Whither virology? Trends and prospects in medical research.

FOR just over three-quarters of a century the study of the viruses has furnished a most exciting chapter in the growth of the natural sciences. The story began with the observations of Ivanovsky upon tobacco mosaic disease in 1892 and of Loeffler and Frosch upon foot and mouth disease in 1898. Both studies showed that the respective diseases could be transmitted by filtered extracts from the affected plants or animals containing no recognizable bacteria. Yet the contagious material in the filtrates could neither be visualized nor cultivated. A similar mystery surrounded Reed's transmission of yellow fever to man in 1902 and that of poliomyelitis to monkeys by Landsteiner and Popper in 1908. Though history credits Buist (1886) and Paschen (1906) with the first demonstrations of virus particles in vaccinial lymph, further progress awaited technical advances in microscopy. When I was first initiated into virus research at the National Institute for Medical Research at Hampstead in 1935, Dr J. E. Barnard was using ultraviolet photomicrography to demonstrate the elementary bodies of the pox viruses. Also W. F. Elford was studying the measurement of size based upon graded collodion filters. The then known particles including viruses were arranged in order of size from bacterium to molecule and Sir Henry Dale, in his Huxley lecture at Imperial College in 1935 entitled 'Viruses and Heterogenesis', relied upon such evidence to dispose of the argument that viruses are products of the cells of other living organisms-an argument which recurs periodically right up to the present day. The techniques which have been pressed into use in the study of viruses are many and varied but periodically all virologists return from their chemical or physical technicalities to the question of the transmission of infection, for it has been this above all which has characterized the virus as an object worthy of study. In the early studies, transmission of