Photomicrographs of histological preparations 24 hours after induction of the inflammation process with 4% papain. (A) Slight presence of hyaline material in the joint space due to plasma extravasation (arrow). (B) Joint surfaces under conditions of normal meniscus and articular signs of ossification (arrow). (C) Intense acute inflammatory exudate filling the part of the joint space (arrow). (D) Neutrophil accumulation in the connective tissue underlying the synovial membrane (arrow). (E), (F) Specimens of normal tissue: (E) intimal layer of the synovial membrane presents usual thickness (arrow), whereas few inflammatory cells are observed in the isolated underlying layer (star); (F) meniscus and articular joint surfaces show signs of tissue integrity. (G) Presence of both the acute inflammatory exudate synovial membrane (star) as well as in the joint space and an association with fibrin hyaline material (arrow). (H) Cellular degenerative process in the marrow spaces of the epiphyses of the joint (arrow). Stained with hematoxylin and eosin 40×. Scale bar, 20 μm. CH: Hyaline Cartilage; EA: Articular Space; MA: Articular Meniscus.