46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS about 26 days, when growth ceases, and the follicle remains quiescent until activity is again initiated. Male rats have coarse hair, and their moderately thick skin is covered with flakes of oxidised lipold. The pelage of females is finer, the skin has no lipoid scales, and spontaneous growth waves tend to lag behind those of males. The cycle of growth in each follicle, however, is the same in both sexes. Sex differences disappear after gonadectomy the fur is intermediate in texture between that of males and females, and spontaneous growth resembles that of prmal males. Re-growth after plucking is normal. Daily treatment with estrogen retards the initiation and the rate of both spontaneous and induced hair growth in gonadectomised, adrenalectomised, hypophysectomised, or thyroid hormone deficient animals. These effects become masked by the accelerating effects of adrenalectomy or hypophy- sectomy. Estrogen induces the growth of fine, sparse hair in all animals except those which have been hypophysectomised. Thus, estrogen produces some of its effects on hair growth independent of the adrenal cortex. Daily treatment with androgen has no apparent effect on hair growth except that it promotes a coarse pelage in all except the hypophysectomised rat. During pregnancy and lactation spontaneous replacement of hair is noticeably retarded. Hair growth, however, is transiently accelerated when the young are removed from the mother induced growth by plucking is normal in these animals. These effects are not duplicated when progesterone is given to intact females, but are partially simulated when luteotrophin is administered to females that have been nursing for a few days. Adrenalectomy accelerates the initiation and the spread of spontaneous follicular activity, but has no effect on the rate or growth of the individual follicles induced growth is normal and the pelage is unaffected. Conversely, daily treatment with small doses of cortisone inhibits the spontaneous initia- tion oi hair growth in the intact, gonadectomised, or adrenalectomised rats. Once growth has staried, however, cortisone has no effect. There is no cumulative effect after long periods of treatment with cortisone, and the follicles do not become "refractory" to the hormone. Large doses of cortisone completely inhibit hair growth in intact rats, except in those follicles which had been plucked 4 or 6 days before the administration of the hormone. All hair growth is inhibited when propylthiouracil-treated or hypophysectomised animals are injected together with small doses of cortisone. In all of these cases growth commences as soon a,s the cortisone is discontinued. The precise mechanism by which cortisone affects the hair follicle is not known. Daily treatment with desoxycorticosterone has no effect on hair growth in intact or adrenalectomised rats. Continuous treatment with adrenaline inhibits spontaneous hair growth in intact animals and delays the response to plucking, but once growth has

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