BACILLUS ANTHRACIS 223 



In gelatin stab cultures growth occurs along the track of the 

 needle as a delicate white thread from which irregular projections 

 soon extend, giving the culture the appearance of an inverted tree ; 

 at the end of two or three days liquefaction commences at the top. 

 In broth after twenty-four hours' incubation growth appears as 

 a flaky sediment which is deposited at the bottom of the tube. 

 The colonies on agar or gelatin plates are particularly character- 

 istic. At first they appear as small, white, opaque points ; later 

 long, wavy filaments project from each colony in all directions, 

 which when examined through the microscope are seen to be 

 composed of bacteria joined end to end. 



Resistance. Anthrax spores retain their vitality and virulence 

 for years under favorable conditions. Exposed to dry heat, a 

 temperature of 140 C. for three hours is required to kill them; 

 moist heat has a much more rapid effect, a temperature of 100 C. 

 being sufficient to destroy them in five minutes. They have been 

 found to retain their vitality after thirty-six days' exposure to a 

 5 per cent solution of carbolic acid at room temperature. In a 

 similar solution, however, they were destroyed after half an hour's 

 exposure at 55 C. In the vegetative form B. anthracis has com- 

 paratively low resistance. 



Pathogenesis. Cattle and sheep, except the Algerian race, 

 are the most frequently infected of all animals. In European 

 countries an outbreak is apt to occur from time to time ; in France 

 the animal mortality among sheep was formerly about 10 per cent. 

 An animal may suddenly show symptoms of collapse and death 

 ensue within a few minutes ; or in milder cases, bloody mucus is 

 seen about the mouth and nose and in the feces, pulse and respira- 

 tion are increased, and chills are followed by high temperature. 

 In such cases death may occur in from twelve to forty-eight hours. 

 In still less severe cases edema and often ulceration and necrosis 

 of the neck lymph glands occur. On autopsy the spleen is found 

 to be soft and of a dark red color and two or three times its natural 

 size. Tissue sections show the capillaries both of the spleen and 

 liver packed with bacilli ; the blood is usually fluid but tar-like, 

 and of a dark color. 



