Professor J.A. MacWilliam occupied the Regius chair of Physiology from 1886 to 1927. Professor MacWilliam was the youngest professor of his time, he was Aberdeens most distinguished graduate of the year in 1880 and took up the Regius chair six years later at the age of 28.

Professor MacWilliam did pioneering work on the propagation of the cardiac impulse and was the first to ascribe "sudden death" in humans to ventricular fibrillation. Between 1883 and 1888 he published seven papers in the Journal of Physiology on the properties of mammalian cardiac muscle and in these he correctly predicted the speed of excitation across the heart. He was elected membership of the Physiological Society in December 1883 and became a Fellow of the Royal Society in 1916.

"What about him as a teacher? He does not have the popular dash of his predecessor, he does not use so many wooden models or slaughter so many frogs, he turns his attention on the actual facts to be learned, picking out their essence and presenting them in the barest simplicity." "He is altogether in touch with the students - in their classes, their societies and their social affairs - a smoking concert he enjoys like one of ourselves."