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.

Treatment - (a) Preventive. - Seeing that many of these cases have their starting-point in stabs or penetrating wounds of the sole, we shall be concerned first with a consideration of the correct treatment to be adopted when we know the wound to have reached the articulation.

Only too frequently the treatment practised is that of poulticing. In other portions of this work we have pointed out the advantages that a continued antiseptic bathing has over the application of a poultice, the greater readiness with which the solution comes into contact with the deeper parts of the wound, and the far greater chance there is of maintaining water in an antiseptic condition than there is of keeping a poultice in the same state. There is no doubt, that in this case also, the cold or warm antiseptic bath is to be preferred to the poultice. It is questionable, however, whether even the bath is sufficient for our purpose here. We have in this case a deep punctured wound, and a wound that in every probability is infected with the organisms of pus or of putrefaction. It is a wound, moreover, which is likely to impede the thorough access to it of the solution in which the foot is fomented, on account of the flakes of coagulated fibrin which fill it.

The most rational treatment, therefore, if we get to the case early enough, is to irrigate the wound freely with a solution of carbolic acid in water (1 in 20), or with a solution of perchloride of mercury (1 in 1,000), injected by means of a glass syringe, or the pattern of syringe devised for quittor. This injecting should be done thoroughly, and by that we mean that several syringefuls of the solution should be injected, the joint after each injection being manipulated so as to distribute the solution as far as possible over it. When this is done the opening in the sole may be plugged with a little perchloride of mercury, or, better still, with a little piece of tow saturated with a concentrated solution of perchloride of mercury or a solution of iodoform in alcohol and an antiseptic pad of tow or lint placed over all. The foot should then be bandaged and encased in a boot or sacking protective. The bandage should be removed daily and the antiseptic pad changed. At each visit the animal's condition must be carefully noted. So long as constitutional disturbance is slight, the foot appears comfortable, is free from marked heat and tenderness, and pawing movements are absent, and so long as the discharge on the pad appears non-purulent, free from marked odour, and small in quantity, then this dressing may be persisted in.

This treatment of open joint, preventive as it is of arthritis, is also indicated in the case of open navicular bursa. In several instances we have practised this treatment for the dressing of wounds implicating the bursae of tendons and the capsules of joints. It is also spoken of favourably by Mr. C.H. Flynn in the American Veterinary Review for June, 1888, whose treatment is as follows: 'Place the patient in a clean, well-ventilated, and drained stable. Have all the litter removed, and insist on the stall being kept clean. Either place the animal in slings, or tie the head so as to prevent lying down. Clip the hair and cleanse the parts well. He prefers the corrosive sublimate solution (1 in 1,000). Should the wound be of two or more days' standing, inject the joint with the corrosive sublimate solution. Now dry the parts with a clean towel and sprinkle the wound with iodoform. Over this place a thick layer of absorbent cotton-wool, filled with iodoform, bandage securely, and keep the patient on a moderate diet, preserving the utmost quietude possible. Should the bandage remain in position and the animal free from pain, leave the bandage and dressing in place from five days to a week. Then change it, and should the discharge be little, do not disturb it, but renew the iodoform and cotton dressing, leaving it on for another week.'

Other treatments for the same condition are practised, in which the wound is dusted with powdered iodoform, with potassium permanganate, or with corrosive sublimate, or where the wound, instead of being dusted, has the corrosive sublimate applied in the form of a plug. In each case the preliminary irrigation with the corrosive sublimate solution is dispensed with. This, however, should on no account be omitted. In our opinion it constitutes the very essence of the rationality of the treatment.

(b) Curative. - It may happen, however, and often does, that this first injection of an antiseptic is unsuccessful in preventing organismal infection of the wound. In this case grave constitutional disturbance and other untoward symptoms such as we have already described quickly make their appearance.

The animal should now be placed in slings and preparations made for actively treating the wound with antiseptics. Whether we fail or not, we have the satisfaction of knowing that we have given to the patient the best and the only chance of recovery.

It should be remembered, however, and should be pointed out to the owner, that with purulent arthritis fully developed, with the grave constitutional changes it occasions, and with the ever-present danger of a general septic invasion of the blood-stream, that the human surgeon under such circumstances offers to his patient the alternatives of amputation or probable death. With us no such alternative is possible. It is either return the joint to some semblance of its former usefulness, or destroy the patient.

In this case we advise the injection of the original wound, and also such fistulous openings as may have formed, with the 1 in 1,000 sublimate solution. Also, in order to avoid the sometimes abortive attempts of the antiseptic pad, to maintain a condition of asepsis around the wound, we advise the continual soaking of the whole foot in a cold antiseptic bath. This may be either carbolic acid 1 in 20, or - what is less volatile, perhaps more effectual, and certainly more economical - perchloride of mercury 1 in 1,000.

It has been our good fortune, even when we have seen the foot almost detached from the limb by the devastating inroads of the pus, to see the suppurative process by this means gradually overcome, a reparative anchylosis set in, and the animal restored to good health and usefulness, if not to soundness.

Once the suppurative process is checked and anchylosis commences, it is good treatment to smartly blister the whole of the region of the coronet, the pastern, and the wound itself with a mixed blister of cantharides and biniodide of mercury, repeated at intervals of a fortnight. This prevents to some extent further infection of the wound, and assists also in promoting the changes that tend to anchylosis.

(d) Anchylosis.

The word anchylosis signifies the stiffening of a joint. When one has read the serious changes occurring within the joint in the more serious forms of arthritis, it is easy to understand how it comes about. In suppurative arthritis, for instance, we have the synovial membrane destroyed, the articular cartilages partly or wholly obliterated, and the former boundaries of the joint entirely lost. If the animal lives, nature is bound to make repair of a sort. The synovial membrane and the articular cartilages utterly destroyed, as we have described, cannot again be replaced. Nature can only build again from such materials as are left to her. In this case the material is bone.

It must be remembered, however, that often the bone has been so diseased that spots of necrosis or caries within it are bound to remain unless moved by operative interference. Such diseased portions, when dealing with the foot, are beyond reach of the surgeon's knife, and we have no alternative but to allow them to remain. We get, therefore, in many cases, a condition of rarefactive ostitis occurring side by side with a slowly progressive caries within the bone, while outside is occurring an osteoplastic periostitis. The concurrence of these conditions leads in time to great increase in size of the parts, together with increasing anchylosis and deformity.