502 BACILLI WHICH PRODUCE SEPTICAEMIA 



acid in six hours (Hueppe). Pasteur (1880) has shown that when 

 cultures of this bacillus (microbe of fowl cholera) in bouillon are 

 kept for some time they gradually lose their pathogenic virulence, 

 and he has ascribed this "attenuation of virulence" to the action of 

 atmospheric oxygen. He also ascertained that the particular degree 

 of virulence manifested by the mother culture after a certain interval 

 could be maintained in successive cultures made at short intervals. 

 He was thus able to cultivate different pathogenic varieties, and to 

 use these in making protective inoculations, by which susceptible ani- 



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*>' **.''.,-, "\ ' . * .- *-* ' : "\ 



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FIG. 131. Bacillus of Scliweineseuche, in blood of rabbit. (Schiitz.) 



mals were preserved from the effects of virulent cultures injected 

 subsequently. 



Attenuated cultures recover their virulence when inoculated into 

 very susceptible animals. Thus a culture which would produce a 

 non-fatal and protective attack in a chicken may, according to Pas- 

 teur, kill a small bird, like a sparrow; and by successive inoculations 

 from one sparrow to another the original degree of virulence may be 

 restored, so that a minute quantity of a pure culture would be f aid 

 to a chicken. 



Pathogenesis. Pathogenic for chickens, pigeons, pheasants, 

 sparrows, and other small birds, for rabbits and mice, also for swine 

 (Sehweineseuche), for cattle (Rinderseuche), and for deer (Will- 

 seuche). (See supra, pp. 285-287.) 



The researches of Smith and of Moore show that " an attenuated 

 variety of bacteria, belonging to the group of swine-plague bacteria 

 and not distinguishable from them, inhabit the mouth and upper air 



