Grassi (1883), Stiles (1889), Calandruccio (1906), and especially Nicoll (1911), have been the chief investigators of the ability of house-flies to carry the ova and embryos of human intestinal parasites. Graham-Smith (1913) summarizes the work along this line as follows: "It is evident from the investigations that have been quoted that house-flies and other species are greatly attracted to the ova of parasitic worms contained in feces and other materials, and make great efforts to ingest them. Unless the ova are too large they often succeed, and the eggs are deposited uninjured in their feces, in some cases up to the third day at least. The eggs may also be carried on their legs or bodies. Under suitable conditions, food and fluids may be contaminated with the eggs of various parasitic worms by flies, and in one case infection of the human subject has been observed. Feces containing tape-worm segments may continue to be a source of infection for as long as a fortnight. Up to the present, however, there is no evidence to show what part flies play in the dissemination of parasitic worms under natural conditions." Enough has been said to show that the house-fly must be dealt with as a direct menace to public health. Control measures are not merely matters of convenience but are of vital importance. Under present conditions the speedy elimination of the house-fly is impossible and the first thing to be considered is methods of protecting food and drink from contamination. The first of these methods is the thorough screening of doors and windows to prevent the entrance of flies. In the case of kitchen doors, the flies, attracted by odors, are likely to swarm onto the screen and improve the first opportunity for gaining an entrance. This difficulty can be largely avoided by screening-in the back porch and placing the screen door at one end rather than directly before the door. The use of sticky fly paper to catch the pests that gain entrance to the house is preferable to the various poisons often used. Of the latter, formalin (40 per cent formaldehyde) in the proportion of two tablespoonfuls to a pint of water is very efficient, if all other liquids are removed or covered, so that the flies must depend on the formalin for drink. The mixture is said to be made more attractive by the addition of sugar or milk, though we have found the plain solution wholly satisfactory, under proper conditions. It should be emphasized that this formalin mixture is not perfectly harmless, as so often stated. There are on record cases of severe and even fatal poisoning from the accidental drinking of solutions.