Certain parts of the peripheral nervous system were observed by a modification of the KOH-collagenase method by MILLER et al. (1982).
The sciatic nerve of the mouse, and dorsal root ganglion, lingual muscle and jejunum of the rat were fixed over one day at room temperature in a fixative containing paraformaldehyde and glutaraldehyde. After fixation, specimens were treated with 5N KOH solution for 5-10min at 60°C, immersed in a collagenase solution for 3-5h at 37°C and processed for scanning electron microscopy (SEM). In adequately treated specimens, connective tissue matrices and basal laminae were completely removed without causing any severe tissue damage. The three-dimensional visualization of cellular elements of peripheral nerves was enabled with the following results:
1) Individual nerve fibers of the sciatic nerve were clearly exposed. Myelinated fibers were non-branching cords with local annular constrictions at the node of Ranvier, while unmyelinated ones branched and anastomosed with one another to form loose networks. The sites of accumulation of the Schwann cell cytoplasm swelled on the surface of the myelinated fibers. Mesaxons were visualized as longitudinal furrows.
2) Ganglion cells covered by satellite cells were observed in the dorsal root ganglion. The ganglion cells were covered by their own convoluted dendro-axonal processes, thus forming the initial glomeruli of Cajal. Satellite cells at the glomeruli extended many fingerlike projections surrounding the dendro-axonal processes.
3) Motor endplates were observed in lingual muscles. Terminal Schwann cells (teloglia) at the endplate were clearly visualized: the round perikaryon extended cytoplasmic processes along the axonal branches within the endplate. The processes issued fine finger-like projections from their margins.
4) Vascular autonomic plexuses were clearly demonstrated in lingual muscles. Unmyelinated nerves branched and anastomosed to form elaborate nerve networks around the vessels. Neuronal processes and associated Schwann cells were identifiable at high magnification.
5) Submucous nerve plexuses in the jejunum consisted of numbers of ganglia and interconnecting strands of fibers which formed very complicated networks.
These observations indicate that this modified KOH-digestion method is useful for the SEM study of the three-dimensional cellular organization of nervous elements in various tissues.

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Transmission electron microscope observation of mouse lymph nodes demonstrated that reticular fibers in the paracortex were invested not only by reticular cells, but occasionally also by migratory cells such as interdigitating cells, macrophages, and lymphocytes. Quantitative analysis of electron micrographs covering wide areas revealed that about 90% of the surface area of the reticular fiber was enclosed in the sheath of reticular cells in both nude and hetero mice, whereas the rest of the surface area was associated with migratory cells. In nude mice, whose lymph nodes contain more numerous interdigitating cells than hetero animals, about 9% of the surface area was occupied by interdigitating cells including Langerhans cells; in hetero mice only about 3% was associated with the interdigitating cells. Actively phagocytizing macrophages occupied about 3% of the surface area in both nude and hetero mice. Contact between lymphocytes and reticular fibers was observed in hetero mice, whereas this relation could not be demonstrated in nude mice whose lymph nodes contain very few lymphocytes. These results suggest that the association between reticular cells and reticular fibers in the paracortex of lymph node is flexible, allowing for the interposing of migratory cells.

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The location of calcium in a rapid-frozen and freeze-substituted maturation stage enamel organ of the rat incisors was demonstrated by means of the glyoxal bis (2-hydroxyanil) (GBHA) staining method, which formed insoluble red precipitates of calcium-GBHA complex. In the ameloblast layer, highly GBHA-reactive tubulo-vesicular structures corresponding to mitochondria and some other membrane-bound structures were localized in both ruffleended and smooth-ended ameloblasts, although no significant GBHA reaction was localized in the nucleus, Golgi region, nor along the plasma membrane of these cells. In addition, numerous granular GBHA reactions appeared exclusively in association with the ruffled border of ruffleended ameloblasts. GBHA reactions were positive, but were considerably weaker in papillary cells than in the ameloblast. These observations provide a first published histochemical mapping of calcium in the maturation stage enamel organ, and suggest the active participation of mitochondria in maturation stage ameloblasts in calcium regulation.

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A cell-maceration/scanning electron microscope (SEM) method was employed to demonstrate the arrangement of the collagen fibrillar network of various tissues. Immersion of fixed tissues in NaOH (25°C) for 3-7 days, followed by rinsing in distilled water successfully removed the cellular elements, exposing collagen fibrils which were identified as such by transmission electron microscopy in their natural locations. SEM observations of the preparations are able to demonstrate the three-dimensional architecture of collagen fibrils much more precisely than other methods, including the silver impregnation method.
Collagen fibrils, forming sheaths for housing individual cardiac myocytes, fused together, thus ensuring an equal stretch of contiguous myocytes and preventing the slippage of adjacent cells. Individual skeletal muscle fibers and nerve fibers were ensheathed by the meshwork of collagen fibrils running in two opposite helices. Such structures seem to play an important role in resisting the stretching impetus. At the epithelial-connective tissue junction of the tongue and fingertip skin, interwoven collagen fibrils formed numerous microridges which probably provide a broad anchorage for the epithelium. In the intestinal mucosa, the collagen fibrillar network immediately below the basal laminae of the villous epithelium possessed heterogeneous pores. As the collagen fibrillar network shows morphological features specific to individual organs and tissues, it is suggested that such formations not only constitute the skeletal framework but also provide those cells which are housed there with a microenvironment suitable for their activities.

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A well developed extra-adrenal cortical body with an axis of 200-700μm was found in eighteen of thirty adult male Wistar rats under a stereomicroscope. All eighteen bodies were located between the kidneys. Blood vascular beds of sixteen of the eighteen bodies were reproduced with a methacrylate casting medium and observed with a scanning electron microscope. The extra-adrenal cortical body was found to contain remarkably numerous capillaries which anastomosed with each other to form a conglomerated network; it received one afferent vessel and issued one to three (usually, one) efferent vessels. The blood capillaries were of sinusoidal and uniform calibers, and resembled those of the adrenal cortex. The network with an axis of 300-700μm possessed a typical, deep efferent rootlet which corresponds to the central vein of the adrenal gland. Histological examination of the two bodies treated with Orth's or Helley's fixative confirmed that they consisted of non-chromaffin cells similar to those of the adrenal cortex. These findings suggest that in the rat, the extra-adrenal cortical bodies persist throughout life, actively producing cortical hormones.

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Serotonin containing enterochromaffin (EC) cells in the human gastric mucosa were observed using serial semithin sections immunostained by Sternberger's PAP method and reconstructed by computer-assisted methods. In oxyntic glands, EC cells displayed a marked pleomorphism which suggests their plasticity or active movement. They sometimes possessed multipolar cytoplasmic processes directly contacting the neighboring epithelial cells and/or gastric lumen. In the antropyloric glands, they are exclusively the “closed-type, ” which fails to contact the lumen, and are often arranged touching other EC cells (cluster formation), apparently exhibiting polynuclear enterochromaffin syncytia. This syncitium-like arrangement is interpreted as the morphological counterpart of a possibly synchronized function of these cells.
The morphological differences of EC cells in their shape, luminal endings and arrangement between both regions may be indicative of regional differences in their functions. Furthermore, the present study provides the first three-dimensional visualization of EC cells in the human stomach.

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Using semithin plastic sections, sequential changes in the mouse peritoneal cells during their intrauterine life were observed by light microscopy.
At 11-13 days of gestation, the peritoneal cavity contained a small number of free mononuclear cells, singly scattered. Most of them were 9 to 12μm in cell diameter, and the N-C (nucleocytoplasmic) ratio was smaller than 0.7. The cytoplasm contained large phagocytic vacuoles, and long processes extended from the cell surface. These cells were considered mature macrophages.
After 15 days, the peritoneal cavity contained smallsized mononuclear cells in addition to mature macrophages. The small mononuclear cells were 5-10μm in cell diameter, and formed the major cell type at this time. The cytoplasm contained occasional small vesicles but no phagocytic vacuoles. The small mononuclear cells showed a larger N-C ratio, 0.8-1.7. In 18-day-old fetuses, the peritoneal cells consisted of mononuclear cells, 79.5%, and mast cells, 20.5%. During the initial 18 days of embryonic life, small lymphocytes, neutrophils and eosinophils were not contained in the mouse peritoneal space.

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The fate of India ink particles and polystyrene latex beads injected into the dermis and subcutis of the skin of the auricle and back in mice was observed with the naked eye, light microscopy and electron microscopy.
The tattoo patterns made by injected ink particles remained essentially unchanged for life as observed with the naked eye. India ink particles and latex beads were endocytosed by fibroblasts as well as macrophages in the dermis and subcutis. Numerous ink particles or small latex beads (0.22μm in diameter) were packed into vacuoles 0.1-10.0μm in diameter which occupied a large volume of the cytoplasm of the cell body and processes of fibroblasts, whereas numerous particles and larger beads (0.22 and 2.0μm) were taken up into the cell body of macrophages in the vicinity. Most fibroblasts, characterized by long cell processes and well developed rough endoplasmic reticulum, are easily distinguished from macrophages, the latter being round or oval in shape, and having many lysosomes and numerous irregularly shaped microvillous projections. It is believed that fibroblasts taking up and storing the ink particles or latex beads move poorly and are almost fixed in the connective tissue: the tattoos therefore do not change markedly.
It is emphasized that the uptake and long-term storage of ink particles and latex beads by the dermal and subcutaneous fibroblasts represent a specific non-inflammatory defense mechanism that protects the living body, without immune reactions, against injuries and invasions by non-toxic foreign agencies. The histiocyte, a term proposed by KIYONO (1914) for a fixed macrophage on the basis of his studies using vital dye staining, is considered to include, in addition to true macrophages, fibroblasts showing endocytotic activities for small foreign bodies such as acid dyes, ink particles, and latex beads.

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The Merkel cells in the taste organ of the frog were investigated by immunohistochemistry using neuron-specific enolase (NSE) antiserum. NSE-immunoreactivity was found exclusively in the Merkel cells lying at the base of the taste organ. The distribution and the profiles of the NSE-immunoreactive Merkel cells coincided with serotonin-containing cells previously reported at the same place.

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