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IT is now generally agreed that the deterioration of oils and fats, whether due to the action of air, light and moisture, or to the action of micro-organisms, is an oxidative process subsequent to partial hydrolysis. In these two forms of rancidity-that of pure fats (where the absence of nidus prevents bacterial or mould growth) and that caused by micro-organisms-the course of the oxidation is not the same. In the latter form the combustion is probably more vigorous and supplies energy to the organism. Much has been written on the deterioration of pure fats, a summary and bibliography being given by Hepburn [1909]; but on biologically produced rancidity comparatively little work has been done, that of Jensen [1902] being probably the most important. As it contains only a small proportion of unsaturated glycerides, coconut oil does not quickly deteriorate when exposed to atmospheric conditions, but eventually acquires the characteristic odour of all fats under these conditions. When subjected to mould action, however, it gives rise to a pungent "perfume" or ester-like odour quite different from that already noted. This has been observed, but not identified, by several investigators [Biffen, 1899; Walker, 1906; Jacobsen, 1918]. Biffen thought, erroneously, that it was amyl butyrate, but the author [1921] has shown it to be due to the formation of methyl ketones; Stiirkle [1924] arrives at similar results and suggests that ketones are formed in a way analogous to Dakin's synthesis of methyl ketones from fatty acids [Dakin, 1910]. Derx [1925] confirms the author's results and his contention that Oidium lactis does not produce ketonic rancidity, and finds further that some Penicillium species produce ketonic or non-ketonic rancidity according to the composition of the medium. The formation of methyl ketones in the decomposition of fats suggests P-oxidation, especially by analogy with the oxidation of straight chain compounds in vivo. P-Oxidation would explain, also, the production of methyl ketones in essential oils (e.g. methylnonyl ketone in oil of rue), and the occurrence of ketones in the "echappees" of coconut oil. Haller and Lassieur [1910] found

The rancidity of coconut oil produced by mould action