48 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS hair remains infantile in hypophysectomised rats treated with gonadal hornhones, it would appear that sex hormones modify the type of hair produced only if growth hormone is present. Aside from this effect, growth hormone has no obvious influence on hair growth. "REGENERATION, WOUND HEALING AND 'DE NOVO' FORMATION" R. E. BILLINGHAM Dept. of Zoology, University College, University of London, London, t•ngland. The many investigations which have been carried out on the heahng of cutaneous lesions caused by a wide variety of injurious treatments--e.g. the topical application of carcinogens, freezing in situ, X-irradiation, burning or the excision of thin shavings--have provided evidence of the remarkable capacity of hair follicles to regenerate provided that the dermal papillae surviv• and make contact with living epidermal cells again. Once the dermal papillae have been destroyed, regeneration does not normally take place, however faithfully the fine fibrous architecture of the dermis, including the connective tissue follicle "sheaths," may have been preserved. Recent studies on the healing of extensive wounds produced by excision of the full thickness of the skin from the sides of adult rabbits' chests have shown that if the process of wound contracture is arrested artificially, or fails to proceed to completion of its own accord, de novo formation of hair follicles takes place. The wound becomes first filled with granulation tissue which is resurfaced by epithelium that grows in from the margins. Within about 40-50 days this epithelialised scar tissue is transformed into a sort of ad hoc skin by the emergence of a dense crop of new medullated hairs. The new follicles possess well developed sebaceous glands but they lack arrector pili muscles and pigment, despite the fact that all the rabbits used belonged to pigmented breeds. The evidence suggests that these hairs are of com- pletely new formation and have not originated from follicle remnants left behind in the wound bed. Unequivocal evidence that completely new follicles can be formed in adult animals is forthcoming from our knowledge about the antlers of deer. These deciduous organs are shed in mid-winter and regenerated during early spring. They are completely covered by a layer of typical, hair-bearing, cervine skin--the so-called "velvet"--until they are fully grown and have reached maturity. The hairs in the velvet are pigmented and have well- developed sebaceous glands but, like the new hairs which appear in the wounds in rabbits' skin, they lack arrector pilorum muscles. Thus, the deer regenerates each year throughout life, a relatively large area of new skin complete with its complement of hair follicles. In the light of this evidence the rather rigid view of the older authorities that hair follicles can only be formed at birth or thereabouts can no longer be sustained.

ABSTRACTS OF PAPERS ON THE BIOLOGY OF HAIR GROWTH 49 "REGIONAL FREQUENCY DISTRIBUTION OF HAIR FOLLICLES AND SWEAT GLANDS IN THE SKIN OF iV•AN" GEORGE SZABO Dept. of .4 natomy, London Hospital 3/Iedical College, London, England. There is a great individual and regional variation in the frequency dis- tribution of hair follicles and sweat glands in the adult skin. The combined averages for cm • of fixed skin are 980 for the head, 270 for the trunk, 250 for the arm, 190 for the leg. In spite of gross difference there is no significant sexual variation in the distribution of hair follicles in the face. In the foetus the density of the appendages is higher than in the adult the regional variation, however, is smaller and it increases during post-natal development. The differential rate of growth of the body surface is respon- sible for these regional variations in the adult. Initially, the density of dis- tribution of the appendages appear to be similar over the entire body, but later the appendages become spaced farther apart in the trunk and extremi- ties than they are in the head. The relative numbers of hair follicles to sweat ducts, however, vary from region to region even in the foetus, and hairs are relatively more abundant in the head. It is assumed, therefore, that hair follicles do not increase in number after they have been formed in the fcetus, and that their relative numbers appreciably decrease.