778 PASTEURELLA 



Subcutaneous or intramuscular inoculation of the guinea-pig is followed by a disease 

 which, depending on the dose and the virulence of the strain, may be acute, subacute, or 

 chronic. The acute disease resembles plague and is fatal in a few days. The differential 

 diagnosis can be made only by cultivation and a thorough study of the organism responsible. 

 Macroscopically, the focal lymphatic glands tend to be more affected in plague than in 

 pseudotuberculosis. The subacute disease proves fatal in about 2 weeks, and the chronic 

 in 3 weeks or longer. Post mortem there is a caseous local swelling, the regional lymphatic 

 glands are enlarged, and there are nodules varying in number, size, and degree of caseation, 

 in the spleen, liver, and lungs. If the animal lives for 3 weeks or so, the nodules are usually 

 very conspicuous. They are more or less spherical, greyish-white in colour, and 0-2 to 30 

 mm. in diameter ; they project above the surface of the organ, and in the liver they show 

 no particular localization for the free border, as do the necrotic areas in rodent typhoid 

 infection. Microscopically the bacilh are generally present in considerable numbers at 

 the site of inoculation and in the regional glands, and they can be readily cultivated from 

 all the lesions. The disease can also be reproduced hy feeding, which is the natural method 

 of infection. Death occurs in 1 to 3 weeks. Nodules of varying size are found in the 

 intestinal wall, the mesenteric glands are enlarged and often caseous, and nodules may 

 be present in the spleen, liver, and lungs. 



Classification and Identification. — The members of this group resemble each 

 other very closely ; between Past, pestis and Past, pseudotuberculosis the similarity 

 is so great that the identification of a given strain is not always easy. Agglutina- 

 tion and precipitation may be of assistance, especially if supplemented by the 

 absorption test. The production of alkali in litmus milk by Past, pseudotuberculosis, 

 and its comparative harmlessness for white rats (Eeport 1912, p. 350), are two 

 differential tests that are sometimes recommended. Past, pseudotuberctdosis is 

 often motile in broth cultures incubalted for 18 hours at 20-22° C. whereas Past. 

 pestis is uniformly non-motile. The greater rapidity and luxuriance of growth 

 of Past, pseudotuberculosis is usualy very striking, particularly if studied on 

 nutrient agar plates incubated aerobically for 24 hours. Under these conditions 

 Past, pestis shows very slight confluent growth restricted to the first line of inocu- 

 lation. Single colonies are rarely seen unless a strong reducing substance is 

 present in the inoculum. On the other hand colonies of Past, pseudotuberculosis 

 reaching 0-5 or 1 mm. in diameter are usually evident over the whole plate. The 

 hgemorrhagic septicaemia bacilli can be differentiated from Past, pestis and Past, 

 pseudotuberculosis by their fermentation of sucrose, their production of indole, 

 and their negative methyl-red reaction ; it must be noted, however, that sucrose 

 is fermented by certain strains of Past, pseudotuberculosis. According to Brigham 

 and Rettger (1935), Past, pestis and Past, pseiidotuberculosis grow on potato at 

 20° C, while Past, septica does not. Between the hsemorrhagic septicaemia strains 

 of different animal origin, there appears to be no constant characteristic of diagnostic 

 value. Most workers therefore agree that these bacilli form a single group, though 

 it appears possible, using a careful technique, to make out antigenic differences 

 between them. At present each member is given a specific name ; probably it 

 would be better to call them all by one specific name, such as Pasteurella septica, 

 and to indicate the animal origin where necessary. 



A group of strains in many respects resembling Past, septica, but differing 

 from it in others, have been described by Jones (1921), Tweed and Edington (1930), 

 Newsom and Cross (1932), and Rosenbusch and Merchant (1939). These strains 

 are characterized by the production of ^S-hsemolysis on horse or rabbit blood agar, 

 failure to produce indole, and non-pathogenicity to mice and rabbits ; most of 



