Keratohyalin

KERATOHYALIN (from Greek keras- horn and hyalinos- glassy, transparent), a name given by Waldeyer (1882) to a substance which in the form of grains is found in the cells of the granular layer of the skin (stratum granulosum), especially in areas with thick epidermis. The grains of keratohyalin are transparent, strongly refract light, are hard, and insoluble in water, alcohol, ether, in glacial acetic acid (with brief action), in ammonia and weak alkalis. They are soluble in strong solutions of caustic potash and soda, in hydrochloric and nitric acids, are digested by pepsin; they are not stained by iodine, turn brown from osmic acid and are well stained by hematoxylin; this staining serves for the detection of keratohyalin in preparations. For some time keratohyalin was identified with eleidin, previously described by Ranvier in the cells of the stratum lucidum; but later research showed that these are two different substances (Rabl): eleidin has a liquid consistency and is stained by acid dyes. When describing keratohyalin, Waldeyer considered it a preliminary stage of keratin substance, but since it was proven that keratinization is associated with fibers and concentrates on the periphery of the cell, keratohyalin came to be considered one of the byproducts of keratinization. Unna assumes that keratohyalin consists of an acid and a basic protein and, breaking down, gives rise to basic eleidin and an acid glycoprotein.