The routine title of the long ‘note’ by Glenny and Südmersen reproduced here [1] hides two of the most significant findings in theoretical and applied immunology: a brief description of diphtheria toxoid and a comprehensive account of the primary and secondary immune response. The introduction of antitoxin treatment of diphtheria was heralded, in 1896, without exaggeration as ‘the most important advance of the [19th] Century in the medical treatment of acute infective disease’ [2]. However, there were problems with the standardization and potency of antitoxin. The former was solved by Ehrlich who, in his analysis of toxin–antitoxin interaction, postulated the existence of ‘toxoid’, a non-toxic component of toxin which combined with antitoxin [3]. The latter was solved by the general observation that repeated injections of gradually increased doses of toxin induced increasingly potent antitoxins, an important basis upon which the present paper was founded.