752 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



it contains iodine, which exists in combination with a nonprotein nitrog- 

 enous base, and is usually called iodothyrin. In the gland itself the 

 iodothyrin may be in combination with protein, forming iodothyro- 

 globulin. E. C. Kendall 7 '-' has recently succeeded in isolating a pure 

 crystalline substance of perfectly constant composition and containing 

 over (io per cent of iodine. It has been identified as an indole compound 

 and has been made synthetically. In extremely minute dosage it greatly af- 

 fects the energy metabolism, and is said to induce symptoms like exophthal- 

 mic goiter. Its therapeutic value in eases of thyroid deficiency is remark- 

 able. Kendall believes this substance to be the active constituent of the thy- 

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

 hyperplastic condition becomes fully developed, scarcely a trace of 

 iodine is contained in the gland. Later, when the hyperplasia gives 

 place to colloid goiter, the iodine increases again, both absolutely and 

 relatively. Moreover, it has been found that if iodide is administered 

 to an animal suffering from hyperplasia, the hyperplastic condition very 

 quickly disappears (Fig. 192) and the animal becomes normal. Thus, in 

 brook trout, the poor nutritive condition of the fish when hyperplasia has 

 developed can be immediately remedied by placing them in larger quan- 

 tities of running water or by adding small traces of iodide to the water. 

 The administration of small amounts of iodine as in ordinary salt from 

 salt deposits also prevents goiter in farm stock, this having been first 

 noted in the State of Michigan, where prior to the discovery of salt 

 deposits sheep breeding was an entire failure. The importance of admin- 

 istering small doses of iodides to school children living in goitrous dis- 

 tricts has recently been emphasized by Marine and Kimball. 78 As small 

 a dose as 0.001 gm. at weekly intervals prevents goiter in puppies sus- 

 ceptible to it. 



Experimental Thyroidectomy 



A- correct interpretation of the functional changes and symptoms which 

 follow upon partial or complete removal of the thyroid gland, or from 

 its disease, has proved a very difficult problem, partly because sufficient 

 care has not been taken to note how much parathyroid tissue was re- 

 moved along with the thyroid, and partly because the fact has been over- 



