CHAPTER IV
CONTAGION THAT INFECTS By FOMES

Now it is not at once obvious that the germs that transmit
contagion by means of fomes are produced in the same manner
and by the same principle as that above described, for the prin—
ciple that exists in fomes seems to be of a different nature, inas—
much as, when it has retired into fomes from the body originally
infected, it may last there for a very long time without any
alteration. 'Things that have been touched by persons suf—
fering from phthisis or the plague are really amazing examples
of this. I have often observed that in them this virus has
been preserved for two or three years; whereas particles that
evaporate from putrefying bodies never seem to have the power
to last as long as that. Nevertheless no one ought on that
account to think that the principle of contagion that is in fomes
is not the same as the principles that infect by contact only,*
because the very same particles that evaporate from the body
originally infected, after being thus preserved, can produce the
same effect as they would have done when they evaporated
from the original body. If one desires to be convinced and
' feel no surprise that they can last and preserve their power
so long in fomes, he should consider similar cases of this sort.
Do we not observe that in wood, clothes, etc., a strange smell
may be preserved for a long time, and that not due to some de—
finite quality in them without material basis, but rather to
bodies so very small as to be invisible to us? " Or take the case
of soot and smoke when walls are covered with it; do not these
too, by the admixture of very small particles, become a dye
that lasts without alteration for a very long time? Surely
there are countless examples of this sort, and if one asks what
are the conditions on which they all depend, I assert that these
are two, namely the fine and volatile nature of the particles,
and the strength and resistance of the combination.  Because
of their fineness and volatility they penetrate and are stored up

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