_Initial Stage._--At this stage the disease is confined to a focus in the bone which has not yet opened into the joint or to the synovial membrane. The onset is insidious, and if injury is alleged as an exciting cause, some weeks have usually elapsed between the receipt of the injury and the onset of symptoms. The child is brought for advice because he has begun to limp and to complain of pain. There is a history that he has become pale and has ceased to take food well, that his sleep has been disturbed, and that the pain and the limp, after coming and going for a time, have become more pronounced. On walking, the affected limb is dragged in such a way as to avoid movement at the hip, and to substitute for it movement at the lumbo-sacral junction. The child throws the weight of the trunk as little as possible on to the affected limb, and inclines to rest on the balls of the toes rather than on the sole. There is usually some wasting of the muscles of the thigh and flattening of the buttock. Diminution or loss of the gluteal fold indicates flexion at the hip which might otherwise escape notice. Pain is complained of in the hip, or is referred to the medial side of the knee, in the distribution of the obturator nerve. Sometimes the pain is confined to the knee, and if the examination is restricted to that joint the disease at the hip may be overlooked. At this stage the attitude of the limb is not constant; at one time it may be natural, and at another slightly flexed and abducted. Tenderness of the joint may be elicited by pressing either in front or behind the head of the bone, but is of little diagnostic importance. Pain elicited on driving the head against the acetabulum may occasionally assist in the recognition of hip disease, but the diagnostic value of this sign has been overrated and, in our opinion, this test should be omitted. Most information is gained by testing the functions of the joint, and if this is done gently and without jerking, it does not cause pain. The child should lie on his back, either on his nurse's knee or on a table; and to reassure him the movements should be first practised on the sound limb. On slowly flexing the thigh of the affected limb, it will be found that the range of flexion at the hip is soon exhausted, and that any further movement in this direction takes place at the lumbo-sacral junction. The child is next made to lie on his face with the knees flexed in order that the movements of rotation may be tested. The thigh is rotated in both directions, and on comparing the two sides it will be found that rotation is restricted or abolished on the side affected, any apparent rotation taking place at the lumbo-sacral junction. These tests reveal the presence of _rigidity_ resulting from the involuntary contraction of muscles, which is the most reliable sign of hip disease during the initial stage, and they possess the advantage of being universally applicable, even in the case of young children.