THE THYROID GLAND. 457 



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 has all the physiological properties of the 

 thyroiodine (iodothyrin). It yields Baumann's thyroiodine on 

 decomposition with mineral acids. This substance is termed thy- 

 reoglobulin. Together with another albuminous substance belonging 

 to the nucleoproteids the thyreoglobulin forms the colloid substance 

 of the gland. 



Thyreoglobulin. The quantity of thyreoglobulin is directly 

 dependent upon the amount of the colloid, and is thus subject to 

 variation. Normal glands contain on an average from 1 to 8 

 grammes of the dried substance. Much larger amounts, viz., 50 to 

 100 grammes, have been observed in goitres that were especially 

 rich in colloid. In sheep it has been found in the proportion of 

 1 : 3, or 2 : 3, as compared with the total amount of solids, and simi- 

 lar 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 follow- 

 ing analyses, which are taken from Oswald : 



Normal. Colloid goitre. 

 Pig. Sheep. Man Mai f 



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 0.2-0.3 0.04-0.09 



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. And it appears that the amount of 

 iodine is the lower, the more advanced the colloid degeneration 

 i. e., the larger the amount of thyreoglobulin. Oswald explains 

 this observation by assuming the simultaneous existence in goitres 

 of an iodized and a non-iodized globulin. The iodized form is found 

 only in glands which contain colloid, while it is never found in 



