METHODS AND MATERIALS Method of assay. The method to be described here is modified from one previously published (Anderson et al. 14), in which the mouse was used. Male rats (Sprague-Dawley strain) six to seven weeks of age and weighing 130 to 150 gm. are hypophysectomized. Four days later a freshly prepared solution of 1 per cent alloxan monohydrate in saline is administered intravenously (40 mg./kg.). The assay is carried out eight days after hypophysectomy. It has been found recently that the hypophysectomized rat without alloxan diabetes is satisfactory as an assay animal four days after removal of the pituitary. The advantages and disadvantages in the use of the ADH rat and the hypophysectomized rat will be discussed later.

On the afternoon preceding the assay, the animals are placed in clean cages without food cups and are fed twice by stomach tube, each feeding consisting of 3 ml. of an egg-milk mixture (1 egg+ 250 ml. of evaporated milk). At 5 pm at the time of the last feeding, the animals receive 2 ml. of 6 per cent glucose in saline by