THE insecticide most in the public mind to-day is that known as D.D.T., concerning the efficacy of which rather extravagant claims have been put forward. Nevertheless, its discovery has already proved an event of major importance in view of its cheapness, adaptability and wide range of application. There remain, however, many aspects needing detailed study. One of these is the toxicity of D.D.T. to man and animals, both in the tropics and in temperate regions.