should be recorded as non-motile from
one observation only; a series of observations at different ages and
under varying conditions should form the basis of an opinion as to the
absence of true locomotion.

_Size._--In the case of non-motile or sluggishly motile organisms,
endeavour to measure several individuals in each hanging drop by means
of the eyepiece micrometer or the eikonometer (_vide_ page 63), and
average the results.

If the organism is one which forms spores, observe--

(a) _Spore Formation._--Prepare hanging-drop cultivations (_vide_ page
78) from vegetative forms of the organism, adding a trace of magenta
solution (0.5 per cent.) or other intra vitam stain (see page 77) to the
drop, on the point of the platinum needle, to facilitate the observation
of the phenomenon by rendering the bacilli more distinct.

Place the preparation on the stage of the microscope; if necessary,
using a warm stage.

Arrange illumination, etc., and select a solitary bacillus for
observation, by the help of the 1/6-inch lens.

Substitute the 1/12-inch oil-immersion lens for the sixth, and observe
the formation of the spore; if possible, measure any alteration in size
which may occur by means of the Ramsden micrometer.

(b) _Spore Germination._--Prepare hanging-drop cultivations from old
cultivations in which no living vegetative forms are present, and
observe the process of germination in a similar manner.

The comfort of the microscopist is largely enhanced in those cases where
the period of observation is at all lengthy, by use of some form of eye
screen before the unemployed eye, such as is figured on page 58 (Fig.
49).

If it is impossible to carry out the method suggested above, proceed as
follows:

(a) _Spore Formation._--Plant the organism in broth and incubate under
optimum conditions.

At regular intervals, say every thirty minutes, remove a loopful of the
cultivation and prepare a cover-slip film preparation.

Fix, while still wet, in the corrosive sublimate fixing solution.

Stain with aniline gentian violet, and partially decolourise with 2 per
cent. acetic acid.

Mount and number consecutively; then examine.

(b) _Spore Germination._--Expose a thick emulsion of the spores to a
temperature of 80 deg. C. for ten minutes in the differential steriliser
(_vide_ page 257).

Transfer the emulsion to a tube of sterile nutrient broth and incubate.

Remove specimens from the tube culture at intervals of,