BACILLUS ANTHRACIS AND ANTHRAX 571 



a cold, dark place. Virulence may be reduced '■ by various attenuating 

 laboratory procedures which are of importance in that they have made 

 possible prophylactic immunization. Heating the bacilli to 55° C. for 

 ten minutes considerably reduces their virulence. Similar results are 

 obtained by prolonged cultivation at temperatures of 42° to 43° C, 

 or by the addition of weak disinfectants to the culture fluids.^ Once 

 reduced, the new grade of virulence remains fairly constant. Increase 

 of virulence may be artificially produced by passage through animals. 



Experimental infections in susceptible animals are most easily accom- 

 plished by subcutaneous inoculations. The inoculation is followed, at 

 first, by no morbid symptoms, and some animals may appear perfectly 

 well and comfortable until within a few hours or even moments before 

 death, when they suddenly become visibly very ill, rapidly go into 

 collapse, and die. The length of the disease depends to some extent, 

 of course, upon the resistance of the infected subject, being in guinea- 

 pigs and mice from twenty-four to forty-eight hours. The quantity of 

 infectious material introduced, on the other hand, has little bearing 

 upon the final outcome, a few bacilli, or even a single bacillus, often 

 sufficing to bring about a fatal infection. Although the bacilli are not 

 demonstrable in the blood until just before death, they nevertheless 

 invade the blood and lymph streams immediately after inoculation, 

 and are conveyed by these to all the organs. This has been demonstrated 

 clearly by experiments where inoculations into the tail or ear were im- 

 mediately followed by amputation of the inoculated parts without pre- 

 vention of the fatal general infection. The bacilli are probably not at 

 first able to multiply in the blood. At the place of inoculation and 

 probably in the organs they proliferate, until the resistance of the in- 

 fected subject is entirely overcome. At this stage of the disease, no 

 longer held at bay by any antagonistic qualities of the blood, they enter 

 the circulation and multiply within it. Autopsy upon such animals 

 reveals an edematous hemorrhagic infiltration at the point of inocu- 

 lation. The spleen is enlarged and congested. The kidneys are con- 

 gested, and there may be hemorrhagic spots upon the serous mem- 

 branes. The bacilli are found in large numbers in the blood and in the 

 capillaries of all the organs. 



The mode of action of Bacillus anthracis is as yet an unsettled point. 

 It is probable that death is brought about to a large extent by purely 



• Toiissaint, Comptes rend, de I'acad. des sci., xci, 1880; Pasteur, Chamberland 

 et Raux, Comptes rend, de I'acad. des sci., xcii, 1881. 

 ' Chamberland et Roux, ibid., xcvi, 1882. 



