REFERRED PAIN 335 



Hunger. — This may be analysed into three sensations : 

 (1) general bodily weakness; (2) a feehng of emptiness 

 referred to the abdomen ; and (3) hunger pains. The last 

 come on at intervals, and are due, as Cannon has shown, 

 to periodic contraction of the stomach wall. 



From the oesophagus the afferent fibres pass up by the 

 vagus ; from the rest of the ahmentary canal, first by 

 the sympathetic, then entering the cord by the posterior 

 roots. 



Localisation of Interoceptive Sensation. Referred Pain 



Compared with sensations arising in the skin, visceral 

 sensations are very poorly localised. Intestinal pain is 

 felt vaguely in some region of the abdomen. But the 

 locahsation of pain is not always confined to the viscera. 

 It is often accompanied by pain and tenderness of a 

 certain area of skin, to which the visceral pain is said to 

 be referred. Referred pain is felt approximately in the 

 part of the skin which belongs to the same primitive body 

 segment as the part of the gut from which the visceral 

 pain arises. It is due apparently to the overflow of 

 impulses as they enter the cord, and to the inability of 

 the higher centres to distinguish from wdiich part of the 

 segment the pain arises. Pain from the stomach, for 

 instance, is referred to the epigastrium ; pain from the 

 ureter to the flank and groin. 



