1. The synovial membrane has specificity in its reaction to intraarticular material, as here illustrated by dyes.

2. This specificity is determined by distinguishing two distinct types of cells in the synovial membrane. The secretory cells, preponderantly present, maintain an absolute integrity against all but finely colloidal solutions. The particulate substances seem to be engulfed entirely by the macrophages.

3. The fluid and colloid elements are transported both through blood and lymphatic channels, and are diffused throughout the entire body.

4. The dye-filled macrophages may remain for some time in the periarticular structures or may be transported, seemingly by the lymphatic structures only, to various structures of the body, chiefly members of the reticulo-endothelial system. These dye-filled macrophages are found largely in lymph nodes, liver, spleen, and bone marrow.

5. Apparently the lymphatic channels of the synovial cavity of the knee drain directly to the inguinal and lumbar nodes, rather than to the popliteal nodes, as generally described.

6. These macrophages may afford a key to the clearer understanding of the behavior of the lymph node, liver, spleen, and bone marrow in the presence of arthritis.