uld be kept on hand. A modified form, known as the "pear-shaped"
(Fig. 2), is preferable for the smaller sizes--i. e., 250 and 500 c.c.

~Erlenmeyer's Flasks~ (Fig. 3).--Erlenmeyer's flasks of 75, 100, and 250
c.c. capacity are extremely useful. For use as culture flasks care
should be taken to select only such as have a narrow neck of about 2 cm.
in length.

~Kolle's Culture Flasks~ (Fig. 4).--These thin, flat flasks (to contain
agar or gelatine, which is allowed to solidify in a layer on one side)
are extremely useful on account of the large nutrient surface available
for growth. A surface cultivation in one of these will yield as much
growth as ten or twelve "oblique" tube cultures. The wide mouth,
however, is a disadvantage, and for many purposes thin, flat culture
bottles known as ~Roux's bottles~ (Fig. 5) are to be preferred.

[Illustration: FIG. 4.--Kolle's culture flask.]

[Illustration: FIG. 5.--Roux's culture bottle.]

[Illustration: FIG. 6.--Guy's culture bottle.]

[Illustration: FIG. 7.--Filter flask.]

An even more convenient pattern is that used in the author's laboratory
(Fig. 6), as owing to the greater depth of medium which it is possible
to obtain in these flasks an exceedingly luxuriant growth is possible;
the narrow neck reduces the chance of accidental contamination to a
minimum and the general shape permits the flasks to be stacked one upon
the other.

~Filter Flasks or Kitasato's Serum Flasks~ (Fig. 7).--Various sizes, from
250 to 2000 c.c. capacity. These must be of stout glass, to resist the
pressure to which they are subjected, but at the same time must be
thoroughly well annealed, in order to withstand the temperature
necessary for sterilisation.

All flasks should be either of Jena glass or the almost equally
well-known Resistance or R glass, the extra initial expense being
justified by the comparative immunity of the glass from breakage.

~Petri's Dishes or "Plates"~ (Fig. 8, a).--These have now completely
replaced the rectangular sheets of glass introduced by Koch for the
plate method of cultivation. Each "plate" consists of a pair of circular
discs of glass with sharply upturned edges, thus forming shallow dishes,
one of slightly greater diameter than the other, and so, when inverted,
forming a cover or cap for the smaller. Plates having an outside
diameter of 10 cm. and a height of 1.5 cm. are the most generally
useful. A batch of eighteen such plates is sterilised and stored i