GENUS BACTERIUM 227 



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

 blooded animals are relatively insusceptible. For man the 

 bacterium is definitely pathogenic, though less so than for some 

 of the animals mentioned above. 



Experimental infection in susceptible animals is most 

 easily accomplished by subcutaneous injections. As a rule the 

 inoculated animals appear perfectly well and comfortable 

 until a few hours before death, when they suddenly become 

 visibly very ill, rapidly go into collapse, and die. The dura- 

 tion of the disease, from the time of infection to death, de- 

 pends to some extent upon the resistance of the infected indi- 

 vidual. In guinea pigs and mice it is usually twenty-four to 

 forty- eight hours. The quantity of infectious material intro- 

 duced, on the other hand, has little bearing upon the final out- 

 come; a few bacteria, or even a single bacterium, may bring 

 about fatal results. Barber 9 found that in one instance a 

 single bacterium was sufficient to kill a mouse, indicating that 

 a sublethal dose does not exist for very susceptible animals. He 

 states that fresh virulent material from the mouse has for mice 

 about 100 times the infectivity of material grown in the first 

 agar or bouillon culture. 



Although the bacteria 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 immediately followed by amputation 

 of the inoculated parts without preventing the fatal general 

 infection. The bacteria are probably not able at first to mul- 

 tiply in the blood, but find the point of inoculation or less re- 

 sistant organs more favorable. When the resistance of the in- 

 fected subject is overcome, they enter the circulation and mul- 

 tiply within it. The bacteria are found in large numbers in 

 the blood and in the capillaries of all the organs at the time 

 of death. 



"Barber. Jour, of Inf. Diseases, Vol. VI (1909) p. 634. 



