iv MICEOBES SIMULATING THE B. PESTIS 75 



a few minims were injected subcutaneously into the dorsum of 

 two mice. 



One of these mice was found dead next morning, i.e. within 

 twenty hours. The second mouse was very ill — lumpy, coat rough, 

 eyes closed, breathing very rapid ; it was found dead the next 

 morning, i.e. within forty hours. 



At the post-mortem examination both mice showed the following 

 appearances : — At the seat of inoculation the subcutaneous tissue was 

 inflamed, cedematous, and with hemorrhagic spots ; the intestines 

 and lungs were very hyperemic and showed hemorrhagic spots ; the 

 spleen was large and dark. Neither in the subcutaneous exudation 

 nor in the spleen or lungs could any B. pestis be discovered, either 

 in stained film specimens or by culture. 1 But in the subcutaneous 

 exudation were numerous bacilli in clumps and in streaks which 

 could at once be recognised as diphtheroid : small bacilli pointed at 

 one end, some with clubs and showing segregation of their chromatic 

 substance ; they stained positive in Gram. Cultures on agar surface 

 and on agar plate were made, and in these came up in pure state 

 numerous colonies of the same diphtheroid bacilli. Subcutaneous 

 injections with these cultures were made into mice and guinea-pigs, 

 and thereby it was shown that the microbe was possessed of distinct 

 pathogenic action : in the guinea-pigs the subcutaneous injection 

 into the groin of a moderate dose of culture — several drops of turbid 

 emulsion — caused after forty-eight hours slight but firm enlargement 

 of the inguinal glands j this enlargement gradually increased, till in 

 about ten days the tumour was of the size of a filbert, changing at 

 the same time from a firm tumour into a tumour containing thick 

 pus. The pus contained crowds of the same diphtheroid bacilli, 

 many in small and large masses. None of the guinea-pigs died, 

 and the animals remained the whole time apparently lively and 

 feeding. The mice showed constitutional disturbance for two or 

 three days, being quiet and off feed, but they soon recovered and 

 showed tumour at the seat of injection. This tumour about the 

 end of a week or ten days began to ulcerate, and became covered 

 with a dry scab about J to J inch in diameter. The mice recovered, 

 and after about three weeks the place was healed up. Several 

 other experiments were made with the culture in guinea-pigs and 

 mice with the same result. 



1 In a subsequent chapter it will be shown that death was due to plague toxin 

 present in the dried plague tissues. 



