Effective poisons are such good exterminators of flies, that the main consideration is how to safely and most suitably employ them. There are some people who have an invincible aversion to the mere thought of poison purposely administered by way of food or drink, though possibly they do not have an equally strong repugnance to the use of insecticides used for stifling. However, one cannot help running counter to much misplaced sentimental humanitarianism in some people on some subjects; reasons and arguments will not move them, for they do not wish to think otherwise than as their prejudices influence them. The house-fly is itself a poisoner of our food, and it, or rather she (the offender being nearly always female), is a more dangerous and a more subtilely baneful enemy than, for instance, the human flea, which even the Brahmans or the disciples of Buddha may kill. Fumigatory insecticides, though occasionally useful, may be left out of consideration in discussing the rival merits of means in a warfare against the house-fly. A liquid or moist food poison employed in a safe and effective way will excel every other weapon of warfare within the house. One of the newest recommended substances is formalin, which has the advantages of being a disinfectant, a strong fly-poison not avoided by flies, and not dangerous or attractive to domestic animals. A tablespoonful of (40 per cent.) formalin should be mixed with one half pint of milk and water; this, when exposed in saucers or shallow dishes, is said to be an attractive and a fatal bait. It would be evidently dangerous and objectionable to use some other commoner poisons in the same way; but it is the opinion of some users that formalin and milk is not sufficiently alluring. Contrary to a generally prevalent idea a powerful odour is not required as an indoor allurement for the common house-fly; again, a saucer or shallow dish with liquid contents is not a good _method_ of presenting the fatal bait. Placed on a table, or on a window sill, or on a shelf, a saucer is liable to be tipped up and its contents spilt; moreover, the form of such receptacles is radically faulty by reason of the strenuous walking habits of the fly on the level. Out of many flies walking over a table ten or twelve may pass by, or round, an overhanging saucer's rim to one fly that will mount the same and sip inside. However, let such a saucer or plate be placed on a table upside-down, and let a slightly moist substance be placed in the shallow central depression, which ordinarily is the base, then the said ten or twelve flies will all mount and sample the moist substance, even though it be not apparently attractive in smell; an inclined plane is ever an irresistible invitation to mount and prospect the summit.