Page 30 - My FlipBook

4 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

SHORT OUTLINE OF THE MORPHOLOGY AND BIOLOGY
OF BACTERIA.
\
Bacteria are microscopic, spherical or elongated, unicellular
organisms, which live upon preformed organic substances, and
increase by fissation, or through the medium of spores.
Each cell possesses a cell-membrane and protoplasmic contents
;
the latter is usually homogeneous, seldom containing vacuoles
or granules (Beggiatoa). The deposits of lime-salts, so common
with other Thallophytes, have been but very rarely observed in
growths of bacteria.
jSIany kinds of bacteria possess the power of locomotion, and
consequently were formerly often classed among the infusoria.
The size of the cells of the different kinds of bacteria varies
very considerably, nor are the cells of one and the same kind
always of the same size. The micrococcus of progressive sup-
puration in rabbits has a diameter of only 0.15/<*; several mil-
lions of this micro-organism could easily dance, if not upon the
point, at least upon the head of a pin. On the other hand, Beg-
giatoa mirabilis is 35// thick, and Spirochiete plicatilis attains a
length of 225// or J millimeter.

1. Forms of Bacteria.
\/According to de Bary, the chief forms of bacteria are :
1. Cocci
' : isodiametric, or at least but very slightly uniaxially
elongated single cells.
2. Rod-forms : uniaxially elongated, cylindrical, less frequently
spindle-shaped cells, or short chains of the same.
3. Screw-forms: rods which are twisted after the pattern of a
corkscrew, partly with shallow, partly with steep spirals.
To the^Vs^ group (coccus-forms) belong :
a. Micrococci: cells spherical, or nearly so (Fig. 1, a, c. (').
b. Macrococci, Megacocci : remarkably large cocci.
c. Diplococci: biscuit-shaped c^lls, which arise during the
lissation of cocci (Fig. 1, 6).
It would probably be more correct to consider diplococci
simply as transition-forms.

*/j. = LQlkro-iiiiUiineier = jj^^ inilLmeter.