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the Fifth Edition of this Manual was published less than three-and-a-half years ago, the advances made in Tropical Medicine in the interval are of sufficient importance to have demanded a careful revision of the text and the provision of further illustrations. Among the more important accessions to our knowledge are those relating to the extracorporeal life-history of Schistosomum hæmatobium, which we owe to the researches of Dr. Leiper, and the demonstration that dengue is conveyed by Stegomyia calopus. I have removed the chapter on Rat-Bite Disease from the section on General Diseases of Undetermined Nature to that on Fevers; and contrariwise the chapter on Pellagra, which in the Fifth Edition appeared in the latter section, has now been transposed to the former. The revision of the chapter on Mosquitoes and of the articles on Tse-tse Flies and Ticks was kindly undertaken by Lieut.-Colonel Alcock, while in the chapter on Pellagra I have had the assistance of Dr. Sambon. My best thanks are due to them both; nor must I omit acknowledgments to Dr. Leiper and Mr. G. C. Robson for allowing me. to reproduce illustrations that have appeared in the Journal of the Royal Army Medical Corps and the British Medical Journal; to the Editors of those journals; and to Dr. John Bell for placing at my service a number of valuable photographs. P. M. September, 1917.