Serum Sickness

BACKGROUND: In the late 19th and early 20th century there was much interest in understanding the reactions to diphtheria antitoxin and the horse serum in which it was produced and administered. OBJECTIVE: Pirquet and Schick reported on their studies of these reactions; particularly the differences in the reaction of those patients who had only one injection, and those who had a re-injection. CONCLUSION: Pirquet and Schick concluded that "due to a single injection of horse serum a change takes place in the reaction of the human organism to the re-introduction of the same substance." This change, Pirquet in a 1906 article, called allergy.