BACILLUS ANTHRACIS. 415 



tive, condition for a vCTy long time. If again placed 

 under favorable conditions, each spore will germinate 

 into a mature cell, and the same series of changes will 

 be repeated until the favorable surroundings become 

 again gradually unfavorable to development, when 

 s})ore-formation is again seen. Spore-formation takes 

 place only at temperatures ranging from 18° to 43° C, 

 37.5° C. being the most favorable temperature. Under 

 12° C they are not formed. With this organism spore- 

 formation does not occur in the tissues of the living 

 animal, its usual condition at this time being that of 

 short rods. Occasionally, however, somewhat longer 

 forms may be seen. 



The bacillus of anthrax is not motile. 



Growth on Agar-agar. — The colonies of this or- 

 ganism, as seen upon agar-agar, present a very typical 

 appearance, from which they have been likened unto 

 the head of Medusa. From a central point which is 



Fig. 90. 





Colony of baeUlus atUhrcteis on agar-agar. 



more or less dense, consisting of a felt-like mass of long 

 threads matted irregularly together, the growth con- 

 tinues outward upon the surface of the agar-agar. (Fig. 

 90.) It is made up of wavy bundles in which the 

 threads are seen to lie parallel side by side or are twisted 



