ADULT AND CHILDREN'S HAIR Table I Fineness and Ellipticity of Hair of American Whites" 161 Age of Group Average Cross-Sectional Average Number of Area, Hair Index, Subjects Square "Units "b 0-4 24 31} 75 5-9 42 42 10-14 40 } 73 47 15-19 35 56 20-29 55 50 77 30-49 100 51 74 50+ 44 46 76 •From Trotter (5). bThe precise units employed are not clear in the original paper. The computed area is bascd on the microscope scaling device employed. CRatio of minor to major axis. Table II Fineness and Ellipticity of Hair of French Canadians and Americans • French Canadians Americans Age Hair Cross-Sect. of No. of Index, Area, Wt./100 No. of Group Subjects % mm 2 X l0 s cm, mg Subjects Wt./100 cm, mg 0-4 46 73 268 3.4 17 5-9 36 74 341 4.2 37 10-14 45 74 378 4.7 36 15-19 46 73 425 5.4 38 20-29 52 72 422 5.3 55 30+ 75 72 380 4.7 137 2 9 3 9 45 53 46 45 •After Trotter and Dawson (6). Table III Cross Section and Hair Index of Children from B•rth to Youth • Individuals Hair Age Group, Index, years Cross-Sect. Area, mm 2 X lO s 15 I 76 75 16 2-4 7O 237 16 5-9 72 312 11 10+ 73 336 •After Trotter et al. (8, 9).

162 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The relationship of age and cross section is very evident and is shown consistently by all of the subjects. The average hair index is not clearly related to maturation, although there is a suggestion that the hair from the one-year-olds is somewhat rounder. This suggestion is reinforced by the detailed results of Trotter and Duggins (8) giving hair index measurements at one month, seven months, and two years for each of 15 children. In 14 out of 15 cases the two-year indices are lower than either of the younger values, and in 13 of the 15 the seven-month indices are lower than the Table IV Medullation and Scale Index as a Function of Age • Proportion of Medullas of Approximate the Broken or No. of Incidence Continuous Individuals of Medullas, Type b Age Group, Years in Group % % Scale Index • 0-9 70 40 48 0.24 10-19 30 82 89 0.085 20-29 40 55 67 0.10 30-49 37 80 68 0.11 50-99 60 76 65 0.135 •After Wynkoop (4). bFour types are described: absent, fragmentary, broken (large segments), and continuous. The latter two represent more definite and massive medullation. •Ratio of scale length (proximo-distal) to fiber diameter. one-month values. Interestingly, the average hair indices measured on three different racial groups of Australian aborigines (7) show a trend to greater flattening of the hair with increasing age. Medullation and Scaliness o[ the Hair Some data on these aspects of morphology are given in Table IV from data obtained by Wynkoop (4). Medullas are less frequently observed in hair sampled from young people. Even when present in youth, the medullas are more often fragmentary in appearance rather than massive or continuous as in older ages. The scale index measurements also indicate that larger scales relative to fiber diameter are observed in youngsters' hair. A rough calculation suggests that the individual scales are absolutely, as well as relatively, larger in the 0- to 9-year group. Curiously, the author rejects the conclusion that the incidence of medullation increases and that the scale index decreases with age. She believes the correlation is most likely with