41 2 PA THOGENIC BACTERfA. Pasteur discovered that when cultures are allowed to remain undisturbed for several months, their virulence is greatly lessened, and new cultures planted from these are also attenuated. When chickens are inoculated with such cultures, no other change occurs than a local in- flammatory reaction by which the birds are protected against virulent bacilli. From this observation Pasteur worked out a system of protective vaccination in which fowls can first be inoculated with very weak, then with stronger, and finally with highly virulent cultures, with a resulting protection and immunity. Unfortunately, the method is too complicated to be very practical. Use has, however, been made of the ability of this bacillus to kill rabbits, and in Australia, where they are pests, they are being exterminated by the use of bouillon cul- ture. It is estimated that two gallons of bouillon culture will destroy 20,000 rabbits irrespective of infection by contagion. The bacillus of chicken-cholera seems not only to be specific for that disease, but seems able, when properly introduced into various other animals, to produce several different diseases. Indeed, no little confusion has arisen in bacteriology by the description of what is now pretty generally accepted to be this very bacillus under the various names of bacillus of rabbit-septicemia (Koch), Bacillus cuniculicida (Fliigge), bacillus of swine-plague (Loffler and Schiitz), bacillus of iC Wildseuche" (Hiippe), bacillus of l' Biiffelseuche " (Oriste-Armanni), etc.