On thyroidectomy in amphibia

Abstract

With due care to technique it was possible to remove successfully the anlage of the thyroid gland from young growing larvae of R. sylvatica and Amblystoma punctatum. The stage best suited for this experiment is that just preceding the beginning of the circulation of the blood. At this time there is no danger of hemorrhage and the chances of regeneration of the removed gland are fewer than with younger larvæ. Chlorotone in salt solution was used to produce anesthesia. Thyroidectomy was performed in 40 frog larvae and 50 Amblystoma larvæ checked against an equal number of control animals. A few of the thyroidectomized frog larvæ developed abnormally shaped external gills in some of which no circulation was to be seen. This was evidently due to injury to the vascular system. One animal developed no external gills although it lived and grew through the period during which external gills normally persist. The operated animals grew less rapidly than the controls. Only one control and one experimental animal survived the normal period of metamorphosis. Of these the control showed hind legs two months after the operation and the other had not developed legs four months after the operation. Serial sections were made of eight experimental frog larva The operation was seen to have prevented development of the thyroid gland in all but one case. The hypophysis as compared with that of the controls showed no changes in size or structure to be attributed to loss of the thyroid gland. Among the Amblystoma lane none developed abnormal gills. The average growth rate of the experimental larvz was less than that of the controls, but of the fourteen which were alive, after three months, the largest had had the thyroid removed.