CHE^fISTRy or tiik 'nivh'oiD ooi 



believes that the thjTeofflobulin, u.s first secreted by the ^daiuhihir epi- 

 thelium, is free from iotlin, and that it combines later with iodin from 

 the circulating blood. Thyro()gl()l)ulin is not, however, simply an 

 iodized protein, for the iodized proteins that can be artificially i)repared 

 do not possess the physiological activity of the thyreoglobulin, nor 

 do other naturally occuring iodin-containing proteins (gorgonin, 

 spongin). F. C. Koch-'-* finds that the full activity of the gland is 

 contained in the thyreoglobulin, and also in the metaprotein fraction 

 of this gloinilin, while simpler cleavage products show less and less 

 activity per unit of iodin content. He could find no thyroid activity 

 in iodin compounds of histidine,and di-iodotyrosinewasfounrl inactive 

 by Strouse and Voegtlin.^" 



The remarkable influence of the thyroid on the development of 

 tadpoles (Gudernatsch") is exhibited by the thyreoglobulin but 

 also by iodized blood proteins. ^^ Swingle'^^ states that inorganic iodin 

 itself, even in thyroidless tadpoles, will bring about metamorphosis 

 that would not take place in the absence of iodine. Bromine will not 

 substitute for iodin in causing metamorphosis. The division rate of 

 even unicellular organisms (/''a /•a?«.eaww) is increased by thyroid ex- 

 tract. ^^ Lenhart^'' considers the effect of thyroid on tadpoles to be 

 merely an expression of the general stimulation of metabolism, rather 

 than a specific effect on differentiation.^^ 



By decomposing thyreoglobulin by boiling with 10 per cent, 

 sulphuric acid, a body is obtained containing as high as 14.5 per 

 cent, of iodin; this is the thyroiodin of Baumann, which gives no 

 biuret reaction, yet is physiologically active. The stability of this 

 active constituent of the thyreoglobulin explains the successful ad- 

 ministration of thyroid preparations by mouth. It appears to be 

 absorbed unchanged and, unless enormous doses are given, none ap- 

 pears in the urine (Oswald). ^^ Long-continued digestion with trj'psin, 

 or autoh'sis of th3-roid glands, causes a complete splitting out of the 

 iodin. One part of the iodin seems to be more firmh' bound than the 

 rest. A small amount of the iodin may exist as inorganic and lipoid 

 compounds. ^^ 



Thyroxin. — ^KendalP^ has isolated from the thyroid, after alkaline 

 hydrolj'sis, a crystalline compound containing 65 per cent, of iodin 

 which seems to be an indole derivative, designated as "thyroxin" 



23 Jour. Biol. Chem., 1913 (14), 101. 



30 Jour. Pharm. and Exp. Ther., 1910 (1). 123. 



31 Rogoff and Marine, Jour. Pharm., 1917 (10), 321. 



'2 Jour. Gen. Phvsiol., 1919 (1), 593; Jour. E.\p. Zool., 1919 (27), 397. 



" Shumway, Jour. Exp. Zool., 1917 (22), 529. 



3^ Jour. Exp. Med., 1915 (22), 739. 



35 See also Kahn, Arch. ges. phvsiol., 1916 (163), 384. 



3« Arch. exp. Path. u. Pharm., 1910 (63), 263. 



3" Blum and Grutzner, Zeit. phvsiol. Chem., 1914 (91), 400. 



38 Jour. Amer. Med. Assoc, 1918 (71), 871; Trans, .\ssoc. Amer. Phvs., 1918 

 (33), 324; Endocrinology, 1919 (3), 156; Jour. Biol. Chem., 1919 (39), 125; 1919 

 (40), 265. 



