ABSTRACTS OF PAPERS ON THE BIOLOGY OF HAIR GROWTH 47 started it proceeds normally. Prolonged treatment with adrenaline produces a local inhibition of spontaneous or induced growth. Growth waves tend to by-pass the area of injection, and induced growth is locally retarded. The hairs which eventually grow near the sites of injection of adrenaline have no pigment. These effects are neither mediated nor potentiated by thyroid hormone. They are, however, partially linked to adrenocortical activity. Adrenalin inhibits hair growth more in cortisone-treated adrenalectomised rats than in adrenalectomised animals not receiving cortisone the effects are not due to the cortisone. Spontaneous replacement is markedly retarded in alloxan-diabetic animals, but after an initial delay induced growth is normal. Phlorhizin treatment does not appear to affect hair growth despite a continued glycosuria and hypoglycemia. Insulin restores spontaneous replacment to normal in alloxan-diabetic animals and tends to enhance growth in intact animals despite the low level of glucose in the blood. Glucose-treated intact animals, on the other hand, display normal re-growth after plucking whereas spon- taneous growth is often retarded. It seems likely, therefore, that insulin is more directly involved in hair growth than is glucose. Perhaps insulin regulates the utilisation of glucose from the blood during the early stages of growth in the hair follicles. Continued intake of propylthiouracil that produces a deficiency in thyroid hormone inhibits the spontaneous waves of hair growth. Except for an initial delay, however, induced growth is normal in animals deficient in thyroid hormone. Injections of thyroxine accelerate spontaneous replacement of hair in propylthiouracil-treated rats and in normal animals the cycle of growth, however, remains normal regardless of how activity is initiated. Thyroxine and cortisone have antagonistic effects on hair growth, and one hormone can be used to offset the effects of the other. No such relationship is found between thyroxine and gonadal hormones. Hypophysectomy accelerates the initiation and spread of spontaneous follicular activity, but has no effect on the rate of growth. The cycle of growth is normal after plucking, but the pelage is infantile. The adminis- tration of ACTH has an inhibitory effect on hair growth in intact, gonadec- tomised and hypophysectomised rats, but is without effect in adrenalecto- •nised animals. ACTH retards the initiation of growth, but the actual rate of hair proliferation is not affected in either the clipped or plucked follicles. This inhibition of hair growth is obviously mediated through the adrenal cortex. The pituitary seems to exert a restraint on hair growth by means of the adrenal cortex. Hypophysectomy removes this restraint. The influences of growth hormone on the hair follicle are still not com- pletely clear. Implants of pituitary tissue or injections of growth hormone restore the pelage of hypophysectomised rats to an adult texture. Since the

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.