EXPERIMENTAL INFECTION 463 



can be definitely excluded as a source of infection in India it is difficult to understand 

 how it alone will explain the Manchurian epidemic.] 



The plague bacillus is capable of retaining its vitality outside the body. Yersin 

 recovered a plague bacillus, less virulent it is true than those isolated from buboes, 

 from the soil of an infected place. [In moist earth previously sterilized the bacillus 

 will survive for months (Gladin, Marsh).] In the bodies of dead rats the organism 

 can retain its virulence for several weeks (Maassen). According to Inghilleri the 

 plague bacillus is able to live in drinking water for about a month. 



SECTION I. THE EXPERIMENTAL DISEASE. 



Monkeys, mice, rats, guinea-pigs and rabbits are all very susceptible to 

 experimental infection with plague : [but domestic animals such as horses, 

 cattle, sheep, goats, pigs and calves, pigeons, geese, fowls, ducks and turkeys 

 are apparently not susceptible " either by ingestion, scarification or sub- 

 cutaneous inoculation " (Bannerman and Kapadia, Haffldne, London, 

 Watkins-Pitchford, de Souza, Arruda and Pinto). ] De Mattei affirms however 

 that pigeons, fowls and ducks succumb if inoculated with large doses of 

 virulent cultures. 



Cultures of the plague bacillus are very virulent for man, and accidents 

 in laboratories have shown that a certain element of danger attaches to 

 working with the organism. 



1. Sub-cutaneous inoculation. To infect a monkey, a mouse, [or other 

 susceptible animal] with plague it is only necessary to scratch the skin 

 lightly with a needle charged with the virus. Rats and mice die in 2 or 3 

 days, guinea-pigs in 2-5 days and rabbits in 3-8 days. 



A few hours after inoculating a guinea-pig a localized oedema makes its appearance 

 at the site of inoculation followed by a swelling of the related glands ; at the 

 end of 24 hours the animal will be found lying on its side and its coat ruffled : 

 death is preceded by convulsive seizures. 



Post mortem there is a reddish oedema at the site of inoculation and around the 

 neighbouring gland : the abdominal organs are congested while the spleen is very 

 much enlarged and often exhibits an eruption simulating small miliary tubercles. 

 [When the disease has been of some duration abscesses are occasionally found in the 

 abdominal wall.] There is a small amount of serous exudate in the pleurae and 

 peritoneum and bacilli can be demonstrated in the fluid : bacilli are also to be found 

 in large numbers in the lymphatic glands, liver, spleen and blood. 



The virulence of the organism is increased by passage through guinea-pigs 

 using in the first instance a scraping from the spleen or a little blood. 



By passing the virus through a series of animals of the same species bacilli can 

 be obtained which are of an exalted and constant virulence for that species. For 

 instance a bacillus can be recovered which will consistently kill a mouse in 2 days ; 

 one which will kill a guinea-pig in 2 or 3 days ; or one which is fatal to a rabbit 

 in 3 days. A bacillus which will kill a mouse in 2 days takes rather a long time to 

 kill a rabbit, but after being passed through a few rabbits will kill these animals in 

 3 days ; it has however now lost its virulence for the mouse and to restore its viru- 

 lence for the latter species it must be passed from mouse to mouse a few times 

 (Yersin, Calmette and Borrel). 



[No alteration in virulence for rats is observed after sub-cutaneous passage 

 through rats.] 



2. Cutaneous inoculation. Guinea-pigs are readily infected by rubbing 

 infected material on the surface of the shaved skin (Weichselbaum, Albrecht 

 and Ghon). A slight inflammation first forms and the disease then runs the 

 same course as in the previous case. 



This affords a valuable test for the detection of plague bacilli in material con- 

 taminated with other organisms, and is the method which should be adopted for 

 the detection .of the bacillus in decomposing carcases, fecal matter, etc. 



