Macdonald, John Smyth (1867–1941), physiologist, was born on 28 April 1867 in Rathgar, Dublin, the elder son and second of the four children of George Macdonald, merchant tailor, and Margaret Macdonald (née Smyth). The family moved to Waterford when he was a baby, and then to Chester. Educated at the King's School in Chester, he entered Emmanuel College, Cambridge, to study mathematics, but his talents as a mathematician were not immediately obvious and he obtained a third-class degree in 1889. He then transferred to Liverpool University, where he studied for a medical degree, graduating with the licentiate of the RCP and the Royal College of Surgeons of Edinburgh and the Royal Faculty of Physicians and Surgeons of Glasgow (1897).
It was while still a medical student that Macdonald first began to carry out research in physiology; he held both the Holt fellowship of physiology (1891) and a teaching position as a demonstrator of physiology (1893–6). Following graduation he was briefly house physician at the Royal Infirmary, Liverpool (1897), before taking up a position as demonstrator in physiology at St Andrew's University (1897–9). Back at Liverpool as lecturer in physiology (1899–1902), he held at the same time a research scholarship from the British Medical Association (1899–1901). From 1903 to 1914 he was at Sheffield University College, where he was appointed professor of physiology, and he became intimately involved in the struggle to obtain a charter and university status for the college, which came to pass in 1905. But he was delighted and extremely proud to return again to Liverpool as Holt professor of physiology at the university, succeeding his former teacher Sir Charles Sherrington (1914–32). On his retirement he was made professor emeritus of physiology. He had been an important influence on the development of medical teaching at both universities while serving in each as dean of the medical faculty.
Macdonald's research work spanned a period of thirty-five years and was concerned entirely with the physiology of nerve and muscle tissue. His contributions to research in this area include the first attempts to measure action currents accompanying impulses in mammalian nerves, an experiment designed to provide evidence of the functional activity of nerves in living animals. It was his work at Liverpool, on the currents in injured nerves, that established his reputation as a highly skilled investigator in the newly emerging field of neurophysiology. He then went on to study the physiology of muscle, producing the first paper to detail the physico-chemical processes involved in muscle contraction, in the Quarterly Journal of Experimental Physiology (ii, 1909, 5–89). This work provided an important basis for others who developed his ideas further, and earned him the fellowship of the Royal Society (1917).
Macdonald's original thought and skill as a researcher were acknowledged when he was elected honorary secretary of the physiology section of the British Medical Association when it met in Sheffield in 1908, and in 1912 he was president for the Liverpool meeting. He published twenty-two papers on the structure and function of nerves and muscles between 1896 and 1931 in journals such as the Proceedings of the Royal Society, the Journal of Physiology, and the Quarterly Journal of Experimental Physiology, his last paper co-authored with his daughter Margaret Macdonald Munday. A list of his publications is included in Raper's obituary notice.
In his teaching, as in his research, Macdonald was thorough and intelligent, taking a deep interest in his students and in continuing the tradition of research and education in physiology at the University of Liverpool. When he spotted a bright student with an enquiring mind, he was an encouraging and supportive tutor. He was an excellent lecturer whose lectures were always well attended, and had a reputation as a strong but fair disciplinarian. However, he was often impatient and tired easily of trivial medical issues and administrative details, which he found tedious. Known for his frankness, he appreciated honesty in others. Once his reserved manner had been penetrated, he had a friendly and generous nature to those who attracted and interested him. His spare time was spent taking long walks and learning shorthand, Esperanto, and German, or improving his French. He had little interest in fiction, except detective novels, which he enjoyed solving.
Macdonald married in 1898 Katherine Mary Stewart, of Holm, Stornoway, and they had three sons and five daughters; one of their daughters died in childhood. Two of his daughters and one of his sons followed him into the medical profession. When he retired he and his wife lived for a while with one of their sons in Lincolnshire. Later they moved to Bridge of Allan, near Stirling, where he died, after a prolonged period of ill health, on 29 March 1941, in his seventy-fourth year. His wife survived him.