THE ENDOCRINE SYSTEM 



618 



30.4 B). The increased size of the thyroid presumably permits maximal 

 use of the small amount of iodine available. Iodine is deficient in the 

 soil and water of certain parts of the world, and hence deficient in 

 plants grown there and in the animals eating these plants. The preval- 

 ence of human goiter has been greatly decreased by the practice of 

 adding iodide to table salt, and by better distribution of food. 



The overproduction of thyroid hormone produces a condition 



B 



Figure 30 4 A, A cretin. B, Simple goiter. C, Exophthalmic goiter. (A and B 

 from Selye- Textbook of Endocrinology', published by Acta Endocrinologia, Inc.; 

 C from Houssay: Human Physiology, published by McGraw-Hill Book Company.) 



