From ancient times there has been a consensus of opinion that there was in some way a connection of cause and effect between swarms of flies and the spread of disease. In the plagues of Egypt, in the reign of Pharaoh of the Exodus, it will be remembered how, after "the land was corrupted by reason of the swarms of flies," Exodus viii. 24, there came "a very grievous murrain" upon cattle, Exodus ix. 3, followed by a "plague of boils and blains" upon man and beast. In our present day insect life is being scientifically investigated with the view of establishing the connection, and of discovering fully the serious _rôle_ of disseminating disease, of which the house-fly has long been suspect. The microscope reveals much, and the art of bacterial culture now explains how it is true that the superabundant creature, which has persistently followed civilised man into every quarter of the globe, has ever had a share in conveying contagion beyond that of any other household pest. That the house-fly is bred in filth matters not much. After emerging from the puparium its first voidance of fæcal matter may be contaminated with live baneful germs, but it voids itself before its first flight. Having six legs it stands upon two pairs, whilst with the other pairs, at one time the front pair and at another time the hind pair, it works frequently and vigorously at brushing and stroking down every part of its body. Though it starts its new life quite a wholesome newborn creature, and though it must be credited with being a most assiduous remover of dirt from its own body, yet from the human point of view its subsequent life is a persistently disgraceful career. It is the evil course of the newly-hatched and self-cleaned fly not to restrict its diet to the honey of flowers, as do some of its relations. Its food includes excrement, sputum, and every kind of putrefying organic matter likely to be swarming with micro-organisms of a character deleterious to humanity. It is certain that, when only a few days old, a fly will practically abound internally and externally (on the feet) with dangerous germs, as amply proved by methods of laboratory culture. As it feeds, it walks over the food; and the hairy joints of its feet, when microscopically viewed, appear conspicuously liable to carry germs in spite of frequent attempts at self-cleaning. Wherever it alights and walks, it prospects with a touch of its trunk, which is the main instrument of evil. It has a very filthy habit, from time to time, of depositing pale vomit spots as well as dark-coloured fæcal droppings. These defilements are visible, wherever it may alight on walls, windows, ceilings, and especially on pendent ornaments, whereon the males delight to rest.