486 



METABOLISM, NUTRITION, AND DIET 



The Nature of the Thyroid Hormone. The active principle produced 

 by the thyroid gland is an iodine compound as was first shown by Baumann 

 in 1895. He prepared an iodine-protein compound called thyroiodinc, 

 which contained as much as 9.3 per cent, of iodine. The compound was 

 stable, readily soluble in dilute alkalies, and did not decompose with high 

 heat or when the gland was digested in strong acid, Kendel's thyroxin 

 we now know to be the pure principle. 



Marine who has extensively studied the thyroid finds that certain types 

 of hyperplasia are associated with a decreased supply of the active iodine 

 compound. If iodine as such be given to such an animal, the symptoms are 

 improved and the iodine compound content of the gland is increased. 



Interesting biological experiments showing the influence of thyroid 

 feeding on immature animals have been performed by Gudernatsch. Dried 



FlG. 312. The influence of thyroid feeding on metamorphosis of tadpole larvae of 

 Bufo vulgaris. a, original size June 5th. b, control, d, and e, thyroid and plants, d, 

 thyroid given three days, e, thyroid given five days, taken June 26th. m, control, n, fed 

 thyroid and muscle, o fed thyroid and plants, p, thyroid and hypophysis, taken July 6, 1912. 

 (After Gudernatsch.) 



thyroid gland fed to different species of tadpoles stopped growth and 

 stimulated differentiation. Tadpole larvae no matter how young were forced 

 into metamorphosis, i.e., the development of fore and hind limbs and the 

 assumption of the adult frog form. Gudernatsch by this means stimulated 

 even tiny tadpoles only a few millimeters long, forcing metamorphosis 

 "within eighteen days after hatching, while normally they would require 

 ten to twelve weeks to reach such a stage. The results of this premature 

 metamorphosis are perfect frogs of minute size, pygmy frogs." The thyroid 

 as food stops tissue growth during this process. "The thyroid possesses a 

 quality that stimulates differentiation, not contained in any other food 

 used." The influence of the thyroid is somewhat modified by the food 

 given with the gland, but one food would prevent the thyroid influence, 

 namely thymus. 



