530 PHYSIOLOGY 



divide all the nerves going to the inferior mesenteric ganglion, leaving 

 the bladder connected with the inferior mesenteric ganglion only 

 by the hypogastric nerves, and then after dividing the left nerve 

 stimulate its central end, we obtain a contraction of the right half 

 of the bladder. This eflect is abolished by 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 , ho we ver , 

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



Sp.cord 



^Pre-qanqlionic fibre 



Post-gangliomc fibre 



Hypogastric nerves 



FIG. 239. 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, 



analogous to Kuhne's gracilis experiment (cf. p. 285). 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. 239). When therefore we stimulate this nerve we 

 are stimulating 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 abdo- 

 minal chain on the pilomotor nerves, but furnish no grounds for 

 ascribing the property of reflex centres to peripheral 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. 



