CAUSES OF FORMATION OF ANTIBODIES 153 



against Eherth's bacillis becomes better able to resist typhoid 

 infection. Where the bacillus acts solely by its albumin 

 (cholera, typhoid fever), or simultaneously by its albumin 

 and its toxin (certain pneumonias, dysenteries, meningitides) , 

 the neutralization of the albumin-antigen by the antibody in 

 excess causes a pathological reaction. 



In such cases, the pathological manifestations which 

 characterize disease are caused not by the direct action of a 

 bacterial poison, but by a reaction resulting from the com- 

 bination of antigen with antibody. 



It is easy today, by carefully analyzing these experimental 

 facts to understand the causes of the confusions, of the 

 apparent contradictions and of the errors in interpretation 

 of certain experiments: The process of immunity is never a 

 simple reaction, because biological antigens are never chemically 

 simple substances. The simplest of all, a diphtheria or 

 tetanus toxin, is a mixture of a large number of complex 

 compounds arising from the culture fluid on the one hand, and 

 from the bacillus on the other. The bacillus body is very 

 probably composed of several kinds of albumins and of sub- 

 stances derived from these albumins, which, when dissociated 

 in the infected organism, may each on its own account be 

 anaphylactic or " antigenic" and may cause different chemical, 

 physiological and pathological, direct or secondary, reactions. 

 Some produce antitoxins, others anaphylactic antibodies, 

 still others produce antibodies which are both antitoxic or 

 anti-infectious and anaphylactic. 



With toxins or very virulent bacilli, certain directly patho- 

 genic principles are so predominant that the reactions caused 

 by the other antigens are practically negligible; in many 

 other cases (syphilis, malaria, trypanosomiasis, typhoid 

 fever, etc.), the contrary has been found: In the case of 

 albumins of only a slightly toxic nature the anaphylactic 

 reactions are predominant. 



We can consider as the two extremes in this order of ideas : 

 on the one hand the filtered broth cultures of tetanus or 

 diphtheria (toxin) directly and nearly exclusively toxic with- 

 out anaphylaxis; on the other hand a heterologous serum or 

 white of egg exclusively anaphylactizing; and between these 



