INNERVATION OF THE DIGESTIVE TUBE 187 



ent chains. According to this doctrine, the only sensory neurones 

 associated with the sympathetic nervous system are the visceral 

 afferent neurones whose cell-bodies are located in the cerebro- 

 spinal ganglia. According to this scheme, all sympathetic reflexes 

 involving sensory neurones must involv^e an entire afferent and 

 an entire efferent chain. Local reflexes involving only sympa- 

 thetic elements, if they occur at all, can occur only as axone- 

 reflexes involving only excitatory neurones. 



This conception of Langley regarding the physiological relation- 

 ships of the sympathetic neurones is based largely on the results 

 of experimental methods which are, doubtless, better adapted to 

 determine the constitution of the visceral afferent and the visceral 

 efferent chains than to determine whether or not local reflexes 

 invoh'ing sensory and motor elements occur in tlie peripheral 

 sympathetic plexuses. 



The facts presented in this paper strongly suggest that the sym- 

 pathetic system, like the other functional divisions of the nervous 

 system, is essentially a system of reflex arcs, involving both sen- 

 sory and motor neurones, some of which are strictly local in char- 

 acter, wliile others are less local or even involve centers in the 

 cerebro-spinal nervous system. 



That local reflexes occur in the peripheral sympathetic plexuses 

 is shown by experimental observations. Recent experimental in- 

 vestigations, notably those of Bayliss and Starling ('99), Cannon 

 ('06) and Auer ('10), have shown conclusively that the motor 

 activities of the digestive tube may be carried on more or less 

 normally for a considerable period after the ner"^es connecting the 

 digestive tube with the cerebro-spinal nervous system have been 

 severed. The possibility that axone-reflexes may occur under 

 such circumstances is not precluded. Furthermore, it is well 

 known that the effect of adrenalin on involuntary muscles is the 

 same as the effect of sympathetic stimulation. Nevertheless; in 

 view of the fact that, as shown in this paper, some of the neurones 

 in the submucous plexus send their dendrites into the gastric folds 

 and plicae and the intestinal villi where many of them terminate 

 on cells of the digestive epithelium, it is highly probable that 

 these neurones are stimulated either directl}^ or indirectly by the 



