Our present concepts ofthe regulation of enzyme activity in the cell have been largely based on the extensive body of work which has been carried out with micro-organisms. A distinction between constitutive and adaptive enzymes had already been made well before World War II and work on enzyme adaptation, both in yeast and bacteria, was done by several workers, especially Marjorie Stephenson and her group in Cambridge in the 1930s. In studies starting about 1947 Stanier demonstrated that the oxidation of aromatic compounds by species of Pseudomonas involved the coordinate and sequential induction of a group of enzymes concerned in the orderly catabolism of a substrate which acted as the inducer. The investigations of Umbarger and of Pardee, both in 1956, established the principle, which is now firmly established for almost all anabolic reaction chains, that the first 'committed' step in a biosynthetic pathway is sensitive to feedback control by the final product of the particular reaction sequence. This control can be exercised in two ways. It can either act on the rate of formation of the enzyme or it can affect the activity of the latter without altering the concentration of the enzyme.

Sir Francis Avery Jones 149 Harley Street, London, WlN 2DE, U.K. This first international symposium on Mucus in Health and Disease brought together medical scientists, physiologists, pharmacologists, physicians, surgeons, gynaecologists, ophthalmologists, anatomists, biologists, medical engineers and biochemists - a spectrum which indicates the wide field of interest in mucus both in health and in disease. The idea for the meeting came from Dr. S. Gottfried whose researches led to the development of carbenoxolone, a substance which stimulates mucus production and in this way favours the healing of peptic ulcers. The idea was enthusiastically welcomed by Professor Dennis Parke and he, and Mr. Max Elstein, have been the dynamo behind the meeting. The opening keynote address by Professor Clamp set the scene for the Symposium, painting a broad canvas and highlighting the main features. We cannot do without mucus, irritating though it may be if there is too much or too little, and in so many systems of the body it plays a vital role. For the first time the specialists in different systems of the body have had the opportunity of coming together and discussing their special problems - a cross-fertilisation which proved to be most valuable, not only for one another but also for the medical scientists who had been closely concerned with the chemistry and physical properties of mucus.