Etiology. . ' 3 



Etiology. The bacillus antliracis is 1.5 to i.O'" long, and 

 1.0 to 1.5^ broad. It is a nonmotile bacterium which multiplies 

 by fission and spore formation, and forms in the body fluids, 

 and still more on artificial media, long chains. 



Staining. The bacilli stain well, while living, with diluted 

 aciueous f uclisin or methylene blue solution ; on dried cover glass slides 

 with the usual solutions of aniline stains, as well as by Gram's and 

 Weigert's methods. Bacilli just stained with fuchsin disclose in their 

 bodies one or more intensely stained granules adherent to the wall 

 (Fig. 1). In stained dry specimens the ends of the bacilli appear 

 sharply cut, sometimes even slightly thicker (resembling the form of 

 I) ; in the chains they are separated by straight lined or double convex 

 light spaces (bamboo-rod forms). The light parts are formed by the 

 nuicin capsule (Serafini, Johne) which surrounds the plasma of each 



Fig. 1. Bacillus anthracis. Fresh sheep 



blood stained with diluted 



fuchsin solution. 



Fig. 2. Bacillus a^Jthracis.^vithcapsulcti. 



Spleen juice from a horse. 



Gram-eosin staining. 



individual bacillus and holds them together in chains (Fig. 2). The 

 capsule is well developed in fully virulent bacilli taken from the blood 

 of animals, particularly of ruminants, as well as in those cultivated in 

 fluid blood serum, while on other media the capsule formation is incom- 

 plete (see also page 11). 



Cultivation. Anthrax bacilli grow on alkaline media in the 

 presence of oxygen at body as well as room temperatures. The highest 

 limit which is suitable for their growth is 43° C, while the lowest tem- 

 perature is 12-15° C. In gelatin of not too strong concentration a 

 white streak develops after 1 to 2 days along the stab from which hori- 

 zontal radiations branch off in all directions (test-tube brush forms. 

 Fig. 3). After 3 to 4 days the gelatin commences to liquefy under the 

 influence of a peptonizing ferment (Fermi) along the streak from the 

 surface downwards, while the bacterial masses later form a layer of 

 flaky sediment on the bottom of the stocking-shaped liquefied part. 

 The liquefied gelatin above this, however, remains entirely clear. On 

 gelatin or agar plates the surface growth appears in the form of white 

 points which consist of braiddike interwoven chains. The streak cul- 

 ture on agar and on potato forms a grayish white, reticulated, viscous 



