PROTOPHYTA. 
249 
mucilage, and this is especially true of the most minute forms, the investigation of 
which is hence rendered extremely difficult. 
The forms and vital phenomena of the Schizomycetes, as far as they are accurately 
known, recall various species of Chroococcaceae and Oscillatoriese ; but they are in 
general much smaller than the corresponding 
forms belonging to the chlorophyllaceous 
series. Thus, for example, Sarcina (Fig. 
166, i), which grows in the human stomach, 
corresponds to Merismopedia, the small cells 
dividing cross-wise and remaining for a time 
united into tetrads. In the remaining 
Schizomycetes, which are commonly known 
as Bacteria, growth takes place only in the 
direction of length, and the cells formed 
by repeated transverse division either sepa- 
rate or remain united into filaments. Cohn 
divides them into four groups: — i. Sphaero- 
bacteria, with extremely small roundish 
, . I , J - 1 J J- Fig. 166.— S.-hizoniycetes : i Sa 
cells which become detached, correspondmg 3 y^^,^^-^. ^ spinutun (after cohn). 
to the most minute forms of the Chroococ- 
caceae and Palmellaceae. They grow on tlie surface of moist dead organic bodies 
forming gelatinous growths, often of an intense yellow-green, blue, or violet colour ; 
these pigments which are contained in the protoplasm are sometimes soluble, sometimes 
insoluble in water. 2. Bacteria proper, in which the cells, when separate, are long, 
rod-like, very minute, and able to swim about in the fluid. Fluids that contain 
albuminoids putrefy and become milk-white from the multiplication of these ordinary 
Bacteria; they correspond in form to the genus Synechococcus among Chroococcaceae 
which forms bluish-green coatings on rocks ^. 3. Filobacteria, in which the slender 
cells remain united into threads, which are either straight, forming the genus Bacillus of 
Cohn, or curved and bent, when they are Vibrio (Fig. 166, 3), They do not excrete 
a gelatinous envelope and resemble small Oscillatorieae. If the Schizomycetes are 
constituted into a distinct group, then Beggiatoa, with contractile filaments, which has 
been hitherto referred to the Oscillatorieae, must be included in it. 4. Spirobaeteria, 
which form spirally curved filaments sometimes of considerable size in comparison to the 
preceding ones. Cohn distinguishes the genera Spirillum (Fig.,166, 4) and Spirochcete, 
which recall Spirulina among the Oscillatorieae. 
D. The Saccharomycetes, of which the genus Saccharomyces is the only one that 
is accurately known, consist of small round cells which live isolated, and resemble in 
form some Chroococcaceae and Palmellaceae ; their organisation is nevertheless capable 
of a more accurate investigation than that of the Schizomycetes, which they also usually 
greatly exceed in size. The genus Saccharomyces, which causes the alcoholic fermentation 
in saccharine fluids, consists of separate cells of an ellipsoidal form with smooth and thin 
walls, the protoplasm in which can be clearly recognised as such and encloses one or 
more vacuoles. When growing in a solution capable of fermentation these cells 
multiply very rapidly; not however by the ordinary mode of division, but by budding 
and abstriction. At some point or other of the yeast-cefl a small protuberance makes 
its appearance, which increases to the size of the mother-cell ; the very narrow point of 
union then gives way, and the two cells then carry on an independent life, and again 
repeat the process. Whether under some circumstances the cells can also grow out 
^ [E. R. Lankester (Quart, Journ. Micr. Sc. 1873, p, 408) believes, from the investigation of a 
peach-coloured Bacterium, that the scries of forms distinguished by Cohn cannot be maintained as 
distinct. Lister (ibid. 1873, p, 393) believes that he has demonstrated the origin of Bacteria from 
a Fungus, a species of Dematiiwi.'] 
