1. The structure ofthe cancellous bone ofthe third lumbarvertebral body from a twenty-year-old woman who died from head injuries was studied, using serial section reconstruction techniques.

2. In addition to the construction of enlarged models from different regions of the vertebral body, measurements were made of the bone area, the surface area, and the thickness and spacing of the bony structures.

3. The vertebral spongiosa consists of a complex network of bony plates perforated by rounded openings of varying size. The plates show preferential orientation in the vertical and horizontal planes, and the amount of bone is greatest towards the upper and lower surfaces of the vertebral body.

4. The mechanical significance of the structure of the vertebral spongiosa is discussed.

1. The literature on pigmented villonodular synovitis has been reviewed and a series of eighty additional cases is reported.

2. The condition usually presents either as a nodule in a finger or knee, or as a diffuse lesion in a knee. The lesions, although benign, sometimes erode or invade the tissue of adjacent bones.

3. Distinction from malignant synovioma can be made on the basis of the macroscopic appearance of the lesion at operation (relationship to joints or tendon sheaths: villonodular appearance: pigmentation), and by histological examination.

4. Treatment of the nodular form by excision is satisfactory but extensive synovectomy for diffuse lesions of the knee gives poor results.

5. The etiology of pigmented villonodular synovitis is unknown, but it appears to be a self-limiting process, possibly inflammatory in nature.

1. In two dogs, approximately one to two years and three to four months of age, an experimental comparison was made between the calcium accretion rate as defined by the Bauer-Carlsson-Lindquist equation, and the bone formation rate determined by double tetracycline labelling.

2. The overall calcium accretion rate was determined from the specific activity of the blood plasma, and the urinary and faecal excretion of isotope, following an intravenous tracer dose of Ca⁴⁵. A time of five days after injection was used for the calculation of accretion rates, but data for shorter times of calculation are included.

3. Local accretion rates were obtained for different parts of the skeleton by determining the specific activities of bone samples at the end of the experiment.

4. The amount of isotope the uptake of which was not related to new bone formation (the diffuse component) was determined autoradiographically.

5. Local values for appositional growth rate and bone formation rate were obtained, using sections of undecalcified bone specimens, by measuring the linear separation between two tetracycline bone markers and the area of new bone enclosed by them.

6. In the older dog, the measurements for cortical bone showed that the accretion rate was two to three times as great as the bone formation rate: the observed diffuse component was sufficient to account for the greater part of this difference. Measurement of the bone formation rate for cancellous bone presented difficulties, but the approximate values obtained suggested that the accretion rate and the bone formation rate were of about the same order for this tissue.

7. In the younger dog, the bone formation rate could be determined only in cortical bone: at the sites studied, the values for the accretion rate and the bone formation rate did not differ by more than 20 per cent. It is suggested that this is due partly to the low specific activity of the diffuse component in this young animal, and partly to the relatively large amounts of new bone formed during the period of the experiment.

8. Despite the important differences between the rates of calcium accretion and bone formation that were found to exist in regions where there was only a small amount of new bone formation, there was a strong correlation between the two rates. The value of the accretion rate as a parameter of bone metabolism is clear.

1. The bone changes in four autopsied cases of Cushing's syndrome are described. The changes take the form of osteoporosis, which is most marked in the spine and the ribs.

2. The osteoporosis results from impaired osteoblastic bone formation in the presence of a normal degree of osteoclastic bone resorption.

3. Histological abnormalities of fracture callus in Cushing's syndrome indicate interference with the proliferation of osteoblasts and cartilage cells and with the formation of new tissue by these cells.

4. The bone changes in Cushing's syndrome are comparable with those produced in experimental animals by the administration of A.C.T.H. or cortisone.

1. Details of clinical, radiological, biochemical and histological investigations of a case of metaphysial dysostosis are presented.

2. The patient was a boy of seven years, and showed widespread lesions (involving long bones of limbs, small bones of hands and feet, pelvis, clavicles, and ribs) characterised by retardation of growth and ossification with masses of partly calcified tissue in the metaphyses.

3. No radiological, clinical or histological evidence of renal osteodystrophy was found in the case described.

4. Metaphysial dysostosis is discussed in relation to other chondrodystrophies.

Two cases of benign osteoblastic tumours of the spine, occurring in young patients, and presenting as expanding osteolytic lesions with some central calcification and ossification, are described. It is suggested that they represent a condition allied to, but usefully separated from, osteoid osteoma of bone. The name osteogenic fibroma of bone, proposed by Lichtenstein for this type of case, is accepted.

1 . The repair of a simple crush injury was studied in rats, in both normally innervated and completely denervated muscle. In each case the histological findings at periods from two hours to thirty-two weeks are described.

2. The denervated muscle showed active and effective repair.

3. A comparison with the findings in normally innervated muscle establishes that the cellular processes of repair do not depend on connections with the central nervous system.

The effect of cortisone on the repair of simple muscle injury was studied in rabbits. The histological findings in the crushed muscle are described for a period up to twenty-one days after injury.

Cortisone defers the onset of muscle regeneration, and retards its progress, but it does not change the course of the repair process or alter its eventual outcome under the conditions of the experiment.

This apparent refractoriness of repair of muscle, as compared with that of other connective tissues, is discussed.

Amputation or post-mortem specimens from eight cases of joint tuberculosis, with immobilisation changes in bone, have been studied by fine-detail slab radiographs and subsequent histological examination. The findings in three of these cases are presented in detail.

The immobilisation changes take the form of a true osteoporosis, which is strikingly focal in nature. In the adult the sites of most marked involvement include the subcortical bone adjacent to articular surfaces and the bone in the neighbourhood of the obliterated epiphysial plates.

Areas of permanent change in bone structure may result, although commencing "repair" is seen in the form of newly developed bone trabeculae in the osteoporotic areas.

In one case, where immobilisation occurred at an early age, changes in the growing epiphysial plates were produced in addition to osteoporosis. This is correlated with the known susceptibility of growing epiphysial cartilage to a wide variety of damaging agents.

Radiologically, it is important to discriminate between these immobilisation changes and the bone destruction which might be produced by extension of the tuberculous lesion itself.

A case is described in which a clinical diagnosis of "metaphysial dysostosis" was made, but in which histological examination of involved bones showed the changes of rickets, presumably renal, with secondary hyperparathyroidism.