40 PATHOGENIC BACTERIA.
monas, while a similar organism of spindle shape is
called a spirulina. One species of spiral bacteria in
whose protoplasm sulphur-grounds have been detected
has been called ophidiomonas.
Some of the spirilla are exceedingly long and deli-,
cate, as the spirochasta of relapsing fever; others which
are stouter, like the spirillum of cholera, habitually occur
in such short individuals as to be easily mistaken for
Classification.—Leeuwenhoek, when he first saw the
bacteria—and his successors even to so recent a date as
to include Ehrenberg and Dujardin—did not doubt that
they belonged to the infusoria.
It was not until biologists had concluded that organ-
isms which take into their bodies particles of solid or
semi-solid material, digest that which is useful, and
extrude the remainder, are animals, and that those which
live purely by osmosis and exosmosis are vegetables, that
the bacteria, which we have seen provided with a resist-
ant cell-wall, allowing of no possibility of nutrition
except by osmosis and exosmosis, could be finally and
correctly classed among the members of the vegetable
The extremely simple organization of bacteria naturally
places them among the lowest members of the vegetable
kingdom, in that class of the Cryptogamia known as
Thallophytae, comprising the algae, lichens, and fungi.
The algse are mostly water-plants, containing chloro-
phyl and obtaining their nourishment from inorganic
The lichens are plants, some of which contain chloro-
phyl. They live upon inorganic matter, which they
generally absorb from the air. According to the new
view of the subject, some, if not all, of these plants are
regarded as fungi growing parasitically upon algae.
The fungi, the lowest group of .all, are minute or large
plants, mostly devoid of chlorophyl, living upon organic
matter, which they obtain as saprophytes from decom-