THE BIOLOGY OF HEALTH 145 



the continued health of body and mind. Deficient 

 thyroid gland results in children who are dwarfish and 

 lumpish and dull, of defective intelligence. In adult 

 life thyroid deficiency may bring on sluggishness, a 

 decline of intelligence, and a disease called myxcedema. 

 It has been one of the triumphs of medical art to cure 

 or ameliorate these conditions by giving the patients 

 injections of thyroid-extract or by feeding them on 

 sheep's thyroid. This recalls the old prescriptions that 

 the coward should eat of the heart of a lion, and the 

 simple of the liver of a fox. 



Thirdly we may mention the adrenal bodies which 

 lie at the anterior margin of the kidney, and produce 

 from their central portion a substance called adrenalin, 

 which is distributed by the blood. When an animal 

 is enraged or in great fear, the secretion of adrenalin 

 increases, blood passes from the abdomen to lungs, 

 heart, nervous system and limbs, the heart beats more 

 vigorously, the amount of sugar (a muscle food) in 

 the blood increases, the blood acquires a greater power 

 of quickly clotting, and the muscles' power of rapid 

 recovery from fatigue is heightened — all a most marvel- 

 lous pre-adaptation to physical struggle. 



Returning now to our engine — with its motor, storage, 

 battery, ventilator, and so on, we see that there are 

 intricate arrangements which supplement the nervous 

 system in securing the smooth working together of 

 parts. The thyroid, for instance, has a good deal to do 

 with the control of speed — with the control of the rate 

 of combustion ; and the adrenals seem to play a con- 



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