30 APPLIED IMMUNOLOGY 



dose of the same serum then be given, its molecule is 

 split up by the proteolytic ferment, and the toxic con- 

 stituent is set free, giving rise to anaphylaxis. There 

 is no setting free of the poisonous elements of the pro- 

 tein molecule immediately after the first injection of 

 serum, because the specific proteolytic ferment de- 

 velops gradually in response to the stimulation of the 

 specific group of the molecule. Hence the toxic ele- 

 ment is only liberated in small amounts as the ferment 

 is formed. But by the time a second injection of 

 serum is administered, a considerable amount of the 

 proteolytic ferment is stored up, and is ready to split 

 up the molecules of the second injection and set free 

 the toxin which gives rise to symptoms of anaphylaxis. 

 The anaphylactic poison affects chiefly the nervous 

 system, and particularly the respiratory centres. The 

 reaction manifests itself in respiratory difiiculty and 

 convulsions, which may result fatally, and is particu- 

 larly liable to occur in asthmatic persons. The injec- 

 tion of antitoxic horse serum has been known to pro- 

 duce anaphylactic phenomena in persons in whom at- 

 tacks of asthma are induced by contact with horses. 

 We do not yet know the nature of the anaphylactic 

 poison. It is now recognized that not only serum, but 

 all forms of toxic and non-toxic protein material, in- 

 cluding milk, extracts of normal and pathologic ani- 



