Scope and Distribution of the RA Problem -- History of the Attempts to Find the Cause of RA -- HLA-DR1/4 and Antibodies to Proteus in London -- Antibodies to Proteus in Irish patients with rheumatoid arthritis -- Antibodies to Proteus in rheumatoid arthritis patients from Bermuda and from Hertfordshire in England -- Antibodies to Proteus in rheumatoid arthritis patients from Brest and Toulouse in France -- Dutch patients with rheumatoid arthritis have antibodies to Proteus -- Anti-Proteus antibodies in Norwegian rheumatoid arthritis patients following a lactovegetarian diet -- Antibodies to Proteus in rheumatoid arthritis patients from Norway, Spain and England -- Antibodies to Proteus in rheumatoid arthritis  patients from southern Japan -- Urine Cultures and Correlation -- Molecular similarity between the “shared epitope” of rheumatoid arthritis and bacteria -- The “shared epitope”, Proteus haemolysin, XI collagen and rheumatoid arthritis -- Gram-negative bacteria possess sequences which resemble the “shared epitope”but only Proteus infect rheumatoid arthritis patients -- Immune responses to Proteus in rheumatoid arthritis patients from Finland and Japan -- Molecular similarity between the rheumatoid arthritis associated motif EQKRAA and structurally related sequences of  Proteus -- Rheumatoid arthritis sera are cytotoxic to cells bearing HLA and collagen susceptibility sequences -- The scientific method of Sir Karl Popper. Rheumatoid arthritis and “Popper sequences”.