An acute subluxation--that is, one resulting entirely from concussion of forces within twenty-four or forty-eight hours prior to the moment of adjustment--rarely produces a condition which could be named as any particular disease. The symptoms are those of “wrenched back,” if any. A single adjustment usually suffices to correct such subluxation just as a single movement might correct a dislocated humerus within the same period, and any symptoms promptly disappear. This is probably the maximum benefit to be derived from adjustment and the best time for its administration, because it leaves the spinal column in an exactly normal condition and no more susceptible to further jars or shocks than before the injury. All disease which might have resulted from that subluxation has been fully prevented. Older subluxations must be dealt with differently because they present a different condition. Adaptative changes have taken place in the shape of the vertebra itself and of every surrounding tissue as they prepare to make the best of their situation. But a vertebra once displaced has lost its poise and broken or modified the reflex arcs through its nerves so that it becomes more likely to respond to further forces applied, or to muscular contractions within the body, by further change of position. Such changes are always followed by further adaptation of the surrounding parts. The degree of nerve impingement must change to keep pace with the developing malposition and thus, by gradually successive steps, disease develops in the area of peripheral distribution of the nerves. The nerve is under a thumbscrew gradually tightening. To adjust such a vertebra many successive movements are required. An apparently full and free movement of a subluxation meets the elastic resistance of the solidly packed tissues and the pull of the modified intervertebral disk--strains at these tissues--and rebounds so as to settle almost, but not quite, in its old abnormal position. The amount gained in a single adjustment can rarely be appreciated by palpation. To the touch it would appear that no change had been made, except occasionally in the Cervical region. But with repeated adjustments the vertebra will be found to have approached its normal position. Sometimes in a few weeks, sometimes in a few months, the gain becomes palpable and then perhaps visible to the eye in thin subjects. The relief of impingement then is not usually an instantaneous process, but proceeds by gradual steps. Each movement of the vertebra is accompanied by a shock to the nerve against some part of which the bone is pressing, which may produce some disturbance in the diseased organs and may even appear to have aggravated disease for a time. Some pain and soreness around the vertebra may accompany the necessary adaptative changes of shape which readapt the tissues to their proper shape and relation.