A more alarming symptom still is when the animal, instead of resting in the slings by his buttocks, casts his weight bodily into the belly-rest and hangs with a heavy head into the head-stall.  This indicates complete exhaustion and a wish for death.  Matters should therefore be explained to the owner, and his consent obtained for immediate destruction.

Pathology.—­The pathological changes occurring in suppurative arthritis we shall pass over briefly.  It is almost sufficient, in fact, to say that the whole of the joint becomes completely disorganized.

The synovial membrane becomes so tremendously thickened and injected as to be scarcely recognisable as such, the thickening in the later stages being due to large growths of granulation tissue which entirely alter the appearance of the membrane as we know it normally.  In the early stages the contents of the joint are composed of thin pus and synovia.  Later, as destruction of the synovial membrane proceeds, the flow of synovia is stopped, while the pus formation goes on until finally nothing but pus and dead tissue products fill the cavity.

If the suppurative process has commenced from within, the pus that is formed is, as a rule, thick and creamy, comparatively unstained, and free from marked odour.  If, on the other hand, air has gained access to the joint, or the suppurative process has started from the materials introduced by a foreign body, the joint contents are thin, blood-stained, and stinking.

The inflammatory changes in the joint soon spread to the ligaments, and to the soft structures in contact with them.  This means that the ligaments become infiltrated with inflammatory exudate, that the fibrous bundles composing them become separated, and that the ligaments are weakened and easily stretched.  As a consequence, a certain amount of displacement or dislocation of the bones is allowed.

In like manner the inflammatory changes keep spreading until we have the periosteum next the ends of the bones affected.  The periostitis thus set up invariably takes the osteoplastic form, and as a result of this we have growths of new bone in the near neighbourhood of the joint.  It is in the later stages of the disease—­that is, when the pus has been evacuated and reparative changes commenced—­that this osteoplastic periostitis is most marked, and it plays a large part in bringing about the condition of anchylosis, which we shall afterwards describe.

Grave changes also occur in the articular cartilages.  They quickly lose their peculiar glistening polish, their semitransparency is lost, and the natural tint of a pearl-like blue gives way to a dirty yellow.  Later this is followed by erosion of the cartilages at such points as they happen to be in greatest contact.  The ends of the bones are thus exposed, and their medullary cavities exposed to infection.  As a result we get in them the changes we have already described under Ostitis.