Cell death in the epithelial tooth germs of mouse mandibular molars from the 12th to the 14th day of gestation was investigated by electron and light microscopy. Light microscopy revealed granular substances in the epithelial portion of the tooth germ on the 12th day, and an increase in their number to the 14th day when the enamel knot developed. In the areas where granular substances were observed by the light microscope, electron microscopy revealed cells with condensed chromatin. The cytoplasm of these cells increased in electron density, the cisterns of rough endoplasmic reticulum were dilated and the cristae of mitochondria disappeared. These cells were comparable to the physiologically degenerative cells reported in other organs.
These degenerative cells are joined to adjacent cells by desmosomes and are believed to be derived from the epithelial cells.
Further, degenerative bodies, composed of amorphous structures and enveloped by a limiting membrane, were observed in the epithelial cells. They are presumed to be derived from the degenerated cells engulfed by neighboring cells. From this evidence, phagocytic ability is attributed to the epithelial cells of the tooth germ.

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Cytochemical study of the“amoeboid cells”in the corpus callosum in the early postnatal rat brain showed that a few of them exhibited peroxidase activity. The enzyme activity was localized in a variable number of cytoplasmic granules measuring 0.2μm and this resembles that of monocyte-derived macrophages.

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The amoeboid microglial cells (AM cells), which were acid phosphatase-positive histochemically, present in the rhombencephalon coated with the leptomeninges of the 8-day incubation chick embryos were investigated by electron microscopy. It was found that the AM cells occurred simultaneously in the leptomeninges, in the roof plate, and in the ventricle. Considering the distribution of the cell in these three sites along with the present author's earlier findings of ACPase reactions for the AM cells, it is highly probable that in the rhombencephalon the AM cells originate from the leptomeninges and then enter the ventricle through the roof plate.

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The microcirculation of the bullfrog kidney was studied by scanning electron microscopy of the corrosion casts. The bullfrog kidney derives its blood supply from a dual origin: one is from the posterior half of the body via the renal portal veins and the dorso-lumbar veins, the other is from the urogenital arteries.
The renal portal veins are linked with the hepatic portal system through the anterior abdominal vein which might serve as a transport route of the potentially renal portal blood to the kidney.
The glomerulus consists of several lobules of anastomosing capillaries which are intercalated between the afferent and efferent arteriole. The efferent arteriole of the glomerulus runs some distance ventrad without branching to join the peritubular sinusoidal capillaries near the ventral surface of the kidney. Usually each glomerulus has a single efferent arteriole, but double efferent arterioles may rarely occur. Near the medial border of the kidney the glomeruli are small, and laterally they become progressively larger.

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The primary formation of germinal centers was induced in the chick spleen by intravenous injection of sheep red blood cells (SRBC) at 21 days of age. In the spleen, SRBC were trapped in the ellipsoids soon after injection. The number of cells of periellipsoidal lymphoid tissues (PELT) was gradually depleted. Large pyroninophilic cells appeared in the periphery of periarterial lymphatic sheaths (PALS) 4hrs after injection. Then they increased in number and migrated centralward in the PALS. On the 4th day they were accumulated in the vicinity of the central arteries to make nodular structures. Morphologically mature germinal centers encapsulated by connective tissue were formed for the first time on the 6th day after injection. They were most numerous on the 8th day and then decreased gradually. It was presumed that the primary germinal centers in the chick spleen might have been formed by the cells of the PELT which were originally derived from the bursa of Fabricius. The process of proliferation of germinal centers in the secondary immune response was discussed.

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The aim of the present investigation was to explore the mitogenic action of ovine and bovine prolactin hormones in the thyroid, the parathyroid and the thymus glands of chicks. Both the hormones in lowest dosage (1.5 i. u.) increased the mitotic rate in majority of these organs, but it failed to accelerate the mitotic incidence further or were almost ineffective with the higher dosages (5 i. u. and 10 i. u.). Ovine prolactin showed a higher mitogenic response than that seen with the bovine hormone. It is suggested that prolactin in optimal dosage promotes mitosis in these organs of chicks.

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Following repeated subcutaneous administrations of 6-OHDA into neonatal rats (a dose; 100μ/g bw), the effect on the brain development was examined. The striatal dopamine fluorescence never disappeared completely even immediately after multiple administrations of 6-OHDA, however a slight reduction of the fluorescence lasted for a long time. Semithin sections stained with toluidine blue showed numerous dark necrotic neurons appearing at a 15-times higher ratio than that in controls. Such necrotic neurons always accompanied a few granular deposits around the wavy surface. In a certain area of the striatum (0.898mm²), there were no clear changes in the cell population in neurons and glia, in the ratio of glia to neurons, and in the ratio of each cell type of glia to the total glia, but some neuronal cell loss was speculated to occur slowly.
The ultrastructural alteration observed at 28, 35 and 42 postnatal days in 6-OHDA treated rats was characterized by an appearance of myelin-like membranous lamellar bodies in the boutons synapsing with neural soma. In some cases intact small synaptic vesicles were seen around the lamellar body which probably rose from cell membranes in the synaptic area. Most of the necrotic neurons corresponded to the post-synaptic side for the boutons including lamellar bodies. Necrotic neurons displayed a dense cytoplasmic matrix, an increase of polysomes and cisternal swelling in rough ER and in the Golgi apparatus. Membranous lamellar bodes were occasionally observed in the periphery of satellite glial cells, probably oligodendrocytes.
In conclusion, a long lasting reduction of striatal dopamine caused by 6-OHDA might disturb the function around the synaptic area and the metabolic regulation in the postsynaptic striatal neuron, thus resulted in the appearance of rather chronic morphological alterations in those areas.

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The fine structural localization of osmium impregnation in the mouse adrenal cortical cell was studied using the electron microscope. After osmication for 40-48hrs all kinds of adrenal cortical cells of the mouse exhibited a selective localization of osmium impregnation in almost all the cisternae of the smooth endoplasmic reticulum in addition to 1-2 or 3 stacks and vesicles of cis-side of the Golgi apparatus. This fact might be implicated with the steroid hormones which may be localized in the cisternae of smooth endoplasmic reticulum. Moreover, the cisternae of the nuclear envelope, and of the characteristic lamellar body closely related to the smooth endoplasmic reticulum, were also stained with OsO₄.

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For a long time, the occurrence of exocytotic discharge of secretory granules from the typical gonadotrophs (Type 1 gonadotrophs) of the anterior pituitary has been doubted. A simple observation with immunocytochemistry and morphometric examination using transmission electron microscopes indicated an increase in number of surface pits and subsurface vesicles of the typical gonadotrophs after castration, which were confirmed by immunocytochemical reaction with anti-LHβ. Large pits and vesicles were also increased progressively as days after castration advanced. Some large pits contained dense granules or less dense flocculent substance. These findings suggest that the typical gonadotrophs also exert granule discharge by the mechanism of exocytosis and concomitant retrieval of surface plasma membrane by the micropinocytosis.

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