Accelerated Metamorphosis of Frog Tadpoles by Injections of Extract of Anterior Lobe Pituitary Gland and the Administration of Iodine.*

T H E accelerated transformation of frog tadpoles to adults by thyroid feeding and also iodine, demonstrated by many workers since Gudernatsch's original experiments, and further, the inability of thyroidless tadpoles to change unless given either thyroid or iodine (Swingle), has established the importance of both thyroid and iodine in amphibian metamorphosis. Various glands of internal secretion, including the pituitary, have been fed to tadpoles and axolotls without noticeable effects, but the extirpation of the pituitary of tadpoles (Smith, 1916; Allen, 1917) was found to prevent metamorphosis, and on the other hand, grafting the anterior lobe into normal tadpoles caused a considerable acceleration in the assumption of adult characters, so that the possibility of pituitary influence has been investigated more thoroughly. As a result Hogben succeeded in inducing metamorphosis in axolotls when injected with commercial extracts of the anterior lobe. In the experiments recorded here an increased rate of change was obtained when tadpoles were injected with such extract, thus confirming the results of implantation work and the functional activity of the anterior lobe secretion during metamorphosis. Allen has shown that the administration of iodine to tadpoles deprived of the pituitary or the thyroid or both induces them to undergo metamorphosis, suggesting independent action of the iodine. Evidence of this effect is obtained from a further series of experiments detailed in this paper, in which