464 THE PLAGUE BACILLUS 



3. Intra- venous inoculation. Inoculation into the veins leads to a more 

 severe disease in laboratory animals than sub-cutaneous inoculation : apart 

 from the local lesion the symptoms are similar in the two cases. 



4. Intra-peritoneal inoculation. This mode of infection is very severe ; an 

 inoculated guinea-pig will die in 24-40 hours. The virulence of the bacillus 

 can be increased by passage through animals by means of collodion sacs 

 inserted into the peritoneal cavity (Roux). 



5. Infection of the mucous membranes. An animal can be infected through 

 any of the mucous membranes (nasal, conjunctival, buccal, vaginal, etc.). 



Rats, mice, guinea-pigs and rabbits die of plague if a trace of the virus be 

 placed on the nasal mucous membrane without injuring it. The disease can 

 be more surely transmitted by this method than by sub-cutaneous inoculation 

 (Roux and Balzaroff). 



An attenuated virus which fails to give rise to a fatal infection when inoculated 

 hypodermic ally will produce the pneumonic form of the disease when inoculated into 

 the respiratory passages, and the virulence of the organism can be recovered in this 

 way, for example by successive passages on the nasal mucous membrane. A virus 

 which has been dried even for several weeks in albuminoid matter gives rise to the 

 pneumonic form of the disease when inoculated into the nose. 



6. Ingestion. Rats, mice and monkeys may be infected by feeding them 

 on living cultures (Simond) or on the viscera of plague-infected animals. 



[The Advisory Committee found that about one-fourth (26' 2 per cent.) 

 of the rats which they fed on the whole carcases or viscera of infected rats 

 and guinea-pigs contracted plague. The majority died on the third and 

 fourth days after receiving the plague-infected meat, though in a few cases 

 death was delayed as long as three weeks. Among the (437) rats which were 

 still alive at the end of three weeks 11 showed undoubted signs of being 

 plague-infected. Post mortem examination of the rats which died showed 

 lesions similar to those found in rats naturally infected save in two very 

 important particulars. In rats infected by feeding the mesentery was by 

 far the commonest situation for the bubo, and in about one-third of the 

 number the Peyer's patches were enlarged, congested, hsemorrhagic and 

 often ulcerated, and the intestines markedly congested (cf. appearances 

 presented by naturally infected rats p. 474).] 



7. Contagion. If a number of healthy mice be placed in a bottle with a 

 number of inoculated mice the former contract the disease and die with 

 lesions characteristic of plague (Yersin) : [but the Advisory Committee 



showed that " close contact of plague-infected 



t + animals with healthy animals, if fleas are ex- 



- "" Q 4, eluded, does not give rise to an epizootic among 



K^ 9 ** ^ J^ the latter " and that aerial infection is not a 



& <* * ^~f % # ' ^ means whereby the disease is spread from an 



* A** Q ** 9 ** " infected animal to a healthy animal. ] 



<Q * ^** & ** 



" -tr" t*- 



SECTION II. MORPHOLOGY. 

 ff^?* ! Microscopical appearance. 



g * . ? The micro-organism of plague as seen in 



$ preparations from the tissues is a short, squat 



bacillus with rounded ends and is more 

 correc % described as a cocco-bacillus : it 

 measures about 2xl/^. [Morphologically 

 it very closely resembles the bacilli of the pasteurella group, the bacillus 

 pseudo-tuberculosis rodentium, and often bacilli of the typhoid-Qolon group.} 



