3. Pipettes of 10 c.c. capacity graduated in o.1 c.c. (Fig. 9, b).

These should be about 30 cm. in length (1 and 2 of fairly narrow bore), graduated to the extreme point, and having at least a 10 cm. length of clear space bętween the first graduation and the upper end. Each variety should be stored in a separate cylindrical copper case some 36 by 6 cm., with “pull-off” lid, upon which is stamped, in plain figures, the capacity of the contained pipettes.

Capillary Pipettes or Pasteur's Pipettes (Fig. 10, a).— These little instruments are invaluable, and a goodly supply should be kept on hand. They are prepared from soft glass tubing of various-sized calibre in the following manner: Hold a 14 cm. length of glass tube by each end, and whilst rotating it heat the central portion in the Bunsen flame until the glass is red hot and soft. Now remove it from the flame and steadily pull the ends apart, so drawing the heated portion out into a capillary tube; break the capillary portion

at its centre, seal the broken ends in the flame, and round off the edges of the open end of each pipette. A loose plug of cotton-wool in the open mouth completes the capillary pipette. After a number have been prepared, they are sterilised and stored in batches, either in metal cases similar to those used for the graduated pipettes or in large-sized test-tubes-sealed ends downwards and plugged ends towards the mouth of the case.

Fig. II.- Blood pipettes and hare-lip pin in a test-tube.

A modification of this pipette, in which a constriction or short length of capillary tube is introduced just below the plugged mouth (Fig. 10, b), will also be found extremely useful in the collection and storage of morbid exudations.

A third form, where the capillary portion is about 4 or 5 cm. long and only forms a small fraction of the entire length of the pipette (Fig. 10, c), will also be found useful.

"Blood" Pipettes (Fig. 11).—Special pipettes for the collection of fairly large quantities of blood (as suggested by Pakes) should also be prepared. These are made from soft glass tubing of 1 cm. bore in a similar manner to the Pasteur pipettes, except that a blowpipe flame must be used in order to obtain the sharp shoulder at either end of the central bulb. The terminal tubes must retain a diameter of at least I mm., in order to avoid capillary action during the collection of the fluid.

For sterilisation and storage each pipette is placed inside a test-tube, resting on a wad of cotton-wool, and the tube plugged in the ordinary manner. these tubes are used almost exclusively for blood work,

As

it is usual to place a lance-headed hare-lip pin inside the tube so that the entire outfit may be sterilised at one time.

Graduated Capillary Pipettes (Fig. 12).—These should also be made in the laboratory, from manometer tubing, of simple, convenient shape,

and graduated by the aid of a 1 c.c. pipette (in hundredths) to contain such quantities as 10, 50, and 90 c.mm., and carefully marked with a writing diamond. These, previously sterilised in large test-tubes, will be found extremely useful in preparing accurate percentage solutions, when only minute quantities of fluid are available.

Fig. 12. - Capillary graduated pipettes.

Sedimentation Tubes (Fig. 13).— These are prepared from 10 cm. lengths of narrow glass tubing by sealing one extremity, blowing a small bulb at the centre, and plugging the open end with cotton-wool; after sterilisation the open end is provided with a short piece of rubber tubing and a glass mouthpiece. When it is necessary to observe sedimentation reactions in very small quantities of fluid,

Fig. 13.-Sedimentation tube.

these tubes will be found much more convenient than the 5 by 0.5 cm. test-tubes previously mentioned.

Fermentation Tubes (Fig. 14).—These are used for the collection and analysis of the gases liberated from the media during the growth of some varieties of bac

teria and may be either plain (a) or graduated (b). A simple form (Fig. 14, c) may be made from 14 cm. lengths of soft glass tubing of 1.5 cm. diameter. The Bunsen flame is applied to a spot some 5 cm. from one end of such a piece of tubing and the tube slightly drawn out to form a constriction, the constricted part

is bent in the bat's-wing flame, to an acute angle, and the open extremity of the long arm sealed off in the blowpipe flame. The open end of the short arm is rounded off and then plugged with cotton-wool, and the tube is ready for sterilisation.

CLEANING OF GLASS APPARATUS.

All glassware used in the bacteriological laboratory must be thoroughly cleaned before use, and this rule applies as forcibly to new as to old apparatus, although the methods employed may vary slightly.

To Clean New Test-tubes.

1. Place the tubes in a bucket or other convenient receptacle, fill with water and add a handful of "sapon" or other soap powder. See that the tubes are full and submerged.

2. Fix the bucket over a large Bunsen flame and boil for thirty minutes.

3. Cleanse the interior of the tubes with the aid of test-tube brushes, and rinse thoroughly in cold water.

4. Invert the tubes and allow them to drain completely.

5. Dry the tubes and polish the glass inside and out with a soft cloth, such as selvyt.

New flasks, plates, and capsules must be cleaned in a similar manner.

To Clean New Graduated Pipettes.

1. Place the pipettes in a convenient receptacle, filled with water to which soap powder has been added. 2. Boil the water vigorously for twenty minutes over a Bunsen flame.

3. Rinse the pipettes in running water and drain. 4. Run distilled water through the pipettes and drain.

5. Run rectified spirits through the pipette and drain as completely as possible.

6. Place the pipettes in the hot-air oven (vide page 35), close the door, open the ventilating slide, and run the temperature slowly up to about 80° C. Turn off the gas and allow the oven to cool.

Or 6a. Attach each pipette in turn to the rubber tube of the foot bellows, or blowpipe air-blast, and blow air through the pipette until the interior is dry.

Glassware that has already been used is regarded as infected, and is treated in a slightly different manner. Infected Test-tubes.

1. Pack the tubes in the wire basket of the autoclave (having previously removed the cotton-wool plugs, caps, etc.), in the vertical position, and before replacing the basket see that there is a sufficiency of water in the bottom of the boiler. Now attach a piece of rubber tubing to the nearest water tap, and by means of this fill each tube with water.

2. Disinfect completely by exposing the tubes, etc., to a temperature of 120° C. for twenty minutes (vide page 42).

(If an autoclave is not available, the tubes must be