To the Editor.
—An article by Warren et al (Arch Intern Med124:629-634, 1969) concerning the transmissibility of rheumatoid arthritis (RA) from men to mice, prompted us to repeat their experiments.Tissues removed from affected joints of digits and wrists of patients diagnosed for RA were used. The material was supplied weekly in small amounts and stored at —90 C until sufficient material had been collected. The tissues were thawed, pooled, and chopped submerged in ice-cold, sterile phosphate buffered saline (PBS). Homogenization took place in two stages (1) a crude slurry was made with a blender, and (2) this thick, fibrous slurry was homogenized using a Potter-Elvehjem glass homogenizer. The extract was collected in sterile glass centrifuge tubes and stored at —20 C. Since fibrous aggregates were often formed upon thawing, the suspension was once more homogenized in the Potter-Elvehjem homogenizer prior to injection. The cell-free tissue extract thus