in, and is led thither by certain Effluvia
which arise from that Body which is in a right State for the preservation
of it. In the Blight of Trees we find, such Insects as are appointed to
destroy a Cherry Tree, will not injure a Tree of another Kind, and again,
unless the Leaves of some Trees are bruised by Hail, or otherwise
Distemper'd, no Insect will invade them; so in Animals it may be, that by
ill Diet the Habit of their Body may be so altered, that their very Breath
may entice those poisonous Insects to follow their way, 'till they can
lodge themselves in the Stomach of the Animal, and thereby occasion Death.
We may likewise suppose that where these Insects have met with their
appointed Nests, they will certainly lay their Eggs there, which the
Breath of the diseased Person will fling out in Parcels, as he has
occasion to Respire; so that the Infection may be communicated to a
stander-by, or else, through their extraordinary smallness, may be
convey'd by the Air to some Distance.

It is observable, that all Insects are so much quicker in passing through
their several Stages to the state of Perfection, as they are smaller, and
the smallest of them are more numerous in their Increase than the others.

Two Years ago when the Plague was at _Amiens_, I pass'd by that Place, and
then found the Contagion began to abate ('twas then about _October_, and
the Rains began to fall) the People told me they were advised to eat
Garlick every Morning to guard their Stomachs against Infection; but
whether it was the Garlick, or the sudden alteration of the Season that
was the occasion of the decrease of that Distemper, we shall examine in
another Place; but we may Note, That all the Ground about that City is a
Morass, so that there is no coming near it but by the Roads which are
Paved and mark'd out. This Marsh or Morass, as all others do in the Summer
Season, produce vast Numbers of Insects which are accounted unwholsome:
But as some are of Opinion, it is rather a Noxious Vapour which occasions
this Infectious Distemper, I shall mention my Opinion of such Vapours
before I conclude.

_In the_ Philosophical Transactions, No 8. _we have the following
Observations of Insects which are the Destroyers of Plants._

Some Years since there was such a swarm of a certain sort of Insect in
_New-England_, that for the space of 200 Miles they poisoned and destroyed
all the Trees of the Country; there being found innumerable little Hol