486 CHEMICAL PATHOLOGY OF THE DUCTLESS GLANDS 



CHEMISTRY OF THE THYROID 



Whether the function of the thyroid is the neutralization of 

 toxic substances, or a complementary action upon intracellular 

 metabolism, there can be little question that it owes its action to 

 constituents of its specific secretion, the colloid. Furthermore, 

 the chief, if not the sole, active ingredient of the colloid is the 

 iodin-containing substance first discovered by Baumann in 1896, 

 and called by him thyroiodin (or iodothyrein). 



The chemical nature of thyroid colloid has been studied 

 particularly by Oswald. 1 He found that all the iodin of the 

 thyroid is dissolved out in physiological salt solution, and that 

 none of it is present in an inorganic form. In the salt solution 

 extract are two proteid bodies : one, precipitated by half satura- 

 tion with ammonium sulphate, contains all the iodin, and seems 

 to be a globulin ; it resembles myosin in being precipitated by 

 weak acids, and it contains an easily separated carbohydrate 

 group. The other, precipitated by saturation with ammonium 

 sulphate (exact limits of precipitation are between 6.4 and 8.2 

 tenths saturation), is a nucleoproteid, containing 0.16 per cent, 

 phosphorus, but no iodin. 



The iodin-containing proteid, called thyreoglobulin, seems to 

 be the sole active constituent of the colloid ; at least, its admin- 

 istration to animals has the same physiological effects as does 

 the entire colloid (great increase in the urea elimination and 

 decrease in blood pressure in animals, curative effect on myx- 

 edematous patients), whereas the nucleoproteid is without these 

 effects. Analysis of the thyreoglobulin from various animals 

 has shown it to be of quite constant quantitative composition 

 except for the iodin, which may vary greatly in amount. Nor- 

 mal human thyreoglobulin (from persons living in non-goitrous 

 districts) had the following percentage composition : 

 = 51.85, H = 6.88, N = 15.49, 1 = 0.34, S = 1.86. 



Thyreoglobulin from goitrous districts contains much less iodin 

 (0.18-0.19 per cent.), and from calves born with goiters a thy- 

 reoglobulin was obtained that agreed in all respects with normal 

 thyreoglobulin, except that it contained no iodin at all. On the 

 other hand, administration of iodides to patients causes the thy- 

 reoglobulin to become rich in organically bound iodin. 2 From 



1 His work is reviewed in his dissertation, " Die chem. Beschaffenheit und 

 die Function der Schildruse " Strassburg, 1900 ; also see Virchow's Arch., 1902 

 (169), 444. 



2 Nagel and Roos (Arch. f. Anat. u. Physiol., 1902, p. 267) found that 

 administration of bromides had no effect upon the amount of iodin in the thy- 

 roid, and no storage of bromin takes place. Administration of pilocarpine 



