hair follicles or of the nail matrix has escaped destruction. The
epithelium of a mucous membrane is regenerated in the same way as that
on a cutaneous surface.

Epithelial cells have the power of living for some time after being
separated from their normal surroundings, and of growing again when once
more placed in favourable circumstances. On this fact the practice of
skin grafting is based (p. 11).

_Cartilage._--When an articular cartilage is divided by incision or by
being implicated in a fracture involving the articular end of a bone, it
is repaired by ordinary cicatricial fibrous tissue derived from the
proliferating cells of the perichondrium. Cartilage being a non-vascular
tissue, the reparative process goes on slowly, and it may be many weeks
before it is complete.

It is possible for a metaplastic transformation of connective-tissue
cells into cartilage cells to take place, the characteristic hyaline
matrix being secreted by the new cells. This is sometimes observed as an
intermediary stage in the healing of fractures, especially in young
bones. It may also take place in the regeneration of lost portions of
cartilage, provided the new tissue is so situated as to constitute part
of a joint and to be subjected to pressure by an opposing cartilaginous
surface. This is illustrated by what takes place after excision of
joints where it is desired to restore the function of the articulation.
By carrying out movements between the constituent parts, the fibrous
tissue covering the ends of the bones becomes moulded into shape, its
cells take on the characters of cartilage cells, and, forming a matrix,
so develop a new cartilage.