Iii. the Chemistry of Mould Tissue. Vi. Factors Influencing the Amount and Nature of the Fat Produced by Aspergillus Fischerpi. by Edward

THE fat content of mould mycelium, as reported by various authors, ranges from 1 to 40 %, depending upon the species and upon the conditions of growth. Even within a single strain of a species certain characteristics of the fat, as well as its amount, have been reported to vaty with the conditions of growth. From what is known about the chemical composition of mould-fat it appears that glycerides together with free fatty acids constitute the major portion of it. In some cases the mould-fat contains a high percentage of free fatty acids [Pruess et al., 1934]. Barber [1929] found that the nature of the fatty acids, both free and combined, produced by a Penicillium sp. remained practically unchanged whether this mould was grown on glucose, sucrose, xylose or glycerol. The more easily extracted fat of A. sydowi, exclusive of the phospholipins [Strong and Peterson, 1934] and that of P. javanicum [Ward and Jamieson, 1934] have both been shown to yield upon saponification glycerol and oleic, linoleic, palmitic, stearic and small amounts of n-tetracosanoic acids. The mould-fat contains variable percentages of phospholipins and sterol, the latter having been definitely shown to be ergosterol in the case of A. fischeri [Pruess et al., 1932]. There also occurs a small amount of some other unsaponifiable material which has not yet been studied. A small amount of pigment is presumably also present, since the mould-fat is usually quite deeply coloured. The mould-fat has been generally regarded as a reserve material [Perrier, 1905], although Kordes [1923], observing that the fat globules in the hyphae persisted even during inanition, believed that this fat should be considered as an "excretory" product. Belin [1926] demonstrated that the fat content of A. niger fell to a low value after prolonged inanition. He postulated that the fats of moulds and of other living organisms should be considered as consisting of an "6element constant" and an "el6ment variable." By the term "element constant" he designated that minimum percentage of fatty material, assumed by him to be phospholipins, intimately associated with the protoplasm, which is indispensable for the life of the organism; and by the term " element variables' he designated any additional amount of fat stored as a reserve material. In the case of animal tissues, three possibilities have been postulated for the function of the phospholipins [Sinclair, 1934]: (1) that they are intermediate