BACTERIOLOGICAL
TECHNIQUE.

I. GLASS APPARATUS IN COMMON

USE.

THE equipment of the bacteriological laboratory, so far as the glass apparatus is concerned, differs but little from that of a chemical laboratory, and the cleanliness of the apparatus is equally important. The glassware comprised in the following list, in addition to being clean, must be stored in a sterile or germfree condition.

Test-tubes. It is convenient to keep several sizes of test-tubes in stock, to meet special requirements, viz.:

1. 18 by 1.5 cm., to contain media for ordinary tube cultivations.

2. 18 by 1.3 cm., to contain media used for pouring plate cultivations, and also for holding sterile "swabs." 3. 18 by 2 cm., to contain wedges of potato, beetroot, or other vegetable media.

4. 13 by 1.5 cm., to contain inspissated blood-serum. The tubes should be made from the best German potash glass, "blue-lined," stout and heavy, with the edge of the mouth of the tube slightly turned over, but not to such an extent as to form a definite rim. (Cost about $4.25, or 9 shillings per gross.) Such tubes are sufficiently stout to resist rough handling, do not usually break if accidentally allowed to drop, can be cleaned, sterilised, and used over and over again,

and by their length of life fully justify their initial

expense.

A point to be noted is that the manufacturers rarely turn out such tubes as these absolutely uniform in calibre, and a batch of 18 by 1.5 cm. tubes usually contains such extreme sizes as 18 by 2 cm. and 18 by 1.3 cm. Consequently, if a set of standard tubes is kept. for comparison, each new supply of 18 by 1.5 cm. tubes may be easily sorted out into these three sizes, and so simplify ordering.

5. 5 by 0.9 cm., for use in the inverted position inside the tubes containing carbohydrate media, as gas-collecting tubes.

6. 5 by 0.5 cm., for sedimentation reactions, etc.

Fig. 1.-Bohemian flask. Fig. 2.-Pear-shaped Fig. 3.-Erlenmeyer flask

flask.

(narrow neck).

These tubes may be of common thin glass, “unrimmed," as less than two per cent. are fit for use a second time.

Bohemian Flasks (Fig. 1).-These are the ordinary flasks of the chemical laboratory. A good variety, ranging in capacity from 250 to 3000 c.c., should be kept on hand. A modified form, known as the “pearshaped" (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 (Fig. 5) are to be preferred.

Filter Flasks or Kitasato's Serum Flasks (Fig. 6).— Various sizes, from 250 to 2000 c.c. capacity. These

C

Fig. 4. Kolle flask. Fig. 5.-Culture bottles. Fig. 6.-Filter flask.

must be of stout glass, to resist the pressure to which they are subjected, and must be thoroughly well annealed, in order to withstand the temperature necessary for sterilisation.

Petri's Dishes or "Plates" (Fig. 7, 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. Such plates are sterilised and stored in batches of eighteen in cylindrical copper boxes with a "pull-off" lid, 30 cm. high by 12 cm. diameter. Inside the box is a copper stirrup with a circular bottom, upon which the plates rest, and by means of which each can be raised in turn to the mouth of the box (Fig. 8).

Capsules (Fig. 7, b and c).—These are Petri's dishes of smaller diameter but greater depth than those termed

plates. Two sizes will be found useful-viz., 4 cm. diameter by 2 cm. high, capacity about 14 c.c.; and 5 cm. diameter by 2 cm. high, capacity about 25 c.c. These are stored in copper cylinders of similar construction to those used for plates, but measuring 20 by 6 cm. and 20 by 7 cm., respectively.

Graduated Pipettes.-Several varieties of these are required, viz.:

1. Pipettes of 1 c.c. capacity graduated in o.1 c.c. 2. Pipettes of 1 c.c. capacity graduated in 0.01 c.c. (Fig. 9, a).