Henle first described the epithelia of the skin and intestines, and defined the structure and function of columnar and ciliated epithelium. He applied the term “epithelium” to all mucous membranes in the body. Modern knowledge of the epithelial tissues starts with Henle. English translation and commentary in L.J. Rather, P. Rather, & J.B. Frerichs, Johannes Müller and the nineteenth century origins of tumor cell theory, Canton, Mass.: Science History Publications, 1986.