It may seem trivial to state that one of the major trends in biological investigation consists in an attempt to explain the structural and functional aspects of living matter in chemical terms, in an effort to obtain insight into the equivalent of macroscopic phenomena on the molecular level. I am sure you are aware of, and this meeting of the Association has brought ample additional evidence, in how many fields this tendency has become apparent. It can be recognized in genetics with the molecular analysis of chromosomes and the enzymatic or metabolic interpretation of hereditary properties like the eyecolor of Drosophila. In a purely morphological branch like histology we do not ask merely for a differentiation of stained cell structure but we ask for the nature of the staining reaction; in nerve physiology we try to interpret conduction as alterations of protein lipoid layers; or in pathology where the age old syndrome of inflammation is explored with biochemical methods. I should mention molecular models of membranes and cell surfaces, the molecular interpretation of secretion and of the macroscopic phenomena of metabolism. Yet insofar as this yield of data could be designated as a trend, it would rather seem to be the natural outcome to be expected from the application of the analytic method of science. In one instance, however, this approach has been carried farther than in all the other fields, and it would seem to be worthwhile to pause for one moment to ask whether this case is important merely because of its technical implications or whether it is meaningful in a wider sense.