There are several histological factors which have made skin grafting possible in man and animals. First, the comparative ease which epithelium can regenerate is a factor. This new growth of tissue occurs either from the periphery of a wound or it may result from proliferation of the external root sheath of the hair follicles providing the dermis has not been completely destroyed. Another feature of skin is that its constituent cells may be kept alive for several days by means of the tissue fluid from below the graft by the process of osmosis. This affords sufficient time for new vessels to be formed which will then nourish the skin. Also, the ability of the capillaries to proliferate and then anastomose with those of the graft make this feat possible. It is only because of these physiological processes that this type of surgery is successful.