by the neutral red, which contrasts
well with the two or three black spots, situated at the poles and
occasionally one in the centre representing protoplasmic aggregations (?
metachromatic granules) stained by the acid methylene-blue.

~Wheal and Chown (Oxford) Method.~--(To demonstrate
actinomyces.)

1. Stain briefly with Ehrlich's haematoxylin (until nuclei
are faint blue after washing with tap water).

2. Wash in tap water.

3. Stain in hot carbol-fuchsin (as for tubercle bacilli) for
five to ten minutes.

4. Wash in tap water.

5. Decolourise with Spengler's picric acid alcohol. This is
prepared by mixing:

Alcohol, absolute 20 c.c.
Picric acid, saturated aqueous solution 10 c.c.
Distilled water 10 c.c.

During the progress of steps 1-5 the preparation must be
repeatedly examined microscopically with the 1/6-inch
objective.

When properly differentiated the clubs appear brilliant red
on greenish ground.

6. Dehydrate in alcohol.

7. Clear in xylol.

8. Mount in xylol balsam.

This method serves equally well for films and for sections.

VII. METHODS OF DEMONSTRATING BACTERIA IN TISSUES.

For bacteriological purposes, sections of tissue are most conveniently
prepared by either the ~freezing method~ or the ~paraffin method~.

The latter is decidedly preferable, but as it is of greater importance
to demonstrate the bacteria, if such are present, than to preserve the
tissue elements unaltered, the "frozen" sections are often of value.

Whichever method is selected, it is necessary to take small pieces of
the tissue for sectioning,--2 to 5 mm. cubes when possible, but in any
case not exceeding half a centimetre in thickness. Post-mortem material
should be secured as soon after the death of the animal as possible.

The tissue is prepared for cutting by--

(a) Fixation; that is, by causing the death of the cellular elements
in such a manner that they retain their characteristic shape and form.

The fixing fluids in general use are: Absolute alcohol; corrosive
sublimate, saturated aqueous solution; corrosive sublimate, Lang's
solution (_vide_ page 82); formaldehyde, 4 per cent. aqueous solution.
(Of these, Lang's corrosive sublimate solution is decidedly the best
all-round "fixative.")

(b) Hardening; that is, by rende