250 A. T. CAMERON 



The table shows that while the relative amount of thyroid tissue 

 appears to increase with evolutionary development, this is not paralleled 

 by the corresponding iodin content. The figures for sex are not sufficiently 

 numerous to permit a definite conclusion, though those for cattle thyroids, 

 based on a very large number of individuals, would seem to indicate 

 definitely that both thyroid and total iodin are relatively greater in the 

 female; on the whole, my figures for fish thyroids support this conclusion 

 of Fenger's. Castrated animals resemble females. 



Age seems a definite factor. For human thyroids Monery (1904) 

 found the maximum iodin content between 40 and 60 years, an increase 

 between 15 and 40, and a decrease after 60. Aeschbacher (1907) found 

 for the first 25 years an average of 2.34 mg., from 25 to 30 years, 8.98, and 

 over 50, 4.6 mg. Pellegrini (a) (b) (1915) obtained his highest figures, 7 

 mg., between 45 and 55 years; from 55 to 65 years, 3 mg. ; lowest figures 

 below 15 years. These figures are based largely on pathological material 

 but are in accord and can be considered relatively correct. 



Fenger's more reliable figures for normal animal tissue show a similar 

 variation. Cattle fetuses, 6 to 12 weeks old, showed respectively for 20 

 males and 20 females, 0.07 and 0.08 per cent iodin in the desiccated fat- 

 free gland. For 4 to 5 months fetuses (6 males, 9 females) the figures 

 were 0.31 and 0.20; for 6 weeks' old calves (17 males, 23 females) 0.21 

 and 0.25. For adult cattle the figures were 0.28 and 0.35. Similar results 

 were obtained for ewes and sows and their fetuses, the figures indicating 

 a definite relation between the amount of iodin in the gland of the preg- 

 nant animal and in those of the corresponding fetuses ; the latter are dis- 

 tinctly smaller (Fenger, 1912). Correspondingly small figures were 

 obtained for human fetuses (1915). 



Seidell and Fenger find a distinct seasonal variation in the iodin con- 

 tent of American sheep, hog and beef thyroids (cf. also Fenger (/), 1918). 

 The percentage between June and November is in general from two to 

 three times that between December and May. Onset of severe cold 

 weather is followed in a week or two by noticeable enlargement of the 

 cattle glands, and lowering of their iodin content. Sheep show this change, 

 but to a less extent (the figures for sheep in the table illustrate the inverse 

 ratio which appears to exist between size of gland and iodin percentage, 

 even in normal animals of the same species). Water, fat, ash and phos- 

 phorus content parallel the change in weight of the gland. The conclu- 

 sion is drawn that phosphorus does not form part of the active iodin com- 

 plex, but only of the glandular tissue, and that neither the composition of 

 the active iodin complex nor that of the supporting tissue of the gland 

 changes with season, but only the relative amounts of the two. It is 

 pointed out that Martin's figures for English sheep and Guyer's for Scotch 

 sheep show a much smaller variation but in the same direction. Seidell 

 and Fenger consider that diet is insufficient to explain the seasonal varia- 



