ABSTRACTS OF PAPERS ON THE BIOLOGY OF HAIR GROV•TH 35 400 A. thick) separates the epidermis from the dermis. The basal layer of epidermal cells, usually somewhat columnar, are attached to the dermal- epidermal membrane, but their plasma membranes are separated from it by a less dense layer. The epidermal {Malpighian) cells contain small mitochondria, agranular vesicles (Golgi type), and large numbers of dense ribonucleoprotein (RNP) particles which are not associated with the membranes to form an endo- plasmic reticulum such as occurs in protein secreting cells. Fibrous keratin first appears as wispy bundles of fine filaments (100 A.) which in hair and feather rapidly aggregate to form definite fibrils lying parallel to the lengthening cells. In skin the filaments show a lesser tendency to form bundles and the orientation is more random. Frequently, the fibrils seem to sprout from the plate-like cell contacts {see later). In the hair cortex the bundles of filaments grow in length and width and, above the bulb constriction, stain more readily with the osmium fixative. High resolution micrographs show that the stain is associated with a material between the original filaments. It is proposed, therefore, that fibrous keratin is a duplex structure consisting of a system of fine parallel •-filaments (ca. 60 A. diameter) cemented together with a material high in cystinc and probably not fibrous (T-component). In the inner root sheath trichohyaline granules accumulate at first and later transform into fibrils. A similar change probably takes place in the keratohyaline of skin. Epidermal tissues show several remarkable, specialised cell contacts. In skir, outer root sheath and feather, these take the form of localised plates comprising a thickened cell membrane and several layers of dense material within the cytoplasm "backing." Fibrils may sprout in tufts from the plates. At higher levels several layers of intercellular material appear between the "plates." A similar dilation of the membranes, with the interpolation of intercellular sheets, occurs generally in the hair and is most marked in the cuticle and inner sheath. These contacts may be associated with strengthen- ing the formations. "THE CHEMISTRY OF KERATINISATION" A. GEDEON M.•TOLTS¾ In the early stage of keratinisation, the formation of cytoplasmic fibrils appears to be a basic mechanism which later becomes associated with decom- position and elimination of certain cytoplasmic and nuclear elements. Although these are common properties of keratinising cells of both hair cortex and epidermis, the actual mechanism of keratinisation is different. In the differentiating cells of the hair cortex, the cytoplasmic fibrils gradually reach a high concentration and the cells practically consist of fibrils when the nuclear and cytoplasmic activities cease. A quite perfect elimination of

36 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS non-keratin constituents also takes place. In differentiating epidermal cells, cytoplasmic fibrillation does not seem to be a gradual process and the fibrils never seem to reach concentrations as high as in differentiating cells of the hair cortex. Elimination of nuclear and cytoplasmic non-keratin components is also less perfect. Differences can be recognised in the chemical composition of the keratin which is formed in both hair cortex and in the epidermis. , While hair keratin contains the basic amino acids: histidine• lsyine and arginine in a character- istic ratio of 1: 3: 10, this ratio is absent in epidermal keratin. The other amino acids also occur in differing quantities. ,It would appear that either the availability of amino acids might be different in the hair follicle and the epidermis, or that keratin synthesis proceeds according to different principles in these keratinising tissues. , "THE BIOSYNTHESIS OF FIBRES" E. H. Mv-RC•R The formation of many fibrous systems follows the following course: primary synthesis of a non-fibrous macromolecular precursor, the trausforma- tion of the precursor into a fibrous modification, the arrangement of these protofibrils into more organised structures and, in some cases, the hardening or tanning of the final formation. Thin sections of a selection of fibre-forming cells, including silk-forming cells of the silkworm, collagen-forming fibroblasts of the skin of the mr, the cells forming the egg case of the cockroach, certain chitin-forming .cells of insects, and mammalian epidermal cells, lead to the following tentative con- clusions: protein fibre formation is associated with the presence of dense ribonucleoprotein (RNP) particles, as is also the case with cells forming soluble proteins chitin-forming cells have few dense RNP particles if the fibre-precursor is to be secreted from the cell the RNP particles are associate•d with reticulum if the protein fibrils merely accumulate within the cells the RNP particles lie in clusters freely in the cytoplasm. The secretion of the protein precursor may be effected through long, thin, finger-like protrusions of the cell membrane or, if synthesis is very rapid, large accumulations may separate in lumps at the cell edge. The transformation of the non-fibrous precursor into protofibrils seems most often to be a kind of aggregation into linear or helical aggregates in which the original structure of the macromolecule is preserved. These protofibrils often separate spontaneously in vitro and may be photographed. The organisation of protofibrils into parallel arrays, networks, membranes, etc., is due to some added control mechanism, such as shear due to flow or the presence of already organised material. Keratin protofibrils form spon- taneously and in hair seem to owe their orientation to a slight initial flow