Page:Encyclopædia Britannica, Ninth Edition, v. 21.djvu/424

Rh 402 SCHIZOMYCETES Cocci : spherical or spheroidal cells, which, according to their relative (not very well defined) sizes are spoken of as Micro- cocci, Macrococci, and perhaps Monas forms. Rods or rodlcts: slightly or more considerably elongated cells which are cylindrical, biscuit-shaped, or somewhat fuaiform. The cylindrical forms are short, i.e., only three or four times as long as broad (Bacterium), or longer (Bacillus) ; the biscuit-shaped ones are Bacteria in the early stages of divi- sion. Clostridia, &c., are spindle-shaped. Filaments (Leptothrix forms) really consist of elongated cylindri- cal cells which remain united end to end after division, and they may break up later into elements such as those described above. Such filaments are not always of the same diameter throughout, and their segmentation varies considerably. They may be free, or attached at one (the " basal ") end. A distinction is made between simple fila- ments ( e.g., Leptothrix) and such as exhibit a false branch- ing (e.g., Cladothrix), Cw~Ked and spiral forms. Any of the elongated forms described above may be curved, or sinuous, or twisted into a corkscrew- like spiral instead of straight. If the sinuosity is slight wo have the Vibrio form ; if pronounced, and the spiral wind- ing well marked, the forms are known as Spirillum, Spirochsete, &c. These and similar terms have been applied partly to individual cells, but more often to filaments con- sisting of several cells ; and much confusion has arisen from the difficulty of defining the terms themselves. Various observers have, moreover, described particular cases where the cells or cell-filaments exhibit irregularities of form ; such " involution forms," "torula forms," &c., appear to be fairly constant in some cases. In addition to the above, however, certain Schizomycetes present aggregates in the form of plates, or solid or hollow and irregular Fio. 3. Types of Zoogloea. (After Zopf.) A, mixed zoogloea fonnd as a pellicle on the surface of vegetable infusions, Ac.; It consists of various forms, and contains cocci (a) and rodlets, in series (6 and c), <fcc. ( x 540). B, egg-shaped mass of zoogloea of Beggiatott roseo-perticinit (Bacterium rubetceru of Lankester) ; the gelatinous swollen walls of the large crowded cocci are fused Into a common gelatinous envelope. C, reticulate zoogloea of the same fx 230). D, E, H, colonies of Jtfyconottoe enveloped in diffluent matrix fx 540). F, branched fruticose zoogloea of Cladothrix (slightly magnified). G, zooglcea of Bacterium meritmopedioides, Zopf, containing cocci arranged in tablets. branched colonies. This may be due to the successive divisions occurring in two or three planes instead of only across the long axis (tiff i,ia), or to displacements of the cells after division (as in the zooglcea conditions, &c., see fig. 8). Grmcth and Division. Whatever the shape and size Reprod of the individual cell, cell-filament, or cell-colony, thetion. immediate visible re- sults of active nutrition are elongation of the cell and its division into two equal halves, across the long axis, by the formation of a DOUVIUI splits i, iriuwu at once TOVUwl or re- mains intact s^?- for a Fio. 4. A, branch of a zoogloea of Cladothrix dichotoma (</. fig. 3, F), x 540. (After Zopf.) It contains short and longer bacillar forms (a and 6), leptothrix forms (c), some of which are curved like Vibrio (d) and Spirillum. B, the same, but the rodlets breaking up into cocci. (After Zopf.) shorter or longer time. This process is then repeated, and so on. In the first case the separated cells assume the characters of the parent-cell whose division gave rise to them; in the second case they form filaments, or, if the further elon- gation and divisions of the cells proceed in different direc- tions, plates or sphe- roidal or other- shaped colonies. It not unfrequently happens, however, that groups of cells break away from their former con- nexion as longer or shorter straight or curved filaments, or as solid masses. In some filamentous forms this " frag- (After Zopf.) mentation " into multicellular pieces of equal length or nearly so is a nor- Spore- formation in Schizomycetes. A, various stages in the develop- ment of the' endogenous spores in a Ciottridium (Bacillus) the small lettcis Indicate the order. B, endogenous spores of the hay bacillus. C, a chain of cocci of Leuconoitoc metenterioidts, with two " resting spores," i.e., arthrospores. (After Van Tiegliem.) D, a motile rodlet with one cllium and with a spore formed inside. E, spore-formation in mal phenomenon, each partial fila- ment repeating the growth, division, and fragmentation as before (cf. figs. 15 and 16). Finally, such filaments may break up into their individual cells, forming "bacilli," "bacteria," or "cocci" as the case may be. By these means hundreds of thousands of cells may be produced in a few hours, 1 and, according to the Fttrfo-like (c) and Spirillum-UkQ (a, b, d) Schizo- mycetes. F, long rod-like form containing a spore (these are the so-called "Ktip/chtnbacteritn" of German authors). G, Vibrio form with spore. (After Prazmowski.) H, Clostridium<ono cell contains two spores (Prazmowski). I, Spirillum containing many spores (a), which are liberated at b by the breaking up of the parent cells. K, germination of the spore of the hay bacillus (B. tubtilis), the axis of growth of the germinal rodlet is at right angles to the long axis of the spore. L, germination of spore of Ciottridium butyricum the axis of growth coincides with the long axis of the spore. 1 Brefeld has 'observed that a bacterium may divide once every half hour, and its progeny repeat the process in the same time. One bacterium might thus produce in twenty-four hours a number of segments amounting to many millions of millions.