The ends of the threads are commonly but not invariably clubbed, and at the periphery of the granule give the appearance of rays. The threads are about 0.5 μ in diameter, and are composed of a central protoplasmic axis surrounded by a gelatinous sheath. In young specimens the threads take up aniline dyes uniformly, but in old cultures the threads tend to stain irregularly and may appear as chains of cocci or bacilli. The clubs do not stain by Gram. In culture media the changes are somewhat different. The branched and tangled mass of threads are formed as colonies of cartilaginous consistency; the clubbing is not marked. The threads stain irregularly after about a week, and the gonidia are well marked, often covering the colony with a white or yellow dusty efflorescence. The typical granules are not formed, although there may be some attempt on liquid blood serum.

The conditions of growth outside the body and the form in which the organism exists when infection occurs is not at present known. It is thought that it may exist in the grains of certain cereals in a similar manner to Puccinia graminis.

Morphology.-Filamentous, branched, and club-shaped forms (fig. 1, i.), with all the morphological forms of bacteria represented at times. The clubs are not formed in cultures. Various changes occur in the threads, which at first stain well but later become granular and stain irregularly. No endospores are formed, but gonidia are present.

Staining Reactions.- Stains with the ordinary aniline dyes, best by Gram's method, which is much the best stain for tissue preparations. The clubs do not retain the stain of Gram's method, but may be counterstained with picric acid.

Biological Characters.-An äerobic facultative anäerobic streptothrix, forming gonidia, non-motile; does not possess flagella. Gelatin is liquefied.

Gelatin. The organism grows slowly at the room temperature, and the medium is gradually liquefied and turns a dark brown colour, the liquid being somewhat viscous. Scattered about in the fluid are small round white nodules, from which filaments radiate.

Agar and Glycerine Agar.-After three days at 37.5° C., minute, hard, spherical, white colonies appear (fig. 45, a); these gradually increase, and become raised at their edges, ultimately forming an ́undulating and crater-form surface, at first yellowish, later greenishgrey (fig. 45, B). The older colonies often resemble lichen (fig. 45, c),

FIG. 45.-STREPTOTHRIX ACTINOMYCES CULTIVATIONS ON GLYCERINE AGAR.
A. Discrete rounded colonies, after about ten days' incubation at 37° C..
B. Limpet-shaped colonies three and a half months old. C. Lichen-like
appearance frequently seen; the growth is three and a half months old. (From
Curtis' "Essentials of Practical Bacteriology.").

and have a yellowish or ashen-grey tint. The corrugated surface is covered with a powdery dusty layer. The colonies are extremely difficult to remove for examination.

Potato. Similar appearance to agar, but more luxuriant growth. The colonies are quite unlike those produced by other bacteria, the streptothrix of madura-foot being the only organism at all resembling them, and this organism colours the potato a dark red.

Pathogenesis. Intra-peritoneal injections of the bacillary or filamentous form of the parasite in rabbits and guinea-pigs is followed in about a month by nodule formation. The nodules, composed of granulation tissue (granuloma), are vascular on the surface, and contain curdy pus, in which the typical colonies are found. In man the disease may take one or both of the forms noted above. Sometimes large areas of bone become carious and necrosed, the disease being classed by Virchow with glanders and tubercle as infective granulomata. Infection of the bowel may occur, ulceration and extensive necrosis following. The organism has also been described in the ovaries and fallopian tubes (Muir and Granger Stewart); it has also been found in the brain, liver, spleen, &c. In the later stages of the disease deposits may occur in the various organs with the formation of metastatic abscesses containing the typical colonies. The diagnosis is easy, both by the typical granules in the pus of the abscesses or other lesion, and the characteristic growth on agar and potato.

(12) BACILLUS GINGIVE PYOGENES (MILLER).

Found by Miller in unhealthy mouths and along the gum margin in such cases. I have also observed this organism in several cases both of dental caries and in gingival inflammation, and have therefore worked out the biological characters, as those given by Miller only include growth on gelatin and agar.

Morphology.- Bacilli from 2 to 6 μ long, 0.5 to 0.75 μ wide, often jointed in pairs or in chains. The elements may at times be curved. Ends square or rounded. Two or three bacilli may at times lie side by side somewhat in the manner of the Klebs-Loeffler bacilli. Involution forms (globular or twisted) are common on old cultures.

Staining Reactions.-Stains by the ordinary aniline dyes and by Gram's method. The flagella may be stained by Pitfield's method. Biological Characters.-An äerobic facultative anäerobic, liquefy

ing, motile, chromogenic bacillus. temperature of 75° C. for half an hour. media, best at 37.5° C.

Forms spores which resist a
Grows in the usual culture

Gelatin Plates, 22° C.-In forty-eight hours irregular spreading, raised colonies, with irregular and wavy edge, yellow centre lying above the outer paler mass of colony. In three days the colonies liquefy the gelatin and float upon the surface of liquid as round crinkled masses with thickened centre, which is now yellow-brown in colour. The gelatin becomes dark brown.

Gelatin Stab, 22° C.-Forty-eight hours, growth to bottom of stab; three days, slight cup-shaped liquefaction which gradually approaches the walls of the tube. In newly isolated cultures the cone may remain empty. White flocculi form in the fluid later.

Gelatin Shake, 22° C.-Forty-eight hours, cloud of minute colonies but no gas bubbles. Liquefaction commences at the surface, and does not take place in the depths.

Gelatin Streak, 22° C.-Forty-eight hours, slight liquefied groove with little other evidence of growth; four days, the fluid becomes filled with yellowish-white flocculi with radiating processes.

Agar, 37.5° C.-Twenty-four hours, heavy growth, with tendency to spread at intervals along the streak in club-shaped processes (lobulate); the central portion of the streak and of the club-shaped processes is buff-yellow, the edge grey-white. The medium may be tinted brown.

Blood Serum, 37.5° C.-In twenty-four hours a broad, deep groove of liquefaction is formed with brown discoloration of medium. Potato, 37.5° C.-Twenty-four hours, well-marked, dry, yellowbrown growth, granular and glistening; the potato becomes coloured throughout.

At 22° C. a good deal of yellow pigment is formed.

Broth, 37.5° C.-Twenty-four hours, faint growth of isolated flocculi in fluid; no general turbidity. The flocculi sink and form a thin deposit in three or four days. Good indol reaction in seven days. HS. scanty.

Litmus Milk, 37.5° C.-Forty-eight hours, well-marked acidity with coagulation which does not become dissolved for two or three days. No gas is formed, and no smell given off.

Glucose broth, lactose broth, maltose broth-acid fermentation in forty-eight hours.

Seven days' agar culture suspended in broth and heated to

75° C. for half an hour gives a good culture on sub-cultivations being made.

The spores, which are small, stain by Möllers' method.

Pathogenesis (Miller).-Pathogenic for mice, rabbits, and guineapigs when intravenously injected in doses of 0.25 cc. of a broth culture. At the autopsy peritonitis, sometimes purulent, is observed. Death occurs in ten to twenty-four hours. Subcutaneous inoculation resulted in local abscess only.

(13) B. GANGRÆNÆ PULPÆ (ARKÖVY).

B. mesentericus niger (fuscus).

Found by Arkövy in dead tooth pulps, in carious dentine, and in the oral secretions.

Morphology.-Bacilli about 4 μ in length, with rounded ends (not sharply defined as first stated, and not pleomorphic); often pairs are united at an acute angle.

Staining Reaction.-Stains with the ordinary aniline dyes, and by Gram's method. The so-called cocci described by Arkövy do not stain by methylene blue, and are spores1 which are large and oval, and may be stained by the usual methods (hot carbolfuchsin, &c.).

Biological Characters.—An äerobic, facultative anäerobic, motile liquefying bacillus ; forms pigment and spores.

Gelatin Plates.—In twenty-four hours minute white colonies make their appearance, resembling flour dust. These gradually become slightly yellow in colour, and in thirty hours are confluent, whilst the whole of the medium is liquefied with a whitish wrinkled pellicle covering and floating on the surface of the fluid. An extremely unpleasant smell is given off resembling old cheese.

Gelatin Stab.-At the end of forty-eight hours liquefaction commences, and soon reaches the wall of the tube. Flocculi form in the fluid, and in ten days a wrinkled pellicle has formed upon the surface. The gelatin is coloured a red brown, the pellicle being of a dirty brown. The liquefied gelatin gives a strongly

alkaline reaction.

Agar Plates, 37.5° C.-At the end of twenty-four or thirty-six hours, small white colonies make their appearance. They have a

'Cent. für Bakteriol., Bd. xxix,, No. 19, 1901.