JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS composed of cells called "prickle cells," because of the protoplasmic bridges which connect one cell to another. Above the stratum Malpiõhii is the (Slide 11) stratum granulosurn, in which the cells contain a number of granules of a chemically ill-defined material known as "eleiden." Above those layers is the stratum lucidurn, of which the cells contain "keratohyalin," and above that the superficial layers are known as the stratum corncure. In this the cells are dead and are largely composed of keratin. Keratin contains a good deal of sulphur, and this element is present in the form of disulphide cross linkages between polypeptide chains. (Slide 12) ....... •.:::: .:. ..•. ,,:• ß .... i• • ........ •'•' '• •'••. •'••• .': •'..., •..•.• ........ '..}:..•:• ..... •....a .', ...•:• ..::.•:.. .•. '• -.:• . %...• .'•/ '•'"•'•'. 2:• •.:::•? .• '"":':':: :•'• ...... , 7¾ •' •'•.•2.':0'"• '...• •...:•z.•.. ? [:.:.%::.: ,,•... .... ..•.-•. ß •{:• ..•:.:,:,:, . ß ...... ß ß •'• :' .' . ... :.... .• • •: •. .:: ../• ' .., .. ß . ::. : • .•... '•}• .. ..., ' •. •...:.::. -.. :...•.. •.,• •:½ ::• /..•..: . ......... :::•g •:-• • ....•'. SLIDE 12 Sulphydryl groups in human epidermis. (A) Epidermis from the scalp with a strongly reactive layer beneath the stratum comeurn. 1Keratohyalin granules in the stratum granulosurn are unreactive. (B) Epidermis from the palm. The stratum granulosum appears as an unreactive band. The stratum lucidurn and the lower part of the stratum corSeurn show strong reaction.

THE STRUCTURE OF SKIN 13 These superficial cells are constantly being desquamated away and are being replaced by continuous multiplication of the cells of the stratum germinativum. Under certain conditions this desquamation can be increased and in others delayed so that a thick horny layer of cells is built up on (Slide 13) the skin. This happens in vitamin A deficiency. The efficacy of mud packs in cosmetic treatment is due to the fact that the mud on removal takes away the surface layers of keratinized cells so that the colour of the underlying blood vessels shines through more clearly, giving the skin a (Slide 14) characteristic warm, pink glow. There is a possibility, however, that frequent mud-packs stimulate multiplication of the cells of the stratum germinivatum so that the more mud packs one has the more they are needed. SLIDE 13 Epidermal cells from the human axilla showing intercellular bridges, nodes of Bizzozero, and faint striations indicating tonofibrils. Section stained with Regaud's hematoxylin.