A few instants’ exposure to an atmosphere containing a fairly high percentage of sulphurous acid will kill any insect, whereas they will be merely stupefied or unaffected by prolonged exposure to a weaker mixture of the poison. I am quite aware that sulphur has been decried as almost useless by several observers, but this is simply because they have not used it properly; for to secure success, something must be added to the sulphur which will make it burn quickly, and what is wanted is, in fact, a weak firework. In well-constructed buildings the sulphur pastiles prescribed in the second edition of my work on the “Gnats or Mosquitoes” answer sufficiently well, but subsequent experience has shown that the proportion of nitre is not enough to secure a sufficiently rapid combustion to instantly flood the air with sulphurous acid, and that nothing short of a slow burning firework, such as a Roman candle or Bengal light, will do this in a building roofed with tiles or thatch. Possibly it might be advantageous to raise the proportion of sulphur; and it is undoubtedly better to pack the material as a powder in paper cases, than to mould it into pastiles. Proper precautions against fire must of course be taken, but in fireworks of this sort the sparks do not fly far, and it is quite safe to use them in any ordinary room if the precaution be taken of placing the cases under a low shield, formed of a sheet of corrugated iron supported on four piles of bricks. The occasional fumigation of a dwelling in this way is a useful adjunct to the destruction of the larvæ; and where combined with proper wire-gauze protection, after the plan described below, may be relied upon to secure immunity from the attacks of insects, even where measures for the destruction of larvæ are impracticable. It has the further advantage that it is fatal not only to mosquitoes, but also to insect pests of all sorts, such as flies, hornets, bugs, or fleas, and even to such more awesome foes as scorpions and centipedes, all of which delight to share the home of the dweller in tropical climes. Mosquitoes are always greatly attracted by draperies, especially those of dark colour, and the fact may be utilised to trap them by means of deep bags of black gauze (_chiffon_), the mouths of which are held open by an oval loop of cane, or some such material. Such bags, if hung up mouth down-wards in tempting dark corners, will usually be found swarming with mosquitoes each morning, and the insects can easily be killed by crumpling the bag in the hands and then shaking out the dead insects.