THE THYROID GLAND. 433 



gland for several hours with a 10 per cent, solution of sulphuric 

 acid, and by subsequently extracting the insoluble residue with 90 

 per cent, alcohol. It is insoluble in water and acids, but readily 

 dissolves in dilute alkaline solutions, from which it is precipitated 

 by adding an excess of an acid. The substance, as first obtained by 

 Baumann, contained 9.3 per cent, of iodine and a small amount of 

 phosphorus. This latter, however, he regarded as a contamination, 

 and he expressed the opinion that future researches would show that 

 the chemically pure body contained even more iodine than the crude 

 product he obtained. Regarding the chemical nature of the thy- 

 roiodine, which itself does not give the biuret reaction, Baumann 

 supposed that it existed in the gland in combination with an albu- 

 min, viz., as a thyro-iodoglobulin- or albumin. This has since 

 been proved, through the researches of Oswald, who succeeded in 

 extracting from the gland a globulin which contains the entire 

 amount of iodine, and which yields Baumann's thyroiodine on 

 decomposition with mineral acids. This substance is termed thy- 

 reocjlobulin. 



Thyreoglobulin is found in the colloid material of the organ 

 together with a nucleo-albumin, which latter, however, is present 

 in much smaller amounts. Its quantity is directly dependent 

 upon the amount of the colloid, and is thus subject to variation. In 

 the human gland it normally represents about one-third of the 

 weight of the dried organ, viz., 1.6 grammes. In that of sheep it 

 has been found in the proportion of 1 : 2, or 2 : 3, as compared with 

 the total amount of solids, and similar results have been obtained 

 in the pig. Its general elementary composition in animals of the 

 same species is quite constant, and varies but little indeed in 

 animals of different species. The amount of iodine, however, 

 which is present in organic combination is subject to fairly wide 

 variations. This is shown in the following analyses, which are taken 

 from Oswald: 



Piv ?hoo rvr Man, Man, 



Sheep - normal. colloid goitre. 



C 52.21 52.32 52.45 51.85 52.02 



H 6.83 7.02 6.93 6.88 6.91 



N 16/59 15.90 15.92 15.49 15.32 



I 0.46 0.39 0.86 0.34 0.07 



S 1.86 1.95 1.83 1.87 1.93 



O 22.15 22.42 22.01 23.57 23.75 



It is thus seen that in colloid goitres especially small amounts of 

 iodine are apparently present. This, however, is only relatively 

 the case, and in accordance with the presence of a larger quantity 

 of colloid the total amount of the thyreoglobulin is increased, 

 and we find that the absolute amount of iodine is actually larger 

 than normal. Its quantity can artificially be increased by the 

 ingestion of iodine or iodides as such, so that it is apparent that 

 the globulin is capable of binding a certain amount that is intro- 

 duced from without. 



28 



