Quotation from: Manual of Surgery

Written by: Alexander Miles and Alexis Thomson

_Healing under a Scab._--When a small superficial wound is exposed to
the air, the blood and serum exuded on its surface may dry and form a
hard crust or _scab_, which serves to protect the surface from external
irritation in the same way as would a dry pad of sterilised gauze. Under
this scab the formation of granulation tissue, its transformation into
cicatricial tissue, and the growth of epithelium on the surface, go on
until in the course of time the crust separates, leaving a scar.