STUDIES ON FOWL CHOLERA 279 



confirmed under conditions in which it was clearly shown that no 

 bacteria were present in the filtrate. Stang, moreover, was able 

 to inject 20 cc. of concentrated filtrate without producing an 

 infection, or signs of poisoning, 



Weil concludes that one cannot demonstrate the slightest 

 toxicity against the most susceptible animals (like the rabbit) 

 in the case of fowl cholera. He pertinently inquires why a 

 toxin-neutralization if present in immune animals should dimin- 

 ish the unlimited development of the bacteria. B. avisepticus 

 shows characters sharply opposed to those of toxin-forming 

 bacteria which never develop in great numbers in the body 

 (diphtheria, tetanus, dysentery). 



Another line of investigation which demonstrates the lack of 

 extracellular toxins in the case of B. avisepticus is found in the 

 experiment of Citron and Piitz (1907) who employed serum ex- 

 tracts and water-extracts of virulent bacterial cultures (artificial 

 aggressins as opposed to natural aggressins of Weil). With these 

 artificial aggressins the authors mentioned inoculated rabbits 

 with the aim of furthering infection, or of producing immunity. 

 The method did not in either case prove so successful as the 

 method of Weil, involving pleural exudates, but the point for our 

 present consideration is that the experiments conducted were 

 such as to demonstrate the total lack of either exotoxins or 

 endotoxins in the materials used for injections. The inoculated 

 animals invariably remained in good health up to the time of 

 infection with the active virus. 



Other evidence showing the absence of toxins in the case of 

 B. avisepticus is supplied indirectly by the studies of Weil and 

 Braun (1909). Weil (1905b) had already shown that his 

 method of inoculation with sterile pleural exudates was not only 

 sufficient to protect animals against infection, but that the serum 

 of such animals possessed protective power. The question nat- 

 urally arose regarding the nature of the protective substances 

 in such serum. Weil and Braun attempted to ascertain whether 

 the protection was due to bactericidal substances. Animals were 

 accordingly inoculated with serum which had been ''treated" 

 (absorbed) with fowl cholera bacteria, and survived infection. 



