In answer to the four questions posed at the beginning of this paper, it seems justifiable to conclude as follows:

1. The two main types of arthritis affect also the apophyseal joints. Atrophic spondylarthritis, associated chiefly with focal or general infection, occurs in an acute reparable form in which the cartilages are not involved; in a localized chronic type, marked by destruction of cartilage; and as a chronic, more or less systemic disease, ankylopoietic spondylarthritis. Hypertrophic spondylarthritis, marked by destruction of cartilage, but not necessarily by bone hypertrophy, is often the result of persistent changes in the position of the vertebrae; in another type, independent of mechanical factors, it is possibly of infectious origin (amoebiasis). Secondary involvement of the articular processes in inflammatory and rarefying diseases of the vertebral bodies is rare. Isolated rarefaction of the articular segments without cartilaginous lesions, another rare condition, is etiologically obscure.

2. Local pain (spontaneous and on pressure) and stiffness caused by muscle tension are found in active phases of any type of spondylarthritis. Rigidity not caused by muscle spasms develops whenever articular cartilages are affected. Rigidity without pain is observed in quiescent hypertrophic and in arrested ankylopoietic spondylarthritis. In diseases of the vertebral bodies and intervertebral discs, local pain and persistent rigidity occur chiefly when the apophyseal articulations are involved. Radiculitis, which may develop in any disease that affects the intervertebral foramina, is not characteristic of particular lesions.

3. Atrophic spondylarthritis is independent of other systemic spinal diseases; there is especially no correlation either with spondylosis ossificans ligamentosa or with the various types of spondylitis. Hypertrophic spondylarthritis, being intimately related to postural alterations (mainly those resulting from "discogenetic" lesions), is often associated with traumatic changes,—hypertrophic spondylitis, scoliosis, and the like.

4. Acute atrophic spondylarthritis can be cured; chronic atrophic spondylarthritis can be arrested by successful treatment of the coexistent infection. In hypertrophic spondylarthritis, the treatment depends upon the underlying lesion (mechanical or infectious).