BACTERIA.	41
posing animal  and vegetable matters,  or as  parasites
upon the tissues or juices of living animals or plants.
This lowest family, the fungi, are divisible into the—
Hyphomycetes or Mucorini, or moulds;
0	Saccharomycetes, or yeasts; and
Schizomycetes, or bacteria.
Cohn divided the bacteria, according to their mor-
phology, into—
Sphero-bacteria, or cocci;
Micro-bacteria—short rods ;
Desmo-bacteria—bacilli;
Spiro-bacteria—spirilla.
Davaine suggested a classification based upon motility,
making four classes—Bacterium, Vibrio, Bacteridiuin,
and Spirillum, neglecting to provide for the cocci.
Zopf arranged them, according to his theory of
pleomorphism, into the coccace^, comprising those
known only in the coccus form, and comprehending
the streptococci, merismopedia, sarcina, micrococcits, and
ascococcus; the bacteriace^, comprehending the genera
bacterium, spirilhim, vibrio, leuconostoc, bacillus, and
clostridium (chiefly coccus, rod, and thread forms ; the
former may be absent; in the latter there is no distinction
between base and apex ; threads straight or screw-like) ;
and the leptothriche^e, comprehending crenothrix,
beggiatoa, phragmidiothrix, and leptothrix (coccus, rod,
.and thread forms ; the latter show a distinction between
base and apex ; threads straight or screw-like ; spore-
formation not demonstrated).
This classification is, however, based upon what is
probably an erroneous principle, the pleomorphism of
the bacteria.
Van Tieghem, DeBary, and Hiippe formed classifica-
tions the main feature of which was the formation of
endospores or arthrospores, but, as the sporulation of
•many species is as yet unknown, they cannot be properly
placed in it.