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Biological Characters.—An äerobic, liquefying streptothrix.

Gelatin Plates, 22° C.-At the end of three to four days (rarely earlier) minute, hard, raised, colourless and spherical colonies appear, which increase somewhat rapidly and occasionally form cone-shaped projecting points the tops of which become coated with a white powder. Liquefaction commences somewhat later and the colonies gradually sink into the fluid gelatin. Occasionally the colonies do not produce the projecting cone-shaped points but remain flat and ring-shaped, the centre remaining clear.

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FIG. 69.-STREPTOTHRIX BUCCALIS. Seven days' cultivation on potato stained Gram, showing involution forms due to fragmentation of the threads. x 1,000.

Gelatin Stab, 22° C.-Slight development occurs along the line of inoculation in minute beaded colonies. Liquefaction commences at the surface about the fifth day and extends to the tube walls; the liquefied medium is separated from the solid by a horizontal plane (stratiform).

Gelatin Shake, 22° C.--No gas bubbles are produced, and a faint cloud of minute colonies, best marked at the surface, appears in four to five days. Liquefaction stratiform.

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Agar Plates, 37.5° C.-In twenty-four hours small, hard, convex colonies, having a cartilaginous consistency; in three or four days they become truncated cones, and later surmounted with white powder composed of gonidia. The cones often crack across the summit. The colonies eventually produce a slight depression in the agar; they are extremely difficult to remove with the platinum needle, and to make a satisfactory coverslip preparation it is best to crush a colony between two cover glasses.

Blood Serum, 37-5° C.-No discolouration on this or any other media, with the exception of an occasional colony in freshly isolated specimens. Liquefaction occurs.

Litmus Milk, 37.5° C.-In two days no change, later precipitation of casein occurs, the milk clearing and taking on a bluishpurple tinge. Morphologically, mostly streptobacilli.

Broth, 37.5° C.-Flaky particulate scum gradually developing into spherical colonies which fall to the bottom. A layer is generally retained around the meniscus, which becomes chalky white.

Potato, 37.5o C.-Yellowish or orange-brown discolouration, not constant, with colonies flat or raised and about the size of small shot. A chalky-white appearance is later caused by the formation of gonidia.

Spore Formation.—No endogenous spores observed ; cultures killed by exposure to 75° C. for ten minutes. Motility not present. No sulphur grains seen.

All the cultures give off a characteristic musty smell like a damp cellar.

CHAPTER XIII.

Saprophytic Bacteria of the Mouth not Described in

Previous Sections.

(36) BACILLUS COLI COMMUNE. FOUND extremely widely distributed, in water, in fæces, in certain diseases of animals and in diseases of men. Commonly present in milk, &c. Often present in the mouth. Frequently present in abscesses situated near digestive tract.

Morphology.-Bacilli 1 to 4 u long, and 0.4 to 0:6 u broad. Often forms rods of considerable length. The ends are rounded. Actively motile in young cultures.

Staining Reactions.—Stains easily with the usual methods, but not by Gram's method. In old cultures polar staining occurs. The flagella may be stained by Pitfield's or van Ermengem's methods ; they are generally twelve, rarely more than fourteen, arranged around the bacilli (peritrichic).

Biological Characters.-An äerobic, facultative anäerobic, nonliquefying motile bacillus. No spore formation. Grows well at 37° C. and at the ordinary room temperature (22° C.).

Gelatin Plates, 22° C. Superficial Colonies.--At first small yellowish punctiform colonies, later becoming large irregular; edge lobulate or dentate, shining. Centre opaque and white and often a little raised.

Deep Colonies.—Punctiform, later wheatstone-shaped, yellowish. No liquefaction.

Microscopically.Irregularly marked surface, showing faint, irregular stripes or traversed by vein-like markings as in marble (marmorated).

Gelatin Stab, 22° C.-Well marked growth to bottom of stab, whitish-grey, granular; no liquefaction. Surface thin, whitishgreen, flat, edge notched.

Gelatin Shake, 22° C.- Three days: well marked cloud of gas bubbles; no liquefaction.

Gelatin Streak, 22° C.-Spreading, white, thin, granular, as on surface of stab.

Agar Streak, 37.5o C.-Grey-white, glistening, moist, translucent. Condensation water clear with slight precipitate.

Potato, 22° C.-Yellow to yellow-brown discolouration of potato occasionally occurs.

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Litmus Milk, 37.5° C.-Coagulation and marked acid reaction. H.S and indol produced.

Broth, 37.5° C.-Dense turbidity with thick sediment. Indol in seven days or less.

Lactose, Maltose, Glucose Broth.Acid fermentation and gas given off (CO2).

Anäerobiosis.—Grows well on glucose formate media, producing much gas on glucose formate broth.

Pathogenesis.—Variable, some cultures producing death in one to five days, with general septicæmia when injected intraperitoneally,

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