708 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (2) Dry, F. W. The coat of the mouse (Mus musculus). J. Genet. 16 287 (1926). (3) Wolbach, S. B. The hair cycle of the mouse and its importance in the study of sequences of experimental carcinogenesis. Ann. N.Y. Acad. Sci. 53 517 (1951). (4) Borum, K. Hair pattern and hair succession in the albino mouse. ActaPathol. Microbiol. Scan& 34 521 (1954). (5) Nay, T. and Fraser, A. S. Growth of the mouse coat. III. Patterns of hair growth. A ustral. J. Biol. Sci. 7 361 (1954). (6) Butcher, E. O. The hair cycles in the albino rat. Anat. tfec. 61 $ (1934). (7) Butcher, E. O. Development of the pilary system and the replacement of hair in mammals. Ann. N.Y. Acad. Sci. 53 508 (1951). (8) Chase, H. B. Growth of hair. Physiol. Rev. 34 113 (1954). (9) Johnson, E. Quantitative studies of hair growth in the albino rat. I. Normal males and females. J. Endocrinol. 16 337 (1958). (10) Chase, H. B. and Eaton, G. J. The growth of hair follicles in waves. Ann. N.Y. Acad. Sci. 83 365 (1959). (11) Bosse, K. Growth and replacement of hair in the guinea-pig. Comparative Physiology and Pathology of the Skin 1õ1 (Blackwell, Oxford) 1965. (12) De Meijere, J. C. H. l•ber die Haare der S•[ugetiere, besonders fiber ihre Anordnung. Morphol Jahrb. •11 312 (1894). (13) Dawson, H. L. A study of hair growth in the guinea-pig (Cavia cobaya). Am. J. Anat. 45 461 (1930). (14) Trotter, M. and Dawson, H. L. The direction of the hair after rotation of skin in the guinea-pig: an experiment on hair slope. Anat. Rec. 50 193 (1931). (15) Strangeways, D. H. The study of the conditions and factors affecting hair growth in the guinea-pig. J. Agr. Sci. •18 359 (1933). (16) Colin, E. C. Hair direction in mammals embryogenesis of hair follicles in the guinea-pig. J. Morphol. 79. 191 (1943). (17) Silberberg, M. and Silberberg, R. Hair growth in the skin of guinea-pigs painted with 20-methylcholanthrene. Arch. Pathol. 44 297 (1947). (18) Wright, S. On the genetics of hair direction in the guinea-pig. III. Interactions between the processes due to the loci R and St. J. Exptl. Zool. 1111 33 (1950). (19) Murray, J. R. Effect of chloral hydrate on growth of hair. Nature 188 984 (1959). (20) Danforth, C. H. Studies on hair with special reference to hypertrichosis. II. The hair of mammals. Arch. Dermatol. Syphilol. 11 637 (1925). (21) Tejima, Y., Okada, Y., Kanno, F., Kikuchi, K. and Isobe, G. Studies on hair cycle in the guinea-pig. Preprint of Scientific Papers (pp. 40-52) 5th Congress of the Inter- national Federation of Societies of Cosmetic Chemists. Tokyo (1968). (22) Pecoraro, V., Astore, I., and Barman, J. M. Cycle of the scalp hair of the new-born child. J. Invest. Dermatol. 411 145 (1964). (23) Priestley, G. C. Rates and duration of hair growth in the albino rat. J. Anat. 100 147 (1966). DISCUSSION DR. K. D. BI•GHA•t: Could you tell me if a particular follicle, having produced one of your fibre types, continues to generate the same type of fibre? Can a type 1 follicle produce a type 2 hair as the animal ages? DR. JAcKson: The evidence available from other species, rather than from the guinea-pig, indicates that type 1 follicles continue to produce type 1 hairs, and similarly type 2 and type 3 follicles. We might add, however, that in human pattern alopecia, there is a gradual regression of the follicle such that it initially produces a long so- called terminal hair, but subsequently consistently shorter and finer hairs. Eventually the follicle produces the very fine and very short type of hair known as yellus hair, which is characteristic of the balding areas. PROF. EB•-t•G: I would like to add one comment, and to ask one question. You are probably familiar with the fact that over most regions of the human body, hair follicles

GUINEA-PIG HAIR FOLLICLE FOR EXPERIMENTAL OBSERVATION 709 occur in groups of three. It is of particular interest that although the periodicity of follicles varies from region to region, follicles within each triad are synchronized with each other. In view of the fact that different types of fibre occur in the guinea-pig, is it possible that there are different types of human hair follicle? DR. JACKSON: I believe that this is quite possible. Perhaps I can best illustrate this by referring to sonhe other work which we have carried out on wonhen of different ages, and in which those with normal heads of hair were compared with those showing sonhe diffuse thinning of their hair on the vertex. The results indicated that in normal women the greatest incidence of hairs are those with a diameter of about 0.08mm. How- ever, during diffuse thinning the diameter decreases, and it seems to produce two differ- ent peaks and thereby possibly reveal two different types of hair, one with a diameter of 0.04 mm and one with a diameter of 0.06mm. Other work carried out on human males has invariably been based on dividing the hairs, more for convenience than anything else, into three groups--thin, intermediate and thick--and we wonder therefore if these results possibly show these three different types in the fenhale. In our case the 0.04mm peak would represent the thinnest hairs, the 0.06mm peak the intermediate hairs, and the 0.08mm peak the thickest hairs present in the scalp. This is perhaps indirect evidence of different types of hair in the scalp. The main difficulty that one encoun- ters in trying to substantiate this, however, is that the duration of follicular activity in the human scalp is of the order of two to three years, compared with 25-40 days in the guinea-pig. Hence it is difficult to find complete human hairs, and make detailed comparisons between them to determine if there are different fibre types. MR. J. M. BLAKEWAY: The duration of the experiment here was only 48 days, which is insufficient, I would imagine, to cover the anagen phase completely. From Fig. 1, the hairs must be 3 or 4cm long. If the hairs grow an average 0.Smm day-1 for 48 days their length will only be about 2.5cm, whereas the type 1 hairs in par- ticular are much longer than that. In other words, the complete growth rate curve presumably goes right back nearly to zero before the hair is finally moulted. DR. JACKSON: Yes, the final length of the type 2 hairs, which we looked at in Fig. 8, is about 15mm, and our experimental observations were only continued long enough to allow the production of complete hairs of this one type. I cannot detect a lower rate of growth than about 0.2 mm day-l, and I suspect that this is the initial rate of growth of this particular type of hair. We have, incidentally, found from other data that the duration of anagen of the type 1 hairs is about 40-44 days when, being a longer and a thicker hair, the rate of growth is also higher. The maximum rate of growth is of the order of 0.7 mm day-•, compared with 0.6 mm day-• for the type 2 hairs. It is of sonhe interest that the final length of the hairs of the guinea-pig and the rat is of the sanhe order, but the way in which the follicles produce the hairs is quite different. In the rat the hairs grow faster, but for a much shorter period of time than the hairs of the guinea-pig. Nevertheless, the hairs produced are of a similar length.