An experimental model of osteoarthritis resulting from laxity of the joint was induced in eighteen mature dogs (at least two years old) by sectioning the anterior cruciate ligament of the right knee (stifle) with a stab incision, the left knee providing a control. A sham operation was also performed in three other dogs, in which a stab incision was made but the ligament left intact. The dogs were killed at various intervals from one to forty-eight weeks later. Morphological changes in bone, cartilage, synovial membrane and joint capsule were examined in all the joints and biochemical changes in the cartilage of three dogs killed after two, eight, and sixteen weeks. All the changes resulting from the operation progressed with time and became indistinguishable from those found in three dogs with natural osteoarthritis of the knee. There were no changes in the joints which had sham operations. As the time of onset is known, this experimental model in a larger species enables a study to be made of the biochemical as well as the morphological changes in the early stages of osteoarthritis.

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The clinical and pathological features of two cases of bacterial endocarditis in the dog are described. Non–organ specific autoantibodies (antinuclear factor and rheumatoid factor) were detected in the sera and their significance is discussed.

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In three adult dogs the cranial cruciate ligament of the right stifle was sectioned. The animals were examined at regular intervals over the following twenty‐nine months and the clinical findings noted. Fluorochrome bone markers were injected at intervals of approximately six months. Following injection of barium sulphate and Berlin blue after euthanasia, the joint tissues of both stifles were examined for evidence of degenerative changes. The right stifles showed typical changes of osteoarthritis, while the left stifles revealed no abnormality.