

6So SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



peripheral nerve cells, and chiefly through nerve cells in the inferior 

 mesenteric ganglion. The same effect is produced by degenerative 

 section of the inferior splanchnics, i.e. the nerve strands running from 

 the spinal cord to the inferior mesenteric ganglion. .Further, the 

 observations tend to show that the same effect is also produced by 

 degenerative section of the roots of the nerves which send efferent 

 fibres to the various viscera in question. And we may conclude that 

 the reflexes are produced by efferent fibres proceeding from the spinal 

 cord, and having some connection with the nerve cells of the inferior 

 mesenteric ganglion. In this case the method of connection can in 

 principle hardly be other than that shown in C, Fig. 315. Some of the 

 efferent fibres from the spinal cord (pre-ganglionic fibres), instead of 

 sending all their terminal branches to the inferior mesenteric ganglion, 

 send one or more to it, and one or more down the hypogastric of the 

 same side to aberrant, more peripheral, ganglia ; of the former, some 

 are in connection with cells which send their axons down the opposite 

 hypogastric. Thus, on stimulation of the central end of one hypogastric, 

 impulses pass up the motor fibres, and spread out in their branches to 

 some of the cells of the inferior mesenteric ganglion of the opposite side. 



Pseiic/o- rsf/fx 



Keflex 



Fig. 316. 



Common Sc/te/n r 



The mechanism of these actions is not that which has been ordi- 

 narily understood as the mechanism of a reflex action. In the latter, 

 special afferent fibres form an essential part of the machinery. So that 

 it is clearly advisable to use some other term than " reflex " for those 

 actions which are brought about by stimulating the central ends of 

 efferent fibres. A good term is not very easy to find. I shall speak of 

 them as pseudo-reflex actions. 1 



Morphologically, a pseudo-reflex action does not differ in principle 

 from a reflex action which is produced by stimulating a nerve trunk. 

 This will be seen on comparing the diagrams, A, B, and C of Fig. 316. A 

 represents a simple reflex action, and B a pseudo-reflex action, and each 

 of these can be reduced to the form C. 



In normal conditions, it does not seem probable that pseudo-reflex 

 actions are often brought into play. So far as the experiments have 

 gone, a nervous impulse set up in a post-ganglionic fibre cannot pass 

 back through the nerve cell, so that the only way of setting up a 

 pseudo-reflex action is by excitation of pre-ganglionic fibres, i.e. of 

 nerve trunks and of ganglia, and not of peripheral endings in the 

 autonomic tissues. Fig. 317 will serve to make this point clear. 



1 They might perhaps be called "deflected " or " deflex " actions. 



