The conduction system of the dog heart was studied morphologically and histochemically.
Seventy five fresh hearts of dogs of both sexes were examined partly in sections (hematoxlyin-eosin, azan, Masson-Goldner trichrome staining and periodic acid-Schiff reaction) and partly in macroscopic preparations treated with iodine reaction and modified PAS reaction (OTSUKA and HARA 1965). The following findings were obtained.
1. The sinus node is composed of an irregular network of muscle fibers finer than the ordinary auricular muscle. They are richly ramified and contain a few myofibrils and abundant sarcoplasma. Connective tissue fibers intervene among the nodal fibers. The sinus node has no clear-cut boundary. Each nodal fiber shows smooth transition to an ordinary muscle fiber at the periphery of the node. A specialized muscular pathway connecting the sinus node with the atrioventricular node is not recognized.
2. The atrioventricular node consists of the posterior and anterior portions. The former is close to coronary sinus-orifice and the latter continues to the atrioventricular bundle. Histologically, the former resembles the sinus node and the latter the atrioventricular bundle. Between the two, there is no boundary. The atrioventricular node is found in the connective tissue of the anulus fibrosus and separated from the ordinary heart muscle. In the posterior part of the atrioventricular node, there is a muscular pathway connecting the right auricle with the atrioventricular node. This pathway consists not of specialized, but of ordinary auricular muscle fibers. There is no other “bypass tracts” (JAMES 1963) between the atrium and the atrioventricular node.
3. The atrioventricular bundle is composed of thick fibers with few ramifications. They are rich in sarcoplasma and glycogen and poor in myofibrils when compared with ordinary cardiac muscle fibers. This specialized tissue resembles that of ungulates. These fibers first run forming a single bundle, then fork into two main bundles, right and left.
4. The right main bundle courses in the subendocardium as a single cord, drawing an arch (convex to pulmonary conus), without branching. Ariving at the anterior papillary muscle, it issues branches for 3 areas: for the conus pulmonalis, for the free wall, and for the septum.
5. The left main bundle becomes visible beneath the aortic valve as a wide bundle and spreads over the subendocardium as a fimbria, giving three groups of branches. Branches of the first group run toward the anterior papillry muscle via pseudotendons. Those of the second group reach the posterior papillary muscle via pseudotendons and give rise to a very thick distribution of Purkinje fibers to the left ventricular free wall. The third group of the peripheral branches spreads directly over the septum without passing pseudotendons.
6. The network of Purkinje fibers in the subendocardium is the thickest on the free wall of the both ventricles and the thinnest on the right side of the interventricular septum.
7. There is much glycogen throughout the conduction system, especially in the atrioventricular bundle and Purkinje fibers. The glycogen is less soluble in water compared with that of the ordinary heart muscle. Physiological meaning of this glycogen is not yet clear.

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The basal clear cell in the gastric gland of the rat and mouse was studied by means of autoradiography after injection of H³-dihydroxyphenylalanine (H³-DOPA), H³-5-hydroxytryptophan (H³-HTP), H³-tyrosine, C¹⁴-5-hydroxytryptamine and H³-tryptophan. The results were as follows.
1. After injection of H³-DOPA and H³-HTP, the characteristic strong radioactivity appeared in the basal clear cells as compared with the chief cells and parietal cells of the gastric glands.
2. The radioactivity in the clear cells was higher on the nucleus than the cytoplasm up to 15 minutes after the intraperitoneal injection of H³-DOPA or up to 30 minutes after the subcutaneous injection of H³-DOPA in contrast with the other amino acids used.
3. The radioactivity in the clear cells after the injection of H³-DOPA, decreased or vanished by the pretreatment, the simultaneous treatment and the posttreatment with α-methyldopa or reserpine.
4. The basal clear cells revealed some differences among them in the ability of incorporation of the amino acids.
6. Moderate radioactivity appeared on the argyrophile cells after the injection of H³-HTP.
From the results mentioned above, it is supposed that the basal clear cells, showing different phases of activity, might be the main sites of amine synthesis in the rat stomach, and more active than the enterochromaffine cells.

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The saccus vasculosus of the globefish, Spheroides niphobles, was studied by means of electron microscopy.
The cytoplasm of the coronet cells is characterized by an elaborate network of tubular or cisternal agranular endoplasmic reticulum extending from its basal region to the apical cytoplasmic protrusion. Near the cytoplasmalemma in the apical cytoplasmic protrusion, from the upper part of which spoon-like globules with a stalk project radially into the saccus cavity, are scatterd also small dense granules with a distinct limiting membrane about 500Å in diameter. The cilium in each stalk is a hollow cylinder which consists of nine pairs of peripheral tubules, lacking the central ones. The cytoplasm of the globules is occupied by a large number of tubules and vacuoles of various sizes, many of which contain dense granules about 400Å in diameter. Though not very often, openings of these tubules and vacuoles into the saccus cavity can be observed. The most striking feature of the globules is that all the membrane-limited structures including the plasmalemma possess at their cytoplasmic surface a pelage about 300Å in thickness which consists of cloud-like material. Its histochemical property is discussed in connection with the possible function of the coronet cell. Within the saccus wall can occasionally be seen bundles of unmyelinated nerve processes. There are distinguished two types of nerve endings: One is characterized by a number of small vesicles with and without dense cores about 500Å in diameter while the other is, on the average, of smaller caliber and contains only a few empty vacuoles and a number of scattered glycogen particles. The basal region of the coronet cells does not reach the basement membrane of capillaries, but both structures are separeted by a cytoplasmic layer of the supporting cells which encloses the coronet cells.

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Light and electron microscopic observation was carried out on the duct of eccrine sweat gland surgically obtained from human axilla.
1. Between the secretory and coiled portions of the duct, a short transitional portion (ITO and ENJO, 1949) was confirmed to exist.
2. The coiled portion comprises double-layered cuboidal cells-surface and basal cells. The former are provided with cuticular border which contains massed tonofilaments presumably serving as an architectural support. The surface of the cuticular border is protruded into the lumen as numerous microvilli which show pictures suggesting microapocrine secretion. Over the whole layer of cuticular border, there occur numerous vesicles containing droplets and particles identical with those found in the duct lumen. This finding implies pinocytotic activity in the cuticular border and favours the hypothesis of reabsorption of certain constituents of sweat, e. g. sodium and chloride, in the duct epithelium.
3. Both the surface and basal cells of the coiled portion are characterized by richness in mitochondria, tonofilament bundles, free ribosomes, smooth vesicles and multivesicular bodies, and by a small Golgi complex. Electron lucent glycogen areas are demonstrated only in the cytoplasm of the basal cells.
4. The transitional portion is represented by a layer of cuboidal cells interruptedly attached by a layer of flattened basal cells. The cuboidal cells possess a few microvilli and apical cytoplasmic projections but neither cuticular border nor distinct intercellular interdigitations. The cytoplasm of the cuboidal cells is characterized by abundant perinuclear tonofilaments, a large Golgi complex composed of prominent lamellae and numerous vesicles, a large amount of free ribosomes and a small number of mitochondria containing numerous intramitochondrial granules. Elongated dense bodies of unknown nature containing microtubular structures are also recognized in the cytoplasm.
5. As the most conspicuous finding of the cuboidal cells of the transitional portion, numerous vesicles occur in the peripheral, especially apical, regions of the cytoplasm which show every morphological feature characteristic of pinocytosis or reverse pinocytosis. This and other observations have lead the authors to the conclusion that the cuboidal cells of the transitional portion also, and even most vigorously, reabsorb certain constituents of the secretion of sweat gland by means of pinocytotic activity. The absorbed substance is believed to be transported, presumably under participation of Golgi complex, to the cell basis to be discharged into pericellular spaces. The flattened basal cells may play a subsidiary role for the transport of substance.
6. The secretion from the secretory cells of the human eccrine sweat gland, while flowing first through the short transitional portion and then through the long coiled portion of its duct, is thus believed to be subjected to successive reabsorption by the lining epithelia.

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The sympathetic ganglion of the toad was studied with the electron microscope.
The ganglion cells can be divided electronmicroscopically into the clear and dark cells because of their different concentration and shape of the Nissl substance in the cytoplasm.
Electron dense granules of 80 to 150mμ in diameter are occassionally observed in the Golgi regions of the ganglion cells. They are very similar in fine structure to the so-called granular vesicles in the presynaptic terminals of the sympathetic axons.
The granular cells in the ganglion have, in many respects, the morphological analogy to chromaffine cells in higher vertebrates. They are occassionally located adjacent to larger blood vessels in the ganglion.
Furthermore, the endothelial cytoplasm of the blood vessels sometimes contain specific granules similar in size and structure to those found in the granular cells.
These last two results suggest that the granules in the endothelial cells may be originated from the granular cells and that the granular cells may have a glandular character like adrenomedullary cells.
Morphological changes in synapses after intense presynaptic volleys are observed. In the stimulated ganglia, synaptic vesicles are often arranged in a regular array being clustered like a crystalloid at a short distance away from the synaptic membrane. This characteristic distribution of the synaptic vesicles after the electrical stimulation may be related to the synaptic blockage which may occur in the neurons during the prolonged stimulation.

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Using the light and electron microscope, the authors studied on the alteration of the seminiferous tubule of the rat testes 5, 10, 20, and 30 days after hypophysectomy.
In all the experimental animals, no normal matured sperms were observed by light microscopy.
The spermatogonia show no marked changes in fine structure even 30 days after the operation.
The characteristic changes are seen in the spermiogenesis in the hypophysectomized animals.
All the spermatids seem to degenerate at the stage of the acrosomal formation. The degenerative process is as follows; (1) elongation and dilatation of the smooth endoplasmic reticulum, (2) alteration, destruction and disappearance of the mitochondria and of the Golgi apparatus, (3) decrease in number of polyribosomes, (4) deposit of the heterogeneously dense substances in the cytoplasmic matrix, and (5) alteration of the nucleus.
The degenerative spermatids are considered to be phagocytized in the Sertoli cell. The dense bodies containing myeline figures and heterogeneously dense materials, and lipid droplets are markedly increased in number and size in the Sertoli cells of all the experimental animals. The acid phosphatase reaction is strongly positive in the dense body, but not in the lipid droplet.
In the spermatid of the early degenerative process, the reaction product of the acid phosphatase is also recognized in the Golgi zone.

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