tos millboard over a bunsen
flame turned low.

8. Smear an even layer of hot cement over the flange of the jar. The
cement is prepared as follows:

Weigh out and mix in an iron ladle

Gutta percha (pure) 4 parts.
Asphaltum 5 parts.

and melt together over a bunsen flame, stirring with an iron rod until
solution is complete.

9. Invert the glass plate over the jar and press down firmly into the
cement. Place a piece of asbestos board on the top and on that rest a
suitable weight until the cement is cold and has thoroughly set.

10. Trim off any projecting pieces of cement with an old knife, burr
over the joint between jar and cover-plate with a hot smooth piece of
metal (e. g., the searing iron).

11. Paint a narrow band of Japan black to finish off, round the joint,
overlapping on to the cover-plate.

_II. Tube Cultivations of Bacteria._--When showing typical appearances
these may be preserved, if not permanently, at least for many years, as
museum specimens, by the following method:

1. Take a large glass jar 25 cm. high by 18 cm. diameter, with a firm
base and a broad flange, carefully ground, around the mouth. The jar
must be fitted with a disc of plate glass ground on one side, to serve
as a lid.

2. Smear a thick layer of resin ointment (B.P.) on the flange around the
mouth of the jar.

3. Cover the bottom of the jar with a layer of cotton-wool and saturate
it with formalin.

4. Remove the cotton-wool plug from the culture tubes and place them,
mouth upward, inside the jar. (If water of condensation is present in
any of the culture tubes, it should be removed by means of a capillary
pipette before placing the tubes in the formalin chamber.)

5. Adjust the glass disc, ground side downward, over the mouth of the
jar and secure it by pressing it firmly down into the ointment, with a
rotary movement.

6. Remove the tubes from the formalin chamber after the lapse of a week,
and dry the exterior of each.

[Illustration: FIG. 202.--Bulloch's tubes.]

7. Seal the open mouth of each tube in the blowpipe flame and label.

If the cultivations are intended for museum purposes when they are first
planted, it is more convenient to employ Bulloch's tubes. These are
slightly longer than the ordinary tubes, and are provided with a
constriction some 2 cm. below the mouth (Fig. 202)--a feature which
renders sealing in the blowpipe flame an easy matter.

XX. THE STUDY OF T