The pathological changes studied in this series include hypertrophic arthritis, nuclear expansions, ballooned discs, thinned discs, nuclear herniations into the vertebrae (Schmorl bodies), anterior and posterior nuclear protrusions, calcification of the nucleus pulposus, infections of the disc, and invasion by malignant tumors.

Nuclear expansions are for the most part physiological, and not pathological; whereas ballooned discs are found almost entirely in the disease entity known as senile osteoporosis of the spinal column.

There are two types of thinned discs: one in which the cartilaginous plate and annulus are intact, the thinning being due to desiccation and necrosis of the nucleus pulposus, and the other type in which the annulus is ruptured, or the cartilaginous plate contains many defects. Dehydration is essentially the cause of thinning in both types.

Intraspongy nuclear herniations or Schmorl bodies are for the most part asymptomatic. Anterior nuclear protrusions are rare and of little clinical interest, whereas posterior nuclear protrusions are of great clinical importance. Eight per cent. of the specimens showed evidence of posterior nuclear protrusions.

Calcification of the nucleus pulposus is a definite entity. However, it is of no clinical significance.

Infection of the disc, resulting in early destruction of the annulus and nucleus, is recognized. The infection is usually blood-borne, and it may be primary or secondary to involvement of the vertebral body. The only example in this group was of infection of the disc, secondary to involvement of the vertebra.

Invasion of the disc space by a malignant lesion is rarely found. Only one example was observed in this series, and in this case no real invasion of the cartilage was seen.