THE ABILITY OF LIVER PREPARATIONS AND VITAMIN B12TO MAINTAIN THYMUS WEIGHT IN THYROID-FED RATS HAVING GREATLY HYPERTROPHIED ADRENAL GLANDS

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Abstract
In an effort to deplete laboratory animals of as yet unidentified nutritional factors and so obtain a suitable animal for assay Betheil (1947) and Ershoff (1947, 1948) have included desiccated thyroid gland or iodinated casein in their experimental diets. This device serves to increase the basal metabolic rate of the animals so treated (Ershoff [1947], Robblee [1948]) and so results in a greater demand for nutritional factors not available in adequate amounts either in the diet or by intestinal synthesis. Elvehjem et al. (1947a, 1947b) observed that the feeding of a natural ration was more satisfactory than a synthetic diet for the assay of unknown factors in commercial liver preparations. They combined this ration with the feeding of desiccated thyroid to chicks and were able to obtain significant growth responses to the administration of liver. Folley (1947) as well as other workers (Zucker [1948]) have observed the decreased growth rates obtained on the litters from animals bred on synthetic