Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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epidermis

A protective, hard-wearing layer of keratinous cells, which, although of varying thickness over the body of the animal, is very thin compared with the underlying DERMIS .

It consists of a continuous mass of cells usually differentiated into the following regions: Stratum corneum, or the uppermost layer, containing dry, dead cells, flattened to form a relatively continuous thin outer membrane skin that is highly cornified or keratinized; Stratum lucidum, which is the region where dying cells are located, and which contain an oily substance that renders them translucent; Stratum granulosum, in which the cells contain large granules; Stratum spinosum, where the cells show marked spines or bridges between each other; Stratum basale, where the cells contain living basal cells called keratinocytes and melanocytes; and the lowest region, the epidermal-dermal junction (often called the basement membrane), which consists of a thin zone of ground substance, containing no fibers, lying between the basal cells and the dermal surface.

The epidermal-dermal layer has little resistance to bacteria and enzymes, and is easily attacked by them, as in enzyme UNHAIRING .

It is also easily disintegrated by alkalis, such as caustic soda, sodium sulfide, etc., which is the basis of common commercial unhairing processes.

The term derives from the Greek "epi" (upon) and "dermis," which had its origins in the Greek "derin" (to flay). See also: LIMING (248 , 291 , 306 , 363 )




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