Page:Encyclopædia Britannica, Ninth Edition, v. 21.djvu/425

Rh SCHIZOMYCETES 403, ; . % . species and the conditions (the medium, temperature, &c.), enormous collections of isolated cells may cloud the fluid in which they are cultivated, or form deposits below or films on its surface j A B C valuable charac- " ., t *: $?$$&>,... ters are sometimes * . .** :.. ^fji] .;; -_ : ,. obtained from s "< ? v. t these appearances, o " . ^ J; When these dense ."* " swarms " of ve- getative cells be- come fixed in a FIG. 6. Characteristic groups of Aficrococci. (After matrix of their Cohn.) A, Aficrococcus prodigiosus. B, M. vaccinx. C, zoogloea stage of a Micrococcus, forming a close OWn swollen COn- membrane on infusion Pasteur's Mycoderma. (Very tiguous cell-walls, hi s hly ma g nifled -) they pass over into a sort of resting state as a so-called zoogloea (fig. 3). One of the most remarkable phenomena in the life- history of the Schizomycetes is the formation of this zooglcea stage, which corresponds to the "palmella" con- dition of the lower Alyse,. This occurs as a membrane on the surface of the medium, or as irre- gular clumps or branched masses (sometimes several inches across) sub- merged in it, and consists of more or less gelatinous ma- trix enclosing in- numerable "cocci," " bacteria," or other elements of the FIG. 7. Ascococcus billrothH. (After Cohn.) It SpTii"7nm-pYofo /nn forms irregular colonies of zoogloea containing ,iuzomyceie con- innumerable m icrococci. (x 65.) cerned. r ormerly regarded as a distinct genus the natural fate of all the various forms the zoogloea is now known to be a sort of resting condition of the Schizomycetes, the various elements being glued together, as it were, by their enormously swollen and diffluent cell-walls becoming con- FIG. 8. Bacterium zopfii. (After Knrth.) A, coils of the filamentous (lepto- thrix) stage still actively growing. B, the same coils observed a few hours later ; the filaments have become cut up into segments by septa, the segments separating as rodlets (bacteria). C, the same coils a few hours later still ; the rodlets broken up into yet shorter segments or cocci, (x 740.) tiguous. The zoogloea is formed by active division of single or of several mother-cells, and the progeny appear to go on secreting the cell-wall substance, which then absorbs many times its volume of water, and remains as a consistent matrix, in which the cells come to rest. The matrix i.e., the swollen cell-walls in some cases consists mainly of cellulose, in others chiefly of " my- coprotein," the substance said to be met with in the protoplasm ; the ma- trix in some cases is horny and resistent, in others more like a thick solution of gum. It is intelligible from the mode of formation that foreign bodies may be- come entangled in the gelatinous matrix, and compound zooglceaB may arise by the apposition FlG - 9.SaeiHiH megaterium. (After De, J , , . ,. r *_ . Bary.) a, a chain of motile rodlets still OI several distinct forms, growing and dividing (bacilli); b, a pair of bacilli actively growing and dividing; p, a rodlet in this condition (but divided into four segments) after treatment with alco- holic iodine solution; c, d, e, f, successive stages in the development of the spores ; r, a rodlet segmented in four, each segment containing one ripe spore ; g l, g 2 , g 3 , early stages in the germination of the spores (after being dried several days) ; h t, h*, i, k, I, and m, successive stages in the germina- tion of the spore, (a x 250; all the rest X 600.) a common event in ma- cerating troughs (fig. 3, A). Characteristic forms may be assumed by the young zoogloea of differ- ent species, spherical, ovoid, reticular, filament- ous, fruticose, lamellar, &c., but these vary considerably as the mass increases or comes in contact with others. Older zooglceae may precipi- tate oxide of iron in the matrix, if that metal exists in small quantities in the medium. Under favourable conditions the elements in the zooglcea again become active, and move out of the matrix, distribute themselves in the surrounding medium, to grow and multiply as before (fig. 4). If the zooglcea is formed on a solid substratum it may become firm and horny; immersion in water softens it as described above. 13 FIG. 10. Bacillus anthracis. (After Koch.) A, Bacilli mingled with blood- corpuscles from the blood of a Guinea pig ; some of the bacilli dividing. B, the rodlets after three hours' culture in a drop of aqueous humour. They grow out into long leptot/irix-like filaments, which become septate later, and spores are developed in the segments. ( x 650.) Spores. Spores or resting-cells are now known in many Spores. Schizomycetes (fig, 5). They may be formed in two ways. In Leuconostoc, Bacterium zopfii, Crenothrix, Beggiatoa, and Cladothrix the spore is simply one of the smallest segments ("cocci") into which the filament at length breaks up. De Bary terms such forms " arthrosporous " (cf. figs. 8, 13, 14, and 16). In others the formation of the spore is " endosporous " (De Bary).. It begins with the appearance of a minute granule in the protoplasm of a vegetative cell ; this granule enlarges, and in a few