tance._

It is well known that there are present in the body certain agencies
which act as guardians of the body against disease; that there are
certain corpuscles of the blood and certain liquids circulating through
the system which immediately attack and if in sufficient numbers or
strength drive out the advancing enemy, so that "taking a disease" in
most cases means that the activity of these resisting organisms is not
forceful enough to successfully combat the germs of the disease. These
agencies, whether circulating liquids or cells or corpuscles, are most
active in the healthy body, and anything that tends to reduce the
general health, such as exposure, overexertion, imperfect nourishment,
overeating or overdrinking, or lack of sleep, tends to diminish their
activity and so makes the individual more susceptible to disease.

_Cell disintegration._

Although disease is caused by the attacks of germs, another and far more
important cause of disease is the breaking down or overstimulation of
some particular organ. This is very plainly seen in diseases involving
the stomach or intestines, where habitual excesses in eating lead,
sooner or later, to consequent inflammation, disease, and death. This is
also true of the lungs; merely living in an atmosphere full of dust will
irritate the lungs to such a degree as to cause inflammation. Cancer is
presumably the result of local inflammation, although the cause of the
original suppuration is unknown. Similarly, appendicitis starts from
some irritating cause, resulting in inflammation and the formation of
pus. In very many cases the cell-disintegration seems to be a matter of
heredity.

_Heredity._

Heredity, the second of the indirect causes of disease seems to be
assuming less importance as it is more studied. Probably in but few
cases is heredity more than a chance factor in the causation of disease.
Heredity, formerly considered to be the most important cause of
consumption, is now understood to have little to do with this widespread
epidemic, although it is agreed that children brought up in the family
with a consumptive mother and father are more likely to contract the
disease than if they were segregated.

It is a providential arrangement that children inherit the tendencies of
both father and mother, and that the good qualities of one parent are
known to offset the bad qualities of the other; probably for this very
important physiological reason marriage between