After serving with the Pellagra Field Commission in 1913 he was appointed as the Director of the Wellcome Tropical Research Laboratories in Khartoum. By then he was a well known name in tropical medicine. While in Colombo he co-authored with Aldo Castellani the Manual of Tropical Medicine, the first edition of which appeared in 1910 and was described by F. H. Garrison as “the best modern book on tropical medicine”.