He worked at the National Institute for Medical Research (NIMR, Medical Research Council) in Hampstead and Mill Hill, where his work on steroids included contributions to the isolation and characterisation of vitamin D, and the synthesis of cortisone from naturally occurring steroids.
In 1932 Otto Rosenheim and Harold King published a paper putting forward structures for sterols and bile acids which found immediate acceptance.
[1] The loose association between Bourdillon, Rosenheim, King and Callow was very productive and led to the isolation and characterisation of vitamin D.[2] At this time the policy of the MRC was not to patent discoveries, believing that results of medical research should be open to everybody.
Callow became involved with a variety of problems related to the work on vitamin D, including the claim that rickets was produced by the action of certain cereals.
In a 1936 paper, written with Frank Young,[4] a footnote states "The term steroids is proposed as generic name for the group of compounds comprising the sterols, bile acids, heart poisons, saponins and sex hormones."
He showed that androgens were excreted in the urine in similar amounts in men, women and eunuchs, which at the time was surprising.
This conclusion was supported by findings made jointly with A.C. Crooke, working at the London Hospital, that patients with Cushing's syndrome, caused by a tumour of the adrenals, had very high levels of androgenic substances in the urine.
He became an armaments officer and spent much of the war in the NW Frontier area of India (Waziristan, now in Pakistan) defusing unexploded bombs.
[5] Later in the war he worked for the Inter-Services Research Bureau, a cover name for Special Operations Executive (SOE), an organisation responsible for sabotage in enemy-occupied territory, with A.G. Ogston, under the leadership of E. Gordon Cox, applying plant and medical chemistry, and developing unusual equipment.
In 1945 he returned to the NIMR, and worked with John Cornforth on a commercially attractive way of synthesising cortisone from naturally occurring steroids.
This was a less direct way of producing cortisone, but the successful extraction and purification of hecogenin from the sisal plant, and its availability made it a suitable commercial source.
After he retired from the NIMR in 1966, Callow joined the staff at Rothamsted Experimental Station in the insecticide department.
His grandfather Edward Callow wrote a history of the Isle of Man: From King Orry to Queen Victoria, Elliot Stock, 1899.