Bacillus fluorescens non liquefasciens is also often found in the mouth. As its name implies, it does not produce liquefaction of gelatin or blood serum, and is non-motile. The green fluorescent pigment produced is often seen in broth cultivations, especially so when the culture is shaken up with air, the colour disappearing again on standing.

The other biological reactions are similar to the organism described above. Ruzicka,' after a prolonged examination of this group of bacteria and the B. pyocyaneus, came to the conclusion that they were all varieties of one species, although perhaps modified by their surroundings, &c. Lehmann and Neumann also support this view. There are a considerable number of organisms described as producing a greenish fluorescence, and it is certainly not improbable that they are also members of this one species.

× 1,000.

(24) BACILLUS SUBTILIS. (The Hay Bacillus.)

Found in soil and water, very common. Often associated with the Mesenteric group in the mouth and in carious dentine.

Morphology.--Bacilli 4-6 to 6 μ long, 0.75 to 1 μ broad, with rounded ends. Often associated in chains (streptobacilli). Sometimes grows out into very long filaments, especially in liquid media. Flagella multiple (peritrichic).

Arch. für Hygiene, Bd. xxxiv., p. 148.
Bacteriology, p. 286.

Staining Reactions.—Stains with the ordinary aniline dyes, and by Gram's method. The spores stain well by Möller's method. The flagella are stained by Pitfield's method.

Biological Characters.-An äerobic, liquefying, motile bacillus. Forms spores, which are generally situated at the ends of the rods. The spore germination is characteristic. The germinating spore splits along one side, and the organism grows out through the rent, the remains of the spore often remaining attached to the end of the bacillus. The motility is of a curious waddling nature, and is not very rapid even when the bacillus possesses many flagella.

Gelatin Plates, 22° C.-In twenty-four hours minute grey-white colonies appear under the obj., they are granular, greenish, and have a well defined but irregular outline. Development progresses rapidly, and in two days well marked liquefaction has taken place, forming saucer-like cavities with granular, translucent contents; the central part being opaque and white. Under the obj. the colonies are greyish-yellow in the centre, and greenish-grey towards the periphery where a tangled mass of filaments is to be seen, which radiate into the surrounding medium and also into the non-liquefied portion (crateriform, turbid, entire, becoming ciliate).

Gelatin Stab, 22° C.-A white growth rapidly appears along the needle track (saccate), and liquefaction soon commences with the formation of a wrinkled mycoderma upon the surface. The pellicle thus formed sinks to the bottom of the liquefied gelatin, and is replaced by another which in turn sinks, so that a thick deposit is formed at the bottom of the tube. The fluid which at first is filled with white flocculi becomes clear as the result. Occasionally the liquefaction does not progress so rapidly, and fine radiating processes extend into the non-liquefied medium, which disappear as liquefaction progresses. Various races of subtilis show considerable variation in their liquefying power. No gas is formed.

Agar Streak, 37-5° C.-In twenty-four hours a grey, opaque flat growth with defined edges, which later becomes dry, irregular and brownish in colour. The whole may be often lifted away from the surface of the nutrient medium. The surface, at first slightly mottled, becomes corrugated and wrinkled (crumpled).

Potato, 37.5° C.—In twenty-four hours the whole surface of the slice is covered with a moist creamy growth which extends on to the glass of the culture tube. The growth is found to be full of spores when examined microscopically.

Blood Serum, 37·5° C.—A wrinkled mycoderma is rapidly formed over the surface, and liquefaction of the medium occurs.

Broth, 37.5° C.-In liquid media general turbidity is rapidly formed, and the characteristic wrinkled mycoderma is formed upon the surface, and becomes firmly attached to the tube walls. On vegetable infusions of all kinds a similar wrinkled pellicle is rapidly formed, and is seen to consist of tangled threads when examined under the microscope. Indol negative.

Litmus Milk.-An acid reaction is generally produced, and the casein is dissolved. Later the reaction becomes alkaline. Various sugars are oxidised, saccharose inverted and then oxidised. The process is continuous if the acid formed is neutralized as formed with precipitated chalk (Lefar).

The organism is extremely sensitive to acids, and in the presence of minute traces forms all sorts of curious involution forms (see fig. 3).

(25) PROTEUS VULGARIS.

The common bacterium present in putrefactive processes; widely distributed. This and other putrefactive bacteria were once described under the term "Bacterium Termo."

Morphology.-Bacilli with rounded ends, 0-8 μ broad, of variable length (1.5 to 3 μ); long filaments 20 μ, and longer are formed; these filaments may be flexible and sometimes spiral in form. The rods are frequently united in pairs; they are motile and have peritrichic flagella (fig. 3 (iii.) a). Involution forms are common, the most frequent being of globular shape, and are generally found in cultures incubated at 37.5° C. Spore formation not observed. Staining Reactions.—Stains well with the ordinary aniline dyes, but does not retain the stain of Gram's method.

Biological Characters.-An äerobic, facultative anäerobic, liquefying, motile bacillus growing in the usual culture media at the room temperature. Optimum temperature 22° C.

Gelatin Plates, 22° C.-In 5 per cent. gelatin in eight hours. small depressions are seen on the surface of the medium. Under the microscope these depressions are seen to have amoeboid-like processes extending on to the surrounding surface. These processes undergo constant change in form, and may become detached and wander over the plate (Sternberg).

The deep colonies have radiating processes extending into the

unliquefied gelatin. No wandering colonies are formed in 10 per cent. gelatin.

Gelatin Stab, 22° C.-Liquefaction takes place to the bottom of the puncture and rapidly spreads to the walls of the tube (saccate); near the surface a white cloudiness is produced and an abundant flocculent deposit is formed at the bottom.

Gelatin Shake, 22° C.-Abundant gas formation and liquefaction of gelatin.

Blood Serum, 37.5° C.-Dirty white growth in twenty-four hours with well-marked liquefaction of medium, which becomes discoloured.

Agar, 37.5° C.-In twenty-four hours a spreading, pale yellowish, glistening, translucent growth covering the whole surface of the medium.

Potato, 37.5° C.-In twenty-four hours a dirty white moist growth. The surface of the potato becomes dissolved. Putrefactive smell and alkaline reaction.

Litmus Milk, 37.5° C.-Slightly acid in twenty-four hours, later distinctly alkaline, but no clotting takes place. The casein becomes dissolved, and the fluid ultimately is clear with a thick precipitate of a brown-blue or yellow colour.

Broth, 37.5° C.-General turbidity and precipitate in twenty-four hours; there is generally a putrefactive smell. Indol formed. H2S present.

Nitrate Broth.-Well marked reaction with naphthylamine (see page 226).

H
CO

Glucose Broth. -Gas formed ; no gas in lactose broth. Pathogenesis. —Pathogenic for rabbits and guinea-pigs when injected into the veins in considerable quantities. Cheyne estimated that a cubic cm. of liquefied gelatin contained 4,500,000,000 bacilli, and that a smaller dose than 9,000,000 produced no ill effect. The organism has often been isolated post mortem from venous thrombi.1 Filtered cultures cause toxæmia.

(26) BACILLUS NECRO-DENTALIS (GOADBY).

Found in dental caries, especially in the deep layers of carious dentine, where the rods may be found blocking up the dentinal canal. When first isolated it grows best in an atmosphere free from

'Bryant, Trans. Path. Soc., 1901.

oxygen, but is facultative äerobic, and grows well under ordinary conditions. It develops well on the ordinary laboratory media used.

Morphology.-Bacilli 0.75 μ broad, and 1 to 5 μ long, often associated in pairs and sometimes in chains (streptobacilli). The ends of the bacilli are square or rounded. In anaerobic cultures the bacilli tend to grow out into long threads; under äerobic conditions the organism is much shorter. The bacilli tend to involute rapidly, and form swollen and contorted masses not unlike the streptococcus.

In broth cultures the bacilli are very short and appear more like cocci. They are slightly motile, best marked on anäerobic cultures. I have not succeeded in staining the flagella.

Staining Reactions.-Stains by the ordinary aniline dyes but takes some time, especially with methylene blue. It retains the stain of Gram's method. The involution forms stain badly and appear granular, but no polar staining has been observed.

Biological Characters.-An anäerobic, facultative äerobic, nonliquefying motile bacillus. No spore formation observed. Nonchromogenic.