豚の鼻皮における求心性神経終末

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  • Afferent Nerve-Endings in the Snout-Skin of a Pig

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A report is made of the end-apparatuses of afferent nerves and their relations to other cells in the snout-skin of an adult pig.<br>Thirty μ frozen sections were impregnated by SUZUKI's modified BIELSCHOWSKY's silver-method. The results obtained are as follows:<br>1. In the epithelium of the snout-skin there occur two sorts of intraepithelial nerve-endings, i. e., main thick fibers which are derived from myelinated fibers and accessory thin fibers that may be primarily of an unmyelinated nature. A few accessory fibers run closely around the main fiber. The main fiber terminates at the uppermost germinal layer with small end-knobs. Both intraepithelial nerve fibers, main and accessory, pass either through the intercellular space or through the cytoplasm of epithelial cells. Knob-like endings are generally situated inside the cytoplasm of the cells forming small vacuoles, not neurofibrillar net-balls. No visualisation was made of the cylindrical columns of epithelial cells associated with intraepithelial nerve fibers, as described by BOEKE in EIMER's organ of a mole.<br>2. In the basal part of the epidermis between coriale papillae there occurs an aggregation of so-called MERKEL's tactile cells. Careful observations led to conclude that there might be two varieties, as reported by IMAKO, in the outer layer of the root-sheath of the tactile hair in a golden hamster. The one belongs to the first type of tactile cell after IMAKO-SUZUKI, in which a nerve fiber terminates in its cytoplasm under the flat nucleus forming a disc-like termination with a vacuole. The other constitutes the second type of tactile cell after IMAKO-SUZUKI, in which there are found neither disc nor vacuole, and the nerve fiber terminates in the cytoplasm simply forming the reticulum with fine meshes around the nucleus. It became clear on careful observations of frozen sections that the second type cells occur less than the first type cells in the pig's snout-skin. The mode of nerve innervation on tactile cells shows a close resemblance to the structure of a rosary. A branch of the nerve fiber passed through each cells to form a series of tactile cells. On its way through the cytoplasm, the nerve fiber swells to shape a knob-like termination. Unlike many author's observations on the tactile cells the present author agreed with BOEKE's observation that the so-called tactile meniscus or disc was situated inside the cytoplasm.<br>3. In the corium under epithelial papillae there occur a kind of corpuscular sensory end-organ. This organ belongs to a type of club-like end-bulb which shows often many windings and twistings. It is covered with a thin capsule of the connective tissue which is likely to be an elongated endoneural sheath of HENLE, and to be composed of two intracapsular bulbs, the dark inner one and the light outer one. Between these two bulbs there exists a thin lamelle with lenticular or oval nuclei. As this thin lamelle was assumed to be a deformed SCHWANN's sheath, the inner bulb might probably be a prolonged medullary sheath of the myelinated fiber. The outer bulb is composed of a homogeneous substance, being devoid of a lamellar structure, as seen in corpuscles of PACINI and TIMOFEEW. The band-like sensory terminal fiber runs into the axis of the inner bulb. Sometimes the terminal fiber bifurcates in the core, but its convolution and ramification are not marked. In many cases it ends at the top of the core forming a vacuole due to the enlargement of neurofibrils, but in a very few cases it terminates only with a fibrillar expansion. It never ends with a sharp spearhead appearance. In a core involving the terminal fiber, there were found small argyrophilic granules and argyrophilic striae, but no thin accessory unmyelinated fiber or ‘Faden-apparat’ of TIMOFEEW. In spite of careful observations an aggregation of coriale tactile cells could not be identified.

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