GUINEA-PIG HAIR FOLLICLE FOR EXPERIMENTAL OBSERVATION 707 The evidence of Tejima et al (21), however, suggests that there may be waves of hair growth in the guinea-pig as found in the rat and the mouse. These authors, using a wild strain of guinea-pig, plucked hairs from 30 different dorsal sites and found that the anagen/telogen ratio varied con- siderably. On the other hand Bosse (11) believed there to be only minimal regional differences in adult guinea-pigs of short haired varieties. Of greater significance, however, are the results obtained by Tejima et al (21) when the anagen/telogen ratio was measured once a week in five regions of two guinea-pigs over a period of five months. Obvious peaks of hairs com- mencing anagen were found in each region, and it appeared that the peak shifted with time from the cranial to the caudal region. Consequently it was concluded that a wave of hair growth is propagated from anterior to posterior in the guinea-pig, i.e. along the long axis of the body. Although the pattern of hair growth in man has also been described as a mosaic, relatively recent evidence has suggested that this may not be so, at least in the new born. Pecoraro, Astore and Barman (22) have calculated anagen/telogen ratios of hair taken from the occipital, parietal and frontal regions of 26 full-term children between 3 and 76 h after birth. They found that in any given region there was generally a predominant phase, usually anagen, of the hair cycle. They found that telogen was most abundant in the frontal region and least abundant in the occipital region, whilst catagen occurred most frequently in the parietal region and least frequently in the frontal region. The relative abundance of hairs in catagen led them to conclude that many hairs were synchronously passing through this stage of the hair cycle, and that there was a growth wave passing from the front to the back of the scalp at the time of birth. Our results therefore question the assumption that the guinea-pig, by reason of some supposed mosaic pattern of follicular activity, is necessarily superior to other rodents for the study of hair growth because it is more like the human scalp. They also emphasize, that in any studies of hair growth it is important to know the age of the animals, and to match con- trols of the same age to each experimental animal. It is essential that the hair follicle types are identified in any such study (23), and that when rates of growth are to be compared, they must be based on the whole of the period of anagen, or, if not, on comparable parts of it. (Received: 12th February 1971) REFERENCES (1) Slee, ]. and Carter, H. B. A comparative study of fleece growth in Tasmanian Fine Merino and Wiltshire Horn ewes. J. Agr. Sci. $7 11 (1961).

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