He showed the opportunities available to GPs for epidemiological observation in two British Medical Journal (BMJ) articles in 1930, on 'catarrhal jaundice' and in 1933, on Bornholm disease.

This contained pioneering work on the incubation periods of common infectious diseases of the time and earned him the reputation of one of the world's leading epidemiologists.

In his third year, he proceeded with his clinical studies at the Leeds General Infirmary, qualifying as a licentiate of the Society of Apothecaries (LSA) in 1909.

[1] Pickles was influenced by the physician-epidemiologist William Budd, and the cardiologist and general practitioner James Mackenzie, who argued that it was the GP as family physician who had the true insight into disease.

He later advised all young doctors and medical students to read McNair Wilson's biography of Mackenzie The Beloved Physician.

Later that year he served as a ship's doctor on voyage to Calcutta and, on his return to England, resumed working for Dr Hime as a second assistant.

[2] Pickles served as surgeon-lieutenant in the Royal Naval Reserve during the First World War[1] where he observed and wrote about sailors with poor oral hygiene that predisposed them to Vincent's disease.

His observations reached a wider audience in his 1939 book Epidemiology in Country Practice, in which he described an unusually severe epidemic of catarrhal jaundice in the Dale that had occurred in 1929.

He used an example of a farm boy who transmitted the measles to his aunt who sat in the aerially connected room below, to demonstrate an incubation period of 12 days.