570 PATHOGENIC MICROORGANISMS 



tivation at temperatures above 42° C. By this procedure, however, 

 virulence, too, is considerably diminished. 



Resistance. — Because of its property of spore formation, the anthrax 

 bacillus is extremely resistant toward chemical and physical environ- 

 ment. The vegetative forms themselves are not more resistant than 

 most other non-sporulating bacteria, being destroyed by a temperature 

 of 54° C. in ten minutes. Anthrax spores may be kept in a dry state 

 for many years without' losing their viability.' While different strains 

 of anthrax spores show some variation in their powers of resistance, 

 all races show an extremely high resistance to heat. Dry heat at 140° 

 C. kills them only after three hours.^ Live steam at 100° kills them in 

 five to ten minutes. Boiling in water destroys them in about ten min- 

 utes. Low temperatures have but little effect upon them. Ravenel ^ 

 found that, frozen by liquid air, they were still viable after three hburs. 



The variability shown by different strains of spores in their resistance 

 to heat is even more marked in their behavior toward chemicals.* Some 

 strains will retain their viability after exposure to five-per-cent carbolic 

 acid for forty days,' while others are destroyed by the same solution in 

 two days. Corrosive sublimate, 1 : 2,000, kills most strains of anthrax 

 in forty minutes. 



Direct sunlight destroys anthrax spores within six to twelve hours." 



Pathogenicity. — ^The' anthrax bacillus is pathogenic for cattle, 

 sheep, guinea-pigs, rabbits, rats, and mice. The degrees of susceptibil- 

 ity of these animals differ greatly, variations in this respect existing even ' 

 among different members of the same species. Thus, the long-haired 

 Algerian sheep show a high resistance, while the European variety are 

 highly susceptible; and, similarly, the gray rat is much more resistant 

 than the white rat. Dogs, hogs, cats, birds, and the cold-blooded ani- 

 mals are relatively insusceptible. For man the bacillus is definitely 

 pathogenic, though less so than for some of the animals mentioned 

 above. 



While separate races of anthrax bacilli may vary much in their de- 

 gree of virulence, a single individual strain remains fairly constant in 

 this respect if preserved, dried upon threads or kept in sealed tubes, in 



' Surmont et Arnould, Ann. de I'inst. Pasteur, 1894. 



2 Koch und Wolffhugel, Mitt. a. d. kais. Gesundheitsamt, 1881. 



» Ravenel, Medical News, vii, 1899. 



* Frankel, Zeit. f. Hyg., vi, 1889. 



» Koch, loc. cit. 



« Momont, Ann. de I'inst. Pasteur, 1892. 



