Raw potato starch and some modified starches cause caecal enlargement when fed to rats as the sole carbohydrate source in synthetic diets containing 18-20 % It has been argued that caecal enlargement is a process of physiological adaptation controlled by osmotic processes.2, However, in the authors' laboratory, deaths occurred among rats fed a diet containing Toxicol. 1974,12,651. 3 . Leegwater, D. C.; de Groot, A. P.; van Kalmthout-Kuyper, M.Extracts of the yeast, Candida tropicah grown on tetradecane, contain a cytochrome P-4.50 (much like the well-known drug-metabolising enzyme of liver) that can hydroxylate fatty acids such as lauric acid and demethylate drugs such as aminopyrine.'s2 Growth conditions have been described in Brewer's yeast Saccharomyces cerevisiae (NCYC NO. 240) for cytochrome P-450 bios~nthesis.~ Yeast grown for 17-40 h in 1 % glucose or 20-70 h in 20% glucose (whole, Heat-Stable Yeast Invertase