SECRETION. 457 



It is evident that the presence of the thyroid is essential to the normal 

 activity of the tissues generally. As to the manner in which it exerts its 

 favorable influence, there is some difference of opinion. The view that the 

 gland removes from the blood certain toxic bodies, rendering them innocuous 

 and thus preserving the body from a species of auto-intoxication, is gradually 

 yielding to the more probable view that the epithelium is engaged in the 

 secretion of a specific material, which finds its way into the blood or lymph 

 and in some unknown way influences favorably tissue metabolism. This 

 view of the function of the thyroid is supported by the fact that successful 

 grafting of a portion of the thyroid beneath the skin or in the abdominal 

 cavity will prevent the usual symptoms which follow thyroidectomy. The 

 same result is obtained by the intravenous injection of thyroid juice or by 

 the administration of the raw gland. It was shown by Murray that myxe- 

 dematous patients could be benefited, and even cured, by feeding them with 

 fresh thyroids or with the dry extract. 



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 thyro-iodin 

 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, thyro-iodin 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. 



It has also been suggested from the clinical side that the symptoms 

 comprised under the term exophthalmic goiter, viz., enlargement (hyper- 

 trophy) of the thyroid, rapid action of the heart, pulsation of the large 

 arteries at the base of the neck, protrusion of the eye-balls and fine tremors 

 of the hands are due to a hypersecretion of the thyroid cells, a condition 

 spoken of as hyperthyroidism. 



The conclusions as to 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 relationship to the 

 thyroid gland it is generally accepted, that in the earlier experiments, espe- 

 cially those made on cats and dogs, and some other carnivorous animals, both 

 sets of glands were removed and hence some of the symptoms which devel- 

 oped 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 myxedema and the failure 

 of the mental powers are attributed to the loss or degeneration of the thyroid, 

 and cretinism to the arrest of its development. 



