BACILLUS ANTHRACIS. 553 
upon the surface of which it floats as an irregular, white 
pellicle. In gelatin stick cultures at first development 
occurs along the line of puncture as a delicate white 
thread, from which irregular, hair-like projections soon 
extend perpendicularly into the culture medium, the 
growth being most luxuriant near the ‘surface, but con- 
tinuing also below. At the end of two or three days 
liquefaction of the medium commences at the surface 
and gradually progresses downward. 
Growth on Agar. The growth on agar plate cul- 
tures in the incubator at 37° C. is similar to that on 
gelatin, and is still more characteristic and beautiful in 
appearance. A grayish-white layer is formed on the 
surface within twenty-four hours, which spreads rapidly 
and is seen to be made up of interlaced threads. 
In bouillon the growth is characterized by the forma- 
tion of flaky masses, which sink as a sediment to the 
bottom of the tube, leaving the supernatant liquid clear. 
Spore formation, as already noted, only takes place 
in the free presence of oxygen, and at a temperature of 
15° to 43° C. There is no development of spores at a 
greater depth than 1.5 metres in the earth, or in the 
bodies of living or dead animals; but spores may be 
found in the fluids containing the bacilli when these 
come in contact with the air, as in bloody discharges 
from the nostrils or from the bowels of the dead animal. 
There are certain non-spore bearing species of an- 
thrax. Sporeless varieties have also been produced 
artificially by cultivating the typical anthrax bacillus 
under unfavorable conditions. The addition of anti- 
septics, as carbolic acid, favors these conditions. Vari- 
eties differing in their pathogenic power may also be 
produced artificially. Pasteur produced an ‘‘ attenu- 
