aqueous humour. They
grow out into long _leptothrix_-like filaments, which become septate later,
and spores are developed in the segments.]

[Sidenote: Zoogloeae.]

One of the most remarkable phenomena in the life-history of the
Schizomycetes is the formation of this zoogloea stage, which corresponds to
the "palmella" condition of the lower _Algae_. This occurs as a membrane on
the surface of the medium, or as irregular clumps or branched masses
(sometimes several inches across) submerged in it, and consists of more or
less gelatinous matrix enclosing innumerable "cocci," "bacteria," or other
elements of the Schizomycete concerned. Formerly regarded as a distinct
genus--the natural fate of all the various [v.03 p.0161] 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 contiguous. 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 a proteid substance; the matrix in some cases is horny and resistant, in
others more like a thick solution of gum. It is intelligible from the mode
of formation that foreign bodies may become entangled in the gelatinous
matrix, and compound zoogloeae may arise by the apposition of several
distinct forms, a common event in macerating troughs (fig. 3, A).
Characteristic forms may be assumed by the young zoogloea of different
species,--spherical, ovoid, reticular, filamentous, fruiticose, lamellar,
&c.,--but these vary considerably as the mass increases or comes in contact
with others. Older zoogloeae may precipitate oxide of iron in the matrix,
if that metal exists in small quantities in the medium. Under favourable
conditions the elements in the zoogloea again become active, and move out
of the matrix, distribute themselves in the surrounding medium, to grow and
multiply as before. If the zoogloea is formed on a solid substratum it may
become firm and horny; immersion in water softens it as described above.

[Illustration: FIG. 8.--Curve of growth of a filament of _Bacillus ramosus_
(Fraenkel), constructed from data such a