502 BACILLI WHICH PRODUCE SEPTICZMIA 
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- 
Fie. 131.—Bacillus of Schweineseuche, 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 asmall 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 fatal 
to a chicken. 
Pathogenesis.—Pathogenic for chickens, pigeons, pheasants, 
sparrows, and other small birds, for rabbits and mice, also for swine 
(Schweineseuche), for cattle (Rinderseuche), and for deer (Wil]. 
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 
