1. Innervation of smooth muscle was electron microscopically studied in the intestinal muscle coat of the mouse and bat. Interstitial cells of Cajal were found in the intercellular connective tissue especially in the circular muscle layer of the mouse. Many nexuses were demonstrated, especially in the same layer between the smooth muscle cells themselves and between the interstitial cells and smooth muscle.
2. The intercellular connective tissue of the muscle coat contained considerable numbers of small axon bundles which were provided with vesiculated varicosities or terminals on their surface. The vesiculated varicosities bore a naked surface directed towards adjacent smooth muscle cells, suggesting the probable release of transmitter substances acting upon the latter over a wide gap of hundreds to thousands Å (synapse per distance). A subsynaptic cistern was often found beneath the sarcolemma of the smooth muscle cells. In mouse intestinal muscle, small axon bundles and “synapses per distance” were prominent, whereas single axons and close contact synapses were seldom seen. Vesiculated varicosities on the border of the neuropil of the myenteric ganglion suggested the “synapse per distance.”
3. The interstitial cells of Cajal were characterized by slender cytoplasmic processes, ample free ribosomes, numerous pinocytotic vesicles and a basement membrane which incompletely or almost completely covered them. They formed a close contact synapse (200Å wide gap) with the vesiculated varicosity of the axon on one hand, and nexuses with adjacent smooth muscle cells on the other hand, thus forming a terminal link between the autonomic nerve and the smooth muscle. The ultrastructural properties of the interstitial cells suggest that they might represent a particular type of undifferentiated or immature smooth muscle cells.
4. Smooth muscle cells abutting on the myenteric plexus often protruded a tongueshaped process towards the ganglion or the axon bundle connecting the ganglia: The process either adhered to the Schwann sheath or came in direct contact with naked axons, with a narrow gap intervening.

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The sweat ducts of human eccrine and apocrine (ceruminous) glands were observed with the transmission electron microscope. Both the dermal and epidermal segments of the eccrine as well as apocrine ducts consist of two epithelial layers: luminal cells and peripheral cells.
Well-developed microvilli, occurrence of cored vesicles, dense granules, multivesicular bodies and phagosomes in the adluminal filamentous zone, and a strong accumulation of mitochondria in the basal part of the duct epithelium at the dermal segment, as well as an accumulation of small clear vesicles beneath the surface of the luminal cells of the epidermal segment are all prominent in the eccrine duct and concomitant with the special function of the human eccrine duct, i.e., absorption of ions to make the sweat hypotonic and an active endocytosis of some material from the sweat.
All of the above enumerated characteristics of the eccrine duct are only rarely or never seen in the apocrine duct. On the other hand, lipid droplets appear in the peripheral cells in a certain level of the apocrine duct near its orifice into the hair follicle, suggesting a kind of metaplasia towards the sebaceous gland.
Epidermal duct cells of both eccrine and apocrine sweat glands may keratinize. In the eccrine duct the process in the duct cells precedes the surrounding keratinocytes, while in the apocrine duct the relationship is reversed.

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Secretory nerve terminals in the posterior pituitaries of normal rats and animals dehydrated for 1, 3, 5, 7 and 9 days were observed with the transmission electron microscope. Neurosecretory granules were markedly decreased after dehydration and reached the minimum number at 5 days. Small vesicles in the terminals may be classified into two types: one is aggregated vesicles about 53nm in diameter and the other is dispersed vesicles 66nm in diameter. The former vesicles are seen in the normal terminals and slightly decreased in number after dehydration, while the latter are hardly seen in normal pituitaries but increase enormously due to dehydration at 3 days and thereafter. It may be conjectured that the former are the real synaptic vesicles probably containing acetylcholine, while the latter are the fragments of limiting membranes of the neurosecretory granules.
Inversely to the slight decrease of dispersed vesicles at 7 and 9 days of dehydration, reticular tubules in the nerve terminals were strikingly increased in volume. Such a terminal reticulum may be formed by fusion of vesicles derived from fragmentation of the envelopes of neurosecretory granules. Finally the reticulum as well as dispersed vesicles may be destroyed by lysosomes.

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Monoamines in the taste bud cells of the mouse circumvallate papilla were studied by fluorescence histochemistry and electron microscopy. With administration of 5-HTP (5-hydroxytryptophan) after a pretreatment with nialamide, yellow fluorescence appeared in some of the taste bud cells, while no fluorescence was observed in untreated, L-DOPA treated or serotonin treated mice.
Electron microscopic study after treatment with both nialamide and 5-HTP showed small dense-cored vesicles intermingled with small clear vesicles (30-60nm in diameter) accumulated at the membranes of the gustatory cells in typical afferent synaptic contacts with nerve terminals. Definite ultrastructural change in large dense-cored vesicles (70-100nm in diameter) could not be observed.
It is suggested that the gustatory cells of the mouse take up 5-HTP and convert it to serotonin. The synaptic vesicles in the gustatory cells are believed capable of storing and releasing serotonin which presumably acts as the neurotransmitter involved in the impulse transmission from the gustatory cells to the sensory nerve fibers.

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A second population of cytoplasmic microvesicles was constantly recognized in the SGC (small granule chromaffin) cells of the mouse adrenal medulla by means of transmission electron microscopy in glutaraldehyde/osmium tetroxide-fixed material. The microvesicles were rounded in shape and of mean profile diameter of between 30, 40nm; some contained several dense precipitates. The vesicles were usually dispersed throughout the cytoplasm among the typical secretory granules of 100-230nm in profile diameter, though they occasionally formed aggregations. The SGC cells were also characterized by a high nucleus to cytoplasm ratio, rich innervation, and long cytoplasmic processes which were traced up to 30μm.
Co-existence of the synaptic-like vesicles and secretory granules in the SGC cells suggests that they may represent an intermediate position between the chromatin and sympathetic nerve cells.

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