Phospholipids are the structural constituents of all of the tissues of the body that are involved in cellular metabolism. They contain phosphoric acids and higher fatty acids of an unusually high degree of unsaturation. This composition gives them a dual function, as they manifest physical and chemical properties in both aqueous and non-aqueous mediums. The phosphoric acid radical makes possible their solubility in aqueous protoplasmic tissue, while the organic fatty acid serves as the colloid substratum that disperses insoluble substances in living matter. The high degree of unsaturation makes the phospholipid a most readily available tissue constituent for immediate metabolic requirement. In recent years this chemical lability, which is so distinct from the stability of body fat, has been related to the metabolism of water and salts in epilepsy, nephrosis and allergic diseases.
Phospholipids in the tissues vary both qualitatively and quantitatively with the nature of the dietary fat ingested,