Some early scientific studies of skin color.

The current notions of the structure and function of skin pigment originated more than a century ago when Simon, Henle, and others discovered that the outer layer of the skin was a self-renewing cellular membrane that contained small, discrete granules of pigment. For almost two centuries before that time, the skin was thought to have three layers: an outer colorless cuticle, an inner colorless cutis, and, sandwiched between them, a layer of a black mucous substance. Although many of the experiments carried out between 1665 and 1840 may appear to us to be "simple" in design, in their own contexts, they were often the results of great effort and even greater ingenuity. Some of these 17thand 18th-century studies of skin color science are summarized in this paper. The notion that there were three layers of skin originated with the Italian anatomist, Marcelo Malphigi. In 1665 he undertook a study of the anatomy of sensation, and wished to identify the structures of the skin related to touch and pain. He found that if he allowed a piece of skin to remain at room temperature for a few days, he could easily separate it into layers. Using a primitive microscope he could identify an outer layer (the "scarf"), and an underlying "cutis" covered with small papillae, which he believed to be the organs of sensation. Most of his studies were on animal skin. One preparation, however, was from the cadaver of an Ethiopian. Malphigi found that a black mucous material was present between the "scarf" and the "cutis." When the skin was examined from above, after the scarf had been removed, the black material in the troughs between the papillae had the appearance of a network. Although he could not isolate the material as a membrane, he considered it to be analogous to the more discrete, perforated layer he had discovered in the tongue a year earlier. He called this layer the rete mucosum or the mucous network. On the basis of this dissection, Malphigi announced to the world that he had discovered the seat of color of Ethiopian skin (1). We now recognize that Malphigi's mucus was an artifact, representing liquefaction of the lower epidermis. In the 17th century, however, the idea seemed logical,