THE AUTONOMIC NERVOUS SYSTEM 199 



might be gotten rid of therein. That this longer rest period be 

 spent in sleep is by no means always desirable. When we recall 

 that the synapses which experience fatigue primarily are the ones 

 that are being used we realize that the essential for rest is often 

 diversion rather than sleep. During the rest periods one's mental 

 activities should be along as different lines as possible from those of 

 his ordinary workaday life. Thus his fatigued synapses can be 

 resting while others are busy. This same fact emphasizes the 

 importance of diversity of interests. Where one's thoughts cling in 

 certain ruts mental fatigue is apt to be more pronounced than 

 where various lines can be followed. In those whose occupation 

 requires prolonged concentration it is particularly advantageous to 

 have widely different interests to turn to during the intervals of 

 relaxation. 



Hormones of the Nervous System. Adrenin. This hormone 

 is interesting chemically because it was the first hormone to be 

 obtained pure, and is even yet by far the best known of the nu- 

 merous hormones produced in the Body. Various names have 

 been applied to it (suprarenin, epinephrin, adrenalin). The name 

 given in the paragraph heading is coming into general use at pres- 

 ent. 



The Suprarenal Capsules or Adrenals are a pair of small organs, 

 weighing together about 12 grams Q oz.) placed one on the top 

 of each kidney. They have, however, no intimate connection 

 with the kidneys, and in many animals are placed at some dis- 

 tance from them. Each consists of a denser less colored external 

 cortex, and a central deep yellow-brown softer medulla. The cor- 

 tex is subdivided into chambers by connective tissue, and the 

 chambers are filled by closely packed, polygonal nucleated cells. 

 Similar cells are found in the medulla, which is, moreover, closely 

 connected with the sympathetic system and is richly supplied 

 with nerves. 



It was noticed some seventy-five years ago by a physician named 

 Addison that certain obscure diseased conditions characterized by 

 great debility and by the appearance of bronzed patches on the 

 skin, and leading to death, were found on post-mortem examina- 

 tion to be accompanied by disease of the adrenals. The disease 

 has since been named Addison's disease. When the suprarenal 

 capsules are completely removed from animals a similar fatal 



