The lesions met with later correspond to those of the tertiary period of the acquired disease, but as they affect bones which are still actively growing, the effects are more striking.  Gummatous disease may come and go over periods of many years, with the result that the external appearance and architectural arrangement of a long bone come to be profoundly altered.  In the tibia, for example, the shaft is bowed forward in a gentle curve, which is compared to the curve of a sabre—­“sabre-blade” deformity (Fig. 132).  The diffuse thickening all round the bone obscures the sharp margins so that the bone becomes circular in section and the anterior and mesial edges are blunted, and the comparison to a cucumber is deserved.  In some cases the tibia is actually increased in length as well as in girth.

[Illustration:  FIG. 132.—­Sabre-blade Deformity of Left Tibia in Inherited Syphilis.

(From a photograph lent by Sir George T. Beatson.)]

The contrast between the grossly enlarged and misshapen tibia and the normal or even attenuated fibula is a striking one.

Treatment is carried out on lines similar to those recommended in the acquired disease.  When curving of the tibia causes disability in walking, the bone may be straightened by a cuneiform resection.

Syphilitic dactylitis is met with chiefly in children.  It may affect any of the fingers or toes, but is commonest in the first phalanx of the index-finger or of the thumb.  Several fingers may be attacked at the same time or in succession.  The lesion consists in a gummatous infiltration of the soft parts surrounding the phalanx, or a gummatous osteomyelitis, but there is practically no tendency to break down and discharge, or to the formation of a sequestrum as is so common in tuberculous dactylitis.

The finger becomes the seat of a swelling, which is more evident on the dorsal aspect, and, according to the distribution and extent of the disease, it is acorn-shaped, fusiform, or cylindrical.  It is firm and elastic, and usually painless.  The movements are impaired, especially if the joints are involved.  In its early stages the disease is amenable to anti-syphilitic treatment, and complete recovery is the rule.

HYDATID DISEASE

This rare disease results from the lodgment of the embryos of the taenia echinoccus, which are conveyed to the marrow by the blood-stream.  The cysts are small, usually about the size of a pin-head, and they are present in enormous numbers scattered throughout the marrow.  The parts of the skeleton most often affected are the articular ends of the long bones, the bodies of the vertebrae, and the pelvis.

As the cysts increase in number and in size, the framework of the bone is gradually absorbed, and there result excavations or cavities.  The marrow and spongy bone first disappear, the compact tissue then becomes thin, and pathological fracture may result.  The bone becomes expanded, and the cysts may escape through perforations into the surrounding cellular tissue, and when thus freed from confinement may attain considerable dimensions.  Suppuration from superadded pyogenic infection may be attended with extensive necrosis, and lead to disorganisation of the adjacent joint.