Rat dorsal skin was fractionated by means of an electrokeratotonie into epidermis and dermis containing the sebaceous glands. These fractions were separately cultured in the presence of ^^P-orthophosphate, '^C-acetate, 'C-glycerol and '^C-mevalonate, and the radioactivity incorporated into different classes of Upids was measured. The nature of the labelled products was different in the epidermis compared with the sehaceous glands: in the former, phospholipids and sterols were the major radioactive lipids synthesized, whereas, in the sebaceous glands labelled triglycerides, sterol esters and wax esters predominated.The nature of individual fatty acids labelled from "C-acetate was studied and it was found that the sterol/wax esters fractions of both epidermis and sebaceous glands contained more radioactive odd-numbered normal chain and iso-and anteiso-branched chain fatty acids than the phospholipids and triglycerides. Isolated epidermal cells were prepared, and lipogenesis studies with radioactive precursors showed labelling patterns very similar to those of the cultured intact epidermis fractions. The presence of biochemically active sebaceous glands in the dermal residues, after excision of the epidermis fractions, was confirmed by treating skin in vivo with methyl testosterone, a hormone which stimulates the function of sebaceous glands, when a higher rate of lipogenesis was observed in the subsequently cultured dermal residue fractions, compared with untreated controls. No such differences were seen in the epidermis after testosterone treatment.MEASUREMENT of lipid synthesis in skin in vitro has been described fornumerous speeies, including human (Vroinan H aL, 1909), guinea-pig (Wheatley ci al., 1970 and mouse (Brooks et al., 1963;1966; Prottey and Ferguson. 1972), but this technique has not been extended to rat skin in such detail, despite considerable data on the cheniieal nature of rat skin lipids (Clayton et al., 1963;Horlick and Avigan. 1963: Nikkari and ilaahti, 1964; Nikkari, 1965). Wilson (1963) described tiie synthesis of sterols from '•*(.'-acetate by rat skin cultured for short times. Similarly, Ziboh and Hsia (1969) demonstrated aetive metabolism of both i*C-acetate and ^^C-glycerophosphate, although the precise identities of the lipid products were not described. Grigor et al. (1970) have demonstrated the synthesis of iso-and anteiso-branched fatty acids in vivo after injection of specific radioactive precursors.Recently, in a comprehensive study of lipogenesis in cultured human skin, Hsia et-al. (1970) have shown that various fractions of the whole tissue possessed difFerent capacities for lipid synthesis: in partic^dar, the sebaceous glands manufa(ttured sqnalene and triglycerides, whereas greater proportions of sterols and polar lipids were synthesized in the epidermis. On a weiglit basis, the epidermis was several times more active than the dermis for lipogenesis. Also, Summerly

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A primary (non-allergic) inflammatory response was elicited in the skin of albino rats by exaggerated application of sodium laurate solution, and the hberation of histamine, a known mediator of cutaneous inflammation in many species, was studied by a histofluorimetric stain specific for this amine which forms a complex with orthophthalaldehyde. Within the first 2 h after irritation both the epidermis and the upper dermis exhibited widespread diffuse, extracellular yellow fluorescence of ihe histamineoithophthalaldehyde complex; dilated blood vessels and many fibroblasts were also fluorescent. The extracellular and vascular staining increased in intensity up to about 6 h and then gradually faded. By about 12 h after irritation, yellow histamine fluorescence was located only as a narrow band in the upper dermis close to the dermo-epidermal junction. The fluorescence was probably contained within cells, tentatively identified as leukocytes. Other than occasional mast cells in deeper regions of the dermis, no other histamine-fluorescent cells were seen throughout the response. None of these features was observed in normal, control rat skin ueated only with distilled water, and routinely we failed to observe more than just an occasional fluorescent mast cell in irritated or control skin alike. The morphological features ofthe inflammation closely resembled those described by others for chemical irritation of skin. This study indicates the presence of histamine in the early stages of cutaneous inflammation ofthe rat, and suggests routes of its dispersal at later stages, when other inflammatory mediators are known to be involved.

SUMMARY Primary cultures of cells harvested from guinea‐pig dorsal epidermis were maintained in vitro for extended periods. The cells which initially attached to the culture vessels within the first 24 h were epidermal basal cells, but it was generally observed under the culture conditions utilized that these cells possessed limited viability, and would subsequently detach and die within the first week of culture. During this time the cultures became overgrown with fusiform cells, closely resembling fibroblasts, which subsequently required regular subculturing. Electron microscopic examination of the fusiform cells revealed that they did not resemble freshly isolated epidermal basal cells; comparison with true fibroblasts derived from guinea‐pig bone marrow strongly suggested that the rapidly proliferating cells were indeed fibroblasts. Demonstration of their ability to synthesize collagen in vitro supported this suggestion. These findings are contrary to those widely reported by others for cell cultures derived from guinea‐pig auricular epidermis, in which the basal cells have extended viability in vitro, and overgrowth by fibroblasts is seldom seen.