254 A MANUAL OF BACTERIOLOGY 



early stage has a finely granular, ground-glass appearance. 

 On blood-serum a thick creamy layer forms, with slow 

 liquefaction of the medium. On potato the organism 

 grows freely as a dry greyish layer, with an abundant 

 formation of spores. In broth it forms a somewhat scanty 

 flocculent deposit, the broth remaining clear and giving 

 the indole reaction. 



In old cultures various involution forms are met with ; 

 the rods lose their regular shape and become swollen, 

 producing the so-called torula forms, while the homo- 

 geneous appearance of the protoplasm changes and 

 becomes granular. Ultra-violet rays are stated by Mme. 

 Henri to produce marked mutations of the anthrax 

 bacillus (see p. 6). Spores are found in all culture media 

 when there has been free access of oxygen, as in surface 

 cultures on potato and agar ; but in a deep broth culture, 

 where the supply is limited, spore-formation is absent 

 or very scanty. Spores are never met with in the living 

 animal ; they only appear some hours after death, or 

 when matter containing the bacilli comes in contact with 

 air, as in the bloody discharge from the nostrils. It has 

 therefore been supposed that oxygen is necessary for 

 spore- formation to take place, but this does not seem to 

 be the whole explanation, for spores form in an atmosphere 

 of nitrogen, though they do not do so in one of hydrogen. 

 The life-history of the organism and the development of 

 spores can be well watched in a hanging- drop specimen 

 prepared by inoculating a droplet of broth with the blood 

 of an infected animal. The preparation can be observed 

 on a warm stage, or examined at stated times, being kept 

 in the intervals in the blood-heat incubator. At the end 

 of twenty-four hours the short filaments, which alone are 

 present in the blood, will have grown so long that they 

 stretch across the field, while the protoplasm has become 

 granular, and minute shining points are visible here and 

 there. In another twenty-four hours the filaments extend, 



