Experimental Production of Cretin-like Rats *

Cretinism is a term frequently applied to forms of thyroid deficiency occurring in utero or early in extra-uterine existence. Experimental cretinism probably had its beginnitgs in the first recorded extirpation of the thyroid in young animals, which seems to have been performed by Raynard' in 1834. Two years later, Astley Cooper' published his observations on thyroid extirpation in pups. His animals recovered, but suffered from "stupidity and malaise." It was not until the careful work of Schiff that any extended observations were made. He demonstrated the first undoubted hypothyroid symptoms due to experimental thyroidectomy and attempted to improve the symptoms by thyroid grafts.' Following this work, observations of the effect of thyroidectomy on young animals were reported by many capable workers.' '-" A difference in operative results has been shown between young and old animals, carnivora and herbivora.' More recently the results of thyroidectomy in newborn rats have been reported." Other experimental methods have been used to produce cretins. Subtotal thyroidectomy of a pregnant animal was shown to result in a high degree of thyroid hyperplasia in the offspring.' If after subtotal thyroidectomy in pregnant dogs iodine was withheld from the diet, litters were produced which all showed extreme hyperplasia of the pups' thyroids and existence of cretin-like characteristics in the pups. If iodine was fed to the pregnant animals, the resulting litter was perfectly normal.19 Harington" believes that the aforementioned method is precisely the way human cretins get their start, with the thyroid terminating in fibrous atrophy. Morgan and Ivy' made use of an antithyroglobulin antibody in newborn rabbits and found that growth was retarded, and that the animals showed "shaggy hair, pot bellies and apathy." Thyroid glands in these animals were smaller than normal, but the histology was not reported. Administration of thyroxine to pregnant dogs and rats was said by Cunningham7 to