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.