a
periosteal gumma breaks down and invades the skin, a syphilitic ulcer is
formed with carious bone at the bottom. A central gumma may eat away the
surrounding bone to such an extent that the shaft undergoes pathological
fracture. In the rare cases in which it attacks the articular end of a
long bone, gummatous disease may implicate the adjacent joint and give
rise to syphilitic arthritis.

[Illustration: FIG. 131.--Syphilitic Hyperostosis and Sclerosis of
Tibia, on section and on surface view.]

_Clinical Features._--There is severe boring pain--as if a gimlet were
being driven into the bone. It is worst at night, preventing sleep, and
has been ascribed to compression of the nerves in the narrowed Haversian
canals.

The _periosteal gumma_ appears as a smooth, circumscribed swelling which
is soft and elastic in the centre and firm at the margins, and shades
off into the surrounding bone. The gumma may be completely absorbed or
it may give place to a hard node. In some cases the gumma softens in the
centre, the skin becomes adherent, thin, and red, and finally gives way.
The opening in the skin persists as a sinus, or develops into a typical
ulcer with irregular, crescentic margins; in either case a probe reveals
the presence of carious bone or of a sequestrum. The health may be
impaired as a result of mixed infection, and the absorption of toxins
and waxy degeneration in the viscera may ultimately be induced.

A _central gumma_ in a long bone may not reveal its presence until it
erupts through the shell and reaches the periosteal surface or invades
an adjacent joint. Sometimes the first manifestation is a fracture of
the bone produced by slight violence.

In radiograms the appearance of syphilitic bones is usually
characteristic. When there is hyperostosis and sclerosis, the shaft
appears denser and broader than normal, and the contour is uneven or
wavy. When there is a central gumma, the shadow is interrupted by a
rounded clear area, like that of a chondroma or myeloma, but there is
sclerosis round about.

_Diagnosis._--The conditions most liable to be mistaken for syphilitic
disease of bone are chronic staphylococcal osteomyelitis, tuberculosis,
and sarcoma; and the diagnosis is to be made by the history and progress
of the disease, the result of examination with the X-rays, and the
results of specific tests and treatment.

_Treatment._--The general health is to be improved by open air, by
nourishing food, a