The evidence that a true lipase which accelerates the hydrolysis of milk fat is a normal constituent of cow's milk is not only inadequate but contradictory as well. It has been customary for most writers in reviewing this question to cite the experiments of Spolverini (1, 2), Maffan and Gillet (3), Moro (4), Gillet (5), Friedjung and Hecht (6) and Hippius (7) as having demonstrated the presence of Iipase in milk, and possibly refer to the experiments of Vandevelde (8) who failed to find this enzyme. As a matter of fact, the examination of the original reports of these various investigators reveals the following facts: Spolverini (1) states that he demonstrated lipase to be more or less active in the milk of the cow, goat, ass, and dog and also in human milk. Neither in this paper nor in the abstract of a later paper (2), where the same statement is made, is any experimental evidence whatever presented. The writer is of the opinion that Spolverini applied a test for esterase, previously worked out by Marfan and Gillet for human milk, to the milk of the animals stated. Marfan and Gillet (3) added 10 cc. of 1 per cent monobutyrin solution and a few drops of alcoholic phenolphthalein to 1 cc. of cow's milk and after incubating for 20 minutes at 25°C. added sodium carbonate solution (approximately 0.SN) to the milk until it was neutral to the indicator. The lipase activity of the milk was reported as the number of drops of Na.~ C03 solution required. This is stated to be 6 to 8 drops for cow's milk as compared to 20 to 30 for human milk under identical conditions.