Corrosion casts of the blood vascular beds of the rat kidney were prepared with methacrylic methyl ester resin. The casts of the individual glomeruli were isolated and coated with carbon and gold to be observed under the scanning electron microscope.
1. True double efferent arterioles arising separately from the glomerulus were encountered in 11 out of the 1, 200 glomeruli examined. They were independent vessels formed separately by the capillaries of different glomerular lobules.
2. In 55 out of the 1, 200 glomeruli, the normal efferent arteriole arising singly from the glomerulus showed precocious branching at the hilum of the glomerulus. This type of vessel perhaps was described erroneously as two efferent arterioles in previous light microscope studies.
3. Constrictions were often found in the juxtaglomerular segment of the afferent arteriole and rarely in the efferent arteriole. This suggests the occurrence of a sphincter at these sites.
4. A preliminary description of the glomerular casts in juvenile rats was made. Occasional duplication of efferent arterioles was found in 8-day-old rats.
5. Microdissection of the isolated glomerular casts softened by alcohol enabled the observation of glomerular lobules and their capillary connections. For this purpose the use of resin not containing plasticizer was recommended.

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The hypothalamus of adult male mice was investigated with the electron microscope. In all hypothalamic nuclei examined the nerve cells frequently contained nucleolus-like inclusion bodies in the cytoplasm. These inclusion bodies appeared to be composed of the same constituent particles as those of the intranuclear nucleolus. This permits consideration of their probable nuclear origin. The accessory nucleolus, tentatively named in the present paper, appearing to consist of nucleolar material with the association of chromatin was frequently encountered attached to the nuclear membrane and sometimes located at evaginated portions of the nucleus. Moreover, near the nucleus in the cytoplasm, inclusion bodies showing a close resemblance in appearance to the accessory nucleolus except for the absence of the association of chromatin particles were observed to be enveloped with a double membrane probably derived from the nuclear envelope. From these results, it was concluded that the direct translocation of the nucleolar substance of accessory nucleoli into the cytoplasm with an investment of a double nuclear membrane may be possible in nerve cells of the mouse hypothalamus.

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The renal glomeruli in experimental hypertension induced by ligation of the unilateral renal artery in the rat were examined by electron microscopy.
1. The glomeruli in the ligated kidney show no noticeable morphological changes at the level of ultrastructure.
2. In the unligated kidney, glomeruli exhibit varying ultrastructural changes, suggesting the processes of glomerular sclerosis.
3. The early changes in the glomerulus in experimental hypertension is an increase in the filtration of blood plasma proteins and a remarkable response of the epithelium, that is, the phagocytosis of proteinic substances in the epithelial cells is enhanced and mitochondria in the cells are remarkably increased in number. Subsequently, these changes cease and then the epithelial foot processes tend to fuse together.
4. Following the epithelial changes, the endothelial cell shows an abnormal reaction, that is, the endothelial cells protrude many microprojections into the capillary lumen, and then the capillary lumen is gradually narrowed and obliterated and disappears.
5. In the severely damaged glomeruli, the mesangium seems to be increased in amount: this might be attributed to the fusion of basement membrane materials after destruction of the capillary and furthermore to the abnormal deposition of plasma proteins leaking through the endothelium owing to the increased permeability in hypertension.
6. The epithelial cells remain rather unchanged until the late stages of glomerular sclerosis, even after the disappearance of blood capillaries.

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Spleens of the dog and rat were thoroughly washed with Ringer solution through the lienal artery and then perfused with buffered glutaraldehyde. Scanning electron microscope (SEM) observation was made on the cut surfaces of the red pulp. Sections of resin embedded tissues of the same specimens were observed under the transmission electron microscope (TEM).
1. The splenic sinus of the dog and rat was lined by a perforated lattice formed by rod-like lining cells and their cytoplasmic processes as observed in the rabbit (MIYOSHI, FUJITA and TOKUNAGA, 1970), though distinct species variations in the pattern of the lattice were recognized.
2. A transiting sinus lacking in perforations was found by the SEM to intervene between the sinus and the trabecular vein.
3. The Billroth cord was a labyrinthic meshwork of thin reticular cell processes under the SEM. TEM observation revealed reticular fibers either ensheathed or sandwiched by reticular cell processes.
4. The reticular cells were attached to the walls of the vein and the sinus by their thin cytoplasmic processes ending in a sole-like expansion.
5. On the external surface of the sinus, thin cytoplasmic processes from the reticular cell feet emerged mainly transversely to the lining cells. Every side bridge of the lining cells was thus backed by a reticular cell process. The ring fibers sandwiched by both cellular elements could be seen only by the TEM.
6. Large, spherical macrophages were found by the SEM dispersed in the cordal spaces and fixed by some reticular fibers. One type of macrophage was covered by bubble-like processses, while another by foliate ones.
7. The TEM observation revealed lysosomes of fine granular content in the former type of macrophage, and large, dense granules of lysosomal nature and large ingested cell debris in the latter.

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Mucous membrane pieces free of pathological changes were taken from different parts of the colon and rectum of 13 patients by biopsy under direct vision with an colonofiberscope. Electron microscope observation of the tissues gave the following results:
1. At least two different types of basal-granulated cells occur in the human colon and rectum: typical EC cells showing irregular-shaped basal granules and second type cells characterized by large, round basal granules. A few cells with small, round granules are occasionally found but their independent nature is still doubtful.
2. In the colon it is probable that every basal-granulated cell is open in type, i.e., reaches the luminal surface with a cytoplasmic process. In the rectum, at least a part of the cells is open to the lumen but it is unkown whether some cells are closed in type, i.e., devoid of an apical process.

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