Again, in those warm Months, I find that we have vast Varieties of the smaller kinds of Insects floating in the Air, and it is a thing constant, that every Insect from the greatest to the smallest has its proper _Nidus_ to hatch and perfect it self 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 Holes in the Ground, out of which those Insects broke forth in the Form of _Maggots_, which turn'd into _Flies_ that had a kind of Sting, which they stuck into the Tree, and thereby envenom'd and killed it.