THE AUTONOMIC NERVOUS SYSTEM 475 



painting the inferior mesenteric ganglion with nicotine, showing that the 

 activity of the cells of this ganglion is involved in the process. It has been 

 shown, however, by Langley and Anderson that this is not a true reflex, but 

 is rather analogous to Kuhne's gracilis experiment (cf. p. 255). A'pre- 

 ganglionic fibre arriving at the inferior mesenteric ganglion branches, one 

 branch ending round the cells of the ganglion, while the other branch passes 

 down in the left hypogastric nerve to a cell situated near the base of the 

 bladder (Fig. 241). When therefore we stimulate this nerve we are stimula- 



Sp.cord 



hrf.mes.g.-(^ ' 



^Pre-qanqlionic fibre 



/ \ \ f 



Post-gangliomc fibre 



nerves 



FIG. 241. Diagram to illustrate Langley and Anderson's explanation of the hypo- 

 gastric reflex as an axon reflex. 

 The division of the axon where the propagation or ' reflexion ' takes place is at X. 



ting a pre-ganglionic fibre, and the excitation spreads up to the point of 

 junction of the two branches and then down the other branch to excite the 

 cell in the inferior mesenteric ganglion. We thus obtain an apparent motor 

 reflex by stimulation of a nerve which is itself motor. Similar pseudo- 

 reflexes can be obtained along the abdominal chain on the pilomotor nerves 

 but furnish no grounds for ascribing the property of reflex centres to peri- 

 pheral ganglia. On the other hand, these axon reflexes are very similar to 

 the spread of the excitatory process which occurs in the diffuse nerve network 

 of an animal such as the medusa. Irreciprocity of conduction would seem 

 therefore to be the most useful criterion of a true reflex. 



INHIBITION IN PERIPHERAL GANGLIA 



The existence of ganglion-cells in the course of the nerves to visceral muscles has 

 often been supposed to account for certain peculiarities in the innervation of visceral, 

 as compared with skeletal, muscle. Chief among the differences between these two 

 kinds of muscle ib the frequency with which inhibition may be brought about in visceral 

 muscle by stimulation of peripheral efferent nerves. In skeletal muscle inhibition is 

 only known as the result of alteration of the activity of the motor centres from -which 

 it is supplied. It has therefore been throught that the peripheral ganglia of visceral 

 muscle play the part of the motor spinal centres of skeletal muscle, and that when 

 we excite an inhibitory nerve, say to the intestine, we are interfering with and diminishing 



