John Gaddum (1900–1965) held the Chair of Pharmacology from 1935 to 1938.
Like A.J. Clark, he had a profound interest in quantitative methods.
He extended A.J. Clark's work on competitive antagonism, and applied the law of mass action to describe the relationship (the Gaddum equation) between receptor occupancy and the concentrations of an agonist and a competitive antagonist at equilibrium with the receptors in a tissue. The theory for two or more competing ligands had been known since Michaelis & Menten (1914), but Gaddum was the first to apply it in a pharmacological context). Like Clark before him, Gaddum failed to spot how to use the theory to estimate equilibrium constants.
Gaddum was also a master of bioassay which was then the preferred, and usually the only, way to determine the concentrations of biologically active molecules such as labile neurotransmitters and the neuropeptides.