[100 years of allergy: Clemens von Pirquet - his idea of allergy and its immanent concept of disease].

Coming from his clinical research in the field of infectiology and immunology the Viennese pediatrician Clemens von Pirquet (1874-1929) introduced the term "allergy" in 1906. With it he wanted to describe in general a change in reactivity of the organism, namely in time, quality and quantity. In contrast to the widely accepted use of the word "allergy" today, where it is restricted to specific immunologic hypersensitivity reactions against harmless foreign antigens, allergy in Pirquets sense comprised as general term likewise increases and decreases of the reactivity and so both "hyper-" and "hyposensitivity reactions". In the context with the expansion of allergy to the human predisposition Pirquet emphasized, that the change of reactivity does not only depend on exogenous substances (so called allergens), but also on endogenous factors of the organism itself. - The orientation towards the organism and his reactivity is the central idea, which can be found in the complete works of Pirquet from 1903 to 1929 and which is presented in this publication for the first time. It is the true essence of his theory of allergy.