The appendix is a prominent example of gut associated lymphoepithelial tissue, whose function is to react to the wide variety of antigens present in the gastrointestinal tract. It is composed of a large number of repeating units, the lymphoid follicles, each of which is divided into an apical dome, a large basal nodule with a germinal center, and laterally extending thymus dependent areas. The dome epithelium consists mainly of columnar absorptive cells and of specialized follicle associated epithelial (FAE) cells which are efficient at transporting material from the lumen to the underlying lymphoid tissue, and may also transport macromolecules from the lymphoid follicle into the lumen. The dome epithelium normally has large numbers of lymphocytes within it, as well as smaller numbers of macrophages and plasma cells. Macrophages, and perhaps FAE cells, are capable of processing and presenting antigens to reactive lymphocytes. Lymphocyte proliferation and differentiation in response to antigenic stimulation begins in the lymphoid follicles, but most of the lymphocytes leave by the lymphatics, migrate through lymph nodes and spleen, frequently to complete differentiation into IgA-secreting plasma cells in the lamina propria of mucosal surfaces. Normal function of appendix probably helps suppress potentially destructive humoral antibody responses while promoting local immunity.

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Ultrastructural changes in the parathyroid glands of dexamethasone-treated mice were examined. Many chief cells of the treated mice contained a decreased number of prosecretory granules, secretory granules and storage granules, and an increased number of lipid droplets, compared with the control mice. In addition, myelin-like structures associated with cisternae of the granular endoplasmic reticulum were observed in the parathyroid glands of the treated mice.
These findings suggest that cellular activity of the parathyroid gland may be suppressed by dexamethasone.

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Electron microscope study of the epiglottis in the rat and mouse reveals bundles of tubular-shaped filaments (11nm diameter) that anchor the basal lamina of the epithelial lining. These anchoring filaments are present both on the laryngeal and oral surfaces of the organ. The filaments are shown to be continuous to elastic fiber microfibrils (EFM) of elastic fibers in the underlying connective tissue. It is suggested that EFM in adults function as anchoring filaments for cells and connective tissue fibers.

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The microcirculation of the pancreas in anesthetized rats was examined by intravital microscopy. Scanning electron microscopic observation of vascular corrosion casts of the same parts of the pancreas as viewed light microscopically in vivo, allowed detailed analysis of microcirculation in particular vessels. Blood vessels with flowing blood cells were clearly observed under incident ultraviolet illumination following systemic injection of an intravascular fluorescent tracer. The islets of Langerhans were easily identified by their brighter appearance than the exocrine portions under incident ultraviolet illumination. Blood leaving the islets passed through the insulo-acinar portal vessels into the capillary network around the acini. The periductular plexus received blood from the periacinar capillary network via either venules or capillaries as well as directly from the inter- or intralobular arteries. The periductular plexus also received blood from the islets located close to the ductules.
The results obtained show blood in the pancreas flowing in a manner in which it carries insular secretions in high concentrations through short and direct vascular routes from the islets to the pancreatic exocrine tissues, including their duct system.

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The arrangement of the various endocrine cells within mammalian islets of Langerhans indicates that the regulation of insulin and glucagon secretion by pancreatic somatostatin may occur mainly by paracrine mechanisms.
In the present study, the relationship of somatostatin-containing D-cells to blood vessels and to other endocrine cells in the islets of the human pancreas were investigated using immunohistochemically stained serial semithin sections (0.5-1.0μm). Morphologic features of 335 D-cells were examined and their anatomical relationship to other endocrine cell types and capillaries was determined by morphometric analysis and graphic or three-dimensional reconstructions. The majority of D-cells (84%) was located in close proximity to the capillaries. The intracellular immunoreactive material was accumulated in those cell parts facing the capillaries or their perivascular spaces. The remaining D-cells did not come into contact with the capillaries and showed only moderate or weak immunoreactivity. —A further characteristic feature of islet D-cells, pertinent to about 67% of these cells, is their tendency to be arranged in contiguity to other D-cells.
The present findings indicate that somatostatin after its release from the D-cell reaches other islet cells mainly via the intrainsular circulation or along the perivascular space.
Concerning the general microarchitecture of human islets of Langerhans, the present data are not sufficient to give a conclusive morphological description, because heterogeneities among the islets were observed. These variations appear to be related to the type of vascular supply which differs among islets.

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The fine structure of the mouse tracheal epithelium from the fetal period to the stage of old age was examined with electron and light microscopes. The tracheal epithelium of the adult mouse is ciliated and single columnar in shape, consisting of three kinds of cells: ciliated, non-ciliated and basal. Neither goblet nor brush cells were found. The earliest signs of the cytodifferentiation of ciliated and non-ciliated cells appear at 15 and 17 days of gestation respectively. The secretory granules in non-ciliated cells appear at 17 days of gestation, and increase in number from 18 days of gestation (one day before birth) to 1 day after birth and decrease in number rapidly, while elements of smooth endoplasmic reticulum appear in this cell. Non-ciliated cells constitute the major component of the tracheal epithelium in the adult mouse. They have two kinds of granules: one a secretory granule surrounded by a single limiting membrane and released by exocytosis, and the other surrounded by double limiting membranes and considered to be derived from mitochondria.
With the advance of age, some parts of the epithelium invaginate into the lamina propria without any noticeable changes in either the epithelial cells or the basal lamina. These invaginations, which the present authors named “cyst-like structures, ” are found in all mice over four months of age examined, and increase in number and size with age. They seem to be physiological structures and are distributed in all parts of the tracheal epithelium from the first tracheal ring to the tracheal bifurcation. They contain concentric circular materials with entangled filaments (15-20nm in diameter) and/or destructed cell debris mainly derived from granular leucocytes.

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The distribution of vasopressin-, oxytocin- and LHRH-containing nerve fibers in the pineal organ of the dog was demonstrated by use of the peroxidase-antiperoxidase immunohistochemical technique. These neuropeptide-containing fibers penetrated through the pineal stalk from the brain, mainly from the posterior commissural region, into the pineal organ. The vasopressin fibers were the most prominent in number, oxytocin fibers and LHRH fibers were the least. Most of these fibers were found in the proximal part of the pineal organ, but some of them were also observed in the distal part. These peptidergic fibers were distributed not only in the perivascular spaces but among the parenchymal cells.

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Cytoplasmic inclusions, particularly crystalloid inclusions of macrophages in mouse bone marrow and splenic red pulp were qualitatively and quantitatively examined by electron microscopy.
In mice younger than 40 days of age, macrophages in the bone marrow contain a variety of inclusions, the majority of which are spherical phagolysosomes. In mice older than 60 days, needle-like crystalloid structures occur within the phagolysosomes. The crystalloids first appear at 60 days of age, and increase in amount with age. They exhibit a remarkable increase between 90 and 120 days in females and between 60 and 90 days in males. The crystalloids are significantly more abundant in adult males than in adult females.
Macrophages in the splenic red pulp have much more spherical inclusions than marrow macrophages. The crystalloid inclusions are also contained in the red pulp, but they are quite small in amount as compared with those in the marrow.
After administration of hydrocortisone, the amount of crystalloids increase significantly in marrow macrophages.
The crystalloids in macrophages are discussed with particular interest to their relation to erythropoietic activity in the hemopoietic tissue.

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Retinas of various vertebrates (bullfrog, crow, bull, pig and human) were treated with HCl and collagenase for removal of the basement membrane. The exposed basal surface of Müller cells was observed under a scanning electron microscope. In the nerve fiber layer, the Müller cells divide into small basal processes which extend towards the basal surface, where they terminate with a mosaic pattern. This pattern varies somewhat from species to species and from region to region of the retina.

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The sinusoidal wall was observed by transmission electron microscopy in crabeating monkey livers. The perikarya of sinusoidal endothelial cells were characterized by numerous macropinocytotic vacuoles and curved smooth-surfaced tubules of high electron density. Size and spacing of fenestrae in endothelial sieve plates corresponded to essentially those in other mammalian species including the human. It was verified that the high concentration of microfilaments was responsible for the electron dense appearance of the sieve plate in tangential sections. Besides occasional overlapping of endothelial sheets, complicated interdigitations of several short lamellae originating from endothelial processes occasionally caused a layered structure of the endothelial lining. Kupffer cells were strikingly rich in lysosomes and contained large mitochondria and phagosomes. They were fixed to the endothelial lining by patches of junctional complexes identical with those between endothelial cells. Ito cells of the monkey liver demonstrated, like those of the human liver, many smooth-surfaced caveolae and vesicles along their perisinusoidal surface, suggesting their micropinocytotic activity. They also contained glycogen β-particles which were partly gathered around lipid vacuoles. The electron dense droplets enclosed by glycogen particles as revealed in human Ito cells and regarded as immature lipid droplets retaining the chemical properties of glycogen, could rarely be confirmed in the present study. Between the Ito cell and hepatocyte there occurred many junctional complexes. The space of Disse contained, besides abundant collagen fibrils, numerous fine filaments forming irregular meshworks or bundles which resembled fibrillar material (precursor of collagen) in appearance in the dilated cisternae of the rough endoplasmic reticulum (RER) of the Ito cell. These filaments often entwined the collagen fibrils in the Disse's space as if to participate by apposition in their development. The question, whether pinocytosis-like structures of the Ito cell might be involved in the precursor transport from the cisternae of the RER to the Disse's space, remained unanswered.

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