CHAPTER XI

HOow IsS CONTAGION RELATED TO POISONS, AND HOow DoES IT
DIFFER FROM THEM?

8ome contagions have a sort of relation and kinship with
poisons, since like them they lurk, hostile and insidious, and
destroy the animal by attacking the heart; and so we call some
fevers 'poisonous' (venomous). But there is an important
difference between them, for poisons cannot, strictly speaking,
cause putrefaction or engender in a second individual a prin—
ciple and germ of exactly the same sort as was in the original
individual. 'The proof of this is that persons who have been
poisoned are not contagious to others.  The reason is this, that
there are two types of poisons; one kind is fatal by means of a
spiritual quality,3? as are snake poisons, for the most part,
and the glance of the catablepha; but the other type operates
by a material quality.  Those that operate by spiritual images
can destroy by driving out the innate heat, and by producing
an intolerable sadness. But they can generate nothing similar
to themselves, because all generation is produced by means of
primary qualities. That is why, in persons who have been
poisoned, we have never observed any such thing as is emitted
by a viper or a basilisk. Of those poisons that operate by a
material quality, some are hot and are called caustic and burn—
ing; others are cold, such as opium, hyosecyamus3' and the like.
Those that are hot and burning are all made up of dry ele—
ments, and so are more fitted to burn than to cause putrefac—
tion and induce contagion. And though some of these are
called by doctors *putrefactive', the term is wrongly used, for
they are simply caustic. They call these putrefactive and the
others caustic, because the caustic first produce a crust, a so—
called 'escara'3?; whereas those that are called putrefactive
first produce a blister, as though the natural heat in them evapo—
rated, just as in putrefying bodies.  But in fact the latter are
also, properly speaking, caustic, for instance, arsenic, orpiment, *3

49