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54

BACTERIOLOGY

(b) Sub-family — Homococcacea:. Division planes regular and definite :—Sarcina, (Goods.), cells non-motile ; growth and division in three successive planes at right angles, resulting in packetlike groups; Planosarcina (Migula), as before, but motile ; Pediococcus (Lindner), division planes at right angles in two successive planes, and cells in tablets of four or more ; Streptococcus (Billr.), divisions in one plane only, resulting in chains of cells. 2. Family—Bacillace.e. Vegetative cells cylindric (rodlets), ellipsoid or ovoid, and straight. Division planes always perpendicular to the long axis. (a) Sub-family—BacillEjE. Sporogenous rodlets cylindric, not altered in shape :—Bacillus (Cohn), non-motile ; Bactrinium (Fischer), motile, with one polar flagellum (Monotrichous); Bactrillum (Fischer), motile, with a terminal tuft of cilia (Lophotrichous); Bactridium (Fischer), motile, with cilia all over the surface (Peritrichous). (b) Sub-family—Clostridie.®. Sporogenous rodlets, spindle-shaped:—Clostridium (Prazm.), motile, peritrichous. (c) Sub-family—Plectridieje. Sporogenous rodlets, drum - stick - shaped : — Pledridium (Fischer), motile, peritrichous. 3. Family—Spirillaceje. Vegetative cells cylindric, but curved more or less spirally. Divisions perpendicular to the long axis :—Vibrio (MiillerLbffler), comma-shaped, motile, monotrichous; Spirillum (Ehrenb.), more strongly curved in open spirals, motile, lophotrichous; Spirochaite (Ehrenb.), spirally coiled in numerous close turns, motile, but apparently owing to flexile movements, as no cilia are found. II. Order—Trichobactcrinae. Vegetative body of branched or unbranched cell-filaments, the segments of which separate as swarm-cells (Goniclia). 1. Family—T richobacteriace.e. Characters those of the Order. (a) Filaments rigid, non-motile, sheathed:— Grenothrix (Cohn), filaments unbranched and devoid of sulphur particles ; Thiothrix (Winogr.), as before, but with sulphur particles; Cladothrix (Cohn), filaments branched in a pseudo-dichotomous manner. (/I) Filaments showing slow pendulous and creeping movements, and with no distinct sheath :—Beggiatoa (Trev.), with sulphur particles. The principal objections to this system are the following(1) The extraordinary difficulty in obtaining satisfactory preparations showing the cilia, and the discovery that these motile organs are not formed on all substrata, or are only developed during short periods of activity while the organism is young and vigorous, render this character almost nugatory. For instance, B. megatherium and B. subtilis pass in a few hours after commencement of growth from a motile stage with peritrichous cilia, into one of filamentous growth preceded by casting of the cilia. (2) By far the majority of the described species (over 1000) fall into the three genera—Micrococcus (about 400), Bacillus (about 200), and Bactridium (about 150), so that only a quarter or so of the forms are selected out by the other genera. (3) The monotrichous and lophotrichous conditions are by no means constant even in the motile stage; thus Pseudomonas rosea (Mig.) may have 1, 2, or 3 cilia at either end, and would be distributed by Fischeris classification between Bactrinium and Bactrillum, according to which state was observed. In Migula’s scheme the attempt is made to avoid some of these difficulties, but others are introduced by his otherwise clever devices for dealing with these puzzling little organisms. The question, What is an individual ? has given rise to much difficulty, and around it many of the speculations regarding pleomorphism have centred without useful result. If a tree fell apart into its constituent cells periodically we should have the same difficulty on a larger and more complex scale. The fact that every bacterial cell in a species in most cases appears equally capable of performing all the physiological functions of the species has led

[general

most authorities, however, to regard it as the individual—a view which cannot be consistent in those cases where a simple or branched filamentous series exhibits differences between free apex and fixed base and so forth. It may be doubted whether the discussion is profitable, though it appears necessary in some cases—e.g., concerning pleomorphy—to adopt some definition of individual. Myxobacteriaceoe.—ln 1857 Berkeley figured a curious organism then named Chondromyces, and in 1892 this and a number of allied organisms were rediscovered by Thaxter, who showed that they form plasmodium-like aggregations and build themselves up into sporogenous stractures quite similar in general features to the cysts of Myxomycetes, except that the plasmodium is filled with — or, according to Thaxter, consists of—swarming bacteria. Several genera and species are described, and if the author’s appreciation of the facts is correct, we have here a remarkable group of organisms partaking of the nature of both Schizomycetes and Myxomycetes as his name implies. Until the details of the life-history are better worked out it is, however, impossible to say whether his views are right, or whether we have here—as seems to the present writer to be the case from the only example he has been able to examine—a case of symbiosis, or possibly parasitism, between true Schizomycetes and Myxomycetes. The discoveries that some species of nitrifying bacteria and pigmented forms are capable of carbon-assimilation, that others can fix free nitrogen, and that a number of decompositions hitherto unsuspected Functions are accomplished by Schizomycetes, have put the questions of nutrition and fermentation in quite new lights. Apart from numerous fermentation

portional to the intervals of time (8.30, 10.0, 10.30, 11.40, and so on) and erect the straightened-out filaments, the proportional length of each of which is here given for each period, a line joining the tips of the filaments gives the curve of growth. Cf. Fig. 5. (Original.) processes such as rotting, the soaking of skins for tanning, the preparation of indigo and of tobacco, hay, ensilage, &c., in all of which bacterial fermentations are concerned, attention may be especially directed to the following evidence of the supreme importance of Schizomycetes in agriculture and daily life. Indeed, nothing marks the attitude of modern bacteriology more clearly than the increasing attention which is being paid to useful fermentations. The vast majority of these organisms are not pathogenic, most are harmless, and many are indispensable aids in natural operations important to man. Fischer has proposed that the old division into sapro-