8 ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 
SECTION 2: SIMPLE STAINING TECHNIQUE 
EXERCISE 7 
PREPARATION AND FIXING OF BACTERIA FOR STAINING 
(1) Using the wire loop, place a small drop of broth culture on a clean 
slide. If the culture is taken from solid media, place a small drop of water on 
the slide and thoroughly mix with it a small bit of the culture growth. 
(2) Spread the drop on the slide to form a thin film. 
(3) Allow the film on the slide to dry in the air or by holding the slide 
high above the flame. 
(4) When the film is dry pass the slide, film side up, three times through 
the Bunsen flame. 
The heat kills the organisms and causes them to adhere to the slide. This 
process is termed “fixing” the preparation. The slide so prepared is ready for 
staining. 
EXERCISE 8 
METHYLENE BLUE STAIN 
Make stained preparations of the cultures furnished and also of saliva, 
using a solution of methylene blue. 
Procedure 
(1) According to the method outlined in Exercise 7, fix the slide. 
(2) Place the slide on the wire staining screen over the waste jar. 
(3) Drop on enough of the methylene blue solution to cover well the film. 
(4) Allow the stain to act about 30 seconds. 
(5) Wash the stained preparation with water from the wash bottle. 
(6) Dry the slide between blotting paper. 
(7) Examine the stained preparation under the microscope and make a 
drawing of a good field. 
Formula 
Methylene blue, U.S.P. medicinal, saturated alcoholic solution............ 30 cc. 
Potassium hydroxide, 0.01% aqueous solution 100 ce. 
