Page 81 - My FlipBook
P. 81
;
METHODS OF BACTERIOLOGICAL INVESTIGATION. OO
of nutrient gelatine by gently warming them over a gas flame,
we transfer to one of them, on the point of a platinum needle, a
small quantity of the material which we wish to examine, and
shake the gelatine gently to distribute the micro-organisms
throughout the mass. The quantity of soil in one tube is,
however, so small, and the organisms would lie so closely
together that we would not be able, as a rule, to distinguish
between the separate colonies. We consequently transfer, on
a loop of platinum wire, three or four small drops or beads
from the iirst tube (first dilution) to a second tube (second
Fig. 17.
a
'm^:
M^
Colonies from the Plate illustrated in Fig. 15,
uxder a i'ower of fifty diameters.
«, 6, c, d, Colonies of four kinds of bacteria
e. Mould colony.
dilution), and if thought necessary six to eight beads from the
second to a third tube (third dilution). TTe now pour the con-
tents of the three tubes upon three separate plates, which are
put into a damp chamber as soon as the gelatine has solidiiied.
If the plates are examined after about forty-eight hours, we
will find, as a rule, that the Iirst dilution has become completely
opaque, through the development of innumerable colonies; the
second plate will appear thickly studded (Fig. 16) with mostly
whitish points (colonies), while the third plate will show but
very few colonies, or possibly none at all. The number of
METHODS OF BACTERIOLOGICAL INVESTIGATION. OO
of nutrient gelatine by gently warming them over a gas flame,
we transfer to one of them, on the point of a platinum needle, a
small quantity of the material which we wish to examine, and
shake the gelatine gently to distribute the micro-organisms
throughout the mass. The quantity of soil in one tube is,
however, so small, and the organisms would lie so closely
together that we would not be able, as a rule, to distinguish
between the separate colonies. We consequently transfer, on
a loop of platinum wire, three or four small drops or beads
from the iirst tube (first dilution) to a second tube (second
Fig. 17.
a
'm^:
M^
Colonies from the Plate illustrated in Fig. 15,
uxder a i'ower of fifty diameters.
«, 6, c, d, Colonies of four kinds of bacteria
e. Mould colony.
dilution), and if thought necessary six to eight beads from the
second to a third tube (third dilution). TTe now pour the con-
tents of the three tubes upon three separate plates, which are
put into a damp chamber as soon as the gelatine has solidiiied.
If the plates are examined after about forty-eight hours, we
will find, as a rule, that the Iirst dilution has become completely
opaque, through the development of innumerable colonies; the
second plate will appear thickly studded (Fig. 16) with mostly
whitish points (colonies), while the third plate will show but
very few colonies, or possibly none at all. The number of
