The method of poisoning flies by the exposure of solutions of sodium arsenite and sugar is one that has been advocated by entomologists in Italy and in South Africa for some years, and yielded good results in Mesopotamia in 1916; for in hot climates, where flies come readily to sugar solutions, the use of an outdoor poison is specially valuable. But there are obvious disadvantages in using any arsenic solutions; for not only are they poisonous in themselves, but the disposal of residues is not easy, as the arsenic and sugar remain poisonous if thrown away, or if they dry on sand or soil. It would thus be useful to substitute for arsenic some compound less poisonous to man and less stable in a soluble form when thrown away.