The immune system has evolved in large part to enable organisms to resist microbial infeetion. Given this very fundamental relationship between the immune system and infeetious microbial agents it is entirely appropriate that avolume in this series should be devoted to the immunology of infeetion. Mieroorganisms have long been used as experimental tools by immunologists, and the study of the immune response to viruses and baeteria has eontributed mueh to our understanding of basie immunologieal meehanisms (for example of the meehanism by whieh non-self determinants on eells are reeognized)....