A splenectomized dog can be kept anemic for months or years in perfectly good condition. A renal bile fistula dog on a suitable diet can be kept in perfect health and activity with normal weight for years. When we combine splenectomy and the bile fistula, after a latent period, we invariably observe a striking reaction with enormous over-production of bile pigment, a definite anemia and finally death from anemia or tissue hemorrhage. The spleen is essential for life in the bile fistula animal and this suggests some contribution from the spleen to body internal metabolism. The spleen and bile together are essential for the normal metabolism of pigment. The bile salts are suspected of playing some obscure role in this reaction. It seems difficult to explain all this great excess of bile pigment as coming from hemoglobin built up from the usual diet factors which in these experiments are well standardized. It is suggested that the body can synthesize the pyrrol aggregate (four pyrrol rings). There is some evidence that the liver can build up bile pigment direct from "building stones." It seems necessary to postulate one or the other mechanism and they do not seem unlike in the final analysis as both bile pigment and the pyrrol aggregate contain four pyrrol rings. Possibly both reactions may take place under these conditions.