Is it not sheer foolishness to try to apply the methods of theoretical physics to biological structures? Physics flowered because it limited itself to the study of very simple systems; on the other hand, the essence of "living things" seems to have to do with the extreme intricacy of their structure. Is it a hopeless endeavour to attempt to bring the two together, or should one try nevertheless? Most of my colleagues in theoretical physics feel one should not waste one's time and stick to "the good old hydrogen atom", but some of them feel one should try anyhow. This minority point of view was shared by Bohr in the thirties, Schrödinger in the fourties, Delbrück in the fifties and sixties, PurceIl in the seventies, etc. The theory of chemoreception represents only a very small part of this immense scientific question. Its study was started by Delbriick and others in the fifties. I was introduced to these problems by Charles DeLisi, during a visit to the National Institutes of Health in the summer of 1980. During the following decade I had the pleasure to collaborate with George Bell, Byron Goldstein, Alan Perelson and others at the Los Alamos National Laboratory. We studied a wide variety of questions, some of them relevant to the theory of chemoreception. I am grateful to them, both for the pleasure which our joint research always gives to me, as weIl as for their friendship and hospitality.

Inhalt
I. General Considerations.- II. Spatial Diffusion.- III. Ligand Current into a Single Receptor.- IV. Theory of One-Stage Chemoreception.- V. Ligand Capture by a System of Many Cells.- VI. Diffusion and Flow in the Cell Membrane.- VII. Excluded Volume Effects in the Diffusion of Membrane Proteins.- VIII. Theory of Two-Stage Chemoreception.- IX. Chemoreception by a Swimming Cell.