View report page

34
which we call infection, has the power of affecting
each such person—has the power of producing in
him a succession of characteristic chemical changes
which tend to an eventual close by exhausting this
material which feeds them.
Strictly analogous to this, in its principle of choice
and in its method of operation, appears the epidemic
action—not on persons indeed, but on places. The
specific migrating power—whatever its nature, has
the faculty of infecting districts in a manner detrimental
to life, only when their atmosphere is fraught
with certain products susceptible, under its influence,
of undergoing poisonous transformation.
These products, it is true, are but imperfectly
known to us. Under the vague name of putrefaction
we include all those thousand-fold possibilities
of new combination, to which organic matters are
exposed in their gradual declension from life. The
birth of one such combination rather than another
is the postulate for an epidemic poison.
Whether the ferment, which induces this particular
change in certain elements of our atmosphere,
may ever be some accident of local origin, or must
always be the creeping infection from similar
atmospheres elsewhere similarly affected; whether
the first impulse, here or there, be given by this
agency or by that—by heat, by magnetism, by planets
or meteors—such questions are widely irrelevant
to the purpose for which I have the honor of