ENDOCRINE GLANDS AND THEIH FUNCTIONS 197 



normally not visible externally, but the pathogenic condition of 

 the organ caused by overgrowth, and kno^vn as goiter, is familiar 

 to everyone. 



The functions of the thyroid gland, as recognized today, are two: 

 that of control, in conjunction with other endocrine organs, of the 

 growth and development of the body ; and, second, a most important 

 role in the regulation of metabolism. Any upset of the normal 

 functioning of the gland or the removal of the gland results in 

 serious physical and mental disorders, if not in death itself. The 

 hormone produced by this organ, designated thyroxine, has been 

 prepared from the fresh thyroid glands removed from various ani- 

 m.als and has also been manufactured synthetically. Chemical diag- 

 nosis of the hormone reveals the presence of iodine in its compo- 

 sition, and the amount of iodine available in the body seems to be 

 the determining factor in the degree of control which this hormone 

 exerts on bodily functions. In regions of the world in which iodine 

 is scarce in water and food, goiter is a prevalent disorder, and only 

 in recent years has the understanding of the cause been complete 

 enough to suggest as a remedy and a preventive the introduction 

 of additional iodine into the diet by use of iodized salt. Since the 

 amount of iodine required for normal purposes is almost infinitesimal, 

 a sufficient quantity is supplied by this means. The correction of 

 disorders due to a deficient functioning of the thyroid gland by use 

 of natural thyroxine or by use of the synthetic product is quite com- 

 mon today among human beings. 



The removal of the thyroid gland in animals which have not ob- 

 tained their complete growth results in delayed or arrested develop- 

 ment. An interesting example of this is found among certain 

 amphibians. The proper functioning of the thyroid gland is essen- 

 tial for the accomplishment of metamorphosis of the frog tadpole 

 into the adult frog. The tadpole Jacking sufficient thyroid extract 

 may grow to an unusually large size, but metamorphosis never 

 occurs without the encouragement of this hormone. In the develop- 

 ment of human beings, a deficient supply of thyroxine in early 

 years results in a condition known as cretinism. The growth of 

 the bones does not take place, the entire body is stunted and de- 

 formed, mental development ceases, the facial features are misshapen, 

 growth of hair is scant, and the development of the sexual organs is 

 incomplete. Before work on the thyroid gland was undertaken, 

 cretins were often seen in certain parts of Europe and occasionally in 



