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is occasionally communicated by contagion: and in two
or three instances I have seen reason to conclude that
the disease has been imported into the district by
persons who had contracted the disease elsewhere.
Still the great fact remains that the origin of
Typhoid fever is essentially connected with the evolution
of miasmata arising from animal and vegetable
matter. These must, however, attain a certain degree
of concentration, and probably, must undergo some
chemical change during stagnation in a confined place,
in order to acquire morbific force. Hence the superlative
importance of free ventilation as a preventative of
Fever. By the free circulation of air in a dwelling,
any miasm arising from inherent causes of infection,
such as over.crowding, or the emanations from cesspools,
may be kept so diluted as to be comparatively
harmless; and stagnation is impossible. This is, of course,
no argument against removing those inherent causes,
to the utmost possible extent: but it is a powerful
argument for the strenuous enforcement of ventilation
in those closely.built and densely.inhabited localities
where the entire prevention of the developement of the
fever.poison is impossible.