No abstract

Synopsis The literature is reviewed. A technique for embedding tissues in polyethylene glycol 1,000 mono‐stearate (Nonex 63B) after preliminary infiltration with polyethylene glycol 900 is described. Preliminary dehydration in alcohol is not required and at no stage is the temperature of the tissue raised above 40° C. Measurement of tissue before and after embedding in Nonex, paraffin and celloidin shows that there is significantly less shrinkage in Nonex. It is shown that the celloidin in celloidin‐Nonex mixtures used experimentally for embedding penetrates tissue. The difficulty of mounting Nonex sections is discussed. Nonex sections stain well, phosphatase activity is well preserved and at least part of the lipid is preserved. It is concluded that the use of Nonex is specially indicated for tissues liable to shrinkage artefacts and may have some advantage for histo‐chemistry.

Mammalian epidermis and oral epithelial possess an intercellular permeability barrier which is located in the superficial region of the tissue. This study reports a staining reaction which appears to demonstrate a histological correlate of this functional property. Specimens of ear skin, palate, buccal and oesophageal mucosa and of cornea and bladder were obtained from adult rabbits and rats, bisected and either incubated in vitro with 2.5% horseradish peroxidase as a tracer or fixed and processed for light microscopy and stained with a modification of Hart's elastin stain. Examination of specimens prepared by each procedure showed a complementary staining pattern in the intercellular spaces of the stratum corneum or in the superficial region of the non-keratinized tissue. In the epidermis and oral and oesophageal epithelia, the region which excluded the tracer stained with the modified elastin stain. In contrast, the corneal and bladder epithelia neither excluded the tracer nor showed intercellular staining. This relationship between staining of the intercellular space and the exclusion of tracer suggests that the intercellular material in the superficial region of epithelia may be chemically altered to form a barrier substance, possibly as the result of the discharge of the contents of the membrane-coating granules which are present in all the epithelia examined except the cornea and bladder.

Methyl green-pyronin is a notoriously difficult stain to reproduce. Although very useful in detecting cells containing substantial amounts of RNA, it is of limited use in broader problems of cell identification. By careful standardization of the proportions of methyl green to pyronin and combination of these stains with hematoxylin to enhance nuclear contrast and with orange G to improve connective tissue staining, it was possible to produce a consistently reliable staining preparation in which it is possible to identify all the component cells of a mixed inflammatory infiltrate in routine paraffin sections.