LEON LILIENFELD, whose death occurred quite unexpectedly at Milan on June 6 through pneumonia contracted whilst engaged on the industrial application of his latest inventions, commenced his professional career as a medical man. A growing interest in cellulose led him to abandon medicine and devote himself to research work on this material. In 1912 he produced new derivatives of cellulose, namely, various cellulose ethers having very widely different properties and capable of diverse applications. The Great War interrupted these activities and Lilienfeld was engaged on X-ray work in the Austrian army. He wrote a book embodying all his experiences which even to-day is regarded as a standard work in this branch of medical research.