Hartley worked in India for four years as a government physiological chemist based at
Muktesar, where he worked on the cattle disease
rinderpest. He returned to the Lister Institute in 1913, as an assistant to
Arthur Harden in the biochemical department. At the outbreak of the First World War, he joined up with the
Royal Army Medical Corps (RAMC) and served as a captain from 1915 to 1919, winning the
Military Cross in 1917. Hartley then worked for two years at the
Wellcome Physiological Research Laboratories, where he developed a culture broth that permitted reliable production of
diphtheria toxin. In 1922 he joined the
National Institute for Medical Research where he became director of biological samples. He stayed till 1946 when he joined the
London School of Hygiene & Tropical Medicine. He worked at the
Sir William Dunn School of Pathology from 1949 to 1953 and at the Lister Institute again from 1949 to 1953. In the 1940s he worked with
Ralph Kekwick. ==Awards and honours==