the great treatises on the physics of diffusion and the flow of heat where, to be sure, we could dig out the information that was needed. It was a great joy then to come across this masterful and schol­ arly discussion on diffusion written for biologists of a physical tum of mind by MERKEL JACOBS. Here were to be found not only the equations that were basic to our knowledge, but also a careful, accurate and logical explanation, both of the physical principles and the mathematical steps. It soon became apparent that we could not keep that one volume of Ergebnisse der Biologie on indefinite loan from the library, and we then found, by good fortune, a remaindered copy of this particular issue. It has become a well-thumbed and treasured possession of the laboratory.