426 THE BACILLUS OF ANTHRAX. 
a small quantity of agar toa gelatin medium prevents liquefaction 
of the gelatin (Fligge). 
Upon blood serum a rather thick, white layer is formed and 
liquefaction slowly occurs. 
Upon potato the growth is abundant as a rather dry, grayish- 
white layer, of limited extent, having a somewhat rough surface and 
irregular margins. 
Spores are formed only in the free presence of oxygen, as in sur- 
face cultures upon potato or nutrient agar, or in shallow cultures in 
liquid media, and at a temperature of 20° to 35° C. They are not 
formed during the development of the bacilli in the bodies of living 
Fic. 101.—Colonies of Bacillus anthracis upon gelatin plates: a, at end of twenty-four hours; 
b, at end of forty-eight hours. x 80. (Fligge.) 
animals, but after the death of the animal the bacillus continues to 
multiply for a time, and spores may be formed where the fluids 
containing it come in contact with the air—as, for example, in 
bloody discharges from the nostrils or from the bowels of the dead 
animal. 
Varieties incapable of spore production have been produced arti- 
ficially, by several bacteriologists, by cultivating the bacillus under 
unfavorable conditions. Roux was able to produce a sporeless va- 
riety by successive cultivation in media containing a small quantity 
of carbolic acid—1 : 1,000. 
Varieties differing in their pathogenic power may also be pro- 
duced by cultivation under unfavorable conditions. Thus Pasteur 
