CHEMisriivoF THE riiYuon) dos 



tion to the iotliii content,'" wliich is tlie best of evidence that tlie for- 

 mation of this compound is one of the chief functions of the gland, 

 and that the iodin in the thjToid is not merely stored there as an unde- 

 sirable foreign substance like copper in the liver. The selective de- 

 position of iodin in the tiiyroid is remarkable, and when iodin is fed 

 to animals it is stored very rapidly but it seems to require several 

 hours before the active growth-modifying hormone is formed.'" Ma- 

 rine and Lenharf- find that the normal human j^land contains an aver- 

 age of 0.4 mg. of iodin per gram of fresh weight (2.17 mg. per gram 

 of dry weight), being less than that of domestic animals in the same 

 part of the country. These figures agree closely with those obtained in 

 thyroids from various parts of America by Wells'*' (2.10 mg. per gram 

 dry weight). They found, as Oswald and Kocher also have, that the 

 amount of iodin varies directly with the amount of colloid, being de- 

 creased when cellular hyperplasia is present, in direct proportion 

 to the amount of hyperplasia, and administration of iodin causes a 

 reduction in the hyperplasia and a return to the colloid type of gland, 

 while the iodin is deposited in the gland. Kocher, however, disputes 

 the regularity of the variation of iodin and colloid content, stating 

 that it is especially the concentrated follicle contents which hold the 

 iodin. Seidell and Fenger'*'* have found a marked seasonal variation 

 in the thyroid iodin of animals, there being about three times as much 

 between June and November as between December and May.'*' 

 In man it has been found that before birth the thyroid of the fetus 

 contains little or no iodin, but in domestic animals the fetal glands con- 

 tain not a little iodin (Fenger).*^ The cells of the gland contain very 

 little iodin (A. Kocher). Extracts of the thyroid have little effect 

 on the blood pressure, except for an alcohol-soluble fraction, poor in 

 iodin, which is a depressor. "^^ On the other hand, thyroid secretion 

 increases the sensitiveness of the sympathetic nervous system to 

 epinephrine.^^ 



Wasting diseases are associated with a considerable decrease in the 

 size of the thyroid and the amount of colloid, and with this a decrease 



^"Fonio, Mitt. Grenz. Med. u. Chir., 1911 (24), 123; Frey, ibid., 1914 (28), 

 349; Hunt, Jour. Amer. Med. Assoc, 1907 (49), 1323; and Jour. Pharm. and exp. 

 Therap., 1910 (2), 15. 



*' Marine and Rogoff, Jour. Pharm., 1916 (9), 1. 



*- Arch. Int. Med., 1909 (4), 440. 



*3 Jour. Amer. Med. Assoc. 1897 (29), 897. 



" Jour. Biol. Chem., 1913 (13)., 517. 



■*= Valuable figures on the iodin content of foods are given bj- Forbes et al., 

 Bullet. Ohio Agric Expt. Station, June, 1916 No. 299. 



« Jour. Biol. Chem., 1912 (11), 489; 1912 (12), 55; 1913 (14), 397. 



"^ Fawcett et al., Amer. Jour. Physiol., 1915 (36), 113. 



'^^ The thyroid is very rich in lipase, catalase and peroxidase; extirpation is 

 followed by a decrease in these enzymes in the blood, while thyroid feeding in- 

 creases them as well as the antitrypsin (Juschtschenko, Biochem. Zeit., 1910 (25), 

 49; Zeit. physiol. Chem., 1911 (75), 141.). 



