360 BACTERIOLOGY. 



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 favor- 

 able surroundings become again gradually unfavorable 

 to development, when spore-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 con- 

 dition at this time being that of short rods. Occa- 

 sionally, however, somewhat longer forms may be seen. 



The bacillus of anthrax is not motile. 



Growth on Agae-agae. — 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 

 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. (Fig. 79.) 



Fig. 79. 



Colony of haoUlus anthracis on agar-agar. 



It is made up of M'avy bundles in which the threads are 

 seen to lie parallel side by side or are twisted in strands 

 like those of a rope — sometimes they have a plaited 



