For the formation of new cells in a part there must be a sufficient amount of formative material; then the circulation of the blood becomes more active, more blood being brought to the part by dilatation of the vessels supplying it.
Repair after a loss can be perfect or imperfect.

The tissue lost can be restored so perfectly that no trace of an injury remains; but when the loss has been extensive, and in a tissue of complex structure, complete restoration does not take place and a less perfect tissue is formed which is called a scar.

Examination of the skin in almost anyone will show some such scars which have resulted from wounds.

They are also found in the internal organs of the body as the result of injuries which have healed.

The scar represents a very imperfect repair.