“…Lassen et al (1949) found that heat polymerization of a number of oils, including herring oil, resulted in some factor(s) which depressed rat growth and efficiency of feed utilization. Irwin et al (1938) found that the rate of absorption of hydrogenated fat by the rat varied inversely with the degree of oxidization. Witting et al (1957) com-pared the effects of thermally polymerized and autoxidized fish oil when fed to rats at a level of 10% of the diet and concluded that thermally polymerized fish oil was more harmful than was oxidatively polymerized oil.…”