THIRD FUNDAMENTAL AGGRESSIN EXPERIMENT. 41 



term, as by injections of natural aggressins. As the possibility of the 

 production of aggressins by a struggle between the bacteria and distilled 

 water can be excluded, it can be taken without further explanation that in 

 the development of those substances which have a tendency to increase the 

 virulence of bacteria, or which can be used to produce an immunity, the 

 bacteria play a passive role, in that they are only extracted by the dissolving 

 agent. The difference between the anti-bacterial and anti-aggressin im- 

 munity is therefore not a qualitative one, as in both instances it is the sub- 

 stances that are set free from the bacteria which stimulate the formation of 

 antibodies. When living virulent bacteria are injected for the purposes of 

 immunization, they increase so rapidly that a proper dosage is impossible 

 and the animals frequently die before enough antibodies are liberated. In 

 addition antibodies are also generated against the capsule of the bacteria 

 (bacteriolysins) . 



The only difference between immunization with morphologically well 

 preserved but dead bacteria and that with aggressins is that within the latter 

 the bacterial substances which tend to bring about the immunity have not 

 been altered by previous heating, but exist in their natural easily absorbable 

 form. Moreover, by using the extracts one does away with certain toxic 

 substances which are found within the bacterial capsules, and which are 

 rather toxic to subcutaneous tissue, producing necrosis and marasmus. 



The Third Fundamental Aggressin Experiment. 



Here, it is demonstrated that the serum of animals immunized by aggres- 

 sins either artificial or natural, contain antibodies which (i) can neutralize 

 that property of aggressins whereby they increase the virulence of bacteria; 

 (2) produce a passive immunity against infection with living bacteria. 



As for the biological structure of these antibodies, or anti-aggressins as 

 they may be called, it may be said that they belong to the class of ambo- 

 ceptors, shown by the complement fixation methods. 



The practical employment of aggressins as a method of immunization 

 offers distinct advantages, namely: 



1. Absence of any possible dangerous effects. 



2. Absence of or only very slight local and general reactions. 



3. The high degree and long duration of the immunity gained by pro- 

 phylactic inoculations. 



4. The possibility of immunization against pure parasites. 



5. The facility with which the inoculation material is preserved. 

 The disadvantages, however, may be summarized as follows: 



1. The manufacture of the inoculation material is rather complex and 

 with some pathogenic bacteria (pest), not without danger. 



2. The increased susceptibility during the interval between the inocu- 

 lation and the onset of Immunity. 



