3. Use the 1/12-inch oil immersion lens of the microscope. Rack down the body tube till the front lens of the objective is in contact with the oil and nearly touching the cover-slip. 4. Rack up the condenser until it is in contact with the under surface of the slide. 5. Apply the eye to the ocular and arrange the plane mirror so as to obtain the greatest possible amount 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_ (Nicollé). Measure out and mix Gentian violet, saturated alcoholic solution 10.0 c.c. Carbolic acid, 1 per cent. aqueous solution 100.0 c.c. Filter. 8. _Anilin Water Solution_ (Koch-Ehrlich). Measure out