ABSTRACTS OF PAPERS ON THE BIOLOGY OF HAIR GROWTH 45 endocrine stimulation tends to act in a trigger-like fashion. The extent to which these states develop, and even the occurrence of certain sex-selective pathologic states, is regulated chiefly by inheritance and ageing. Studies of twins and members of large familie% supplemented by comparisons of Caucasians and Japanese (including Japanese living in Tokyo, U.S., New York), delineate and emphasise the large measure of coptrol exerted by genetic factors. Endocrine indicators of the quantitative type employed in these studies are thus to be regarded as somewhat analogous to the comb in fowl, reflecting not only the nature and type of the existent endocrine stimulation but also the vitally important responsiveness both of target organs and the organism. The inter-relations of endocrine, hereditary and ageing factors observed in studies of the beard seem relevant to growth of hairs in other regions such as eyebrow, nasal vestibule, external ear, and much of the body with the excep- tions of scalp, axilla, and pubis. The mean age-curves for axillary hair conform more closely than those for beard to the waning of gonadal secretions, as judged by titres of urinary androgens and ketosteroids. Secondary sex characters merge almost indistinguishably x•.ith male- selecting pathologic states like common baldness and the severe forms of ache. There are suggestions that this spectrum may extend to some of the more lethal male-selecting pathologic states and to the shorter duration of life in males than in females in man and other species. It is of considerable interest, therefore, that in some aspects the modes of control of piliary secondary sex characters seem to be analogous, and may provide insight to those of certain sex-selecting pathologic states. "HORMONAL FACTORS' • M•.LV•N P. MOHN Dept. of Anatomy, State University of New York, 450 Clarkson Ave., Brooklyn 3, 2Vew York. Previous investigations on the effects of hormones on hair growth have been limited to observations on the spontaneous replacement of hair. The present studies provide information on the influences of hormones by comparing spontaneous replacement to growth initiated by plucking the hair from resting follicles in gonadectomised, adrenalectomised, hypophy- sectomised, thyroid hormone deficient, diabetic, and intact male and female black rats. The effects of various hormone prepaxations have also been observed in these experimental animals. In the rat, spontaneous growth starts periodically in the belly skin and spreads dorsally as a wave in plucked areas the follicles grow simultaneously. Once a hair follicle becomes active, its cycle of growth is the same r •.gardless of how activity is initiated. In the rat, growth of a hair normally requires

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