Henry Barcroft was a highly distinguished physiologist, known especially for his work on the circulatory system in human limbs, as well as being greatly admired and highly popular as a teacher and supervisor. He was born in Cambridge, one of two sons of the eminent physiologist Sir Joseph Barcroft, FRS, who himself was the son of the linen merchant, inventor and engineer Henry Barcroft, from County Down, High Sheriff of County Armagh and Deputy Lord-Lieutenant for County Down; his mother was the daughter of Sir Robert Stowell Ball FRS, the celebrated mathematician who became Astronomer Royal of Ireland and subsequently Professor of Astronomy and Geometry at Cambridge.

Barcroft was educated mostly in Cambridge, at King's College choir school as a non-choral day boy; and after four years as a boarder at Marlborough College, where he won a Bethune Baker scholarship, he entered Cambridge University with the "top" Exhibition to King's College, where he studied botany, zoology and chemistry; during this time he and his father jointly published two papers on blood circulation, and haemoglobin in invertebrates. By 1927 he had graduated in Natural Sciences with a double first, and completed the Cambridge MB. Winning a Harold Fry Studentship, he began research work in physiology, his particular area being the effect of intravenous adrenaline on aortic blood flow in dogs, using a stromuhr (a device for measuring average blood flow) he had developed himself and which concentrated on moment-to-moment measurements as opposed to the then-prevalent method of measurement of averages over prolonged periods. Though he won a George Henry Lewis Studentship and later the Gedge Prize, he nevertheless was unsuccessful in securing a Fellowship, and so took up a Harmsworth Scholarship at St Mary's Hospital in London, where he qualified MRCS and LRCP in 1932.

He was immediately appointed lecturer at in the Department of Physiology at University College, London. In spite of a heavy teaching load (150 lectures a year, as well as practical classes and supervision of research students) he continued to work on blood flow in animals; he was also interested in work being done on human circulation at the nearby University College Hospital by no fewer than four future Fellows of the Royal Society. Also during this time he completed his Cambridge MD.

In 1935, Barcroft was appointed Dunville Professor of Physiology at Queen's University, Belfast. He succeeded TH Milroy, the incumbent since 1902, when he had been appointed in preference to Henry's father, Sir Joseph. At this time the Belfast Medical School, the fourth-largest in the British Isles, had fine reputation for clinical instruction, but Barcroft was appointed by Queen's principally to stimulate research. Facilities for this were very limited, and Barcroft had quickly to assume a formidable workload, being the only full-time member of staff for a Faculty of 678 students. Barcroft increased practical classes threefold, with the aid of medical graduates working on short-term contracts as demonstrators, set frequent class exams which he had to mark himself (he did have one permanent lecturer, OE Edholm, after 1938), and gave all the physiology lectures himself at 9:00 every morning from Monday to Saturday.

He was also expanding his principal research interest, that of the human peripheral circulation; following on from his earlier work, he studied the regulation of blood flow in the human limbs, using as subjects consenting patients, healthy volunteers, and also himself, having decided that results from studies of anaesthetised and therefore certainly shocked animals was unsatisfactory. In conjunction with OG Edholm, Barcroft used and developed the technique of venous occlusion plethysmography to show, amongst other findings, that the sympathetic nervous fibres can both actively dilate and constrict the blood vessels of skin and muscle, this finding being essential in the study and treatment of high blood pressure. During the War he also, along with Edholm, carried out some research at the British Postgraduate Medical School, Hammersmith, on the effects of haemorrhage, work they continued in Belfast, in some experiments by inducing fainting in healthy volunteers, after an unplanned fainting had provided an unexpected study opportunity. They found that fainting is an active process occurring when blood vessels to muscle are suddenly dilated, leading to blood rushing into muscle and blood pressure dropping sharply, depriving the brain of blood and oxygen.

In 1948 he was appointed to the chair of Physiology at the Sherrington School of Physiology, St Thomas's Hospital, London; similarly to his career in Belfast, he entered a department in a very basic condition, earning it, by his retirement in 1971, with a distinguished reputation. He continued his research work, over a wide range of physiological areas but especially in muscle blood flow in rhythmic exercise, the mechanism of functional hyperaemia and vascular responses to catecholamines (hormones released into the blood during times of physical or emotional stress).

Barcroft was elected to a Fellowship of the Royal Society in 1953, the same year he co-authored Sympathetic Control of Human Blood Vessels, still estimated today as an exemplary publication.  His list of publications in learned journals was extensive, as was that of academic and professional distinctions, including honorary doctorates from Queen's University, Belfast, the University of Western Australia and the Leopold-Franzens University, Innsbruck, together with recognitions from France, Japan and Czechoslovakia. From 1966-1975 he was a Wellcome Trustee and in 1963 had been Visiting Professor at the University of Adelaide. In 1975 he was Robert Campbell Memorial Orator at the Uster Medical Society.

Remembered by generations of colleagues and students as most encouraging, charming and of legendary kindness, Barcroft also enjoyed a reputation as being of formidable intellect and tenacity whose impact on the understanding of human peripheral circulation was described by one of his many junior colleagues as "remarkable".

Born:	18 October 1904
Died:	11 January 1998