INTERNAL SECRETION 497 



istered to myxedematous patients with the result of relieving them of their 

 unfortunate symptoms and of restoring them to a normal physiologic condi- 

 tion. Equally, if not more surprising, are the results which have followed 

 the internal administration of thyroids to cretins. The long-continued 

 treatment changed the entire metabolism resulting in an increase in growth 

 and weight and an awakening of the child's mentality. 



Hyperthyroidism. If the gland extracts are administered in sufficient 

 quantity and for a sufficient length of time when the body is in a normal con- 

 dition the internal secretion influences very markedly the general metabolism 

 as shown by an increased oxidation of fat and protein and a decline in body 

 weight. If the dosage be large toxic symptoms may arise, e.g., vertigo, in- 

 creased cardiac action, flushing, tremors, glycosuria, and in monkeys, exoph- 

 thalmos and a widening of the palpebral fissure. From these facts the 

 inference has been drawn from the clinical side that the symptoms com- 

 prised under the term exophthalmic goiter, viz. : rapid action of the heart, pul- 

 sation of the large arteries at the base of the neck, protrusion of the eyeballs 

 and fine tremors of the hands are due to an enlargement of the gland and a 

 hypersecretion of the thyroid cells, a condition spoken of as hyperthyroidism. 

 This inference has apparently 'been confirmed by the disappearance of the 

 symptoms after the removal of a large portion of the gland, care being taken 

 to leave behind a small portion sufficiently large, however, to produce the 

 necessary amount of the internal secretion. 



The Thyroid Secretion. The chemic features of the material secreted 

 and obtained from the structures of the thyroid indicate that it is a complex 

 protein containing iodin, which, under the influence of various reagents, 

 undergoes cleavage, giving rise to a non-protein residue, which carries with 

 it the iodin and phosphorus. The amount of iodin in the thyroid varies 

 from 0.33 to i milligram for each gram of tissue. To this compound the 

 term iodo-thyrin has been given. The administration of this compound 

 produces effects similar to those which follow the therapeutic administration 

 of the fresh thyroid itself, viz.: a diminution of all myxedematous symptoms. 

 In normal states of the body, iodo-thyrin influences very actively the general 

 metabolism. It gives rise to a decomposition of fats and proteins and to a 

 decline in body- weight. In large doses it may produce toxic symptoms, e.g., 

 increased cardiac action, vertigo, and glycosuria. 



The Functions of the Thyroid Gland. The functions of the thyroid 

 gland which have been drawn from the results that have followed its removal 

 from animals by surgical procedures, have been made questionable, since the 

 discovery of the parathyroid glands and a study of the phenomena which 

 follow when they alone are removed. From their situation and close rela- 

 tionship to the thyroid gland it is generally accepted, thatyjn the earlier ex- 

 periments, especially those made on cats and dogs, and some other carnivor- 

 ous animals, both sets of glands were removed and hence some of the symp- 

 toms which developed after the removal of the thyroids were due to the loss 

 of function not of the thyroid but of the parathyroids. 



This is especially true of the fibrillar contractions, tremors and spasms. 

 These it is now more generally believed arise only in consequence of the 

 simultaneous removal of the parathyroids. 



The function or the physiologic action of the thyroid is to produce an 

 internal secretion which after its entrance into the blood promotes favorably 

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