John I. Quin, son of John George Quin and his wife Emmerentia M. Quin, born Botha, obtained his BVSc (with honours) at the Transvaal University College in 1924 as one of the first class of students to graduate from the newly created Faculty of Veterinary Science at Onderstepoort. Continuing his studies at the same institution, a DVSc (cum laude) was awarded to him by the University of South Africa in 1929 for his thesis Studies on anthrax immunity. He started his career in 1925 as veterinary research officer in the Bacteriology Section of the Veterinary Research Institute, Onderstepoort. In 1937 he was promoted to senior veterinary research officer in the Physiology Section, a position he filled until 1949 when he became director of veterinary services. From 1934 to 1950 he was simultaneously professor of physiology at the Onderstepoort Faculty of Veterinary Science and from April 1949 Dean of the faculty until March 1950, when he died in office on the train returning from an official visit to Nelspruit.
Quin conducted pioneering research on immunity against anthrax; studied physiological aspects of digestive disturbances of cattle under South African conditions; researched photosensitivity due to plant poisoning in sheep and goats and porphyria in cattle; and studied the formation and role of sex hormones in cattle. He will probably best be remembered for discovering, with Claude Rimington*, that the photodynamic agent in hepatogenous photosensitizations (such as geeldikkop and Lantana poisoning) is phylloerythrin, a degradation product of chlorophyll. This work was published in a series of articles culminating in: "Studies in the photosensitization of animals in South Africa. VIII. The biological formation of phylloerythrin in the digestive tracts of various domestic animals" (Onderstepoort Journal of Veterinary Science and Animal Industry, 1935, Vol. 4, pp. 461-471). Noted for his concise and lucid style, his articles have served as examples to countless young researchers of how publications should be written. His work was recognized internationally. He was a member of the South African Association for the Advancement of Science and of the South African Biological Society, served as president of the latter in 1934, and was awarded its Senior Captain Scott Medal in 1944.
Quin was married to Petronella Woudenberg, with whom he had three children.