Besides these substances,
which we have considered as appertaining to the atmosphere at all heights
that are accessible to us, there are others accidentally mixed with them,
especially near the ground, which sometimes, in the form of miasmatic and
gaseous contagia, exercise a noxious influence on animal organization.
Their chemical nature has not yet been ascertained by direct analysis; but,
from the consideration of the processes of decay which are perpetually going
on in the animal and vegetable substances with which the surface of our
planet is covered, and judging from analogies deduced from the comain of
pathology, we are led to infer the existence of such noxious local
admixtures. Ammoniacal and other nitrogenous vapors, sulphureted hydrogen
gas, and compounds analogous to the polybasic ternary and quaternary
compounds analogous to the polybasic ternary and quaternary combinations of
the vegetable kingdom, may produce miasmata,*
p 313
which, under various forms, may generate ague and typhus fever (not by any
means exclusively on wet, marshy ground, or on coasts covered by putrescent
mollusca, and low bushes of 'Rhizophora mangle' and Avicennia).
[footnote] *Gay-Lussac, in 'Annales de Chimie', t. liii., p. 120; Payen,
Mem.
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