Further studies on the specific infectious agent isolated in rheumatoid arthritis.

The active agent in crude or extracted materials from patients with acute rheumatoid arthritis (RA), when injected into embryonated eggs, produced an increased percentage of characteristic "crooked toe" defects in the bioassay. Experimental RA chick materials also produced these defects. A protein-free ribonucleic acid extract from RA synovia and joint fluids of patients with acute or subacute classical RA produced the same experimental RA lesions as did the crude materials, but non-RA materials and controls did not. The injected RA material produced the "crooked toe" disease in chicks in direct proportion to the clinically diagnosed severity of the RA in the patient, and inversely with dilution.