64 ORIENTAL PLAGUE chap. 



a positive reaction in neutral-red broth. On potato at 

 37° C. the microbe forms a thick, moist, whitish cream- 

 coloured growth in which copious gas bubbles appear : 

 this condition obtains when the surface of potato of some 

 age is inoculated ; on recently prepared potato the gas 

 bubbles are not evident. Fig. 46 is an accurate illustra- 

 tion of this appearance, and the character in question 

 conclusively eliminates this microbe from the B. coli 

 communis, and places it amongst the group of B. lactis 

 aerogenes. Culturally, then, the B. Bristolense stands 

 somewhere between B. coli communis and B. lactis 

 aerogenes. 



As already mentioned, B. Bristolense is pathogenic to 

 rats and to guinea - pigs both by subcutaneous and by 

 intraperitoneal injection ; and, further, the pathological 

 appearances induced by it in the infected animals — particu- 

 larly the distribution, aspect, and staining power of the 

 microbe in the tissues of these animals — might be easily 

 mistaken for those oipestis bubonica. In this connection 

 it is necessary to insist on what has been already said as 

 to the nature of the tumour at the seat of injection and 

 as to the bipolar-stained numerous bacilli in the tissue of 

 the tumour, in the peritoneal exudation, and in the spleen 

 of the experimental animals ; for a diagnosis made from 

 the morphological appearances alone or from the results of 

 intraperitoneal and subcutaneous injections of rats and 

 guinea-pigs might lead to serious mistakes. The culture 

 test is, however, in this instance decisive against B.pestis. 

 But, as already noted, neither a culture nor the patho- 

 logical products of the experimental animals can repro- 

 duce the disease in other animals by cutaneous inoculation 

 alone ; and this fact is an important help towards a correct 



