CHAPTER III
cCoNTAGION THAT INFEcCTS By coxTAcT ONLyT

An especially good instance of the contagion that infects by
contaet only is that which occurs in fruits, as when grape in—
fects grape, or apple infects apple; so we must try to discover
the principle of this infection. It is evident that they are in—
fected because they touch, and that some one fruit decays first,
but what is the principle of the infection? " Since the first fruit
from which all the infection passes to the rest, has putrefied,
we must suppose that the second has contracted a precisely
similar putrefaection, seeing that we defined contagion as a
precaisely similar infection of one thäng by another. Now putre—
faction is a sort of dissolution of a combination due to evapora—
tion of the innate warmth and moisture. 'The principle of
that evaporation is always foreign heat, whether that heat be
in the air or in the surrounding moisture; hence, in both fruits
the principle of contagion will be the same as the principle of
putrefaction, namely extraneous heat; but this heat came to
the first fruit either from the air or some othersource, and we
may not yet speak of contagion; but the heat has passed on to
the second fruit by means of those imperceptible particles that
evaporate from the first fruit, and now there is contagion, since
there is a similar infection in both fruits; the heat that evapo—
rates from the first fruit has power to produce in the second fruit
what the air produced in the first, and to make it putrefy in a
similar way, all the more because there is analogy.** Now
some of the particles that evaporate from the first fruit are hot
and dry, either independently or when in combination, where—
as others are hot and moist, either independently or when in
combination.  Those that are hot and dry are more apt to burn
the fruit, whereas those that are hot and moist are more apt to
produce putrefaction and less apt to burn. For the moisture
softens and relaxes the parts of the fruit that it touches, and
makes them easily separable, while the heat lifts them up and

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