Should the injury be seated in the sensitive laminae, then the brittle nature of the horn secreted by the injured tissues makes itself apparent by the appearance of cracks in the wall of the quarter. Why this should occur will be readily understood by a reference to Fig. 100.

[Ill.u.s.tration: FIG. 100.--INNER SURFACE OF THE WALL OF THE QUARTER, SHOWING CHANGES IN THE h.o.r.n.y LAMINae BROUGHT ABOUT BY CHRONIC CORN.]

It will here be seen that the injury to the keratogenous membrane has led to great interference with the secretion of horn from the sensitive laminae.

As a result, the regularly leaf-like arrangement of the h.o.r.n.y laminae has been largely broken up. Certain of the laminae are altogether wanting, while others are broken in their length and rendered incomplete. With this condition there is always more or less contraction of the quarter.

Microscopic examination of the structures involved in such a case reveals the fact that with the contraction is an alteration in the normal direction of the h.o.r.n.y and sensitive laminae.

They become bent backward, and, instead of the regular and normal arrangement depicted in Fig. 32, show the distorted appearance given in Fig. 101.

From the appearances and characters of the blood-stain in the h.o.r.n.y sole we are able to deduce evidence relative to the duration and nature of the injury.

[ILl.u.s.tRATION: FIG. 101.--PERPENDICULAR SECTION OF THE WALL OF A CONTRACTED QUARTER IN A CASE OF CHRONIC CORN. Both the sensitive and h.o.r.n.y laminae are bent backwards, and haemorrhages have taken place at the base of the sensitive laminae.]

When, for instance, the stain is not to be found in the superficial layers of the sole, but is only discoverable by deep paring, then the injury is a recent one.

Where the stain _is_ met with in the superficial layers of horn, and is quickly pared out, then the injury has been inflicted some time before, and has not been repeated. When, as is sometimes the case, layers of horn that are stained are found alternated with layers that are healthy, then we have evidence that the cause of the corn, whatever it may be, is not in constant operation.

Similar indication of the age of the injury is also afforded by the colour of the lesion.

A stain that is deep red is proof that the injury is comparatively recent.

A distinct yellow or greenish tinge, on the other hand, is evidence that the injury is an old one.

_In the Moist Corn_ we have, in addition to the blood extravasation, the outpouring of the inflammatory exudate. In the most superficial layer of the horn this may not be noticeable. As one cuts deeper into the sole with the knife, however, it will be found that the lower layers of horn are more or less infiltrated with the discharge. This gives to the horn a soft consistence, a yellow appearance, and a touch that is moist to the fingers.

With the accompanying inflammation the cells in the neighbourhood of the injury are enfeebled and their normal functions interfered with. We may thus expect a corresponding interference with the growth of horn. This is exactly what happens, and as one cuts deeper still into the horn a point is finally reached when a well-marked cavity is encountered. A pale yellow and usually watery exudate fills it. This cavity points out the exact spot where the force of the injury has been greatest, where death of certain cells of the keratogenous membrane has resulted, and where the natural formation of horn has for a time been suspended.

_In the Suppurating Corn_, as in moist corn, we have pathological changes due to the tissue reaction to the injury, _plus_ the addition of pus organisms. Confined within the h.o.r.n.y box we have a discharge that, by reason of the living and constantly multiplying elements it contains--the pus organisms--is always increasing in bulk. This must be at the expense of the softer structures of the foot. Accordingly, as the formation of pus increases, we get pressure upon and final gangrene of the sensitive sole and of the sensitive laminae of the bars and the wall. With no outlet below, the pus formation increases until finally it finds its way out of the hoof by emerging at the coronet.

This in some instances it may do by confining its necrotic influences solely to the sensitive laminae of the wall, in which case, if a dependent orifice is quickly made at the sole, the injury to the laminae is soon repaired by the healthy tissue remaining.

In other cases, however, the necrosis has spread deeper. Caries of the os pedis, of the lateral ligaments of the pedal-joint, or of the lateral cartilages, is a result. When this occurs the exuding discharge from the coronet becomes thinner and more putrescent, and its feel, when rubbed between the fingers, sometimes gritty with minute fragments of broken-up bone. Here, unless operative measures prevent it, necrosis soon spreads deeper still. The deeper portions of the os pedis become affected. The capsular ligament of the joint is penetrated by the suppurative process, and a condition of septic arthritis results. The cavity of the joint becomes more or less tensely distended, according to the amount of drainage present, which in this case is almost nil, with matter in a state of putrescence. As a consequence, the surrounding ligaments become softened and yield, and the articular surfaces displaced. The articular cartilages also suffer, become necrotic in patches, and frequently wholly destroyed.

The end result is one of anchylosis of the joint and permanent lameness.

_Prognosis_.--With the ordinary dry corn a return to the normal may nearly always be looked for. Similarly, with moist corn, and even with careful treatment of the suppurating variety, the same favourable termination may be looked for and promised.

What cannot so safely be a.s.sured is that a relapse will not occur. In other words, the extent of the injury, no matter how serious, does not often offer anything that cannot be overcome by Nature and careful surgery; but the conformation of the animal does. A vicious predisposing conformation once there is there always, and although the injury resulting from it may easily give way to correct treatment, the same injury is bound to re-occur when the animal is again put to work.

Although with care suppurating corn, like other cases of suppuration within the hoof, may yield to treatment, the owner of the animal should, nevertheless, be warned that the condition is a serious one, especially should the joint become affected. It may so happen, as sometimes in fact it does, that the animal may die as a result of the infective fever so set up.

From no surface in the body can absorption take place quicker than from the synovial membrane of a joint. So soon, therefore, as this membrane comes in contact with septic material, so soon does a severe septic fever make its appearance. The septic matter has gained the blood-stream, and the patient succ.u.mbs to septic poisoning.

Apart from death occurring naturally, the changes taking place in the joint in the shape of bony growths or of actual anchylosis may be so severe as to render the animal useless, and slaughter may have to be advised.

_Treatment_.--We have already said that by far the most active cause in the production of corn is the shoe. It follows from this that it is to the shoeing we must largely look for a successful means of their prevention, and that the treatment of corn in its most simple form is really a matter for the smith, and not for the veterinary surgeon.

The faults in connection with the shoeing we have mentioned fully when treating of the _causes_ of corn. From those we learn that a shoe with a flat-bearing surface, or one moderately seated but flat at the heels, is the correct shoe for nearly all feet. The heels of the shoe should not be too high, should not be too short, and should be wide enough apart from each other to insure the wall of the foot obtaining a fair share of the bearing. Finally, even with the present method of shoeing, whenever it is possible to allow the frog to come to the ground, it should be encouraged to do so, and excessive paring either of the latter organ or of the bars or the sole should be strictly discountenanced. Where the sole is thin, or the frog wasted, use a leather sole or a rubber pad. With these precautions, corns may be prevented from occuring even in a foot with a predisposing conformation.

When corn is present, the first treatment usually adopted is that of 'paring it out.' This is advocated by Percival and by many other writers.

We cannot say, however, that we agree with it--at any rate, not in the case of simple dry corn.

'Paring it out,' and by that we mean thinning down the sole until close on the sensitive structures, can only be advised in the case of suppurating corn, or in cases where doubt exists as to whether pus is present or not.

In the latter case paring becomes necessary as an exploratory means to diagnosis.

When it appears fairly certain, even in the case of a moist corn, that pus does not exist, then paring is to be discountenanced, for the reason that it only tends to weakening of the parts and to a.s.sist largely in the corn's recurrence.

Those who advocate it do so for the reason that it relieves pressure on the injured parts.

That it does so directly from below cannot be denied; but that it also favours contraction and compression from side to side is equally certain.

A moderate paring may, however, be indulged in, say, to about one-half the estimated thickness of the sole. Softening of the horn and consequent lessening of pressure may then be brought about by the use of oil, oil and glycerine, tincture of creasote, or by poulticing.

In the case of a moist corn the paring should be stopped immediately the true nature of the injury has made itself apparent. Warm poultices or hot baths should then be used in order to soften the surrounding parts, lessen the pressure, and ease the pain. After a day or two day's poulticing, should pain still continue with any symptom of severity, the formation of pus may be expected, and it is then time for the paring to be carried further, until the question 'pus or no pus?' is definitely settled.

Should the moisture be due simply to the presence of the inflammatory exudate, then poulticing alone will have the desired effect, and the pain will be lessened. With the decrease in pain the poulticing may be discontinued, and the horn over the seat of the injury dressed with some antiseptic and hardening solution. Sulphate of zinc, a mixture of sulphate of zinc and lead acetate, sulphate of copper, or the mixture known as Villate's solution,[A] may either of them be used. Suitably shod, and with a leather sole for preference, the animal may then again be put to work.

[Footnote A: The composition of the escharotic liquid bearing his name was published by M. Villate in 1829 as under:

Subacetate of lead liquid ... ... ... 128 grammes.

Sulphate of zinc [=a=a] ... ... ... 64 grammes.

Sulphate of copper, [=a=a] ... ... ... 64 grammes.

Acetic acid ... ... ... ... 1/2 litre.

Dissolve the salts in the acid, add little by little the subacetate of lead, and well shake the mixture.]

When dealing with suppurating corn, then, a considerable paring away of the horn of the sole becomes a matter of necessity. The freest possible exit should be given to the pus, and this even when an opening has already occurred at the coronet. Unless this is done, and done promptly, the putrescent matter still contained within the hoof will make further inroads upon the soft structures therein, and later upon the ligaments, and even bone itself.

Having given drainage to the lesion by the dependent orifice in the sole, poulticing should again be resorted to and maintained for at least three or four days. The poulticing may then be discontinued, and the openings in the sole injected with a weak solution of Tuson's spts. hydrarg. perchlor., a 1 in 20 solution of carbolic acid, a solution of copper sulphate, with Villate's solution, or with any other combined antiseptic and astringent.

The success of the treatment is soon seen in the cessation of pain and in the decreased amount of discharge from the opening in the sole.

Should pain unfortunately continue, the discharge remain, and a state of fever reveal itself, then it may be understood that the suppurative process has not been checked, that a portion of necrosed ligament, cartilage, or bone still remains, which, surrounded as it is by pus organisms and putrefactive germs, is sufficient to excite a constant irritation and maintain the internal structures in a state of infection. In other words, we have what is known as a quittor.

This will call for deeper operation. The horn of the wall must be removed, and the diseased structures, whether gangrenous keratogenous membrane, necrosed ligament, or carious bone, carefully excised or curetted. This will be better understood by a reference to the chapter on Quittor, where the means for carrying out the necessary operative measures will be found described in detail.

_Surgical Shoeing for Corn_.--In the case of an ordinary dry corn, where the injury has been definitely ascertained to be accidental, no alteration in the shoeing will be necessary. Where, however, the corn is attended with a more than ordinary degree of inflammation, or where for some reason or other excessive paring has been practised, then it will become needful to shoe with a special shoe. The object to be attained is the removal of pressure from that portion of the wall next to the seat of corn.

The most simple shoe for effecting this is the ordinary three-quarter shoe.

The only way in which this differs from the ordinary shoe is that about an inch and a half of that branch of the shoe adjoining the corn is cut off (Fig. 102). If at the same time contraction of the heels exists, then, perhaps, a better shoe is that known as the three-quarter bar (Fig. 103).

Or, if preferred, a complete bar shoe such as that described for sand-crack may be used, and the upper portion of the web in contact with the foot at the seat of corn thinned out so as to avoid pressure on the wall at this point. With this shoe we shall at the same time supply a certain amount of pressure to the frog, and aid in the healthy development of the part indirectly involved in the disease.

The same pressure may also be given to the frog, and protection afforded the sole, by the use of a leather sole, or rubber pad on leather, as described when dealing with contracted feet.

A further method of relieving pressure on this portion of the wall, without removing the wall itself (a practice which should never be advised) is to make certain alterations in the web of the shoe. This may be done in one of two ways.

[Ill.u.s.tration: FIG. 102.--THREE-QUARTER SHOE.]

[Ill.u.s.tration: FIG. 103.--THREE-QUARTER BAR SHOE.]