(b) De Fay's. - Among other shoes of the expansion class may be mentioned that of De Fay. Like the preceding, it is a shoe with a flat bearing surface, and provided with bar-clips. It is, however, un hinged. The requisite degree of periodic expansion is in this case arrived at by a forcible widening of the heels of the shoe, accomplished by bending the substance of which it is made, and for this purpose the instrument illustrated in Fig. 75 is employed.
The foot is first properly trimmed by levelling the heels and thinning the sole on each side of the frog. The shoe is then fixed by nails in the ordinary manner, taking care that the last nails come not too far back, and that the clips rest evenly and firmly on the inside of the bars.
The dilator, hoof-spreader, or vice, as it is variously called, is then applied, its two jaws (a and b) fitting against the inner edge of the shoe at the heels. Careful note is taken of the width of the hoof as measured on the graduated scale (e, e), and the double screw (g, h) revolved by means of the wrench (k), until the opening of the jaws thus obtained registers an expansion of 1/12 to 1/8 inch.
The dilatation is repeated at intervals of from eight to ten days, until, at the expiration of a month or six weeks, the amount of total expansion of the heels registers nearly an inch. That the method requires the greatest care may be gathered from the reports of continental writers. They state that frequently the pain and consequent lameness keep the patient confined to the stable for several days.
Numerous and but slightly differing forms of the dilator are on the market. As in principle they are all essentially the same, and are to be found illustrated in any reliable instrument catalogue, they need no description here.
Fig. 75. - De Fay's Vice.
(c) Hartmann's. - A further useful expansion shoe is that of Hartmann's (Fig. 76), in that it may be adapted for either unilateral or bilateral contraction. This shoe is also provided with bar-clips, and forcibly expanded at the heels by means of a dilator. The expansion is governed by saw-cuts through the inner margin of the shoe directed towards its outer margin, and running only partially through the inner half of the web (see Fig. 76).
According as the contraction is confined to the inner or outer heel, the saw-cuts, one or two in number, are placed to the inner or outer side of the toe-clip. When the contraction is bilateral, the saw-cuts, one or more in number, are placed on each side of the toe-clip.
(d) Broué's. - This is one of the forms of so-called 'slipper' shoes (see Fig. 77). We have already indicated that the shape of the bearing surface of the ordinary shoe - by its 'seating' or sloping from outside to inside - is sometimes a cause of contraction. In the 'slipper' of Broué this bearing is reversed, and the slope is from inside to outside. In the original form of this shoe the slope to the outside was continued completely round the shoe. Experience taught that the strain this enforced upon the junction of the wall with the sole was injurious, and that the 'reversed seating,' if we may so term it, was best confined to the hinder portions of the shoe's branches.
Fig. 76. This Figure Illustrates The Principle Of The Hartmann Expanding Shoe. A, A, The Clips To Catch The Inside Of The Bars; B, C, Saw-Cuts.
The amount of slope should not be excessive. If it is, too rapid and too forcible an expansion takes place, and pain and severe lameness results. Dollar gives the requisite degree of incline by saying that the outer margin of the bearing surface of the shoe should be from 1/12 to 1/8 inch lower than the inner.
In the case of the Broué slipper, it is the animal's own weight that brings about the widening of the heels, the slope or outward incline of the slipper simply causing the inferior edge of the wall at the heels to spread itself outwards instead of sliding inwards on the bearing surface of the shoe.
Fig. 77. - The Slipper Shoe Of BrouÉ.
(e) Einsiedel's. - Like the 'slipper' of Broué, the Einsiedel shoe depends for its effects upon the slope of the bearing surface.
It differs from the Broué in being provided with a 'bar-clip.' This, in addition to gripping the bars like the bar-clips of other expanding shoes, also assists, under the body-weight, in expanding the heels by the pronounced slope given to its upper surface. The expanding force exerted by the body-weight falls thus, through the medium of the bar-clip, clip, partly upon the bars, instead of, as in the Broué, solely upon the wall. We say partly advisedly, for, in addition to the slope upon the outer side of the bar-clips, the bearing surface of the heels of the shoe is slightly sloped outwards also. The good office served by the bar-clip is the lessening of any tendency to strain upon the white line.
Fig. 78. - The Slipper And Bar-Clip Shoe Of Einsiedel.
Those we have described by no means exhaust the number of expansion shoes that have been devised. There are numerous others, many of which are composed of three-hinged portions, the two hindermost of which are gradually separated by a toothed arrangement of their inner margins and a travelling bar, the disadvantage of which is that it is liable to work loose. In the majority of this class of shoe the hinges are placed far forward, one on each side of the toe. They there become exposed to excessive wear. In fact, against the bulk of this form of shoe it may be urged that they cannot be worn by the animal at work, that they are expensive, difficult to make, and easily put out of order.