or of hair follicles, may spring up in the centre of the raw area.  Such islets may also be due to the accidental transference of loose epithelial cells from the edges.  Even the fluid from a blister, in virtue of the isolated cells of the rete Malpighii which it contains, is capable of starting epithelial growth on a granulating surface.  Hairs and nails may be completely regenerated if a sufficient amount of the 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.

Conversely, it is observed that when articular cartilage is no longer subjected to pressure by an opposing cartilage, it tends to be transformed into fibrous tissue, as may be seen in deformities attended with displacement of articular surfaces, such as hallux valgus and club-foot.

After fractures of costal cartilage or of the cartilages of the larynx the cicatricial tissue may be ultimately replaced by bone.

Tendons.—­When a tendon is divided, for example by subcutaneous tenotomy, the end nearer the muscle fibres is drawn away from the other, leaving a gap which is speedily filled by blood-clot.  In the course of a few days this clot becomes permeated by granulation tissue, the fibroblasts of which are derived from the sheath of the tendon, the surrounding connective tissue, and probably also from the divided ends of the tendon itself.  These fibroblasts