Abstract
Seidell and Fenger 1 observed very striking seasonal fluctuations in the amount of iodine in the thyroid glands of hogs, sheep and beef, more being present and the gland being smaller during the summer than during the winter season. Fenger 2 confirmed these results. Martin 3 working with sheep glands arrived at similar conclusions. Loeb 4 in studying the compensatory hypertrophy of the thyroid gland of the guinea pig noted that this hypertrophy was considerably less in the summer than in the winter months.
We may then assume that during the colder periods of the year the thyroid gland is much more active, perhaps owing to the fact that more demands are made on this organ than during the warmer season. As a result of the lessened need for thyroid hormone during the summer months, iodine, instead of being used in the metabolism of the gland is stored up in the acini.
It has now been established that the functional state of the thyroid gland is to a marked extent influenced by a hormone of the anterior pituitary. Following previous observations of Allen, 5 Smith, 6 and Uhlenhuth and Schwartzbach 7 in amphibian larvae, Loeb and Bas-sett 8 observed that in mammals (guinea pigs) injections of extracts of the anterior pituitary cause a marked hypertrophy and hyperplasia of the acinus cells of the thyroid, a liquefaction and absorption of colloid, indications of an increased hormone action (loss of weight), therefore, in general, changes corresponding to those observed in Graves disease. To these changes corresponded a marked rise in basal metabolism under the influence of anterior pituitary extracts. (Siebert and Smith. 9 )
Under these conditions it was conceivable that the seasonal variations in the thyroid gland were due to corresponding variations in the activity of the anterior pituitary.
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