CHAPTER II
THE FUNDAMENTAL DIFFERENCES IN CONTAGIONS

There are, it seems, three fundamentally different types of
contagion: the first infects by direct contaet only; the second
does the same, but in addition leaves fomes,* and this contagion
may spread by means of that fomes, for instance scabies, phthisis,
bald spots, elephantiasis and the like.  By fomes I mean clothes,
wooden objects, and things of that sort, which though not
themselves corrupted can, nevertheless, preserve the original
germs of the contagion and infect by means of these: thirdly,
there is a kind of contagion which is transmitted not only by
direct contaet or by fomes as intermediary, but also infects
at a distance; for example, pestilent fevers, phthisis, certain
kinds of ophthalmia, exanthemata of the kind called variolae,
and the like. These different contagions seem to obey a cer—
tain law; for those which carry contagion to a distant object
infect both by direct contact and by fomes; those that are con—
tagious by means of fomes are equally so by direct contact; not
all of them are contagious at a distance, but all are contagious
by direct contact. Hence the most simple kind of contagion
is that by direct contact only, and it is naturally first in order.
So I shall treat of this first, and try to discover how and by means
of what principle (primary agent) it arises; next I shall treat of
the others, in order to see whether there is a certain principle
common to them all, or a different principle in each, and what
is the peculiar characteristic of each.