The fatty substances of the surface of the skin are physically and chemically of great importance in the economy of the body. Not only do they provide a water-repelling protective film for the skin and its appendages, and serve to keep the skin supple and soft, but there is reason to believe that they contain the precursor of vitamin D and perhaps other valuable substances which are activated by irradiation at the surface of the skin. It is also possible that they play an important part in many as yet little understood skin phenomena such as "contact dermatitis." It seemed important, therefore, to know something of the nature of these lipids, because of theoretical as well as practical interest, since applying similar substances may prove of benefit in many cases of xeroderma. For the present knowledge concerning the nature of the superficial lipids of the skin one is indebted to