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CLINICAL BACTERIOLOGY.

PART I.

L. MORPHOLOGY AND BIOLOGY OF BACTERIA. THE minute forms of life constituting in largest part the exciting agents of the infectious diseases occupy the lowest level in the vegetable kingdom. They are designated bacteria or fission-fungi. The latter term is, however, not well chosen. The botanic conception of fungi includes those lower forms of vegetable life that are without the coloringmatter of leaves (chlorophyl) or similar coloring-matters (chromophyls). There are not a few bacteria, however, that are capable of generating such coloring-matters, and, thus, also of decomposing carbon dioxid and its combinations, and utilizing the products of this activity. There is, thus, no justification for the term fission-fungi, and it is, therefore, preferable to designate the minute forms of life under consideration as bacteria.

There is as yet no strictly scientific, natural classification of bacteria. For the present the adoption of an artificial system, based upon such physical features as the size, the shape, and the arrangement of the bacteria, must suffice (F. Cohn). (See Figs. 1, 2, 3.) Three main divisions are recognized: (1) Spheric bacteria (cocci, micrococci, coccaceae); these are spheric cells. (2) Rod-shaped bacteria (bacilli, bacteriacea); these are rod-like, cylindric cells. (3) Spiral bacteria (vibrios, spirilla, spirillacea); these are twisted in both the horizontal and the vertical direction, and are, thus, comparable to the windings of a screw or of a corkscrew.

The individual bacterial cells exhibit at times a homogeneous translucent, at other times a granular protoplasmic, structure that, on the whole, possesses the properties of all other protoplasmic structure, but that is not, as in the cells of the higher orders of plants it is, differentiable

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Fig. 1. Various forms of bacteria: 1 and 2, Round and oval micrococci; 3, diplococci; 4, tetracocci, or tetrads; 5, streptococci; 6, bacilli; 7, bacilli in chains, the lower showing spore-formation; 8, bacilli showing spores, forming drumsticks and clostridia; 9 and 10, spirilla; 11, spirochetæ (McFarland).

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Fig. 2.-Diagram illustrating the morphology of the spirilla: a, b, c, Spirilla; d, e, spirochetæ (McFarland).

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Fig. 3.-Diagram illustrating the morphology of the bacilli: a, b, c, Various forms of bacilli; d, e, bacilli with flagella; f, chain of bacilli, individuals distinct; g, chain of bacilli, individuals not separated (McFarland).

into a cell-nucleus and a cell-body. Nevertheless, some observers consider the so-called central body in certain large bacteria as the virtual nucleus, and believe the plasma to have a honeycomb arrangement—a view that has recently been put forth also with regard to the large species of spirilla. According to others, the interior of the bacterium

consists of a lining layer of protoplasm, and a loculated space for the cell-fluid. Not rarely the protoplasm of the bacteria contains granules that stain deeply with aniline dyes. The significance of these so-called Babes-Ernst bodies has not been established; they have been looked upon as the progenitors of spores, as nuclear structures, as degeneration-products, and, finally, as reserve substances.

The ground-substance of the bacterial cell is surrounded by a cell-capsule or cell-membrane constituted of albuminoid material, in rare instances of cellulose and of varying amounts of a carbohydrate that stains blue with iodin. When the outer layers of this membrane possess the property of swelling up greatly and becoming viscid and gelatinous, an appearance is created as if the bacterium possessed a special capsule, and under such circumstances it is customary, in view of the physical appearance, to speak of an encapsulated bacterium. (Fig. 4) mucoid transformation of the capsule of the cell occurs in the case of pathogenic bacteria usually only in the animal body, and but seldom in artificial culture-media.

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Fig. 4. Encapsulated bacteria.

The length of bacteria varies greatly from one to several micromillimeters (twenty and more), while their thickness is generally less than one micromillimeter.

Bacteria are in part motile, in part nonmotile. When motility is present, it is dependent upon special motor organs-so-called flagella (Fig. 5)—which are connected with the body of the cell in varying number and arrangement. These represent protoplasmic structures of extreme attenuation, which arise directly from the cell-membrane, and do not extend into the actual ground-substance. The following varieties of motile bacteria may be distinguished: I. Monotrocha, with a single flagellum at the pole of the cell.

2. Amphitrocha, with a single flagellum at each pole. 3. Lophotrocha, with a cluster of flagella at one pole. 4. Peritrocha, with a varying number of flagella surrounding the body of the bacterium.

The shape and length of these flagella are extremely variable in the different varieties of motile bacteria. The movement itself is forward, and is always combined with a

certain amount of rotation. It is most marked in quite young cultures, but is in greater degree dependent upon the variety of bacterium, the culture-medium, and the temperature. Many species of bacteria possess spontaneous movement throughout their whole life; others only during certain phases, losing it, for instance, preceding sporeformation.

The multiplication of bacteria takes place usually by means of fission in pairs. The time in which this division occurs varies for different varieties. In the case of some species, if all of the extrinsic conditions (culture-medium,

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Fig. 5.-Bacteria showing flagella: 1, Bacilli of typhoid fever; 2, bacilli coli communes; 3, spirilla of Finkler and Prior; 4, spirilla of Deneke; 5, vibrios of Metschnikoff; 6, spirilla of Asiatic cholera (Nicolle and Morax).

temperature) are favorable, it is half an hour; in that of others it is somewhat longer-from one to two hours; while in that of still others, as, for instance, the tubercle-bacillus, it is as much as several days. When the division always takes place in the same direction, and the newly formed individuals remain attached to one another, a chain-like formation results. In the case of rods bacillary filaments result, or pseudofilaments; the dividing walls between the individual cells of the strand are frequently recognizable with difficulty. In the case of spherules streptococci (chain-cocci) result. (Fig. 6.) The bacteria may, however, after division be arranged,

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