ted locality; which
poison, while doubtless requiring for its development and dissemination a
certain degree of heat, and terrestrial and atmospheric moisture, a
certain amount of nightly condensation after evaporation, and the presence
of fermenting or decomposing materials, cannot be produced by either of
these agencies alone, and though indicated by the chemist, betrays its
presence by producing on those exposed to its influence the peculiar
morbid changes characterizing fever."

He quotes the following from the Researches of Dr. Chadwick:--

"In considering the circumstances external to the residence, which affect
the sanitary condition of the population, the importance of a general
land-drainage is developed by the inquiries as to the cause of the
prevalent diseases, to be of a magnitude of which no conception had been
formed at the commencement of the investigation. Its importance is
manifested by the severe consequences of its neglect in every part of the
country, as well as by its advantages in the increasing salubrity and
productiveness wherever the drainage has been skillful and effectual."

La Roche calls attention to these facts:--That the acclimated residents of
a malarious locality, while they are less subject than strangers to active
fever, show, in their physical and even in their mental organization,
evident indications of the ill effects of living in a poisonous
atmosphere,--an evil which increases with successive generations, often
resulting in a positive deterioration of the race; that the lower animals
are affected, though in a less degree than man; that deposits of organic
matter which are entirely covered with water, (as at the bottom of a
pond,) are not productive of malaria; that this condition of saturation is
infinitely preferable to imperfect drainage; that swamps which are shaded
from the sun's heat by trees, are not supposed to produce disease; and
that marshes which are exposed to constant winds are not especially
deleterious to persons living in their immediate vicinity,--while winds
frequently carry the emanations of miasmatic districts to points some
miles distant, where they produce their worst effects. This latter
statement is substantiated by the fact that houses situated some miles to
the leeward of low, wet lands, have been especially insalubrious until the
windows and doors on the side toward the source of the miasm were closed
up, and openings made on the other side,--and thence