A text-book of physiology for medical students and physicians . ached to the ganglion remains intact, and there is nodegeneration in the nerve peripheral to the ganglion (Fig. 55). If,however, this root is severed peripherally to the ganglion degenera-tion takes place only in the spinal nerve beyond the ganglion. Thenutritive center, therefore, for the sensory fibers must he in the pos-terior root ganglion, and not in the cord. This conclusion has also ?Waller, Mullers Archiv, 1852, p. 392; and Comptes rendus delAcad. de la Science, vol. xxxiv., 1852. 126 THE PHYSIOLOGY OF MUSCLE AND NERVE. be
A text-book of physiology for medical students and physicians . ached to the ganglion remains intact, and there is nodegeneration in the nerve peripheral to the ganglion (Fig. 55). If,however, this root is severed peripherally to the ganglion degenera-tion takes place only in the spinal nerve beyond the ganglion. Thenutritive center, therefore, for the sensory fibers must he in the pos-terior root ganglion, and not in the cord. This conclusion has also ?Waller, Mullers Archiv, 1852, p. 392; and Comptes rendus delAcad. de la Science, vol. xxxiv., 1852. 126 THE PHYSIOLOGY OF MUSCLE AND NERVE. been abundantly corroborated by histological work. It is knownthat the sensory fibers arise from the nerve cells in these the same means it has been shown that the motor fibers in thecranial nerves arise from nerve cells (nuclei of origin) situated inthe brain, while the sensory fibers of the same nerves, with theexception of the olfactory and optic nerves which form special cases,arise from sensory ganglia lying outside the nervous axis, such, for. Fig. 55.—Diagram to show the direction of degeneration on section of the anteriorand the posterior root, respectively. The degenerated portion is represented in black. instance, as the spiral ganglia of the cochlear nerve, or the gan-glion semilunare (Gasserian ganglion) of the fifth cranial nerve. Nerve Degeneration and Regeneration.—When a nervetrunk is cut or is killed at any point by crushing, heating, or othermeans all the fibers peripheral to the point of injury undergo de-generation. This is ,an incontestable fact, and it is important tobear in mind the fact that the definite changes included underthe term degeneration are exhibited only by living fibers. Adead nerve or the nerves in a dead animal show no such changes.*The older physiologists thought that if the severed ends ofthe nerves were brought together by sutures they might uniteby first intention without degeneration in the peripheral know now that
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