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Potato.—Luxuriant growth, at first green, later turning brown, both at 22° and 37.5° C.

Blood Serum, 37.5° C.-Similar to agar, but liquefaction occurs in a well-marked groove.

Litmus Milk, 37.5° C.-Well marked coagulation of casein, which later is dissolved and ammonia given off.

Broth, 37.5° C.-Well marked fluorescence and general turbidity. A scum, often a distinct pellicle, is formed, and a thick precipitate collects at the bottom of the tube. Both pigments are produced ; the fluorescin being soluble in chloroform may be separated for the insoluble pyocyanin.

Peptone Water.— With the addition of 5 per cent. glycerine the blue pigment pyocyanin only is formed. No indol formed.

Egg Albumin.The green pigment fluorescin alone is formed. It is soluble in chloroform, and crystallises out as long needles. On the addition of weak acid the colour changes to red.

Glucose Broth.- Acid, no gas. Nitrates reduced to nitrites.

Pathogenesis.-One cubic centimetre of broth culture injected intraperitoneally or subcutaneously generally causes death in rabbits and guinea-pigs in twenty-four to thirty-six hours. At the autopsy inflammatory medema and infiltration, sometimes a well-defined abscess, are found at the seat of inoculation. The peritoneal cavity shows a similar fibrinous inflammation when the organism is injected into that cavity. The organisms may be found in small numbers in the blood and various organs.

Intravenous injections generally produce rapidly fatal septicæmia with nephritis, occasionally chronic wasting accompanied with albuminuria. Immunity may be produced by the injection of gradually increasing doses, commencing with a sub-fatal dose. The animals thus immunised show a decidedly increased resistance to infection by the anthrax bacillus. Woodhead and Wood also found that the injection of sterilised cultures of B. pyocyaneus directly following injection with anthrax bacilli protected against that organism.

A large number of varieties of this organism have been described, some of them being no doubt varieties of the B. pyocyaneus, in which the power of pigment production has become, as Gessard has shown it may, so modified that the production of either pigment may be prevented by alteration of the nutrient medium. The antagonism of the B. pyocyaneus and B. anthracis referred to above is interesting as an example of protection afforded by dissimilar diseases. The relation of the B. pyocyaneus to the tetanus bacillus is of quite another order. The tetanus bacillus, under ordinary circumstances a strict anäerobe, will grow in broth freely exposed to the air if B. pyocyaneus is also present in the culture.

There is usually little difficulty in recognising the B. pyocyaneus, when obtained from pus or other material, by the peculiar pigments formed.

(11) STREPTOTHRIX ACTINOMYCES. The fungus of actinomycosis was discovered in 1877 by Bollinger, although Langenbeck, as early as 1845, had found that the disease of cattle known as actinomycosis could be transmitted to man.

The disease is almost confined to animals, for the most part. cattle, but since attention has been directed to the disease it appears to be more frequent in man than was at first supposed, and a large number of cases are now on record.

The organism itself belongs to the higher bacteria, and shows a far greater complexity of form than is exhibited by the majority of schizomycetes.

The point of infection is commonly the mouth, the organism gaining access to the tissues either through a carious tooth, or as. the result of some slight local injury. In a number of cases. inoculation has apparently taken place through the medium of an awn of barley containing the fungus, which has become imbedded in the soft tissues. It is common to find these grains imbedded in the local lesion. Two chief varieties of the disease are known, the one: in which considerable local reaction with enlargement and thickening of the tissues and bone occurs, the other a condition of general infection with deposits and abscesses in various organs, notably the liver. The chronic form with local swelling was for a long time confounded with osteo-sarcoma. In the pus from the abscesses or local lesion small yellowish-grey granules are to be seen even with the naked eye. Microscopically these granules show the peculiar rosette-shaped fungoid masses, consisting of a central mass surrounded by tbreads which give the rayed appearance to which the fungus owes its name (Hertz). The granules are each composed of a central mass of cocci-like bodies (gonidia) often containing a quantity of dark pigment. Surrounding the central portion is a zone of tangled threads showing true branching, generally lateral. 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 m 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 pot 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, 1.), 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),

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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 GINGIVÆ 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 intlammation, 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 u long, 0.5 to 0.75 u 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-Leffler bacilli. Involution forms (globular or twisted) are common on old cultures.

Staining Reactions.—Stains by the ordinary aniline dges and by Gram's method. The flagella may be stained by Pitfield's method.

Biological Characters.-An aerobic facultative anäerobic, liquefy

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