6io COMMUNICABLE DISEASES OF LABORATORY ANIMALS 



recent shipment of animals is transferred to the stock without a previous quarantine 

 or search for carriers. Probably owing to subtle differences in microbic virulence and 

 host susceptibility, the frequency with which paratyphoid of guinea pigs may occur 

 in different localities and during certain years varies considerably. Thus during the 

 years 1914-16 Holman' never encountered paratyphoid bacilli in the organs of guinea 

 pigs, while the studies of Thomas^ in 1922 at the same laboratory were seriously 

 handicapped by the endemic existence of a latent paratyphoid infection. 



The causative organism of the disease is indistinguishable morphologically, culturally, 

 and biochemically from the representatives of the paratyphoid-enteritidis or Salmonella 

 group. The strains are highly tolerant toward brilliant and malachite green; irregular 

 ionsite fermentation has been reported by Krumwiede, Valentine, and Kohn.-s As a rule, 

 normal, smooth colonies have been isolated ; according to Raebiger and Lerche,'' the "Schleim- 

 wall" formation is always missing. Nelson ,5 however, found early in the endemic stage of an 

 outbreak very carefully studied by him and Smith two cultures which were distinctly 

 mucoid and flocculated spontaneously in broth. These mucoid variants differed neither in 

 agglutinability nor antigenic properties from the normal types. An experimental study failed 

 to reveal the stimuli which were responsible for these variants. The writer has from time 

 to time examined several hundred cultures prepared from paratyphoid-infected guinea pigs 

 and has failed to observe mucoid colonies. Furthermore, the paratyphoid cultures of guinea- 

 pig origin have not displayed, as the observations of Nelson also indicate, any marked tend- 

 ency toward variations or reversion of the mucoid to the smooth type. 



The agglutinative affinities of the strains which have thus far been studied have not 

 always been definitely established. Krumwiede, Valentine, and Kohn* found a number of 

 guinea pig strains received from various sources to fall into a group which is distinct from 

 the suipestifer and paratyphoid B group, and on the basis of these agglutination differences 

 they applied to these bacilli a new name, B. pestis caviae. Howell and Schultz^ found their 

 strains readily distinguishable from B. paratyphosus A and B, B. entcritidis, and B. suipestifer . 

 but they were unable to reach any conclusion as to the occurrence of a distinct rodent group of 

 paratyphoid organisms. Thomas^ identified his cultures as either B. entcritidis or B. paratyphi 

 of animal origin, and Steinmetz and Lerche' state that the guinea pig strains are serologically 

 identical with the Bacterium entcritidis Breslau. According to the careful comparative studies 

 of Jordan,'" six of the sixteen strains of paratyphoid bacilli isolated by different workers from 

 guinea pigs in this countrj^ are B. entcritidis Gartner while ten belong to the B. paratyphosus 

 B aertrycke type. These conclusive studies are quite in harmony with those of Savage and 

 White." Enteritidis organisms have also been found by Ten Broeck," Bainbridge and 



' Holman, W. L.: loc. cil. ^Thomas, B. G. H. : loc. cil. 



3 Krumwiede, C, Valentine, E., and Kohn, L. A.: /. Med. Research, 34, 449. igig. 



''Raebiger, M., and Lerche, P.: loc. cil. 



5 Nelson, J. B.: /. Exper. Med., 45, 391. 1927. 



* Krumwiede, C, Valentine, E., and Kohn, L. A.: loc. oil. 



7 Howell, K. M., and Schultz, O. T.: loc. cit. 



8 Thomas, B. G. H.: loc. cil. 

 'Steinmetz, M., and Lerche, P.: loc. cit. 



"Jordan, E. O.: /. Inject. Dis., 36, 309. 1925. 



"Savage, W. G., and White, B.: "Medical Research Council Special Report Series," No. 92. 

 1925. 



"Ten Broeck, C: /. Exper. Med., 32, 32. 1920. 



