The general structures of the pars intermedia of the rat hypophysis including two kinds of light cells, dark cells, marginal zone, cysts and nervous elements were described, and effect of dexamethasone on the pars intermedia, especially on the light cells of the first type of intact and experimental rats was studied by electron microscopy.
Three hours after a single injection of dexamethasone secretory granules of the light cells of the first type were extremely increased in electron density, but after 3 weeks the electron density of the granules was decreased nearly to the normal level.
Prolonged daily injection of dexamethasone caused a cumulative effect on the light cells as an increase of dilated endoplasmic reticulum at 7 days and considerable degeneration of whole cells at 10 days.
One day after adrenalectomy the light cells which were also treated with dexamethasone 6 hours after the operation contained numerous clear vesicles, while in later adrenalectomized animals which received dexamethasone 24 hours prior to sacrifice the cells successively increased their dark secretory granules from 3 to 7 days and reached the maximal number at from 10 to 14 days after the operation. Four weeks after adrenalectomy the light cells appeared to have a large cell volume and to contain granules of various densities, extensive Golgi apparatus and cisternae of the endoplasmic reticulum filled with dense material.
Two and a half minutes after laparotomy, the light cells which were pretreated with dexamethasone 24 hours before the operation contained a mixture of dark and light granules. The dark granules were decreased in number one day after the operation and were replaced by electron lucent vesicles 3 days after the operation.
These results apparently indicated that the release of granule content of the light cells of the pars intermedia was inhibited by dexamethasone which had been known to prevent a release of ACTH from the adenohypophysis, and that the pars intermedia responded to stressful stimuli such as adrenalectomy and laparotomy, showing morphological alterations of the density of secretory granules. The morphological changes showed a good parallelism with changes of blood and pituitary ACTH concentrations. From these findings two possibilities may be suggested either the pars intermedia cells might produce an ACTH-like substance, or the intermedia hormone might be a precursor of ACTH in biosynthesis in the pars distalis.

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In normal human livers obtained in surgical operations the sinusoidal wall has been observed with the electron microscope.
The “endothelial cells” and the “Kupffer cells” lining the sinusoid are regarded as two functional states of the same cell lineage and show alike the ultrastructures suggesting phagocytic activity. They differ from each other especially in that the endothelial cells consist of two distinct portions, the perikaryon and the sheet-like cytoplasmic extension, the latter occupying the major part of the sinusoidal lining, while the Kupffer cells are of simple rounded-up form bulking into the sinusoidal lumen; the endothelial cell sheets extend to the Kupffer cell body to contact with the latter. On the other hand, the marginal ends on the neighboring endothelial sheets may overlap like roof tiles. In both connections there occur no functional structures like terminal bars and desmosomes.
The endothelial lining of the sinusoid which is discontinuous because of the presence of intracellular gaps or pores and lacking in general in continuous basement membrane, is as a rule a simple layer. Frequent figures of stratified endothelial sheets are caused for the most part by the occurrence of subendothelial fat-storing cells which extend thin processes as if to reinforce the endothelial lining. The perisinusoidal or Disse's space is filled with blood plasm filtered through the discontinuous endothelial lining of the sinusoid. This space which represents the blood-tissue barrier of the liver contains, besides abundant microvilli of the hepatocytes and collagen or reticular fibers and fibrils, fat-storing cells, unmyelinated nerve fibers with their Schwann cells and occasional round, probably hemopoietic cells. The fat-storing cells are constant residents in the Disse's space and frequently extend into the recesses between the hepatocytes. They are lacking in their own basement membrane and contact directly with the collagen fibers, which are sometimes embraced in the invaginations of their plasma membrane. They send out a considerable number of cytoplasmic processes in the Disse's space which interlace with the microvilli of the hepatocytes. Close contacts between the even surfaces of the fat-storing cells and of the hepatocytes are occasionally encountered.
The fat-storing cells possess relatively well-developed Golgi complex containing a diplosome, sparse small mitochondria, fairly well-developed elements of granular endoplasmic reticulum, small lysosomes, glycogen particles and, occasionally, a single cilium into the Disse's space which arises from one of the paired centrioles of the diplosome. Though the fat-storing cells exhibit no cytological signs indicating a phagocytic activity, many invaginations of the plasma membrane and vesicles including the bristle-coated ones are found along their free surfaces suggesting a vigorous pinocytotic activity. As constant and characteristic cytoplasmic inclusion bodies, the fat-storing cells contain small fat droplets, each of which (about 2μ in diameter) is bounded by a weak limiting membrane and does not fuse with each other into larger ones. The fat-storing cells may occasionally contain no fat droplets; the “pericytes” observed by some authors in the Disse's space, probably correspond to these empty fat-storing cells.
The following possible functions of the fat-storing cells are proposed: 1) Fat synthesis and fat-droplet formation, 2) the storing of fat droplet and fat-soluble vitamin A, 3) the participation in intralobular fibrilogenesis and 4) the reinforcement of the endothelial lining of the sinusoid by sending subendothelial processes.

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In ferrets born in June, testicular development started in December and reached maturity by February. The functional period lasted from March until July. The period of quiescence extended from August until December, redevelopment beginning again in January, and reaching the second functional period in March. Infantile testes were characterized by the lack of a germinal cycle, by undifferentiated precursors of Sertoli cells, by the absence of a tubular lumen, and by small interstitial cells. The prepubertal testes become large as a result of the development of the germinal epithelium, and tubular lumen, and by virtue of the growth of the Sertoli and interstitial cells. In the degenerating testis, there was no germinal cycle, and the tubule lumen was filled with structureless matrix, bounded immediately by primitive Sertoli cells, and externally by inactive interstitial cells. The histological appearance of the redeveloping testis resembled that seen at the prepubertal stage. Regular periodic changes were also observed in the thickness of the tunica albuginea and basement membrane, in the diameter of the tubules and cellular composition of germinal epithelium, and in the appearance and location of glycogen and RNA in the testis.

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