In this way Nature protects the subluxated vertebra from further contact with the environment surrounding man, the rounded process offering less opportunity for a blow or shock to affect it. Changes in Shape Bone diseases such as rachitis osteomalacia, etc., and especially Potts’ Disease, or spinal caries, make marked changes in the shape of vertebrae. Also a subluxated vertebra may gradually assume a shape suited to the abnormal position it occupies, the commonest change being the assumption of a wedge shape by the centrum. This is a great obstacle to adjustment, as the abnormal shape of the vertebra makes it tend to settle after each movement into the old abnormal position. There are few spines without some more or less misshapen vertebrae. Ankylosis also makes great changes in the shape of vertebrae. There are two kinds of ankylosis--true and false. The first is a deposit of bone cells upon bone, often the formation of a bridgelike structure to hold contiguous vertebrae together. This may bind any portions of the vertebrae but most commonly holds the bodies, in which case it can only be appreciated by detecting the lack of movement between normally separable vertebrae. False ankylosis occurs with fever in bone and consists in an exudation of bone substance which sometimes produces remarkable distortions of shape. TECHNIC OF ADJUSTING Definitions Vertebral Adjusting is the art of correcting by hand the malpositions of subluxated vertebrae. A Vertebral Adjustment, strictly speaking, should mean the complete restoration of normal relation between previously subluxated vertebrae. As used in Chiropractic, it means either a partial or complete restoration of such normal relation. Maladjustment, as used in the profession, designates any movement of vertebrae by hand which produces or increases subluxation. GENERAL PRINCIPLES OF ADJUSTING It will be well for the student to master first the general rules and principles which govern vertebral adjustment and then to proceed to a detailed investigation of each movement, in turn, before practicing it. The art of adjusting can only be acquired by practice, and a high degree of excellence in it only by _long-continued_ practice. However, the rapidity with which it can be mastered depends largely upon the formation of a clear pre-conception of the work to be done and the manner of its doing. As the student progresses in the art he finds himself occasionally guilty of errors which mar, in some degree, the efficiency of his work. These may arise from unconscious modification of the technic first learned or from unconscious repetition of some necessary modification demanded by a special peculiarity in one or more cases.