ANAPHYLAXIS OR HYPERSUSCEPTIBILITY 29 



body formation. He applied this theory to the period 

 of incubation and symptoms of infectious diseases, all 

 of which may be regarded as anaphylactic phenomena. 

 In short, according to von Pirquet, the causative 

 agents of disease do not show their deleterious effects 

 until antibodies are formed which split them up, set- 

 ting free toxic substances. Theobald Smith observed 

 that guinea-pigs, which had been injected with toxin- 

 antitoxin mixture, were hypersensitive to subsequent 

 injections with normal horse serum and rapidly suc- 

 cumbed to small doses of the latter. The most attrac- 

 tive and rational explanation of the phenomena fol- 

 lowing protein sensitization or anaphylaxis was first 

 brought forward by Vaughan in 1907 {Jour. Infec- 

 tions Diseases, 1907, iv, 476). Vaughan's views may 

 be briefly stated as follows: Every protein molecule 

 consists of a poisonous group and a non-poisonous or 

 specific group. The latter group, when the molecule 

 is introduced into the body, induces the development 

 in the body of a specific proteolytic ferment, which 

 has the power of splitting up similar protein mole- 

 cules, setting free the poisonous or non-specific group. 

 The poison thus set free produces the phenomena of 

 anaphylaxis. Upon the first injection of a serum, 

 therefore, the specific group of the molecule causes the 

 formation in the body of a specific proteolytic ferment. 

 The animal is now said to be *' sensitized." If a second 



