1. The three age types of acute haematogenous osteomyelitis are conditioned in their respective clinical features by the differing nature of their vascular bone pattern.

2. In the infant the condition causes severe and often permanent epiphysial damage and joint infection, a large involucrum but only transient damage to the shaft and metaphysis.

3. In the child the condition is responsible for extensive cortical damage with involucrum formation, but, except for some stimulation of growth, permanent damage to the growth cartilage and to joints is exceptional. Chronicity of the disease is rare if treatment has been effective.

4. In the adult acute osteomyelitis of the long bones is rare. It causes very frequent joint infection; the cortex is absorbed instead of sequestrating. The whole of the bone is invaded and frequently leaves chronic infection in the bone marrow.

5. The vascular characteristics of the bones in each age group and their relation to the onset of infection are described.

6. Some general directives for management based on these facts are suggested.

1. Vascular anatomical studies of the spine are described and the possibility of spread of infection from pelvis to spine through the paravertebral venous plexus is discussed.

2. Though a venous route does exist, our studies do not support the supposition that infection is likely to spread by this route; nor is there any clear clinical, pathological or anatomical evidence that such spread occurs.

3. Nineteen cases of pyogenic osteomyelitis of the spine are recorded, six of which followed urinary infections. The condition is compared with osteomyelitis as it occurs in the other bones of adults.

1. In five series of experiments in eighty-two rabbits we succeeded in causing rarefaction of the calcaneum of all the animals soon after it was relieved from muscular compressing forces; new bone was generated when the calcaneum was subjected again to the stresses and strains of muscle contraction.

2. We found evidence that during muscle action pressure forces are transmitted through the bone, and that the presence or absence of these pressure forces conditions the balance between bone formation and bone removal.

3. In the calcaneum of the rabbit lack of muscular action seems to be the most important factor inducing osteoporosis. It is possible that the origin of post-traumatic osteoporosis has the same basis.

4. In our experiments bone rarefaction was characterised by a great increase in the vascularity of the bone; this increase ceased when the bone reached its final precarious bone density. Thus, vascular over-activity accompanied the removal of bone; but bone reconstruction was also seen to be accompanied by a more localised increase in vascularity.

5. From our experiments we cannot suggest that the inhibition of muscle contraction accompanying Sudeck's syndrome is responsible for this disorder, because we were unable in our animals to cause any of the other signs characteristic of Sudeck's bone atrophy. But the constancy with which we caused bone atrophy by the removal of muscle action may possibly help to explain the mechanism of bone absorption accompanying Sudeck's disease.

1. A study of normal and osteoarthritic hyaline cartilage has been made with the electron microscope and x-ray diffraction.

2. Normal cartilage consists of a three-dimensional network of collagen fibrils with no preferred orientation, surrounded by a matrix containing polysaccharide.

3. In the osteoarthritic joint the collagen fibrils show definite orientation and a decreased proportion of ground substance. X-ray diffraction confirms this and shows the orientation to be at right angles to the surface of the femoral head.

4. Tensional forces across the joint may explain why osteoarthritic changes first appear in the non-weight-bearing area of the joint.

1. The results of a study of the characteristics of the vessels found in forty-six human femoral heads during the growth period are described.

2. Of the three different sources of blood entering the human adult femoral head it was found that from birth to about three to four years the vessels of the ligamentum teres do not contribute to the nourishment of the head.

3. After the fourth year the metaphysial vessels decrease in importance until they finally disappear, leaving the head with only one source of blood through the lateral epiphysial vessels; the ligamentum teres is not yet contributing to the circulation of the head.

4. After about eight or nine years it was found that the vessels of the ligamentum teres contribute to the blood supply of the head while the metaphysial blood flow is still arrested.

5. Finally, at puberty, after a period of activity of the metaphysial vessels, epiphysial fusion takes place, bringing together the three sources of blood characteristic of the adult.