252 A. T. CAMERON 



jected as ipdid, reaches and is retained to a considerable degree by the 

 thyroid in very short time (when injected into a vein, within a few min- 

 utes; cf. also Blum and Griitzner; Boruttau considers that true storage of 

 iodin does not occur). 



In view of these facts it seems possible that part of the seasonal varia- 

 tion found to exist by Seidell and Fenger can be referred to changes 

 which normally occur in the iodin content of a changing diet. 



The distribution of iodin within the gland is not known with certainty. 

 Justus (1902) using a histochemical method, claimed to have shown that 

 each cell nucleus contained iodin, and that the iodin content of the colloid 

 was much smaller. Babij (1913) showed his method to be incorrect. It 

 is well established that feeding with iodids or thyroid increases the colloid 

 material of the gland (Fordyce, Kojima, Cameron and Carmichael) 

 whence it would appear probable that the iodin is chiefly contained in the 

 colloid, especially as this is commonly regarded as the form of storage of 

 the internal secretion. Oswald (d) (1902) found that only those glands 

 which on microscopic examination appeared free from colloid contained no 

 iodin (detectable by Baumann's method). Claude and Blanchetiere, using 

 an inexact chemical method, found considerable iodin in diseased glands 

 containing scarcely any colloid. Pellegrini (6) (1916) states that there is 

 no definite relation between the amount of colloid and of iodin per gram 

 dry substance of the human thyroid. Tatum (1920), utilizing the fact 

 that frozen section preparations of unfixed thyroid glands do not retain 

 the colloid when floated in isotonic salt solution, separated the colloid from 

 the cell material, and found iodin in both cells and colloid of beef, sheep, 

 and pig thyroid glands. The ratio of iodin percentage in cells to that in 

 whole glands appears to be relatively constant, even though the glands vary 

 both in morphology and in total iodin content, Bensley's results are dis- 

 cussed in another section of this article. 



The Forms of Iodin Combination in the Thyroid Gland. It will be 

 instructive, before dealing with the thyroid gland itself, to consider what is 

 known of iodin compounds present in other tissues. Okuda and Eto 

 (1916) found that nearly all the iodin present in algse is in soluble organic 

 non-protein combination, a, trace only being present as iodid. Drechsel (a.) 

 (1896) found an iodo-amino-acid in the digest from the horny skeleton 

 (gorgonin) of the coral Gorgonia cavolinii, which was subsequently identi- 

 fied as 3.5 diiodo-1-tyrosin (Wheeler and Johns); Morner (&) (1913) 

 found that bromin is similarly combined in corals as dibromtyrosin. 

 Wheeler and Mendel showed that cliiodotyrosin is present in sponges, Os- 

 wald (li) (1911) found that the amount of diiodotyrosin obtainable repre- 

 sented only 7.4 per cent of the total iodin present in gorgonin, and only 

 15.7 per cent of that in spongin. He concluded that more than one iodin 

 compound was present. Similarly, Morner obtained dibromtyrosin corre- 

 sponding only to 2.5 per cent of the total bromin present, and drew a simi- 



