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A single injection of any one of several long-acting adrenal corticosteroids at birth induces progressive cystic changes in nephrons which develop in the subcapsular zone of the rabbit kidney until 10 days after birth. These cystic lesions enlarge progressively and become visible within a few days after birth. When the animal is 2 weeks old, renal size has become three times as large as that of uninjected littermates. Adrenal corticosteroids prolong the duration of nephrogenic activity in the renal cortex. The cysts are blind and represent dilatation of the developing end of the collecting ducts. When the steroid-induced hypokalemia is prevented with repeated potassium chloride injections, renal cystic disease is almost completely prevented. Certain long-acting steroids induce cystic renal changes without systemic signs of toxicity.

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The antibody response of young rabbits to the injection of killed Brucella abortus was abolished by prior extirpation of intestinal lymphoepithelial tissues combined with lethal xirradiation and reconstitution with rabbit fetal liver cells. Extirpative surgery alone, like lethal x-irradiation and reconstitution without surgery, did not abolish this response. Intestinal lymphoepithelial tissues of rabbits apparently play a central lymphoid function and are responsible for the differentiation of the lymphoid cell line which produces specific antibody and immunoglobulins.

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The role of calcitonin in the regulation of serum calcium has been extensively documented (1-3). Its serum calcium luwering effect is mediated by its inhibition of bone resorption. This mechanism of action has been demonstrated in vivo (4, 5 ) as well as in vitro (6, 7 ) . However, there is little evidence that calcitonin is essential for the normal processes of bone growth and remodeling during early development. We have studied this relationship by removal of the chicken ultimobranchial body which is the source of calcitonin in birds (8).Materials and Methods. White leghorn cockerels were obtained from the Ghostley Chicken Hatchery ( Anoka, Minn.) shortly after hatching and were fasted until 4 hr after surgery. One-day-old male chicks were anesthetized by hypothermia and the ultimobranchial glands were removed by blunt dissection under a dissecting microscope. Sham operations were performed by exposure of the glands without further dissection. There were 12 birds in each group. The location of the ultimobranchial glands was invariably dorsal to the bifurcation of the brachiocephalic artery into the carotid and the branchial arteries and proximal to the carotid artery (9). Bleeding was minimal, and there was no evidence of interference with the blood supply to nearby vital structures. All chickens were allowed free access to tap water and to a standard poultry feed (Purina, Co., St. Louis, Mo.) containing 18%