THE THYROID AND PARATHYROID GLANDS 



793 



per cent of iodine. It is called thyroxin and has been identified as an indole 

 compound and has been made synthetically ./In extremely minute dosage it 

 greatly affects the energy metabolism, and is said to induct symptoms like 

 exophthalmic goiter. Its therapeutic value in cases of thyroid deficiency is 

 remarkable. Kendall believes this substance to be the active constituent of 

 the thyroid and to be associated with the metabolism of amino acids. For one 





Fig. 195. Microphotographs of thyroid gland of dog. A, normal gland; B, active hyperplasia; C, 

 colloid goiter. (From Marine and lyenhart.) 



thing, when it is given alone no change occurs in pulse rate, whereas if 

 amino acids are given along with it, there is acceleration. 



The importance of the relationship between the function of the thyroid 

 and the iodine-containing material is indicated by the changes which 

 occur in the percentage of iodine in the glands under varying condi- 

 tions of activity. Marine observed that the amount of iodine is inversely 

 proportional to the degree of hyperplasia of the gland, and when the 



