Dease, William (1752–98), surgeon, was born in Lisney, Co. Cavan, into an ancient landed family, younger son of Richard Dease and Anne Dease (née Johnson). After a classical education at Dr Clancy's school in Dublin, he was apprenticed to a Dublin surgeon, Dr Keogh (most likely Michael Keogh, a member of the Dublin Society of Surgeons and the RCSI), and completed his medical training after four years in Paris. Returning to Dublin, he established a practice successively in Meath St., on Usher's Quay, and finally in Sackville (O'Connell) St., where he boasted that he had fourteen peers as neighbours. He was appointed surgeon at the United Hospitals of St Nicholas and St Catherine, the Lock Hospital (1785), and the Meath Hospital (1793–8).
A pioneer of medical education, he advocated the withdrawal of the surgeons from the Barber-Surgeons Guild and their incorporation into a royal college, arguing that the University of Dublin taught medicine but ignored surgery, thereby often forcing medical students to complete their education abroad. A founder member of the Dublin Society of Surgeons in 1780, he chaired the committee that successfully campaigned for a royal charter, which was granted in 1784 when the RCSI, a non-denominational college, was established. Dease, a catholic, was its most energetic founder and contributed generously to the costs incurred in procuring the charter. Elected treasurer (1784) and president (1789), he was the college's and Dublin's first professor of surgery (1785–98). In 1789 he and James Henthorn (1744–c.1823) acquired the premises that became known as the Schools of the College, Dease advancing money for the purchase.
He practised midwifery and published a popular textbook, Observations in midwifery (1783), but later specialised in surgery. An expert surgeon, he made lasting contributions in both fields, inventing and improving instruments, especially those for removing urinary stones, and writing valuable treatises including Observations on wounds of the head (1776; 2nd ed., 1778), which is perhaps his most important work and gained him an international reputation. Other works, listed in Cameron's History of the Royal College of Surgeons in Ireland (2nd ed., 1916), 49–50, include the Radical cure of hydrocele (1782), Different methods of treating the venereal diseases (1779), and Remarks on medical jurisprudence intended for the general information of juries and young surgeons (1793), which was among the earliest works of its kind in the English language.
A subject of gossip, he was accused of carrying a stone in his pocket ready to slip into the bladder in case of a mistaken diagnosis, and was suspected by Scottish surgeons John Bell (1763–1820) and Robert Liston (1794–1847), of concealing his method of lithotomy, which was stoutly denied by his student, Sir Philip Crampton (qv). In the absence of any record of an inquest, various explanations have been given for his sudden death (21 January 1798) at his home: that it was caused by the rupture of a blood vessel during a bilious attack (Hibernian Journal); that he committed suicide from remorse after his colleague Solomon Richards (1758–1819) misdiagnosed a suppurated aneurysm as an abscess, which Dease opened, resulting in the patient's death; or, according to R. R. Madden (qv), that having been warned of his imminent arrest as a suspected United Irishman, he severed his femoral artery and died of haemorrhage. A bust (1812) carved by John Smyth (qv) and a superb statue (1886) by Thomas Farrell (qv), described as Farrell's masterpiece, are held in the RCSI and his books are preserved in the library. His elder brother, John Dease, was appointed deputy governor of Upper Canada.
William married (date unknown) Eliza Dowdall; they had one son, Richard Dease (c.1774–1819), surgeon, who was born in Dublin. Having been indentured to his father in 1790, he entered TCD and graduated BA (Dubl.) in 1794, and was admitted licentiate (1795) and elected member (1795) of the RCSI before graduating MD (1796) from Glasgow University. An accomplished anatomist and skilful surgeon, he was appointed surgeon (1795–1819) and member of the medical board at the Meath Hospital, Dublin, and surgeon and lecturer in clinical surgery at the Charitable Infirmary, Dublin (1813). He succeeded his father at the RCSI; appointed professor of anatomy and physiology (1798–1819) and of surgery (1799–1918), he was elected president in 1809. Richard was a catholic and a United Irishman. He died 21 February 1819 at his home in Sackville St., Dublin, from septicaemia contracted while performing a pathological demonstration. His surgical instruments were purchased (1824) by the museum of the RCSI. He married first (1799) Judith Humphrys; they had four children. He married secondly (1814) Anna Maria O'Reilly, heiress, of Charleville, Co. Louth; they had two sons and two daughters. The elder son, William (c.1799–1824), was elected MRCSI (1822). The second son, Matthew O'Reilly Dease (1819–87), barrister, JP and DL, of Charleville, Co. Louth, was educated at the University of Paris. Appointed sheriff of Louth (1857) and of Cavan (1861), he was elected Liberal MP (1868–74) for Co. Louth. He donated money to the RCSI and paid for the statue of his grandfather, carved by Thomas Farrell, and commissioned the restoration of the front hall of the Meath Hospital in memory of his father and grandfather. Matthew died 17 August 1887 at his home, 1 Idrone Terrace, Blackrock, Co. Dublin, and bequeathed his fortune towards the reduction of the national debt.