PAIN AND PLEASURE 255 



which cause no convulsions or other signs of irritation and shock, produce 

 no effect on sensibility to pain. Destruction of the cortex alone does not 

 disturb the threshold for the painful or uncomfortable aspects of sensation." 



Some recent experiments by Cannon have revealed a very 

 intimate relation between emotion and some of the ductless 

 glands. The suprarenal (or adrenal) glands, situated above the 

 kidneys, secrete and pour into the blood a remarkable substance 

 known as adrenalin or epinephrin. This substance exerts upon 

 structures which are innervated by sympathetic nerves the same 

 effects as are produced by impulses passing along those nerves. 

 The glands may themselves be excited to activity by nervous 

 impulses passing out through the sympathetic nerves. Cannon 

 has shown that the emotions of fear, rage, and pain excite these 

 glands to activity and cause the secretion of adrenalin. The 

 blood of a caged cat which has been tormented by the barking of 

 a dog will show an increased percentage of adrenalin. The 

 addition of adrenalin to the blood has the further effect of caus- 

 ing liberation of sugar from the liver into the blood to such an 

 extent that sugar may appear in the urine (glycosuria) ; and sugar 

 is known to be the most available form in which energy can be 

 quickly supplied to tissues which have been exhausted by exer- 

 cise. Adrenalin will in this and other ways act as an antidote to 

 muscular fatigue. It also renders more rapid the coagulation of 

 the blood. 



If a muscle is fatigued, the threshold of irritability rises. It 

 may rise as much as 600 per cent., but the average increase is 

 approximately 200 per cent. If the fatigued muscle is allowed 

 to rest, the former irritability is gradually regained, though two 

 hours may pass before the recovery is complete. If a small dose 

 of adrenalin is administered intravenously, or the adrenal glands 

 are stimulated to secrete, Cannon has found that the former irri- 

 tability of the fatigued muscle may be recovered within three 

 minutes. In this way adrenal secretion may largely restore 

 efficiency after fatigue. 



Fear and anger as well as worry and distress are attended 

 by cessation of the contractions of the stomach and intestines. 

 These mental states also reduce or temporarily abolish the secre- 

 tion of gastric juice. Adrenalin injected into the body has the 

 same effect. Besides checking the functions of the alimentary 



