mal kingdom, both in
domestic species and in wild animals in the natural state such as the
larger carnivora and the gorilla; evidence of it has also been found in
the bones of animals buried with prehistoric man.

The morbid changes in the joints present a remarkable combination of
atrophy and degeneration on the one hand and overgrowth on the other,
indicating a profound disturbance of nutrition in the joint structures.
The nature of this disturbance and its etiology are imperfectly known.
By many writers it is believed to depend upon some form of
auto-intoxication, the toxins being absorbed from the gastro-intestinal
tract, and those who suffer are supposed to possess what has been called
an "arthritic diathesis."

The localisation of the disease in a particular joint may be determined
by several factors, of which trauma appears to be the most important.
The condition is frequently observed to follow, either directly or after
an interval, upon a lesion which involves gross injury of the joint or
of one of the neighbouring bones. It occurs with greater frequency after
repeated minor injuries affecting the joint and its vicinity, such as
sprains and contusions, and particularly those sustained in laborious
occupations. This connection between trauma and arthritis deformans led
Arbuthnot Lane to apply to it the term _traumatic_ or _trade arthritis_.

The traumatic or strain factor in the production of the disease may be
manifested in a less obvious fashion. In the lower extremity, for
example, _any condition which disturbs the static equilibrium of the
limb as a whole_ would appear to predispose to the disease in one or
other of the joints. The static equilibrium may be disturbed by such
deformities as flat-foot or knock-knee, and badly united fractures of
the lower extremity. In hallux valgus, the metatarso-phalangeal joint of
the great toe undergoes changes characteristic of arthritis deformans.

A number of cases have been recorded in which arthritis deformans has
followed upon antecedent disease of the joint, such as pyogenic or
gonorrhoeal synovitis, upon repeated haemorrhages into the knee-joint in
bleeders, and in unreduced dislocations in which a new joint has been
established.

[Illustration: FIG. 157.--Arthritis Deformans of Elbow, showing
destruction of articular surfaces and masses of new bone around the
articular margins.

(Anatomical Museum, University of Edinburgh.)]

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