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In the second paper of this series (1) the disorders of calcium phosphate metabolism were divided into three fundamental groups. It was believed that under normal conditions body fluids contain all the calcium phosphate which that particular fluid system can hold at that particular time. The first and commonest group was that in which the body fluids contain less than this saturating amount of calcium phosphate. Because of this, calcium phosphate is not deposited into osteoid tissue with the resulting pathological picture of wide osteoid seams on the trabeculae (cf. rickets and osteomalacia). The second group was that in which the body fluids, because of certain extraordinary circumstances, contain more than the normal quota of calcium phosphate and deposition in tissues other than osteoid tissue results (e.g. ergosterol poisoning and cases of metastatic malignancy and myeloma). Finally, a third possibility presented itself. It is conceivable that the body fluids might contain a normal saturating amount of calcium phosphate, but that the proportion of the calcium ions to the phosphate ions might be abnormal. Such, it was believed, is the disorder in diseases of the parathyroid glands. To recapitulate then, we conceived of three possible variations from the normal saturation of body fluids with calcium phosphate: (a) subsaturation, (b) supersaturation, and (c) anomalous-saturation (i.e. quantitatively normally but qualitatively abnormally saturated).In the first paper of this series (2), the hypothesis was advanced that this abnormality in the relation of the calcium ion to the phosphate ion in parathyroid disorders was dependent upon changes in phosphorus excretion in the urine brought about by the parathyroid hormone. Thus it was believed that on administration of the parathyroid hormone the first effect was an increased phosphorus excretion; that this resulted in a decreased serum inorganic phosphorus; that this tended to leave the serum's capacity to take up calcium phosphate unfulfilled; that calcium

A review of the literature concerned with the anatomy, histology, and physiology of normal joints reveals that our knowledge and understanding of many details is very meagre, indefinite, and inadequate. Therefore, we have undertaken studies which it is hoped will lead to a better understanding of the physiology of articulations. Further knowledge of the anatomy, histology and physiology of normal joints should have an important bearing on the physiology of pathological joints and the treatment of arthritis. Much of our work will concern the normal and pathological joints of cows, because of our ready access to an unlimited amount of material. This paper is the first of a series of studies of joints of cattle, and is a cytological study of normal synovial fluid.A clear, viscid liquid known as synovial fluid is found in all normal joints. In the smaller laboratory animals, as well as in man, this fluid is present in such minute amounts that the aspiration of quantities sufficient for careful cellular and chemical study is difficult or impossible. The astragalotibial (hock) joint of normal cattle is a source of a large quantity of easily obtainable synovial fluid. Smaller amounts can be aspirated from the carpometacarpal (front knee) joint.

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