HAIR CUTICLE 841 of layers and the dimensions of these cells are identical in fine and coarse hairs (Figs. 2 and 3), the fraction of the cuticular material varies with the diameter of the fiber it may, in fine hairs, account for as much as 40% of the total weight of the hair. The protective function of the cuticle has often been stressed. In- deed, in the case of human hair, nature, ahnost as if predicting sonhe cos- metic misuse, has endowed the fiber with a formidable shield. That such a guard is an essential element of the integrity of hair is very apparent from Fig. 4. This is a scanning electronphotomicrograph of a hair fiber from which sonhe of the scales have been abraded. The underlying ilia- merits of the cortex are clearly visible, and the lack of any substantial lateral cohesion among the fibrils is evident. Fibrillation of the cortex occurs readily, as a result of either chemical or mechanical action. The tight ring of cuticle cells is often the only restrictive element the fiber has at its disposal. ....• ... ...• • ..... .. ,?',-(•:•-._ •..e?• •:• %". Ws .. ' :- ..... ' • .. ' . . . "&• : • .'•. ::• --•." -.• . •'s.• . . •y . ' y--,-. . • ............ • ß . ...... • -. . .• ....... • .... •.. •'½'• i _. • .•?....• '.'....,.,.4. •:-• -• •a•"..• .•. •..• ,..• . ": .• ' ::.,: ..... •:? _.-&• '•' [ " -: •d •- ':•" ' '• -:• '• •:,":-•'":-" "•:': '"'%'--•:"• "• ---' '• ' 5 .• .... •,-.. .. . ,....-•-:.• •-•- .,.: ,'..-•"•':: ....... .--,'..• I'. • '•¾ ' '":::: " • '* ": -•' •" • '•.• .... :'• ' •.•_ •' "'• ..... •'-:• . . .• • •-- •, . '•.• ::. •:. .• • • •.'•:..• •' .... . •:•- '. --.:.¾.. . ..'• • •-:-A •.-,• ... .... ... •:../-. • •'j, •,:.-, ,:.• .... .:,., -•.... •. •.. • •:. •'f•-..•- •:•: :,..:... :.•?.'::'-: :•:•? :• ß •,.....:: .... . '-.-.... -. z '.•:'k• • ..•.- 'C . .. .•... k•:..•. '.': .,--•'.%.:'.'..:-': .. •,' ..... :•" ::' -.?': .... :• •z: ß :,- e. • '•:,• •- • .:. ,.•:: ,. • '•}• ..• ,•,fi.-- •.[.., .... • :' .... •2 -• .... ','. :• :• • •--• -- - ..' '• • : ,'•':'- '- .. ,: • '•& • ..•.•.•..-.::' -... A.•. ': ,.,, • .• .......... .: .•* :•, •'.• :•'•::..:•F•¾: •::• :•: F '•,::.. ': •:':• }•: .,•:•.. ¾•.' •--•?'... • ...-... :: •: •:• .... '. .... • ,.• • ............. .:-• ...... ..•. :.• --• '• •:• '•:• •., ?:- .... '.•":.'-.": '•:'7. ?::::] ' . , -• ..... • .... :: .• ... •.::....•..•...-? .• •'% ..• :..:.:. -...•:•... :. •-- •..•.• ?' . .•::. -... •. --- • •.. -.•.... %•&. .. ::• ..... -: .• • ......... -. Figure 2. Cross-section o• human hair viewed by optical mi•oscope. Magnification, 360

842 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 3. Electron micrograph of transverse sections of 3 human hairs of various diameters. Magnification, 950 in each case