30 THE INTERNAL SECRETIONS 1920 



supply has been called by Langley 21 the "enteric ner- 

 vous system" and it governs the entire tract from the 

 esophagus to the rectum. He mentions the fact that 

 the character of their connections with the autonomic 

 system and their control of the gastroenteric tract is 

 little known, but that they seem to have an action inde- 

 pendent of the central nervous system. This has been 

 ably proven by Cannon 22 in his experiments, and he con- 

 cludes that when this canal is entirely separated from 

 the central nervous system it has a remarkable power 

 of developing an independent tonic state, that is, it soon 

 recovers its tone. This shows that it supplies the resil- 

 iency that causes the state of tension when the canal 

 was filled. This tension is the occasion for the contrac- 

 tion of viscera, which are walled with smooth muscle, 

 holding a nerve plexus. That this tonicity is funda- 

 mental is accounted for in the failure of efferent motil- 

 ity in atonic states. 



It is a common observation that tonic contraction and 

 rhythmic peristalsis disappear in asthenic and exhaus- 

 tive states, and Cannon's conclusions agree with these 

 observations that anxiety, morbid fear, worry, mental 

 distress, and kindred disorders lessen or stop gastro- 

 enteric movements, and decrease or abolish the tonus of 

 the alimentary canal. 



There is still considerable difference of opinion as to 

 the make-up of the afferent nerves of the vegetative 

 system. Some investigators believe the afferent nerves 

 contain somatic fibres, and yet, if so, why should there 

 be a difference in their functional activity? It is well- 

 known when pain is experienced in the viscera that it is 

 usually due to a mechanical cause, and its action upon 

 the body is, as Head terms it, reflex. This has been 

 shown by Sherrington 23 to be due to an elevation in the 

 threshold of the excitability of the arc in the viscera. 

 This difference also is extended centrally in that 

 antonomic afferent fibres have no central connection. 



