In a previous article (Popper and Greenberg, '41) evidence was obtained that the green fading fluorescence in fixed tissue sections is specific for vitamin A. I n 1937, Lederer and Rosonova and Edisbury, Morton and Simpkins reported a substance with an absorption maximum in the ultraviolet region at a wave-length longer than that of vitamin A in the liver oils of fresh water fish. This material also evidenced an absorption maximum at a longer wave length after treatment with antimony trichloride. It was found to be growth-promoting, and consequently termed vitamin Aa, by Gillam, Lederer and Rathman ( '38).
The present communication describes the differentiation between
vitamins A, and A, by the method of fluorescence microscopy previously described by Popper ( '41).
METHODS AND MATERIAL
The fluorescence microscopic technique used is described in a paper by Popper ( '41). Methylene blue and phosphin 3R were used as the fluorescent stains for fats. The fish livers were obtained as fresh as Read at the Convention of the American Physiological Society, New Orleans, Louisiana, March, 1940. 'Research Fellow of the Cook County Graduate School of Medicine.