THE STRUCTURE OF SKIN I I be warm but pale. This happens when the sub-papillary plexus is shut off and the flow of blood through the papillary capillaries is increased. Red and cold skin is also possible. This occurs when the capillary bed opens up and less blood flows through the papillary capillaries. When this happens, the rate of blood flow often slows up and the blood loses more oxygen and gives a blue appearance to the skin this is what happens when a person goes "blue" with the cold. Red, warm skin is, of course, well known, particularly after sunburn. (Slide 10) EPITHELIUM The epithelial cells of the skin are divided into a series of layers. These are easily distinguished in a thick epidermis, such as that of the palm of the hand less easily in parts where the epidermis is thinner. The lowest epithelial layer is called the stratum Malpighii, and is itself composed of a single basal layer--the stratum germinatum, and a succession of layers above it which form the stratum spinosum. These layers are SLIDE 11 Enlarged detail of Slide 1, to show more clearly the stratifica- tion of the epidermis.

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.