252 A MANUAL OF BACTERIOLOGY 



produced results the same as had previously been obtained 

 by inoculation with the blood of an infected animal. 



Morphology. The Bacillus anihmcis is a rod-shaped 

 organism varying slightly in size in different animals and 

 under cultivation ; in the blood it measures from 5 to 20 //. 

 in length and 1 to 1-25 /x breadth (Plate IV. a), but in 

 cultures long filaments develop. Examined in the fresh 

 and living condition in a hanging- drop preparation, these 

 rods and filaments appear homogeneous or slightly granular ; 

 in stained preparations, however, they are seen to be made 

 up of a series of segments with unstained interspaces, 

 each segment measuring about 4 to 5 /x in length, and the 

 ends of the segments appear cut off square, provided care 

 has been taken not to overheat in fixing and to stain with 

 an aqueous solution ; they also appear to be encapsuled 

 (p. 263). In the blood the filaments never exceed about 

 five or six segments in length, except perhaps in swine, in 

 which animals they may be somewhat longer. In cultures, 

 however, the filaments may be of almost unlimited length, 

 and lie parallel to one another or in more or less tangled 

 masses. In the animal body during life, and for some 

 hours after death, spores never occur ; but in cultures 

 more than a day or so old, and from which oxygen has not 

 been excluded, they are always present, almost every 

 segment containing one. The spores are ellipsoidal, 

 measuring about 1 ^ by 1-25 /x, and are centrally placed 

 in each segment, the long axis corresponding with the 

 long axis of the segment. 



Cultural reactions. The anthrax bacillus is aerobic and 

 facultatively anaerobic ; it is non-motile, and stains well 

 with the ordinary anilin dyes, and especially so by Gram's 

 method. It grows readily on all culture media at from 

 20 to 37 C., the latter being the optimum. Develop- 

 ment ceases at temperatures below about 15 and above 

 5 C. Small, cream-coloured, granular colonies develop 



