Abstract
In previous work 1 we found that Armour's commercial anterior lobe powder contains a specific substance which, when injected intraperitoneally, not only induces precocious metamorphosis of the injected salamander larvae (Ambystoma tigrinum), but alone among other substances tested (inorganic iodine, thyroid substance, adrenalin, pilocarpin) causes a typical display of the complete functional phase of the thyroid gland of the injected larvae, such as takes place normally during metamorphosis. We concluded that anterior lobe is the extrinsic thyroid stimulator for which one of us has been searching since 1919, and that it causes metamorphosis of the amphibian larvae only indirectly, by forcing the thyroid to excrete. The existence and action of an extrinsic thyroid stimulator (excretor substance) has been shown in a long series of experiments, 2 but the stimulator itself could not be found until 1926. 1 Hogben 3 and later Spaul 4 had found that intraperitoneal injection of an extract made from Armour's anterior lobe powder and other commercial anterior lobe products induces precocious metamorphosis of the Mexican axolotl. But Smith claimed 5 , 6 that the metamorphosis-accelerating action of Armour's commercial anterior lobe product is the effect, not of anterior lobe substance, but of a very high iodine content of the commercial product and probably of an admixture of thyroid substance. Spaul 7 demonstrated that an extract prepared from fresh anterior lobe had the same effect as Armour's anterior lobe powder, provided that the anterior lobe is separated from the posterior lobe immediately after the death of the bovine donator.
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