103) recently reported biochemical methods by which P. pestis and P. pseudotuberculosis can readily be differentiated: on ordinary urea (Difco) slants with phenol red as indicator, the former does not affect the medium whereas the latter produces a red coloration of the medium; with desoxj'cho- late citrate agar, the colonies of P. pestis are rather scant, reddish and pin-point in size after 48 hours at 37° C, while those of P. pseudotuberculosis are abundant, large, opaque and, like the medium in general, become yellow. Source: Isolated from buboes, blood, pleural effusion, spleen and liver of infected rodents and man; also from sputum in pneu- monic plague and from infected fleas. Habitat: The causative organism of plague in man and in rats, ground squirrels and other rodents. Infectious for mice, guinea pigs and rabbits. Transmitted from rat to rat and from rat to man by the in- fected rat flea. 6. Pasteurella pfaffii (Hadley et al., 1918) Hauduroy et al., 1953. (Bacillus der Kanarienvogelseuche, Pfaff, Cent. f. Bakt., I Abt., Orig., 38, 1905, 276; Bacterium pfaffi, (sic) Hadley, Elkins and Caldwell, Rhode Island Agr. Exp. Sta. Bull. 174, 1918, 169; Pasteurella pfaffi (sic) Hauduroy et al.. Diet. d. Bact. Path., 2" ed., 1953, 377.) pfaffi. i. M.L. gen. noun pfaffii of Pfaff; named for Dr. Franz Pfaff of Prague, who isolated this species. Description taken largely from Hadley et al. {op. cit., 1918, 180). Rods, 0.5 by 1.0 to 2.0 microns, occurring singly. Non-motile. Gram-negative. Gelatin colonies: Small, grayish, translu- cent. Gelatin stab: No liquefaction. Agar colonies: Small, yellowish gray, homogeneous, translucent, entire. No odor. Agar slant: Slight, yellowish gray, trans- lucent streak. Broth: Turbid; flocculent sediment (Pfaff, op. cit., 1905, 280). Litmus milk: Unchanged. Potato: Moderate, whitish streak. Indole not produced. Hydrogen sulfide not produced. Acid but no gas from glucose, fructose, arabinose, xylose, maltose, dextrin, salicin and mannitol. Lactose, sucrose, rafiinose, inulin, adonitol and dulcitol not attacked. Nitrites not produced from nitrates. Aerobic, facultatively anaerobic. Optimum temperature, 37° C. Pathogenic for canaries, sparrows, pi- geons, white mice, guinea pigs and rabbits. Not pathogenic for chickens (Pfaff, loc. cit.). Source: First encountered in an epidemic of septicemia in canaries. Caused a necrotic enteritis. Habitat: Not known from other sources. 7. Pasteurella pseudotuberculosis (Pfeiffer, 1889) Topley and Wilson, 1931. (Bacillus pseudotuberkulosis (sic) Pfeiffer, Ueber die bacillare Pseudotuberculose bei Nagethieren, Leipzig, 1889, 5; Streptohacillus pseudotuberculosis rodentium Preisz, Ann. Inst. Past., 8, 1894, 231; Topley and Wilson, Princip. Bact. and Immun., 1st ed., 2, 1931, 825.) pseu.do.tu.ber.cu.lo'sis. Gr. adj. pseudes false; L. noun tubercnlum a small swelling; M.L. neut.n. tuberculosis tuberculosis; M.L. noun pseudotuberculosis pseudotuberculosis. The tabular description by Eisenberg (Bakt. Diag., 3 Aufl., 1891, 294) is very in- complete. Description taken from Topley and Wilson (Princip. Bact. and Immun., 2nd ed., 1936, 607) and from Bessonowa, Lenskaja and Molodtzowa (Office Internat. d'Hyg. Publ., 29, 1937, 2106). Small rods which vary in size and shape: ellipsoidal or coccoid forms are 0.8 by 0.8 to 2.0 microns, with rounded ends, occurring singly; rod-shaped forms are 0.6 by 1.5 to 5.0 microns, with rounded ends, occurring singly, in groups or in short chains; occa- sionally long, curved, filamentous forms occur. Motile by means of one to six peri- trichous flagella. Not acid-fast. Gram- negative. Gelatin stab: After 7 days at 22° C, good filiform growth extending to bottom of tube. No liquefaction. Agar colonies: After 24 hours at 37° C, circular, 0.5 to 1.0 mm in diameter, um- bonate, granular, translucent, grayish yel- low, butyrous; edge entire; dull, finely
