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.