ABSTRACT
I. INTRODUCTION A variety of terms have been used to define the substance that stimulates an atopic reaction. Which words are used depends upon the terms chosen to denote the sensitivity. In the context of a general immunological reaction, the triggering substance is called an antigen. An antigen in modem usage is any substance that, as a result of coming into contact with appropriate tissues of an animal body, induces a state of sensitivity and/or resistance to infection or other substances after a latent period. In addition, the stimulating substances react specifically and in a demonstrable way with the responding tissues and/or antibody of the sensitized subject in vivo or in vitro. When allergy, defined as an adverse immune reaction, is used to express the state of sensitivity, von Pirquet called the exciting substances (or "antigen") that causes the sensitivity an "allergen." He stated that "the allergens comprise, besides the antigen proper, the many protein substances which lead to non-production of antibodies but to supersensitivity." The antibody that is produced by the
allergen was given the name "allergin," a term rarely used today. Coca coined the word "atopy" as a type of sensitized state and called the exciting substance an "atopen" and the reacting antibody a "reagin" or skin-sensitizing antibody. For experimental anaphylaxis in animals, the antigen is called an anaphylactogen, and the antibody an anaphylactin or anaphylactic antibody (1,2).
