MacDonnell, John (1796–1892), pioneer of surgical anaesthesia in Ireland, was born 11 February 1796 in Belfast into an ancient and distinguished family, younger son among two sons and one daughter of James MacDonnell (qv), an eminent doctor, and Elizabeth MacDonnell (née Clarke; d. 1798). He was educated at the Belfast (Royal) Academy before graduating BA (1818) from TCD. Apprenticed (1813) to Richard Carmichael (qv), who became his patron and friend (naming him as executor of his estate and bequeathing him £5,000), he studied at the Richmond Hospital and was admitted LRCSI (1821). He spent several years studying in Edinburgh, London, and Paris before graduating MD (Edin.) (1825).
He established a practice in Dublin, became MRCSI (1827), and was elected MRIA (1827). On the founding of the Richmond Hospital (later Carmichael) School (1826), he became demonstrator in anatomy and subsequently lecturer in anatomy and physiology (1828) and a proprietor of the school. He was appointed, but never served, as foundation professor of surgery in the Belfast Academical Institution (1835), resigning on his appointment as surgeon to the Richmond (later St Lawrence's ) Hospital (1836), a position that had been held by Carmichael, who resigned to ensure that both Robert Adams (qv) and MacDonnell would serve the hospital.
MacDonnell carried out the first operation under general anaesthesia in Ireland. On 30 December 1846 he had planned to amputate the arm of his 18-year-old patient, Mary Kane, on the following day, but read an article ‘On a new means of rendering surgical operations painless’ (British and Foreign Medical Review, xxiii (1847), 309–12), describing the efficacy of ether inhalation, which had first been administered in America (16 October 1846) and subsequently in London (21 December). MacDonnell immediately postponed the planned operation, constructed an ether dispenser, experimented on himself, and on the morning of New Year's Day 1847, with four assistants including Carmichael, watched by medical students and eminent doctors, he successfully performed the operation, which his patient later described as painless. That evening he fully reported the event in ‘Amputation of the arm, performed at the Richmond Hospital, without pain’, and submitted it for publication in the Dublin Medical Press, xvii (Jan. 1847), 8–9. He described this innovation as one of the most important discoveries of the century and as one of the greatest benefits that medical science had bestowed on man. Realising that his crude apparatus was unsuitable for long operations, he proposed experimentation on animals to develop a system by which known ratios of air and ether could be administered to patients. He became a member of a committee of the Surgical Society of Ireland established to examine the use of ether in surgery, which in its report (20 January 1847) warned that it should be administered with great care and that it was unsuitable for patients suffering from cardiac and pulmonary complaints.
A member of the board of examiners (1844), he was appointed professor of descriptive anatomy at the RCSI (1847–51). He resigned to become medical member (1851–76) of the Poor Law Commission, retaining his position after its absorption by the Local Government Board. He was editor (1842–6) of the Dublin Journal of Medical Science and contributed papers to professional journals: ‘General doctrines of fracture’ in the Cyclopaedia of practical surgery, parts xi, xii (London, 1841–61), was his most important work. He published a monograph on Darwinism (1884), discussing the controversial topic of the development of the vertebrate eye. Turning to history, he published The Ulster civil war of 1641 (1879) – in which he vindicated the character of his ancestor Sir Alexander (Alasdair) MacDonnell (qv) (d. 1647) against charges of cruelty – and a pamphlet, The light of history respecting the massacres in Ireland from about A.D. 1580 to the end of the civil war of 1641 (1886).
Vigorous in mind and body until his death (20 January 1892) at his home in Fitzwilliam Square, Dublin, MacDonnell was buried in the family plot at Kilsharvan graveyard, Co. Meath. He married (1826) Charity Dobbs (d. 1890); they had six sons – including James (1826–1904) and Randall William (1833–75), both barristers; Robert McDonnell (qv), a pioneering doctor; and Alexander McDonnell (qv), an eminent engineer – and five daughters, including Barbara McDonnell(qv). His elder brother, Sir Alexander MacDonnell (qv), was commissioner of the board of education of Ireland.