Not many years ago, problems of membranes and transport attracted the attention of but a few dozen enthusiasts, mainly physiolo­ gists who recognize~ the significance of membranes for the stabilization of the general steady state of organisms. The first symposium organ­ ized some fifteen years ago could boast of the attendance of perhaps fifty scientists (the remaining fifty were not yet sure that membranes was the topic of their choice), ranging in specialization from physical chemistry to bacterial genetics, who clairvoyantly decided to study what now has become the number one subject at most congresses of biophysics, physiology, and even biochemistry and microbiology. As is the case with many rapidly developing fields, the interest in membranes and transport seems to be growing out of bounds and the whole field of membra no logy, interdisciplinary as it is, has penetrated into the realms of a number of branches of physics, chemistry, and biology. Its subject is primarily biological and, although much has been done in the world to increase the "exactness" of biology over the past thirty years, one cannot strive for a rigorous mathematical description of biological phenomena since, as M. H.