PEKIPHEEAL-NERVE BOOTS, SPINAL GANGLIA, SPINAL COED. 



333 



It is an important question, however, whether, in reality, all sensory 

 nerves arise from cells in the spinal ganglia. The experiment of Waller, 

 since oftentimes successfully repeated, answers it completely. 



Every nerve-fibre, separated from its source, degenerates. If one out the fibers 

 of a sensory nerve across, just peripheral to the spinal ganglion, all its fibers de- 

 generate, while the ganglion itself and the fibers leaving it to form the corresponding 

 root of the cord remain fairly normal. This shows that all the fibers have been 

 divided from their cells. If the section be made of the root close to the ganglion, 

 but few of the fibers in the sensory nerve die; the majority retain their vitality. 

 These fibers must, therefore, spring from the cells of the ganglion, for they remain 

 in connection with them. The few fibers of the nerve which have degenerated must 

 arise in the cord itself, because separated from it alone, and not from the ganglion. 



Fig. 214. — Scheme of the fibers in a spinal ganglion. Hintere Wurzel, 

 Posterior root. Sens. Nerv., Sensory nerve. 



In fact, examination of the spinal root furnishes the proof of this. The root, being 

 separated from its ganglion, is found to contain only a few living fibers, the ma- 

 jority being degenerated. The intact fibers must arise from cells in the cord, as 

 they remain in connection with such cells only; the degenerated fibers must come 

 from the ganglion, because they are divided only from it. {Cf. the text on pages 

 6 and 7.) 



These experiments show that from the ganglion-cell processes pass in 

 two directions, and that there are other processes from the cord which only 

 pass through the ganglion. Probably there are still other fibers from pe- 

 ripheral (sympathetic) cells which end in the eord,_(Fig. 33). Accordingly 

 one may consider the relations of the sensory roots to the spinal ganglia 

 much as represented in Fig. 214. 



