cii i:\iisTin OF Tin: riiynoiit 503 



tilt" t'ollowiiiLj staltMiiciit : "Tlic tliyi'oid is a secretory orjraii which 

 (lischaf<i('s its secretion eventually into the blood, in tlie form of an 

 i()(lin-c()ntainin«i- ])rotein. Tliis secretion acts as a horniont', in that 

 it niodilics the activities of remote tissues. As far as we now know 

 the thyi-oid secretion i)lays the role of a 'disassiniilatory' hormone, in 

 that it eauses an increased disassimilation and increase of normal activ- 

 ity in many tissues. This effect is exemplified by the au<,nncnted 

 metabolism, the activity of the heart and many parts of the symi)a- 

 thetic nei'vous system, and of a series of internal secretory organs 

 (adrenals, liypophysis). In other tissues are found evidence of the 

 action of an inhibiting' and assimilatory hormone, as shown in the in- 

 crease in growth of bone, development of the sex glands, and de- 

 creased internal secretion of the pancreas." 



CHEMISTRY OF THE THYROID i" 



Whether the function of the tliyroid 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 

 b}- Oswald.'* lie 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 protein bodies ; 

 one, precipitated by half saturation with ammonium sulphate, con- 

 tains 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 am- 

 monium sulphate (exact limits of precipitation are between 6.4 and 

 8.2 tenths saturation), is a nucleoprotein, containing 0.16 per cent, 

 phosphorus, but no iodin. 



The iodin-containing protein, called fhyreoglohulin, constitutes one- 

 fourth to one-half the dry weight of the gland, and seems to be the 

 sole active constituent of the colloid ; at least, its administration to 

 animals has the same physiological effects as does the entire colloid 

 (great increase in the urea elimination and decrease in blood pressure 



17 C4ood reviews are triven bv Rahel Hirsch. Handb. d. Biocbem., 1900, III (,), 

 271; and A. Kocber, Vircbow's Arch.. 1912 (208), 86. 



i"a Beyond tlie cliaracteristio roHoid se -retion product, tlie tbyroid presents no 

 cbemical features of interest; it ditTers from tbe otlier endocrine glands in l)ein<i 

 poor in lipoids ( Fenger, Jour. Biol. Clieni., IflKi (27), .SO."?). 



17b Iodin is present in tbe tbvroid of all species, most in marine fornis (Cam- 

 eron, Jour. Biol. Cbem.. 1014 (Ki). 4(i.'); Biocbem. .Tour., 1014 (7). 406). 



1^ His work is reviewed in liis dissertation, ''Die cbem. BescbafTenheit nnd die 

 Function dcr Scbilddruse," Strassburg, 1000; also see Vircbow's Arcb., 1002 

 (169), 444. 

 38 



