1. The astragalotibial (hock) joints of normal young beef cattle contain large and uniform quantities of synovial fluid which is easily accessible for study.
2. Nucleated cells found in such synovial fluid are similar in numbers and types to those described previously in normal rabbits' synovia.
3. The fact that 90 to 95 per cent of all nucleated cells present are actively phagocytic implies that the function of these cells is the removal of the products of wear and tear from the articular cartilages and synovial membranes.
4. Red blood corpuscles seem to be present in numbers directly proportional to the trauma to which the synovial membrane is subjected.
5. The astragalotibial joints of young beef cattle contain from 3 to 5 times more fluid than do the corresponding joints of stable cattle. More débris and unidentified solid material is found in the latter group of animals.
6. The total nitrogen content of this synovial fluid was found to be 169 mg. per 100 cc. The approximate total protein content was calculated to be 680 mg. or 0.68 per cent per 100 cc.
7. No correlation between the total protein level and the total cell counts of isolated specimens of synovial fluid is possible from these data.
8. Further studies of synovial fluid and of its chemical similarity to blood serum of the same animals are in progress.
9. Articular cartilage defects occurring in the articular cartilages of the carpometacarpal joints are described. (A more detailed study of these articular cartilage lesions, the age at which they appear, possible causative factors, etc., is now being made.)