30 THE INTERNAL SECRETIONS—1920 
supply has been called by Langley*! 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” 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?? 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, 
