Chapter 17

DISEASES ARISING FROM FAULTY CONFORMATION

A. SAND-CRACK.

_Definition_.--A solution of continuity of the horn of the foot, occurring usually in the wall, and following the direction of the horn fibres.

_Classification_.--It is usual to classify sand-cracks according to--

_(a) Their Position_.--_Toe-crack_ when occurring in the middle line of the horn of the toe, and _quarter-crack_ when occurring in the horn of the quarters.

Sand-crack of the frog and sand-crack of the sole may also each be met with. They are, however, of rare occurrence, and are seldom serious enough to merit special attention.

The toe-crack is met with more often in the hind-foot than in the fore, while the quarter-crack more often than not makes its appearance in the fore-foot, and is there, as a rule, confined to the inner side. The reasons for these positions being so affected we shall deal with when treating of the causes of sand-crack in general. It is interesting to note that the portions of wall known as inside and outside toe are seldom affected.

_(b) Their Length_.--_Complete_ when they extend from the coronary margin of the wall to its wearing edge; _Incomplete_ when not so extensive.

_(c) Their Severity_.--_Simple_ when they occur in the horn only, and do not implicate the sensitive structures beneath; _Complicated_ when deep enough to allow of laceration and subsequent inflammation of the keratogenous membrane. Such complications may vary from a simple inflammation set up by laceration and irritation of the sensitive structures by particles of dirt and grit that have gained entrance through the crack, to other and more serious changes in the shape of the formation of pus, hæmorrhage from the laminal vessels, caries of the os pedis, or the development of a tumour-like growth of horn on the inner surface of the wall known as a keraphyllocele.

_(d) Their Duration_.--_Recent_ when newly formed; _old_ when of long standing.

_(e) Their Starting-point_.--This last distinction we make ourselves, and, referring to cracks of the wall, term them _high_ when commencing from the coronary margin, _low_ when starting from the bearing surface.

_Causes_.--We have already classified sand-crack as a disease arising from faulty conformation. Thus, in just so far as a predisposing build of body may be handed down from parent to offspring, we may regard sand-crack as hereditary. If we do so, however, we must afterwards make up our minds to sharply distinguish between the sand-crack plainly brought about by accidental cause, and that occurring as a result of hereditary evil conformation.

With regard to the latter, we need hardly say that feet with abnormally brittle horn are extremely liable. But with this, as with many other affections of the feet, we shall find it necessary to consider several causes acting in cooperation. In this case, for instance, given the brittle horn, it becomes necessary to further look for exciting causes of its fracture.

We will take conformation first. In the animal with turned-out toes a more than fair share of the body-weight is imposed on the horn of the inner quarter. Here, then, three causes exert their influence together: The horn is brittle; the wall of the inner quarter is thinner than that of the outer; additional weight is imposed upon it. Fracture results.

Take, again, the vice of contracted heels. Here, in the first place, we have a variety of causes tending to bring about the contraction. With the contraction, and its consequent pressure upon the sensitive structures in the region of the quarters and the frog, has arisen a low type of inflammation. The horn of the part has become dry and brittle. The exciting cause of its fracture is found in an excessive day's work upon a hard, dry road, with, perhaps, a suddenly-imposed improper distribution of weight, due to treading upon a loose stone, or a succession of such evil transfers of weight due to travelling upon a road that is rough in its whole extent.

In their turn, too, such defects of the feet as we have mentioned in the last chapter--as, for example, the foot with the pumiced horn, the foot with abnormally upright heels, or that which is upright on one side only, or crooked--each offers a condition which is predisposing to the formation of a sand-crack. In each case it wants but the uneven distribution of the body-weight, which, as a matter of fact, some of these conditions themselves give, to bring about a fracture.

Apart from the predisposition conferred by conformation, must be remembered the simpler predisposing causes leading to brittleness of the hoof. We refer to the after-effects of poulticing, the moving from pasture to stable, the emigration from a damp to a dry climate, or the alternate changes from damp to dry in a temperate region. Each may have a deteriorating influence upon the horn, rendering it liable to the condition we are describing. Excessive dampness alone, especially when the animal is called upon to labour at the drawing of heavy loads upon a rough road, is not infrequently a cause. In this case the wet, together with the constant friction of the sharp materials of which the road is made, serves to destroy the varnish-like periople. The wet gains access to the inner structures of the wall, the agglutination of the horn fibres is weakened, and fissures begin to appear.

Other causes of sand-crack are purely accidental. An animal at fast work over-reaches. The secretion of horn at the injured coronet is interfered with, a diminished supply at an isolated spot being the result. From this point grows down a fissure in the wall.

An injury of the same character may also be sustained in various other ways--treads from other animals when working in pairs, accidental wounding with the stable-fork, blows of any kind, or a self-inflicted tread with the calkin of an opposite foot--each with the same result.

So far as causation is concerned, toe-crack stands in a class almost by itself. It is met with nearly always in a heavy animal in the hind-foot, and is directly attributable to the force exerted in starting a heavy load.

Unskilful shoeing also plays a part in the causation of sand-crack. Removal of the periople by excessive rasping of the wall is most certainly a predisposing cause. Cracks, or their starting-points, may also be caused by using too wide a shoe, or by the use of nails too large in the shank. Also, they may arise from unskilful fitting of the toe-clip, especially in the hind-foot of a heavy animal. It must be admitted, however, that the part shoeing plays in the causation of sand-crack is not a large one; far more depends upon the state of the horn and the animal's conformation than upon the exciting cause.

So far, our observations on the causes of sand-crack have referred to that form occurring in the wall. Sand-crack of the sole or frog we have already said is but seldom met with, and then it is always in connection with some exceptionally deteriorated quality of the horn, as in the case of badly pumiced feet, or occurs as a result of direct injury. Extensive slit-like cuts in this region, when deep enough to lacerate the keratogenous membrane, are sometimes followed by the growth of a fissure in the horn, and what might almost be termed a permanent sand-crack results. Such cuts may be occasioned by sharp flints, broken glass, or other sharp objects picked up on the road, or may result from the animal treading on the toe-clip of a partially cast shoe.

_Symptoms_.--In every case the fissure, or evidence of its commencement, is a diagnostic symptom. It is well to remember, however, that this may be easily overlooked, especially when the crack is one commencing at the coronary margin. The reason is this: Sand-cracks in this position often commence in the wall proper, and not in the periople. They may, in fact, be first observed as a fine separation of the horn fibres immediately beneath the perioplic covering. A crack of this description may even show hæmorrhage, and have been in existence for some time, without the periople itself showing any lesion whatever. Thus, unless lameness is present, or a more than specially keen search is directed to the parts in question, the sand-crack goes undiscovered, until of greater dimensions.

Further, the fissure may be hidden, either accidentally or of set purpose. It may be covered by the hair, filled in and covered over with mud, or intentionally concealed by being 'stopped' with an artificial horn, with wax, or with gutta-percha, or, as is more common, be hidden by the lavish application of a greasy hoof-dressing.

In this latter connection it is well to warn the veterinary surgeon, especially the beginner, when examining for soundness, to be keenly critical before passing an animal who is presented with feet smothered with tar and grease or any other dressing. More especially should this warning be heeded when examining any of the heavier breeds of animal with an abundance of hair about the coronet.

Referring again to the search for the crack, it is well to know that with toe-crack the fissure is the more readily seen when the foot is lifted from the ground. With quarter-crack, on the other hand, the fissure is wider, and consequently the easier detected with the foot bearing weight.

Although commencing in the insidious manner we have described, the lesion is not thus often seen by the veterinary surgeon. Usually, the animal with sand-crack is brought for his inspection when lameness has arisen from it. In this case the cause for the lameness will reveal itself in the crack, which is now too large to escape observation. The coronet is hot and tender to the touch, and a sensation of warmth is sometimes conveyed to the hand by the horn of the surrounding parts of the wall. It is hardly necessary to say that, with accompanying conditions such as these, the sand-crack is a _deep_ one.

Where the lameness is but slight, we may attribute it almost solely to the pain occasioned by the mere wounding of the keratogenous membrane, and to no very extensive inflammatory changes therein. By some authorities this is said to be due to the pinching of the sensitive structures between the edges of the fissure in the horny covering. In our opinion, however, pinching does not occur unless inflammatory exudation into the sensitive structures adjoining the crack has led to sufficient swelling to cause them to protrude. In other words, the movements of the horny box, communicating themselves to the structures beneath, and so occasioning movement in the wounded keratogenous membrane, are quite sufficient to give rise to the lameness without actual pinching of the structures implicated.

The severity of the lameness will vary with the rapidity of the gait, and with the character of the road upon which the animal is made to travel. For instance, many animals in which the lameness is imperceptible at a walk become 'dead' lame at a fast trot. It is sufficiently explained when one remembers the greater movements of expansion and contraction of the posterior parts of the wall brought about by the increase in the rate of progression. The same animal, too, will go distinctly more lame upon a hard than upon a soft surface.

In like manner the lameness from toe-crack also varies in degree with the rate of progression and the character of the travelling, though not to such a noticeable extent as in the lameness from quarter-crack. A greater variation may in this case be brought about by moving the animal on ascending and descending ground. Descending an incline, with a more than ordinary share of the body-weight thus thrown upon the heels, the lameness is most marked. The reason would appear to be that the greater expansion of the wall of the heels thus brought about leads to a proportionate contraction of the wall at the toe, especially at the edges of the crack, thus causing undue pressure upon the exact spot of the wound in the sensitive structures. Ascending--the weight in this case transferred from the posterior to the anterior portion of the foot--the expansion of the heels becomes a contraction, with a corresponding lessening of the contraction at the toe and a distinct decrease in the lameness.

In the case of a deep but recent crack there is always more or less hæmorrhage. This favours risk of infection of the lesion with pus-forming organisms, and so leads to a more or less pronounced lameness, a degree of swelling, heat and tenderness in the coronet above, and a certain amount of surgical fever.

The acute symptoms subdued, but the fissure still remaining, gives us the crack we have classified as 'old.' This may in every case be distinguished from a more recent lesion by the amount of thickening of the overhanging coronet, and the presence of an increased quantity of sub-coronary horn in the region immediately about the crack. The previous inflammatory changes in the adjoining sensitive structures have here led to an increased secretion of horn, and a greater or less deposition of inflammatory connective tissue in the wounded coronary cushion.

Sand-crack of the toe always follows the direction of the horn fibres. That of the quarter, however, may on occasion run a course that is somewhat zigzag, first following the direction of the horn fibres for a short distance, then travelling in a horizontal direction, and finally continuing its course again in a line with the horn fibres, commonly at a point posterior to that at which it commenced.

In a quarter-crack that is old, and when contraction of the heels exists (which in this case it usually does), then will often be found overlapping of the edges of the crack. The expansion of the wall brought about when the body-weight is on the heels, cannot, by reason of the break in it, continue itself anterior to the crack. As a consequence, repeated expansion of the wall posterior to the crack, with the portions anterior to it in a state of enforced quiescence, leads in time to the posterior edge of the crack coming to lie over that of the anterior.

_Complications_.--The first complication likely to arise in a case of sand-crack is that attending simple laceration of the sensitive structures in a _deep_ lesion. With the laceration all the phenomena of a repairing inflammation make their appearance. As a result, there is more or less heat according to the degree of inflammatory hyperæmia, swelling according to the amount of inflammatory exudate, and pain according to the amount of pressure the two foregoing bring to bear on the nerves in the inflamed area.

A second and more serious complication is the greater inflammation set up by the introduction into the crack of foreign substances. Small portions of gravel and flint, both by the irritation set up by their friction and by the infection they carry in with the dirt surrounding them, are responsible for the mischief.

When, from direct communication with the blood-stream, due to extensive hæmorrhage, bacteria from the outside gain entrance, this simple inflammation is further complicated by the formation of pus, or a limited gangrene of the keratogenous membrane.

In cases of great severity the gangrene of the keratogenous membrane spreads until the deeper structures are involved. We then get a necrosis (in the case of toe-crack) of the extensor pedis, and sometimes caries of the os pedis.

In like manner the necrotic changes occurring under these circumstances may invade the deeper structures in the region of quarter-crack. As a result of this, we may have the starting-point of suppurating corn, or necrosis of the lateral cartilage--in other words, cartilaginous quittor.

Commonly accompanying quarter-crack is the condition of contracted heels and atrophied frog. Sometimes described as a complication of sand-crack, it appears to us more rational to rather regard the sand-crack as a result or complication of the vice of contraction.

The overlapping of the edges of the crack before referred to occasionally gives rise to the condition known as false quittor. A probe or a director passed beneath the overhanging ledge of horn reveals sometimes a fissure of 1 inch or considerably more in depth, and quittor is diagnosed. A careful paring away of the overhanging horn, however, reveals the true state of affairs, and exposes to view the original cause of the mischief--a simple fissure in the wall.

A serious complication--one fortunately met with but rarely--is that of keraphyllocele. This is a tumour-like growth of horn, varying in size from the thickness of an ordinary quill pen to that of one's middle finger, growing down from the coronary cushion, and attached to the inner side of the wall of the hoof. With this lameness is always present, and more or less deformity of the hoof results. This condition will be found described at greater length in Chapter IX.

_Prognosis_.--In the case of sand-crack this should always be guarded. It may be taken as a general rule that cracks commencing from the coronary margin are more troublesome to deal with than those originating below. The reason is not far to seek. They here affect the wall just where the bevel in it for the accommodation of the coronary cushion has rendered it weakest. Not only is it weakest, but being more resilient than the portions below it, it suffers more from the alternate movements of expansion and contraction of the foot than does the horn below.

Although in many cases a cure of the existing crack may be easily accomplished, regard should be paid to the possibility of its recurrence, either in the same position or elsewhere. Really, in offering an opinion as to the future usefulness of an animal so affected, a greater attention should be directed to the animal's conformation than to the crack itself. Where the vice of conformation giving rise to it (as, for example, contracted heels or upright hoof) gives hope of being remedied, then naturally it may be safely said that the liability to sand-crack goes with it.

A like favourable prognosis may be given in the case of cracks occasioned by purely accidental causes.

Ordinarily, however, cracks once commenced tend rather to increase than decrease in size and severity. From being superficial and incomplete, they become complete and deep, with every unfavourable circumstance that an increase in size and depth brings with it.

This much, however, may be promised to the owner. A simple crack, even though originating from the coronary margin, is, in the vast majority of cases, curable. Under a rational treatment its increase in size may be prevented, and a sound wall caused to grow down from the coronet.

_Treatment_.--The principles governing the treatment of sand-crack are simple enough in themselves, if not always followed by success.

1. _Preventive_.

This, as a rule, does not suggest itself until a crack of greater or less extent has made its appearance. Then, simultaneously with the treatment proper of the lesion, preventive measures should be adopted, to aid both in the healing of the fissure already present, and to ward off the occurrence of others that might be likely to form. The hoof, if abnormally brittle, should be regularly dressed with a suitable ointment (one containing glycerine for preference), and its horn kept as nearly as possible in a normal condition. When the condition of the horn predisposing to its fracture is brought about by excessive wet, then the appropriate preventive measures to be adopted suggest themselves.

With regard to the lesion itself, we may term 'preventive treatment' all those measures having for their object the prevention of increase in the size of the crack. They are as follows:

_(a) Blistering the Coronet_.--In a simple case, where the crack is superficial and close under the coronary margin of the wall, a sharp cantharides blister to the coronet immediately above it will have the desired effect. An increased secretion of horn is brought about, and by this simple means the crack prevented from becoming longer. Very often this is all that is necessary. In fact, we may say here that, no matter what other treatment is adopted, the simultaneous application of a blister to the coronet is always beneficial. To derive full advantages therefrom, the blistering should be repeated several times at intervals of about a fortnight.

_(b) Clamping the Crack_.--When the services of a skilled smith are at hand, one of the readiest methods of performing this is to draw the edges of the crack together with an ordinary horse-nail.

On each side of the crack a small horizontal furrow is burned or cut into the wall, leaving the horn for about 1/4 inch on each side of the crack intact. This provides a groove for the ends of the clamping-nail to rest in, and brings them flush with the outer surface of the wall. The nail is then driven carefully home through the crack, and the pointed end grasped by the farrier's pincers. The edges of the crack are then drawn tightly together, and the nail firmly clenched.

'The horse-nails are prepared in the ordinary way as for driving, with the exception that each is pointed on the reverse side, to prevent puncturing the sensitive structures. Before being used the nails are put in a vice, and the head hammered to form a shoulder, to prevent their being driven too far into the wall, and breaking out the hold.'[A]

[Footnote A: _Veterinarian_, vol. xlviii., p. 100.]

Before driving the nail some operators burn or bore a hole for it. Opinion seems to differ as to whether this is at all necessary.

A method of clamping which, on account of its simplicity, has become greatly popular, is that of Vachette. For this operation is needed the outfit depicted in Figs. 86 and 87.

With the special firing-iron (Fig. 86) an indentation, sufficiently large to admit the points of the clamp (Fig. 87), is made on each side of the crack. The clamp is then adjusted, and pressed home tight by means of the sand-crack forceps (Fig. 87). According to the length of the crack, one, two, or three clamps may be necessary. Another useful clamp, though far more complicated in its structure, is that of Professor McGill (Fig. 88).

'The object of this invention is to arrange on a spindle, which is screw-threaded at one end with a right-hand thread and at the other with a left-hand thread, two clips or clamps, free to travel on the thread, there being a nut between the two which can be turned by a spanner. The clips are placed on the hoof, one on each side of the sand-crack, the hoof being prepared to receive the instrument by filing a groove or notch for the clamps to fit into, and by turning the nut on the screw the clamps are brought towards each other, and the crack thus prevented from spreading.'[A]

[Footnote A: _Veterinarian_, vol. lxi., p. 141.]

Still a further useful clamp is that of Koster. This is considerably broader than the clamp of Vachette, and its gripping edges are provided with teeth (see Fig. 89).

As with the clamp of Vachette so with this, a groove is burned into the wall on each side of the crack for the accommodation of the jaws of the instrument, and the clamp itself pressed home by means of a special pair of forceps. This form of clamp holds well, and has the advantage of securing a wider area of horn than that of Vachette or McGill.

Clamping by any method should be advised or undertaken only under certain conditions. The horn should be moderately strong, and the wall should be thick. This practically restricts the use of the clamp to cracks of the toe, and it is there, as a fact, they are found of most benefit. While burning the grooves for the clamp, and while tightening the clamp itself, the animal's foot should be on the ground and bearing weight at the heels, thus insuring the greatest possible approximation of the edges of the crack.

With all methods of clamping an untoward result is sometimes the formation of a fresh crack at the point of insertion of the clamps.

(c) _By the Use of Thin Metal Plates_.--These are of use when the horn of the wall is too thin to allow of clamping, and are therefore of especial use in cracks of the quarters. The plates are made so as to cover the greater part of the length of the lesion, and are fastened to the wall by two or more screws on either side of the crack. It is an advantage to slightly let the plate into the wall by means of fitting it hot. In a complicated crack the plate serves the further useful purpose of holding in position antiseptic pledgets, and so keeping the lesion free from dirt and grit.

_(d) By Various Methods of bandaging the whole Circumference of the Wall_.--In our opinion this method of attempting to secure immobility of the crack, and so prevent its extension, is not often followed by success. The main objection to the method is that it subjects the whole of the wall to the same pressure, and does not restrict the operation to the point at which it is required. As in the case of the metal plate, however, this method has the advantage that antiseptic dressings may be kept in position in the case of a complicated crack.

The binding of the wall may be accomplished in two ways. The simpler of the two is to merely apply the sand-crack belt depicted in Fig. 90. Beneath this should be applied a compress of tar and tow or other material, and the whole tightened up and kept in position by means of the buckle and strap. This method of binding admits of after-tightening should it unfortunately work loose.

The older method of binding the wall, and one now often practised by the smith, is to use a quantity of so-called 'tar-band' or other stout cord. With this the foot is neatly bound after the manner of a cricket-bat handle, and all movement of the crack apparently restricted. There is always a tendency, however, for such a dressing to work loose, and in the case of a complicated crack it has the disadvantage of permanently hiding from view the changes taking place in the discharge from the fissure.

_(e) By wedging the Crack_.--This is the exact opposite of clamping. Whereas in clamping we obtain immobility of the crack by keeping it fixed in the position of greatest approximation of its edges, in wedging, the crack is rendered free from movement by maintaining it in that position where its edges are most widely separated. In this case the edges of the crack are pared smooth, the cavity thoroughly cleansed, and a wedge of hard wood firmly driven in so as to fit exactly the fissure.

On the face of it it appears that this procedure would really tend to force open and so lengthen the crack, especially at its coronary extremity. What one should really remember, however, is that the crack _is not made wider_ than before, but that it is simply maintained in a position occurring with every contraction of the heels of the foot, when it is normally at its widest. Movement of the edges is thereby stopped, the immediately surrounding structures are rested, and a new growth of horn, free from crack, induced to grow down from the coronet.

This method of treatment only serves to emphasize the fact that, with a sand-crack once formed, it is the constant movement of the parts that tends most to keep it in existence, and not any particularly marked exertion of force.

Some practitioners, with the wedge, apply also a clamp, thus assuring additional firmness and solidity to that portion of the wall under treatment.

The method of wedging is undoubtedly successful, if neatly performed.

_(f) By Surgical Shoeing_.--A partial rest is given to the affected parts by easing the bearing of the shoe at the point required. This may be done either by removal of part of the wall at the spot indicated, or by thinning the web of the shoe in the same position. The former is the method usually practised. Cessation of movement given in this way is, as we have already said, only partial; for, while the effects of pressure and concussion from below are minimized, the crack is still able to suffer from the movements of expansion and contraction of the foot. Still, as an auxiliary to other treatments, 'easing' of the wall under the affected part should always be practised.

Figs. 91 and 92 show respectively the manner of 'easing' by removal of the wall, and by thinning the web of the shoe. In this connection it is necessary to point out that on no account should 'springing' of the heels of the shoe be allowed. Fig. 93 illustrates the ill-practice.

In this case, when the entire weight is thrown on to the heels, the portion of wall posterior to the crack is bound to participate unduly in the downward movement, and so tend to widening of the crack at its highest point.

We have already referred to the matter of 'clips.' In no case, whether the crack be at the toe or in the quarters, should a clip be placed immediately below it. If the crack is at the toe, the usual clip should be dispensed with, and a clip at each side made to take its place. At the same time care should be taken to avoid throwing the weight far forward. For that reason a shoe with calkins or with very high heels should be removed, and a shoe with an ordinary flat web substituted.

In the case of quarter-crack, where the constant movement of the parts under expansion and contraction of the foot makes itself most felt, it is wise to apply a shoe with clips fitting moderately tight against the inside of the bars. By this means movement will to a very large extent be curtailed.

Where a marked tendency to contraction is found, as is often the case with quarter-crack, then the shoe with the clips may be rendered more marked in its operation by giving to the outer face of each clip--that face applied to the bar--a slope from above downwards and outwards. In other words, a slipper shoe should be applied and the contraction given equally as much attention as the sand-crack itself.

Where the crack is situated far back in the quarter, and easing of the bearing cannot be accomplished without tending to spring the heels, then the most suitable shoe is a bar shoe. With it the bearing may, of course, be eased in exactly the position required, and the heels still allowed to take their fair share in bearing the body-weight, and thus assist in closing the crack. The bar shoe, if properly fitted, gives us also a bearing on the frog, and aids greatly in counteracting contraction.

2. _Curative_.

_(a) The Application of Dressings to the Lesion_.--In the case of a recent crack, deep, and attended with hæmorrhage, the foot should be thoroughly cleansed. Where possible, a constant flow of cold water from a hose-pipe should be allowed to run over the foot. By this means the inflammatory symptoms will be held in check and pain prevented. Later the shoe may be eased at the required place, and a blister applied to the coronet. This, with rest, will sometimes prove all that is needed.

Should a crack be of old standing, and complicated by the presence of pus, a course of hot poulticing will often prove of benefit. The poultice should be medicated with any reliable disinfectant, and should be renewed, or at any rate reheated, two or three times daily. The crack itself should be thoroughly cleaned after the removal of each poultice, and a concentrated antiseptic solution--such as Tuson's spts. hydrarg. perchlor., carbolic acid, and water, (1 in 10) or liquor zinci chlor.--poured into it. On discontinuing the poulticing, the strength of the antiseptic solutions may be decreased, the parts rested by correct shoeing, and a blister applied to the coronet as before.

If these measures alone should prove insufficient, then the surgeon will either fall back on those we have just related, or proceed to methods next to be described.

_(b) Immobilizing the Crack by Means of grooving the Wall_.--To our minds, this is as ready and withal as successful a method of dealing with sand-crack as has yet been devised. It may be done in a variety of ways: (1) By two grooves arranged about the crack in the form of a V, as Fig. 94; (2) by a perpendicular groove on either side of the crack, about 1 inch in distance from it, and parallel with the horn fibres, as Fig. 95; (3) by a single horizontal groove at the extreme upper limit of the crack; (4) by drawing two horizontal grooves, one at its upper and one at its lower end (see Fig. 96).

The points to be observed in carrying out this line of treatment are simple enough. In all cases see that the crack is rendered as clean as possible by the use of suitable dressings, and if an excess of horn is present immediately around it, as in the case of a long-standing and complicated lesion, have it thinned down by rasping.

All that is then needed is one or two moderately sharp, flat firing-irons. The groove is then burned into the horn in the positions indicated, and that portion of the wall containing the sand-crack thus prevented from participating in the movements of the foot. For our own part, we consider the V-shaped incision, or either of the horizontal methods of grooving, preferable to lines running in the direction of the horn fibres. With the latter there is certainly a greater tendency to the formation of new cracks than with either of those we advocate. The V-shaped incision we consider most suitable of all, for the reason that by its means a greater degree of immobility is conferred upon the necessary portion of the wall.

Whichever method is adopted, care should be taken to carry the grooves deep enough into the horn, taking them down as near as possible to the sensitive structures. At the same time, especial care should be exercised in not carrying them too deep at their extreme upper limit, or in that case the liability to the formation of fresh cracks in those positions will be greatly increased.

After grooving, a sharp blister should be applied to the coronet every three or four weeks, and the animal, if free from lameness, put to work.

_(c) By stripping away a V-shaped Portion of the Wall around the Crack_.--This method is only indicated when the crack is greatly complicated by the presence of pus, or by the growth of adventitious horn on the inner surface of the wall. A radical cure is thus obtained, but the animal for a longer time incapacitated from work.

The operation is best performed by first grooving a line to connect the points _a_ and _c_ (Fig. 97). This should run immediately under the coronary margin of the wall, and should stop short of injuring the coronary cushion beneath. Grooves forming the sides _ab_ and _bc_ of the triangular piece of horn are next made, and the horn contained within the lines _ab, bc_, and _ca_, carefully removed. The grooves are the easiest made by a cautious use of the firing-iron. The greater thickness of the horn may thus be penetrated, and the grooves afterwards carried to their full and requisite depth by the use of the drawing-knife.

With the removal of the horn the diseased structures are exposed to view. All such should be removed by a free use of the scalpel, and a suitable dressing afterwards applied. A necessary factor in the treatment is the employment of pledgets of antiseptic tow. With these the exposed tissues are covered, and the successive turns of a bandage run tightly over them, so as to exert a moderate degree of pressure. When hæmorrhage has accompanied the operation, this dressing should be removed on the following day, the wound dressed, and the pledgets of tow and the bandage renewed. Any after-dressing need only then be practised at intervals of a week. Repair after this operation is rapid, and takes place both from the exposed podophyllus membrane and from the coronary cushion.

_(d) By stripping the Wall from the Coronary Margin to its wearing Edge on Either Side of the Crack_.--This is merely a more extensive application of the method just described, and is only indicated in a _complete_ and _complicated_ crack that has refused to yield to other modes of treatment (see Fig. 98).

As in the previous case, a groove is run from _a_ to _c_. The grooves _ab_ and _de_ are then continued to the lowermost edge of the wall, and the whole of the wall within these points removed. To facilitate removal, the white line should be grooved between the points _b_ and _d_. After-treatment is exactly the same as that just referred to.

B. CORNS.

_Definition_.--In veterinary surgery the term 'corn' is used to indicate the changes following upon a bruise to that portion of the sensitive sole between the wall and the bar. Usually they occur in the fore-feet, and are there found more often in the inner than in the outer heel.

The changes are those depending upon the amount of hæmorrhage and the accompanying inflammatory phenomena occasioned by the injury.

Thus, with the hæmorrhage we get ecchymosis, and consequent red staining of the surrounding structures. As is the case with extravasations of blood elsewhere, the hæmoglobin of the escaped corpuscles later undergoes a series of changes, giving rise to a succession of brown, blue, greenish and yellowish coloration.

With the inflammation thereby set up we get swelling of the surrounding bloodvessels, pain from the compression of the swollen structures within the non-yielding hoof, and moistness as a result of the inflammatory exudate.

In a severe case the inflammation is complicated by the presence of pus.

_Classification_.--Putting on one side the classification of Lafosse _(natural_ and _accidental_), as perhaps wanting in correctness, seeing that all are accidental, and disregarding the suggested divisions of Zundel _(corn_ of the _sole_ and _corn_ of the _wall_) as serving no practical use, we believe, with Girard, that it is better to classify corns according to the changes just described.

Following his system, we shall recognise three forms: (1) _Dry_, (2) _moist_, (3) _suppurating_.

The _dry_ corn is one in which the injury has fortunately been unattended with excessive inflammatory changes, and where nothing but the coloration imparted to the horn by the extravasated blood remains to indicate what has happened.

The _moist_ corn is that in which a great amount of inflammatory exudate is the most prominent symptom. It indicates an injury of comparatively recent infliction.

The _suppurating_ corn, as the name indicates, is a corn in which the inflammatory changes are complicated by the presence of pus.

_Causes_.--The causes of corns we may consider under two headings--namely, _predisposing_ and _exciting_.

_Predisposing Causes_.--By the heading of this chapter we have already intimated that corns are due to faulty conformation of the foot. It is, therefore, merely a description of such shapes of foot as favour their formation that will need mention here.

The wide, flat foot, with low heels, may be first considered. Here the posterior portions of the sole, those portions between the wall and the bars, fall very largely in the same plane as the wearing surface of the bars and the wall. As a consequence, these portions of the sole are more prone to receive injury from stones and rough roads and from the pressure of the shoe.

The low heels, too, favour a more than due proportion of the body-weight being thrown on to the posterior parts of the foot. Two evils, both inclining to the production of corn, result from this. In the first place, the sensitive structures of the posterior portions of the foot are subjected to undue pressure from above; secondly, the posterior half of the foot, by reason of the extra weight thrown upon it, is exposed also to greater effects of concussion than normally it should meet. Added to this we find that the abnormally flat condition of the sole has resulted in a great loss of resiliency. With undue pressure above, and a loss of resiliency and added effects of concussion below, the sensitive structures included between the opposing pedal-bone and the horny sole are bound to suffer more or less bruising each time the foot comes to the ground, especially if the animal is moved at a rapid pace.

Writing here of the effects of pressure and concussion affords a fitting occasion to mention the fact that corns occurring in feet affected with side-bones are always worse than in feet with normal elastic cartilages. The explanation of this is simple, for there can be no doubt that the loss of resiliency in the diseased cartilage is only another aid to undue pressure and concussion. The sensitive structures are pinched between unyielding bone above and practically unyielding horn below.

Feet with high and contracted heels are also predisposed to corn. The contraction in this case interferes with the downward movements of the os pedis during progression, while in a state of rest there is a more or less constant pressure upon the sensitive structures, due to the correct downward displacement of the pedal-bone being opposed by the amount of contraction present. In the contracted foot, too, the nutrition of the vessels supplying the secretory apparatus of the horn is largely interfered with. The horn loses its natural elasticity, fails to respond to the normal movements of the parts within, and aids in the compression and laceration of the sensitive structures.

Weak feet, with horn too thin to withstand the expansive movements continually going on--in other words, feet with weak, spreading heels--are also prone to suffer from corns. In this case the flatness induced by the spreading, and the insufficient protection afforded by the thin horn, both combine to lay the sole open to the effects of concussion and direct injury.

Brittle feet--feet with horn of undue dryness, by reason of the contraction thus brought about--are, again, particularly subject to corn.

So also with long feet. Whether occurring as a natural deformity, or as the result of insufficient paring, bruises of the sole in feet thus shaped are common. The reason for this will be better understood when we come to deal with the shoeing.

Other and minor predisposing causes are those mainly referring to an unnatural dryness of the hoof when animals reared in the country are put to work in large towns. We here really get several predisposing causes combining. A sudden change is made from a more or less moist condition underfoot to one excessively dry. The character of the travelling is wholly altered from occasional work upon soft lands to continual labour upon hard-paved roads. The horn is often exposed to the vicious influences of unsuitable litter, the application of unsuitable dressings, and the deleterious effects of the street mud of our cities. All these play their part in determining a condition of the horn, rendering it open to receive the effects of the more exciting causes which we shall next consider.

_Exciting Causes_.--Than the shoeing, no more frequent and exciting cause of corn exists. Whatever the predisposing influences may be, it is the shoeing that in nearly every case completes the list, and finally inflicts the injury.

The evils in this connection we shall consider under two headings--viz., (1) the manner in which the foot is pared; (2) the make and fitting of the shoe.

First among the faulty preparations of the foot comes that of excessive thinning of the sole, especially in the regions subject to corn. The farrier addicted to this is not as a rule content to confine his operations to the sole alone. In addition, the frog and the bars also suffer from the too lavish use of his knife. His main object is doubtless that of giving a broad and open appearance to the foot. It follows from this that his operations are confined more to the posterior than the anterior parts of the foot, and that the toe is therefore left too long. This gives us a combination of causes leading to pressure and bruises upon the sensitive structures at the seat of corn.

By this unequal paring of the toe and the heels greater weight is thrown upon the posterior half of the foot. What then happens to the structures thinned as we have described is this: the pared frog, lessened in volume, does not meet the ground. It therefore fails to expand laterally with weight, and cannot assist, as normally it should, in aiding the heels generally in their movements of expansion. The weakened bars and the thinned sole, meeting with no opposition from the frog, give downwards and inwards with the body-weight at the precise moment these movements should be directed mainly outwards. As a further result of non-resistance on the part of the frog, this time in a lateral direction, the bars, the sole, and the wall at the heels all contract at the exact time they should expand. The end result must mean abnormal pressure and bruising of the sensitive structures in that particular region. Naturally, also, the excessive thinning of the horn renders direct injury to the sole from stones or other objects in the road far more probable.

For this one reason alone--the manner in which it favours the production of corn--too great a condemnation cannot be placed upon excessive paring of the sole, the bars, and the frog.

When corns are already present, as they may be from other causes, the same remarks will again apply to excessive paring. It is the custom with many smiths to carefully pare down the discoloured horn in every case of corn they meet with, and at the same time to again weaken the bars and even part of the wall at the heels, with the laudable idea of relieving pressure on the part diseased. After what has gone before, we need hardly say that their well-meant efforts have a precisely opposite effect to the one they intend.

The fitting of the shoe is, perhaps, to a greater extent responsible for the causation of corn than is the paring we have just described.

A few of the evils connected with the shoe may, however, be justly described as unavoidable. We _must_ shoe; we cannot shoe and leave a normal foot!

A shoe excessively seated, especially from the last nail-hole backwards, may be regarded as dangerous. In this case, with every application of the body-weight, there is given to the foot a tendency to contract, especially at its lower margin. Result: undue pressure upon the tissues around and the production of corn.

On the other hand, varying with the form of foot, the seating may be insufficient. In the case of flat-foot, or dropped sole, for instance, insufficient seating will lead to undue pressure of the web of the shoe upon the sole, and in that way bring about bruising of the sensitive sole beneath.

Shoes with heels or calks too high, by destroying the counter-pressure of the frog with the ground, serve to bring about a series of changes we have described under contraction, and again result in pinching and bruising of the sensitive structures.

The opposite excess--a shoe thick at the toe and thin at the heels--is blamed by Zundel for causing a like injury. In our opinion, the reason this author gives--namely, that the throwing of greater weight upon the heels leads to bruising of the sensitive structures--can only correctly apply to a _wrongly-applied_ shoe of this type, and not to the shoe itself. True, a shoe with a thick toe and thinned heels will throw an undue proportion of the body-weight upon the heels if the foot is not properly prepared for it. A wise man, however, will most certainly so cut down the toe for the reception of this shoe that, with the shoe in position, there will still be maintained a tread that is normal. To our minds harm is far more likely to arise from a shoe of this class through the thinned iron heels of the shoe becoming attenuated under wear to the point of bending, and so inflicting an injury upon the adjoining sole.

Similarly, this last remark with regard to the thinning of the heels of the shoe will apply to a shoe with too broad a web. As the thinning of the shoe proceeds with wear, the inner portion of the thinned branch is bent up on to the sole, and again inflicts the injury.

The matter of bearing is also of importance when considering the causation of corn. In a previous chapter we have already described the correct bearing as that which includes the whole of the lower margin of the wall and the white line, and just impinges on the sole. Any marked deviation from that will, if long continued, be followed by injury to the foot.

With the bearing surface of the shoe too narrow--in contact with the wall solely, or perhaps only a portion of it--it is evident that a large proportion of the foot that should properly bear weight is thrown out of action. A heavy strain is imposed on the white line, and undue descent of the sole and contraction of the heels brought about. Again the result of this is compression and bruising of the tissues around the seat of corn.

With its bearing surface too wide, the shoe immediately exerts direct pressure upon the sole with every movement of the animal. The sole normally is not made to receive this, and harm is bound to result.

Among other ill-fitting shoes we may mention the one with branches too short, and the one with the extremities of the branches too pointed. In the first case, as wear of the shoe proceeds, the thinned end is far more likely to turn in under the seat of corn than is a shoe with branches of ordinarily correct length. It is evident in the second case that the pointed branch, when thinned, is a more dangerous agent than the branch which is nearer the square at its end.

The matter contained in the first half of the foregoing paragraph explains in a large measure the rarity of corns in the hind-feet. Here there is nothing to prevent a shoe with branches of full length being used. The correct bearing is thus maintained, even with a shoe excessively thinned with wear, and the liability to injury from it decreased. An exception is to be found in the case of a feather-edged shoe, such as is used to prevent cutting or brushing. The thinning by wear from above to below of the branch already purposely thinned from side to side leads to the formation of a thin and narrow piece of iron admirably calculated to bend over and injure the sole.

Even with a shoe of correct length, with a flat-bearing surface at the heels, and other conditions favourable to correct application, evil may still result from the shoe itself being made too narrow. As a result of this, the branch of _each_ side is set too far under the foot, with consequent injury to the sole. This is, of course, sheer carelessness on the part of the smith. When practised, however, it is not easy of detection, as in all cases the foot is rasped down to cover what has been done. In other words, the foot is made to fit the shoe and not the shoe the foot.

Recognising this close fitting of the shoe as a cause, we are able to explain in some measure how it is that corns should occur with greater frequency in the inner than in the outer heel. There is no doubt that the inner branch of the shoe is nearly always fitted closer than is the outer. In the fore-foot it is also often shorter. Take these two evils and add to them the fact that the inner heel is called upon to bear more of the body-weight than is the outer, and the frequency of corns in the inner heel will no longer be wondered at.

Indirectly, the shoe may still be a cause of corn by reason of the irritation set up by gravel and small pieces of flint becoming firmly fixed between the sole and the web of the shoe. In nearly every case of this description the part to be injured is the white line.

Corns may also result from the animal picking up a stone. The stone becomes firmly wedged in between the inner border of the branch of the shoe and the bar or the frog. With every step the animal takes it becomes wedged more tightly into position. Projecting below the level of the lower surface of the shoe, it imparts the concussion it thus obtains directly to the sole. A bruise--and a bad bruise--is the result.

Finally, it cannot be denied that the work the horse is put to is largely responsible for the causation of corn. In country animals corns are comparatively rare, while in animals in town, almost constantly upon hard paving, they are common. This seems to point strongly to the fact that concussion through constant work upon unyielding roads is a great factor in their production.

_Symptoms_.--Unless the discoloration of the horn is accidentally discovered by the smith, the simple, dry corn may go undetected. The disturbance excited by it is so small, and the pain occasioned so slight, that the patient may offer no indication of its existence.

Ordinarily, however, the first symptom is that of pain. The animal goes feelingly with one or both feet, in some cases even showing decided lameness. The lameness, however, is in no way diagnostic, and the lesion itself must be discovered before an exact opinion can be pronounced.

As an aside, it is well to observe in this connection that a negative opinion as to the existence of corn should never be given unless the superficial layers of horn have first been removed with the knife.

When standing at rest the animal exhibits signs more or less common to all foot lamenesses. He 'points' the foot--in other words, the limb is slightly advanced, the fetlock partly flexed, and the heels from off the ground. When both feet are affected they are pointed alternately, and the animal often manifests his uneasiness by repeated pawing movements, and by scraping his bedding behind him.

Should the injury run on to suppuration, the lameness becomes most acute. The pawing movements become more pronounced, and there is evident disinclination on the part of the animal to place the foot squarely on the ground. One is then led to manipulate the foot. The hoof is hot to the touch. Percussion causes the animal to flinch, and to flinch particularly when that portion of the wall adjoining the corn is struck. Finally, exploration with the knife reveals the serious extent to which the injury has developed. In a neglected case of this description it is even possible to detect the presence of pus by the amount of swelling and fluctuating condition of the coronet. The suppurative process has advanced in the direction of least resistance, and is on the point of breaking through the tissues immediately above the horn.

Lameness due to corn is oftentimes intermittent. With a simple corn, dry or moist, this intermission is largely dependent on the degree of dryness of the hoof or the road, and also on the character of the road surface. With a neglected, suppurating corn, on the other hand, variation in the degree of lameness, in addition to depending on circumstances such as these, is dependent to a larger extent upon the changes occurring with the suppuration. In this case the time of greatest lameness is immediately before the pus gains outlet. Immediately after its exit at the coronet the animal will go almost sound. Soundness continues so long as the opening at the coronet remains clear. The tendency, however, is for the opening thus made to quickly close again. Pus again accumulates, lameness arises as before, and disappears again with the second discharge of the contents of the sinus now formed.

_Pathological Anatomy_.--When dealing with their classification we gave in outline the main pathological changes to be met with in corns. It now only remains to give the same matter in slightly greater detail.

_In dry corn_ the changes we meet with are those accompanying blood extravasation. From excessive compression of the parts, or from the effects of direct injury, a portion of the sensitive sole has become lacerated. The escaping blood stains the surrounding soft tissues after the manner of blood extravasation elsewhere. If the escape of blood is sufficiently large, the horn fibres in the immediate vicinity also are stained. It is this stain in the horn that is the direct evidence of the injury, and is itself popularly known as the corn. It may vary in size from quite a small spot to a broad patch as large as half a crown, while its colour may be a uniform red, or a mottled red and white. The microscopic changes in this connection are illustrated in Fig. 99.

Ordinarily, this ecchymosis of the horny sole is due to injury of the sensitive sole _immediately beneath_ it. It may, however, proceed from injury to the vessels of the laminæ either of the bars or of the wall. In this case the ecchymosis of the horny sole may be explained by the fact that the escaped blood tends to _gravitate_ to that position.

When the corn is of long standing, or is due to _repeated_ injuries on the same spot, the horn adjacent to the lesion becomes hard and dry, and often abnormally brittle, simply on account of the inflammatory changes thus kept in continuation. This is often seen when attempts are made to _pare out_ the corn with the knife.

Should the injury be seated in the sensitive laminæ, 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.

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 laminæ. As a result, the regularly leaf-like arrangement of the horny laminæ has been largely broken up. Certain of the laminæ 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 horny and sensitive laminæ.

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 horny sole we are able to deduce evidence relative to the duration and nature of the injury.

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 horny 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 laminæ 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 laminæ of the wall, in which case, if a dependent orifice is quickly made at the sole, the injury to the laminæ 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 assured 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 succumbs 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 assist 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.

In the first, that portion of the bearing surface of the heel of the shoe is 'dropped' about 1/8 inch from the plane of the remainder, so that the shoe at this position does not come into contact with the foot at all (see Fig. 104).

In the second case the shoe is what is termed 'set' at the heel. Here it is the plane of the _wearing_ surface of the shoe that is altered. The hinder portion of the required heel is thinned so that its lower surface does not come into contact with the ground. By this means the wall is freed from concussion and pressure. At the same time the upper surface of the shoe is in contact with the wall of the foot (see Fig. 105).

This 'setting' of the shoe is preferable to the method first described. It affords a greater protection to the foot, and does not allow of fragments of stone and flint getting in between the foot and the shoe, and so giving rise to further mischief.

The 'set' portion should be fitted full and long. It is obvious, too, that the animal should not be allowed to carry the shoe too long; otherwise, as the other portion of the shoe wears down to the level of the 'set' heel, pressure on the tender part of the foot will again result.

In applying surgical shoes for corn of long standing, it must be remembered that the protection so afforded must be continued for some time. It is not sufficient to see the lesion itself disappear. In addition to that there is also, in the majority of cases, a certain amount of contraction to be overcome. This can only be done by continuing the use of a leather sole or some form of frog or bar-pad as recommended for the relief of that condition.

C. CHRONIC BRUISED SOLE.

A similar condition to that of corn may be met with in other positions on the sole. It is described by Rogerson as sand-crack of the sole[A], and is invariably met with around that portion of the sole in contact with the shoe.

[Footnote A: _Veterinarian_, vol. lxiii., p. 51.]

The animal is lame, and the shoe is removed in order to ascertain the cause. Nothing at first is noticeable except that the animal flinches when pressure is applied to the spot with the pincers, or the sole is tapped with the hammer.

On removing the sole with the knife, however, a distinct black mark is discovered, which, when followed up by careful paring, is often found to have pus at the bottom.

In this case the injury has resulted, as we have already intimated elsewhere, from causing the animal to wear for too long a time a shoe with too broad a web or insufficiently seated. Or it may have originated with the irritation set up by foreign and hard substances between the web of the shoe and the foot.

In his description of this condition Mr. Rogerson draws attention to the fact that the pus found should not be wrongly attributed to accidental pricking of the foot. He says:

'Considering that the cracks or splits are always found in the immediate vicinity of the nail-holes, a certain amount of discretionary skill is required in order that the lameness may be attributed to its proper cause. This is an instance in which the presence of the veterinary surgeon is imperative, in order to prevent undue blame being attached to the shoeing-smith. Misconception in these cases might very easily arise when parties concerned are disposed to accept an unskilled opinion, sometimes resulting in danger to the proprietor of the forge, not only of losing a shoeing contract, but also of being involved in other ways which would probably prove even more disastrous.

'Horses that stand on sawdust or moss litter are sometimes found with extensive discoloration of the horny sole in front of the frog. Their bedding material collects in the shoe as snow does, and forms a mass, which keeps a continued and uneven pressure upon the sole. A sound foot is not injuriously affected, but a very thin sole is, and so also is a sole which has been bruised by a picked up stone. Even a slight bruise becomes serious if pressure is allowed to remain active over the injured part. Lameness increases, serous fluid is effused between the horn and sensitive part, or even hæmorrhage may take place.'[A]

[Footnote A: Hunting, _Veterinary Record_, vol. xiv., p. 593.]

_The Treatment of Chronic Bruised Sole_ offers no special difficulty. Removal of the cause (in nearly every case incorrect bearing of the shoe) is the first consideration. That done, the lesion may be searched for and treated in the ordinary manner as described for corn. When pus is present it must, of course, be given exit, and an antiseptic solution applied to the wound. Should the sensitive structures be laid bare when allowing the pus to escape, then the wound so made should afterwards be protected with a leather sole and antiseptic stopping.