living
make different their vital resistance, the principles of hygiene are not
affected by the incident of sex.

_Occupation._

Inasmuch as this discussion is a part of rural hygiene and is assumed to
apply to only one occupation, namely, that of cultivating the soil, or
of raising stock, it may not be considered pertinent to discuss the
effect of occupation on disease. It is worth while pointing out,
however, that occupation is a very important factor as an indirect cause
of disease, and that one's chances of life are vastl