This is a revision and extension of the mimeographed edition that appeared under the same title in 1935. Numerous typographic errors and omissions have been eliminated. The material has been rearranged and extended so that the physiologic aspects are discussed in connection with the chemistry of each type of lipid. Much use is made of interpretations and presentation of data from x-ray analyses and of recent work on surface tension phenomena, various colloidal phenomena, iso-electric ranges and melting points. In this manner the author treats the lipins in the following order: fatty acids, soaps, alcohols, waxes and hydrocarbons, the sterols and related compounds, fats and oils, the phospholipids, cerebrosides, carbohydrate esters of the higher fatty acids, and emulsions. The work is well done and excellently presented for advanced students in biochemistry. The compilation of the recent observations on emulsions, buffer action, pH, antioxidants and unsaturation is especially valuable. It