638 



THE AUTONOMIC NERVOUS SYSTEM 



that, in the lower forms, its cells are typically bipolar, while in the 

 mammals they are unipolar, possessing a single process which divides 

 into two branches, one of which enters the spinal cord and the other, ' 

 the spinal nerve. As commonly conceived, the function of these 

 fibers is to conduct impulses from the periphery to the posterior region 

 of the spinal cord. Naturally, the severance of the corresponding pos- 

 terior root would render these fibers useless for reflex action, because 

 they would thereby be disconnected from their efferent channels 

 and motor-organs. A moment ago, however, we have noted that the 

 spinal ganglia receive certain afferent fibers from 

 the sympathetic system. Under experimental con- 

 ditions these afferent sympathetic fibers may also 

 be made to conduct in a centrifugal or eft'erent 

 direction. It need not surprise us, therefore, to 

 learn that the stimulation of these spinal ganglia 

 frequently gives rise to vasodilator effects in that 

 region of the body from which the aforesaid afferent 

 fibers have been derived. It is highly improbable 

 that an effect of this kind is produced under normal 

 conditions, although it may arise in consequence of 

 inflammatory reactions in the region of the spinal 

 ganglia, multiple neuritis and other conditions. 



While our search for axon-reflexes within the 

 realm of the cerebrospinal system has thus proved 

 negative, it cannot be doubted that the ganglia of 

 the autonomic system are well adapted for this 

 form of reflex action, because practically every one 

 of them is a reflex center .dominating the function 

 of a rather circumscribed region of the body. No 

 definite facts, however, are at hand to prove that 

 the sympathetic system is especially constructed 

 for true axon-reflexes. The example usually given 

 is the following: If the inferior mesenteric ganglion 

 (Fig. 315) is isolated from the central nervous 

 system by the division of its preganglionic path 

 (P), but is left in functional relation with the blad- 

 der (B) through the two hypogastric nerves (H), the stimulation 

 of the central end of one of these nerves invariably evokes a con- 

 traction of the musculature of the opposite half of this organ. If 

 the aforesaid ganglion is now moistened with a solution of nicotin, 

 this motor effect cannot be obtained. The conclusion to be de- 

 rived from this experiment is that this ^' reflex'^ cannot be effected 

 without the help of the cells of the inferior mesenteric ganglion, but 

 since the normal conditions of conduction have been reversed in this 

 case, we cannot justly regard this reaction as a true reflex. For this 

 reason, Langley and Anderson^ have applied to it the term of pseudo- 

 1 Jour, of Physiol., xvi, 1894, 410. 



Fig. 315.— Dia- 

 gram Showing Ner- 

 vous Innervation 

 OF Bladder. 



C, Spinal cord; 

 JM, inferior mesen- 

 teric ganglion; P, 

 preganglionic path ; 

 Po, post-ganglionic 

 path formed by H, 

 the hypogastric 

 nerves; B, bladder. 



