MORPHOLOGY 



525 



Sometimes the arborization is wanting in which case the culture is reduced to the 

 central streak. Branching cultures are especially observed when the medium is 

 sown with anthrax blood. 



(b) Plate cultures. Towards the second day small greyish-white points 

 appear scattered through the gelatin on 

 the plates. 



These points increase rapidly in size 

 and form brownish, granular rounded 

 spots with wavy margins. A low power 

 lens shows these colonies to be made up 

 of interlaced filaments which give them 

 the appearance of a tangled ball of silk. 

 Towards the fourth or fifth day the 

 colonies look as though they were made 

 up of twisted threads and resemble curly 

 hair [Judge's wig appearance] . The gela- 

 tin then becomes liquefied around the 

 colonies which break up and form flakes 

 floating in the liquefied gelatin. 



Agar. After incubation for 24 hours 

 at 35-37 C. a whitish streak appears on 

 the sloped surface of the agar which 

 rapidly thickens, becomes rather dry and friable and has lightly notched 

 borders. The growth on agar is not very characteristic. 



Potato. On this medium at a temperature of 35-37 C. there appears 

 after the second day a whitish deposit which rapidly thickens and assumes a 



dull white colour, becoming brown on keeping 

 (fig. 258). 



Serum. Liquid serum. After incubation for 

 2 days at 35 or 37 C. flakes are seen floating 

 in the medium which subsequently fall to the 

 bottom of the tube. 



Coagulated serum. The growth appears as a 

 dull white streak becoming greyish after a few 

 days ; the serum is partly liquefied. 



Milk. When sown in a tube of milk and incu- 

 bated at 35 or 37 C. coagulation takes place 



towards the third or fourth day. The coagulum is redissolved about the 

 end of the week. If a flask be used no coagulation takes place but the milk 

 acquires a yellowish colour. 



Litmus-lactose-gelatin. The medium is slightly reddened by the growth 

 of the anthrax bacillus. 



x 240 x 530 



FIG. 257. Bacillus anthracis. Impression 

 preparation from glycerin-agar. From Cur- 

 tis' Essentials of Practical Bacteriology. 



YlG.ZM.-Bactilusanthracis. Culture 



on potato (3 days at 37 c.). 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Viability. Resistance. 



The non-sporing bacillus is quickly killed by exposure to a temperature 

 above 50 C. At 51 C. anthrax blood is sterilized in half an hour. Exposure 

 even to very low temperatures ( - 100 C. for 1 hour) does not kill the bacillus. 

 The absence of oxygen or immersion in compressed oxygen kills the non- 

 sporing bacillus. 



Spores, the resistant form of the organism, possess the full virulence of the 

 bacillus. In soil the spores can retain their vitality as well as their virulence 

 for more than 15 years (Sirena). Spores in the moist condition resist a tern- 



