The foregoing volumes of the handbook show the unmistakable mark of its founder and first editor, RoBERT DoERR. He and other prominent expert specialists cooperated to show the uniformity of the problems and the methods of virus research, to take due account of the value of theo- retical perception and to ensure a fruitful influence of this on other branches of science. Since the demise of the great master it has been the main task of suc- ceeding editors to keep up this great tradition, yet to do justice to other requirements as well. In the present (fourth) volume this wider scope has been taken into account. It deals not only, as heretofore, in a general part with the actual problems and the development of techniques and methods of virus research, but also in a special part, in a monographic manner, with the individual virus species. With such reviews of the re- search on various virus species, planned also for future issues, the hand- book shall attempt to fulfill its role as a reference work. A tribute of gratitude is due the publishers for their understanding cooperation and their most liberal readiness to complete the text with unusually numerous illustrations. San Francisco and Bern, January, 1958. K. F. MEYER c. HALLAUER Vorwort. Die bisher erschienenen Bande des Handbuches tragen den untrug- lichen Stempel seines Begrunders und ersten Herausgebers, RoBERT DoERR.