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out the fundamental functions of nutrition, growth, and multiplication which mark the generalized activities of the bacterial cell, and at the same time rendered as accessible to the environment by isolation and consequent extension of surface, we should doubtless find them exerting changes in the fermentible fluids necessary to their life similar to those exerted by an equal mass of bacteria, and that in proportion to their approximation in size to the latter. Ciliary movements, which undoubtedly contribute in bringing the surface into contact with larger supplies of oxygen and other fluids in unity of time, are not so rapid or so extensive when compared with other standards than the apparent dimensions of the microscopic field. The microscope magnifies the distance traversed as well as the organism, and although a bacterium which covers 9-10 cm. or more in 15 minutes —say O'l mm. or 100 p per second— appears to be darting across the field with great velocity, because its own small size — say 5x1 p—comes into comparison, it should be borne in mind that if a mouse 2 inches long „iio. 11.—A plate-culture , only, travelled colony of a species of , •, Bacillus—Proteus (Hauser)—on the fifth day. twenty times its The flame-like processes and outliers are coni- own length i e 40 6 posed of writhing filaments, and the con- . , . ’ ‘ ' tours are continually changing while the inches 111 a Second, (C0OSaT)VeSaSawhoIe- sli*htVmagnified, the distance traversed in 15 minutes at that rate, viz., 1000 yards, would not appear excessive. In a similar way we must be careful, in our wonder at the marvellous rapidity of cell-division and growth of bacteria, that we do not exaggerate the significance of the phenomenon. It takes any ordinary rodlet 30-40 minutes to double its length and divide into two equal daughter cells when growth is at its best (see Figs. 4 and 5); nearer the

minimum it may require 3-4 hours or even much longer. It is by no means certain that even the higher rate is greater dtan that exhibited by a tropical bamboo which will grow over a foot a day, or even common grasses, or asparagus, uring the active period of cell - division, though the phenomenon is here complicated by the phase of exten-

61 sion due to intercalation of water. The enormous extension of surface also facilitates the absorption of energy from the environment, and, to take one case only, it is impossible to doubt that some source of radiant energy must be at the disposal of those prototrophic forms which decompose carbonates and assimilate carbonic acid in the dark and oxidize nitrogen in dry rocky regions where no organic materials are at their disposal, even could they utilize them. It is usually stated that the carbon-dioxide molecule is here split by means of energy derived from the oxidation of nitrogen, but apart from the fact that none of these processes can proceed until the temperature rises to the minimum cardinal point, Engelmann’s. experiment shows that in the purple bacteria rays are used other than those employed by green plants, and especially ultra-red rays not seen in the spectrum, and we may probably conclude that “ dark rays ”—i.e., rays not appearing in the visible spectrum—are absorbed and employed by _ these and other colourless bacteria. The purple bacteria have thus two sources of energy, one by the oxidation of sulphur and another by the absorption of “dark rays.” Stoney (Scient. Proc. P. Dub. Soc., 1893, p. 154) has suggested yet another source of energy, in the bombardment of these minute masses by the molecules of the environment, the velocity of which is sufficient to drive them well into the organism, and carry energy in of which they can avail themselves.

Aitthorities.—General: Fischer. The Structure and Functions of Bacteria. Oxford, 1900. — Mioitla. System der Bakterien, Jena, 1897 ; and in Engler and Prantl, Die natiirliche PJlanzen~ familien, I. Th. 1 Abtli. a.—Lafar. Technical Mycology, vol. i. London, 1898. Fossil Bacteria: Renault. <<Reeherches sur les Bacteriacees fossiles.” Ann. des Sc. Nat., 1896, p. 275. Bacteria in Water: Frankland and Marshall Ward. “ Reports on the Bacteriology of Water.” Proc. P. Soc. vol. li. p. 183, vol. liii. p 245, vol. Wi. p. 1.—Marshall Ward. “On the Biology of B. ramosus. Proc. P. Soc. vol. Iviii. p. 1; and papers on Bacteria of the river Thames in Ann. of Bot. vol. xii. pp. 59 and 287, and vol. xiii. p. 197. Cell-membrane, &c. : Butschli. WeitereAusfuhrungen iiber den Bau der Cya/nophyceen nnd Bakterien. Leipzig, 1896.—Fischer. Unters. iiber den Bau der Cyanophyceen und Bakterien. Jena, 1897.—Rowland. “Observations upon the Structure of Bacteria.” Trans. Jenner Institute, 2nd ser. 1899, p. 143, with literature. Cilia: Fischer. “Unters. iiber Bakterien.” Pringsh. Jahrb. vol. xxvii. ; also the works of Migula and Fischer already cited. Nucleus: Wager in Ann. Bot. vol. ix. p. 659 ; also Migula and Fischer, l.c. Spores, &c. r Marshall Ward. “On the Biology of B. ramosus.” Proc. R. Soc., 1895, vol. Iviii. p. 1.—Sturgis. “A Soil Bacillus of the type of de Bary’s B. megatherium.” Phil. Trans, vol. cxci. p. 147.— Klein, L. Ber. d. dcutschen bot. Gesellsch., 1889, B. vii. ; and Cent, f. Bakt. und Par., 1889, B. vi. Classification: Marshall Ward. “On the Characters or Marks employed for classifying the Schizomycetes.” Ann. of Bot., 1892, vol. vi.—Lehmann and Neumann. Atlas and Essentials of Bacteriology, 1897 ; also the works of Migula and Fischer, already cited. Myxobacteriacese : Berkeley. Introd. to Cryptogamic Botany, 1857, p. 313.—Thaxter. “A New Order of Schizomycetes.” Bot. Gaz. vol. xvii. p. 389 ; and “Further Observations on the Myxobacteriacepe,” ibid. vol. xxiii. p. 395. Growth: Marshall Ward. “On the Biology of B. ramosus.” Proc. P. Soc. vol. Iviii. p. 1, 1895. Fermentation, &c.: Warington. The Chemical Action of some Micro-organisms. London, 1888.—Winogradsky. “Recherchea sur les organismes de la nitrification,” Ann. de l’Inst. Past., 1890, pp. 213, 25/, /60, 1891, pp. 92 and 577 ; “Sur 1’assimilation de 1’azote gazeux, &c.” Compt. Pend. 12 Feb. 1894; “Zur Microbiologie des Nitrifikationsprozesses,” Cent. f. Bakt. II. Abt. B. ii. 1896, p. 415; “Ueber Schwefel - Bakterien, ” Bot. Zeitg., 1887, Nos. 31-37 ; Beitr. zur Morph, u. Phys. der Bakterien, H. 1, 1888 ; “Ueber Eisenbakterien,” Bot. Zeitg., 1888, p. 261.—Marshall Ward. “On the Tubercular Swellings on the Roots of Vicia Jaba.’ Phil. Trans., 1887, p. 539.—Dawson. “Nitrogen and the Nodules of Leguminous Plants,” Phil. Trans., 1899, vol. cxcii. p. 1; and “Further Observations on the Nature and Functions of the Nodules, &c.” Phil. Trans., 1900, vol. cxciii. p. 51.— Omelianski. “ Sur la fermentation de la cellulose. ” Compt. Pend. 4 Nov. 1895.-—Van Sends. Beitr. zur Kenntn. der Cellulosegdhrung. Leiden, 1890.—Yan Tieghem. “Sur la fermentation de la cellulose.” Bull, de la Soc. Bot. de Fr. t. xxvi. 1879, p. 28.—Beyerinck. “Ueber Spirillum desulphuricans, etc.” Cent.