THE AGGRESSIVE IMMUNITY 43 



4./VII. Infection: i/ioo loopful of swine pest culture subcutaneously. 



I5./VIL Small local infiltrate. Very active. 



3-/X. Animal alive and perfectly well. 



Control animals inoculated on the days of infection died within twenty-four hours 

 after inoculations of 1/100,000 loopful of culture intravenously, 1/10,000 loopful 

 subcutaneously. 



It is evident from the above, that an immunity against pure parasites 

 can be obtained just as well by one or several injections of extracts of living 

 bacteria, as by injections of natural aggressins. Since 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 dis- 

 solving agent. The difference between the anti-bacterial and anti-aggres- 

 sin immunity is therefore not a qualitative one, as in both instances they 

 are the substances 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 absorb- 

 able 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 

 thai-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 cf 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. 



