BACILLUS ANTHRACIS. 143 



remaining imeolored ; but the latter are easily stained by any 

 of the special methods for staining spores described in the 

 chapter on Staining. By Gram's method it retains the gentian- 

 violet. 



Biologic Characters. The Bacillus anthrads is anaerobic, 

 but can grow without the presence of oxygen. When grown 

 with free access of oxygen in artificial culture-media it forms 

 long filaments or threads, which are formed by the union of a 

 number of bacilli. In the presence of free oxygen elliptical 

 bright spots, one to each segment of the thread, are observed; 

 these are the spores. 



This bacillus grows at all temperatures between 12 and 

 45 C., but it does not form spores at a temperature below 

 18 or above 42 C. Its maximum of growth is at 37.5 C. 

 (Fig. 54). 



In the blood and tissues of animals it does not sporulate. 

 The bacterium is non-motile and has no flagella. 



In bouillon it grows very rapidly, forming twisted thread- 

 like masses, resembling cotton, in the mass of the bouillon 



FIG. 55. 



Colony of Bacillus anthracis on agar-agar. (Abbott.) 



and at the bottom of the tube, but it does not cloud the 

 medium. 



On agar its growth is quite characteristic, forming colonies 

 which look like irregularly twisted knots of thread resem- 

 bling cotton-wool ; this peculiar growth has been given the 

 name of the head of Medusa (Fig. 55). 



On gelatin its growth is very like that on agar, but it 



