160 OMENTAL PLAGUE chap. 



and I have therefore limited myself to only few experi- 

 ments with them. It would seem that tame rats (white 

 or white and black) are in respect of susceptibility more 

 nearly related to Mus rattus (the Oriental rat) than to 

 Mus decumanus (the brown sewer rat). 



Experiment 2. — Three rats were fed with a mixture of 

 bread and sloped surface gelatine and agar cultures of 

 B. pestis. The gelatine cultures had been kept growing 

 at 20° C. for some six, those on agar for some three weeks. 

 At the margin of the slopes of these cultures both the 

 gelatine and agar were dried up, but the free sloped 

 surface was covered with typical colonies of B. pestis; 

 colonies which were angular, granular, opaque, raised, and 

 dry -looking. After melting the gelatine by immersing 

 the tubes in warm water — in the case of the agar the glass 

 tubes had to be broken — the contents of the tubes were 

 mixed with bread. The above animals were fed with this 

 mixture on May 2. In the morning on May 5 two 

 of the rats, No. 1 and No. 2, were found very ill, in fact 

 dying; one died at about 10 a.m., the other at noon. 

 The third rat, No. 3, looked quiet, its coat was rough, and 

 seemingly it did not feed. This rat did not improve for 

 the next few days, but on May 8 was noticed to be 

 again lively and to feed normally. It was killed on 

 May 10. The post-mortem examination of this animal 

 did not reveal any pathological changes, and cultures 

 made from the spleen and heart's blood proved sterile. 



But the post-mortem examination of rats No. 1 and 

 No. 2 showed the following appearances : — 



Eat No. 1. — No swollen subcutaneous lymph glands. 

 The omentum much congested with numerous petechia ; 

 in the lower ileum a patch of haemorrhage around a 



