BACTERIA.	39
out of use. Some of the flexile bacilli, whose movements
are sinuous, much resembling the swimming of a snake
or an eel, were described as vibrio, but this name also has
passed into disuse.
o The long filaments formed by the division of bacilli
without their distinct separation are sometimes called
leptothrix, and when these long threads form distinct
masses surrounded by a jelly-like material, the name
myconostoc is sometimes applied to them.
Certain forms much resembling bacilli in their isolated
state, characterized by the formation of long filaments
with a peculiar grouping which gives the appearance
of a false branching, are described as cladothrix; others
in which true branchings are seen, as streptothrix. One
other bacillus-like form, consisting of long, thick, not
distinctly segmented, straight threads, is called beggiatoa.
The only important difference between it and leptothrix
is that its filaments are thick and coarse, while those of
leptothrix are very delicate.
Some of the elongate bacteria have a remarkably
twisted form and bear some resemblance to a cork-
screw. These are called spirilla (Fig. 4). A subdivision

fig. 4.—Diagram illustrating the morphology of the spirilla: a, l>, c, spirilla;
d, <?, spirochseta.
of them, whose individuals are not only twisted but are
also very flexible, is called spiroch&ta. Though not.
formerly differentiated from vibrio, these forms are quite
distinct.
A spiral organism of a ribbon shape is called spiro-