Scrapings of subcutaneous nodules from ten patients with rheumatic fever were examined microscopically after being stained with supravital dyes. From the uniform results obtained, the following conclusions have been drawn.
1. Supravital staining of cells from these lesions gives information unobtainable with ordinary histologic methods.
2. The scrapings show a great predominance of certain cells almost entirely devoid of phagocytic power and not characterized by the reactions with neutral red which distinguish monocytes, epithelioid cells, and clasmatocytes. Hence they differ from the essential cells of the lesions of tuberculosis and experimental syphilis. These differences are probably of a functional and developmental rather than of a genetic nature.
3. The cells probably arise from the undifferentiated mesenchymal elements of loose connective tissue, although it is possible that endothelial cells take part in their formation in some instances.
4. Since there is little doubt that the subcutaneous rheumatic nodules are pathologically identical with rheumatic granulomata else-where in the body, these conclusions are considered applicable also to the Aschoff body cells of the myocardial submiliary nodules.