1. In consideration of the important part played by the RES in dealing with inflammatory foci, an attempt was made in finding a method of quantitatively evaluating the defense reaction of this system. The authors succeeded in demonstrating the possibility of evaluating the intensity of the reaction by cytological examination at stated intervals of the infantilization of the RES cells, their numerical increase and the number of detected round histiocytes appearing in the inflammatory foci against foreign bodies induced by insertion of slideglasses beneath the back skin of rabbits, and that the actual state of the cytological reaction is reflected on the surface of the inserted glass pieces.
2. It is herewith proposed that for evaluating the defense capacity of the RES by this method, the count of the mononuclear cells on the glass on the second day and the comparative observation of the number of giant cells detected on the glass surface on the second and the third days after the insertion of glass give serviceable criteria.
3. A general parallelism was observed between the findings on the subcutaneous histiocytes before and their extent of proliferation after the glass insertion.