One of the most archaic structures in the body, the subcommissural organ occurs throughout the vertebrate series, from the lowest fishes to the primates (Sargent, '00, '01; Nicholls, '17; Jordan, '19). Situated at the oral end of the posterior commissure, the organ gives rise to fibrils which unite to form Reissner's fiber, a delicate thread extending down the center of the spinal canal. Since the time of Sargent 's hypothesis (1900) that the sabcommissural organ and Reissner's fiber constitute a mechanism for the facilitation of optic reflexes, there has been considerable disagreement concerning the function of this strangely persistent structure. Recent histochemical studies (Leduc and Wislocki, '52 ; Wislocki and Leduc, '52a, '52b, '54) have indicated that the organ is secretory and exhibits a high level of enzymatic activity. Preliminary experiments by the author, in which the organ was electrically ablated, have suggested a role for the subcommissural organ in water-electrolyte metabolism. The experiments presently described represent an extension of these studies in an attempt to ascertain more clearly (1) the effects of electrocoagulative ablation of the subcommissural organ, relating to the water metabolism; and (2) whether the organ manufactures a secretion of physiological significance.
Methods
(A) Forty-six white rats, of both sexes, weighing 200 to 250 gm, were used. The daily consumption of food and water 253