CHAPTER ^XXVII 

 ANAPHYLAXIS 



IT is generally believed that when an animal previously injected with 

 an antigenic substance is subsequently reinjected with the same sub- 

 stance, the antibodies induced by the first injection are reenforced, and 

 that a continuation of the process of immunization will eventually lead to 

 a high degree of immunity. Under certain circumstances, however, this 

 is not the case, because severe and even fatal symptoms, as well as other 

 manifestations, may set in after the second injection, indicating that, 

 instead of being immune, the animal is indeed hypersusceptible or 

 hypersensitive to the affects of the antigenic substance. 



Similarly, it is a common observation that whereas certain infections, 

 such as smallpox, scarlet fever, and measles, confer a state of immunity, 

 others, as, for example, pneumonia, erysipelas, and influenza, not only 

 are not followed by immunity, but, indeed, that a decreased resistance 

 or predisposition to subsequent infection by the same microorganism 

 may be induced. 



Before experimental investigation of this subject was undertaken, 

 not a few observations were made and described by the early workers 

 in the fields of bacteriology and immunity that correspond exactly with 

 the phenomenon of hyper sensitiveness, as we understand it today, 

 although the true explanation of their unexpected results was not sus- 

 pected, and they were modestly ascribed to faulty technic, embolism, 

 toxicity of the inoculum, etc. From this it followed that the discovery 

 that the experimental injection of such ordinary innocuous substances 

 as normal serum and milk may produce violent symptoms and death 

 gave rise to much surprise and incredulity, since scientists had long been 

 accustomed to regard the reaction of an animal to an injection as a 

 process of immunization, or diminished sensitiveness, instead of one of 

 increased sensitiveness. Here, as Besredka remarked, the rules of 

 immunity are " standing on their heads." 



To this state of hypersensitiveness Richet, one of the earliest in- 

 vestigators in this field, applied the term " anaphylaxis," meaning 

 "without protection." While it appears to be the exact antithesis of 

 "immunity," which means "with resistance to infection," recent re- 



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