THE THYROIDS AND ACCESSORY THYROIDS 485 



who has further purified the hormone and determined its chemical struc- 

 ture. He applies the term thyroxin to the compound. Thyroxin is a 

 compound containing 60 per cent, of iodine and its rate of production 

 depends upon the presence of iodine in the intake of the body foods. The 

 determination of the influence of the thyroid has been a long and interest- 

 ing process. The steps have been progressive and cumulative. The 

 methods used have been four. First, the study of metabolism in thyroi- 

 dectomy. Second, the grafting of thyroid. Third, the feeding of 

 thyroid tissue. Fourth, the isolation and physiological administration 

 of the purified thyroid hormone. The specific dynamic action of the 

 thyroid hormone is of such definite character that at the present time the 

 chief dependence of medical men for the determination of variations in 

 the gland function is on scientific measurement of the metabolic rate 

 under the conditions known as basal metabolism. 



a. Thyroidectomy. It was noted in the middle of the last century that 

 complete removal of the thyroid glands produced a marked derangement of 

 the functions of the body and generally resulted in death. Later studies 

 have shown that death was due to the fact that the parathyroids were also 

 removed. The influence which is now attributed strictly to the removal of 

 thyroids consists of a condition of malnutrition characterized by marked 

 myxedema, a trouble that also appears in certain thyroid diseases. Failure 

 of the hormone or hypothyroidism leads to a depression of the neuro- 

 muscular tone, and malnutrition of the vascular and lymphatic systems. 

 In the early atrophy of this gland the body fails to develop and cretinism 

 is the result. 



b. Thyroid Grafting. If a portion of the thyroid gland be engrafted in 

 any other locality in an animal and the graft be allowed to grow before the 

 thyroids are removed, then the characteristic symptoms no longer develop. 

 The small amount of grafted tissue is able to produce enough of the thyroid 

 hormone to supply the needs of the body. Successful and beneficial 

 results have now been obtained by transplanting thyroid gland in man 

 (McPherson) . If in experimental cases, the thyroid graft be removed, then 

 the usual symptoms immediately appear. 



c. Thyroid Feeding. If the thyroid is fed either as the purified hormone or 

 merely as the gland itself, it seems to stimulate certain types of metabolism, 

 as indicated by an increase in nitrogenous wastes, and by more healthful 

 reaction of the nerve tissue. There is also an increased oxidation of fats, 

 a property that has brought extracts of this gland into extensive but more or 

 less dangerous use as an antifat remedy. Thyroid feeding has the same 

 effect on the body as hvperthyroidism characteristic of certain types of enlarged 

 or hypertrophied gland, exophthalmic goiter, or in hypothyroidism from any 

 cause, extraneous use of the thyroid hormone in any form antagonizes the 

 symptoms of malnutrition. Even following thyroidectomy if the gland or its 

 extract be fed by way of the mouth the symptoms disappear or are reduced. 



