CHAPTER VII

HOW THE GERMS OF CONTAGIONS ARE CARRIED TO ^ DISTANT
OBJECT AND IN A CIRCLE

Let us first enquire by what sort of movement these germs
of contagions are impelled, since it is clear that they are car—
ried far and to persons far distant, a fact that many people
think so astonishing. First we should consider precisely simi—
lar instances, that we may be less surprised. Who would
imagine that tears could be drawn from us, even from a long
distance, by onions and garlic; that pepper, iris or ptarmicum'5
could make one sneeze, or that saffron, solanum,'* and strych—
nus eould induce sleep; or that handling things made of metal
ecould make a man apoplectic? It is because from all these,
imperceptible bodies whose activities and powers are diverse,
are exhaled and carried in all directions. 'This appears very
clearly in things that are corrupted and putrefy. Now the

principle of movement in these small bodies, in all directions,
is in part independent, in part given by something else. Al
evaporation independently rises upwards, as may be seen in
smoke and many other things, for everyone knows that all
evaporation is warm; but the movement may be derived from
something else, and then the thrust is sideways and finally
downwards. 'This is due to two main causes, one being the
resistance of the air or of floors, or things of that sort, on which
fall the particles that are first exhaled; when these particles
cannot be carried further, they are thrust sideways by the
particles that follow them, and these by others, till the whole
surrounding space is filled. The second cause is the air itself,
which divides into its smallest and indivisible parts all evapora—
tion that is tenuous and easily soluble. For it is the nature of
elements and of all liquids that they seek, so far as is possible,
a suitable position; and a position is most suitable when the
parts are continuous, or if not continuous, are the least possible
distance apart from one another; for thus they are less ex—

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