144 THEORIES CONCERNING IMMUNITY 



of diphtheria or tetanus toxins could be repeated at will 

 on the same animal without ever causing an anaphylactic 

 crisis, and that, on the contrary, the result of these injections 

 had been the formation in the blood of the injected animal 

 of an antitoxin which neutralized the noxious action of these 

 toxins. 



Richet was therefore perfectly justified in considering 

 anaphylaxis as a new and peculiar phenomenon. He speci- 

 fies the conditions of its evolution by insisting on the neces- 

 sity of an "incubation period" (as in immunity), during 

 which the organism prepares its anaphylactic state and he 

 explains it by the formation of a "prepoison" (toxogenin), 

 which becomes a poison when in contact with a new quan- 

 tity of antigen. Interpreted in this way, Richet's discovery 

 contributed a new complication to the explanation of the 

 immunity process. 



How and why is toxogenin formed, through what mechan- 

 ism does it become apotoxin when it combines with the 

 antigen? These were further questions that had to remain 

 unanswered at the time. 



However, in spite of ignorance as to explanation and 

 classification, these phenomena created much interest, 

 exactly because they were in formal contradiction to the 

 fundamental principle on which was founded not only pre- 

 ventive vaccination but also the preparation of antitoxic 

 sera. 



These were questions which closely affected the most 

 important, the most stirring problems of general biology. 

 It was impossible to leave them in suspense, or to be con- 

 tented with provisional, incomplete and often contradictory 

 explanations; and in order to arrive at more satisfactory 

 answers it was necessary to penetrate still further into the 

 mechanism of these reactions. And so research into the 

 properties and the action of heterologous albumins became 

 the order of the day in every laboratory of experimental 

 biology. 



Soon after the publication of Richet's work, which con- 

 cerned itself only with anaphylactic shock, Arthus discovered 

 local and chronic anaphylaxis by showing that successive 

 injections of horse serum into rabbits, no longer into the 



