Animal physiology / by John G. M'Kendrick.

  • John Gray McKendrick
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Animal physiology / by John G. M'Kendrick. Source: Wellcome Collection.

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    160. Characters of Nervous Matter to the Naked Eye.— Nerve matter is of two kinds, white and gray^ and may be readily seen by cutting through the brain of a sheep or of any other animal, when it will be observed that there is an outer layer of gray matter, while the interior is white. In the spinal cord these relations are reversed, the gray matter lying in the centre. 161. Structii7'e of Nerves.—These consist of a number of delicate fibres, each of which is transparent as glass when examined in a perfectly fresh state, but usually seen with two well-defined lines on each side of a broad clear space. The central part is called the axis cylinder^ and the outer part, the white substance of Schwann. Very minute nerve-tubes, as from those obtained near the surface of the brain (fig. 86, e^f), shew no white substance. The nerve-tubes vary much Fig. 86.—Nerves: Cy ordinary-sized nerve-tube, shewing axis cylinder sur- rounded by white substance; d, smaller nerve-tube, with white substance scarcely visible ; (?, still smaller, with no white substance visible; varicose nerve-tube, from gray matter near surface of brain ; cz, nerve-tube, coloured by perosmic acid, shewing one of the nodes of Ranvier, or complete inter- ruption of the axis cylinder ; 3, nerve-tube shewing nucleus and node of Ranvier (the axis cylinder is blackened by the action of the perosmic acid); non-medullated nerve-tubes from sympathetic, having no white substance, and nucleated at intervals. in diameter. Those of the sympathetic have no white sub- stance. Recently it has been shewn that at certain dis- tances the axis cylinder is interrupted, constituting the so-called nodes of Ranvier. During life, the substance in the interior of the sheath of the nerve-tube (the neurilemma) is in a semi-fluid state, and the conception of a nerve-tube to be formed is, a thin cylinder {neurilemma) inclosing a
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