82 ORIENTAL PLAGUE chap. 



(7) B. pseudo-tuberculosis in litmus milk has a tendency to form 

 alkali ; B. pestis, on the other hand, has a slight tendency to form 

 acid. 



(8) B. pseudo-tuberculosis on potato forms a straw-coloured, pale- 

 yellow growth ; B. pestis forms no visible growth on potato. 



It is therefore obvious that, apart from these last points, the 

 different staining characters, the rapid growth on agar, the slow and 

 different action on the guinea-pig both subcutaneously and peri- 

 toneally, and the absence of pathogenic action by cutaneous inocula- 

 tion are quite sufficient to enable even the inexperienced readily to 

 distinguish the two microbes. 



Bacillus of Fowl Cholera and Allied Microbes. — I add this microbe, 

 because it has the well-known character of staining bipolarly, of 

 being Gram -negative, of producing on agar a translucent growth, 

 which, like that of B. pestis, does not emulsify well and is more or 

 less tenacious. I do not think that this group of microbes can be 

 easily mistaken for B. pestis; but it has to be remembered that, 

 although of rare occurrence generally, in some places it is fairly 

 widely distributed, and further, that the subcutaneous injection into 

 rodents of materials containing this microbe causes hemorrhagic 

 infiltration with crowds of bipolarly stained bacilli. This character 

 of showing bipolar staining, and of yielding on agar surface round, 

 translucent, cohesive colonies, might lead one, not fully acquainted 

 with this group, to assume that he is dealing with B. pestis. I have 

 quite recently come across a microbe which is a close relation to the 

 bacillus of fowl cholera, and which at first sight might be still more 

 easily mistaken for B. pestis ; this microbe (B. equi) had been obtained 

 from the blood of a horse spontaneously dead. 



The bacillus of fowl cholera, although giving distinct bipolar 

 appearance on staining, is smaller than the B. pestis, but the B. equi, 

 which also conspicuously shows bipolar staining, is larger than the 

 bacillus of fowl cholera and nearly as large as the B. pestis. The 

 photo shown (Fig. 74) is the B. equi of the blood of a rabbit dead within 

 twenty hours after intravenous injection with B. equi. It will be seen 

 that except for the enormous number of the microbes present in 

 the blood — in plague the bacilli, even under the most favourable 

 conditions, are never present in the blood in such numbers — the 

 aspect of the bacilli both as to size and staining is remarkably like 

 that of B. pestis. 



The members of the group of bacillus of fowl cholera do not act 



