Thin sections of human eccrine sweat glands were observed with the transmission electron microscope. The fine structures of the secretory coil, transitional portion and coiled duct were compared.
The secretory coil consists of dark cells, clear cells and myoepithelial cells. Dark cells contain irregularly shaped secretory granules which appear dark after glutaraldehydeosmium double fixation. If osmium is applied first to the specimen, the electron density of the secretory granules is lowered, and they often become vacuoles. These granules originate as an accumulation of secretory substance in the innermost cisterna of the Golgi stack which may correspond to the GERL. This secretory substance contains mucopolysaccharides as it stains intensely with methenamine-silver. Exocytosis of the granules was demonstrated. Clear cells abut the intercellular canaliculi but contain no secretory granules. Well developed smooth ER is spread over the entire cytoplasm, except for the very surface of the cell. The Golgi apparatus is situated near the smooth ER, and sometimes the elements of the Golgi apparatus and smooth ER are intermingled. Glycogen particles are heavily loaded in the cytoplasm of clear cells.
The transitional portion, which has not been examined precisely, contains epithelial cells which form a simple cuboidal epithelium and resembles the clear cells of the secretory coil. These cells contain a triangular mass of filaments attached to the zona adherens which are forerunners of the terminal web (periluminal filamentous zone) of the coiled duct. The intercellular interdigitation is weak and basal infoldings are absent in the transitional portion. This portion is provided with myoepithelial cells, which are numerous at the proximal end but sparse in the distal half.
The coiled duct consists of two layers of epithelial cells, i. e., luminal and peripheral cells, but the myoepithelium is absent. Numerous mitochondria are heaped in both cells reflecting active reabsorption of sodium ion in the coiled duct.
In conclusion, the transitional portion contains structures intermediate between the secretory coil and the coiled duct, and its function may be neither secretion nor absorption; the well developed myoepithelium at the initial segment of this portion may act as a sphincter of the duct system regulating the flow of sweat in the gland.

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After administration of monoamine precursors, taste buds in the fungiform and foliate papillae of the mouse were observed by means of electron microscopy and fluorescence histochemistry. The taste buds in the fungiform papillae differed in the ultrastructure of their apical regions from those in the foliate papillae, which contained the same taste buds as those described in the circumvallate papillae. The gustatory cells in both the fungiform and foliate papillae were capable of taking up monoamine precursors, although this ability was greater in the latter papillae. The results suggest that, not only in the circumvallate papillae but also in both the foliate and fungiform papillae, monoamines might be involved in neurotransmission from the gustatory cells to the nerves.

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Postnatal erythropoiesis in the spleen and bone marrow was morphometrically examined by electron microscopy in female mice.
In the splenic red pulp, erythroblasts increase in number in early life, particularly until 20 days of age. On the basis of a cytometric analysis, erythroblasts can be classified into four types: small, medium, large and extra-large. In the neonatal spleen, small erythroblasts constitute 16% of all the erythroblasts; medium 55%; large 23%; and extra-large 6%, respectively. In mice older than 20 days, medium erythroblasts are reduced in proportion, and small erythroblasts account for more than 500 of all the erythroblasts.
In the bone marrow, small erythroblasts represent the largest population until 40 days of age. At 60 days, however, medium erythroblasts are increased, being largest in proportion. The erythroblast types in the marrow at 60 days are similar in proportion to those in the neonatal spleen. This finding seems to suggest an active state in erythrocytopoietic activity. The population pattern of erythroblasts is thought to serve to evaluate erythrocytopoietic activity.

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Thrombocytes of early chick embryos were observed in blood smear and whole embryo preparations stained with PAS. In the blood smear preparations, thrombocytes usually had one large glycogen mass in the cytoplasm until 3 days of incubation, and it became progressively smaller with the advance of embryonal development. While, the application of PAS to whole embryo preparations was shown to be a very useful method for observation of the blood cells in embryos at early stages when their blood could not be collected. Thrombocytes were clearly identified in situ in the embryo by PAS staining even in very early stages when no blood circulation occured. At stage 12, distribution of the thrombocytes coincided with that of blood islands, but was limited within the area opaca. Mitotic figures of the thrombocytes were frequently found in and near the blood islands. This suggests that blood islands are the proliferation sites of the thrombocytes in early chick embryos.

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In biopsy specimens from two normal human livers, fat-storing cells and Kupffer cells were observed by electron microscopy with the following results: 1) In the human Ito cells numerous micropinocytotic caveolae and vesicles occurred either scattered beneath the plasma membrane or fused into short tubules. In the cytoplasm abutting on these structures, minute clusters of glycogen β-particles were revealed which presumably had been synthesized in the local cytoplasm from carbohydrate (glucose) ingested by pinocytosis. 2) Lipid droplets (vacuoles) were formed within the accumulations of the glycogen β-particles. These findings support the view that the glycogen synthesized in the Ito cells may represent a transitional compound in the process of lipid synthesis from carbohydrate. 3) Among lipid vacuoles, electron-dense droplets equally large were found, often containing electron-lucent areas in their center. On the surface of these dense droplets, compact clusters of glycogen particles adhered as if they might have permeated into the droplets. These droplets may possibly be immature lipid droplets retaining chemical properties of the glycogen in their superficial part; they remained insoluble during the preparation procedures for ultrathin sections. 4) The occurrence of the worm-like structure has for the first time been revealed in the human Kupffer cells. Besides its short tubular profiles, a more complex structure was demonstrated.

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In rats treated with 6-OHDA in early postnatal days, myelin degeneration was observed in large and medium-sized myelinated nerve fibers belonging to the mesencephalic tract of the trigeminal nerve. Splitting of mylin lamination at the intraperiodic line and irregular excess scrolls were frequent in these fibers, whereas the smaller sized fibers remained intact. Occasionally, naked axons with numerous neurofilaments and neurotubules appeared near the empty myelin scrolls, indicating autolysis of the once-formed myelin sheaths. Some sheaths showed decompaction through loose lamination around the axons.
The perikarya of the mesencephalic neurons showed no visible damage, but dark terminals making axo-somatic synapses in the motor nucleus were regarded as degenerating features of the axon-collaterals of the mesencephalic neurons. Thus, the myelin abnormalities were partially attributed to a kind of Wallerian degeneration.
A survey of the glial cells in the corpus callosum indicated no remarkable changes in the ratio of the various glial types and in the myelin structures in comparison with those of the controls, although insufficient maturation of oligodendrocytes resulted in a 5-day delay in the onset of myelinogenesis.
These findings suggest that the myelin degeneration in the mesencephalic tract is a regionally specific alteration induced by 6-OHDA administrations, probably because of the abnormal accumulation of NA in this area.

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The intrahepatic biliary passage in five species of birds was investigated with the transmission electron microscope. The avian liver was characterized by a frequent occurrence of intralobular bile ductules and canaliculo-ductular junctions in the parenchyme. It was further characterized by solitary bile ductular epithelial cells intercalated among hapatocytes surrounding bile canaliculi. The present study first revealed that avian bile ductular epithelial cells possess a long single cilium. Its basal body (distal centriole) was connected to a basal foot and slender rootlet and accompanied by a proximal centriole. The hepatocytes facing the bile passage possessed no cilium, although they frequently had a diplosome in their apical cytoplasm. The single cilia of the bile ductular epithelium gradually tapered toward the tip. The original fiber pattern in the most proximal part was peripheral 9 doublets +0. In the ciliary shaft, the doublets altered into singlets which were diminished in number gradually toward the distal parts of the shaft, so that in the tip only one singlet remained. Since these fiber patterns in the single cilia markedly deviated from the 9+2 fiber pattern of the ordinary motile cilia, they may not be motile, but properly regarded as sensory or chemoreceptors.

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