The importance of antibody molecules was first recognized in the 1890s, when it was shown that immunity to tetanus and diphtheria was caused by antibodies against the bacterial exotoxins (1). Around the same time, it was shown that antisera against cholera vibrios could transfer immunity to naïve animals, and also kill the bacteria in vitro (1). However, although antitoxin antibodies rapidly found clinical application, there was little understanding regarding the nature of the antibody molecule. Indeed, the earliest theories suggested that the antitoxins were derived by modification of the toxinintriguingly similar “antigen incorporation” theories were propounded as late as 1930 (1).