of light.

6. Rack up the body tube until the stained film comes into view.

7. Focus the condenser accurately on the film.

8. Focus the film accurately by means of the fine adjustment.

VI. STAINING METHODS.

In the following pages are collected the various "stock" stains in
everyday use in the bacteriological laboratory, together with a
selection of the most convenient and generally useful staining methods
for demonstrating particular structures or differentiating groups of
bacteria. The stains employed should either be those prepared by
Gruebler, of Leipzig, or Merck, of Darmstadt. The methods printed in
ordinary type are those which a long experience has shown to be the most
reliable, and to give the best results--those relegated to small type
comprise such as are not so generally useful, but give excellent results
in the hands of the experienced worker.

BACTERIA STAINS.

~Methylene-blue.~--

1. _Saturated Aqueous Solution._

Weigh out

Methylene-blue 1.5 grammes

Place in a stoppered bottle having a capacity of from 150 to 200 c.c.
and add

Distilled water 100.0 c.c.

Allow the water to remain in contact with the dye for two weeks, shaking
the contents of the bottle vigourously for a few moments every day.
Filter.

2. _Saturated Alcoholic Solution._

Weigh out

Methylene-blue 1.5 grammes

Place in a stoppered bottle of 150 c.c. capacity and add

Alcohol, 90 per cent 100.0 c.c.

Allow the alcohol to remain in contact with the dye for two hours,
shaking vigourously every few minutes. Filter.

3. _Carbolic Methylene-blue_ (Kuehne).

Weigh out

Methylene-blue 1.5 grammes
Carbolic acid 5.0 grammes

and dissolve in

Distilled water 100.0 c.c.

and add

Absolute alcohol 10.0 c.c.

Filter.

4. _Alkaline Methylene-blue_ (Loeffler).

Measure out and mix

Methylene-blue, saturated alcoholic solution 30.0 c.c.
Caustic potash, 0.1 per cent. aqueous solution 100.0 c.c.

Filter.

~Gentian Violet.~--

5. _Saturated Aqueous Solution._

Weigh out

Gentian violet 2.25 grammes

and proceed as in preparing the corresponding solution of
methylene-blue.

6. _Saturated Alcoholic Solution._

Weigh out

Gentian violet 5.0 grammes

and proceed as in preparing the corresponding solution of
methylene-blue.

7. _Carbolic Gentian Violet_ (Nicolle).