cultures the filaments are homogeneous and composed of single cells; with increas- ing age, fine granules and alternate light and dark bands appear in the filaments together with a tendency to fragment into irregular, bacillary and coccobacillary ele- ments which give the typical strepto- bacillary appearance. Under certain con- ditions, large, spindle-shaped or spherical swellings, sometimes packed with gran- ules, are very common, occurring any- where, terminally, subterminally or centrally, in the rods and filaments. Besides these cellular swellings, extra- cellular, ether -soluble, oil -droplet -like globules are very characteristic ; these have been shown to consist mainly of cholesterol (Partridge and Klieneberger, Jour. Path, and Bact., 52, 1941, 219). The morphology, to a considerable extent, depends upon the medium, culture conditions and the age of the culture. Under favorable conditions the cells tend to be regular and rod-shaped, while under unfavorable conditions pleo- morphism is most pronounced. In smears from pathological material, such as exudates or blood from infected animals, the cells occur only as rods or occasionally as short filaments which lie singly or in clumps without definite arrangement. True branch- ing has often been reported, but it is now generally recognized that branching does not occur. Not encapsulated. Non-motile. The Monilia-k.e swellings take stains more intensely than do the filaments; they do not take the spore stain. Not acid-fast. Gram- negative; sometimes reported to be weakly and irregularly Gram-positive in very young cultures. Requires media enriched with ascitic fluid, blood serum or whole blood. CO 2 generally does not stimulate growth. Mois- ture is essential for good growth; incubation of cultures on solid media in incubators wath a moisture-saturated atmosphere is recommended. Gelatin: No liquefaction. Plain and glucose agarorbroth: No growth with recently isolated strains; occasionally very slight growth after prolonged artificial culture. Ascitic fluid or serum agar: Discrete colo- nies, 1.0 to 2.5 mm in diameter after 3 days, circular or irregularly round with sharp edges, low-convex, colorless or grayish to whitish, smooth glistening surface, buty- rous consistency. Smaller colonies (type X colonies of Brown and Nunemaker, Bull. Johns Hopkins Hosp., 70, 1942, 201; a. colo- nies of 0rskov, Acta Path, et Microbiol. Scand., 19, 1942, 575), which have a rough and more coarsely granular appearance, are sometimes found; these colonies are intermediate in size and structure between those of the streptobacilli and those of the Li forms. Horse-blood agar colonies: Similar to those on serum agar. No hemolysis or change of color. Loeffler's serum colonies: Smaller than those on serum agar, being less than 1 mm in diameter. Ascitic fluid and serum broth: Whitish, flocculent growth at the bottom or along the side of the tube in 24 hours; growth oc- curs either as small, compact balls or granules with perfectly clear supernatant fluid or as soft, fluffy masses, occasionally with some general turbidity. No surface growth. No odor. Medium composed of equal parts of gly- cerol extract of potato and infusion broth to which egg yolk is added (Parker and Hud- son, op. cit., 1926, 357): Excellent growth. Milk : Growth generally poor ; good growth is reported bj' some authors. No coagula- tion. Indole not produced. Hydrogen sulfide produced in slight or moderate amounts. Acid from glucose, fructose, maltose, galactose, mannose, glycogen, dextrin and starch. Sucrose, lactose and salicin may or may not be attacked. No acid from xylose, inulin, dulcitol, rhamnose, arabinose, inositol, raffinose, sorbitol, trehalose, gly- cerol or mannitol. Nitrites not produced from nitrates. Urea not hydrolyzed. Methylene blue is rapidly reduced. Sodium tellurite not reduced. Catalase-negative. Oxidase-negative. Aerobic, facultatively anaerobic; anaero- bic conditions sometimes produce the best growth on primary isolation. Optimum temperature, between 35° and 38° C. No or scant growth at 22° C.
