278 PHILIP HADLEY 



the nature and biological features of the bacterial species in 

 question 



In a series of classic papers which appear to have attracted 

 less attention than they deserve among American students of 

 immunological problems, Edmund Weil (1905a, 1905b, 1907a, 

 1907b, 1908) following the steps of Bail, has presented the clearest 

 evidence as to the elements favoring infection which characterize 

 the activity of the bacteria of the fowl cholera group. An analy- 

 sis of the situation as based upon his studies and those of his 

 collaborators (Weil and Braun, 1909) may briefly be summarized 

 as follows : 



1. Rabbits, inoculated in the pleural cavity with virulent fowl 

 cholera cultures produce an exudate which harbors substances 

 favoring infection — the aggressins. 



2. These aggressins, which are manifestly equivalent to the 

 virulins of Rosenow and to the antiphagines of Tchistovitch and 

 Yourevitch, possess in high degree the property of furthering 

 infection. Treated animals die with a sub-lethal dose of virus 

 while control animals resist ten times that dose. 



3. The infection-furthering property of the exudate does not 

 lie in poisonous substances, since animals easily tolerate 12 cc. 

 or eight times the dose necessary to determine a fatal issue when 

 administered together with a non-lethal dose of virus. 



4. The results cannot be due to an inactivating influence in the 

 opsonic sense, since leukocytes (whether in immune or normal 

 animals) manifest no, or slight, phagocytosis either in vitro or 

 in vivo. 



5. Toxicity and aggressivity are not identical; toxicity is most 

 noteworthy in organisms which are not highly aggressive; and 

 the most aggressive organisms are non-toxic. B. avisepticus, 

 the causative agent in cholera of fowls, is the most aggressive 

 organism that has been studied. 



Weil's tests, devised to show whether toxins can be held respon- 

 sible for the highly fatal results following inoculation with fowl 

 cholera virus, are elaborately planned and (so far as one may 

 judge) carefully executed. Pasteur's observation on the toxicity 

 of the concentrated filtrates of B. avisepticus has never been 



