Although dissertations on clothing and its function appear from the 19th century as colonising countries dealt with new environments, concerted scientific research into psycho-social, physiological and other functions of clothing (e.g. protective, cartage) occurred in the first half of the 20th century, with publications such as J. C. Flügel's Psychology of Clothes in 1930, and Newburgh's seminal Physiology of Heat Regulation and The Science of Clothing in 1949. By 1968, the field of environmental physiology had advanced and expanded significantly, but the science of clothing in relation to environmental physiology had changed little. While considerable research has since occurred and the knowledge-base has grown significantly, the main concepts remain unchanged, and indeed Newburgh's book is still cited by contemporary authors, including those attempting to develop thermoregulatory models of clothing development.