264 A. T. CAMERON 



of the intestine, a decrease in tuberculosis, anemia, inflammation of the 

 lungs, pellagra, and chronic inflammatory processes of the intestine, but 

 in all cases individual variations are great. Zunz's observations are in- 

 teresting and his results are worthy of study. 



lodothyroglobulin from colloid goiter does not differ from that pre- 

 pared from normal glands except for its lesser iodin content, whence its 

 metabolic effects are slighter (Oswald, 1901, 1902, 1). 



Wilson and Kendall (1916) obtain results similar to those of Marine 

 and Lenhart. Hyperplastic glands show, in the early stages, a fall in 

 iodin percentage and total iodin content, which lessens with the regression 

 of the hyperplasia, hence it seems probable that the total amount of iodin 

 in the entire gland in hyperplastic goiters with very advanced regressions 

 averages more than the total amount in non-hy per plastic cases. Adenomas 

 and carcinomas show low iodin percentages. Thyroxin is present in the 

 actively hyperplastic glands of exophthalmic goiter to a much smaller 

 extent than in normal glands ; this is interpreted as the result of its greatly 

 increased diffusion from the gland into the blood stream. 



General Conclusions 



The evidence available indicates that the thyroid gland differs chem- 

 ically from other glands chiefly in its power of retaining iodin and elab- 

 orating one or more specific iodin compounds. One of these, iodothyro- 

 globulin, exists as such in the gland, and may amount to as much as 50 

 per cent of the dried tissue. Amongst the cleavage products of thyroid 

 and probably of iodothyroglobulin occurs thyroxin, stated to be 4-5-6-trihy- 

 dro-4-5-6-triiodo-2-oxybeta-indolepropionic acid, containing 65 per cent of 

 iodin, and closely related to tryptophan. It is interesting to note that earlier 

 workers generally considered that the iodin was contained in the trypto- 

 phan or some similar radical, though it was reserved to Kendall to isolate 

 the actual compound. The total thyroxin present in the gland contains 

 only one-fourth of the total iodin, and there is as yet no information as to 

 the form of combination of the remaining three-fourths, except that it is 

 organic. The maximum amount of iodin observed in dry thyroid tissue is 

 1.16 per cent; the corresponding maximum thyroxin content is therefore 

 0.44 per cent, and the ordinary content can be considered as between 0.05 

 and 0.15 per cent. Thyroxin has not yet been shown to exist as such in 

 the gland, but it produces all the physiological and metabolic effects of 

 thyroid tissue, and on a priori grounds the essential constituent of the secre- 

 tion would be expected to consist of some such compound. 



While it is doubtful if the thyroid secretion is absolutely essential to 

 normal adult individuals, especially herbivora, its chief general effect is 

 undoubtedly to stimulate the general metabolic activity (Easterbrook, von 



