1. The results of thirty-five acutely slipped upper femoral epiphyses, treated from 1950 to 1969, are presented. Avascular necrosis of the femoral head occurred in five cases.

2. Skin traction with medial rotation, followed in three to four days by internal fixation, without further manipulation, is recommended so that this iatrogenic complication may be avoided.

1. Osteogenesis imperfecta is characterised by osseous fragility. Patients with the "congenita" form have multiple fractures before birth; those with the "tarda" form have osteoporosis, and develop multiple fractures and milder deformities of long bones at varying times after birth.

2. The frequency of blue sclera, dentinogenesis imperfecta, bruising, ligamentous laxity, and deafness are recorded in sixty patients seen at the Hospital for Sick Children, Toronto, from 1949 to 1969. The major orthopaedic deformities of long bones were antero-lateral bowing of femur and anterior bowing (sabre shin) of tibia.

3. The incidence of scoliosis (40 per cent) is high in osteogenesis imperfecta. Two patients, one in Toronto and one in Seattle, have had Harrington instrumentation and fusion for this.

4. Fractures were commonest in the femur and tibia and few in the cervical spine and femoral neck. There were four cases of disturbing hyperplastic callus formation.

5. Twenty-one patients were operated on for long bone deformities and recurrent fractures by the Sofield technique. Despite extensive subperiosteal dissection non-union is rare (four cases). Fourteen of twenty-one patients so treated are able to walk, with or without assistance. Surgical intervention to both correct and prevent deformities is justified.

6. Patients with osteogenesis imperfecta compensated for their disability by reasonable academic achievement and by choosing a sedentary occupation.

1. Forty patients with solitary eosinophilic granuloma of bone from the Hospital for Sick Children, Toronto, have been reviewed. They had clinical and laboratory findings similar to those reported by others except for the erythrocyte sedimentation rate, which was raised in nearly half the patients tested.

2. Radiographs in all cases showed the lesion to be osteolytic. In the skull and cervical spine there was no bony reaction ; in the thoracic and lumbar spine the typical picture of Calvés disease was produced; in long bones the cortex commonly showed endosteal erosion and periosteal reaction.

3. In one patient the lesion progressed so rapidly that the body of a cervical vertebra was destroyed within ten days.

4. The differential diagnosis includes sarcoma. Biopsy is essential.

5. All the patients improved regardless of the treatment they received. Complications were due either to the site of the lesion or to its treatment.

6. Expansion of the lesion after biopsy indicates a more widespread manifestation of histiocytosis X.

1. A hypothesis outlining an auto-immune mechanism for antibody production against autogenous nucleus pulposus is presented.

2. Auto-antibodies to autogenous nucleus pulposus have been experimentally produced in rabbits.

3. These antibodies are cell-bound within lymphoid cells and are greatest in primary lymph nodes. This antibody is demonstrated by a positive pyronin reaction.

4. Lymphoid cells fixed in Carnoy's fluid and stained for pyronins also show a distinct natural yellow fluorescence. This fluorescence occurs only in the cytoplasm of those cells which are pyronin-positive and presumably producing antibody.

5. The lymph node phase of the reaction is greatest at four days and is sustained for three weeks. A secondary generalised lymph node response occurs in all lymph nodes at six weeks.

1. Experimental avascular necrosis of the femoral head was produced in rabbits and the histological and radiographic changes were compared.

2. Avascular bone which was not re-ossified or altered in any way showed no change in density to x-rays.

3. Areas of avascular bone which were being repaired by the formation of appositional new bone showed an absolute increase in density in the radiographs. This is apparently due to simple increase in bulk of bone to be penetrated by the x-ray beam. On this basis, increasing density in radiographs of bone suspected of being dead is a sign of increasing re-ossification rather than of increasing necrosis.

4. Re-ossification of dead bone occurred rapidly in the absence of simultaneous resorption of necrotic trabeculae. It is thus suggested that the term "creeping substitution" is misleading and does not reflect accurately the histological findings, at least as they occur in rabbits.