VIIL] BACTERIUM. 95 



attenuation shows itself in this that according to the length 

 of time the culture is kept, the number of animals killed by 

 its inoculation gradually diminishes, and it ultimately ceases 

 to kill at all. Each culture of diminished virulence transmits 

 its attenuation to the next following culture (?). It is 

 possible to obtain cultures of such a low degree of virulence 

 that when inoculated into the skin of a fowl only a local 

 effect is produced, a peculiar infiltration ; but the animal 

 survives, and is then protected or " vaccinated " against the 

 more virulent material. But in order to produce this pro- 

 tection, it >is necessary that the culture (vaccine) should be of 

 the proper strength. If it does not produce a local effect it 

 gives no protection. 



In fresh cultures the bacterium is more in the shape of a 

 rod, constricted in the middle ; in cultures several days old 

 it looks very much more like a dumb-bell of micrococcus (see 

 note on previous page). 



Babes l has found the bacteria in the tissues and blood- 

 vessels of animals dead of the disease, both inoculated and 

 epizootic, in the shape of rods of about 0*0015 to 0*002 mm. 

 in length and about 0*00025 mm. in thickness; the ends 

 always staining more deeply than the middle part. 



1 Archives de Physiologic, July 1883, p. 49. 



