Book I CONTAGION 33

also viscous bodies, defend themselves from many alterations,
if only these are moderate; but they cannot endure violent al—
terations. Herce the germs of all contagions are consumed
by fire, and are broken up by very cold water also.

But if I am asked by some enquiring mind why these germs
do not suffer intrinsic alteration, at any rate, since they are
a combination of diverse elements, I reply that this question
does not apply to germs alone, but to many other things, such
as pepper, lime, euphorbium,'S pyrites,'? metals and many
other substances. 'They too are composed of diverse elements,
yet suffer no alteration, or none of any consequence, from with—
in, but last unchanged for many years; it is surprising how
stones can last a thousand or two thousand years.  In all these
cases the reason is that the combination, though made up of
diverse elements, has been mixed down to the very smallest
particles, which, because of their smallness, have not between
them that excessive bulk which is needed that they may be—
come active. Hence, so long as that sort of combination re—
mains in that condition, so long as its fiery parts are separate,
scattered and buried in the others, there is no alteration from
within. 'That is why pepper, euphorbium etc. feel cold when
handled. But when, by some chance or other, that combina—
tion is dissolved and changed, and parts which are of the same
type unite and aequire a greater bulk and power for action,
then they become active and do act; hence lime, pepper and
euphorbium then feel warm to the touch, whereas previously
they were only potentially warm; but now, when in action,
they behave differently. For the same reason, the germs, al—
though they consist of diverse elements, do not suffer intrinsie
alteration, inasmuch as they are mixed. As for the amount
of force that can exist in so small a bulk, lightning illustrates
that, for lightning is merely vapor; and so do the tiny particles
of euphorbium and pepper and the like, which no eye can see.
Vet nature has endowed them all with great force, such a dif—
ference does it make when fire is contained in dense matter,
however little there may be present.

Of such sort are the germs of contagions also, for they are all
per se acute, although constituted in viscosity, and they be—
come active when the animal heat vaporises that combination
and brings together the similar parts. Now germs of this
kind have great power over the humors and spirits, so that