They also pride themselves on expelling diseases. If this were done
through temperance, by a well regulated life, as do the philosophers,
this claim might be respected. But they insist that diseases are
demons, which they can expel by their words, and they boast of this
in order to achieve reputation among the common people, that is
always inclined to stand in awe of magic. They could not persuade
rational individuals that diseases do not have natural causes, such as
fatigue, satiety, lack of food, corruption, or some change depending
on an interior or exterior principle. This is proved by the nature
of diseases. Sometimes a disease is expelled by moving the bowels,
or by the administration of some potion; diet and bleeding are also
often resorted to. Is this because the demon is hungry, or the potion
destroys him? When a person is healed on the spot, the demon either
remains or departs. If he remain, how does his presence not hinder
recovery? If he depart, why? What has happened to him? Was he fed by
the disease? In this case, the disease was something different from
the demon. If he enter without any cause for the disease, why is the
individual into whose body he enters not always sick? If he enter
into a body that contains already a natural cause of disease, how far
does he contribute to the disease? The natural cause is sufficient to
produce the disease. It would be ridiculous to suppose that the disease
would have a cause, but that, as soon as this cause is active there
would be a demon ready to come and assist it.