Perhaps in no field of human disease, more than in the field of rheumatism and connective-tissue disorders, have such great technical advances been made in methods of biological study. Some of the knowledge thus gained and some of the ideas suggested are at present difficult to apply directly to the clinical problems that face rheumatologists. Moreover, some of the newly discovered facts seem at first sight to be incompatible with traditional pathological teaching.These are the reasons that led me on to shape this address in the form of a short but broad review of what is happening in rheumatism on the pathological side, and to attempt, with a historical glance backwards, to put recent work in proper perspective.Virchow's Die Cellularpathologie (1858) It is indeed little more than a century since the cellular organization of living creatures was observed and, in medicine, the concept of the nature and mechanism of disease thereupon underwent a great revolution. Pathology expanded into the system of cellular pathology that still guides our teaching and investigations, whereby we believe that all the manifestations of disease, whatsoever its cause, are the result of vital reactions of the cellular tissues of the body or disturbances of cellular functions.One hundred years ago Rudolf Virchow, then a young professor in Berlin, was laying the foundations of pathology as we know it to-day. Early in 1858 he gave a course of postgraduate lectures with the purpose of publicizing all that was then known about * Paper delivered at a Plenary