234 BACTERIOLOGY. 



unfavorable to development, when the spore-formation 

 is again seen. The spore-formation takes place only at 

 temperatures ranging from 18° to 43° C, 37.50° C. 

 being the most favorable temperature. Under 12° C 

 they are not formed. With this organism, spore-forma- 

 tion 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. 



Geowth 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 hair of a 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 continues 

 outward upon the surface of the agar. It is made up of 

 wavy 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 arrangement. These 

 bundles twist about and cross in all directions, and 

 eventually disappear at the periphery of the colony. 

 The colony itself is not circumscribed in its appearance, 

 but is more or less irregularly fringed and ragged, or 

 scalloped. To the naked eye they look very much like 

 minute pellicles of raw cotton which had been pressed 

 into the surface of the agar-agar. At the extreme peri- 

 phery of the colonies it is sometimes possible to trace 

 single bundles of these threads for long distances across 

 the surface of the agar-agar. 



As the colonies continue to grow, they become more 

 and more dense ; they become opaque in color, and gran- 

 ular and rough on the surface. When touched with a 



