264 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



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Fig. 15.8. The metamorphosis of tadpoles of bullfrogs (Rana catesbiana) is 

 hastened by implanting crystals of iodine in their bodies. A, Animal killed two 

 weeks after the crystals were implanted. B, The untreated control of the same age. 

 Compare the mouths, tails and paired appendages. In nature bullfrogs are two to 

 three years old before they become adults. (Courtesy, Turner: General Endo- 

 crinology. Philadelphia, W. B. Saunders Co., 1948.) 



thyroids were sometimes removed with the thyroids, with extremely serious 

 results. When the thyroid was removed from cats and dogs, it almost always 

 resulted in tetany, an extreme cramplike contraction of the muscles, and 

 death, but in rabbits the same operation made hardly any disturbance. The 

 reason proved to be that in rabbits one pair of parathyroids was located so 

 far behind the thyroid gland that it was not removed with it. Parathyroids 

 regulate the amount of calcium and phosphorus in the blood and their 

 metabolism in the body (Fig. 15.10). Failure in this regulation produces ex- 

 treme irritability in the motor nerves and tetany. Tetany may also occur with 

 rickets, a vitamin-D deficiency, the softening of bones being due to lack of 

 calcium. 



Adrenal Glands 



In man one of the adrenal (suprarenal) glands is in contact with the upper 

 end of each kidney (Figs. 15.1, 15.1 1) and in animals generally they are near 

 the kidneys. The adrenal gland is actually two glands in one, a central medulla 

 and surrounding cortex. 



Medulla. The medulla originates from cells allied to the autonomic nervous 



