PRESERVATIVE Fumigations are largely talked of by all, on these Occasions, and they with good Reason deserve to be practised, because while the Poison is on Float in the Air, it may undoubtedly be entangled so as to lose its Power of acting as such; but then for this Purpose such Things ought to be used as exhale very subtile Sulphurs, as the spicy Drugs and Gums. And on this Account I suspect Wood-Fires to be bad, because they raise into the Air a very gross and viscid Humidity, which is not only very unfit to lay hold on, and unite with, the extreamly minute Agents that are to be provided against, but also carry into the Lungs with the Air in Respiration, such Particles, as dispose of themselves to Viscidities, and such Changes in the Blood, as are the Production of the worst Fevers, without any other co-operating Cause; for the Fire only forces out that Moisture, which, while a Tree is in its Growth, naturally perspires from it; and how an Air so impregnated is like to be of Service against a Pestilence, any one may soon be a Judge, who considers those Kinds of Fevers which are most commonly epidemical in wood-land Countries. SUCH Drugs however as are from a vegetable Production, and abound with subtile, volatile Parts, are of Service to be exhaled into the Air this way, both by their Fitness to join with, and cover those venomous _Spicula_ that are on float; and to mix with the Animal Fluids by Respiration and Insinuation into the Pores, whereby they convey, as it were, an _Antidote_, wheresoever the Poison is able to penetrate, and which grosser Vapours can by no means do. OF this kind are chiefly _Storax_, _Benjamin_, _Frankincense_, and all the Aromatick Roots and Woods; and amongst them all, I cannot think the Smell of _Tar_, _Pitch_, &c. is inferior in any Respects, where its Scent is not particularly offensive. And these Things should be burnt at such Distances of Time from each other, that the Air may be always sensibly impregnated with them. BUT as some have sad Apprehensions from the Air being still, and as it were stagnant at such Times, and not without good Reason, as it favours the Collection of poisonous _Effluvia_, and aggravates an Infection; for the Prevention of which, it is proposed at certain Intervals to fire off great Guns, and the like: I cannot but imagine, that for this End, it would be much more effectual to let off small Parcels of the common _Pulvis Fulminans_, in such Openings of a large Town, as Squares and Market-Places; for whosoever hath been accustomed to any Experiments with this Composition, must have perceived a much greater Shock given to the Air by its Explosion, than by the largest Pieces of Ordnance; insomuch that if any Objection can lie against the Practice of this in _London_, should there be Occasion, it is the crasie Condition of the City Buildings, which perhaps may not well stand its Shocks, were they to be made with good Quantities of it at a time.