30 INTERNAL SECRETION 



gland being low and its iodine content high. The absolute iodine 

 content of goitrous glands is, however, considerably higher, and 

 'may reach 50, or even 100 mg. Oswald pointed out that the 

 amount of iodine in the thyroid gland is a parallel to its colloid 

 content. True parenchymatous goitres, the goitres of Graves's 

 disease in so far as these are parenchymatous the purely fibrous 

 goitres, portions of goitres which have undergone cell- 

 degeneration, and the hyperplastic goitre of calves, do not contain 

 iodine, or, at least, contain very little; while, on the other hand, 

 goitres containing much colloid substance are very rich in iodine. 

 Oswald is of the opinion that, wherever there is pronounced 

 colloid degeneration, the proportion of iodine decreases and may, 

 indeed, disappear altogether. 



Iodine is present in very nearly all the human organs, though 

 this was not Baumann's original opinion. The thyroid gland is, 

 however, 8-10 times richer in iodine than the other organs 

 (hypophysis, liver, kidney, ovaries). According to Baldi, bromine 

 is also present in the thyroid ; and Gautier and Bertrand assert 

 that arsenic is present in both the thyroid and the ectodermal 

 organs. The presence of arsenic, however, is denied by 

 Hodelmoser. Fiirth and Schwarz, as previously stated, believe 

 that choline is present in the thyroid. 



Iodine is undoubtedly the most characteristic, as it is the most 

 important, of the chemical constituents of the thyroid gland, and 

 it occurs, according to Baumann, in combination with an 

 albuminoid. Baumann gave the name of thyroidin to this sub- 

 stance, but the name was afterwards altered to iodothyrin. 

 lodothyrin is obtained by boiling the thyroid gland for several 

 hours in 10 per cent, sulphuric acid, and extracting the residuum 

 with 90 per cent, alcohol. 



Oswald believes that thyroid colloid is a mixture of two 

 albuminoids, the thyroglobulins. Of these, one contains iodine 

 and, after treatment with boiling mineral acids, yields iodothyrin 

 as the product of hydrolytic division. lodothyrin is a peculiar 

 atom-complex contained in the larger molecule of thyroglobulin. 

 Oswald has recently shown that, if it is treated with trypsin for 

 several weeks, iodine-thyroglobulin also breaks up into the final 

 products of hydrolytic division, for by this means the iodine 

 is set free and passes into the ionised state. The second 

 albuminoid is free from iodine, but contains phosphorus, and is a 

 nucleoproteid. 



Iodine-thyroglobulin forms by far the largest proportion of 

 the weight of the dried thyroid gland, being one-third to one-half ; 

 while it forms three-quarters and more of the weight of colloid 

 goitres. In hyperplastic goitre and the goitre of Graves's disease, 

 the amount of iodine-thyroglobulin is reduced, while the amount 

 of the albuminoids containing phosphorus is much increased. 

 The amount of iodine in thyroglobulin obtained from the thyroid 



