boarding" of the muscles of the back is one of the
earliest and most valuable diagnostic signs of Pott's disease.

_Deformity._--The most common and characteristic deformity is an
abnormal antero-posterior curvature, with its convexity backwards. The
situation, extent, and acuteness of the bend vary with the region of
the spine affected, the situation of the disease in the bone, and the
number of vertebrae implicated. When the disease has destroyed the
bodies of one or two vertebrae, a short, sharp, angular deformity
results; when it affects the surface of several bones, a long, wide
curvature.

Lateral deviation is occasionally met with in the early stages of the
disease as a result of unequal muscular contraction, and in the later
stages from excessive destruction of one side of a vertebra, or from
partial luxation between two diseased vertebrae.

_Abscess Formation._--Spinal abscesses occur with greater frequency
and at an earlier stage in adults than in children, because in adults
the disease usually begins on the surface of the vertebrae. Pyogenic
infection of such abscesses after they have burst externally
constitutes one of the chief risks to life in Pott's disease.

_X-Ray Appearances._--These, when considered along with the clinical
signs, usually afford valuable information as to the exact seat and
nature of the lesion and the number of vertebrae involved. It is
recommended to compare the skiagram with that of the normal spine from
the same region and from a patient of approximately similar age. The
outlines of the bodies are woolly or blurred; in the early stage there
may be clear areas corresponding to cheesy foci. In progressive cases
the bodies may be altered in shape and in size, and from destruction
and collapse of the bones there is altered spacing, both of the bodies
and of the ribs. In the interpretation of skiagrams, help is often
obtained from an alteration in the axis of bodies, an angular
deviation often drawing attention to the lesion which is located at
the "angle." In children (Fig. 213) there is often a spindle-shaped
shadow, outlined against the vertebral column, which is due to a cold
abscess, and which extends above and below the bodies actually
involved in the tuberculous process. The fusion of the bodies by new
bone, which accompanies repair, can be followed in skiagrams taken at
intervals.

[Illustration: FIG. 213.--Radiogram of Child's Thorax, showing
spindle-shaped shadow at site