as a specific germ or virus, then the offspring of consumptives would
have an attenuated form of the disease, which, by reasoning from
analogy, ought to secure them exemption from any further danger along
that line. Such, however, is not the case. But if we say a special
fitness is inherited, then we can understand how the offspring of
consumptives are prone to develop it, since they are not only born
with hereditary qualifications, but not infrequently they are cradled
amid the very agencies which fostered the evil in their parents, if,
indeed, they were not primarily causative.

That the contribution of heredity to consumption is great is
undoubtedly the case, and, more than any other factor, it would seem
to have a directing power in the army of inducing evils. But the fact
that the greater number of the offspring of consumptives escape the
disease, even where the general family resemblance is quite
pronounced, is readily explained by the difference in personal habits,
the circumstances of different periods or the domestic regulations
instituted by medical counsel. Also the fact that consumptives so
frequently spring from neurotic parentage and the victims of
dissipation, especially alcoholic, still farther goes to show that the
hereditary element is essentially a reduced power of resistance to
formative evils, and that as a negative condition it may hold the
balance of power in focusing the forces. Thus, heredity, in disease,
can be understood as in no sense implying a specific force, but rather
an atonic or susceptible condition, varying in its precise character
and producing a _pars minoris resistentiæ_--a special weakness in a
special way.

That the germ _bacillus_ does not originate consumption there can be
no doubt, unless consumption is not to be regarded as a disease until