and a friend of mine who has lived for many years in Italy, and who has
made a number of experiments with it, by exposing himself to the danger
of fever in the worst seasons and in the worst places, believes that it
is a secure preventive. I am not convinced of this; but it can do no
harm; and in waiting for more evidence of its utility, I employ it
without putting the least confidence in its power; nor do I expose myself
to the same danger as my friend has done for the sake of an experiment."
I said, "I believe several scientific persons--Brocchi amongst
others--have doubted the existence of any specific matter in the
atmosphere producing intermittent fevers in marshy countries and hot
climates; and have been more disposed to attribute the disease to
physical causes, dependent upon the great differences of temperature
between day and night and to the refrigerating effects of the dense fogs
common in such situations in the evening and morning; and, on this
hypothesis, they have recommended warm woollen clothing and fires at
night as the best preventives against these destructive diseases, so
fatal to the peasants who remain in the summer and autumn in the
neighbourhood of the maremme of Rome, Tuscany, or Naples." The stranger
said, "I am acquainted with the opinions of the gentlemen, and they
undoubtedly have weight; but that a specific matter of contagion has not
been detected by chemical means in the atmosphere of marshes does not
prove its non-existence. We know so little of those agents that affect
the human constitution, that it is of no use to reason on this subject.
There can be no doubt that the line of malaria above the Pontine marshes
is marked by a dense fog morning and evening, and most of the old Roman
towns were placed upon eminences out of the reach of this fog. I have
myself experienced a peculiar effect upon the organs of smell in the
neighbourhood of marshes in the evening after a very hot day; and the
instances in which people have been seized with intermittents by a single
exposure in a place infested by malaria in the season of fevers gives, I