METABOLISM, NUTRITION AND DIETETICS 



561 



tissue from an animal of the same species, these effects are en- 

 tirely obviated so long as the graft survives. It has not been 

 established that a hetero-thyroid graft i.e., a graft of thyroid 

 tissue from an animal of a different kind even temporarily 

 succeeds. The alien thyroid cells are destroyed by cytolysins 

 (p. 29) in the serum and tissue liquids of the animal. When a small 

 part of a thyroid is left, it may undergo great hypertrophy, and 

 the same is true of the accessory thyroids. The administration 

 of extracts of the thyroid glands or the glands themselves by 

 the mouth brings about a cure, permanent so long as the thyroid 

 treatment is continued, in cases of myxcedema in man, and 

 prevents the development 

 of the symptoms in ani- 

 mals or removes .them 

 when they have appeared. 

 The same is true of 

 a compound rich in 

 iodine, the so-called thy- 

 roiodin, which has been 

 extracted from the organ. 

 Under this treatment the 

 total metabolism, which in 

 myxoedema is below the 

 normal, is markedly in- 

 creased. This is partly 

 due to an increase in the 

 metabolism of protein. 

 An increase in the de- 

 struction of protein is also 

 caused in normal persons. 

 For this reason the use of 

 thyroid preparations to 

 reduce weight in cases of 

 obesity, without evidence 

 of thyroid insufficiency, is .a dangerous remedy. For while 

 a fat man can very well spare a great deal of his fat, 

 he cannot spare much of his tissue-protein. The question 

 whether the thyroid or parathyroid is, in addition, concerned 

 in the carbo-hydrate metabolism is at present the subject of 

 lively discussion, but the data are so contradictory that it 

 would not be advisable to enter into the matter here. 



The relations of iodine to the gland itself, and the modifications 

 in its structure and function determined by the giving or with- 

 holding of iodine, recently studied by Marine, are of great 

 interest. In all animals, so far as examined, the normal thyroid 

 contains iodine. The amount is variable, but the minimum 



36 



FlG. l88. MlCROPHOTOGRAPH OF ACTIVE 



THYROID HYPERPLASIA FROM A CASE OF 



EXOPHTHALMIC GOITRE (MARINE). \ ~.\*.\ 



The characteristic changes in the hyper- 



plastic gland the in foldings and plications of 



the alveolar epithelium, the great reduction in 



the colloid, and the increase in the stroma 



are shown. 



