nd 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. R. 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.

[Illustration: FIG. 22.--Portions of a colony such as that in fig. 21,
highly magnified, showing the kinds of changes brought about in a few
minutes, from A to B, and B to C, by the growth and ciliary movements of
the filaments. The arrows show the direction of motion. (H. M. W.)]

AUTHORITIES.--General: Fischer, _The Structure and Functions of Bacteria_
(Oxford, 1900, 2nd ed.), German (Jena, 1903); Migula, _System der
Bakterien_ (Jena, 1897); and in Engler and Prantl, _Die natuerlichen
Pflanzenfamilien_, I. Th. 1 Abt. a; Lafar, _Technical Mycology_ (vol. i.
London, 1898); Mace, _Traite pratique de bakteriologie_ (5th ed. 1904).
Fossil bacteria: Renault, "Recherches 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. R. Soc._, vol. li. p.
183, vol. liii. p. 245, vol. lvi. p. 1; Marshall Ward, "On the Biology of
_B. ramosus_," _Proc. R. Soc._, vol. lviii. 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, _Weitere Ausfuhrungen ueber den Bau
der Cyanophyceen und Bakterien_ (Leipzig, 1896); Fischer, _Unters. ueber
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. ueber
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._; Vejdovsky, "Ueber den Kern der Bakterien und
seine Teilung," _Cent. f. Bakt._ Abt. II. Bd. xi. (1904) p. 481; _ibid._
"Cytologisches ueber die Bakterien der Prager Wasserleitung," _Cent. f.
Bakt._ Abt. II. Bd. xv. (1905); Mencl, "Nachtraege zu den
Strukturverhaeltnissen von Bakterium gammari" in _Archiv f.
Protistenkunde_, Bd. viii. (1907), p. 257. Spores, &c.: Marshall Ward, "On