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512 
the most satisfactory method for use in human protection against plague. 
However, my experiments have shown that with an extract of the plague 
bacillus I have been able to produce in monkeys a certain degree of 
immunity against plague infection, similar to that brought about by 
Hueppe and Kikuchi with peritoneal exudates from animals dead of 
plague, but since the extract I have obtained, while it exerts an action 
similar to that of the so-called aggressin exudates, is prepared by a 
different method, namely, from the bacteria which have been cultivated 
outside of the animal body and which have not been acted upon by an ani- 
mal exudate, I shall propose to call it merely plague bacillus extract. In 
regard to the use of the term “anti-aggressin” for those sera obtained 
during the process of immunization against such diseases as anthrax, 
rinderpest, plague, ete., and in which diseases it has long been recognized 
that there is no true bacteriolytic immunity, it would appear that the 
previously proposed term of anti-infectious sera would answer as well if 
not better. The aggressins in spite of the work of Bail and his associates, 
must still be regarded as hypothetical substances. 
