=Symptoms.= Strain is accompanied by lameness, most marked when the animals endeavour to turn, by exaggerated sensibility of the entire hock region, and, in grave cases, by subcutaneous œdema. =Diagnosis and prognosis.= Diagnosis is simple. The prognosis is sometimes grave, because a spavin or a permanent chronic enlargement of the capsule of the true hock joint may form. =Treatment.= It is often desirable at once to apply an extensive blister over the whole hock and to supplement this at a later stage by cold applications, or by continuous cold irrigation for half an hour or more both night and morning. In exceptional cases the use of the actual cautery becomes necessary. III.—LUXATION OF JOINTS. Luxation consists of permanent displacement of the bony surfaces forming a joint, and may follow violent mechanical injury or any other cause. Luxations have been divided into congenital, _i.e._, such as exist from the time of birth; spontaneous, _i.e._, those which result from some defect of conformation or constitution; and acquired or accidental, which occur as results of falls, wounds, accidents, etc. From the point of view of their duration, luxations are termed temporary when they do not necessitate reduction, progressive when the tendency is towards greater and greater displacement of the surfaces, or permanent when reduction is impossible. Those commonest in bovines are luxations of the femur, luxation of the patella, femoro-tibial luxation, and luxation of the scapulo-humeral joint. LUXATION OF THE FEMUR. Luxation of the head of the femur with displacement beyond the cotyloid cavity is very frequently congenital. The condition also occurs with some frequency in adults or aged animals in consequence of relaxation of the articular ligaments and the absence of the subpubic ligament (pubio-femoral ligament). =Causation.= Luxation may be congenital, the head of the femur being displaced backwards and carried above the cotyloid cavity. This form is of no practical interest, because the animals are not usually reared. More frequently in young or adult animals it assumes the spontaneous progressive form, in consequence of degenerative changes in and relaxation of the coxo-femoral interosseous ligament. The head of the femur presses on the upper margin of the cotyloid cavity, which it injures, and eventually becomes lodged in the neighbourhood of the neck of the ilium, in the great sciatic notch.