ADULT AND CHILDREN'S HAIR Table V Medullation in Children's Hair • 163 Age Group No. of Hairs No. of Subjects Showing Showing Any Medullas, Medullas, Types of % % Medullas Seen 6 At birth 1-2 mos. 3-5 mos. 6-7 mos. 1.0 17 f Scanty and extremely 0.4 32 fragmented 7.7 31 Scanty-broken 34 73 Broken -continuous 1 yr. 48 Most 2-4 yrs. 25 Most 5-9 yrs. 36 Most 10 q- yrs. 31 Most •Aftcr Duggins and Trotter (9). bSce footnote, Table IV. fiber diameter, but her evidence and argument in the published paper are not persuasive. Hausman (10) also concludes that medullation and scaliness are functions of diameter from a consideration of a large number of animal species, but he did not study age per se Wynkoop was probably a student of Hausman and, thus, was led to the same conclusion. In a later paper, Hausman ( 11 ) briefly notes "a study of 483 specimens of human head hair taken from individuals ranging from 3 hours to 91 years of age" with correlation bei_ng found with diameter of the hair shaft. A good review of the earlier literature and views on hair morphology is given by Noback (12). Duggins and Trotter (9), in following the same group of children referred to earlier, also examined medullation in samples from the same heads. Data compiled from this paper (Table V) show the rapid increase in the incidence of medullation in the first months of life the change in character of the medulla from scanty-fragmentary to broken and continuous is noteworthy. These authors conclude that the presence of medullas is a developmental characteristic related to age. The same authors (13) also examined these children's hair for scaliness by counting the number of scales per unit length in a direction parallel to fiber axis. They found no relationship with age and very high individual and sample variability. A good summary of all of the work with this single group of children is given by these authors (14).

164 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS With the groups of Australian natives mentioned earlier (7), the fre- quency of observed hairs containing medullas rises with age and extends into the older age groups as well. No correlation of scale count with age could be asserted for this group. Fourt (15) interested himself in hair structure in relation to physical properties of human hair. Some of his findings are assembled in Table VI. In the upper portion of this table, the tendency for finer hairs to have a large fraction of their cross section in the cuticle is to be noted in this case the finest hairs come from children. The relationship between coarseness and medulla frequency is also shown, with the fine children's hair being less often medullated. Fourt observes that fibers with high cuticle-to-cortex ratio tend to be finer and rounder. In a second series of measurements (lower half of Table VI), he sorted two lots of adult hair into fine and coarse subgroups. His results indicate that fine hair from a given adult contains proportionately more cuticle, is less frequently medullated, and is rounder than the coarse hair from the same head. These sorting experiments lend support to the view of Wynkoop and Hausman referred to earlier that fineness is the primary correlate rather than age per se nonetheless, vestigial fine hair on an adult head may involve a lack of maturation from the developmental point of view. The actual thickness of the cuticle is slightly larger for the coarse than for the fine hair, but not very much so. Fourt's limited data on fiber mechanical properties show no consistent effect relating to age, size, or morphology. Table VI Fineness, Cuticle Thickness, Medullation, and Ellipticity of Human Hair • Sample Cuticle Area Average Cross- Fraction Minor/ Sect. % of % of of Sample Major Area, Cross Cortex Medullated, Axis, mm 2 X 105 Sect. Area Cuticle Thickness, microns A 610 16.6 .... 66 B 448 18.9 .... 32 C 435 19.0 .... 34 2« yr. girl 325 21.4 .... 16 6mo. boy 136 26.3 .... 4 RMH--Coarse 331 .... 18.7 20 Fine 143 .... 27.2 0 146 --Coarse 568 .... 16.3 91 Fine 210 .... 21.8 16 70.1 91.9 64.7 79.6 2.60 2.42 2.96 2.35 Note: All samples adult hair except where noted. aAfter Fourt (15).