MacAlister remained a fellow of St. John's College until the end of his life, and was senior tutor from 1900 to 1904. In 1879, he published a paper in the Proceedings of the Royal Society on "The Law of the Geometric Mean." The work was in response to a question put by Francis Galton and contains what is now called the log-normal distribution. After a spell teaching mathematics at Harrow School, MacAlister returned to his original intention of studying medicine, first at Cambridge, later in 1879 at St. Bartholomew's Hospital, and for a short time at Leipzig. In 1881, he settled in Cambridge, and took up medical teaching, investigation, and practice, and in 1884, when he graduated M.D., became physician to Addenbrooke's Hospital. He was elected Fellow of the Royal College of Physicians in 1886. In addition to his great talent in mathematics and his accomplishments in medicine, MacAlister was also an extraordinary linguist. In addition to his native Gaelic and English, he was said to have spoken well German, Norse, French, Italian, Dutch, Spanish, Portuguese, Czech, Basque, Turkish, Greek, Arabic, Swedish, Russian, Serbian, Afrikaans and Romany: nineteen languages total. MacAlister was a contemporary at St. John's of the first Japanese graduate of Cambridge named Kikuchi Dairoku and they were lifelong friends. MacAlister also assisted Inagaki Manjiro with a petition to the Council of the Senate to allow Japanese students to obtain exemption from the study of Latin and Greek for entrance examinations. MacAlister played a very important part in the work of the General Medical Council. He was elected to it in 1889 as representative of Cambridge University and became its president in 1904. In 1931, after an unbroken twenty-seven years in office, he stood down on grounds of ill health. In 1907, MacAlister was appointed Principal of the University of Glasgow, a position from which he retired in 1929. During those years, the university grew substantially. Upon his resignation, he was elected Chancellor of the university by the General Council. MacAlister took a leading part in the university business of the country. He was one of the founders of the Universities Bureau of the British Empire, and was for many years Chairman of the Standing Committee of Vice-Chancellors and Principals of the British universities. MacAlister's work was widely recognised; he received honorary doctorates from thirteen universities and was appointed KCB in 1908 and created a baronet, of Tarbert, Cantire, in the County of Argyll, in 1924. In 1917, he was elected a Fellow of the Royal Society of Edinburgh. His proposers were Ralph Allan Sampson, Frederick Orpen Bower, John Horne, and Thomas James Jehu. He died in 1934 and is buried in the Parish of the Ascension Burial Ground in Cambridge, with his wife, Edith Florence Boyle. They had no children and the baronetcy became extinct upon his death.
