1. I am indebted to Professor D. Murray Lyon end Professor D.M. Dunlop for permission to report these cases which were studied in their Wards at the Royal Infirmary. 2. It is obvious that little progress will be made in the treatment of Rheumatoid Arthritis until the question of Etiology is cleared up and for that reason I have laid most stress on that part of the study. At the same time the pathology, clinical features, treatment and prognosis are discussed quite fully. 3. The case of Rheumatic Fever is not entirely typical and is used to illustrate points of similarity and dissimilarity between the two conditions end the possible relationship between them. Consequently I have not gone into e detailed discussion of the ...