584 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



Langley would explain the discharge of these reflexes (axon reflexes') in 

 the following manner. Nerve fibers, as we know, convey impulses in both direc- 

 tions; hence an impulse starting from R (Fig. 258) is transmitted along the 

 efferent fiber toward the ganglion (A). Here a collateral is given off, and it is 



FIG. 258. Schema of an axon reflex through peripheral ganglion cells, after Langley. 



this which excites the nerve fibers springing from the cells of the ganglion and 

 proceeding to the bladder (B). 



In a similar manner Langley explains the fact that stimulation of the lum- 

 bar sympathetic causes an erection of hairs on regions of the skin innervated 

 from the second, third, and fourth ganglia higher up (cf. Fig. 259), and similar 

 phenomena from stimulation of the sympathetic in the thorax. 



We must be on our guard in this matter of reflexes through peripheral gan- 

 glia lest we be deceived by recurrent fibers. Suppose, for example, A (Fig. 260) 

 to be a ganglion, 2 and 3, two nerve fibers passing from it. We stimulate 2 and 



FIG. 259. Schema of a reflex through peripheral ganglion cells, after Langley. Sp.y., sympa- 

 thetic ganglia. The arrows indicate the direction in which the excitation aroused by stimula- 

 tion of a lumbar sympathetic nerve is propagated. 



get an effect in the organ innervated by 3. Such an effect may be a reflex; but 

 it would be obtained also if some of the nerve fibers in 2 were to turn back and 

 enter 3, as indicated by the dotted line. 



The chief purpose of the spinal ganglia consists in the purely nutritive 

 influence by which not only their afferent nerve fibers, but the posterior roots 

 and their prolongations and collaterals in the spinal cord as well, are main- 

 tained in normal condition. 



Since most of the cells of the spinal ganglion give off only one process which 

 sooner or later splits into two fibers (the T-shaped fibers), one going each way, 

 it might be supposed that the stimuli coming from the periphery are conveyed 

 directly to the spinal cord without having anything to do with the ganglion cell. 



This question can be tested experimentally by determining whether a stimu- 



