Growth and Metamorphosis of Anuran Larvae on Thymus Extracts. ∗

Abstract

Since the early experiments of Gudernatsch, 1 who produced an acceleration of growth and a delay of metamorphosis of tadpoles fed upon fresh thymus tissue, several investigators have obtained diverse results by feeding thymus glands, either fresh or dried, to amphibian larvæ. Uhlenhuth 2 , 3 found that when only thymus tissue was given to newly hatched urodeles, their growth was retarded. This was attributed to the particular food value of the thymus since the animals grew at a normal rate when other food was added to the diet. Contrary to the above observations, Kahn 4 and Romeis 5 found that thymus accelerated the growth of amphibian larvae. Swingle, 6 however, fed fresh and powdered thymus to Rana larvae and observed no retardation or acceleration of growth or metamorphosis. The rather extensive literature has been covered in a brief review by Gudernatsch. 7

Asher and Ratti 8 prepared a thymus extract, thymocrescin, which in their hands has produced marked acceleration of growth as well as a gonadotropic effect upon rats on deficient diets. More recently. Rowntree, et al., 9 have obtained accelerated growth and differentiation in rats through the use of thymus extract (Hanson) in successive generations.

The writers have thought that if a growth-promoting factor is present in such extracts, it may have some effect, beyond that of its food value, upon amphibian larval development.

A clutch of Rana pipiens eggs was divided into 3 parts, each of which was placed in one of 3 aquaria containing 2200 cc of water. After hatching, the larvae were fed dried boiled beef liver and boiled lettuce. On alternate days when the water was changed, 10 mg of thymocrescin† was added to one aquarium, 1 cc of Hanson's extract‡ to another, and the third aquarium served as a control.