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and Israel, has been cultivated by Boström, Affanassieff, and others. This second variety of actinomyces grows more energetically in the presence than in the absence of air—an important differential diagnostic point in relation to that already described. The temperature-optimum is 37° C. (98.6° F.), although the fungus will grow well also at ordinary room-temperature. Upon gelatin-plates, and still better upon agar-plates, there form at first fine, radiating colonies, which develop with comparative activity to opaque nodules, whose periphery presents a delicate filamentous network. In agar streak-culture a continuous deposit does not form, as a rule, but a series of more or less closely approximated nodules. The latter not rarely exhibit a brick-red color upon blood-serum, and become covered by a whitish, down-like coating consisting of airhyphæ. From these there develop, through a process of segmentation, a series of roundish bodies arranged like chains, the so-called actinomyces-spores. These are destroyed only after exposure for five minutes to a temperature of 75° C. (167° F.), whereas the mature forms die at as low a temperature as 60° C. (140° F.). When kept in the thermostat for some time, a wrinkled, coherent membrane eventually develops upon blood-serum, while the nutrient medium is softened. Upon potato the aerobic actinomyces grows as a brick-red deposit, and likewise with air-hyphæ. In bouillon floating and in part granular membranes form that sink to the bottom, while the overlying fluid remains clear. Milk is gradually peptonized.

With regard to the microscopic appearances, the granules and the druses, which constitute the characteristic feature of the morbid process from which the aerobic actinomyces is obtained, resemble in every detail those already described, so that it is only necessary to refer to the account of these. Preparations made from pure cultures, however, display great differences. Long filaments with rectangular branches may be seen that have arisen through the process of budding. Terminal enlargements are encountered but rarely in old colonies that have developed in the depth of the culturemedia. Transmission of the aerobic ray-fungus to animals has not yet been effected with certainty-a third point in contradistinction from the anaerobic species of Wolff and Israel.

With regard to the botanic position of the actinomyces, it was formerly included among the pleomorphic bac

teria. Kruse (Flügge's Microorganisms) includes it among the streptothrices. These represent, to a certain degree, a connecting link between molds and bacteria. They consist of long, cylindric filaments, dividing by budding, and eventually developing a true mycelium. Individual species produce fruit-bearers, which, after the fashion of oidia (see p. 338), constrict off spores directly, without especial fruitheads. These spores must, however, not be placed upon the same plane as the similarly designated permanent forms of the bacteria, as they succumb to exposure for five minutes to a temperature of 70° C. (158° F.), as has been mentioned in connection with the aerobic actinomyces. In old cultures the branching filaments break up into bodies resembling bacteria, bacilli, cocci, and even spirilla. If, however, these disintegrated products are transferred to new culture-media, true filamentous networks will again develop from them. According to our own investigations, we have likewise reached the conclusion that the entire group of actinomyces is to be included among the hyphomycetes. The bacteriologic diagnosis of actinomycosis requires only microscopic demonstration of the actinomyces-druses in the pus. Culture is not necessary to establish the

diagnosis. Treatment. According to recent statements, actinomycosis is specifically influenced by potassium iodid. It is said that recovery from the disease will take place without any surgical intervention upon administration of moderate doses of this drug-from two to three grams daily.

PATHOGENIC STREPTOTHRICES.

In connection with the actinomyces, brief mention will be made of the streptothrix Eppinger and the streptothrix farcinica. The former was found by Eppinger in an abscess of the brain. The fungus presented a branch mycelium. Air-hyphæ and spores are, however, found only upon potatoes. The fungus can be stained by Gram's method. It grows best at a temperature of 37° C. (98.6° F.) in the absence of air. Upon gelatin elevated, wart-like yellow colonies form, which do not liquefy the culture-medium. Upon glucose-agar a wrinkled, orange-colored deposit forms, and upon potatoes a thin, yellowishred deposit. Bouillon remains clear, although flocculent islands develop. A variety of pseudo-tuberculosis develops in guineapigs and rabbits inoculated with the streptothrix Eppinger.

The streptothrix farcinica (also designated "bacille du farcin des boeufs Nocard") likewise gives rise to the formation of a branched mycelium, with air-hypha and spores. Growth takes place between 30° C. (86° F.) and 40° C. (104° F.) in the presence of air. The fungus can be stained by Gram's method. Upon agar whitish, dry scales form that subsequently become yellow and finally confluent. Bouillon is not rendered turbid, but presents flocculi. A similar change takes place in milk, which is not otherwise altered. The farcin des boeufs is a pseudo-tuberculous affection of the skin and the internal viscera in cattle. Experimentally the streptothrix farcinica induces pseudo-tuberculosis in cows, sheep, and guinea-pigs.

PATHOGENIC YEASTS.

The recognition of the pathogenic yeasts has been made only within recent years, and is due especially to the labors of Busse, Sanfelice, Curtis, and Rabbinowitsch.

The following varieties of pathogenic yeasts have been found in human beings:

The saccharomyces hominis has been observed in an infectious disease that began with subperiosteal inflammation of the tibia, and finally terminated in the clinical picture of pyemia. The organism appears in the form of round or oval cells, with double contour and a capsule. Upon gelatin-plates it forms round, projecting colonies that do not cause liquefaction; upon agar, a whitish deposit; upon potatoes, a grayish-brown deposit; in bouillon, marked turbidity, with the formation of a membrane; and upon blood-serum, a dewdrop deposit. The saccharomyces hominis possesses the property of inducing fermentation of grapesugar, with the generation of alcohol and carbon dioxid. It is pathogenic for guinea-pigs, inducing local suppuration, and for mice, which die exhibiting septic manifestations.

The saccharomyces subcutaneus tumefaciens has been cultivated from a myxomatous tumor of the thigh. It consists of oval or round cells that frequently possess a large, transparent capIn gelatin stab-cultures development takes place in the form of small colonies; the culture-medium is not liquefied. Upon agar a thick, creamy deposit forms, and upon potatoes a whitish deposit, later becoming brown; upon beerwort-agar a brownish coating, and upon beerwort, a dense sediment without development of membrane-formation. The fungus has slight fermentative activity for saccharose, generating ethylic alcohol and acetic acid. This yeast is pathogenic for white mice and rats, in which extensive local vegetation occurs. Microscopically, the tumor-like formations present no true structure, but are found to consist of enormous parasitic infiltrations.

II. INFECTIONS WITH THE LOWEST FORMS OF ANIMAL LIFE.

The protozoa, the lowest forms of animal life, have hitherto taken part in the etiology of but a small number of diseases in human beings. Perhaps the future will show that they occupy a larger field of activity. In a number of infectious diseases whose exciting agents are as yet unknown, animal parasites are believed to have been observed -as, for instance, in whooping-cough, in carcinoma, and others. The connection of disease with the lowest forms. of animal life has, however, been established with certainty only for two affections-namely, dysentery and malaria.

DYSENTERY (AMEBIC ENTERITIS) AND TROPICAL ABSCESS OF THE LIVER.

The cause of dysentery was recognized by Lösch in 1871 as peculiar animal parasites belonging to the class of protozoa amebe-which were found in dysenteric stools. Koch, on the occasion of his cholera-expedition to Egypt, noted the same organisms in the base of the ulcers of the intestine in four fatal cases of dysentery. Kartulis, Ogata, and others, and in Germany recently Kruse and Pasquale, and, further, Quincke and Roos, have since studied the amebæ carefully, and confirmed their etiologic relation to dysentery.

Th amebæ of dysentery are unicellular organisms of varying size, with ameboid movement. The smallest cells are about 10 μ in diameter; the largest, 50 p (giant amebæ); the majority, at rest, from 20 to 25 μ. The protoplasmic body of the amebæ can be differentiated on movement into an outer zone, the ectoplasm, which is homogeneous and less refractive, and the entoplasm, which in part is apparently almost structureless, containing a small number of disseminated granules and differentiated from the ectoplasm only by its greater refractive power, and in part highly granular, and completely filled with irregular, mostly quite fine granules (granular plasma), or, finally, exhibiting a greater or lesser number of large and small vacuoles. The two layers are distinctly differentiable from each other only when the ameba is in motion, while the differentiation is

lost in a state of rest. Frequently, foreign bodies, especially red blood-corpuscles, also bacteria, much less commonly leukocytes, may be seen within the entoplasm; at times the protoplasmic body is literally stuffed with blooddiscs. The ameba invariably contains a nucleus, which, however, is not always clearly visible in the moving cells. The nucleus is usually eccentric, and with change in shape, often near the periphery. It has a diameter of between 6 and 8, is round in shape, generally with a sharp contour, and a punctate nucleolus. At times the contents of the

nucleus are slightly granular.

The characteristic of the ameba is its mode of movement, which is designated ameboid. The ectoplasm is extended at

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any given point in the form of a blunt, roundish, homogeneous process, and the protoplasm flows after it. In this way an actual change in position can be brought about by a slow, at times backward, crawling movement. The process may further be retracted, to appear immediately at the same or at another point. The ameba is thus engaged in constant change in shape. At times the ectoplasmic processes move around the central mass in waves without locomotion taking place.

Little is known regarding the nutrition of the amebæ. In general the foreign bodies so frequently seen in the entoplasm, especially the red blood-corpuscles, are considered as nutrient material. These are taken up by a process of

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