EXPERIMENTS ON THE EPIDERMIS OF ANIMALS WHICH MAY BE OF VALUE TO THE COSMETIC CHEMIST* By O. Chairman, Dept. of/lnatomy, College of Dentistry, and the Graduate School of/lrts & Science New York University, New York, N.Y. T•E SKIN OF most laboratory animals is devoid of sweat glands and provides no opportunity for making studies on the control of perspiration. The hair coat has a cyclic growth during which time the hair grows actively for a period and then rests for an interval. The cycle in the rat (1) lasts 34 days equally divided into resting and growing periods. Further studies have shown that the metabolism of the skin (2) is low during the resting period (0.92 cmm. O2 mg./hr.) and that it increases greatly just prior to growth (1.26 cram. O2 mg./hr.). Likewise the fluid content of the skin is 55 per cent during inactivity of the hair and then increases to 67 per cent prior to the formation of the new hair (3). This growth of hair with asso- ciated metabolic and fluid changes in the skin has provided many oppor- tunities for learning to what extent hair growth may be affected both by factors from within the organism and from environmental conditions. In experimental work on hair growth in animals, the animals and the cyclic activity of their hair coat must be well understood to obtain reliable results. Changes also occur in the epidermis. At the age of 22 days when the hair coat is resting, the stratum germinativum consists of one or two layers, there are occasional granular cells which represent the granulosum, there is no definite lucidurn and the comeurn consists of four or five layers of very flat cells (Fig. 1). The latter stratum is often lost in histological preparations, indicating that the layer is dry and brittle. In the 30-day-old rat, when activity begins in the hair coat the stratum germinativum consists of several layers of cells and a very distinct granulo- sum is present. Even occasional lucidum cells are found. More of the corneum is retained, indicating that it is not as dry as in the 22-day-old rat (Fig. 2). * Presented at the May 14, 1954, Meeting, New York City. • Many of the investigations reviewed have been aided by a grant from John H. Breck, Inc, Springfield, Mass. 229

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS • • '.c.• .4jl•.- ':'• ' ,• • • •' - •' .... • • '----•' ' • ..--- .:: - -,:.,-.- . X/- . .. ' .½?-'"--- .... *. : ::• } :: -.• :% .., :•"• •. % - .•.:.-...• •.•*,• ..: '.. / -, :c:'.. ,'•,. .-,: -- .,"" ",.: , ......... : :':., . ',• .... /?$',',.:•..--- .".,-- :, .... .• . •-c •.: . .-. . ---:.:.. .... .......: •.½ 6 ,•..:¾/,-..-.½ .. _.• . ... ½.• .... . •. ,* • - [: -- ,. ...... Z• ..... t•.:,• " . ?... ,• ::'• "': .-,.• .' • ... '.?"Z"' •'-:"..•.& '• ,::•"' *• ? , •'l, .' " • ..,• ..... ,. .: '• .... '. ' -:- *" •. ' • .... .' - • . . . •..::.•. -- .•. • -- * ....:•.... -½.• i. • "....:' .- - " ' • '*'... :'- . .. ' . •. '•. . . . --- . . • ' ," .. *.... -.::• ,: w..: • , , "."' .' .... . : "--.. ""' L..'•" ' ,' :.' :½',•s ' :'....' .... •--- -'*..--, a' %½ ' -*••• : :: *.*• ....... ' - '•'. '"': ' ß :.'-..?.. :.:'---E?' '-?.--"' '"'" '"' '"** '"'* ..... " Figure 1.•Skin of 22-day-old rat showing a single-layered germinativum, little indication of a granulosum, and a hard, brittle comeurn. Figure 2.--Skin of 30-day-old rat showing the many-layered germinativum, a granulosum, and a moist comeurn. Figure 3.•Normal skin of a 31-day-old rat. Figure 4.--Skin of rat receiving wool fat applications (twice daily) from 21st to 31st day of life. Figure 5.--Skin to which mineral oil was applied (twice daily) from the 21st to 33rd day of life. Biopsy taken at age of 3• days. Figure 6.--Oleic acid applications from 21st to 27th day (twice daily) caused this effect.